Search

Neural stem cells and/or progenitor cells (NSCs/NPCs) in the subventricular and subgranular zones of the adult mammal forebrain generate new neurons and are involved in partial repair after injury. Recently, NSCs/NPCs were identified in the area postrema (AP) of the medulla oblongata of the hindbrain. In this study, we used the properties of fenestrate capillaries to observe specific neuronal elimination in the AP of adult mice and investigated subsequent neuronal regeneration by neurogenesis. Subcutaneous administration of monosodium glutamate (MSG) induced prominent Fos expression in HuC/D + neurons in the AP 2 h after administration. MSG administration caused a marked decrease in HuC/D + neuronal density by neuronal death 3 to 21 days after administration, which recovered to the control level 35 days later. After MSG administration, the density of TUNEL + dying neurons and phagocytic microglia surrounding or engulfing neurons increased. Within 7 days of MSG administration, the number of BrdU + 　Sox2 + and BrdU + Math1 + cells increased markedly, and at least the BrdU + Math1 + cells similarly increased for the next following 7 days. A remarkable number of HuC/D + neurons with BrdU + nuclei were observed 35 days after MSG administration. This study reveals that neurogenesis occurs in the AP of adult mice, recovering and maintaining normal neuronal density after neuronal death., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 International Brain Research Organization (IBRO). Published by Elsevier Inc. All rights reserved.)

Neuronal splicing regulator RNA binding protein, fox-1 homolog 3 (NeuN/RbFox3), is expressed in postmitotic neurons and distributed heterogeneously in the cell. During excitotoxicity events caused by the excess glutamate, several alterations that culminate in neuronal death have been described. However, NeuN/RbFox3 organization and distribution are still unknown. Therefore, our objective was to analyze the nucleocytoplasmic distribution and organization of NeuN/RbFox3 in hippocampal and cortical neurons using an excitotoxicity model with monosodium glutamate salt (MSG). We used neonatal Wistar rats administered subcutaneously with 4 MSG mg/kg during the postnatal day (PND) 1, 3, 5, and 7. The control group was rats without MSG administration. On 14 PND, the brain was removed, and coronal sections were used for immunodetection with the antibody NeuN, DAPI, and the propidium iodide staining for histological evaluation. The results indicate that in the control group, NeuN/RbFox3 was organized into macromolecular condensates inside and outside the nucleus, forming defined nuclear compartments. Additionally, NeuN/RbFox3 was distributed proximal to the nucleus in the cytoplasm. In contrast, in the group treated with MSG, the distribution was diffuse and dispersed in the nucleus and cytoplasm without the formation of compartments in the nucleus. Our findings, which highlight the significant impact of MSG administration in the neonatal period on the distribution and organization of NeuN/RbFox3 of neurons in the hippocampus and cerebral cortex, offer a new perspective to investigate MSG alterations in the developmental brain., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier GmbH. All rights reserved.)

Neonatal exposure to monosodium glutamate (MSG) induces circadian disorders in several physiological and behavioural processes regulated by the suprachiasmatic nucleus (SCN). The objective of this study was to evaluate the effects of neonatal exposure to MSG on locomotor activity, and on morphology, cellular density and expression of proteins, as evaluated by optical density (OD), of vasopressin (VP)-, vasoactive intestinal polypeptide (VIP)- and glial fibrillary acidic protein (GFAP)-immunoreactive cells in the SCN. Male Wistar rats were used: the MSG group was subcutaneously treated from 3 to 10 days of age with 3.5 mg/g/day. Locomotor activity was evaluated at 90 days of age using 'open-field' test, and the brains were processed for immunohistochemical studies. MSG exposure induced a significant decrease in locomotor activity. VP- and VIP-immunoreactive neuronal densities showed a significant decrease, while the somatic OD showed an increase. Major axes and somatic area were significantly increased in VIP neurons. The cellular and optical densities of GFAP-immunoreactive sections of SCN were significantly increased. These results demonstrated that newborn exposure to MSG induced morphological alterations in SCN cells, an alteration that could be the basis for behavioural disorders observed in the animals., (© 2016 The Authors. International Journal of Experimental Pathology © 2016 International Journal of Experimental Pathology.)

Introduction: Calretinin (CR) is a protein, which is present in GABAergic neurons and belongs to the calcium-binding proteins family. It may reduce the excitotoxicity phenomenon through its Ca2+ buffering properties. This phenomenon is due to the increase of calcium ions levels caused by the excess of glutamate—the main excitatory neurotransmitter. The aim of the study was to investigate alterations of calretinin-immunoreactivity in neurons of hippocampal CA1 region and dentate gyrus with hilus in 10 day-old rats treated with monosodium glutamate (MSG)., Material and Methods: Ten 7 day-old Wistar rats were used. The MSG-group consisted of 5 MSG-treated rats at a dose of 4 g/kg b.w. for 3 consecutive days and the second group consisted of 5 control animals. After euthanasia the brains containing hippocampus were dissected and embedded in paraffin blocks. The immunohistochemical peroxidase-antiperoxydase reaction was performed on tissue sections. The morphometric analyses of CR-immunopositive neurons: density, percentage ratio to the density of all cells and an assessment of digital immunostaining intensity were performed., Results: The distribution of the CR-immunoreactive neurons in the hippocampus was irregular. In the MSG-group there were single cells, which were more intensely stained than in control animals. Some of cells contained processes of different length. The density of CR-immunopositive cells and their percentage ratio to the density of all cells did not change significantly after MSG treatment. However, there was a statistically significant increase in the staining intensity of CR-immunopositive cells., Conclusions: The obtained results indicate that CR-positive cells in P7-P10 rats are only slightly affected by MSG in CA1 region and dentate gyrus with hilus of the hippocampus.

Umami is considered to be the fifth basic taste quality and is elicited by glutamate. The mouse is an ideal rodent model for the study of this taste quality because of evidence that suggests that this species, like humans, may sense umami-tasting compounds as unique from other basic taste qualities. We performed single-unit recording of taste responses in the parabrachial nucleus (PbN) of anesthetized C57BL/6J mice to investigate the central representation of umami taste. A total of 52 taste-responsive neurons (22 sucrose-best, 19 NaCl-best, 5 citric acid-best, and 6 quinine-best) were recorded from stimulation period with a large panel of basic and umami-tasting stimuli. No neuron responded best to monopotassium glutamate (MPG) or inosine 5'-monophosphate (IMP), suggesting convergence of input in the central nervous system. Synergism induced by an MPG-IMP mixture was observed in all sucrose-best and some NaCl-best neurons that possessed strong sensitivity to sucrose. In more than half of sucrose-best neurons, the MPG-IMP mixture evoked stronger responses than those elicited by their best stimulus. Furthermore, hierarchical cluster analysis and multidimensional analysis indicated close similarity between sucrose and the MPG-IMP mixture. These results strongly suggest the mixture tastes sweet to mice, a conclusion consistent with previous findings that show bidirectional generalization of conditioned taste aversion between sucrose and umami mixtures, and suppression of taste responses to both sucrose and mixtures by the antisweet polypeptide gurmarin in the chorda tympani nerve. The distribution pattern of reconstructed recording sites of specific neuron types suggested chemotopic organization in the PbN.

We report that satiation evokes neuronal activity in the ventral subdivision of the hypothalamic dorsomedial nucleus (DMH) as indicated by increased c-fos expression in response to refeeding in fasted rats. The absence of significant Fos activation following food presentation without consumption suggests that satiation but not craving for food elicits the activation of ventral DMH neurons. The distribution pattern of the prolactin-releasing peptide (PrRP)-immunoreactive (ir) network showed remarkable correlations with the distribution of activated neurons within the DMH. The PrRP-ir fibers and terminals were immunolabeled with tyrosine hydroxylase, suggesting their origin in lower brainstem instead of local, hypothalamic PrRP cells. PrRP-ir fibers arising from neurons of the nucleus of the solitary tract could be followed to the hypothalamus. Unilateral transections of these fibers at pontine and caudal hypothalamic levels resulted in a disappearance of the dense PrRP-ir network in the ventral DMH while PrRP immunoreactivity was increased in transected fibers caudal to the knife cuts as well as in perikarya of the nucleus of the solitary tract ipsilateral to the transections. In accord with these changes, the number of Fos-expressing neurons following refeeding declined in the ipsilateral but remained high in the contralateral DMH. However, the Fos response in the ventral DMH was not attenuated following chemical lesion (neonatal monosodium glutamate treatment) of the hypothalamic arcuate nucleus, another possible source of DMH inputs. These findings suggest that PrRP projections from the nucleus of the solitary tract contribute to the activation of ventral DMH neurons during refeeding, possibly by transferring information on cholecystokinin-mediated satiation.

Feeding behavior is regulated by feeding-related peptides in the hypothalamus. The neurons of the arcuate nucleus (ARC), which produces feeding-related peptides, develop and function by three weeks of age in rodents. Because rodents are weaned at three weeks, we studied whether the process of weaning is involved in the development of ARC neurons using monosodium glutamate. Rat pups injected neonatally with monosodium glutamate ingested a large amount of mother's milk at weaning. Monosodium glutamate treatment induced a decrease in the number of ARC cells and mRNA levels of neuropeptide Y and agouti-related protein in the hypothalamus. The alteration of milk consumption following monosodium glutamate treatment appears to cause failure of ARC neuron development and neuropeptide expression.

The intergeniculate leaflet (IGL) has been shown to be a functional constituent of the circadian timing system. The IGL receives a monosynaptic input from the retina and is known to mediate some of the effects of light on the circadian clock. In the majority of retinal ganglion cells, glutamate functions as an excitatory neurotransmitter. The effect of monosodium glutamate and N-methyl-D-aspartate (NMDA), on the extracellularly recorded discharge activity of IGL neurons was studied in vitro. The application of monosodium glutamate induced either an excitatory, a biphasic or an inhibitory response. Application of NMDA induced an excitatory response in the majority of tested neurons. To determine the role of NMDA receptors in the response to glutamate application, the selective antagonist of NMDA receptors- AP-5, was applied to the incubation medium. The presence of AP-5 reduced the response of the IGL cells to focal application of glutamate and completely blocked their responsiveness to NMDA. To clarify whether GABAergic interneurons are involved in mediation of the inhibitory effects of glutamate, we repeated our experiments in the presence of bicuculline in the incubation medium. Since bicuculline did not influence the observed inhibitory effects, the involvement of GABAA receptors was excluded. The present study provides the first electrophysiological evidence that neurons in the rat IGL, respond to glutamate probably through NMDA receptors. However, our results also suggest that other types of glutamate receptors may play an additional role in mediating the action of this excitatory amino acid on the IGL neurons.

Background: The neonatal administration of a 4 mg/g dose of monosodium glutamate (MSG) to rodents leads to neuronal death in the hypothalamus arcuate nucleus, which leads in turn to obesity in the adult animal. However, few studies have investigated the effects on the enteric nervous system. This study evaluated the effects of the neonatal administration of MSG on the frequency and morphometry of the myenteric as well as the ileum wall morphometry of adult Wistar male rats., Methods: Whole-mount preparations of ileum samples were stained by the Giemsa or NADH-diaphorase histochemical methods. For histological processing, hematoxylin and eosin staining was used., Results: The treatment with MSG led to obesity, as shown by the higher values for Lee's index and the weights of periepididimal and retroperitoneal adipose tissues. The Giemsa staining revealed a significantly larger neuronal density in the MSG group, which is explained by smaller physical growth and a reduction in the weight of the small intestine. The mean neuronal profile did not change between groups. The NADH-diaphorase-positive neuronal subpopulation kept its neuronal density but its average cellular profile was reduced in the MSG group. A morphometric analysis of the intestinal wall, muscular layer, villi, and intestinal crypts showed that their characteristics did not change., Conclusions: The treatment with MSG did not cause alteration of the total myenteric population of the ileum, but it influenced the NADH-diaphorase-positive subpopulation. From the maintenance of the morphometric parameters of the ileum intestinal wall, we inferred that intestinal function was preserved in obese animals.

We have previously shown the protective effects of pituitary adenylate cyclaseactivating polypeptide (PACAP) in monosodium glutamate (MSG)-induced retinal degeneration. In the present article, we have investigated the optimal model for examining this neuroprotective effect. One MSG treatment on postnatal (P) days 1 or 5, in spite of leading to same ultrastructural changes, does not cause enough damage to study neuroprotection. When retinas were treated three times with MSG, the entire inner retina degenerated. Neuroprotection with PACAP was achieved with at least two treatments. Evidence suggests that PACAP provides protection against excitotoxicity, therefore, it may be a useful agent in reducing excitotoxic damage in the retina.

In long-term two-bottle tests, mice from the C57BL/6ByJ (B6) strain drink more monosodium L-glutamate (MSG) and inosine-5'-monophosphate (IMP) compared with mice from the 129P3/J (129) strain. The goal of this study was to assess the role of afferent gustatory input in these strain differences. We measured integrated responses of the mouse chorda tympani and glossopharyngeal nerves to lingual application of compounds that evoke umami taste in humans: MSG, monoammonium L-glutamate (NH(4) glutamate), IMP and guanosine-5'-monophosphate (GMP) and also to other taste stimuli. Chorda tympani responses to MSG and NH(4) glutamate were similar in B6 and 129 mice. Chorda tympani responses to IMP and GMP were lower in B6 than in 129 mice. Responses to umami stimuli in the glossopharyngeal nerve did not differ between the B6 and 129 strains. Responses to MSG, IMP and GMP were not affected by sodium present in these compounds because B6 and 129 mice had similar neural taste responses to NaCl. This study has demonstrated that the increased ingestive responses to the umami stimuli in B6 mice are accompanied by either unchanged or decreased neural responses to these stimuli. Lack of support for the role of the chorda tympani or glossopharyngeal nerves in the enhanced consumption of MSG and IMP by B6 mice suggests that it is due to some other factors. Although results of our previous study suggest that postingestive effects of MSG can affect its intake, contribution of other gustatory components (e.g. greater superficial petrosal nerve or central gustatory processing) to the strain differences in consumption of umami compounds also cannot be excluded. Strain differences in gustatory neural responses to nucleotides but not glutamate suggest that these compounds may activate distinct taste transduction mechanisms.

Aim: To inquire into the effects and mechanism of Zuogui Wan (Pills for Kidney Yin) on neurocyte apoptosis in nuclei of arcuate hypothalamus (ARN) of monosodium glutamate (MSG)-liver regeneration rats, and the mechanism of liver regeneration by using optic microscope, electron microscope and in situ end labeling technology to adjust nerve-endocrine-immunity network., Methods: Neurocyte apoptosis in ARN of the experiment rats was observed by using optic microscope, electron microscope and in situ end labeling technology. Expression of TGF-beta1 in ARN was observed by using immunohistochemistry method., Results: The expression of TGF-beta1 in rats of model group was increased with the increase of ARN neurocyte apoptosis index (AI) (t = 8.3097, 12.9884, P<0.01). As compared with the rats of model group, the expression of TGF-beta1 in rats of Zuogui Wan treatment group was decreased with the significant decrease of ARN neurocyte apoptosis (t = 4.5624, 11.1420, P<0.01)., Conclusion: Brain neurocyte calcium ion overexertion and TGF-beta1 protein participate in the adjustment and control of ARN neurocyte apoptosis in MSG-liver regeneration-rats. Zuogui Wan can prevent ARN neurocyte apoptosis of MSG-liver regeneration in rats by down-regulating the expression of TGF-beta1, and influence liver regeneration through adjusting nerve-endocrine-immune network.

A stimulation of the gigantocellular tegmental field (FTG) in the medulla oblongata often increases systemic arterial blood pressure (SAP) and decreases heart rate (HR). We investigated if the cardioinhibitory/depressor areas, including the nucleus ambiguus (NA), the dorsal motor nucleus of vagus (DMV) and the caudal ventrolateral medulla (CVLM), underlied the functional expression of FTG neurons in regulating cardiovascular responses. In 73 chloralose-urethane anesthetized cats, the HR, SAP and vertebral nerve activity (VNA) were recorded. Neurons in the FTG, NA, DMV and CVLM were stimulated by microinjection of sodium glutamate (25 mM Glu, 70 nl). To study if the NA, DMV, and CVLM relayed the cardioinhibitory messages from the FTG, 24 mM kainic acid (KA, 100 nl) was used as an excitotoxic agent to lesion neurons in the NA, DMV or CVLM. We found that the cardioinhibition induced by FTG stimulation was significantly reduced by KA lesioning of the ipsilateral NA or DMV. Subsequently, a bilateral KA lesion of NA or DMV abolished the cardioinhibitory responses of FTG. Compared to the consequence of KA lesion of the DMV, only a smaller bradycardia was induced by FTG stimulation after KA lesion of the NA. The pressor response induced by Glu stimulation of the FTG was reduced by the KA lesion of the CVLM. Such an effect was dominant ipsilaterally. Our findings suggested that both NA and DMV mediated the cardioinhibitory responses of FTG. The pressor message from the FTG neurons might be partly working via a disinhibitory mechanism through the depressor neurons located in the CVLM.

To elucidate the effectiveness of the drug in the treatment of vertebrobasilar insufficiency (VBI), we performed an electrophysiological study to examine the effects of ipenoxazone hydrochloride, a glutamate blocker, on hypoxia-induced firing in the medial vestibular nucleus (MVN) neuron, using alpha-chloralose-anesthetized cats. The single neuronal activity of the MVN was recorded extracellularly with a glass-insulated silver wire microelectrode attached along a seven-barrel micropipette. The firing rate of MVN neurons showed a transient increase [hypoxic depolarization (HD)] during 5% O(2) inhalation, followed by a gradual decrease and disappearance. HD and the time to disappearance of firing induced by hypoxia were inhibited by iontophoretic application of ipenoxazone hydrochloride. These results suggest that ipenoxazone hydrochloride protects against hypoxic neuronal dysfunction, and may be an effective drug for vertigo caused by VBI.

The origin of neuropeptide Y (NPY) afferents to GnRH neurons was investigated in male mice. Neonatal lesioning of the hypothalamic arcuate nuclei (ARC) with monosodium glutamate markedly reduced the number of NPY fibers in the preoptic area as well as the frequency of their contacts with perikarya and proximal dendrites of GnRH neurons. Dual-label immunofluorescence studies to determine the precise contribution of the ARC to the innervation of GnRH neurons by NPY axons were carried out on transgenic mice in which enhanced green fluorescent protein was expressed under the control of the GnRH promoter (GnRH-enhanced green fluorescent protein mice). The combined application of red Cy3 and blue AMCA fluorochromogenes established that 49.1 +/- 7.3% of NPY axons apposed to green GnRH neurons also contained agouti-related protein (AGRP), a selective marker for NPY axons arising from the ARC. Immunoelectronmicroscopic analysis detected symmetric synapses between AGRP fibers and GnRH-immunoreactive perikarya. Additional triple-fluorescence experiments revealed the presence of dopamine-beta-hydroxylase immunoreactivity within 25.4 +/- 3.3% of NPY afferents to GnRH neurons. This enzyme marker enabled the selective labeling of NPY pathways ascending from noradrenergic/adrenergic cell populations of the brain stem, thus defining a second important source for NPY-containing fibers regulating GnRH cells. The absence of both topographic markers (AGRP and dopamine-beta-hydroxylase) within 26% of NPY contacts suggests that additional sources of NPY fibers to GnRH neurons exist. Future studies will address distinct functions of the two identified NPY systems in the afferent neuronal regulation of the GnRH system.

Using chemical lesioning we previously identified hypothalamic neurons that are required for leptin antiosteogenic function. In the course of these studies we observed that destruction of neurons sensitive to monosodium glutamate (MSG) in arcuate nuclei did not affect bone mass. However MSG treatment leads to hypogonadism, a condition inducing bone loss. Therefore the normal bone mass of MSG-treated mice suggested that MSG-sensitive neurons may be implicated in the control of bone mass. To test this hypothesis we assessed bone resorption and bone formation parameters in MSG-treated mice. We show here that MSG-treated mice display the expected increase in bone resorption and that their normal bone mass is due to a concomitant increase in bone formation. Correction of MSG-induced hypogonadism by physiological doses of estradiol corrected the abnormal bone resorptive activity in MSG-treated mice and uncovered their high bone mass phenotype. Because neuropeptide Y (NPY) is highly expressed in MSG-sensitive neurons we tested whether NPY regulates bone formation. Surprisingly, NPY-deficient mice had a normal bone mass. This study reveals that distinct populations of hypothalamic neurons are involved in the control of bone mass and demonstrates that MSG-sensitive neurons control bone formation in a leptin-independent manner. It also indicates that NPY deficiency does not affect bone mass.

Neuronal death and lactate dehydrogenase (LDH) activity were evaluated in the cerebral cortices of neonatal rats after exposure to monosodium L-glutamate (MSG) to induce neuroexcitotoxicity. A time-response profile for tumor necrosis factor-alpha (TNF-alpha) expression was drawn, with measurements taken every 6 h after the first dose of MSG during the first 8 postnatal days, and at days 10 and 14 after birth. An increase in neuronal loss accompanied by high LDH activity and high TNF-alpha levels was observed at 8 and 10 days. These results indicate that neuronal loss may occur via an apoptosis-like mechanism directed selectively against neurons that express glutamate receptors, mainly the N-methyl-D-aspartate, which it may be strengthen by high TNF-alpha levels through a feedback mechanism to induce cell death via apoptosis.

Glutamatergic post-synaptic receptors are closely related to the known excitotoxic effects of high doses of L-glutamate. Several behavioral abnormalities, glial reaction, and an increase of expression of the NMDA receptor sub-units have been observed in the rat hippocampus after early monosodium glutamate exposure. Thus, a quantitative morphological study was carried out to determine the effects of early exposure to monosodium glutamate on post-synaptic structures that mediate glutamate excitatory neurotransmission in the hippocampal CA1 field. Four milligrams per gram body weight of monosodium glutamate was subcutaneously injected into neonatal Wistar rats, at 1, 3, 5, and 7 days. Cell loss and several cytoarchitectonic parameters were evaluated in pyramidal cells from the hippocampal CA1 field in the treated rats at 60 days of age. An untreated group of rats were used as controls. Cell number in the hippocampus of experimental rats was 11.5% less than that in control animals. In addition, both dendritic arborization and dendritic spine density were adversely affected, and thin and mushroom-shaped spines became proportionally more numerous, while the opposite occurred to stubby spines. These results strongly suggest the occurrence of cell death and also show some cytoarchitectural modifications in the surviving neurons. These could lead to functional alterations in the hippocampal integrative activity, due to an early cytoexcitotoxic effect of monosodium glutamate.

The effects of interleukin-1beta in the paraventricular nucleus or caudal arcuate nucleus on hypertensive and tachycardiac responses induced by excitation of the central amygdaloid nucleus were studied. We observed that microinjection of sodium glutamate into central amygdaloid nucleus resulted in hypertension and tachycardia. Microinjection of interleukin-1beta into paraventricular nucleus or caudal arcuate nucleus induced significant pressor and tachycardiac responses while pretreatment with microinjection of rabbit anti-rat interleukin-1beta antibody into bilateral paraventricular nuclei or arcuate nuclei attenuated the hypertensive response induced by microinjection of 40 nmol sodium glutamate into central amygdaloid nucleus. The above results suggest that the pressor effect of central amygdaloid nucleus is mediated by interleukin-1beta in paraventricular nucleus or arcuate nucleus.

Monosodium glutamate (MSG) was administered subcutaneously to male neonate rats, and the effects on N-methyl-D-asparatate (NMDA) subunit receptor types NR2C and NR2D from different brain regions were studied. A semi-quantitative reverse transcription-polymerase chain reaction was used to measure NR2C and NR2D expression levels in the cerebral cortex, hippocampus and striatum. MSG treatment (4 mg/g body weight, on postnatal days 1, 3, 5, and 7) produced an important increase of NR2C and NR2D subunit gene expression levels in the hippocampus and striatum of adults rats. No change was observed in the cerebral cortex. We propose that an early excessive activation of glutamate receptors could modify NMDA subunit expression and its structural composition on postnatal development. This, as part of a compensatory response by an altered neuronal circuitry, mainly in the hippocampus and striatum, suggests that the NMDA receptor could be a determinant factor to modulate the dendritic arrangement and the synaptogenesis.

The effect of neonatal treatment with monosodium L-glutamate (MSG) on the dopaminergic systems of the medial basal hypothalamus has been investigated using tyrosine hydroxylase (TH) and aromatic L-amino acid decarboxylase (AADC) immunocytochemistry. Changes in plasma levels of prolactin (PRL) and alpha-melanocyte-stimulating hormone (MSH) have also been determined in intact and in MSG-treated rats after inhibition of TH by alpha-methyl-p-tyrosine (alpha-MpT) or without inhibition of enzyme activity. Monosodium glutamate resulted in a 40% reduction in the number of TH immunopositive tuberoinfundibular neurons, but no change in the number of AADC-positive tuberoinfundibular nerve cells, indicating that this reduction has occurred mainly in TH-positive but AADC-negative elements, i.e., in L-DOPA-ergic neurons. In contrast, MSG did not cause changes in the number of TH and AADC immunoreactive neurons of the periventriculohypophysial and tuberohypophysial dopaminergic systems, and it did not influence basal plasma PRL levels. alpha-methyl-p-tyrosine has increased plasma PRL concentrations in both control and MSG-treated rats of both sexes, but significantly higher responses were detected in females. None of the treatments had any effect on plasma MSH level. These findings suggest that MSG affects primarily L-DOPA-ergic neurons located in the ventrolateral part of the arcuate nucleus, but not dopaminergic neurons situated in the dorsomedial part of the arcuate nucleus; neither PRL nor MSH secretion is altered by MSG; a significant sex difference exists in the pituitary PRL response to inhibition of TH, and this response is not affected by MSG.

Aim and Methods: In 36 anesthetized spontaneously breathing Sprague-Dawley rats, the types of respiratory neurons and the state of neurotransmitters and receptors in nucleus paragigantocellularis lateralis (PGCL) were studied with extracellular recording technique and multibarrel microelectrode techniques., Results: At the caudal part of the PGCL(cPGCL) in 14 rats, a total of 39 respiratory neurons (RNs) were recorded including 24 inspiratory, 12 expiratory and 3 phase-spanning neurons. At the cPGCL in another 22 rats, we discovered that out of 14 RNs tested, 12 were excited by iontophoretic application of sodium glutamate (L-GLu), and all the 22 RNs tested were inhibited by gamma-aminobutyric acid (GABA). DL-2-amino-5-phosphonovaleric acid (AP5), an antagonist of N-methyl-D-aspartate (NMDA) receptor, and bicuculline (BIC), an antagonist of GABA(A) receptor, both showed three kinds of effects on the RNs discharge: excitatory, inhibitory and no-effect. AP5 could block partially the excitatory effect of L-GLu on a large part of RNs tested (6/9). BIC blocked, partially or completely, the inhibitory effect of GABA also on a large part of the RNs tested (9/11)., Conclusion: It is implied that PGCL is one of the important neural substrates responsible for the regulation of respiration. There might exist endogenous glutamate and GABA acting as neurotransmitters in the cPGCL area and excitatory amino acids (including NMDA and non- NMDA) and GABA(A)-receptors on cPGCL neurons. These neurotransmitters and receptors may mediate the regulatory action of cPGCL on respiration.

The present study investigated the effects of repeated cold stress on single neuron activity in the lateral hypothalamic area (LHA) and medial hypothalamic area (MHA) of behaving rats. The rats were trained to lick a protruding spout in response to one of several cue-tone stimuli (CTSs) to ingest water, or amino acid, NaCl or glucose solution. Following this training, the rats were raised under either stressed (repeated temperature changes between -3 and 24 degrees C) or control (24 degrees C) condition for 2 mo. During this period, neuronal activity was recorded in the LHA and MHA. For rats raised under the stressed condition, mean spontaneous firing rate of LHA neurons was significantly greater than for rats under the control condition. More LHA neurons in the stressed rats responded, with an accompanying decrease in activity (inhibitory response), to CTSs than in the control rats. During extinction learning, some LHA neurons enhanced or reversed the responses to CTSs in the stressed rats, whereas no LHA neurons showed such response changes in the control rats. In contrast to the effects of the stressed condition on LHA neuron activity, mean spontaneous firing rate of MHA neurons in the stressed rats was significantly smaller than in the control rats. Fewer MHA neurons in the stressed rats responded to CTSs and/or ingestion of sapid solutions. The preceding results suggested that repeated cold stress produces a specific pattern of changes in spontaneous activity and responses to sensory stimuli in LHA and MHA neurons; this could underlie the behavioral changes induced by repeated cold stress such as hyperphagia and hyper-reactivity to sensory stimuli.

Recent demonstrations of the feeding-inhibitory properties of putative peptides derived from cocaine- and amphetamine-regulated transcript (CART) raise the question of interactions between CART peptides and other messenger molecules implicated in the control of food intake. The present study investigated the histochemical relationship of CART to the neuropeptides thyrotropin-releasing hormone (TRH), melanin-concentrating hormone (MCH), orexin/hypocretin and neuropeptide Y (NPY) in the hypothalamus. Double-label in situ hybridization showed that CART to a great extent is co-expressed with TRH in hypothalamic paraventricular nucleus neurons. This technique was also used to demonstrate that MCH, but not orexin/hypocretin, mRNA colocalized with CART in neurons of the dorsomedial hypothalamic nucleus/lateral hypothalamic area. CART-peptide immunoreactive cell bodies in this region, as well as in the arcuate nucleus and the medial posterodorsal nucleus of the amygdala, were all seen to have close appositions formed by NPY-immunoreactive nerve terminals. Lastly, in a study of mice treated with the neurotoxin, monosodium glutamate, which targets the arcuate nucleus, a near-total ablation of CART peptide immunoreactive cell bodies in this nucleus was accompanied by decreased terminal staining for CART peptide in the paraventricular hypothalamic nucleus, the arcuate nucleus itself and in the dorsomedial hypothalamic nucleus. These findings further define the position of hypothalamic CART neurons within the hierarchy of brain circuitries regulating energy balance, demonstrating the presence of CART peptide in several cell populations that form putative down-stream targets of NPY terminals, including hypophysiotropic TRH neurons and lateral hypothalamic MCH neurons.

Gene expression for agouti-related protein (AGRP), an endogenous antagonist of melanocortin receptors, has been localized to the hypothalamic arcuate nucleus, where it colocalizes with neuropeptide Y (NPY). Having reported that the NPY innervation of hypophysiotropic TRH neurons in the hypothalamic paraventricular nucleus (PVN) originates primarily from NPY-producing neurons in the arcuate nucleus, here we examined the possibility that TRH neurons in the PVN are similarly innervated by AGRP nerve terminals. Using immunohistochemistry, AGRP-containing cell bodies were found almost exclusively in the arcuate nucleus, but their projections were distributed widely in the hypothalamus, most conspicuously in the paraventricular (PVN), arcuate and dorsomedial nuclei, and the posterior hypothalamic area. Ablation of the arcuate nucleus by the neonatal administration of monosodium glutamate obliterated nearly all AGRP-immunoreactivity in the hypothalamus. In the PVN, double-labeling light and electron microscopic immunohistochemistry revealed that TRH neurons receive dense innervation by AGRP nerve terminals, with the frequent occurrence of axosomatic and axodendritic synapses (mainly of the symmetrical type). These findings provide morphological basis to hypothesize a role for AGRP in the arcuato-paraventricular pathway, in the down-regulation of the hypothalamic-pituitary-thyroid axis, which occurs as an adaptive response to starvation.

The cardiac actions of microinjecting sodium glutamate (0.5-2 nmol) among sympathetic premotor neurons of the subretrofacial nucleus in the rostral ventrolateral medulla (RVLM) were studied in chloralose-anesthetized cats after bilateral vagotomy, sinoaortic denervation, adrenalectomy, and alpha1-receptor blockade. Glutamate microinjections increased heart rate by 25.9 +/- 1.8 beats/min (17. 5%), systolic rate of rise in left ventricular pressure (LVdP/dt) by 1,443 +/- 110 mmHg/s (119%), and arterial blood pressure by 26.9 +/- 1.7 mmHg (50%), whereas they shortened the electrocardiogram P-R interval in 85 of 103 cases by 7.5 +/- 1.2 ms (11.4%), triggering junctional rhythms on five occasions. The increase in LVdP/dt usually led the rise in blood pressure, and its magnitude greatly exceeded any increase attributable to changes in heart rate, diastolic filling, or afterload. Right-sided microinjections caused significantly greater tachycardias than did left-sided microinjections, but only left-sided microinjections triggered junctional rhythms (5 of 52 vs. 0 of 51; P < 0.05), whereas microinjections on either side raised LVdP/dt equally. Subretrofacial neurons thus drive positive chronotropic, inotropic, and dromotropic actions via the cardiac sympathetic nerves, whereas subsets among them preferentially control different aspects of cardiac function.

An exogenous glutamate injection into the hypothermic hippocampal CA1 during 5-min ischemia produced the same extent of extracellular glutamate levels as observed in the normothermic CA1 during 5-min ischemia; however, neuronal death was not induced in the hypothermic CA1. Glutamate is released excessively into the extracellular space during ischemia, and is thought to induce brain injury by its neurotoxicity. It has been reported that the massive glutamate release is reduced by mild hypothermia, and it has been proposed that the reduction of ischemia-induced glutamate release exerts the neuroprotective effect on postischemic neuronal death. In the present study, to determine whether the neuroprotective effect of mild hypothermia on postischemic hippocampal CA1 neuronal death is due to the reduction of ischemia-induced glutamate release, gerbils were subjected to 5-min ischemia under hypothermic condition at 31 degrees C and were simultaneously injected exogenously with L-glutamate, so that the hypothermic CA1 around a microdialysis probe was exposed to the same extracellular glutamate levels as seen during normothermic ischemia, and the histological outcome was examined. An injection with 1 mM L-glutamate into the hypothermic CA1 during 5-min ischemia produced a similar extent of increased glutamate (17-fold increase) to that observed in the normothermic CA1 during 5-min ischemia (16-fold increase). However, neuronal death was not induced in the hypothermic CA1. This result indicates that the neuroprotective effect of mild hypothermia cannot be explained in terms of a reduction of glutamate release during ischemia.

Neonatal monosodium glutamate (MSG)-treated rats were used in this study to answer two questions: (1) whether or not the dopamine-responsive dorsomedial arcuate (dm-ARN) neurons are tuberoinfundibular dopaminergic (TIDA) neurons, and (2) whether or not the remaining TIDA neurons in MSG-treated rats are functioning normally. MSG (4 mg/g b. wt., subcutaneously [s.c.]) or saline was given to neonatal Sprague-Dawley rats on days 1, 3, 5, 7, and 9 after birth. The female rats were ovariectomized at 50 days of age and treated with estrogen for 1 week before they were used between 65-90 days of age. The tyrosine hydroxylase-immunoreactive (TH-ir) neurons located in the dm and ventrolateral (vl) parts of the ARN were significantly reduced in MSG-treated rats, as determined by immunohistochemical method. Some TH-ir cells, however, were visible along the border of the third ventricle. Using single-unit recording in brain slices, we found that dopamine inhibited significantly fewer percentage of dm-ARN neurons in MSG-treated (28.2%, n = 39) than in saline-treated rats (73.3%, n = 15). In contrast, bombesin exhibited similar effects (over 70% excitation) in both groups. Using neurochemical means, neonatal MSG treatment produced significant decreases of both 3,4-dihydroxyphenylacetic acid and dopamine levels, but not their ratios, in the median eminence. Moreover, the diurnal change of TIDA neuronal activity persisted in the MSG-treated rats; so did the estrogen-induced afternoon prolactin surge. All these results indicate that neonatal MSG-treatment reduced the number and altered the location of TIDA and dopamine-responsive dm-ARN neurons. The remaining TIDA neurons seemed to be able to maintain their basal activities and diurnal rhythm.

Longitudinal muscle-myenteric plexus strips of the guinea pig ileum were used to investigate a possible transmitter role of glutamate (Glu) in the enteric nervous system. Glu was released from this nerve muscle preparation by high K(+)-depolarization in a Ca2(+)-dependent manner, by electrical field stimulation and by the ganglionic stimulant dimethylphenylpiperazinium which indicates its neural origin. Contractions of the longitudinal muscle evoked by electrical stimulation of the myenteric nerves or by Glu, were significantly reduced by the N-methyl-D-aspartate (NMDA)-receptor antagonist FR115427 (9 and 18 microM), whereas contractions induced by histamine were unaffected. The results show that the amino acid Glu is likely to play an excitatory neurotransmitter role via NMDA receptors in the myenteric plexus of the guinea pig.

We mapped the distribution of calretinin-immunoreactive neuron populations in a circumventricular organ of the rat, the area postrema, and investigated their sensitivity to excitotoxic stimuli mediated by subcutaneously administered monosodium glutamate. We were specifically interested to ascertain whether the presence of calretinin can, per se, confer an in vivo intrinsic resistance for area postrema neurons to glutamate excitotoxicity. We found that dense populations of calretinin-positive neurons displayed a subregional compartmentation in coronal sections of the area postrema along its rostrocaudal axis. We demonstrated that calretinin-positive neurons differ in their sensitivities to monosodium glutamate depending on their position within the area postrema. Neurons in the caudal area postrema were the most sensitive ones, while those in the rostral area postrema were spared of degeneration. We conclude that calretinin-positive neurons in the area postrema are not uniformly protected against glutamate excitotoxicity. It is possible that differences in the local concentrations of monosodium glutamate due to regional heterogeneities in density and permeability of the capillary bed rather than neuronal expression of calretinin account for the observed effects.

Neuropeptide Y (NPY) immunoreactive (-ir) nerve fibers densely innervate hypophysiotropic TRH perikarya and dendrites in the hypothalamic paraventricular nucleus (PVN). To evaluate the contribution of the arcuate nucleus (Arc) to this innervation, the effect of Arc ablation by neonatal monosodium glutamate (MSG) treatment on the density of NPY-fibers contacting TRH neurons in the PVN was investigated. After the lesioned animals and vehicle-treated controls reached adulthood, the number of contacts between NPY-ir boutons and TRH-ir perikarya in the PVN was determined in double-immunostained sections. In controls, numerous contacts between NPY-ir terminals and TRH perikarya and dendrites were observed, confirming earlier findings. MSG treatment resulted in a marked reduction of the size of the Arc and also the number of NPY-perikarya with a concomitant reduction of 82.4 +/-2.1% in the relative number of NPY terminals contacting TRH perikarya and first order dendrites in the medial parvocellular and periventricular subdivisions of the PVN. In contrast, lesioning of the ascending adrenergic bundle in the brain stem caused no statistically significant change in the number of NPY-terminals in close apposition to hypophysiotropic TRH neurons in the PVN. These data confirm earlier findings that NPY-containing axon terminals innervate TRH neurons in the PVN and further demonstrate a potentially important anatomical relationship between NPY-producing neurons in the Arc and hypophysiotropic TRH neurons.

Background: The neonatal administration of monosodium L-glutamate (MSG) has been used in investigations of the possible role of the arcuate nucleus in neuroendocrine regulation during postnatal development. We used this method to examine whether the mouse arcuate contained cell bodies immunoreactive with antisera to growth hormone releasing hormone (GHRH) or luteinizing hormone releasing hormone (LHRH), and whether these hypothalamic peptides affect synthesis and secretion of growth hormone and gonadotropin and the testis., Methods: The hypothalamus, pituitary, and testes of adult male mice treated with MSG during the neonatal period were fixed in Bouin's fluid or 10% neutral formalin. The hypothalamus was used in immune staining, the pituitary was used in both morphometry and immune staining, and the testis was stained with hematoxylin and eosin., Results: Body weights in control and treated mice were not different. The treated mice had more subcutaneous adipose tissue and a shorter body than the control mice. The testes were heavier in the controls. Many perikarya immunoreactive with antisera to GHRH or LHRH were found in the arcuate nucleus in control mice, but few such perikarya were found in this nucleus in treated mice. The size of the anterior lobe and the number and size of GH cells, follicle stimulating hormone (FSH) cells, and prolactin (PRL) cells in treated mice were less than those of control mice., Conclusions: GHRH and LHRH neurons in the arcuate nucleus in male mice may cause body and testis weight to increase via GH and LH cells, respectively, in the adenohypophysis during postnatal development. There are some differences in the hypothalamo-pituitary-testis axis of mice and rats.

Simultaneous recordings were made in chloralose-anesthetized cats from muscle vasoconstrictor (MVC), visceral vasoconstrictor (VVC), and renal (RSN) sympathetic fibers. Their barosensitivity was demonstrated, after which all baroreceptor nerves were cut. Multiple microinjections of sodium glutamate (5 nl, 0.1 M) were made in a grid pattern covering the rostral ventrolateral medulla (RVLM) pressor area on seven sides of four animals. Injections increased blood pressure by up to 87 +/- 22 mmHg and MVC, VVC, and RSN activities by up to 169 +/- 55, 62 +/- 23, and 67 +/- 36%, respectively. The relative responses between nerves (taken in pairs) showed significant inhomogeneity across injections into 5/7, 6/7, and 1/7 RVLMs for MVC vs. VVC, MVC vs. RSN, and VVC vs. RSN, respectively. Calculation showed that overall, less than half the response spikes due to RVLM glutamate injections could be accounted for by a hypothetical population of neurons that excited MVC, VVC, and RSN outflows in fixed proportion. Sites that exclusively drove MVC, VVC, or RSN outflows were found in 7/7, 3/7, and 5/7 RVLMs, respectively. Sites that selectively drove either nerve of a given pair were ubiquitous. The RVLM territories from which the three outflows could be activated overlapped but showed clear differences. Their shapes and sizes differed between animals and even between sides. They covered the subretrofacial (SRF) nucleus plus a variable rostromedial extension. The data support the view that the RVLM neurons driving these three sympathetic outflows are largely, perhaps entirely, separate populations.

Ketamine and L-glutamate were applied microiontophoretically to neurones of several central nervous system (CNS) structures in urethane anaesthetized Wistar rats. The spontaneous single-unit activities of all the hippocampal CA1 and CA3 neurones were suppressed by ketamine in an iontophoretic current-dependent manner. The spontaneous single-unit activities of eight of nine neurones in the thalamus were not affected by ketamine and suppressed in one. Spontaneous neurone activities in the midbrain reticular formation were not significantly affected by ketamine. Spontaneous activities of the cerebellar Purkinje cell were suppressed by ketamine in four of eight neurones. L-Glutamate excited all 13 hippocampal and nine thalamic neurones in a current-dependent manner. L-Glutamate-induced excitation of all CA1, CA3 and thalamic neurones was inhibited by ketamine. The inhibitory effects of ketamine on L-glutamate-induced excitation were dependent on the injection current intensity, although the sensitivity of thalamic neurones to the injection current was approximately three times that of hippocampal neurones. We conclude that the effects of ketamine on spontaneous activities of neurones vary according to the brain region, probably because of the distribution of NMDA receptors. Moreover, the actions of the drug on NMDA receptors appear to differ between the hippocampus and thalamus. These regionally differential actions of ketamine may reflect characteristics of anaesthesia induced by this drug.

The RNA content of the ventromedial hypothalamus (VMH), the lateral hypothalamic area (LHA), and the cortical neurons of male and female rats, neonatally treated with monosodium glutamate (MSG), were investigated. MSG (2 g/kg b.wt.) was injected subcutaneously to male and female rat pups daily for 5 days after birth. At 12 weeks of age a significant decrease of RNA content in the VMH cells and significantly increased body fat in neonatally MSG-treated animals were found. Correlation of these data showed a significant negative correlation between the body fat content and the RNA content in VMH neurons. The results a) confirm a closed relationship between the body fat content and the functional activity of VMH, b) indicate that obesity of neonatally MSG-treated animals should be due to decreased functional activity of the VMH cells.

Fetal (17-18 days of gestation) mediobasal hypothalamic tissue (MBH) was transplanted into the third ventricle of adult, male rats which had been treated neonatally with monosodium glutamate (MSG). MSG treatment caused a marked reduction of growth hormone-releasing factor-like-immunoreactive (GRF-i) perikarya in the arcuate nucleus and GRF-i fibers in the median eminence (ME), as compared to littermate controls. When normal fetal MBH was transplanted into the third ventricle of MSG recipients, numerous GRF-i perikarya were located within the graft four weeks following surgery. GRF-i fibers in the ME of MSG-treated rats were enhanced when MBH grafts were in close contact with the ME, but not when transplants were located dorsally or rostrally in the third ventricle without making contact with the recipient's ME. Fetal cerebral cortex, which was grafted as a control tissue, did not contain GRF-i neurons. These immunohistochemical results suggest that grafted fetal GRF-i perikarya may contact the recipient's ME to increase the content of GRF previously depleted by exposure to MSG.

Behavioural effects of carbachol given into the hypothalamic/preoptic area have been demonstrated but there is a paucity of information about the response of single neurons to carbachol. The aim of the present study was to determine the response of spontaneously firing neurons in the rat hypothalamic/preoptic area to application of carbachol by iontophoresis or by pressure injection in a dose and volume comparable with that used in behavioural studies. Extracellular single unit recordings showed a significant decrease in mean firing rate in 82% of neurons responding to iontophoretic carbachol and in 75.5% of neurons responding to carbachol injected about 600 microns away. An increase in firing rate occurred in only 15 and 17.6% of neurons, respectively. Application of saline did not alter the mean firing rate while application of glutamate into the same areas or ejection into the vicinity of the same neurons caused an increase in mean firing rate in 94% of responding neurons. The results indicate that a decrease in mean firing rate is the predominant neuronal response to carbachol in the anteromedial hypothalamic/preoptic area of the rat and we suggest that this decrease may be associated with behavioural responses to carbachol.

Single electrode voltage clamp recordings were made during Pavlovian conditioning of single units of the motor cortex of cats. Units that developed a conditioned spike discharge in response to a click conditioned stimulus (CS) after pairing the click with glabella tap and local ionophoretic application of glutamate showed increases in input resistance and reductions of an early outward current induced by depolarizing commands and by return to holding potentials after hyperpolarizing commands. Changes in later currents were also found in some cells. Units that failed to develop a conditioned response did not show these changes. The decreases in membrane currents could contribute to an increased spike discharge in response to the CS as could the increased input resistance observed after conditioning. Conductance changes of this type may serve as engrams by which some forms of memory and learning are expressed across both vertebrate and invertebrate species.

Cross-correlation analysis of interdependence of the background spike activity was carried out for pairs of adjacent neurons simultaneously recorded in the incubated slices of the neocortex of guinea-pig. Statistical correlation of spike discharges was detected in 16 out of 26 recorded pairs of the neurons. Significant correlation was observed mainly in the range of +/- 100 ms from the null point. Cross-correlation had symmetric or asymmetric maxima up to 150 ms long and negative shifts up to 200 ms long. More complex positive-negative types of cross-correlations were also obtained. The data were compared to those known from other authors for the intact brain. The contribution of intrinsic intracortical interactions and extrinsic afferent influences in these correlations of activity is discussed.

The hypogonadal (hpg) mouse lacks GnRH due to a severe truncation of the gene by which it is encoded. This results in an infertile animal with an infantile reproductive system. When fetal or 1-day postnatal septal/preoptic area of a normal mouse is grafted into the third ventricle of an hpg mouse, GnRH-containing fibers grow out of the grafts and innervate the host median eminence (ME), a normal target of these fibers. GnRH axons exiting the graft course follow a very stereotyped pathway through host tissue. They are observed passing through the ependymal wall of the ventricle directly into the ME or arching through the host arcuate nucleus to terminate in the host ME. Given the fixed pattern of outgrowth, we wanted to determine if the neurons of the arcuate nucleus, which lie between the graft and its target, are exerting an influence on the growth and direction of these fibers. The excitotoxin monosodium glutamate (MSG) has been shown to destroy the vast majority of arcuate neurons when administered neonatally. Mutant host animals treated with MSG received fetal grafts of normal septal/preoptic area. Brains were examined for GnRH fiber outgrowth 30 days later to assess early outgrowth which preferentially uses the arcuate route. We report here that the pattern of outgrowth is virtually identical to that observed in saline-injected, grafted animals. There is also no difference in the success rate of grafts placed in control vs MSG-treated hosts nor in the stimulation of testicular growth. The results of this experiment imply that axonal outgrowth to the ME does not rely on arcuate neurons for guidance information or trophic substances. These functions may be subserved by glia, tanycytes/ependyma, or the target.

In cats anesthetized with Nembutal and immobilized with Flaxedil, extracellular recordings were made from dorsal horn neurons and lamina X neurons in the lumbar spinal cord. The nociceptive responses of these neurons elicited by peripheral nerve stimulation were significantly inhibited by stimulation of the nucleus tractus solitarius (NTS) at low intensity without any noticeable cardiovascular reaction. As usual, the late response or C-response was found to be preferentially inhibited by NTS stimulation as compared with the early response or A-response. The effective current intensity for NTS stimulation-produced inhibition ranged from 80 microA to 200 microA. Stronger inhibition was induced when the stimulating site was within or in the immediate vicinity of the NTS. There was no significant difference in the efficacy of the NTS stimulation-produced inhibition of nociceptive response between dorsal horn neurons and lamina X neurons. A similar inhibitory effect was elicited by microinjection of monosodium glutamate into the NTS area. The results demonstrate that the NTS may be involved in the control of nociceptive transmission at the spinal cord level.

A single subcutaneous injection of monosodium-L-glutamate induces severe ultrastructural alterations in certain AChE positive parenchymal cells of the Area postrema of the adult rat. Signs of cellular degeneration include massive intracellular edema, swelling of mitochondria, vacuolization of the cisternae of the rough endoplasmic reticulum and marked alterations in the chromatin pattern of the nucleus. Identification of these cells as neurons is based on the presence of axosomatic synapses.

1. The whole-cell and outside-out configurations of the patch-clamp method were used to investigate the properties of the channels activated by N-methyl-D-aspartate (NMDA channels) in mouse central neurones in culture. Recording was made in Mg2+-free solutions. 2. In the whole-cell recording mode the currents induced by both NMDA and L-glutamate were accompanied by a large increase in noise. In both cases the noise power spectra were well fitted by single Lorentzian functions and the corresponding mean time constant, tau, was about 6 ms at room temperature. The single-channel conductance, gamma n, estimated from the ratio of the noise variance to the total current, varied between 22 and 40 pS. 3. Endogenous amino acids known to activate NMDA receptors (L-glutamate, L-aspartate, L-cysteine sulphinate and quinolinate) as well as exogenous NMDA agonists such as ibotenate and trans-2,3-piperidine dicarboxylate (trans-PDA) all produced similar responses. In particular, analysis of the current noise yielded tau values between 4 and 8 ms in all cases. 4. NMDA responses were antagonized by 2-amino-5-phosphonovalerate (APV) without any effect on gamma n or tau values measured by noise analysis; NMDA responses were also diminished by D-alpha-aminoadipate and cis-2,3-piperidine dicarboxylate. 5. In outside-out patches, it was observed that the single-channel current amplitude varies linearly as a function of membrane potential between -80 and +60 mV. The reversal potential is near 0 mV. NMDA channels are permeable to Na+, K+ and Cs+, but blocked by choline. The single-channel conductance, gamma e, varies between 40 and 50 pS at room temperature. 6. The NMDA channels open in bursts of short openings interrupted by brief closures. At -60 mV, the closures had a mean duration, tc, of 0.4 +/- 0.2 ms. The mean channel open time, to, was 5.9 +/- 1.0 ms for NMDA and 5.3 +/- 1.7 ms for L-glutamate. The mean burst duration, tb, was 10.5 +/- 0.7 ms for NMDA and 8.5 +/- 2.0 ms for L-glutamate. 7. When the temperature was increased between 14 and 24 degrees C, the NMDA channel conductance increased with a Q10 of 1.6 while the mean open time decreased with a Q10 close to 2. 8. The NMDA channel showed, in addition to the 'main' conductance state (40-50 pS), smaller conductance states of 15 and 35 pS.(ABSTRACT TRUNCATED AT 400 WORDS)

Neurotoxin induced nerve cell degeneration has been studied in sensory ganglia of newborn and in the area postrema of adult rats following the administration of the selective sensory neurotoxin, capsaicin and the amino acid excitotoxin, glutamic acid, respectively. Light microscopic histochemical, autoradiographic, electroncytochemical and X-ray microanalytical studies revealed that degeneration of certain small-sized, type B primary sensory neurons, induced by capsaicin, was associated with a marked accumulation of calcium predominantly in mitochondria of the damaged ganglion cells. Similarly, monosodium glutamate treatment resulted in the appearance of calcium-containing electron-dense granules in mitochondria of degenerating area postrema neurons. In addition, after a combined administration of 45Ca2+ and capsaicin or monosodium glutamate, significantly higher levels of radioactivity have been detected by liquid scintillation spectroscopy in the Gasserian ganglia and the area postrema, respectively. It is concluded that an enhancement in intracellular calcium level may be intimately involved in the process of neuronal cell death and may represent a common basic mechanism responsible for the development of cellular events leading ultimately to the degeneration of nerve cells.

Intrahypothalamic somatostatin-containing neurons were investigated immunohistochemically. In intact rats, immunoreactive cell bodies appeared in the rostral periventricular area, and immunoreactive beaded fibers were observed to terminate in the median eminence and to form delicate networks surrounding immunonegative cell bodies within the medial preoptic, suprachiasmatic, arcuate, ventromedial and premammillary nuclei. Intraventricular colchicine infusion resulted in the appearance of immunoreactive cell bodies in the arcuate, ventromedial and suprachiasmatic nuclei, and an increase in the number of cell bodies seen in the periventricular area. Complete deafferentation of the medial-basal hypothalamus excluding the rostral periventricular area caused the immunoreactive structures in the median eminence to disappear and enhanced the staining of periventricular cell bodies. In the arcuate and ventromedial nuclei, the immunoreactive fiber networks were left intact and the immunoreactive cell bodies were occasionally recognized. Horizontal knife cut between the arcuate nuclei and median eminence did not alter immunoreactivity in either region. Neonatal administration of MSG caused only the disappearance of arcuate nuclei. The results indicate that two kinds of somatostatin neuronal systems exist in rat hypothalamus: one is involved in the production of hormonal somatostatin and the other serves for the regulation of neuronal activities in restricted hypothalamic nuclei.

Monosodium glutamate given at a concentration of 5 X 10(-6) M to whole-brain dissociated cultures of 18-day-old rats promotes neuronal growth. Neurons are larger due to an increased size of both cytoplasm and nucleus. Rough endoplasmic reticulum is more developed and mitochondria are more abundant. Synaptic vesicles are significantly increased in number with respect to control cultures. Synapses are more abundant and show a more differentiated morphology. These findings are interpreted as evidence for accelerated development secondary to the stimulatory effects of glutamate.

A displacement of structures in the hypothalamic region of the rat has been reported in previous papers. 1 micron granules located in neuroblast like cells containing catalase activity (which were detected by enzyme histochemical methods) undergo a shift from the median eminence (at day 22 after birth) towards the ventromedial part of the hypothalamus (at day 35 after birth). This displacement terminates in the medio-basal part of the arcuate nucleus (at day 55 after birth). A similar displacement of dopaminergic fluorescent perikarya has been described following the same route, with the same time sequence. Neonatal application of monosodium glutamate (MSG) leads to an acceleration of the displacement of both the catecholaminergic and the catalase containing perikarya. However after day 25 (after birth) all fluorescent perikarya disappear whereas the catalase containing cell survive when they finally reach the arcuate area.

The techniques of microelectrophoresis and antidromic identification have been utilized in the female rat anesthetized with urethane to localize the tuberoinfundibular neurons and to determine their pharmacological sensitivity to dopamine (DA), norepinephrine (NE) and glutamate (GLUT). Extracellular recordings were made of 149 single units in the arcuate (ARC) nucleus; 79 of which were antidromically identified (43 were spontaneously active and 36 were silent) and the remaining 70 cells were determined to be spontaneously active but could not be antidromically identified (unidentified ARC neurons). The mean latency of the antidromically activated potentials was 9,5 msec, which gave a conduction velocity of 0.05 mm/msec. The spontaneous firing rate of antidromically identified ARC neurons varied from less than 1/sec to 8/sec while unidentified cells discharged at rates from less than 3/sec to 10/sec. These data indicate that ARC neurons exist which are capable of conducting impulses and send their axons into the external layer of the ME. Successful drug applications were made on 104 ARC neurons; of the 43 antidromically identified units, 37 were spontaneously active and 6 were silent. There were 61 spontaneously active, unidentified neurons. Two distinct pools of antidromically identified ARC neurons were found based on their sensitivity to NE and DA. Neurons displaying excitation to NE(N = 23) were either inhibited (N = 10) or non-responsive (N = 13) to DA applied electrophoretically; no NE-sensitive ARC neurons were excited by DA. The second pool of neurons (N = 14) was excited by DA. These neurons when tested with NE were either reproducibly inhibited (N = 3) or nonresponsive (N = 11); no DA-sensitive neurons were excited by NE. In the unidentified ARC neurons, iontophoretically applied NE and DA gave reproducible effects on individual neurons, so that some neurons were excited by both NE and DA, some were inhibited by both, and still others were excited by one and inhibited by the other chemical. Glutamate (GLUT) had a powerful excitant action on nearly all the neurons tested, increasing the electrical activity of the spontaneously active neurons as well as initiating activity in quiescent ARC neurons. These data are suggestive of a tuberoinfundibular neuronal system whose activity is modulated by either DA or NE. This evidence is certainly compatible with a functional role for both DA and NE in regulating pituitary function by altering the activity of presumed neurosecretory neurons which release hypophysiotropic hormones.