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Sleep disturbances and persistent pain conditions are public health challenges worldwide. Although it is well-known that sleep deficit increases pain sensitivity, the underlying mechanisms remain elusive. We have recently demonstrated the involvement of nucleus accumbens (NAc) and anterior cingulate cortex (ACC) in the pronociceptive effect of sleep restriction. In this study, we found that sleep restriction increases c-Fos expression in NAc and ACC, suggesting hyperactivation of these regions during prolonged wakefulness in male Wistar rats. Blocking adenosine A 2A receptors in the NAc or GABA A receptors in the ventral tegmental area (VTA), dorsal raphe nucleus (DRN), or locus coeruleus (LC) effectively mitigated the pronociceptive effect of sleep restriction. In contrast, the blockade of GABA A receptors in each of these nuclei only transiently reduced carrageenan-induced hyperalgesia. Pharmacological activation of dopamine D 2 , serotonin 5-HT 1A and noradrenaline alpha-2 receptors within the ACC also prevented the pronociceptive effect of sleep restriction. While pharmacological inhibition of these same monoaminergic receptors in the ACC restored the pronociceptive effect which had been prevented by the GABAergic disinhibition of the of the VTA, DRN or LC. Overall, these findings suggest that the pronociceptive effect of sleep restriction relies on increased adenosinergic activity on NAc, heightened GABAergic activity in VTA, DRN, and LC, and reduced inhibitory monoaminergic activity on ACC. These findings advance our understanding of the interplay between sleep and pain, shedding light on potential NAc-brainstem-ACC mechanisms that could mediate increased pain sensitivity under conditions of sleep impairment., 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. Published by Elsevier Ltd.)

Rett Syndrome (RTT) is an X-linked neurodevelopmental disorder caused mainly by mutations in the MECP2 gene. One of the major RTT features is breathing dysfunction characterized by periodic hypo- and hyperventilation. The breathing disorders are associated with increased brainstem neuronal excitability, which can be alleviated with GABA agonists. Since neuronal hypoexcitability occurs in the forebrain of RTT models, it is necessary to find pharmacological agents with a relative preference to brainstem neurons. Here we show evidence for the improvement of breathing disorders of Mecp2-disrupted mice with the brainstem-acting drug cloperastine (CPS) and its likely neuronal targets. CPS is an over-the-counter cough medicine that has an inhibitory effect on brainstem neuronal networks. In Mecp2-disrupted mice, CPS (30 mg/kg, i.p.) decreased the occurrence of apneas/h and breath frequency variation. GIRK currents expressed in HEK cells were inhibited by CPS with IC 50 1 μM. Whole-cell patch clamp recordings in locus coeruleus (LC) and dorsal tegmental nucleus (DTN) neurons revealed an overall inhibitory effect of CPS (10 μM) on neuronal firing activity. Such an effect was reversed by the GABA A receptor antagonist bicuculline (20 μM). Voltage clamp studies showed that CPS increased GABAergic sIPSCs in LC cells, which was blocked by the GABA B receptor antagonist phaclofen. Functional GABAergic connections of DTN neurons with LC cells were shown. These results suggest that CPS improves breathing dysfunction in Mecp2-null mice by blocking GIRK channels in synaptic terminals and enhancing GABA release., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Limited information exists on the link between purinergic class P2X7 receptors (P2X7Rs) and calcium ion channels in epilepsy; no data has been reported regarding the interaction between P2X7Rs and T-type calcium ion channels in epilepsy. Thus, this study is an evaluation of the role that T-type calcium ion channels play in the effect of P2X7Rs on penicillin-induced epileptiform activity. In the first set of experiments, P2X7R agonist BzATP (at 25-, 50-, 100- and 200-μg doses), P2X7R antagonist A-438079 (at 5-, 10-, 20- and 40-μg doses) and T-type calcium ion channel antagonist, NNC-550396 were administered for electrophysiological analyses 30 min after penicillin injection (2.5 μl, 500 IU). In the second set of experiments, the effective doses of these substances were used for biochemical analyses. Malondialdehyde (MDA), advanced oxidation protein product (AOPP), glutathione (GSH), glutathione reductase (GR), glutathione peroxide (GPx), catalase (CAT) and superoxide dismutase (SOD) levels were measured in the cerebrum, cerebellum and brainstem of rats. BzATP (100 μg, icv) increased the mean frequency of epileptiform activity, whereas A-438079 (40 μg, icv) and NNC-550396 (30 μg, ic) reduced it. Both A-438079 and NNC-550396 reversed BzATP's proconvulsant action. BzATP increased lipid peroxidation and protein oxidation; it also altered other antioxidant enzymes measured in this study, which were all then reversed via A-438079 and NNC-550396, at least in the cerebrum. The electrophysiological and biochemical analysis of present study suggest that P2X7Rs and its interaction with T-type calcium ion channels play an important role in the experimental model of epilepsy., (Copyright © 2019. Published by Elsevier Ltd.)

Serotonin (5-HT) neurons are involved in wake promotion and exert a strong inhibitory influence on rapid eye movement (REM) sleep. Such effects have been ascribed, at least in part to the action of 5-HT at post-synaptic 5-HT 1A receptors (5-HT 1A R) in the brainstem, a major wake/REM sleep regulatory center. However, the neuroanatomical substrate through which 5-HT 1A R influence sleep remains elusive. We therefore investigated whether a brainstem structure containing a high density of 5-HT 1A R mRNA, the GABAergic Gudden's dorsal tegmental nucleus (DTg), may contribute to 5-HT-mediated regulatory mechanisms of sleep-wake stages. We first found that bilateral lesions of the DTg promote wake at the expense of sleep. In addition, using local microinjections into the DTg in freely moving mice, we showed that local activation of 5-HT 1A R by the prototypical agonist 8-OH-DPAT enhances wake and reduces deeply REM sleep duration. The specific involvement of 5-HT 1A R in the latter effects was further demonstrated by ex vivo extracellular recordings showing that the selective 5-HT 1A R antagonist WAY 100635 prevented DTg neuron inhibition by 8-OH-DPAT. We next found that GABAergic neurons of the ventral DTg exclusively targets glutamatergic neurons of the lateral mammillary nucleus (LM) in the posterior hypothalamus by means of anterograde and retrograde tracing techniques using cre driver mouse lines and a modified rabies virus. Altogether, our findings strongly support the idea that 5-HT-driven enhancement of wake results from 5-HT 1A R-mediated inhibition of DTg GABAergic neurons that would in turn disinhibit glutamatergic neurons in the mammillary bodies. We therefore propose a Raphe→DTg→LM pathway as a novel regulatory circuit underlying 5-HT modulation of arousal., (Copyright © 2018 The Authors. Published by Elsevier Ltd.. All rights reserved.)

The cancer anorexia-cachexia syndrome (CACS) is a frequent and severe condition in cancer patients. Currently, no pharmacological treatment is approved for the therapy of CACS. Centrally, glucagon-like peptide-1 (GLP-1) is expressed in the nucleus tractus solitarii (NTS) and is implicated in malaise, nausea and food aversion. The NTS is reciprocally connected to brain sites implicated in the control of energy balance including the area postrema (AP), which mediates CACS in certain tumour models. Given the role of GLP-1 as a mediator of anorexia under acute sickness conditions, we hypothesized that brainstem GLP-1 signalling might play a role in the mediation of CACS. Using hepatoma tumour-bearing (TB) rats, we first tested whether the chronic delivery of the GLP-1R antagonist exendin-9 (Ex-9) into the fourth ventricle attenuates CACS. Second, we investigated whether a genetic knockdown of GLP-1 expression in the NTS ameliorates CACS. Ex-9 attenuated anorexia, body weight loss, muscle and fat depletion compared to TB controls. Similarly, TB animals with a knockdown of GLP-1 expression in the NTS had higher food intake, reduced body weight loss, and higher lean and fat mass compared to TB controls. Our study identifies brainstem GLP-1 as crucial mediator of CACS in hepatoma TB rats. The GLP-1R represents a promising target against CACS and possibly other forms of disease-related anorexia/cachexia., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Glycinergic inhibitory neurons of the spinal dorsal horn exert critical control over the conduction of nociceptive signals to higher brain areas. The neuronal glycine transporter 2 (GlyT2) is involved in the recycling of synaptic glycine from the inhibitory synaptic cleft and its activity modulates intra and extracellular glycine concentrations. In this report we show that the stimulation of P2X purinergic receptors with βγ-methylene adenosine 5'-triphosphate induces the up-regulation of GlyT2 transport activity by increasing total and plasma membrane expression and reducing transporter ubiquitination. We identified the receptor subtypes involved by combining pharmacological approaches, siRNA-mediated protein knockdown, and dorsal root ganglion cell enrichment in brainstem and spinal cord primary cultures. Up-regulation of GlyT2 required the combined stimulation of homomeric P2X 3 and P2X 2 receptors or heteromeric P2X 2/3 receptors. We measured the spontaneous glycinergic currents, glycine release and GlyT2 uptake concurrently in response to P2X receptor agonists, and showed that the impact of P2X3 receptor activation on glycinergic neurotransmission involves the modulation of GlyT2 expression or activity. The recognized pro-nociceptive action of P2X 3 receptors suggests that the fine-tuning of GlyT2 activity may have consequences in nociceptive signal conduction., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Rett Syndrome (RTT) is a neurodevelopmental disorder caused by mutations of the MECP2 gene, affecting predominantly females. One of the characteristic features of the disease is defective brainstem autonomic function. In Mecp2 -/Y mice, several groups of brainstem neurons are overly excitable, which causes destabilization of neuronal networks for the autonomic control. We have previously shown that the extrasynaptic GABA A receptor agonist THIP relieves many RTT-like symptoms in Mecp2 -/Y mice. Although neuronal activity is inhibited by acute THIP exposure, how a chronic treatment affects neuronal excitability remains elusive. Thus, we performed studies to address whether increased excitability occurs in brainstem neurons of female Mecp2 +/- mice, how the MeCP expression affects the neuronal excitability, and whether chronic THIP exposure improves the neuronal hyperexcitability. Symptomatic Mecp2 +/- (sMecp2 +/- ) female mice were identified with a two-step screening system. Whole-cell recording was performed in brain slices after a prior exposure of the sMecp2 +/- mice to a 5-week low-dose THIP. Neurons in the locus coeruleus (LC) and the mesencephalic trigeminal nucleus (Me5) showed excessive firing activity in the sMecp2 +/- mice. THIP pretreatment reduced the hyperexcitability of both LC and Me5 neurons in the sMecp2 +/- mice, to a similar level as their counterparts in Mecp2 -/Y mice. In identified LC neurons, the hyperexcitability appeared to be determined by not only the MeCP2 expression, but also their environmental cues. The alleviation of LC neuronal hyperexcitability seems to benefit brainstem autonomic function as THIP also improved breathing abnormalities of these sMecp2 +/- mice., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

During infection-induced inflammation food intake is reduced. Vagal and brainstem pathways are important both in feeding regulation and immune-to-brain communication. Glutamate is released by vagal afferent terminals in the nucleus of the solitary tract and by its neurons projecting to the parabrachial nuclei. We therefore studied the role of brainstem glutamate receptors in spontaneous food intake of healthy animals and during sickness-associated hypophagia after peripheral administration of bacterial lipopolysaccharides or interleukin-1beta. Brainstem group I and II metabotropic, but not ionotropic, glutamate receptor antagonism increased food intake both in saline- and lipopolysaccharide-treated rats. In these animals, expression of the cellular activation marker c-Fos in the lateral parabrachial nuclei and lipopolysaccharide-induced activation of the nucleus of the solitary tract rostral to the area postrema were suppressed. Group I metabotropic glutamate receptors did not colocalize with c-Fos or neurons regulating gastric function in these structures. Group I metabotropic glutamate receptors were, however, found on raphé magnus neurons that were part of the brainstem circuit innervating the stomach and on trigeminal and hypoglossal motor neurons. In conclusion, our findings show that brainstem metabotropic glutamate receptors reduce food intake and activate the lateral parabrachial nuclei as well as the rostral nucleus of the solitary tract after peripheral bacterial lipopolysaccharide administration. They also provide insight into potential group I metabotropic glutamate receptor-dependent brainstem circuits mediating these effects., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

The neurobiological underpinnings of anxiety are of paramount importance to selective and efficacious pharmaceutical intervention. Hippocampal theta frequency in urethane anaesthetized rats is suppressed by all known (and some previously unknown) anti-anxiety (anxiolytic) drugs. Although these findings support the predictive validity of this assay, its construct validity (i.e., whether theta frequency actually indexes anxiety per se) has not been a subject of systematic investigation. We reasoned that if anxiolytic drugs suppress hippocampal theta frequency, then drugs that increase anxiety (i.e., anxiogenic agents) should increase theta frequency, thus providing evidence of construct validity. We used three proven anxiogenic drugs--two benzodiazepine receptor inverse agonists, N-methyl-β-carboline-3-carboxamide (FG7142) and β-carboline-3-carboxylate ethyl ester (βCCE), and one α2 noradrenergic receptor antagonist, 17α-hydroxy-yohimban-16α-carboxylic acid methyl ester (yohimbine) as pharmacological probes to assess the construct validity of the theta model. Although all three anxiogenic drugs significantly increased behavioural measures of anxiety in the elevated plus-maze, none of the three increased the frequency of hippocampal theta oscillations in the neurophysiological model. As a positive control, we demonstrated that diazepam, a proven anxiolytic drug, decreased the frequency of hippocampal theta, as in all other studies using this model. Given this discrepancy between the significant effects of anxiogenic drugs in the behavioural model and the null effects of these drugs in the neurophysiological model, we conclude that the construct validity of the hippocampal theta model of anxiety is questionable., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

The use of glucagon-like peptide-1 (7-36) amide (GLP-1) receptor agonists for the treatment of type 2 diabetes mellitus is commonly associated with nausea and vomiting. Therefore, the present studies investigated the potential of GLP-1 receptor ligands to modulate emesis and feeding in Suncus murinus. Exendin-4, a selective GLP-1 receptor agonist, was administered subcutaneously (1-30 nmol/kg) or intracerebroventricularly (0.03-3 nmol) after 12-h of fasting. In other studies, animals were pretreated with the GLP-1 receptor antagonist, exendin (9-39), or saline (5 μl) 15 min prior to exendin-4 (3 nmol, i.c.v.). Behaviour of animals and food and water intake were then recorded for 1-2 h; c-Fos expression was also assessed in the brains of animals in the i.c.v. studies. The subcutaneous administration of exendin-4 reduced food and water intake (p < 0.001) and induced emesis in 40% of animals (p > 0.05). The intracerebroventricular administration of exendin-4 also prevented feeding, and induced emesis (p < 0.01). In these studies, exendin (9-39) (30 nmol, i.c.v.) antagonised emesis induced by exendin-4 and the increased c-Fos expressions in the brainstem and hypothalamus (p < 0.05), but it was ineffective in reversing the exendin-4-induced inhibition of food and water intake (p > 0.05). These data suggest that exendin-4 exerts its emetic effects in the brainstem and/or hypothalamus via GLP-1 receptors. The action of exendin-4 to suppress feeding may involve non-classical GLP-1 receptors or other mechanisms., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Mechanisms underlying stress-induced depression and antidepressant drug action were shown to involve alterations in serotonergic (5-HT) neurotransmission and expression of genes coding for proteins associated with neurotrophic signaling pathways and cell-survival in the hippocampus and cortex. Expression of these genes in the brainstem containing 5-HT neurons may also be related to vulnerability or resilience to stress-related psychopathology. Here we investigated 5-HT markers and expression of genes for Brain-Derived Neurotrophic Factor (BDNF) and apoptotic proteins in the brainstem in relation to swim stress-induced behavioral despair. We found that anti-apoptotic Bcl-xL gene is sensitive to stress during the course of fluoxetine administration. Responsiveness of this gene to stress appeared concomitantly with an antidepressant-like effect of fluoxetine in the forced swim test. Bcl-xL transcript levels showed negative correlations with duration of immobility in the test and 5-HT turnover in the brainstem. In contrast, BDNF and pro-apoptotic protein Bax mRNA levels were unchanged by either fluoxetine or stress, suggesting specificity of Bcl-xL gene responses to these treatments. We also found that the levels of mRNAs for tryptophan hydroxylase-2 (TPH2) and 5-HT transporter (5-HTT) were significantly down-regulated following prolonged treatment with fluoxetine, but were not affected by stress. Unlike TPH2 and 5-HTT, 5-HT1A receptor mRNA levels were not altered by fluoxetine but significantly increased in response to swim stress. These data show that long-term fluoxetine treatment leads to changes in 5-HT and Bcl-xL responses to stress associated with antidepressant-like effects of the drug. This article is part of a Special Issue entitled 'Anxiety and Depression'., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Zolpidem is a widely prescribed sleep aid with relative selectivity for GABA(A) receptors containing alpha1-3 subunits. We examined the effects of zolpidem on the inhibitory currents mediated by GABA(A) receptors using whole-cell patch-clamp recordings from DMV neurons in transverse brainstem slices from rat. Zolpidem prolonged the decay time of mIPSCs and of muscimol-evoked whole-cell GABAergic currents, and it occasionally enhanced the amplitude of mIPSCs. The effects were blocked by flumazenil, a benzodiazepine antagonist. Zolpidem also hyperpolarized the resting membrane potential, with a concomitant decrease in input resistance and action potential firing activity in a subset of cells. Zolpidem did not clearly alter the GABA(A) receptor-mediated tonic current (I(tonic)) under baseline conditions, but after elevating extracellular GABA concentration with nipecotic acid, a non-selective GABA transporter blocker, zolpidem consistently and significantly increased the tonic GABA current. This increase was suppressed by flumazenil and gabazine. These results suggest that alpha1-3 subunits are expressed in synaptic GABA(A) receptors on DMV neurons. The baseline tonic GABA current is likely not mediated by these same low affinity, zolpidem-sensitive GABA(A) receptors. However, when the extracellular GABA concentration is increased, zolpidem-sensitive extrasynaptic GABA(A) receptors containing alpha1-3 subunits contribute to the I(tonic)., (Copyright 2010 Elsevier Ltd. All rights reserved.)

Several small chain fatty acids, including butyrate, valproate, phenylbutyrate and its derivatives, inhibit several HDAC activities in the brain at a several hundred micromolar concentration. Gamma-hydroxy-butyrate (GHB), a natural compound found in the brain originating from the metabolism of GABA, is structurally related to these fatty acids. The average physiological tissue concentration of GHB in the brain is below 50 microM, but when GHB is administered or absorbed for therapeutic or recreative purposes, its concentration reaches several hundred micromolars. In the present scenario, we demonstrate that pharmacological concentrations of GHB significantly induce brain histone H3 acetylation with a heterogeneous distribution in the brain and reduce in vitro HDAC activity. The degree of HDAC inhibition was also different according to the region of the brain considered. Taking into account the multiple physiological and functional roles attributed to the modification of histone acetylation and its consequences at the level of gene expression, we propose that part of the therapeutic or toxic effects of high concentrations of GHB in the brain after therapeutic administration of the drug could be partly due to GHB-induced epigenetic factors. In addition, we hypothesize that GHB, being naturally synthesized in the cytosolic compartment of certain neurons, could penetrate into the nuclei and may reach sufficient levels that could significantly modulate histone acetylation and may participate in the epigenetic modification of gene expression.

Numerous studies, focused on the hypothalamus, have recently implicated endocannabinoids (EC) as orexigenic factors in the central control of food intake. However, the EC system is also highly expressed in the hindbrain autonomic integrator of food intake regulation, i.e. the dorsal vagal complex (DVC). Previous studies have shown that exogenous cannabinoids, by acting on cannabinoid 1 receptor (CB1R), suppress GABAergic and glutamatergic neuronal transmission in adult rat dorsal motor nucleus of the vagus nerve (DMNV), the principal efferent compartment of the DVC. However, no endogenous release of EC has been demonstrated in DVC to date. Using patch-clamp techniques on mouse coronal brainstem slices, we confirmed that both inhibitory and excitatory neurotransmission were depressed by WIN 55,212-2, a CB1R agonist. We demonstrated that DMNV neurons exhibited a rapid and reversible depolarization-induced suppression of electrically evoked GABAergic IPSCs (eIPSCs), classically known as DSI (depolarization-induced suppression of inhibition), while spontaneous or miniature IPSCs activity remained unaltered. Further, no depolarization-induced suppression of glutamatergic eEPSCs (DSE) occurred. Our results indicate that DSI was blocked by SR141716A (Rimonabant), a selective CB1R antagonist, and was dependent on calcium elevation in DMNV neurons, suggesting a release of EC in the DVC. Moreover, the analysis of the paired-pulse ratio, of the coefficient of variation and of the failure rate of eIPSCs support the fact that EC-mediated suppression of GABAergic inhibition takes place at the presynaptic level. These results show for the first time that DMNV neurons release EC in an activity-dependent manner, which in turn differentially regulates their inhibitory and excitatory synaptic inputs.

In this study, the P2 receptor-mediated modulation of [3H]glutamate and [3H]noradrenaline release were examined in rat spinal cord slices. Adenosine 5'-triphosphate (ATP), adenosine 5'-diphosphate (ADP), and 2-methylthioadenosine 5'-diphosphate (2-MeSADP) decreased the electrical stimulation-evoked [3H]glutamate efflux with the following order of potency: ADP>2-MeSADP>ATP. The effect of ATP was antagonized by suramin (300microM), the P2Y12,13 receptor antagonist 2-methylthioadenosine 5'-monophosphate (2-MeSAMP, 10microM), and partly by 4-[[4-Formyl-5-hydroxy-6-methyl-3-[(phosphonooxy)methyl]-2-pyridinyl]azo]-1,3-benzenedisulfonic acid (PPADS, 30microM) and the P2Y1 receptor antagonist 2'-deoxy-N6-methyladenosine 3',5'-diphosphate (MRS 2179, 10muM). ATP, ADP and 2-MeSADP also decreased evoked [3H]noradrenaline outflow; the order of agonist potency was ADP> or =2-MeSADP>ATP. The effect of ATP was reversed by 2-MeSAMP (10microM), and partly by MRS 2179 (10microM). By contrast, 2-methylthioadenosine-5'-triphosphate (2-MeSATP, 10-300microM) increased resting and electrically evoked [3H]glutamate and [3H]noradrenaline efflux, and this effect was prevented by the P2X1 receptor selective antagonist 4,4',4'',4'''-[carbonylbis[imino-5,1,3-benzenetriyl bis (carbonyl-imino)]] tetrakis (benzene-1,3-disulfonic acid) octasodium salt (NF449, 100nM). Reverse transcriptase polymerase chain reaction (RT-PCR) analysis revealed that mRNAs encoding P2Y12 and P2Y13 receptors are expressed in the brainstem, whereas P2Y13 but not P2Y12 receptor mRNA is present in the dorsal root ganglion and spinal cord. P2Y1 receptor expression in the spinal cord is also demonstrated at the protein level. In conclusion, inhibitory P2Y and facilitatory P2X1-like receptors, involved in the regulation of glutamate (P2Y13 and/or P2Y1) and noradrenaline (P2Y13 and/or P2Y1, P2Y12) release have been identified, which provide novel target sites for analgesics acting at the spinal cord level.

We have previously demonstrated that gabapentin supraspinally activates the descending noradrenergic system to alleviate neuropathic pain. In this study, we investigated whether pregabalin, an antiepileptic and analgesic drug that is also designed as a structural analogue of gamma-aminobutyric acid (GABA), exhibits supraspinal analgesic effects similar to those of gabapentin involving the descending noradrenergic system. Both systemically (intraperitoneally; i.p.) and locally (intracerebroventricularly or intrathecally; i.c.v. or i.t.) injected pregabalin reduced thermal and mechanical hypersensitivity in a murine chronic pain model that was prepared by partial ligation of the sciatic nerve (the Seltzer model), suggesting that pregabalin acts at both supraspinal and spinal loci. The supraspinal analgesic action of pregabalin was observed only after peripheral nerve injury, and pregabalin (i.p. and i.c.v.) did not affect acute thermal and mechanical nociception. Depletion of spinal noradrenaline (NA) or pharmacological blockade of spinal alpha(2)-adrenoceptors with yohimbine (i.p. or i.t.), but not alpha(1)-adrenoceptors with prazosin (i.p.), reduced the analgesic effects of pregabalin (i.p. or i.c.v.) on thermal and mechanical hypersensitivity. Moreover, i.c.v.-administered pregabalin dose-dependently increased the spinal 4-hydroxy-3-methoxyphenylglycol (MHPG) content and the MHPG/NA ratio only in mice with neuropathic pain, whereas the concentrations of NA, serotonin, 5-hydroxyindoleacetic acid and dopamine were unchanged, demonstrating that supraspinal pregabalin accelerated the spinal turnover of NA. Together, these results indicate that pregabalin supraspinally activates the descending noradrenergic pain inhibitory system coupled with spinal alpha(2)-adrenoceptors to ameliorate neuropathic pain.

The anterior pretectal nucleus (APtN) participates in nociceptive process and controls spinal nociceptive inputs, and its integrity reduces the severity of the responses to persistent injury. In this study we examined whether the pedunculopontine tegmental nucleus (PPTg) or the gigantocellularis nucleus pars alpha (GiA), stations that relay APtN inputs to the spinal cord, can control the persistent pain induced by a hind paw incision in rats with disrupted APtN. The withdrawal threshold to mechanical stimulation of the incised paw measured with von Frey filaments was significantly reduced in rats with contralateral APtN lesion or neural block of this nucleus with 2% lidocaine. Intrathecal xylamine, an inhibitor of noradrenaline uptake, inhibited the neural block of the APtN-induced increase in the incisional pain. Injection of glutamate into the contralateral PPTg or ipsilateral GiA reduced the incisional pain. Neural block of the PPTg or GiA reduced the threshold, mainly in APtN-disrupted rats. We conclude that persistent noxious stimulation activates descending pathways involving the contralateral APtN and PPTg, and ipsilateral GiA. Disruption of the APtN allows the activation of alternative circuitry involving at least the PPTg and GiA as intermediary stations that might maintain the control of nociceptive inputs in the spinal cord, probably involving noradrenergic mechanisms.

We investigated the role of nitric oxide (NO) in the modulation of respiratory-like activity recorded from hypoglossal rootlets in brainstem slices of neonatal rats (P0-P8). Sodium nitroprusside (SNP), S-Nitroso-N-acetyl-D,L-penicillamine (SNAP) and diethylamine-NO (DEA-NO), three NO-donors, reversibly increased hypoglossal burst amplitude with inconsistent effects on burst frequency. Similar effects were also obtained with the endogenous substrate of nitric oxide synthase (NOS), L-arginine, whereas the inactive enantiomer D-arginine had no effect. The NO-trap agent methylene blue significantly depressed both the amplitude and frequency of hypoglossal activity while hemoglobin depressed only the amplitude. Furthermore, the addition of NO-trap agents significantly attenuated the excitatory response to SNP. Inhibiting NOS with either N(omega)-Nitro-L-Arginine (L-NNA) or 7-Nitroindazole (7-NI), decreased the amplitude of hypoglossal activity with no effects on frequency. Histochemical analysis of NADPH-diaphorase activity, a marker for NOS, was performed on slices not treated pharmacologically and in brainstem sections of newborn rats, perfused in situ. Comparison between in vitro and in vivo conditions indicated that NOS activity was maintained in slice preparations. Neurons in the ambiguus and hypoglossal nuclei (dorsal division) exhibited a granular staining, suggesting the presence of NADPHd-positive terminals. Neurons with cytoplasmic staining were identified in regions connected to the hypoglossal nucleus (nucleus tractus solitarius, paramedian and gigantocellular reticular nuclei). These neurons might be involved in nitrergic control of hypoglossal activity. Both pharmacological and histochemical data suggest that endogenous NO may reinforce the output activity of the medullary respiratory network.

The site of the anti-emetic action of the neurokinin1 receptor antagonist CP-99,994 was studied in the ferret using the centrally acting opiate receptor agonist loperamide at a dose (0.5 mg/kg s.c.) which induced emesis in all animals tested. CP-99,994 (1 mg/kg, s.c.x2) abolished the emetic response (retching and vomiting) and the behaviours (licking, wet dog shakes, mouth scratching and gagging) induced by loperamide over a 2-h observation period. The enantiomer of this compound CP-100,263 (1 mg/kg, s.c.x2) did not have any significant effect on emesis or related behaviours. Loperamide (0.5 mg/kg s.c.) administration (but not its vehicle) resulted in dense fos-like immunoreactivity (FLI) mainly throughout the rostro-caudal extent of the nucleus tractus solitarius but not the area postrema. Although CP-99,994 (1 mg/kgx2) abolished the loperamide-induced emesis, it did not have any statistically significant effect on FLI in the brainstem. In loperamide and CP-100,263 (1 mg/kg, s.c.x2) treated animals FLI was comparable to that in animals treated with loperamide and CP-99,994. The results from this study taken together with those from previous studies indicate that loperamide exerts its emetic effect via nucleus tractus solitarius dendrites projecting into the area postrema. The lack of significant effect of CP-99,994 on the FLI induced by loperamide in this nucleus suggests that it is acting at a site "deep" in the nucleus tractus solitarius or elsewhere. The marked reduction in behaviours associated with loperamide administration by CP-99,994 provides a preliminary indication that NK1 receptor antagonist (as represented by CP-99,994) may in the clinic have effects on behaviours induced by emetic agents in addition to their previously described effects on retching and vomiting.

In this study, we evaluated the gastric effects of methylnaltrexone, an opioid receptor antagonist that does not cross the blood-brain barrier in vivo, on mu, kappa and delta opioid agonists induced brainstem unitary responses in an in vitro neonatal rat brainstem-gastric preparation. Single units in the medial subnucleus of the nucleus tractus solitarius (NTS), responding to electrical stimulation of subdiaphragmatic vagal fibers, were recorded. Selective opioid receptor agonists and antagonists were applied only to the gastric compartment of the bath chamber and thus, the brainstem functions of the preparation were not affected by the drugs. The peripheral gastric effects of a mu opioid receptor agonist, DAMGO, and a kappa opioid receptor agonist, U-50,488H, were evaluated on 58 tonic units that received the subdiaphragmatic vagal inputs. For approximately 78% of the units observed, DAMGO (1.0 microM) and U-50,488H (1.0 microM) induced a concentration-dependent inhibition of 62.1+/-9.3% (mean +/- SE) and 49.2+/-6.5% of the control level of the NTS neuronal activity, respectively. Methylnaltrexone competitively antagonized the DAMGO-induced brainstem neuronal effects. Methylnaltrexone at an 18.8-fold higher concentration also reversed U-50,488H-induced NTS neuronal responses. Naloxone, a non-selective opioid receptor antagonist, reversed the inhibitory effects of DAMGO and U-50,488H at much lower concentrations (3.8% and 0.5%, respectively) compared to methylnaltrexone. Only 18% of the NTS neurons evaluated showed inhibitory responses to a delta receptor agonist, DPDPE, (19.7+/-5.0% at 10 microM), and this inhibition could not be reversed by methylnaltrexone in the concentration range we tested. In addition, when methylnaltrexone (1.0 microM) alone was applied to the gastric compartment, there was an activation (8.5+/-2.1%) of the NTS neurons receiving subdiaphragmatic vagal inputs, suggesting an endogenous gastric opioid action in the modulation of brainstem neuronal activities.

We report on the autoradiographic distribution of 5-HT1B, 5-HT1D and 5-HT1F receptor subtypes in human brain, focusing on the brainstem and cervical spinal cord. We have used [3H]sumatriptan as a radioligand in the presence of suitable concentrations of 5-CT (5-carboxamidotryptamine) to define 5-HT1F receptors, and ketanserin, to discriminate between 5-HT1B and 5-HT1D receptors. In the brainstem the highest concentrations of [3H]sumatriptan binding sites were seen in substantia nigra. The spinal trigeminal nucleus, substantia gelatinosa of the spinal cord, nucleus of the tractus solitarius and periaqueductal grey, also showed significant levels of [3H]sumatriptan binding sites. In the brainstem and spinal cord the total population of 5-CT-insensitive receptors, corresponding to 5-HT1F receptors, ranged from 9.8% in the periaqueductal grey to 53.4% in the substantia gelatinosa. This population represented 67.0% of binding in layer V of the frontal cortex. The decrease in [3H]sumatriptan binding in the presence of 200 nM ketanserin, indicative of the presence of 5-HT1D receptors, was very limited throughout the human brain, only reaching 20% of total specific binding over the periaqueductal grey. The proportion of [3H]sumatriptan binding sites displaced by 5-CT and insensitive to ketanserin, corresponding to 5-HT1B receptors, was, in general, the most abundant, ranging from 43.8% in substantia gelatinosa to 69.9% in the periaqueductal grey. Significant levels of 5-HT1B and 5-HT1D receptors found in migraine control pain areas suggest their involvement in antinociceptive mechanisms.

The depolarization of adult and neonatal rat facial and spinal motoneurones by 5-hydroxytryptamine (5-HT) in part involves an enhancement of the hyperpolarization-activated, inward-rectifier, IH. Under experimental conditions which promote this action, 5-HT evokes an inward current which can be mimicked by intracellularly applied adenosine 3',5'-cyclic monophosphate (cAMP) and potentiated by the cAMP-specific phosphodiesterase inhibitor Ro 20-1724. In this study, we show that this action of 5-HT can be blocked by the adenylyl cyclase inhibitors 2'3'-dideoxyadenosine (2',3'-DDA). 5'-adenylimidodiphosphate (AMP-PNP) and SQ-22536 (9-(tetrahydro-2-furyl)adenine), but not by external or internal application of the protein kinase inhibitors H-7, staurosporine and chelerythrine. The most recently cloned 5-HT receptor subtypes, 5-HT4, 5-HT6 and 5-HT7, can all stimulate adenylyl cyclase when activated. In the presence of internal GTP-gamma-S, 5-HT irreversibly enhanced IH. The 5-HT-induced inward current could be reversibly blocked by methysergide, but not by the 5-HT4 receptor antagonist GR-113808A, the 5-HT6 and 5-HT7 antagonist clozapine and the 5-HT1A antagonist WAY-100365. 5-Methoxytryptamine (5-MeOT) and 5-carboxamidotryptamine (5-CT) mimicked the action of 5-HT with a rank order of potency of 5-HT = 5MeOT > 5-CT. Surprisingly, 8-hydroxy-2-(di-N-propylamino)-tetralin (8-OH DPAT), a 5-HT1A and 5-HT7 agonist was inactive on facial motoneurones unlike its reported agonist action on spinal motoneurones. It is proposed that cAMP produced by 5-HT-mediated stimulation of adenylyl cyclase acts in a phosphorylation-independent manner, possibly directly, on the IH channel. The 5-HT receptor subtype mediating this response cannot be correlated with any of the classified 5-HT receptor subtypes that stimulate adenylyl cyclase.

Mental illness, such as panic disorder and depression, display comorbidity as well as common therapeutic treatments. These features point toward a common etiology and/or therapeutic pathway. There is evidence to suggest that some antipanic agents may mediate their effects by altering gamma-aminobutyric acid (GABA) levels or by modulating the activity of the GABAA receptor. Chronic stimulation of GABAA receptors by agonists or modulators results in changes in the pharmacological properties of the receptor concomitant with alterations in the expression of specific GABAA receptor subunits. Therefore, we investigated the hypothesis that long-term exposure to three antidepressant/antipanic drugs (imipramine, phenelzine and alprazolam) would produce changes in the steady-state levels of those subunit mRNAs that are believed to encode the major GABAA receptor subtype. Further, these changes in gene expression would be different to those produced by the non-antipanic anxiolytic (buspirone). We report here that, following a 21 day treatment, imipramine, phenelzine, alprazolam and buspirone differentially altered rat brainstem levels of GABAA receptor alpha 1-, beta 2- and gamma 2-subunit RNAs. These results demonstrate novel actions of antidepressant/antipanic drugs on GABAergic neurotransmission.

The modulatory effects of taurine on [35S]-t-butylbicyclophosphorothionate (TBPS) binding to rat brain synaptic membranes were evaluated and compared with that of GABA. Taurine allosterically inhibited TBPS binding by interacting with a bicuculline-sensitive site, similar to GABA. Taurine was as effective as GABA but less potent. The potency of taurine inhibition of TBPS binding varied among brain regions with cerebellum > olfactory bulb > cortex, similar to that of GABA. Inhibition of TBPS binding to cortical membranes measured under nonequilibrium conditions yielded a dynamic biphasic inhibition curve that was similarly shaped for GABA and taurine. The effect of taurine on TBPS binding was pharmacologically specific in that beta-alanine and guanadinoethanesulfonate were as effective as taurine, while hypotaurine and alpha-aminoethylhydrogen sulfate were only partially effective at high concentrations, and isethionic acid was without effect. Taurine, similar to GABA, enhanced the effects of pentobarbital on TBPS binding when present at concentrations that were otherwise ineffective on their own. The results of these studies support the notion that taurine interacts with the GABA recognition site of the GABAA receptor complex.

The effect of sulphated cholecystokinin octapeptide (CCK-8S) on immediate early gene expression in the rat CNS was investigated using the technique of in situ hybridization. A rapid and transient induction of c-fos, NGFI-A and NGFI-B (nerve growth factor-induced genes A and B) mRNA was demonstrated in the nucleus tractus solitarius (NTS), area postrema (AP), hypothalamic paraventricular (PVN) and supraoptic (SON) nuclei, and central nucleus of the amygdala, following peripheral administration of CCK-8S (1-100 micrograms/kg i.p.). In contrast, levels of c-jun, junB and junD mRNA were unaffected by the peptide. The closely related decapeptide, caerulein (50 micrograms/kg i.p.), induced the same pattern of IEG expression as CCK-8S, whereas the desulphated octapeptide, CCK-8DS (50 micrograms/kg i.p.), had no effect on levels of mRNA for any IEG studied. Expression of IEG mRNA in these areas was suppressed by bilateral subdiaphragmatic vagotomy, and by pretreatment with the selective CCKA receptor antagonist, devazepide (0.1 and 1 mg/kg i.p.). In contrast, CCK-8S induction of IEG mRNA was not blocked by pretreatment with the selective CCKB receptor antagonist, CI-988 (1 or 10 mg/kg i.p.). In addition, the selective CCKB receptor agonists, CCK-4 (50 micrograms/kg i.p.) or pentagastrin (2 mg/kg i.p.), failed to induce IEG expression in any of the areas studied. These results suggest that systemic CCK-8S primarily acts via CCKA receptors on vagal afferents to stimulate IEG mRNA expression in the rat CNS.

The effects of the metabotropic glutamate receptor (mGluR) agonist (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid [(1S,3R)-ACPD] and a series of phenylglycine-derived putative mGluR antagonists were examined on electrophysiological responses mediated by glutamate and GABA receptors in the nucleus of the tractus solitarius (NTS) in transverse brainstem slices of the rat. Monosynaptic excitatory currents (EPSC's) evoked by electrical stimulation in the region of the tractus solitarius (TS) were reduced in the presence of (1S,3R)-ACPD in > 90% of neurons recorded in the dorsomedial subdivision of the NTS adjacent to the area postrema (AP). Monosynaptic evoked inhibitory currents (IPSC's) were similarly inhibited by (1S,3R)-ACPD. The inward current evoked by pressure application of alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (IAMPA) was potentiated in the presence of (1S,3R)-ACPD, whereas the outward current evoked by the gamma-amino-butyric acid-A (GABA-A) receptor agonist muscimol (IMUSC) was inhibited. (1S,3R)-APCD also produced a postsynaptic inward current (IK(ACPD)) associated with a decrease in membrane conductance in approximately 50% of cells. The novel mGluR antagonists (S)-4-carboxy-3-hydroxy-phenylglycine (4C3H-PG), (R,S)-4-carboxy-phenylglycine (4C-PG) and (R,S)-alpha-methyl-4-carboxy-phenylglycine (alpha M4C-PG) reversibly antagonized the effects of (1S,3R)-ACPD on EPSC's IPSC's, IAMPA and IMUSC. The first two compounds also displayed weak agonist activity. However, none of the antagonists significantly inhibited IK(ACPD) at concentrations which blocked (1S,3R)-ACPD effects on synaptic transmission. These results suggest that pharmacologically distinct mGluR's may be present in the NTS.

5-Hydroxytryptamine (5-HT) and the novel anti-aggressive drug eltoprazine (1-(2,3-dihydro-1,4-benzodioxin-5-yl) piperazine hydrochloride) were applied by microiontophoresis to spinal motorneurones and also to neurones in the brainstem which gave two distinctly different responses to 5-HT. In vitro microiontophoretic release studies showed that the electrophoretic mobility of eltoprazine and 5-HT were similar and that similar amounts of each drug would be applied by similar iontophoretic currents. Cells in the brainstem have been shown previously to be excited by 5-HT, acting at a 5-HT2 receptor. Eltoprazine only occasionally and weakly mimicked the excitatory effect of 5-HT on these cells. Although a potent antagonism of the 5-HT excitation by eltoprazine was observed, this was a non-selective effect, as responses to glutamate and D,L-homocysteic acid were also reduced. Cells in the lateral brainstem are depressed by 5-HT, acting on a receptor which has previously been shown to be of the 5-HT1-like group. At this receptor, 8-OH-DPAT (8-hydroxy-2-(di-n-propylamino)-tetralin) and 5-carboxamidotryptamine, are potent agonists. Eltoprazine was a more potent depressant agonist than 5-HT on these brainstem neurones. The antagonist metergoline did not antagonise responses to either 5-HT or eltoprazine. It is suggested however that both drugs act at the same receptor to depress these cells because desensitizing the receptor by repeated, frequent applications of 5-HT abolished responses to 5-HT and eltoprazine, without altering responses to GABA.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of alpha-chloralose were examined on the brainstem auditory evoked potential of the rat. Subjects were given one of four different doses of chloralose. These were a sedative dose (50 mg/kg), an anaesthetic dose (100 mg/kg), a usually fatal dose (150 mg/kg) or an invariably fatal dose (200 mg/kg). Recordings were made 60 min later. There was no evidence of any dose-dependent increase or decrease in the amplitudes of the four principal components (waves I, II, III and IV) of the brainstem auditory potential. There were only minor dose-dependent increases in latency. These were less than 0.1 msec for waves I, II and III and just over 0.1 msec for wave IV. Wave IV was the component which was most sensitive to chloralose, although this was apparent only at a large dose. In general, the latencies showed little or no difference from those recorded previously from awake animals. The results are discussed in relation to a series of experiments, where animals were initially immobilized with chloralose in order to study the effects of a variety of pharmacological agents on the brainstem auditory potential.

Acetylcarnitine is an endogenous substance, active in the CNS, but its exact role in neurotransmission is still unknown. The present study was made to analyze by means of iontophoretic administration on single neurones of the medullary-pontine reticular formation in the rat the effects of the D- and L-acetylcarnitine on spontaneous and glutamate-evoked firing and on responses to applications of some other putative transmitters, such as acetylcholine, 5-hydroxytryptamine (5-HT), gamma-aminobutyric acid (GABA) and noradrenaline. L-Acetylcarnitine increased both spontaneous and evoked discharges, and potentiated cholinergic and serotonergic responses. The D-isomer was found to be almost ineffective. Neuronal responses to L-acetylcarnitine were reduced by dihydro-beta-erythroidine and enhanced by eserine, while atropine was ineffective. L-Acetylcarnitine increased both excitatory and inhibitory responses to 5-HT and its effect on the increase in firing rate induced by serotonergic drugs was reduced by dihydro-beta-erythroidine, but not by atropine. L- and D-Acetylcarnitine did not affect GABAergic or noradrenergic transmission. These results suggest a stereospecific facilitatory action of acetylcarnitine on neuronal responses to acetylcholine and 5-HT. It is hypothesized that this action could be exerted at a presynaptic level, at least with regard to serotonergic-induced responses, and that nicotinic receptors may be involved in the synaptic mechanism of release or reuptake of both acetylcholine and 5-HT.

The involvement of the central nervous system in the hypothermia induced by chlordecone was studied by evaluating the effects of infusions of chlordecone injected into the lateral and third ventricles and the cisterna magna on colonic temperature (Tcol). Compared to rats given vehicle, infusions of 40, 320 or 800 micrograms of chlordecone into the lateral ventricle or 320 or 800 micrograms of chlordecone into the third ventricle, through chronic indwelling cannulae, did not change significantly Tcol. However, intracisternal infusions of 80, 160, 320 or 800 micrograms of chlordecone produced significant hypothermia (maximally 2.2 degrees C) which persisted for as long as 6 hr. Intracisternal infusions of chlordecone also produced a rapid increase in the temperature of the tail skin (Tsk) which persisted throughout the period of hypothermia. This suggests that the hypothermia produced by central administration of chlordecone is related to peripheral vasodilation. Since chlordecone has been reported to induce release of NE in the brainstem, and NE is known to modulate tonic vasomotor control in the medulla, the effects of NE infused intracisternally were studied. Intracisternal infusions of NE (16 micrograms) significantly decreased Tcol and increased Tsk, supporting the hypothesis that hypothermia induced by chlordecone is associated with vasodilatory effects, mediated by an adrenergic mechanism in the brainstem.

Opioid peptide involvement in the fall in blood pressure resulting from stimulation of alpha-receptors in the brainstem has been investigated in the urethane-anaesthetised rat. Unilateral microinjection of alpha-methylnoradrenaline into the nucleus tractus solitarii (NTS) induced a dose-related fall in blood pressure and heart rate. The depressor response induced by the amine was prevented by pretreatment with naloxone, administered either subcutaneously or directly into the nucleus. Pretreatment with antiserum to beta-endorphin, applied locally, also blocked the depressor response, however a similar dilution of antiserum to met-enkephalin was ineffective in this respect. The local application of phentolamine into the n. tractus solitarii caused an initial fall in both blood pressure and heart rate, and blocked the cardiovascular changes induced by alpha-methylnoradrenaline for at least 90 min. Pretreatment with the alpha-receptor antagonist attenuated the fall in blood pressure produced by microinjection of beta-endorphin. These results suggest that the fall in blood pressure observed after administration of alpha-methylnoradrenaline involves a beta-endorphin-like peptide, a probable site of this interaction being the n. tractus solitarii.

Multiunit activity was recorded simultaneously in the substantia nigra pars compacta, the pyramidal layer of the hippocampus dorsalis CA 1 area, the nucleus locus coeruleus and the nucleus raphé dorsalis of encéphale isolé rats; drugs were injected intravenously in increasing doses. Chlordiazepoxide decreased multiunit activity dose-dependently to a similar extent in substantia nigra, hippocampus and dorsal raphé, but was less effective in the locus coeruleus. Midazolam reduced multiunit activity in all 4 nuclei to a similar degree and was more potent than chlordiazepoxide. Specific benzodiazepine antagonists completely reversed the effects of the two benzodiazepines. Pentobarbitone was a less potent depressant than chlordiazepoxide, and its effect was not reversed by the benzodiazepine antagonist Ro 15-1788.

Quipazine produced a dose-dependent decrease in the discharge rate of serotonin-containing neurons in the dorsal raphe nucleus of freely-moving cats. This ranged from a 10% decrease at 0.5 mg/kg, (i.p.), to a virtually complete depression of activity at 5.0 mg/kg. The effects of quipazine on raphe units occurred with a short latency (5--10 min) and its duration of action was dose-dependent and lasted from 1 to 6 hr. The degree of depression of raphe unit activity was directly related to the frequency of occurrence of a number of behaviors such as limb flicking and abortive grooming. There was a close temporal correlation between the depression of raphe unit activity and the occurrence of these behaviors. These data reveal that quipazine produces behavioral and raphe unit changes similar to those observed after administration of hallucinogens with an indole nucleus.

D-L, Acetylcarnitine was applied microiontophoretically to neurones in the brainstem of the rat, to evaluate its possible effects. The results support the hypothesis that D-L, acetylcarnitine acts on the neuronal membrane, producing selective excitatory responses of the neurones examined. The possible role of this substance at the single neurone level is discussed in relation to the results obtained by investigating the interaction between D-L, acetylcarnitine and neurotransmitters, such as acetylcholine, gamma-aminobutyric acid (GABA), serotonin and noradrenaline.

In view of the involvement of noradrenaline (NA) in the regulation of adrenocortical secretion, its role in the rise of plasma corticosterone following neural stimuli was evaluated in rats. The injection of the catecholamine neurotoxin 6-hydroxydopamine (6-OHDA) into the ventral noradrenergic bundle in the brain stem, which projects to the hypothalamus, caused an average depletion of NA of 72% and 78% in the mediobasal hypothalamus and the paraventricular nuclei respectively, when compared to the rats injected with vehicle. In the animals injected with 6-OHDA, the basal level of corticosterone in plasma and the response to stress induced with ether were not affected. However, the adrenocortical discharge was very significantly inhibited following photic, acoustic and sciatic nerve stimulation. The present experiments support the results of previous studies on the stimulatory effect of NA on adrenocortical secretion.

Pentylenetetrazol (PTZ), administered systemically, enhanced the auditory responses of neurons of the mesencephalic reticular formation (MRF). Responses evoked in the mesencephalic reticular formation by electrical stimuli in several primary auditory nuclei (cochlear nucleus, superior olivary complex and lateral lemniscus, but not inferior colliculus) were also enhanced by pentylenetetrazol in the majority of cases. Bilateral cryoprobe cooling in the lateral lemniscal tract substantially reduced the auditory-evoked field potentials (EPs) in the mesencephalic reticular formation before and after administration of pentylenetetrazol. Cooling in the inferior colliculus (IC) produced a small reduction in auditory-evoked field potentials in the mesencephalic reticular formation before drug but a more substantial degree of reduction after administration of pentylenetetrazol. A relatively small degree of pentylenetetrazol-induced enhancement of the response was seen in neurons of the inferior colliculus (158% of control) as compared to that of neurons in the mesencephalic reticular formation (410%). These findings would be consistent with the reported ability of pentylenetetrazol to block presynaptic inhibition if the input from the inferior colliculus to the mesencephalic reticular formation has inhibitory as well as excitatory components. These data along with the present authors' recent finding of enhancement of response with microapplication of convulsants strongly suggest that enhancement of responses of neurons of the mesencephalic reticular formation, induced by systemically administered convulsants such as pentylenetetrazol is exerted, to a large extent, by direct actions on synaptic elements of the reticular formation.

Dorsal root potentials (DRPs) are thought to reflect presynaptic inhibition of primary afferent activity. Electrical stimulation of sites near the nucleus raphe magnus evokes two such potentials (DRP-1 and DRP-2) along dorsal roots of the lumbar and sacral spinal cord in the anaemically decerebrated cat. Dorsal root potential-2 is thought to be serotonergically mediated, while the neurochemical mediator of dorsal root potential-1 is not known. Serotonin antagonists selectively inhibit dorsal root potential-2 while the shorter latency dorsal root potential-1, which can be elicited anywhere in the brain stem, is potentiated by these drugs. The present study showed that most general anesthetics, such as ether or barbiturates, uniformly depressed both dorsal root potentials 1 and 2. The present studies indicate that two dissociative anesthetics, ketamine and phencyclidine, selectively inhibited dorsal root potential-2. This inhibitory effect of ketamine was dose-related, such that a dose of 11 mg/kg completely blocked dorsal root potential-2, but had no effect on dorsal root potential-1. Time-course studies indicated that the effect of phencyclidine on dorsal root potential-2 lasted much longer than that of ketamine. These results suggest that the effect of dissociative anesthetics on the descending pathways is unique compared to that of other anesthetic agents and that their effect correlates well in time-course and dose-range to their sedative/anesthetic effects.

The effects of chronic administration of the nonselective monoamine oxidase (MAO) inhibitor, phenelzine, and two selective inhibitors, clorgyline, and pargyline on adrenergic receptor binding and MAO activity were studied in the rat brain. Chronic but not acute administration of both phenelzine and the MAO-A inhibitor, clorgyline, resulted in significant decreases in cortical beta-adrenoreceptor binding ([3H]dihydroalprenolol) of 47 and 24% respectively. In contrast pargyline, which only partially inhibited MAO-A, caused only a nonsignificant (7%) change in rat cortical beta-receptor binding. In a more detailed study, chronic administration of clorgyline also caused changes in alpha-adrenergic receptor binding: by day 3 of treatment, significant changes were already observable in alpha-2-adrenergic receptor binding ([3H]clonidine), although changes in alpha-1 ([3H]WB4101)- and beta ([3H]dihydroalprenolol)-cortical receptor binding were not present until day 10. After 21 days of clorgyline treatment, the Bmax's of alpha-2-, alpha-1- and beta-adrenergic cortical receptors were reduced by 62, 36 and 34% respectively. In brainstem, alpha-2- and beta-receptors were reduced by 60 and 74%. The magnitude of these changes and particularly the rapidity of the alpha-2 changes suggest that clorgyline-induced alpha-2 autoreceptor changes may precede and contribute to the changes in postsynpatic alpha-1- and beta-receptors. These sequential alterations in adrenergic receptors may be pertinent to the efficacy and delay in onset of the clinical changes which follow treatment with these antidepressants.