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A former study indicated that hypoxic-ischemic encephalopathy in rat sustained during early postnatal life may result in permanent epileptic activity in the baseline electroencephalogram. We, therefore, investigated whether the presumed higher firing frequency and metabolic activity of neurons in such hypoxia-damaged cortical areas would be reflected by an enhanced light microscopic immunoreactivity of gamma-aminobutyric acid (GABA), the two isoforms of glutamic acid decarboxylase (GAD67 and GAD65), the mitochondrial enzymes cytochrome c oxidase and ATP synthase, and/or glial fibrillary acidic, protein (GFAP). To that end rat pups, 12-13 days of age, were unilaterally exposed to hypoxic-ischemic conditions and, after a survival period of 2 and 6 1/2 months, respectively, killed by perfusion fixation. After dissection of the brain, coronal vibratome sections of animals showing cortical damage were immunostained for the presence of the above-mentioned antigens. Subsequent qualitative analysis revealed that the surroundings of cortical infarctions were unambiguously characterized by a disordered neural network containing numerous nerve cells, fibers and/or endings showing an enhanced immunoreactivity for GABA, both isoforms of glutamic acid decarboxylase, and cytochrome c oxidase and ATP synthase, while the astrocytes showed an enhanced immunoreactivity for GFAP. The diverse patterns of enhanced immunoreactivity suggested, furthermore, a wider low-to-high range of metabolic activities in both excitatory and inhibitory neurons.

To reveal brain regions and transmitter systems involved in control of pancreatic hormone secretion, specific vagal and sympathetic denervation were combined with injection of a retrograde transsynaptic tracer, pseudorabies virus (PRV), into the pancreas. After sympathetic or vagal transsection first-order neurons were revealed in the dorsal motor nucleus of the vagus (DMV) or in preganglionic spinal cord neurons (SPN), respectively. Careful timing of the survival of the animals allowed the detection of cell groups in immediate control of these DMV or SPN neurons. A far larger number of cell groups is involved in the control of DMV than of SPN neurons. Examples are given of a high level of interaction between the sympathetic and parasympathetic nervous system. Several cell groups project to both branches of the autonomic nervous system, sometimes even the same neurotransmitter is used, e.g., oxytocin neurons in the paraventricular nucleus and melanin-concentrating hormone and orexin neurons in the lateral hypothalamus project to both the DMV and SPN neurons. Moreover, the appearance of third-order neurons located in the sympathetic SPN after complete sympathectomy and in the DMV after complete vagotomy illustrates the possibility that motor neurons of the sympathetic and parasympathetic system may exchange information by means of interneurons. The presence of second-order neurons in prefrontal, gustatory, and piriform cortex may provide an anatomic basis for the involvement of these cortices in the cephalic insulin response. The observation that second-order neurons in both vagal and sympathetic control of the pancreas contain neuropeptides that are known to play a role in food intake indicates a direct association between behavioral and autonomic functions. Finally, the observation of third-order neurons in the suprachiasmatic nucleus and ventromedial hypothalamus shows the modulatory action of the time of the day and metabolic state, respectively.

In view of mounting evidence that the suprachiasmatic nucleus (SCN) is directly involved in the setting of sensitivity of the adrenal cortex to ACTH, the present study investigated possible anatomical and functional connections between SCN and adrenal. Transneuronal virus tracing from the adrenal revealed first order labelling in neurons in the intermedio-lateral column of the spinal cord that were shown to receive an input from oxytocin fibres and subsequently second-order labelling in neurons of the autonomic division of the paraventricular nucleus. The latter neurons were shown to receive an input from vasopressin or vasoactive intestinal peptide (VIP) containing SCN efferents. The true character of this SCN input to second-order neurons was also demonstrated by the fact that third-order labelling was present within the SCN, vasopressin or VIP neurons. The functional presence of the SCN-adrenal connection was demonstrated by a light-induced fast decrease in plasma corticosterone that could not be attributed to a decrease in ACTH. Using intact and SCN-lesioned animals, the immediate decrease in plasma corticosterone was only observed in intact animals and only at the beginning of the dark period. This fast decrease of corticosterone was accompanied by constant basal levels of blood adrenaline and noradrenaline, and is proposed to be due to a direct inhibition of the neuronal output to the adrenal cortex by light-mediated activation of SCN neurons. As a consequence, it is proposed that the SCN utilizes neuronal pathways to spread its time of the day message, not only to the pineal, but also to other organs, including the adrenal, utilizing the autonomic nervous system.

The suprachiasmatic nucleus (SCN), which functions as a biological clock, contains several neuropeptides such as vasoactive intestinal peptide (VIP), peptide histidine isoleucine (PHI), and gastrin-releasing peptide (GRP). Studies from several laboratories have provided evidence for the coexistence of VIP with PHI and GRP, but reliable data about the proportions of colocalization and a possible diurnal rhythmicity are lacking. In the present study, we therefore aimed at studying these aspects. To this end, rats were killed by perfusion fixation during the middle of the day (Zeitgeber time [ZT] 7) and during the second part of the night (ZT 19). Coronal Vibratome sections through the SCN were double-immunolabeled for the presence of VIP and PHI or for VIP and GRP. Analysis of the sections was done by semi-quantitative confocal laser scanning fluorescence microscopy. It turned out that, in keeping with previous literature data, VIP and PHI always coexist at the cellular level. This was seen in all possible ratios, both during the day and at night. Part of these VIP/PHI-containing neurons (21%) and part of the GRP-containing neurons (33%) showed colocalization during the middle of the day. During the second part of the night, these percentages increased significantly to 28% and 40%, respectively. This increase in percentages was due to a significant, nocturnal increase of the number of profiles showing colocalization, in contrast to the number of profiles exclusively immunoreactive for VIP or GRP.

Two groups of four rats each received a 15-minute light stimulus during the first part of the night (ZT14) and the second part (ZT19), respectively. After 45-60 minutes, the animals were killed by perfusion fixation. Adjacent Vibratome sections through the suprachiasmatic nucleus (SCN) were double-immunostained for the presence of peptide histidine isoleucine (PHI), gastrin releasing peptide (GRP) or vasoactive intestinal peptide (VIP) with Fos by using fluorophore-conjugated secondary antibodies. A few sections were triple-immunostained for PHI, GRP or VIP with vasopressin (VP) and Fos. Sections were analyzed with a confocal laser scanning microscope. It turned out that the ZT19 light stimulus induced 4.2 times more nuclear profiles in the SCN immunoreactive for Fos than the light stimulus given at ZT14. The SCN of control animals did not show any Fos immunoreactivity. After the ZT14 light stimulus, approximately 33% of the Fos profiles showed colocalization with a perikaryal profile immunoreactive for PHI, GRP or VIP, whereas at ZT19, this percentage had doubled to approximately 65%. After the light stimulus at ZT14, the relatively low Fos induction was numerically and proportionally most prominent in the PHI-immunoreactive perikarya. As compared with ZT14, the increase of Fos after the ZT19 light stimulus was most pronounced in the GRP-immunoreactive perikarya (21x) followed by VIP (15x) and PHI (5x). This outcome suggests that at least three different cell groups characterized by, respectively, PHI alone, GRP, and VIP fully or partly colocalized with PHI, play a prominent role during light-induced phase shifts: the PHI neurons during light-induced phase delays, the GRP and VIP/(PHI) neurons during light-induced phase advances.

The results presented in this study show that the rabbit pineal organ cultured in vitro retained its in vivo fine structure for at least eight days. However, the Golgi complex in the light pinealocytes stopped forming dense core vesicles while vesicle-crowned ribbons increased in number. After addition of norepinephrine to the culture medium, the Golgi complex once more began the production of dense core vessicles. Terminals of light pinealocytic processes then often contained Golgi dense core vesicles in close contact with the cell membrane, suggesting the release of the vesicular content into the intercellular and perivascular spaces. A close topographical relationship between Golgi dense core vesicles and vesicle-crowned ribbons was observed.

The ultrastructure of the rabbit pineal gland was investigated after sympathectomy (extirpation of decentralization of the superior cervical ganglia), parasympathectomy, continuous illumination and continuous darkness. The similarity of the ultrastructural changes in the light pinealocytes occuring after sympathectomy and after continuous illumination was striking. It is supposed that these changes have a common cause, viz. the lack of free noradrenaline, the pinealotropic neurotransmitter. The smooth endoplasmic reticulum present in the terminals of the offshoots of the light pinealocytes is possibly involved in pineal indoleamine synthesis.

The influence of certain drugs on the ultrastructure of rabbit pinealocytes was studied. The results obtained after administration of p-chlorophenylalanine and p-chloroamphetamine support the hypothesis proposed earlier that the smooth endoplasmic reticulum in the light pinealocytes is involved in indoleamine synthesis. The administration of either one of the sympatholytic agents, 6-hydroxydopamine or alpha-methyl-p-tyrosine, induced typical fine structural changes corresponding to those observed after surgical sympathectomy.

The value of γ-aminobutyric acid (GABA) immunogold labeling in the quantification of nerve endings was studied in dissociated rat neocortex cultures. Adjacent sections were processed in 3 series according to the same staining protocol. Of all nerve ending profiles examined, 20% appeared to be GABA-positive, while 7% could not be classified. In cultures pretreated with gabaculine, GABA-positive endings were labeled more heavily. Cell bodies could always be discriminated as GABA-positive or GABA-negative. Of all neuronal cell profiles, 14% appeared to be GABA-positive. These neurons could also be identified by light microscopy using the peroxidase-anti-peroxidase method.

Electron microscopic evidence is given that the small dark granules in the rabbit dark pinealocytes represent glycogen. The conception is put forward that this glycogen, synthesized at the membranes of the rough endoplasmic reticulum, is taken up by lysosomes to participate then in the conversion of the lysosomes into pigment bodies.

We tested whether hypoglycemia, like hypoxia, would preferentially destroy GABAergic nerve cells in the neocortex. To this end, rat neocortex explants dissected from 6-day-old rat pups and cultured up to a developmental stage approximately comparable to that of the newborn human neocortex, were exposed to hypoglycemia for different periods. Quantitative light microscopic and immunocytochemical evaluation of the cultures demonstrated that hypoglycemia does not preferentially destroy GABAergic but rather non-GABAergic neurons, a finding quite opposite to what was found after hypoxia. Recent biochemical data from other laboratories which seem to support this difference in neuronal vulnerability are discussed. It is concluded that perinatal hypoglycemia may not form such a serious threat with respect to the genesis of epilepsy as does hypoxia.

In the rabbit pineal gland two types of postganglionic nerve endings were found which are characterized by the presence of small dense-core vesicles or small clear vesicles. Pharmacological and cytochemical experiments showed then to be noradrenergic and cholinergic, respectively. Both types were often present in the same nerve bundle, occasionally in close opposition. Intrapineal neurons were only rarely observed. They showed cholinergic synapses on their perikaryon and dendrites as well as noradrenergic axo-dendritic close contacts. Bilateral extirpation of the superior cervical ganglia revealed the postganglionic sympathetic origin of the pineal noradrenergic nerve fibres. Moreover, it appeared that these ganglia are hardly, if at all, involved in the pathway of pineal cholinergic innervation. The results obtained from lesions of both facial nerves, taken together with the results reported in the literature, led to the conclusion that the postganglionic cholinergic nerve fibers in the pineal are of parasympathetic origin. A model for the sympathetic and parasympathetic pineal innervation is proposed.

Evidence is given of diurnal rhythms in the mean number of dense-core vesicles surrounding a Golgi complex in the perikaryon of light rabbit pinealocytes and of those present per terminal of light pinealocyte processes. These rhythms show their top at noon and in the evening, respectively.