Neuropeptide-containing neurons of the cerebral cortex are also GABAergic

Differential localization of two glutamic acid decarboxylases (GAD65 and GAD67) in adult monkey visual cortex

Adult monkey primary visual cortex contains a diverse population of stellate neurons that utilize the neurotransmitter gamma aminobutyric acid (GABA). Two glutamic acid decarboxylase (GAD) enzymes that synthesize GABA, GAD65 and GAD67, were localized within these stellate neurons by in situ hybridization of 35S or digoxigenin (DIG) labeled riboprobes. Double labels were done by using 35S GAD67 riboprobe and GABA immunocytochemistry on the same section to verify that the neuronal population identified by immunocytochemistry was the same one studied in the in situ hybridization experiments. We find that GAD65 mRNA and GAD67 mRNA are widely distributed in the cortex, with four bands of heavily labeled neurons in upper layer 2, lower 3, 4C, and 6. GAD67 labeled neurons were more obvious in layer 4C beta, while GAD65 containing neurons were common in layer 1 and white matter. Northern blots and in situ hybridization on sections with both 35S and DIG riboprobes indicate that cortical neurons typically contain more GAD67 mRNA. Cell counts show that 18% of all cortical neurons contain GAD67 mRNA and 13% contain GAD65 mRNA, suggesting that a small population of GABA neurons might lack GAD65. Cell bodies that contain high amounts of GAD65 mRNA are prominent in layers deep 3, 4B, 4C alpha, and 6 and often are the largest cells in their respective layers. Double labels demonstrate that 96% of all GABA+ neurons contain GAD67 mRNA. Neurons heavily labeled for GABA tend to have smaller cell bodies and contain less GAD67 mRNA, while lightly labeled GABA neurons are larger and contain more GAD67 mRNA. These data indicate that most GABA neurons in monkey striate cortex contain both GAD enzymes. Although the differences in GABA content, cell size, laminar distribution, and GAD mRNA concentration suggest different requirements for GAD67 and GAD65 in cortical circuits, our experiments do not reveal what different roles these two enzymes subserve within GABAergic stellate neurons.

Immunohistochemical localization of hyaluronic acid in rat and human brain

The immunohistochemical localization of hyaluronic acid (HA) was studied in rat and human brain using the monoclonal antibody NDOG1, which specifically recognizes HA. In both rat and human brain, HA-like immunoreactivity formed characteristic coats around neurons in highly selective areas. The staining was abolished by pretreatment of sections with testicular and Streptomyces hyaluronidases, indicating that the staining was specific for HA. In rat brain, positive neurons were located in the cerebral cortex, subiculum, amygdala, thalamic reticular nucleus, nuclei of the inferior colliculus, nuclei of the trapezoid body, and vestibular nuclei. They were also scattered in the hypothalamus, substantia nigra pars reticularis, red nucleus, parabrachial nuclei, brainstem reticular nuclear group, ventral cochlear nucleus, nuclei of lateral lemniscus, and deep cerebellar nuclei. Double immunohistochemical studies showed that many neurons staining for HA were positive for parvalbumin, with minor exceptions in the amygdala and piriform cortex, where some HA-positive neurons were also positive for calbindin-D28k. In the areas studied in human brain, the distribution of HA-positive neurons was virtually identical to that in rat brain. HA-positive neurons were not significantly altered in Alzheimer disease (AD) brain, suggesting that these neurons are resistant to the pathological process of AD.

Postnatal development of the cholecystokinin innervation of monkey prefrontal cortex

Although the structure and function of primate prefrontal cortex undergo substantial modifications during postnatal development, relatively little is known about the maturation of neurotransmitter systems in these cortical regions. In the primate brain, cholecystokinin is present in the greatest concentrations in prefrontal regions. Thus, in this study, we used immunohistochemical techniques to investigate the postnatal development of the cholecystokinin innervation of monkey prefrontal cortex. In animals aged 4 days through adult, cholecystokinin immunoreactivity was present in nonpyramidal neurons that appeared to represent at least two distinct cell types. The most common type was a vertically oval bitufted neuron, located in layers II-superficial III, which typically had a radially descending axon that gave rise to short collaterals in layer IV. Another frequently observed cell type was a larger multipolar neuron located in the superficial half of layer III. The axon of these neurons branched locally in the vicinity of the cell body. The greatest density of cholecystokinin-containing neurons and processes was present in monkeys less than 1 month of age. The density of immunoreactive structures in every prefrontal region then progressively declined with increasing age, with the most marked changes occurring during the first postnatal year. As a result, the density of labeled neurons in adult monkeys was less than one-third of that in neonatal monkeys. However, labeled structures were significantly more dense in some ventromedial and orbital regions than in dorsal regions of the prefrontal cortex in neonatal, but not in older animals. In all animals, cholecystokinin-containing neurons were present in highest density in layers II-superficial III, and labeled terminal fields were observed in layers II, IV, and VI. In animals less than 1 month of age, fascicles of radial fibers traversed through layers III and V, whereas in animals 1 to 3 months of age, individual radial fibers rather than fiber bundles were present in layers III and V. In addition, immunoreactive pericellular arrays, which appeared to surround unlabeled nonpyramidal cells, were present in layers V and VI and the subcortical white matter in the youngest monkeys. Although many aspects of the cholecystokinin innervation of monkey prefrontal cortex remain constant during postnatal life, the distinct developmental changes in the cholecystokinin innervation of these regions suggest that it may play an important role in the maturation of the cortical circuitry that mediates the acquisition of certain cognitive abilities.

Descending efferent connections of the sub-pallidal areas in the cat: projections to the subthalamic nucleus, the hypothalamus, and the midbrain

The efferent connections of the sub-pallidal regions to the mediodorsal thalamic nucleus, the subthalamic nucleus, the lateral hypothalamic area, and the midbrain were investigated in the cat, using Phaseolus vulgaris--leucoagglutinin (PHA-L) as an anterograde label. The results indicate that the sub-pallidal regions of the cat project to the (dorso)medial tip of the subthalamic nucleus and the adjoining lateral hypothalamic area as well as to the ventral tegmental area and the greater extent of the dorsolateral tier of the substantia nigra pars compacta. Extensive projections were also found to the peripeduncular nucleus. The central gray as well as the mesencephalic locomotor region receive some input from the basal forebrain too. In contrast only very limited projections were found to the mediodorsal thalamic nucleus. The results are discussed in view of the possible role of these output regions in oro-facial dyskinesia.

Release of cholecystokinin-like immunoreactivity in the frontal cortex of conscious rats as assessed by transcerebral microdialysis: effects of different depolarizing stimuli

The release of cholecystokinin-like immunoreactivity (CCK-LI) from the frontal cortex of freely moving rats has been studied using a transcerebral microdialysis technique coupled to a radioimmunoassay procedure. Basal levels of CCK-LI in the dialysate were above detection limits (2.4 +/- 0.7 pg/20 min; n = 8). High-K+ media evoked CCK-LI overflow in a concentration-dependent manner. The threshold concentration was 50 mM KCl. The peak overflow evoked by 100 mM K+ amounted to 42.7 +/- 2.8 pg/20 min (n = 6); it was totally Ca2+ dependent but insensitive to 1 microM tetrodotoxin. Infusion of 4-aminopyridine (1 mM; 20 min) evoked an overflow of CCK-LI (32 +/- 2.3 pg/20 min; n = 4), which was totally Ca2+ dependent and tetrodotoxin sensitive. Depolarization with 100 micrograms/ml of veratrine (20 min) provoked a CCK-LI overflow (62.2 +/- 10 pg/20 min; n = 6), which was also blocked by tetrodotoxin or by the absence of Ca2+ ions. The CCK-LI material collected under basal conditions or during veratrine infusion consisted essentially of CCK octapeptide sulfate. The veratrine-induced CCK-LI overflow did not change significantly when the infusion time was prolonged to 100 min. A second 20-min stimulus with 100 micrograms/ml of veratrine applied 200 min after a first 20-min stimulus evoked a barely significant CCK-LI overflow. These data suggest that one single 20-min stimulus with 100 micrograms/ml of veratrine may be sufficient to deplete the CCK-LI releasable stores and that > 200 min are required to replenish the depleted CCK-containing vesicles.(ABSTRACT TRUNCATED AT 250 WORDS)

Glutamic acid and gamma-aminobutyric acid modulate each other's release through heterocarriers sited on the axon terminals of rat brain

The effects of gamma-aminobutyric acid (GABA) on the spontaneous release of endogenous glutamic acid (Glu) or aspartic acid (Asp) and the effects of Glu on the release of endogenous GABA or [3H]GABA were studied in superfused rat cerebral cortex synaptosomes. GABA increased the outflow of Glu (EC50 17.2 microM) and Asp (EC50 18.4 microM). GABA was not antagonized by bicuculline or picrotoxin. Neither muscimol nor (-)-baclofen mimicked GABA. The effects of GABA were prevented by GABA uptake inhibitors and were Na+ dependent. Glu enhanced the release of [3H]GABA (EC50 11.5 microM) from cortical synaptosomes. Glu was not mimicked by the glutamate receptor agonists N-methyl-D-aspartic, kainic, or quisqualic acid. The Glu effect was decreased by the Glu uptake inhibitor D-threo-hydroxyaspartic acid (THA) and it was Na+ sensitive. Similarly to Glu, D-Asp increased [3H]GABA release (EC50 9.9 microM), an effect blocked by THA. Glu also increased the release of endogenous GABA from cortex synaptosomes. In this case the effect was in part blocked by the (RS)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione, whereas the 6-cyano-7-nitroquinoxaline-2,3-dione-insensitive portion of the effect was prevented by THA. GABA increased the [3H]D-Asp outflow (EC50 13.7 microM) from hippocampal synaptosomes in a muscimol-, (-)-baclofen-, bicuculline-, and picrotoxin-insensitive manner. The GABA effect was abolished by blocking GABA uptake and was Na+ dependent.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparative localization of mRNAs encoding two forms of glutamic acid decarboxylase with nonradioactive in situ hybridization methods

Nonradioactive in situ hybridization methods with digoxigenin-labeled cRNA probes were used to localize two glutamic acid decarboxylase (GAD) mRNAs in rat brain. These mRNAs encode two forms of GAD that both synthesize GABA but differ in a number of characteristics including their molecular size (65 and 67 kDa). For each GAD mRNA, discrete neuronal labeling with high cellular resolution and low background staining was obtained in most populations of known GABA neurons. In addition, the current methods revealed differences in the intensity of labeling among neurons for each GAD mRNA, suggesting that the relative concentrations of each GAD mRNA may be higher in some groups of GABA neurons than in others. Most major classes of GABA neurons were labeled for each GAD mRNA. In some groups of GABA neurons, the labeling for the two mRNAs was virtually identical, as in the reticular nucleus of the thalamus. In other groups of neurons, although there was substantial labeling for each GAD mRNA, labeling for one of the mRNAs was noticeably stronger than for the other. In most brain regions, such as the cerebellar cortex, labeling for GAD67 mRNA was stronger than for GAD65 mRNA, but there were a few brain regions in which labeling for GAD65 mRNA was more pronounced, and these included some regions of the hypothalamus. Finally, some groups of GABA neurons were predominantly labeled for one of the GAD mRNAs and showed little or no detectable labeling for the other GAD mRNA, as, for example, in neurons of the tuberomammillary nucleus of the hypothalamus where labeling for GAD67 mRNA was very strong but no labeling for GAD65 mRNA was evident. The findings suggest that most classes of GABA neurons in the central nervous system (CNS) contain mRNAs for at least two forms of GAD, and thus, have dual enzyme systems for the synthesis of GABA. Higher levels of one or the other GAD mRNA in certain groups of GABA neurons may be related to differences in the functional properties of these neurons and their means of regulating GABA synthesis.

Somatostatin-like immunoreactivity in the pigeon visual system: developmental expression and effects of retina removal

The distribution of somatostatin (SS)-containing neurons was investigated by immunocytochemical methods in the central visual system of adult, developing, and retina-ablated pigeons. In normal adult brains, SS-positive cells and processes were present in the optic tectum, the nucleus of the basal optic root, the visual Wulst, and the ectostriatum. During development, progressive increase or decrease in the numerical density and the total number of SS-containing neurons occurred as determined by quantitative analysis. Changes in SS immunoreactivity also occurred as a consequence of unilateral and bilateral retina removal immediately after hatching, i.e. before retinofugal connections have been established. In spite of the segregation of visual inputs due to the almost completely crossed retinal projections, unilateral and bilateral deafferentation differentially affected SS-containing visual regions. In addition, different effects were observed on the relative packing density of labeled cells as compared to their total number. A possible role of retinal axons in regulating the distribution of SS immunoreactivity was suggested by its altered expression induced by retinal deafferentation. In addition, parallels with the distribution of SS immunoreactivity in the pigeon's visual system were used to suggest possible equivalence between cell populations in the avian and the mammalian brains.

Regulation of neuropeptide expression in cultured cerebral cortical neurons by brain-derived neurotrophic factor

The neuropeptide-inducing activity of neurotrophic factors was tested in cultured cerebral cortical neurons. Brain-derived neurotrophic factor (BDNF) specifically increased contents of the neuropeptides somatostatin (SOM) and neuropeptide Y (NPY), but its effect on contents of cholecystokinin octapeptide and GABA was much less significant. The maximal induction of NPY content (15-fold increase) was achieved by 20 ng/ml of BDNF. These changes were also reproduced at the mRNA level. In contrast, neurotrophin-3 was much less potent at increasing NPY and SOM contents, and nerve growth factor had no effect on them. The expression of mRNA for NPY and SOM was fully dependent on the presence of BDNF in culture but irrelevant to the survival-promoting activity of BDNF, which has been reported previously. Most of the NPY immunoreactivity induced by BDNF was colocalized with glutamate decarboxylase immunoreactivity in cultured cortical neurons. These results suggest that BDNF regulates the peptidergic expression of GABAergic neurons in the cerebral cortex.

A comparison of the development of neuropeptide and MAP2 immunocytochemical labeling in the macaque visual cortex during pre- and postnatal development

The appearance of Substance P (SP) and Neuropeptide Y (NPY) has been studied using light microscopic immunocytochemical labeling throughout the complete developmental span of Macaca nemestrina monkey striate cortex. In the adult, 80% of the NPY+ neurons occur in the white matter (WM) and most of the remainder are medium to large multipolar neurons in layer 2. Fibers occur in all layers except 4C and are very numerous, given the relatively small number of NPY+ cell bodies. NPY+ neurons first were seen at embryonic day (E) 75. Most neurons were in the intermediate zone (IZ), but a few were in the immature cortical plate (CP). An adult-like distribution was present by E125 for neurons and by birth for fibers, but fiber staining intensity and number increased to postnatal year 1 (P1yr). In adult cortex, numerous SP+ nonpyramidal neurons were present in layers 2-6 and WM, but SP+ fibers were surprisingly infrequent. During development, significant numbers of SP+ neurons were not seen in the CP until E113-125. Later prenatal ages had a prominent plexus of SP+ cell bodies and fibers at the layer 5/6 border. This plexus disappeared by P12wk due to either down-regulation of SP or cell death. SP+ neurons in IZ/WM were very sparse until birth after which they increased in number and staining intensity up to P1yr, suggesting a postnatal up-regulation of SP in a preexisting WM subpopulation. Cell densities were determined for SP, NPY, and the neuron-specific marker microtubule-associated protein 2 (MAP2) to clarify the developmental dynamics of IZ/WM neurons. MAP2+ cell densities in WM peaked around birth and then declined 20% in the outer half and 77% in the inner half of WM. SP+ cell density rose 57% from birth to P20wk and then declined 20% into adulthood. NPY+ cell density was fairly constant prenatally and then rose 300% by adulthood. Neuropeptide cell density changes took place predominantly in the outer WM. These data indicate that cell death does occur in the general population of monkey striate cortical WM neurons. In contrast, both SP+ and NPY+ cells are characterized by minimal cell death and a late expression of neuropeptides which causes an increase in neuropeptide+ cell density in postnatal WM.

Electron microscopy of Golgi-impregnated interneurons: notes on the intrinsic connectivity of the cerebral cortex

The Golgi-electron microscope technique has opened new avenues to explore the synaptic organization of the brain. In this article, we shall discuss basic methodological principles necessary to analyze axonal arborizations with this combined technique. To illustrate the applications of the method, we shall review the forms and distribution of the synapses in which the axonal arborizations of local cortical interneurons engage.

Changes in cholecystokinin receptor binding in rat brain after selective damage of locus coeruleus projections by DSP-4 treatment

Brain cholecystokinin (CCK)- and noradrenergic activities are two neurochemical systems implicated in anxiety and deficits in novelty-related behaviour. In order to clarify a possible interaction between CCK- and noradrenergic neurotransmission in the brain, DSP-4 [N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine], a neurotoxin that selectively destroys noradrenaline-containing nerve terminals originating from the locus coeruleus, was administered to rats IP (10 and 50 mg/kg) seven days before decapitation. Noradrenaline uptake was very markedly reduced in the frontal cortex and hippocampus of the DSP-4 treated animals, whereas the decrease in the hypothalamus was smaller but still statistically significant. Dopamine uptake in the corpus striatum, as well as serotonin uptake in the frontal cortex, hippocampus and hypothalamus, were not influenced by DSP-4 treatment. Concomitantly, CCK receptor binding in certain brain regions was markedly affected. Thus, CCK receptor density was significantly higher in the frontal cortex and hippocampus of DSP-4-treated rats. If desipramine (25 mg/kg) was administered before DSP-4 treatment, the DSP-4-induced changes both in noradrenaline uptake and CCK receptor binding were not present, suggesting that both effects were exerted after uptake of the neurotoxin by the nerve terminals. The time-course of the development of changes in CCK-8 binding paralleled with some lag the development of changes in noradrenaline uptake. These findings demonstrate the denervation of noradrenergic input from the locus coeruleus induces certain alterations in the CCKergic neurotransmission. These alterations are similar to those seen in rats with deficits in response to novel stimuli, and may therefore mediate the neophobic responses observed in animals after lesions of noradrenergic innervation of the forebrain.

Distribution of calbindin and parvalbumin in the developing somatosensory cortex and its primordium in the rat: an immunocytochemical study

Immunocytochemical techniques were used to analyze the distribution of the calcium-binding proteins calbindin and parvalbumin during the pre- and postnatal development of the rat somatosensory cortex. Calbindin occurs in most early differentiated neurons that form the primordial plexiform layer at embryonic day 14. This expression in transient; during the perinatal period, calbindin becomes immunologically undetectable within the structures derived from the primordial plexiform layer, i.e., the prospective layers I and VIb. Immunoreactive neurons are also absent from adult layers I and VIb. Calbindin is also detected in a second population of neurons which, from embryonic day 18 onwards, distributes diffusely within the cortical plate. Some neurons of this population show morphological traits of immaturity, while others show complete dendritic arborization. The definitive pattern of distribution of calbindin-immunoreactive neurons is achieved by postnatal day 22. Infragranular layers contain intensely-immunoreactive cells whose numerical density decreases during postnatal development, whereas in supragranular layers similar neurons are interspersed among numerous faintly-stained neurons. Parvalbumin is detected for the first time at postnatal day 6, within a small group of neurons located in cortical layer V, and extends afterwards through the whole thickness of the cerebral cortex. At this same postnatal stage, groups of immunoreactive puncta are also found in layer IV of the somatosensory cortex; these puncta increase in density progressively and, at embryonic day 13, immunoreactive cells appear also grouped at this level. At this postnatal age, parvalbumin immunostaining delineates the somatosensory map in cortical layer IV. From this stage to adulthood, the number of immunoreactive neurons increases in the whole thickness of the somatosensory cortex. Barrels in layer IV become less distinct as immunoreactive cells and processes invade the septa. Layer IV in the adult somatosensory cortex appears more densely populated by parvalbumin immunoreactive neurons and puncta than in the surrounding areas.

gamma-Aminobutyric acid and glycine modulate each other's release through heterocarriers sited on the releasing axon terminals of rat CNS

The ability of gamma-aminobutyric acid (GABA) and glycine (Gly) to modulate each other's release was studied in synaptosomes from rat spinal cord, cerebellum, cerebral cortex, or hippocampus, prelabeled with [3H]GABA or [3H]Gly and exposed in superfusion to Gly or to GABA, respectively. GABA increased the spontaneous outflow of [3H]Gly (EC50, 20.8 microM) from spinal cord synaptosomes. Neither muscimol nor (-)-baclofen, up to 300 microM, mimicked the effect of GABA, which was not antagonized by either bicuculline or picrotoxin. However, the effect of GABA was counteracted by the GABA uptake inhibitors nipecotic acid and N-(4,4-diphenyl-3-butenyl)nipecotic acid. Moreover, the GABA-induced [3H]Gly release was Na+ dependent and disappeared when the medium contained 23 mM Na+. The effect of GABA was Ca2+ independent and tetrodotoxin insensitive. Conversely, Gly enhanced the outflow of [3H]GABA from rat spinal cord synaptosomes (EC50, 100.9 microM). This effect was insensitive to both strychnine and 7-chlorokynurenic acid, antagonists at Gly receptors, but it was strongly Na+ dependent. Also, the Gly-evoked [3H]GABA release was Ca2+ independent and tetrodotoxin insensitive. GABA increased the outflow of [3H]Gly (EC50, 11.1 microM) from cerebellar synaptosomes; the effect was not mimicked by either muscimol or (-)-baclofen nor was it prevented by bicuculline or picrotoxin. The GABA effect was, however, blocked by GABA uptake inhibitors and was Na+ dependent. Gly increased [3H]GABA release from cerebellar synaptosomes (EC50, 110.7 microM) in a strychnine- and 7-chlorokynurenic acid-insensitive manner. This effect was Na+ dependent. The effects of GABA on [3H]Gly release seen in spinal cord and cerebellum could be reproduced also with cerebrocortical synaptosomes.(ABSTRACT TRUNCATED AT 250 WORDS)

Regional distribution of neuropeptide somatostatin gene expression in the human brain

The regional distribution of mRNA coding for the neuropeptide somatostatin has been studied in the human brain by in situ hybridization histochemistry using 32P-labeled oligonucleotides. We show that somatostatin mRNA-containing neurons are widely distributed in a number of nuclei and grey areas of the human brain, including neocortex, putamen, nucleus caudatus, nucleus accumbens, amygdala, midbrain, medulla oblongata, hippocampal formation, reticular nucleus of the thalamus, and posterior nucleus of the hypothalamus. No significant hybridization signal was observed in the substantia nigra, claustrum, globus pallidus, thalamus, and cerebellum. The topographic localization of neurons containing SOM mRNA in the human brain is in agreement with previous studies using immunocytochemical or radioimmunoassay techniques. These results show that in situ hybridization histochemistry with oligonucleotide probes can be used to map the distribution of neurons expressing SOM mRNA in human postmortem materials.

Paucity of glutaminase-immunoreactive nonpyramidal neurons in the rat cerebral cortex

Glutaminase has been considered to be a synthesizing enzyme of transmitter glutamate in pyramidal neurons of the cerebral cortex. In the present study, an attempt was made to examine with a double immunofluorescence method whether or not nonpyramidal neurons of the cerebral cortex are immunoreactive for glutaminase. Glutaminase was stained with mouse anti-glutaminase IgM and FITC-labeled anti-[mouse IgM] antibody. In the same section, parvalbumin (PA), calbindin (CB), choline acetyltransferase (CAT), vasoactive intestinal polypeptide (VIP), corticotropin releasing factor (CRF), cholecystokinin (CCK), somatostatin (SS), or neuropeptide Y (NPY) was visualized as a marker for nonpyramidal neurons with an antibody to each substance, biotinylated secondary antibody and Texas Red-labeled avidin. Virtually no glutaminase immunoreactivity was seen in PA-, CB-, CAT-, VIP-, CRF-, CCK-, SS-, or NPY-immunoreactive neuronal perikarya in the neocortex and mesocortex (cingulate and retrosplenial cortices), although it was detected in a few PA-, CB-, VIP-, CCK-, SS-, or NPY-immunoreactive nonpyramidal neurons in the piriform, entorhinal, and hippocampal cortices. PA- and CB-positive neurons have been reported to constitute the major population of GABAergic neurons in the cerebral cortex. Thus, the present results, together with the previous reports, suggest that most GABAergic, cholinergic and peptidergic nonpyramidal neurons in the neo- and mesocortex do not contain glutaminase.

Neuropeptides and anxiety disorders

In this review article four neuropeptides: adrenocorticotrope hormone (ACTH), corticotrope releasing hormone (CRH), neuropeptide- Y(NPY) and cholecystokinin (CCK) are discussed with respect to their possible role in the pathogenesis of anxiety disorders. First the presumable working mechanism of these peptides in the brain is mentioned. In addition, the relationship of these peptides and anxiety is outlined using neuroanatomical and electrophysiological research data. Subsequently, animal experiments and human research findings are discussed. Most of the research findings so far are obtained from animal data. Only with respect to CCK, there is increasing evidence, also from human studies, that this peptide might play a role in the pathogenesis of anxiety disorders. The putative role of the other peptides remains to be estab lished in future research.

Converging GABA- and glutamate-immunoreactive axons make synaptic contact with identified hypothalamic neurosecretory neurons

To study the neurochemical identity of axons in synaptic contact with identified hypothalamic neurosecretory neurons in rats, we combined retrograde axonal transport of a marker molecule with postembedding immunogold staining for amino acid neurotransmitters. After intravenous injections of horseradish peroxidase, neurosecretory neurons with axons in the median eminence or neurohypophysis transported the peroxidase retrogradely back to the cell body of origin. Serial ultrathin sections from the paraventricular and arcuate nuclei were immunostained with glutamate or GABA antisera. Peroxidase-labeled neurons and their dendrites received synaptic contact from colloidal gold-labeled axons immunoreactive for GABA or for glutamate. Axons which were highly immunoreactive for GABA and other axons immunoreactive for glutamate but not for GABA consistently made converging synaptic contact with the same peroxidase-labeled cell. Some of the peroxidase-labeled neurons from the arcuate nucleus which were postsynaptic to both GABA and glutamate axons were themselves identified as being GABA immunoreactive. Serial ultrathin sections revealed that multiple presynaptic axons immunoreactive for glutamate or GABA made repeated contacts with single neurons. These results suggest a widespread convergence of the major inhibitory and excitatory amino acid transmitter on the neurons which control both the anterior and posterior pituitary hormones.

Distribution of neuropeptide Y-like immunoreactivity in the brain of the lizard Gallotia galloti

The distribution of neuropeptide Y (NPY)-like immunoreactivity was studied in the brain of the lizard Gallotia galloti, in order to gain insight into the comparative topography of this peptide. Antisera against both NPY and its C-terminal flanking peptide (C-PON) were used, demonstrating a general coexistence of both peptides, as described in other vertebrates. Most NPY-like immunoreactive (NPY-LI) cell bodies were observed in the telencephalon, specifically in various olfactory structures, all cortices, septum, basal ganglia (except for the globus pallidus), the nucleus of the diagonal band of Broca, the amygdaloid complex, and the bed nucleus of the anterior commissure. NPY-LI cells were also seen in the preoptic and hypothalamic regions and the dorsal thalamus (mainly in the perirotundal belt), as well as in the mesencephalic tegmentum (in the ventral tegmental area, the substantia nigra, and the retrorubral area). NPY-LI fibers and terminals were widely distributed in the brain. All visual and auditory neuropiles were densely innervated. Specially dense plexuses were seen in the nucleus accumbens, the ventral pallidum, the suprachiasmatic and ventromedial hypothalamic nuclei, the nucleus medialis thalami, the left habenula, and the central nucleus of the torus semicircularis. Our analysis shows that the distribution of NPY-like immunoreactivity in the forebrain of Gallotia largely resembles that of other vertebrates, whereas differences are mainly observed in the brainstem. The widespread distribution of NPY in the lizard brain suggests several modulatory functional roles, either in local-circuit systems of the forebrain, or in various limbic, neuroendocrine, and sensory pathways.

Ontogeny of cholecystokinin-immunoreactive structures in the primate cerebral neocortex

Distribution of cholecystokinin (CCK)-immunoreactive structures was studied in various neocortical areas of macaque monkeys during prenatal and postnatal development. The largest number of CCK-immunoreactive cells was observed at embryonic day 140, and subsequently they decreased in number until postnatal day 60. A few cells which were presumably degenerated neurons were observed during postnatal development. A higher density of CCK-immunoreactive cells was observed in the supragranular layers (layers II and III) than in the infragranular layers (layers V and VI). The number of CCK-immunoreactive cells was larger and changed more conspicuously in the association areas than in the other areas during development. In contrast, in the occipital area, the number of such cells was small and changed only a little. These findings suggest that CCK may be involved in the development and special function of each neocortical areas of the primate.

Morphology and laminar distribution of neuropeptide Y immunoreactive neurons in the human striate cortex

The morphology, laminar distribution, and distribution relative to cytochrome oxidase patches of neuropeptide-Y immunoreactive (NPY-ir) neurons were studied in the human striate cortex. The density of NPY-ir cells was highest in the white matter. NPY-ir neurons were sparsely distributed within the cortical layers. NPY-ir neurons were located in both cytochrome oxidase dense patch and interpatch regions. However, the paucity of NPY-ir neurons in layer III, where cytochrome oxidase patches are most clearly demonstrated, precluded establishing a clear relationship of NPY-ir neurons to cytochrome oxidase patches. NPY-ir neurons exhibited a variety of nonpyramidal morphologies, and many of them had axons with recurrent or looped trajectories. A dense plexus of NPY-ir axons was located just beneath the pia, and these axons were concentrated at the entry points of pial blood vessels. Other NPY-ir neurons had cell bodies or processes in close proximity to cerebral capillaries. These results suggest a role of NPY in cortical metabolism, control of cerebral circulation, or activity-related changes in local blood flow.

A developmental perspective on the pathology and neurochemistry of the temporal lobe in schizophrenia

Neuropathological, neuroimaging, clinical and epidemiological evidence suggests that many cases of schizophrenia are developmental in origin. Dysplastic changes in the medial temporal lobes appear to be of particular importance. However, research implicating a neurodevelopmental origin for schizophrenia has proceeded largely in isolation from knowledge concerning the neurochemistry of the disorder. This paper attempts to integrate these disparate lines of research, and examines the role of trophic mechanisms in the formation of the hippocampus. Those neurotransmitters which have been most consistently found to be abnormal in the temporal lobes of schizophrenics (excitatory amino acids and CCK), are involved in the control of hippocampal development. We suggest that these neurotransmitter findings are the residue of abnormalities in their role as trophic factors in foetal or neonatal life, and that the latter contribute to the developmental aberrations considered fundamental to schizophrenia.

Neuropeptide Y-like immunoreactivity in the diencephalon of the little brown bat (Myotis lucifugus): localized variations with physiological state

The current study used light microscopic immunocytochemistry to demonstrate and compare neuropeptide Y-like immunoreactivity (NPY-IR) in the diencephalon of the little brown bat (Myotis lucifugus) at different stages in its annual cycle of activity and hibernation. Animals were sacrificed in each of three discrete physiological states: euthermic, hypothermic, and hibernating. In general, NPY-IR was abundant in the hypothalamus and sparse in other diencephalic areas. Immunoreactivity was present in a number of pathways which project to or originate from diencephalic nuclei; these include the ansa peduncularis, medial forebrain bundle, inferior thalamic peduncle, stria terminalis, stria medullaris, mammillary peduncle, and dorsal longitudinal fasiculus. Dense fiber plexuses were present throughout the hypothalamus; however, NPY-IR was conspicuously absent from the suprachiasmatic nucleus. Immunoreactive perikarya were located in the supraoptic, dorsomedial, ventromedial, and arcuate nuclei, in the external division of the ventral lateral geniculate nucleus, and in the pineal gland. Localized changes in density and/or distribution of NPY-IR were correlated with changes in physiological state.

GABAergic neuronal populations in monkey primary auditory cortex defined by co-localized calcium binding proteins and surface antigens

The primary auditory cortex (A1) of monkeys was investigated by immunohistochemistry, using antibodies to gamma-aminobutyric acid (GABA), to the calcium binding proteins parvalbumin and calbindin, and to certain proteoglycan epitopes. The two calcium binding proteins were found to be localized in subpopulations of GABAergic neurons. Parvalbumin immunoreactive cells were mostly found in the middle layers of the cortex. Parvalbumin immunoreactivity was found in fibres in the white matter underlying A1 and a particularly dense concentration of parvalbumin immunoreactive fibers and terminals occurred in layer IV suggesting that a significant population of geniculocortical fibers is also parvalbumin positive. Calbindin positive cells were mostly located in superficial layers and in these layers the neuropil staining was also dense. Two monoclonal antibodies (MAbs) raised against monkey brain tissue and which had previously been shown to recognize neuronal surface antigens stained overlapping subpopulations of GABAergic cells. Occasional pyramidal cells were also immunoreactive. Most of the MAb positive cells were found in the middle layers and all were parvalbumin but not calbindin immunoreactive. Although the physiological roles in the brain for calcium binding proteins and the relevant cell surface markers have not yet been clarified, the presence of these markers in selected subpopulations of cells suggests the existence of functionally distinct circuits in AI cortex.

Organization and plasticity of GABA neurons and receptors in monkey visual cortex

The GABA neurons of monkey area 17 are a morphologically and chemically heterogeneous population of interneurons that are normally distributed most densely within the geniculocortical recipient zones of the visual cortex. In adult monkeys deprived of visual input from one eye, the levels of immunoreactivity for GABA and GAD within neurons of these geniculocortical zones is reduced. Similar changes are seen in the levels of proteins that make up the GABAA receptor sub-type. The effects of monocular deprivation on other substances suggest that specific types of GABA neurons, such as those in which the tachykinin neuropeptide family and parvalbumin coexist with GABA, are greatly influenced by changes in visual input. That some proteins remain normal within deprived-eye neurons and that other proteins are increased indicates the changes in the GABA cells of the cortex are not the result of a general reduction in protein synthesis. Comparisons of what is known about the morphological and synaptic features of GABA cells in area 17 and the characteristics of cells affected by monocular deprivation suggests that certain classes, such as the clutch cell, may be preferential targets of deprivation. Such a selective loss of certain GABA neurons would have broad implications for the possible physiological plasticity of cortical cells, for if ongoing studies determine that specific receptive field properties are affected by monocular deprivation in adults, the correlation of functional properties and classes of GABA cells would be possible.

GABAergic interneurons containing calbindin D28K or somatostatin are major targets of GABAergic basal forebrain afferents in the rat neocortex

The arborization pattern and postsynaptic targets of the GABAergic component of the basal forebrain projection to neo- and mesocortical areas have been studied by the combination of anterograde tracing and pre- and postembedding immunocytochemistry. Phaseolus vulgaris leucoagglutinin (PHAL) was iontophoretically delivered into the region of the diagonal band of Broca, with some spread of the tracer into the substantia innominata and ventral pallidum. A large number of anterogradely labelled varicose fibres were visualized in the cingulate and retrosplenial cortices, and a relatively sparse innervation was observed in frontal and occipital cortical areas. Most of the labelled axons were studded with large en passant varicosities (Type 1), whereas the others (Type 2) had smaller boutons often of the drumstick type. Type 1 axons were distributed in all layers of the mesocortex with slightly lower frequency in layers 1 and 4. In the neocortex, layer 4, and to a smaller extent upper layer 5 and layer 6 contained the largest number of labelled fibres, whereas only a few fibres were seen in the supragranular layers. Characteristic type 2 axons were very sparse but could be found in all layers. Most if not all boutons of PHAL-labelled type 1 axons were shown to be GABA-immunoreactive by immunogold staining for GABA. Altogether 73 boutons were serially sectioned and found to make symmetrical synaptic contacts mostly with dendritic shafts (66, 90% of total targets), cell bodies (6, 8.2% of total), and with one spine. All postsynaptic cell bodies, and the majority of the dendritic shafts (44, 60.3% of total targets) were immunoreactive for GABA. Thus at least 68.5% of the total targets were GABA-positive, but the majority of the dendrites not characterized immunocytochemically for technical reasons (15.1%) also showed the fine structural characteristics of nonpyramidal neurons. The target interneurons included some of the somatostatin- and calbindin-containing subpopulations, and a small number of parvalbumin-containing neurons, as shown by double immunostaining for PHAL and calcium-binding proteins or neuropeptides. We suggest that the innervation of inhibitory interneurons having extensive local axon arborizations may be a mechanism by which basal forebrain neurons-most notably those containing GABA--have a powerful global effect on the majority of principal cells in the entire cortical mantle.

Somatostatin release from rat cerebral cortex synaptosomes

Rat cerebral cortex synaptosomes were exposed in superfusion to various depolarizing stimuli and the release of somatostatin-like immunoreactivity (SRIF-LI) was measured by means of a radioimmunoassay procedure. High KCl (9-50 mM) concentration dependently evoked SRIF-LI release; the evoked overflow reached a plateau at 25 mM KCl and was completely abolished when Ca2+ ions were omitted from the superfusion medium, independently of the concentration of KCl used. The 15 mM K(+)-evoked release of SRIF-LI increased sharply as the Ca2+ concentration was raised to 0.8 mM, then leveled off and reached a plateau at 1.2 mM. The 15 mM K(+)-evoked overflow, but not the spontaneous outflow, was partially decreased (50%) by 1 microM tetrodotoxin. The presence in the superfusion fluid of a mixture of peptidase inhibitors did not improve the recovery of SRIF-LI both in the absence and in the presence of high K+. Exposure of synaptosomes to veratrine (1-50 microM) induced release of SRIF-LI in a concentration-dependent way. The effect of the alkaloid was strictly Ca2+ and tetrodotoxin sensitive. Replacement of extracellular Na+ by sucrose caused an acceleration of the spontaneous SRIF-LI outflow that was inversely correlated to the Na+ content in the superfusion medium. The release evoked by the sodium-deprived media did not exhibit any calcium dependence. HPLC analysis of the samples collected during superfusion showed that greater than 90% of the SRIF-LI released either during the spontaneous outflow or by 15 mM KCl was represented by SRIF-14 (SRIF-28(14-28]. These values reflected the ratio SRIF-14/SRIF-28 found in synaptosomes at the end of the experiments.

Distribution of somatostatin-immunoreactive cell bodies and fibers in the neocortex of Macaca fuscata

The distribution of somatostatin-immunoreactive cell bodies and processes was studied in the cerebral cortex of the macaque monkey (Macaca fuscata), by applying an immunohistochemical technique with a monoclonal antibody raised against somatostatin tetradecapeptide. Many somatostatin-immunoreactive cell bodies and processes were observed in all regions of the cerebral cortex, i.e., frontal, parietal, temporal, insular, occipital, and cingulate cortices, and also in the underlying white matter. Three types of somatostatin-containing cell bodies were distinguished in the cerebral cortex. These cell bodies were distributed in layers II to VI of the cortex, and also in the underlying white matter. There were dense deposits of somatostatin-containing granular structure in layers I and II, and many somatostatin-containing processes in layers IV and V. The present observations demonstrate that in the primate neocortex somatostatin 14-containing neuronal systems are as highly developed as other prosomatostatin-derived peptides but differ from the latter systems in terms of cell morphology and fiber distribution.

Distribution of neuropeptide Y (NPY) in the cerebral cortex of the lizards Psammodromus algirus and podarcis hispanica: co-localization of NPY, somatostatin, and GABA

The aim of the present study was to analyze the distribution and characteristics of NPY immunoreactive structures in the cerebral cortex of lizards and to investigate the degree of co-existence of this neuropeptide with somatostatin and GABA. The immunoperoxidase method was applied to vibratome sections as well as to semithin sections. NPY neurons are multipolar or fusiform and were unevenly distributed throughout the brain cortex. Within the medial, dorsomedial and dorsal cortices, most NPY perikarya were located in the plexiform layers, especially in the deep one. This suggests that these cells could be regarded as interneurons. In the lateral cortex, NPY neurons were found throughout all layers. The dorsomedial cortex displayed the highest NPY cell density. Here, neuronal perikarya projected many immunoreactive processes toward two distinct zones: the deep plexiform layer of the medial cortex and the superpositio medialis. The NPY neurons of the dorsomedial cortex differed from the other NPY cortical immunoreactive cells in that the latter displayed very few immunoreactive processes. A high degree of co-existence among NPY, somatostatin, and GABA (approx. 80%) was found. This co-existence rate is very similar to that reported in mammals and suggests that co-localization is a phylogenetically ancient phenomenon.

Ultrastructural Relationships Between GABAergic Terminals and Cardiac Vagal Preganglionic Motoneurons and Vagal Afferents in the Cat: A Combined HRP Tracing and Immunogold Labelling Study

The ultrastructural relationships between gamma-aminobutyric acid-immunoreactive (GABA-ir) neurons and other neurons of the nucleus tractus solitarius (NTS) and motoneurons of the nucleus ambiguus (NA) and dorsal motor vagal nucleus (DMVN), were examined by electron microscopic (EM) immunogold labelling with an anti-GABA antiserum on brain stem sections in which vagal motoneurons and vagal afferent fibres were labelled with horseradish peroxidase (HRP). HRP was applied to the cervical vagus or the cardiac vagal branch of anaesthetized cats. After 24 - 48 h survival, brains were glutaraldehyde-fixed and a stable HRP-tetramethylbenzidine reaction product compatible with EM processing was revealed on 250 microm vibratome sections. Following osmium postfixation, dehydration and resin embedding, GABA-ir was localized on ultrathin sections by an immunogold technique. GABA-ir axon terminals, heavily and specifically labelled with gold particles, were very numerous within NTS, DMVN and NA. All terminals contained small, clear, pleomorphic vesicles and a few also contained larger dense cored vesicles. The density of gold particles over clear vesicles, dense cored vesicles and mitochondria was significantly greater than over the cytoplasm of these terminals. GABA-ir synapses were found on the soma and dendrites of neurons, but rarely on other axon terminals within NTS, where GABA-ir cell bodies and dendrites were also seen. These received synaptic contacts from both GABA-ir terminals and from HRP-labelled vagal afferents. In both the DMVN and NA, similar GABA-ir synapses were present on both the soma and dendrites of HRP-labelled motoneurons. GABA synapses were also present on other cell types in DMVN. These observations provide an anatomical basis for a GABAergic inhibition of neurons forming the central pathways of cardiovascular and other autonomic reflexes.

Distribution of GABA and neuropeptides in the human cerebral cortex. A light and electron microscopic study

Antibodies were used to identify neurons in human frontal and temporal cortex that were immuno-positive to gamma-aminobutyric acid (GABA) and the neuropeptides vasoactive intestinal polypeptide (VIP), substance P (SP) and somatostatin (SOM). Specimens were taken at surgical biopsy and fixed immediately after removal. The results described for both light and electron microscopy were obtained when relatively high concentrations of glutaraldehyde (2.5-3%) were present in the fixative. Specimens were examined from three adults and an infant aged 5 months. GABAergic neurons were present in all cortical layers, with fewest in layers I, deep III and V, and were mainly small, and round or oval. No labelled pyramidal neurons were detected. GABAergic puncta were common in the neuropil, probably representing axonal profiles. VIP-neurons were also found in all layers, including layer I, and were approximately twice as numerous as GABA-cells. SP-positive cells were found throughout the layers, but were sparse in layers I and VI. They were about three times commoner than GABAergic neurons. SOM-reactivity was demonstrated in about the same number of cells as that for SP. Again, this involved all layers, but layer I least. Peptidergic neurons were larger, on the average, than GABAergic cells, and were frequently pyramidal in character. In the infant, the distribution, size and frequency of immunoreactive neurons were similar to those in the adult. However, GABAergic puncta were commoner.

A selective loss of somatostatin in the hippocampus of patients with temporal lobe epilepsy

Although neuropeptides have been demonstrated to be hippocampal neuromodulators in laboratory animals, their role in human hippocampal physiology or pathophysiology remains to be defined. The concentrations of somatostatin, cholecystokinin octapeptide, vasoactive intestinal polypeptide, and dynorphin A 1-17 were determined in hippocampal tissue resected from patients with cryptogenic temporal lobe epilepsy, a common seizure disorder originating in or near the hippocampus. Control tissue was obtained from cadavera or epilepsy patients in whom the hippocampus was removed during the resection of temporal lobe tumors. Peptide determinations were performed on extracts of punch biopsy specimens taken from six different hippocampal regions. A significant decrease in immunoreactive somatostatin concentration was identified in the dentate gyrus and in region cornu ammonis 4 of cryptogenic temporal lobe epilepsy specimens. No significant changes were present in any other hippocampal region or in the levels of other peptides. In situ hybridization studies performed on cryostat sections from similar patients confirmed a marked loss of neurons expressing the somatostatin gene, which was restricted to the dentate hilus. The density of specific 125I-somatostatin binding to cryostat sections, as determined by semiquantitative in vitro autoradiography, was significantly increased in the dentate gyrus of the cryptogenic epilepsy patients, compared with tumor control specimens. We conclude that a loss of somatostatin-producing interneurons with an upregulation of dentate somatostatin receptors is a specific and characteristic element in the pathophysiology of human cryptogenic temporal lobe epilepsy.

GABA neurons in seizure disorders: a review of immunocytochemical studies

Immunocytochemical studies have identified alterations in GABA neurons in several models of seizure disorders. However, the changes have varied among different epilepsy models, and these variations presumably reflect the diversity of mechanisms that can lead to seizure disorders. In models of cortical focal epilepsy, there is strong evidence for decreases in the number of GABAergic elements, and the changes closely parallel the time course of seizure development. By contrast, in some genetic models of epilepsy, increases in the number of immunocytochemically-detectable neurons have been observed in selected brain regions. In several models of temporal lobe epilepsy, there presently is little immunocytochemical evidence for alterations of GABA neurons within the hippocampal formation despite physiological demonstrations of decreased GABA-mediated inhibition in this region. However, it remains possible that certain types of GABA neurons could be differentially affected in some seizure disorders while other types are preserved. Thus, distinguishing between different classes of GABA neurons and determining their functional roles represent major challenges for future studies of GABA neurons in seizure disorders.

Patterns of synaptic input on corticocortical and corticothalamic cells in the cat visual cortex. I. The cell body

Immunocytochemical and electron microscopic methods were used to examine the ultrastructure and synaptology of callosal and corticothalamic pyramidal cell somata in the cat visual cortex (area 17). Callosal and corticothalamic cells were labeled after injection of horseradish peroxidase (HRP) in the contralateral visual cortex or in the ipsilateral lateral geniculate nucleus. The synaptic relationship between each of the two populations of pyramidal cells and cells containing the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) was examined at the light and electron microscope level using the combined techniques of retrograde transport of HRP and GABA immunocytochemistry. We found that callosal and corticothalamic cell somata have an ultrastructure and synaptology that distinguishes them from each other. Reconstructions from electron micrographs of serial sections revealed that the vast majority of synapses (89-96%) on the cell body of pyramidal cells were formed by GABAergic axon terminals, and that within each population of pyramidal cells there was variability in the number and density of axosomatic synapses. Callosal pyramidal cells received a greater number and higher density of axosomatic synapses than corticothalamic cells. These data suggest that callosal cells receive more inhibition than corticothalamic cells at the level of their somata.

Molecular cloning of the mouse CCK gene: expression in different brain regions and during cortical development

In this paper we describe experiments that address specific issues concerning the regulation of the mouse cholecystokinin gene in brain and intestine. The mouse cholecystokinin gene was cloned and sequenced. Extensive homology among the mouse, man and rat genes was noted particularly in the three exons and the regions upstream of the RNA start site. RNAse protection assays for each of the three exons were used to demonstrate that CCK is expressed in only a subset of tissues and that the same cap site and splice choices are used in brain, intestine as well as in cerebellum, cortex, midbrain, hypothalamus and hippocampus. CCK RNA was also noted to be detectable in kidney. Thus the same gene using the same promoter is expressed in subsets of cells that differ in their biochemical, morphologic and functional characteristics. The level of expression of CCK was also monitored during mouse cortical development and the appearance of CCK RNA was compared to glutamate decarboxylase (GAD), enkephalin and somatostatin. It was noted that each of these cortical markers was first expressed at different times during cortical development. The appearance of CCK RNA during intestinal development was also measured and found to precede appearance in cortex by several days.

GABA: a dominant neurotransmitter in the hypothalamus

To study the organization and distribution of the inhibitory amino acid neurotransmitter GABA in the medial hypothalamus, we used a postembedding immunocytochemical approach with colloidal gold. Quantitative analysis showed that half (49%) of all synapsing boutons studied were immunoreactive for GABA, based on immunogold staining of the suprachiasmatic, arcuate, supraoptic, and paraventricular nuclei. This was corroborated with pre-embedding peroxidase immunostaining with antisera against glutamate decarboxylase, the GABA synthetic enzyme. These data suggest that GABA is the numerically dominant neurotransmitter in the hypothalamus, and emphasize the importance of inhibitory circuits in the hypothalamus. Serial ultrathin sections were used to reconstruct GABA immunoreactive boutons and axons in three dimensions. With this type of analysis we found less morphological heterogeneity between GABA immunoreactive boutons than with single ultrathin sections. Single sections sometimes showed boutons containing only small clear vesicles, and other with both clear vesicles and small dense core vesicles. However, with serial sections through individual boutons, dense core vesicles were consistently found at the periphery of the pre-synaptic GABA immunoreactive boutons, suggesting probable co-localization of GABA with unidentified peptides in most if not all boutons throughout the hypothalamus. A positive correlation was found between the density of small clear vesicles and the intensity of immunostaining with colloidal gold particles. GABA immunoreactive axons generally made symmetrical type synaptic specializations, although a small percentage made strongly asymmetrical synaptic specializations. Vesicles in GABA immunoreactive boutons were slightly smaller than those in non-reactive boutons. Synaptic efficacy is related to the position of the synapse on the post-synaptic neuron. While the majority of GABA immunoreactive axons made synaptic contact with dendrites, the distribution of GABA immunoreactive synapses on somata and dendrites was the same as would be expected from a random distribution of all boutons. No preferential innervation of cell bodies by GABA immunoreactive terminals was found. Serial ultrathin sections showed that a GABA immunoreactive axon would sometimes make repeated synaptic contacts with a single postsynaptic neuron, indicating a high degree of direct control by the presynaptic GABAergic cell. Other immunoreactive axons made synaptic contact with a number of adjacent dendrites and cells, suggesting a role for GABA in synchronizing the activity of hypothalamic neurons. Based on the density of immunogold particles per unit area, varying concentrations of immunoreactive GABA were found in different presynaptic boutons in the hypothalamus.

GABA neurons in the rat suprachiasmatic nucleus: involvement in chemospecific synaptic circuitry and evidence for GAD-peptide colocalization

Dual labelling methods were employed for the electron microscopic detection of glutamate decarboxylase (GAD) immunoreactivity, together with vasoactive intestinal peptide (VIP) or neuropeptide Y (NPY) immunoreactivity in the suprachiasmatic nucleus (SCN) of colchicine pretreated and untreated rats. These methods involved the combined use of diaminobenzidine and benzidine dihydrochloride as distinct chromogens to visualize peroxidase-anti-peroxidase (PAP) immunostaining, and a combination of the PAP procedure with a radioimmunocytochemical method employing 125I-labelled secondary antisera. We were thereby able to demonstrate that gamma-aminobutyric acid (GABA) terminals provide an important afferent synaptic input to VIP neurons. Some of these VIP-immunoreactive neurons also exhibited GAD immunoreactivity. Examples of direct appositions between GABA and NPY terminals, and of a convergence of the two types of terminals on to the same postsynaptic targets, were frequently encountered. NPY/GAD colocalization within a few axonal varicosities was also demonstrated. These data provide additional information concerning chemospecific neuronal interactions that could be of functional importance in the regulation of circadian rhythmicity at the level of the SCN.

Neuropeptide Y in cortex and striatum. Ultrastructural distribution and coexistence with classical neurotransmitters and neuropeptides

NPY-neurons in the striatum and cortex have many morphological and chemical features in common. They are intrinsic, medium sized, aspiny and exhibit ultrastructural characteristics typical of neurons undergoing active synthesis and release of peptides. Most of the NPY-neurons in the two regions coexist with somatostatin, exhibit high levels of NADPH-diaphorase and are resistant to degeneration associated with Huntington's disease. Ultrastructural analysis suggests that the ensheathment by glia and sparsity of asymmetric (putatively excitatory) inputs may render NPY neurons resistant to excitotoxicity. Although NPY-neurons receive few inputs, they make numerous contacts with dendrites within a small region of the neuropil. Among their targets are GABAergic neurons. These NPY-receptive GABA neurons differ from other GABAergic neurons in the vicinity in that they receive few other inputs along their somata and proximal dendrites. This suggests that NPY may exert more influence on a specific class of GABAergic neurons. Many more of the NPY-terminals are found at sites that would be strategic for the simultaneous modulation of the release of transmitters and postsynaptic responses. The differences among NPY-neurons in the striatum versus cerebral cortex are mainly chemical. Most notably, the NPY-neurons are GABAergic in the cortex and not GABAergic in the striatum. In addition, some of the NPY-axons in the ventral portions of striatum and cerebral cortex may be catecholaminergic, and thus originate in brainstem areas recognized to contain NPY and epinephrine or norepinephrine. NPY- and catecholaminergic fibers converge onto same dendrites. Thus, the two transmitters may interact through intercellular biochemical pathways postsynaptically. Finally, the sites where the two fibers directly contact each other may be where NPY stimulates the turnover of dopamine.

Cholecystokinin innervation of monkey prefrontal cortex: an immunohistochemical study

Knowledge of the circuitry of chemically identified systems in primate prefrontal cortex is limited. Although cholecystokinin is very abundant in prefrontal cortex (Geola et al.: Journal of Clinical Endocrinology and Metabolism 53(2):270-275, 1981; Taquet et al.: Neuroscience 27(3):871-883, 1988), the organization of cholecystokinin-containing structures in primate prefrontal cortex has not been investigated. Using immunohistochemical and retrograde transport techniques, we characterized the cholecystokinin innervation of prefrontal cortex in macaque monkeys. The use of two antibodies directed against different portions of the cholecystokinin molecule revealed that distinct forms of the molecule were differentially localized in the same cortical neurons. These small, nonpyramidal cholecystokinin-positive neurons had a variety of somal morphologies and the density of labeled cells did not differ among cytoarchitectonic regions. Labeled neurons had a distinctive laminar distribution with the greatest density of cells present in layers II-superficial III. Labeled fibers also had a distinctive laminar pattern of distribution that differed from that of the immunoreactive neurons. In granular prefrontal cortex, terminal fields were evident in layers II, IV, and VI, with the greatest density in layer VI. Agranular area 24 exhibited a bilaminar pattern of immunoreactivity with a band in layer II and a very dense terminal field in layers V-VI. A high density of cholecystokinin-binding sites has been found in layers III-IV of prefrontal cortex and other association areas in the monkey; this finding has been attributed to possible cholecystokinin-containing afferents from the thalamus (Kritzer et al.: Journal of Comparative Neurology 263:418-435, 1987). The mediodorsal nucleus of the thalamus is known to be a source of afferents which terminate in layer IV of prefrontal cortex. However, combined retrograde transport and immunohistochemical techniques failed to reveal the presence of cholecystokinin-positive neurons in the mediodorsal nucleus of the thalamus that project to prefrontal cortex. These findings, and other observations, suggest that the terminal field in layer IV is formed by descending axons that arise from cholecystokinin-containing neurons in layers II and superficial III. This study demonstrates that the cholecystokinin innervation of prefrontal cortex has a laminar specific organization that is preserved across cytoarchitectonic regions. This distribution of immunoreactive structures suggests a distinctive role of cholecystokinin in cortical circuitry that is common to every region of prefrontal cortex.

Effects of centrally administered neuropeptide Y (NPY) and NPY13-36 on the brain monoaminergic systems of the rat

The effects of centrally administered NPY on the brain monoamine systems were investigated in the rat. Neuropeptide Y (0.2-5.0 nmol), its C-terminal 13-36 amino acid (a.a.) fragment, NPY13-36 (0.4-10.0 nmol), or saline were injected into the right lateral cerebral ventricle of unrestrained rats. After 1 h the animals were decapitated, and the brains were taken out. Two cortical regions ('frontal' and 'parietal'), the striatum, the hypothalamus, and the brain stem were dissected out. The tissue contents of noradrenaline (NA), dopamine (DA) and serotonin (5-HT), as well as of their major metabolites, 3-methoxy-4-hydroxy-phenylethylene glycol (MHPG), 3,4-dihydroxyphenylacetic acid (DOPAC) and 5-hydroxy-indole acetic acid (5-HIAA) were measured. The most consistent finding was a dose-related increase of both DA and DOPAC levels after treatment with NPY. This effect was reproduced by NPY13-36 in cortical tissue, whereas, in the sub-cortical regions, NPY13-36 only reproduced the effects of NPY on the DOPAC levels. Less consistent effects were found on the NA systems, in which NA levels showed a tendency to increase following low, and decrease after high doses of NPY. These effects were largely reproduced by NPY13-36. In addition, NPY increased tissue levels of MHPG in frontal cortical tissue in a dose-related manner. The brain 5-HT systems were not affected.

Distribution of cholecystokinin-like-immunoreactive neurons in the guinea pig forebrain

The distribution of cholecystokinin (CCK)-immunoreactive nerve fibers and cell bodies was studied in the forebrain of control and colchicine-treated guinea pigs by using an antiserum directed against the carboxyterminus of CCK octapeptide (CCK-8) in the indirect immunoperoxidase technique. Virtually all forebrain areas examined contained immunoreactive nerve fibers. A dense innervation was visualized in; neocortical layers II-III, piriform cortex, the medial amygdala, the medial preoptic area, a circumventricular organ-like structure located at the top of the third ventricle in the preoptic area, the subfornical organ, the posterior bed nucleus of the stria terminalis, the posterior globus pallidus (containing labeled woolly fiber-like profiles), the ventromedial hypothalamus, the median eminence, and the premammillary nucleus. A moderately dense innervation was visualized elsewhere excepted in the septum and thalamus where labeled axons were comparatively few. Immunoreactive perikarya were abundant in: neocortex (especially layers II-III), piriform cortex, amygdala, the median preoptic nucleus, the bed nucleus of the stria terminalis, the hypothalamic paraventricular (parvicellular part), arcuate, and dorsomedial (pars compacta) nuclei, the dorsal and perifornical hypothalamic areas, and throughout the thalamus. Areas also containing a moderate number of labeled cell bodies were the medial preoptic area, the globus pallidus, the caudate-putamen, and the periventromedial area in the hypothalamus. Immunostained perikarya were absent or only occasionally observed in the septum, the suprachiasmatic nucleus, the magnocellular hypothalamoneurohypophyseal nuclei, and the ventral mesencephalon. In the adenohypophysis, corticomelanotrophs were labeled in both males and females, and thyrotrophs were labeled in females only. This distribution pattern of CCK-8 immunoreactivity is compared to those previously recorded in other mammals. This shows that very few features are peculiar to the the guinea pig. It is discussed whether some interspecific differences in immunostaining are real rather than methodological.

The axon terminals of vasoactive intestinal polypeptide (VIP)-containing bipolar cells in rat visual cortex

In vasoactive intestinal polypeptide (VIP)-immunoreacted preparations, bipolar neurons are the cells most commonly labelled. The VIP-positive axon terminals form symmetrical synapses, and their most common postsynaptic targets are small and medium sized dendrites. These are of both smooth and spiny types. Additionally, there is a concentration of VIP-positive axon terminals around the cell bodies of pyramidal neurons, and it is suggested that an important function of VIP-labelled bipolar cells is to inhibit vertically oriented groups of pyramidal cells. In order to further examine the features of axon terminals that label with VIP antibodies, conventionally prepared material was examined by electron microscopy. Those terminals which label with VIP antibody are characterized by irregular profiles of varying sizes and shapes, and by containing closely packed pleomorphic vesicles. Such terminals form symmetrical synapses. The junctions are not well marked by associated cytoplasmic densities, but there is an inherent density within the synaptic cleft. It is suggested that these features characterize all axon terminals in which GABA coexists with peptides in cerebral cortex.

Neuropeptide Y-like immunoreactivity in schizophrenia. Relationships with clinical measures

Neuropeptide Y-like immunoreactivity (NPY-li) was measured in CSF of 35 drug-free chronic schizophrenic patients. Compared to a group of drug-free controls, CSF NPY-li was significantly higher in these patients. CSF NPY-li decreased with age and longer duration of illness. Measures of structural brain abnormalities on CT scans were significantly associated with lower CSF NPY-li. Relationships between NPY-li and schizophrenic behavior, i.e. positive symptoms, were observed only in the clinically stable (nonrelapsed) drug-free patients. In 31 of the patients CSF was obtained before and after withdrawal from haloperidol maintenance treatment. This withdrawal from haloperidol treatment was associated with a significant increase in CSF NPY-li. There was no significant difference in CSF NPY-li between patients who did and those who did not relapse within 6 weeks following haloperidol withdrawal. The present findings suggest a relationship of CSF NPY-li with various aspects of schizophrenia.

Distribution and relative abundance of neurons in the pigeon forebrain containing somatostatin, neuropeptide Y, or both

Immunohistochemical studies in several mammalian species and in red-eared turtles have shown that somatostatin (SS) and neuropeptide Y (NPY) co-occur in a substantial proportion of the telencephalic neurons containing either. To explore further the possibility that telencephalic neurons co-containing SS and NPY may be evolutionarily conserved among amniotes, we determined the distribution and co-occurrence of SS and NPY in forebrain neurons in pigeons. Single-label immunohistochemical studies revealed the presence of overlapping populations of SS+ neurons and NPY+ neurons in most of the major subdivisions of the telencephalon. Double-label immunofluorescence studies revealed that in subdivisions of the telencephalon that are comparable to mammalian cortex (i.e., those dorsal and lateral to the basal ganglia), the vast majority of NPY+ neurons were also SS+, whereas a major and regionally variable percentage of the SS+ neurons were not NPY+. In contrast, within the basal telencephalon (including the basal ganglia and several other structures) neurons labeled only for NPY or only SS were more abundant than those containing both neuropeptides. Outside the telencephalon, the only forebrain cell group containing neurons in which SS and NPY were co-localized was in the lateral hypothalamus. A series of double- and triple-label immunohistochemical studies was undertaken to determine the extent of co-occurrence of SS and NPY in striatal neurons and the relationship of these neurons to striatal neurons containing other neuropeptides. In addition, immunohistochemical single- and double-label techniques were employed in conjunction with retrograde-labeling by fluorogold to determine the projections of SS+ and NPY+ striatal neurons. The results indicate that: 1) a population of striatal interneurons containing both SS and NPY exists in pigeons and constitutes approximately the same fraction of all striatal neurons as reported in mammals, 2) neurons containing NPY (but not SS) form a second, larger population of striatal interneurons, 3) neurons containing SS (but not NPY) form a third population of striatal interneurons that is approximately half as abundant as the NPY+ interneuron population, and 4) one-third of the substance P-containing striatonigral projection neurons also contain SS. The existence in pigeons of a major population of neurons containing both SS and NPY throughout the telencephalon, the existence of a population of neurons containing only SS in cortex-equivalent parts of the telencephalon, and the existence of a population of interneurons containing only NPY in the striatum is consistent with findings in mammals and turtles.(ABSTRACT TRUNCATED AT 400 WORDS)