Immunocytochemical localization of somatostatin in cell bodies of the rat hypothalamus

Neuropeptide and Small Transmitter Coexistence: Fundamental Studies and Relevance to Mental Illness

Neuropeptides are auxiliary messenger molecules that always co-exist in nerve cells with one or more small molecule (classic) neurotransmitters. Neuropeptides act both as transmitters and trophic factors, and play a role particularly when the nervous system is challenged, as by injury, pain or stress. Here neuropeptides and coexistence in mammals are reviewed, but with special focus on the 29/30 amino acid galanin and its three receptors GalR1, -R2 and -R3. In particular, galanin's role as a co-transmitter in both rodent and human noradrenergic locus coeruleus (LC) neurons is addressed. Extensive experimental animal data strongly suggest a role for the galanin system in depression-like behavior. The translational potential of these results was tested by studying the galanin system in postmortem human brains, first in normal brains, and then in a comparison of five regions of brains obtained from depressed people who committed suicide, and from matched controls. The distribution of galanin and the four galanin system transcripts in the normal human brain was determined, and selective and parallel changes in levels of transcripts and DNA methylation for galanin and its three receptors were assessed in depressed patients who committed suicide: upregulation of transcripts, e.g., for galanin and GalR3 in LC, paralleled by a decrease in DNA methylation, suggesting involvement of epigenetic mechanisms. It is hypothesized that, when exposed to severe stress, the noradrenergic LC neurons fire in bursts and release galanin from their soma/dendrites. Galanin then acts on somato-dendritic, inhibitory galanin autoreceptors, opening potassium channels and inhibiting firing. The purpose of these autoreceptors is to act as a 'brake' to prevent overexcitation, a brake that is also part of resilience to stress that protects against depression. Depression then arises when the inhibition is too strong and long lasting - a maladaption, allostatic load, leading to depletion of NA levels in the forebrain. It is suggested that disinhibition by a galanin antagonist may have antidepressant activity by restoring forebrain NA levels. A role of galanin in depression is also supported by a recent candidate gene study, showing that variants in genes for galanin and its three receptors confer increased risk of depression and anxiety in people who experienced childhood adversity or recent negative life events. In summary, galanin, a neuropeptide coexisting in LC neurons, may participate in the mechanism underlying resilience against a serious and common disorder, MDD. Existing and further results may lead to an increased understanding of how this illness develops, which in turn could provide a basis for its treatment.

Distribution of somatostatin immunoreactive neurons and fibres in the central nervous system of a chondrostean, the Siberian sturgeon (Acipenser baeri)

Somatostatin (SOM) is a neuropeptide that is widely distributed in the central nervous system of vertebrates. Two isoforms of somatostatin (SS1 and SS2) have been characterized in sturgeon and in situ hybridisation studies in the sturgeon brain have demonstrated that mRNAs of the two somatostatin precursors (PSS1 and PSS2) are differentially expressed in neurons [Trabucchi, M., Tostivint, H., Lihrmann, I., Sollars, C., Vallarino, M., Dores, R.M., Vaudry, H., 2002. Polygenic expression of somatostatin in the sturgeon Acipenser transmontanus: molecular cloning and distribution of the mRNAs encoding two somatostatin precursors. J. Comp. Neurol. 443, 332-345.]. However, neither the morphology of somatostatinergic neurons nor the patterns of innervation have yet been characterized. To gain further insight into the evolution of this system in primitive bony fishes, we studied the distribution of somatostatin-immunoreactive (SOM-ir) cells and fibres in the brain of the Siberian sturgeon (Acipenser baeri). Most SOM-ir cells were found in the preoptic area and hypothalamus and abundant SOM-ir fibres coursed along the hypothalamic floor towards the median eminence, suggesting a hypophysiotrophic role for SOM in sturgeon. In addition, SOM-ir cells and fibres were observed in extrahypothalamic regions such as the telencephalon thalamus, rhombencephalon and spinal cord, which also suggests neuromodulatory and/or neurotransmitter functions for this peptide. Overall there was a good correlation between the distribution of SOM-ir neurons throughout the brain of A. baeri and that of PSS1 mRNA in Acipenser transmontanus. Comparative analysis of the results with those obtained in other groups of fishes and tetrapods indicates that widespread distribution of this peptide in the brain is shared by early vertebrate lines and that the general organization of the somatostatinergic systems has been well-conserved during evolution.

Distribution of somatostatin-like immunoreactivity in the brain of the caecilian Dermophis mexicanus (Amphibia: Gymnophiona): comparative aspects in amphibians

The organization of the somatostatin-like-immunoreactive (SOM-ir) structures in the brain of anuran and urodele amphibians has been well documented, and significant differences were noted between the two amphibian orders. However, comparable data are not available for the third order of amphibians, the gymnophionans (caecilians). In the present study, we analyzed the anatomical distribution of SOM-ir cells and fibers in the brain of the gymnophionan Dermophis mexicanus. In addition, because of its known relationship with catecholamines in other vertebrates, double immunostaining for SOM and tyrosine hydroxylase was used to investigate this situation in the gymnophionan. Abundant SOM-ir cell bodies and fibers were widely distributed throughout the brain. In the telencephalon, pallial and subpallial cells were labeled, being most numerous in the medial pallium and amygdaloid region. Most of the SOM-ir neurons were found in the preoptic area and hypothalamus and showed a clear projection to the median eminence. Less conspicuously, SOM-ir structures were found in the thalamus, tectum, tegmentum, and reticular formation. Both SOM-ir cells and fibers were demonstrated in the spinal cord. The double-immunohistofluorescence technique revealed that catecholaminergic neurons and SOM-ir cells are largely intermingled in many brain regions but form totally separated populations. Many differences were found between the distribution of SOM-ir structures in Dermophis and that in anurans or urodeles. Some features were shared only with anurans, such as the abundant pallial SOM-ir cells, whereas others were common only to urodeles, such as the organization of the hypothalamohypophysial SOM-ir system. In addition, some characteristics were found only in Dermophis, such as the localization of the SOM-ir spinal cells and the lack of colocalization of catecholamines and SOM throughout the brain. Therefore, any conclusions concerning the SOM system in amphibians are incomplete without considering evidence for gymnophionans.

Novel neuronal phenotypes from neural progenitor cells

We report the first isolation of progenitor cells from the hypothalamus, a derivative of the embryonic basal plate that does not exhibit neurogenesis postnatally. Neurons derived from hypothalamic progenitor cells were compared with those derived from progenitor cultures of hippocampus, an embryonic alar plate derivative that continues to support neurogenesis in vivo into adulthood. Aside from their different embryonic origins and their different neurogenic potential in vivo, these brain regions were chosen because they are populated with cells of three different categories: Category I cells are generated in both hippocampus and hypothalamus, Category II cells are generated in the hypothalamus but are absent from the hippocampus, and Category III is a cell type generated in the olfactory placode that migrates into the hypothalamus during development. Stem-like cells isolated from other brain regions, with the ability to generate neurons and glia, produce neurons of several phenotypes including gabaergic, dopaminergic, and cholinergic lineages. In the present study, we extended our observations into neuroendocrine phenotypes. The cultured neural precursors from 7-week-old rat hypothalamus readily generated neuropeptide-expressing neurons. Hippocampal and hypothalamic progenitor cultures converged to indistinguishable populations and produced neurons of all three categories, confirming that even short-term culture confers or selects for immature progenitors with enough plasticity to elaborate neuronal phenotypes usually inhibited in vivo by the local microenvironment. The range of phenotypes generated from neuronal precursors in vitro now includes the peptides found in the neuroendocrine system: corticotropin-releasing hormone, growth hormone-releasing hormone, gonadotropin-releasing hormone, oxytocin, somatostatin, thyrotropin-releasing hormone, and vasopressin.

Somatostatin and somatostatin receptor physiology

Since the discovery of somatostatin (SST) over three decades ago, its ubiquitous distribution and manifold functions are still being documented. SST is synthesized in the hypothalamus and transported to the anterior pituitary gland where it tonicaly inhibits GH and TSH secretion as well as being responsible for GH pulsatile release. Several internal feedback loops, sleep, exercise, and chemical agents control and influence SST release. SST also impacts the function of a wide variety of cells and organ systems throughout the body. Knowledge of the structures of the SSTs has resulted in recognition of the essential four core conserved residues responsible for their actions. The SSTs act through six separate SST cell surface receptors (SSTRs), members of the family of G protein-coupled receptors. Receptor ligand binding (SST/SSTR) results in cellular activities specific for each receptor, or receptor combinations, and their tissue/cell localization. Understanding the structure/function relationship of the SSTs and their receptors, including the internalization of SST/SSTR complexes, has facilitated the development of a variety of novel pharmacologic agents for the diagnosis and treatment of neuroendocrine tumors and unfolding new applications.

Somatostatin-like immunoreactivity in the brain of the urodele amphibian Pleurodeles waltl. Colocalization with catecholamines and nitric oxide

The neuronal structures with somatostatin-like immunoreactivity have been studied in the brain of the urodele amphibian Pleurodeles waltl. Intense immunoreactivity was observed in neurons and fibers distributed throughout the brain. Within the telencephalon, the subpallial regions were densely labeled containing both cells and fibers, primarily in the striatum and amygdala. The majority of the somatostatin immunoreactive neurons were located in the preoptic area and hypothalamus, although less numerous cells were also found in the thalamus. A conspicuous innervation of the median eminence was revealed, which arises from the hypothalamic cell populations. In the brainstem, intense fiber labeling was present in the tectum and tegmentum, whereas cell bodies were located only in the tegmentum of the mesencephalon and in the interpeduncular, raphe and reticular nuclei of the rhombencephalon. Longitudinal fiber tracts throughout the brainstem were observed and they continued into the spinal cord in the laterodorsal funiculus. The localization of somatostatin in catecholaminergic and nitrergic neurons was studied by double labeling techniques with antisera against tyrosine hydroxylase and nitric oxide synthase. Catecholamines and somatostatin only colocalized in a cell population in the ventral preoptic area. In turn, the striatum and amygdala contained neurons with somatostatin and nitric oxide synthase. Our results demonstrated that the somatostatin neuronal system in the brain of Pleurodeles waltl is consistent with that observed in anuran amphibians and shares many characteristics with those of amniotes. Colocalization of somatostatin with catecholamines and nitric oxide is very restricted in the urodele brain, but in places that can be easily compared to those reported for mammals, suggesting that interactions between these neurotransmitter systems are a primitive feature shared by tetrapod vertebrates.

Development of the neuroendocrine hypothalamus

The development of the neuroendocrine hypothalamus has been studied using a variety of neuroanatomical and molecular techniques. Here, the major findings that mold our understanding of hypothalamic development are reviewed. The rat hypothalamus is generated predominantly from the third ventricular neuroepithelium in a "lateral early to medial late" pattern dictated perhaps by the medially receding third ventricle. Neuroendocrine neurons seem to exhibit a delayed migrational strategy, showing relatively early birthdates, although they are located in the latest-generated, periventricular nuclei. Several homeobox genes seem to play a role in hypothalamic development, and gene knockout experiments implicate a number of genes of importance in the generation of the neuroendocrine cell type.

GHRP-6-induced changes in electrical activity of single cells in the arcuate, ventromedial and periventricular nucleus neurones [correction of nuclei] of a hypothalamic slice preparation in vitro

Previously, we demonstrated that systemic injection of the growth hormone secretagogue, growth hormone-releasing peptide (GHRP)-6, selectively activated cells in the hypothalamic arcuate nucleus, as reflected by increased electrical activity and induction of the immediate early gene c-fos. The growth hormone secretagogue receptor distribution is not confined to the arcuate nucleus, suggesting that additional sites of action may exist. In the present study we characterized the electrophysiological responses of cells in the arcuate nucleus, ventromedial nucleus and periventricular nucleus in an in-vitro hypothalamic slice preparation, following bath application of GHRP-6. Additionally, since central somatostatin administration has been shown to attenuate the induction of the c-fos gene by GHRP-6, we sought to determine whether the arcuate cells activated by GHRP-6 are also somatostatin-sensitive. Male Wistar rats (100-150 g body weight (BW)) were anaesthetized (urethane; 1.2 g/kg BW) and the brains removed. Coronal sections (400 microm thickness) were cut through a block of hypothalamus and were transferred to a slice chamber perfused with artificial cerebrospinal fluid. Forty-one arcuate nucleus cells were tested with bath application of 15 microm GHRP-6 for 10 min, 16 of which were tested subsequently (>30 min later) with application of 10 microM somatostatin. Following GHRP-6 administration, 19 cells (46. 3%) showed a significant increase in firing rate during the 15-min period after GHRP-6 application (P<0.001), 17 cells (41.5%) did not respond and the remaining five cells (12.2%) were significantly inhibited. Six of the eight arcuate nucleus cells that were excited by GHRP-6 were significantly inhibited by somatostatin. By contrast, five of the six arcuate nucleus cells that were unresponsive to GHRP-6 were also unresponsive to somatostatin. In the ventromedial nucleus, of 19 cells tested, eight cells (42.1%) were excited by GHRP-6, eight cells (42.1%) were unresponsive and the remaining three cells (15.8%) were significantly inhibited. Of 19 cells recorded in the periventricular nucleus, 13 (68.4%) were unresponsive to GHRP-6 and six (31.6%) were significantly inhibited. Thus, electrophysiological studies in vitro suggest that: (1) neurones in the hypothalamic arcuate nucleus, ventromedial nucleus and periventricular nucleus show changes in electrical activity in response to GHRP-6; and (2) the arcuate nucleus cells excited by GHRP-6 are also subject to inhibitory control by somatostatin.

Role of octreotide on release of intact 1-84 parathyroid hormone from human parathyroid cells

BACKGROUND

Octreotide has been shown to lower urinary calcium in primary hyperparathyroidism although the mechanism remains unclear. This study examined the effect of octreotide on parathyroid hormone (PTH) secretion from human parathyroid cells in culture and as isolated cells. Additionally in situ hybridization was performed for somatostatin receptor messenger RNA (mRNA) and immunocytochemistry for somatostatin in eight parathyroid adenomas.

METHODS

Tissue from three hyperplastic glands and three adenomas was studied as dispersed cell suspensions. Incubation was in buffers containing high (2.0 mmol/l) and low (0.5 mmol/l) calcium concentrations, with or without octreotide 200 ng/ml. Cells were also seeded into tissue culture wells for 24 h to allow receptors to regenerate. Supernatant was removed at regular intervals and PTH levels were estimated using a two-site chemiluminescent assay.

RESULTS

Mean(s.e.m.) PTH secretion at 90 min in hyperplastic cells was 445(75) pmol/l in low calcium and 160(42) pmol/l in high calcium (P< 0.02), and in adenoma cells was 170(21) pmol/l in low calcium and 137(27) pmol/l in high calcium (P=0.37). There was no significant difference in secretion of PTH from cells incubated with octreotide either in culture or as dispersed cells. In situ hybridization failed to demonstrate any mRNA for the somatostatin receptors and no somatostatin was detected in any cells with immunocytochemistry.

CONCLUSION

Somatostatin has no direct action on PTH production and release from human parathyroid cells and is unlikely to be of any therapeutic value in the treatment of hyperparathyroidism.

Immunohistochemical and cytochemical localization of the somatostatin receptor subtype sst1 in the somatostatinergic parvocellular neuronal system of the rat hypothalamus

Somatostatin is known to mediate its actions through five G-protein-coupled receptors (sst1-sst5). We have studied the expression of the sst1 receptor in the rat hypothalamus by using a subtype-specific antiserum. In Western blotting, the antiserum reacted specifically with a band with an apparent molecular weight of 80,000 in membranes prepared from hypothalamic tissue. The localization of the sst1 receptor was investigated by immunohistochemistry in hypothalamus sections. Additionally, an immunofluorescent double-labeling was performed for the sst1 receptor and somatostatin. Light microscopy revealed that the sst1 receptor is located in perikarya and nerve fibers in the rostral periventricular area surrounding the third ventricle as well as in nerve fibers projecting from the perikarya to the external layer of the median eminence. In these neuronal structures, sst1 immunoreactivity was found to be colocalized with somatostatin. Furthermore, the location of sst1 receptors was studied by immunoelectron microscopy in the median eminence. In the external layer, receptor immunoreactivity was confined to nerve terminals. Immunoreactive nerve terminals were seen to make synapse-like junctions with other both stained and unstained nerve terminals. Thus, the sst1 receptor is present in the classic somatostatinergic hypothalamic parvocellular system inhibiting hormone secretion from the anterior pituitary gland. These findings indicate that the sst1 receptor may act as an autoreceptor and inhibit the release of somatostatin from periventricular neurons projecting to the median eminence.

Immunocytochemical localization of somatostatin and autoradiographic distribution of somatostatin binding sites in the brain of the African lungfish, Protopterus annectens

The anatomical distribution of somatostatin-immunoreactive structures and the autoradiographic localization of somatostatin binding sites were investigated in the brain of the African lungfish, Protopterus annectens. In general, there was a good correlation between the distribution of somatostatin-immunoreactive elements and the location of somatostatin binding sites in several areas of the brain, particularly in the anterior olfactory nucleus, the rostral part of the dorsal pallium, the medial subpallium, the anterior preoptic area, the tectum, and the tegmentum of the mesencephalon. However, mismatching was found in the mid-caudal dorsal pallium, the reticular formation, and the cerebellum, which contained moderate to high concentrations of binding sites and very low densities of immunoreactive fibers. In contrast, the caudal hypothalamus and the neural lobe of the pituitary exhibited low concentrations of binding sites and a high to moderate density of somatostatin-immunoreactive fibers. The present results provide the first localization of somatostatin in the brain of a dipnoan and the first anatomical distribution of somatostatin binding sites in the brain of a fish. The location of somatostatin-immunoreactive elements in the brain of P. annectens is consistent with that reported in anuran amphibians, suggesting that the general organization of the somatostatin peptidergic systems occurred in a common ancestor of dipnoans and tetrapods. The anatomical distribution of somatostatin-immunoreactive elements and somatostatin binding sites suggests that somatostatin acts as a hypophysiotropic neurohormone as well as a neurotransmitter and/or neuromodulator in the lungfish brain.

Biology of hypothalamic neurons and pituitary cells

Results obtained by examining hypothalamic neurons producing precursors to neurohormones, and pituitary cells synthesizing peptide and glycoprotein families of hormones, and recent advances in comparative endocrinology, have been summarized and considered from the following viewpoints: species specificity in the organization and communication of the hypothalamic neurons with different brain areas lying inside the BBB and with CVOs; sensitivity of hypothalamic neurons and pituitary cells to the environmental stimuli; gonadal steroids as modulators of gene expression needed for neuronal differentiation and synaptogenesis; dose(s)-dependent pituitary cell proliferation and differentiation; an inverse relationship between PRL and GH synthesis and release and also between degree of hyperplasia and hypertrophy of PRL cells and retardation of GTH cell differentiation; and responsiveness of neurons producing CRH, and of neurons and pituitary cells synthesizing POMC hormones, to stress and glucocorticosteroids. These data show that growth of the animals may be stimulated, retarded, or inhibited; reproductive properties and behavior may be under hormonal control; and character of responsiveness in reaction to stress, and ability for adaptation and other related functions, may be controlled.

Electrical stimulation of the rat periventricular nucleus influences the activity of hypothalamic arcuate neurones

In rats, the release of growth hormone (GH) is inhibited during electrical stimulation of the periventricular nucleus but after the end of stimulation, there is a rebound 'hypersecretion' of GH. We examined the responses of arcuate neurones in pentobarbitone-anaesthetized male rats, following electrical stimulation of the periventricular nucleus to test the hypothesis that the effects of periventricular nucleus stimulation on GH secretion are mediated via effects upon GH-releasing hormone (GRF) neurones in the arcuate nucleus. The electrical activity of 2 groups of arcuate neurones were analysed before, during and after periventricular nucleus stimulation (10 Hz, 5 min, 0.5 mA biphasic, 0.5/1.0 ms): a) putative neurosecretory cells which were antidromically identified (AD) as projecting to the median eminence (n = 53) and b) non-neurosecretory cells, identified by their spontaneous 'bursting' pattern of activity (n = 29). During stimulation predominantly inhibitory responses were observed in both AD and bursting cell groups. Of the 39 AD cells which were spontaneously active, 25 were inhibited during the periventricular nucleus stimulation, and 10 of these showed a rebound hyperactivation following the end of stimulation. Fifteen bursting cells were inhibited during stimulation and 4 of these displayed a rebound hyperactivation following the end of stimulation. Additional evidence was sought for the identity of these cells by testing their response to electrical stimulation of the basolateral amygdala (which has previously been shown to increase plasma GH concentration without influencing the release of other pituitary hormones).(ABSTRACT TRUNCATED AT 250 WORDS)

Periventricular nucleus lesioning modulates specific somatostatin binding in various brain regions and anterior pituitary

The effects of periventricular nucleus (Pe) lesioning on the plasma growth hormone (GH) levels and the anterior pituitary (A.P.) and brain somatostatin (SRIF) receptors were studied. A transient significant increase in plasma GH level in lesioned rats was detected 1 day after the operation. This elevated level of plasma GH started to decrease 3 days after lesioning. These changes were paralleled by an increase in binding of 125I-Tyr11-SRIF-14 to the A.P. 1 day after lesioning. This result could further confirm that the SRIF inhibitory action on GH release takes place at the A.P. level. Also, a transient increase in binding of the radioligand was detected in some brain areas 1 and 4 days after the lesion. However, the mechanism by which this increase takes place remains to be elucidated.

Quantitative autoradiography of somatostatin receptors in the rat limbic system

The distribution of somatostatin receptors (SRIF-R) was analyzed in the limbic system of the adult rat by in vitro autoradiography with [125I-Tyr0,DTrp 8]S14 as a radioligand. Precise quantification of the density of binding sites, at 0.2 mm intervals throughout the different areas revealed a marked heterogeneity of labeling in most structures. In particular, SRIF-R were concentrated in the basal (104.4 +/- 3.3 fmol/mg proteins) and basolateral amygdaloid nuclei (94.8 +/- 4.3 fmol/mg proteins), and in the nucleus of the lateral olfactory tract (121.6 +/- 2.4 fmol/mg proteins), whereas moderate densities were detected in the amygdalo-hippocampal nucleus (76.4 +/- 2.8 fmol/mg proteins). The medial (41.3 +/- 1.9 fmol/mg proteins) and the central (24.0 +/- 1.4 fmol/mg proteins) amygdaloid nuclei contained lower SRIF-R concentrations. It appears from these observations, in the light of the anatomical pathways of the amygdala, that intra-amygdalian SRIF-containing neurons project to the amygdalo-hippocampal nucleus, and that SRIF-R in the basolateral complex are the target of afferents from limbic cortical areas. SRIF-R were detected at different levels of the hippocampal formation but their distribution was more restricted than that of SRIF-containing fibers. The maximal density of sites was detected in the ventral and dorsal parts of the subiculum (115.0 +/- 3.4 and 87.0 +/- 2.8 fmol/mg proteins, respectively) and in the parasubiculum (100.1 +/- 5.4 fmol/mg proteins). In Ammon's horn, the stratum oriens and stratum radiatum of the CA1 field were the only sites enriched in SRIF-R (74.1 +/- 2.0 and 74.6 +/- 1.9 fmol/mg proteins, respectively). The apparent lack of receptors in the pyramidal cell layer indicated that, in Ammon's horn, SRIF is involved in intra-hippocampal communication. Low levels of receptors were found in the hippocampal CA2 and CA3 fields. SRIF-R in the dentate gyrus were mainly concentrated in the molecular layer (57.3 +/- 1.2 fmol/mg proteins). A very high density of sites was also observed in the entorhinal cortex (up to 123.1 +/- 1.5 fmol/mg proteins). A clear mismatch between SRIF and SRIF-R was detected in the septum and the habenula. In the profound layers of the cingulum and retrosplenial cortex, a heterogeneous distribution of SRIF-R was observed. High concentrations of sites were detected in the rostral zone of the cingulate cortex (93.4 +/- 2.0 fmol/mg proteins) while the posterior cingulate only exhibited moderate concentrations of sites (66.5 +/- 0.7 fmol/mg proteins).(ABSTRACT TRUNCATED AT 400 WORDS)

Role of somatostatin in the acute immobilization stress-induced GH decrease in rat

In the present work we have investigated to what extent somatostatin (SRIF) release from median eminence (ME) is affected by stress immobilization (IMO) in unanesthetized rats stereotaxically implanted with a push-pull cannula (PPC). One week after implantation, the ME was perfused with artificial cerebrospinal fluid for 1 hour in basal, stress and recovery conditions respectively. Samples were collected every 15 min and SRIF was measured by RIA. In another group of animals, a jugular cannula was inserted the day before and plasma samples were taken off simultaneously with the ME perfusate for GH and SRIF analysis respectively. SRIF release from the ME is rapidly (15 min) and significantly increased (58 +/- 11 vs 28 +/- 5 pg/15 min; n = 7; P < 0.01) in rats bearing only PPC. Intriguingly, animals bearing a jugular catheter plus a PPC showed no increase in SRIF release during the first 15 min of IMO in spite of a striking decrease of plasma GH (27.2 +/- 3.8 vs 3.6 +/- 1.3 ng/ml; n = 6; P < 0.001) observed at this time. However, in spite that the animals responded with a significant increase in SRIF, the response was later and more reduced than in animals without jugular cannula. Since our two rat groups--as result of jugular cannula surgery 24 hours before--showed differences such as a food intake, body weight gain, plasma GH levels and basal SRIF release, we think that these differences could explain the modifications in the regulatory mechanisms involved in GH control under acute stress.

Immunoreactive somatostatin content in the pineal gland increases after lesion of the hypothalamic periventricular nucleus in male rats

Immunoreactive somatostatin (IRS) content in the pineal gland increased about two-fold when the hypothalamic periventricular nucleus (Pe) of male rats, which contains many tuberoinfundibular somatostatin (SRIF) neuron cell bodies, was lesioned. However, the mechanism by which this increase takes place remains to be elucidated. Using 125I-Tyr11-SRIF-14 as a ligand and autoradiography, specific binding was detected in several brain areas. However, we were unable to detect specific SRIF binding sites either in the pineals of control or lesioned animals. This undetectable binding of SRIF-14 could be due to the localization of low-affinity receptors that were not demonstrated by the present method. Another possibility for the undetectable binding of the radioligand to the pineal could be due to the fact that the majority of IRS may be within the nerve terminals and the receptors in a different location.

Distribution of somatostatin immunoreactivity in the forebrain of the squirrel monkey: Basal ganglia and amygdala

The distribution of somatostatin immunoreactivity in the basal ganglia and amygdala of the squirrel monkey (Saimiri sciureus) was studied with specific polyclonal antibodies directed against somatostatin-28 and somatostatin-28(1-12). Both antibodies gave similar results with regard to the distribution of somatostatin-immunoreactive neuronal profiles. A moderately dense and highly heterogeneous network of somatostatin-positive fibers was observed throughout the striatum. A dorsoventral gradient of increasing immunoreactivity was noted in the striatum and the caudate nucleus was found to strain generally less intensely than the putamen. The immunoreactive fibers within the striatum were mostly thin and varicose and formed patches corresponding to the striosomes, as visualized on adjacent sections immunostained for calbindin. Although some somatostatin cell bodies rimmed the striosomes, most of the positive cells were rather uniformly scattered in the striatum. These medium-sized cells were significantly smaller in the caudate nucleus (93 microns2, S.D. = 26 microns2) than in the putamen (122 microns2, S.D. = 39 microns2), but their density was significantly higher in the caudate nucleus (29.7 cells/mm2, S.D. = 8.8 cells/mm2) than in the putamen (20.5 cells/mm2, S.D. = 7.0 cells/mm2). The nucleus accumbens stained moderately and positive cell bodies were evenly dispersed throughout this structure. In contrast, the olfactory tubercle displayed a heavily stained neuropil but positive neurons were encountered only in its polymorph layer. In the sublenticular region, dense fiber plexuses appeared in register with nonreactive cell clusters of the nucleus basalis of Meynert and of the nucleus of the anterior commissure. More caudally, a dense bundle of positive fibers was observed at the level of the ansa lenticularis, the inferior thalamic peduncle, and the adjoining bed nucleus of the stria terminalis. Several fibers contributing to this bundle were of the woolly type. Woolly fibers also coursed in the substantia innominata between the ventral aspect of the globus pallidus and the optic tract, and ascended in the internal medullary lamina separating the internal and external segments of the globus pallidus. Somatostatin-immunoreactive cell bodies were uniformly scattered throughout the substantia innominata. The various nuclei of the amygdala showed a wide range of immunoreactivity. The central nucleus was lightly reactive, whereas the intercalated masses displayed a moderate staining. A dorsoventral gradient of immunostaining was noted in the ventrolateral portion of the amygdala, the lateral nucleus being moderately to densely stained and the basal nucleus very lightly to lightly immunoreactive.(ABSTRACT TRUNCATED AT 400 WORDS)

Helodermin- and helospectin-like immunoreactivities in the rat brain: an immunochemical and immunohistochemical study

Helodermin is an amidated peptide of 35 amino acid residues isolated from the lizard Heloderma suspectum. Homologous peptides, helospectins I and II, peptides of 38 and 37 amino acid residues, respectively, have been isolated from the lizard Heloderma horridum. This group of peptides stimulates the adenylate cyclase activity. Helodermin- and helospectin-like immunoreactivities were studied in the rat brain by using immunohistochemistry and radioimmunoassay in combination with high-performance liquid chromatography. The highest concentrations of helodermin-like immunoreactivity were found in the cerebellum and hypothalamus. The chromatographic analysis of rat brain extract revealed one main immunoreactive peak with elution properties similar to those of authentic lizard helodermin. Helodermin-immunoreactive neurons were located in the supraoptic nucleus, suprachiasmatic nucleus, periventricular nucleus, arcuate nucleus and central gray. Fibers and terminals of varying densities were observed in the bed nucleus of the stria terminalis, medial part of the central nucleus of amygdala, external layer of the median eminence, thalamus and central gray. The highest concentrations of helospectin-like immunoreactivity were found in the cerebral cortex, hypothalamus and medulla. The chromatographic analysis of brain extract revealed one major peak with elution properties similar to those of authentic helospectin I. Helospectin-immunoreactive neurons were located in the suprachiasmatic nucleus, central gray, cerebral cortex, dorsomedial hypothalamic nucleus and supramammillary nucleus. Helospectin-immunoreactive fibers and terminals were found in the bed nucleus of the stria terminalis, medial part of the central nucleus of amygdala, median eminence, lateral parabrachial nucleus, central gray, cerebral cortex, thalamus and nucleus of the solitary tract. The present study has revealed novel neuronal systems in the rat brain by using antisera against the lizard peptides helodermin and helospectin. The patterns of immunostaining suggest a role for the helodermin- and helospectin-like peptides in the hypothalamo-hypophyseal control of endocrine functions.

Somatostatin-28 (1-12)-like immunoreactivity in the cat diencephalon

Using an indirect immunoperoxidase technique, the location of somatostatin-28 (1-12)-like immunoreactive fibres and cell bodies in the cat diencephalon was studied. The hypothalamus was richer in somatostatin-28 (1-12)-like immunoreactive structures than the thalamus. A high density of immunoreactive fibres was observed in the nuclei habenularis lateralis, paraventricularis anterior (its caudal part), filiformis, hypothalami ventromedialis, and regio praeoptica, whereas a moderate density was found in the nuclei paracentralis, supraopticus, supra chiasmaticus, hypothalamus posterior and area hypothalamica dorsalis. The nuclei lateralis dorsalis, lateralis posterior, medialis dorsalis, rhomboidens, centralis medialis, ventralis medialis, reuniens, anterior dorsalis, parataenialis, interanteromedialis, hypothalamus lateralis, hypothalamus dorsomedialis and arcuatus had the lowest density of immunoreactive fibres. In addition, a high or moderate density of somatostatin-28 (1-12)-like immunoreactive cell bodies was observed in the nuclei paraventricularis hypothalami, supraopticus, supra chiasmaticus, area hypothalamics dorsalis, subparafascicularis, hypothalamus posterior and hypothalamus anterior, whereas scarce immunoreactive perikarya were visualized in the nuclei lateralis dorsalis and parafascicularis. The distribution of somatostatin-28 (1-12)-like immunoreactive structures is compared with the location of other neuropeptides in the cat diencephalon.

Immunohistochemical evidence for synaptic connections between neuropeptide Y-containing axons and periventricular somatostatin neurons in the anterior hypothalamus in rats

By employing a pre-embedding double immunolabeling technique, we examined light and electron microscopically synaptic associations between neuropeptide Y (NPY)-containing axons and somatostatin (SRIH)-containing neurons in the anterior periventricular area (APV) of the rat hypothalamus. For light microscopy, the immunoreactions for NPY and SRIH were visualized with silver-gold and diaminobenzidine (DAB), respectively, and the reverse labeling was used for electron microscopy. Light microscopy disclosed many brown SRIH perikarya surrounded by several black beads of NPY fibers in the APV. In electron microscopy, immunoreactive SRIH neurons revealed silver-gold particles scattered throughout the cytoplasm and accumulated in the Golgi area and the secretory granules. SRIH perikarya and dendritic processes indicated synaptic associations with DAB-labeled NPY fiber terminals and immunonegative fibers. NPY presynaptic terminals possessed numerous small clear vesicles and a few dense core vesicles; vesicular membranes and cores were labeled with DAB chromogen. Both the pre- and postsynaptic membranes were thickened equally to be a symmetric synapse. These findings suggest that NPY neurons are involved in the regulation of growth hormone secretion from the pituitary by affecting periventricular SRIH neurons.

Presence of sex difference of cytochrome P-450 in the rat preoptic area and hypothalamus with reference to coexistence with oxytocin

Localization of female type cytochrome P-450 (F1) in the preoptic area and hypothalamus of the rat was examined immunocytochemically using antiserum against purified hepatic P-450 (F1). This antiserum recognizes both P-450 (F1) and P-450 (M3). Western immunoblotting using the antiserum demonstrated that female rat brain contains P-450 (F1) but not P-450 (M3), since microsomes from the brain and liver displayed only one immunoreactive band at 50 kD, coinciding with that of P-450 (F1) purified from female rat liver. On the other hand, the male brain has P-450 (M3) but not P-450 (F1), as liver- and brain-derived microsomes produced single band at 49 kD, which represents a mol. wt. identical to that of P-450 (M3) extracted from male rat liver. These results indicate that P-450 (F1)-like immunoreactivity (LI) occurs in the female rat brain, while P-450 (M3)-LI takes place in the male rat brain. Immunocytochemical analysis further demonstrated the detailed cellular localization of these two P-450-LIs in the preoptic area and hypothalamus of female and male rats. Localization of P-450 (F1)-LI in the female rat hypothalamus resembled that of P-450 (M3)-LI in the male rat hypothalamus. Magnocellular neurosecretory neurons in the paraventricular nucleus and supraoptic nucleus were labeled and were found to contain oxytocin but lack vasopressin when serial sections of these areas were analyzed. In addition, groups of immunoreactive cells were seen in the median preoptic nucleus, medial and lateral preoptic area, caudal portion of the bed nucleus of the stria terminalis, lateral hypothalamus at the level of the paraventricular nucleus, periventricular zone from the preoptic area to the paraventricular nucleus, and parvocellular portion of the paraventricular nucleus.

Immunohistochemical distribution of somatostatin in the infant hypothalamus

Somatostatin (SS)-containing neurons were mapped in the normal infant hypothalamus with immunohistochemistry, using the peroxidase anti-peroxidase technique. Neurons displaying SS immunoreactivity show a widespread distribution throughout the hypothalamic region. Principal SS-immunoreactive like (SS-IL) perikarya are located in the paraventricular, infundibular and posterior nuclei and in the preoptic region. High SS innervation is also found in the ventromedial and in the lateral mammillary nuclei, and in the median eminence. In general this distribution of SS-IL agrees well with that reported for rat. Compared to the immunohistochemical distribution of SS in human adult hypothalamus, this mapping in the infant hypothalamus is grossly similar. However some differences may be underlined: the presence of a moderately dense group of SS-IL perikarya in the tuberal and posterior nuclei, and a dense innervation of the ventromedial nucleus and in the median eminence. This first detailed distribution of SS immunoreactivity in infant hypothalamus can provide basic knowledge for further studies of infant neuropathology.

Distribution of somatostatin receptors in the brain of the frog Rana ridibunda: correlation with the localization of somatostatin-containing neurons

The biochemical characterization and anatomical distribution of somatostatin binding sites were examined in the brain of the frog Rana ridibunda, and the distribution of the receptors was compared with the location of somatostatin immunoreactive neurons. The pharmacological profile of somatostatin receptors was determined in the frog brain by means of an iodinated superagonist of somatostatin, [125I-Tyr0,DTrp8]S-14. Membrane-enriched preparations from frog brain homogenates were shown to contain high-affinity receptors (KD = 0.78 +/- 0.34 nM; Bmax = 103 + 12.7 fmoles/mg protein) with pharmacological specificity for [DTrp] substituted S14 and S28 analogs. The distribution of somatostatin-binding sites was studied by autoradiography on coronal sections of frog brain. Various densities of somatostatin receptors were detected in discrete areas of the brain. The highest concentration of binding sites was observed in the olfactory bulb, in the pallium, and in the superficial tectum. Moderate binding was observed in the striatum, amygdaloid complex, preoptic area, and cerebellum. Immunocytochemical studies of the distribution of somatostatin-28 (S28) related peptides were also conducted in the frog brain. Two antisera that recognize distinct epitopes of the somatostatin molecule have been used for immunohistochemical mapping of the peptide. Antiserum SS9 recognizes both S28 and somatostatin-14 (S14) and allowed the labelling of perikarya. Antiserum S320 recognizes the N-terminal fragment (1-12) resulting from enzymatic cleavage of S28. This latter antiserum, which does not cross-react with S28, stained mainly neuronal processes. At the infundibular level, however, both antisera stained cell bodies and fibers. Immunoreactive somatostatin-related peptides were detected in many areas of the frog brain. In the diencephalon, a heavy accumulation of perikarya and fibers was seen in the preoptic nucleus, the dorsal and ventral infundibular nuclei, and the median eminence. Immunoreactive perikarya were also observed in the telencephalon, especially in the pallium and in thalamic nuclei. Immunostained processes were detected in many telencephalic areas and in the tectum. There was good correlation between the distribution of somatostatin-immunoreactive elements and the location of somatostatin-binding sites in several areas of the brain, in particular in the median pallium, the tectum, and the interpeduncular nucleus.(ABSTRACT TRUNCATED AT 400 WORDS)

Somatostatin expression in the cerebellar cortex during postnatal development. An immunohistochemical study in the rat

The distribution of somatostatin-immunoreactive (SOM-IR) elements in the cerebellar cortex of the rat has been studied at different stages of postnatal development (from birth to day 30) and in adult animals using immunohistochemistry. The results showed that in vermis of new born animals there are three main groups of SOM-IR structures within the cortex which subsequently spread along the Purkinje cell layer. In addition, both in the vermis and in the lateral lobes, numerous more evenly distributed SOM-positive cells and fibers could be seen. SOM-IR Golgi cells, Purkinje cells and climbing fibers could then be recognized during the subsequent developmental stages. In the vermal zone, SOM-IR Purkinje cells formed patches, which seemed to be part of a sagittal columnar or band-like organization. This was most obvious between days 5 and 21 of postnatal development. Subsequently there was a reduction in the number of immunoreactive Purkinje cells but a patchy disposition remained. In addition high numbers of SOM-IR Purkinje and Golgi cells and also climbing fibers were identified in the flocculus and paraflocculus at all stages of development studied, and they were also seen in the adult rats in these regions. In the lateral lobes expression of SOM-like immunoreactivity (LI) decreased and almost completely disappeared in adult animals. The present results demonstrate that a SOM or a SOM-LI peptide can be transiently detected in many Purkinje and Golgi cells in the cerebellar cortex, suggesting a role in events related to developmental processes. However, in some regions and structures SOM-LI can be seen also in adult animals.

Immunohistochemical approach to the functional morphology of the hypothalamic-hypophysial system

Immunohistochemical studies at the light and electron microscopic levels have provided much information on functional morphology in the hypothalamic-hypophysial system. The present paper describes the immunohistochemical techniques available at present and their use to determine the localizations of neurons containing hypophysiotrophic substances, the co-storage of plural signals in these neurons, and the synaptic regulation of these neurons in rats.

Neuronal localization of prosomatostatin mRNA in the rat brain with in situ hybridization histochemistry

Individual neurons containing prosomatostatin mRNA were identified with in situ hybridization histochemistry. Our results demonstrate a widespread distribution of prosomatostatin mRNA in several regions of the rat central nervous system. Neurons containing this transcript were most abundant in the anterior olfactory nucleus, hypothalamus, hippocampus, and amygdala as well as in all regions of the cerebral cortex. Moreover, the distribution of mRNA-containing perikarya was coextensive with the location of neurons containing somatostatin-like immunoreactivity in all areas of the brain examined. Somatostatin neurons varied in their morphology and amount of hybridization signal from region to region. The widespread distribution and regional variations in neuronal morphology and the amount of hybridization signal are consistent with a neurotransmitter and/or a neuromodulator role for somatostatin in addition to its well-established neuroendocrine role. These results demonstrate that both the peptide and its mRNA are found in perikarya in the same areas and that they are therefore the sites of synthesis for somatostatin.

Somatostatin-containing neuron systems in the rat hypothalamus: retrograde tracing and immunohistochemical studies

By employing a combination of the immunohistochemistry for somatostatin (SRIF) and retrograde tracing with biotinylated wheat germ agglutinin (b-WGA) injected into the posterior pituitary (group 1) or into the median eminence (group 2), functional topography of hypothalamic SRIF neurons was determined in the rat hypothalamus. In group 1, large numbers of WGA-labeled neurons appeared in the rostral periventricular region and in the magnocellular division of the paraventricular and supraoptic nuclei; none of them were SRIF immunoreactive. In group 2, WGA-labeled neurons were numerous in the rostral periventricular region, the parvicellular division of the paraventricular nucleus, and the arcuate nucleus; most of the WGA-labeled neurons in the rostral periventricular region and some in the paraventricular nucleus were SRIF immunoreactive, but none in the arcuate nucleus showed immunoreactivity for SRIF. It is concluded that, in the rat hypothalamus, the locations of neurons containing hypophysiotrophic SRIF are confined within the rostral periventricular region and the parvicellular paraventricular nucleus. Our results do not support previous suggestions that SRIF immunoreactive axons innervate the posterior lobe of the pituitary.

GABAergic innervation of somatostatin-containing neurosecretory cells of the anterior periventricular hypothalamic area: a light and electron microscopy double immunolabelling study

Double immunolabelling on semithin sections revealed glutamate decarboxylase immunopositive dots surrounding somatostatin-containing cell sections in the rat periventricular hypothalamic area. Up to 12 appositions were observed per cell section with an average number of 2-3 and a unimodal distribution. At the electron microscopical level pre-embedding staining of glutamate decarboxylase showed that most immunoreactive elements consisted of immunolabelled axonal endings. Most of these glutamate decarboxylase immunopositive boutons were found within the neuropil where they frequently made synapses on unidentified dendrites. Some of them were apposed to somatostatin-containing cell bodies that were identified according to the presence of immunolabelled granules using combined immunogold post-embedding staining. In many instances glutamate decarboxylase immunoreactive endings were also found to be involved in synaptic contact with somatostatin-labelled perikarya, or neuronal processes. These contacts provide the morphological basis for a direct GABAergic control of the somatostatin-containing cells regulating the secretion of growth hormone.

Rostromedial septal area controls pulsatile growth hormone release in the golden hamster

Limbic forebrain inhibits growth and growth hormone (GH) secretion in mature golden hamsters as shown by acceleration of growth and increases in serum GH concentrations following the electrolytic lesions of septum, transection of the hippocampus and surgical separation of these two regions. The growth-inhibitory function of this circuit is most probably mediated by somatostatinergic (SRIF) neurons. Such lesions induce hypoactivity possibly due to damage to endogenous opiatergic (EOP) neurons. EOP neurons facilitate spontaneous running in hamsters and mediate exercise-induced acceleration of growth and GH pulses. The coincidence of hypoactivity and growth acceleration after such lesions suggested the coexistence of SRIF and EOP fibers within the growth-inhibitory limbic forebrain circuit which control the rate of growth in mature hamsters by the variable inhibition of SRIF neurons by the EOP neurons. This hypothesis posits that accelerated growth is due to increased GH pulse frequency, and hypoactivity due to damage to EOP neurons, and was tested in this study by measuring pulsatile GH release (and as a measure of specificity, pulsatile prolactin release) in the presence and in the absence of opiate-receptor blocker naloxone in 21 female hamsters which sustained electrocoagulative lesions of rostromedial septum and 30 hamsters subjected to control surgery. Lesions doubled GH but not PRL pulse frequency, neither of which was affected by naloxone. Results support the hypothesis that opiatergic neurons facilitate pulsatile GH release by inhibiting the action of somatostatin neurons.

Quantitative autoradiographic analysis of somatostatin binding sites in discrete areas of rat forebrain

Somatostatin has been localized in several hypothalamic and extrahypothalamic brain regions where it may function as a classical neurotransmitter or as a modulator of neural activity. In the present study, somatostatin binding sites were studied by incubation of coronal sections of rat forebrain with 125I-Tyr1-somatostatin, Ultrofilm autoradiography, computerized microdensitometry and comparison with 125I standards. Highest concentrations of somatostatin binding sites (fmol/mg protein) were found in the claustrum (151), basolateral nucleus of the amygdala (90), deep layers of the cerebral cortex (61), lateral olfactory nuclei (58), CA1 and CA2 areas of hippocampus (57), medial and lateral septal nuclei (54), and the medial habenula (44). Scatchard analysis of individual forebrain areas with high densities of somatostatin binding sites was also performed. Regulation of brain somatostatin binding sites may be studied as one approach to examining the involvement of central somatostatin pathways in various physiological and behavioral states.

Release of growth hormone, prolactin and somatostatin during perifusion of anterior pituitary and preoptic-medial basal hypothalamus from male and female rats

These experiments were designed to determine whether it is possible using in vitro perifusion to identify a sex difference in anterior pituitary (AP) release of growth hormone (GH) and, if so, to determine whether this difference is correlated with a sex difference in hypothalamic release or content of somatostatin (SRIF). Age-matched rats of both sexes were decapitated at approximately 09.00 h, and blood was collected for determination of non-stress plasma concentrations of GH. Each pituitary was rapidly removed and prepared for perifusion of the AP, and each preoptic-medial basal hypothalamus (PO-MBH) was removed and placed in a separate perifusion chamber. The effluent fractions from perifused APs were assayed for GH and prolactin (Prl), and those from PO-MBH blocks were assayed for SRIF. Non-stress plasma GH concentrations were similar in males and females. During perifusion, baseline GH release was higher (P less than 0.001) from male than from female APs. Release of GH from the APs of both sexes was similarly inhibited (P less than 0.001) by a 1-h administration of SRIF (10(-7) M), and high K+ (50 mM) caused larger (P less than 0.05) GH responses from male than from female APs. In contrast, baseline Prl release was higher (P less than 0.01) from female than from male glands, and Prl release was not affected by SRIF. Male and female PO-MBH tissues showed similar baseline release of SRIF and similar responses to high K+. After perifusion, GH content and concentration were higher in APs from males than from females, but SRIF content in the perifused male and female PO-MBH tissues was similar.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of periventricular lesions on the release of somatostatin during perifusion

Hypothalamic periventricular (PV) nucleus lesions reduce median eminence (ME) SRIF content by approximately equal to 80% without affecting non-stress plasma growth hormone (GH) levels or the GH response to stress. Our aim was to study the effects of PV lesions on SRIF released during perifusion of preoptic-anterior hypothalamic (PO-AH) tissue. Female rats received anterior or posterior PV lesions; sham-lesioned and intact rats served as controls. Non-stress and stress plasma GH levels were similar in all groups at 2, 4 and 16 weeks after surgery. At 18 weeks after surgery, the perifused PO-AHs of the PV- and sham-lesioned rats released similar amounts of SRIF, and these were higher (P less than 0.001) than amounts released from PO-AHs of intact rats. The PO-AHs from all groups showed similar increases in SRIF release after 56 mM K+. Two rats were chosen randomly from each group to assess ME SRIF content; PV lesions caused almost 80% depletion of SRIF, sham lesions did not. These results confirm that most SRIF neurons in the PV nucleus and 80% of ME SRIF content are not essential for the control of GH levels under non-stress conditions or for the GH response to stress and indicate that PV or sham lesions in the rostral forebrain enhance in vitro SRIF release, perhaps from neurons outside the PV nucleus.

In vivo synthesis and processing of rat hypothalamic prosomatostatin

The in vivo incorporation of [3H]phenylalanine into an apparent 15 kDa prosomatostatin was observed in the hypothalamus of rats injected with the labeled amino acid in the third ventricle. Precursor-product relationships were established between this newly synthesized material and both somatostatin-28 and -14.

Somatostatin receptors: distribution in rat central nervous system and human frontal cortex

Somatostatins are a brain peptide family centered on a 14-amino acid cyclic peptide (SS-14) and a 28-amino acid N-terminally extended form (SS-28). Using radioiodinated analogs of SS-14 and SS-28, we have identified specific binding sites in rat and human brain sections that display pharmacological properties anticipated for somatostatin receptors and discrete patterns of anatomical localization. High binding densities are found in many forebrain regions, with special densities in infragranular cerebral cortical laminae in rat and human brain. In the rat, other densities lie in olfactory zones, lateral and triangular septal nuclei, the CA-1 hippocampal region, and claustrum with moderate densities in the striatum. Discrete hypothalamic areas, especially the median preoptic, paraventricular, and periventricular nuclei, display elevated binding levels, while the thalamus shows only scattered areas of modest binding. Midbrain receptor concentrations are found in portions of the periaqueductal gray, interpeduncular nucleus, and the substantia nigra. Notable pontine and medullary densities lie in the locus coeruleus, fourth ventricular floor, parabrachial, solitary, prepositus hypoglossal, dorsal column, and caudal trigeminal zones. Although the cerebellar cortex shows unimpressive densities, each of the deep cerebellar nuclei is heavily labeled. Modest spinal cord receptor densities are concentrated in the substantia gelatinosa and central cord regions. These localizations show many parallels with the distributions of SS-immunoreactive neurons, fibers, and terminals determined previously by immunohistochemistry. They provide plausible loci for several reported physiological or pharmacological activities of the SS-peptides, and may improve understanding of the role of the SS alterations described in several human neurodegenerative disorders.

Dendritic arborization and axon trajectory of neurons in the hypothalamic arcuate nucleus of the rat--updated

Neurons in the hypothalamic arcuate nucleus (arcuate neurons) were traced on Golgi-impregnated sections. Dendrites of arcuate neurons showed characteristic orientation patterns. Dendrites along the lateral side follow the convex border of the nucleus by running parallel to the tanycyte processes. Neurons located in the ventrolateral portion of the nucleus have dendrites running parallel to the basal surface of the hypothalamus. Fine, beaded axons of arcuate neurons project mostly ventrally, and less frequently dorsally and dorsolaterally. Ventrally projecting axons converge towards the tuberoinfundibular sulcus which emerges into the ventral portion of the arcuate nucleus from below.

An antiserum to locust adipokinetic hormone reveals a novel peptidergic system in the rat central nervous system

Using an antiserum to locust adipokinetic hormone I, a novel peptidergic system was identified in the rat central nervous system. Immunoreactive fibers were present in the hypothalamic median eminence and periventricular nucleus and the spinal cord dorsal horn, intermediolateral cell column and sacral parasympathetic nucleus. Immunoreactive cells were present in the dorsal gray commissure of lumbosacral spinal cord, the hypothalamic periventricular nucleus and cerebral cortex.

Central somatostatin systems revealed with monoclonal antibodies

The distribution of central neurons displaying somatostatin immunoreactivity was studied using three monoclonal antibodies to cyclic somatostatin. The sensitive ABC immunoperoxidase technique was employed. A large number of positive cell groups including many previously undescribed populations were detected throughout the brain and spinal cord. Telencephalic somatostatin neurons included periglomerular cells in the olfactory bulb, mitral cells in the accessory olfactory bulb, and multipolar cells in the anterior olfactory nuclei, neocortex, amygdala, hippocampus, lateral septum, striatum, and nucleus accumbens. Within the hypothalamus, positive neurons were found in the periventricular, suprachiasmatic, and arcuate nuclei, and throughout the anterior and lateral hypothalamus. The entopeduncular nucleus and zona incerta contained many positive neurons, and the lateral habenula had a dense terminal field suggesting a pallidohabenula somatostatin pathway. Somatostatin neurons were also found in association with many sensory systems. Positive cells were present in the superior and inferior colliculi, the ventral cochlear nuclei, the ventral nucleus of the lateral lemniscus, nucleus cuneatus, nucleus gracilus, and the substantia gelatinosa. Various cerebellar circuits also displayed somatostatin immunoreactivity. Golgi cells throughout the cerebellar cortex were intensely stained, and some Purkinje cells in the paraflocculus also showed a positive reaction. Positive fibers were present in the granular layer and large varicose fibers were present in the inferior cerebellar peduncle. Many nuclei known to project to the cerebellum, including the nucleus reticularis tegmenti pontis, the medial accessory inferior olive, the nucleus prepositus hypoglossi, and many areas of the reticular formation contained positive neurons. These studies demonstrate that these new monoclonal antibodies are of great value for the study of central somatostatin systems. Previously described somatostatin systems are readily detected with these antibodies, and in addition, many otherwise unrecognized somatostatin cell groups have been discovered.

Long-term suspension culture of isolated hypothalamic nuclei of the rat: morphological differentiation and release of substances influencing corticotropin and growth hormone secretion

Individual hypothalamic nuclei were removed from 17-day-old rat embryos with 300 microns punches and maintained in suspension culture. Suspension culture of isolated nuclei appears to be suitable for studying morphological and functional differentiation of neural tissue and release of bioactivity influencing corticotropin and growth hormone release. During the 4 weeks in culture, neurons and glial cells differentiated well in each nucleus studied. The fine structure of the arcuate, periventricular, ventromedial and dorsomedial nuclei resembled that of the adult nuclei with many mature synapses; in contrast, in the neuropil of cultured preoptic, paraventricular and posterior hypothalamic nuclei mature synapses were very few or absent. The release of substances influencing corticotropin and growth hormone secretion by the cultured nuclei was tested in bioassays using anterior pituitary cell cultures and radioimmunoassay of hormones released into the medium. Corticotropin-releasing bioactivity was tested at weekly intervals. Cultured preoptic and paraventricular nuclei released corticotropin-releasing activity for up to 4 weeks whereas arcuate nuclei released corticotropin-releasing activity at 1 week only. The ventromedial and dorsomedial nuclei did not release corticotropin-releasing activity. The release of substances influencing growth hormone secretion was studied between 3 and 11 days in culture. After 3 days the medium of some hypothalamic nuclei stimulated growth hormone secretion, but after 7 and 11 days all cultured nuclei strongly inhibited it. The present findings demonstrate that hypothalamic nuclei can be cultured separately and suggest that neurons capable of releasing corticotropin-releasing activity(ies) are present in the preoptic and paraventricular nuclei of the rat whereas all hypothalamic nuclei studied contain intrinsic neurons capable of synthesizing and secreting somatostatin-like bioactivity.

Ultrastructural studies on the afferent synaptic input to oxytocin-containing neurons in the paraventricular nucleus of the hypothalamus

A diverse afferent synaptic input to immunostained oxytocin magnocellular neurons of the paraventricular nucleus of the rat hypothalamus is described. By electron microscopy, immunoreactive material is present within cell bodies and neuronal processes and it is associated primarily with neurosecretory granules and granular endoplasmic reticulum. Afferent axon terminals synapse on perikarya, dendritic processes, and possibly axonal processes of oxytocin-containing neurons. The presynaptic elements of the synaptic complexes contain clear spherical vesicles, a mixture of clear spherical and ellipsoidal vesicles, or a mixture of clear and dense-centered vesicles. The postsynaptic membranes of oxytocinergic cells frequently show a prominent coating of dense material on the cytoplasmic face which gives the synaptic complex a marked asymmetry.

Immunocytochemical studies of somatostatin neurons in brain

Immunohistochemical studies with antisera to somatostatin have, in many instances, led the way to our present understanding of the peptidergic nervous system. Somatostatin was among the first of the hypophysiotropic hormones shown to be contained in diverse neuronal circuits outside of the hypothalamus. For example, somatostatin is found within neurons ranging in location from the cerebral cortex to primary sensory neurons to enteric neurons within the gut wall. Somatostatin was also the first neuropeptide demonstrated to coexist within vertebrate neurons that also produce a classical neurotransmitter. Since this initial demonstration in sympathetic ganglionic neurons, somatostatin and numerous other neuropeptides have been demonstrated to coexist with a variety of classical neurotransmitters. The "rules" for coexistence are not clear, since somatostatin coexist in some instances with norepinephrine, in other cases with GABA, and probably with other classical transmitters as well. In some neurons, somatostatin also coexists with certain other neuropeptides. Finally, the specificity of immunohistochemical localizations of somatostatin has now been confirmed by virtue of the co-staining of somatostatin neurons with antisera to other portions of the biosynthetic precursor to somatostatin.

Immunohistochemical distribution of somatostatin-like immunoreactivity in the central nervous system of the adult rat

The localization and distribution of somatostatin (growth hormone release-inhibiting hormone; somatotropin release-inhibiting factor) have been studied with the indirect immunofluorescence technique of Coons and collaborators and the immunoperoxidase method of Sternberger and coworkers using specific and well-characterized antibodies to somatostatin, providing semiquantitative, detailed maps of somatostatin-immunoreactive cell profiles and fibers. Our results demonstrate a widespread occurrence of somatostatin-positive nerve cell bodies and fibers throughout the central nervous system of adult, normal or colchicine-treated, albino rats. The somatostatin cell bodies varied in size from below 10 micron up to 40 micron in diameter and could have only a few or multiple processes. Dense populations of cell somata were present in many major areas including neocortex, piriform cortex, hippocampus, amygdaloid complex, nucleus caudatus, nucleus accumbens, anterior periventricular hypothalamic area, ventromedial hypothalamic nucleus, nucleus arcuatus, medial to and within the lateral lemniscus, pontine reticular nuclei, nucleus cochlearis dorsalis and immediately dorsal to the nucleus tractus solitarii. Extensive networks of nerve fibers of varying densities were also found in most areas and nuclei of the central nervous system. Both varicose fibers as well as dot- or "dust-like" structures were seen. Areas with dense or very dense networks included nucleus accumbens, nucleus caudatus, nucleus amygdaloideus centralis, most parts of the hypothalamus, nucleus parabrachialis, nucleus tractus solitarii, nucleus ambiguus, nucleus tractus spinalis nervi trigemini and the dorsal horn of the spinal cord. One exception is the cerebellum which only contained few somatostatin-positive cell bodies and nerve fibers. It should be noted that somatostatin-positive cell bodies and fibers did not always conform to the boundaries of the classical neuroanatomical nuclei, but could often be found in areas between these well-established nuclei or occupying, in varying concentrations, only parts of such nuclei. It was difficult to identify with certainty somatostatin-immunoreactive axons in the animals studied. Some pathways could, however, be demonstrated, but further experimental studies are necessary to elucidate the exact projections of the somatostatin-immunoreactive neurons in the rat central nervous system.

Motilin: a novel growth hormone releasing agent

Motilin, a gastrointestinal peptide recently detected in the rat brain, was capable of stimulating growth hormone (GH) release from dispersed anterior pituitary cells in a dose-related fashion. In initial experiments, the minimum effective concentration was 10(-7) M and the effect was specific for just GH. Subsequent experiments demonstrated that concentrations of synthetic motilin as low as 10(-9) M could significantly stimulate GH release. Only large IV doses (100 micrograms) of motilin significantly elevated circulating GH levels in vivo. However, administration of antiserum to porcine motilin (100 microliters, IV) significantly depressed plasma GH levels, suggesting a physiologic role for median eminence and hypothalamic motilin in the control of GH secretion. Furthermore, infusion of motilin into the third ventricle of conscious rats resulted in a significant depression of GH levels, suggesting an ultrashort loop feedback action of motilin on the release of motilin itself or somatostatin. In light of motilin's only minor structural similarity to human pancreatic tumor GH-releasing factor (GRF) and the ability of passive immunoneutralization of motilin to lower GH, this 22-amino acid peptide must now be considered a physiologic GRF.

Somatostatin in the brain of the turtle Testudo hermanni Gmelin. An immunohistochemical mapping study

An immunohistochemical mapping study in the brain and upper spinal cord of the turtle Testudo hermanni Gmelin revealed a wide distribution of somatostatin perikarya and fibres. Within the telencephalon, somatostatin perikarya are present in the anterior olfactory nucleus, in the medial, dorsomedial and dorsal cortex, in the pallial thickening, in the piriform cortex, paleostriatum augmentatum, in the dorsoventricular ridge, core nucleus of the dorsoventricular ridge, in area c and d, and in the amygdala. In the diencephalon, the periventricular nucleus of the hypothalamus contains many somatostatin perikarya. Cerebrospinal fluid contacting somatostatin perikarya of the infundibular nucleus terminate with club-like endings in the ventricular cavity. Some somatostatin perikarya are present in the nu. reuniens of the thalamus and in the lateral habenular nucleus of the epithalamus. Within the mesencephalon somatostatin perikarya are located in the interpeduncular nucleus, area tegmentalis ventralis and in the nu. reticularis isthmi. In the rhombencephalon, somatostatin perikarya are encountered in the nu. raphe superior, nu. reticularis magnus, periventricular grey matter, bed nucleus of the fasciculus longitudinalis medialis and in the nu. solitarius-vagus complex. Somatostatin fibres form a circular band in the olfactory bulb. In the telencephalon, dense aggregations of somatostatin fibres are present in the anterior olfactory nucleus, in the pallial thickening, in the parahippocampal gyrus, cortex medialis, dorsomedialis, dorsalis and piriformis, in the dorsal ventricular ridge, paleostriatum augmentatum, area c and d, in the septum, nu. diagonalis of Broca, in the amygdala and in the anterior commissure. In the diencephalon, somatostatin fibres terminate at the vessels of the organum vasculosum of the lamina terminalis. A dense band of somatostatin fibres surrounds the rostral third ventricle. Somatostatin fibres terminate in the infundibulum at portal capillaries, and in the neural lobe. Somatostatin fibres are found in the periventricular, ventromedial and lateral nucleus of the hypothalamus. In the thalamus, the area triangularis, the dorsomedial and dorsolateral area and the nu. reuniens contain somatostatin fibres. Somatostatin fibres are very dense in the lateral habenular nucleus. At the mesencephalic level, somatostatin fibres are found in the pretectal nucleus, in the deep layers of the tectum, in the nu. tori semicircularis lateralis, in the interpeduncular nucleus, area tegmentalis ventralis, nu. ruber, substantia nigra and periventricular grey.(ABSTRACT TRUNCATED AT 400 WORDS)