Immunocytochemical localization of somatostatin in human brain

Neurochemistry of the mammillary body

The mammillary body (MB) is a component of the extended hippocampal system and many studies have shown that its functions are vital for mnemonic processes. Together with other subcortical structures, such as the anterior thalamic nuclei and tegmental nuclei of Gudden, the MB plays a crucial role in the processing of spatial and working memory, as well as navigation in rats. The aim of this paper is to review the distribution of various substances in the MB of the rat, with a description of their possible physiological roles. The following groups of substances are reviewed: (1) classical neurotransmitters (glutamate and other excitatory transmitters, gamma-aminobutyric acid, acetylcholine, serotonin, and dopamine), (2) neuropeptides (enkephalins, substance P, cocaine- and amphetamine-regulated transcript, neurotensin, neuropeptide Y, somatostatin, orexins, and galanin), and (3) other substances (calcium-binding proteins and calcium sensor proteins). This detailed description of the chemical parcellation may facilitate a better understanding of the MB functions and its complex relations with other structures of the extended hippocampal system.

Activation of Somatostatin-Expressing Neurons in the Lateral Septum Improves Stress-Induced Depressive-like Behaviors in Mice

Depression is a debilitating mood disorder with highly heterogeneous pathogenesis. The limbic system is well-linked to depression. As an important node in the limbic system, the lateral septum (LS) can modulate multiple affective and motivational behaviors. However, the role of LS in depression remains unclear. By using c-Fos expression mapping, we first screened and showed activation of the LS in various depression-related behavioral tests, including the forced swim test (FST), tail suspension test (TST), and sucrose preference test. In the LS, more than 10% of the activated neurons were somatostatin-expressing (SST) neurons. We next developed a microendoscopic calcium imaging method in freely moving mice and revealed that LS^SST neural activity increased during mobility in the TST but not open field test. We hypothesize that LS^SST neuronal activity is linked to stress and depression. In two mouse models of depression, repeated lipopolysaccharide (LPS) injection and chronic restraint stress (CRS), we showed that LS neuronal activation was suppressed. To examine whether the re-activation of LS^SST neurons can be therapeutically beneficial, we optogenetically activated LS^SST neurons and produced antidepressant-like effects in LPS-injected mice by increasing TST motility. Moreover, chemogenetic activation of LS^SST neurons increased FST struggling in the CRS-exposed mice. Together, these results provide the first evidence of a role for LS^SST neurons in regulating depressive-like behaviors in mice and identify them as a potential therapeutic target for neuromodulation-based intervention in depression.

The Organization of Somatostatin-Immunoreactive Cells in the Visual Cortex of the Gerbil

Somatostatin (SST) is widely expressed in the brain and plays various, vital roles involved in neuromodulation. The purpose of this study is to characterize the organization of SST neurons in the Mongolian gerbil visual cortex (VC) using immunocytochemistry, quantitative analysis, and confocal microscopy. As a diurnal animal, the Mongolian gerbil provides us with a different perspective to other commonly used nocturnal rodent models. In this study, SST neurons were located in all layers of the VC except in layer I; they were most common in layer V. Most SST neurons were multipolar round/oval or stellate cells. No pyramidal neurons were found. Moreover, 2-color immunofluorescence revealed that only 33.50%, 24.05%, 16.73%, 0%, and 64.57% of SST neurons contained gamma-aminobutyric acid, calbindin-D28K, calretinin, parvalbumin, and calcium/calmodulin-dependent protein kinase II, respectively. In contrast, neuropeptide Y and nitric oxide synthase were abundantly expressed, with 80.07% and 75.41% in SST neurons, respectively. Our immunocytochemical analyses of SST with D₁ and D₂ dopamine receptors and choline acetyltransferase, α₇ and β₂ nicotinic acetylcholine receptors suggest that dopaminergic and cholinergic fibers contact some SST neurons. The results showed some distinguishable features of SST neurons and provided some insight into their afferent circuitry in the gerbil VC. These findings may support future studies investigating the role of SST neurons in visual processing.

Chemoarchitecture of the bed nucleus of the stria terminalis: Neurophenotypic diversity and function

The bed nucleus of the stria terminalis (BNST) is a compact but neurophenotypically complex structure in the ventral forebrain that is structurally and functionally linked to other limbic structures, including the amygdala nuclear complex, hypothalamic nuclei, hippocampus, and related midbrain structures, to participate in a wide range of functions, especially emotion, emotional learning, stress-related responses, and sexual behaviors. From a variety of sensory inputs, the BNST acts as a node for signal integration and coordination for information relay to downstream central neuroendocrine and autonomic centers for appropriate homeostatic physiological and behavioral responses. In contrast to the role of the amygdala in fear, the BNST has gained wide interest from work suggesting that it has main roles in mediating sustained responses to diffuse, unpredictable and/or long-duration threats that are typically associated with anxiety-related responses. Further, some BNST subregions are highly sexually dimorphic which appear contributory to the differential stress and social interactive behaviors, including reproductive responses, between males and females. Notably, maladaptive BNST neuroplasticity and function have been implicated in chronic pain, depression, anxiety-related abnormalities, and other psychopathologies including posttraumatic stress disorders. The BNST circuits are predominantly GABAergic-the glutaminergic neurons represent a minor population-but the complexity of the system results from an overlay of diverse neuropeptide coexpression in these neurons. More than a dozen neuropeptides may be differentially coexpressed in BNST neurons, and from variable G protein-coupled receptor signaling, may inhibit or activate downstream circuit activities. The mechanisms and roles of these peptides in modulating intrinsic BNST neurocircuit signaling and BNST long-distance target cell projections are still not well understood. Nevertheless, an understanding of some of the principal players may allow assembly of the circuit interactions.

Distribution of somatostatin-28 (1-12), calcitonin gene-related peptide, and substance P in the squirrel monkey brainstem: an immunocytochemical study

Using an immunocytochemical technique, we have studied the distribution of fibers and cell bodies containing somatostatin-28 (1-12) [SOM-28 (1-12)], calcitonin gene-related peptide (CGRP), and substance P (SP) in the brainstem of Saimiri sciureus. The distribution of the peptidergic cell bodies was very restricted: perikarya containing SOM-28 (1-12) were only observed in the substantia grisea centralis, while no immunoreactive cell bodies containing CGRP or SP were visualized. Fibers containing SOM-28 (1-12), CGRP, or SP were widely distributed in the brainstem: immunoreactive fibers containing SOM-28 (1-12) showed the most widespread distribution and were the most abundant. The distribution of SOM-28 (1-12)-, CGRP- or SP-immunoreactive fibers was very similar. Colocalization of immunoreactive fibers containing SOM-28 (1-12), CGRP or SP was observed in many brainstem nuclei. A neuroanatomical relationship between CGRP- and SP-immunoreactive fibers was observed, although this relationship was less marked for SOM-28 (1-12) and SP and lower still for SOM-28 (1-12) and CGRP. The widespread distribution of the peptidergic fibers suggests that the studied neuropeptides are involved in many physiological actions.

Distribution of Neurotensin and Somatostatin-28 (1-12) in the Minipig Brainstem

Using an indirect immunoperoxidase technique, an in depth study has been carried out for the first time on the distribution of fibres and cell bodies containing neurotensin and somatostatin-28 (1-12) (SOM) in the minipig brainstem. The animals used were not treated with colchicine. The distribution of neurotensin- and SOM-immunoreactive fibres was seen to be quite similar and was moderate in the minipig brainstem: a close anatomical relationship between both neuropeptides was observed. The distribution of cell bodies containing neurotensin or SOM was quite different and restricted. Cell bodies containing neurotensin were found in four brainstem nuclei: nucleus centralis raphae, nucleus dorsalis raphae, in the pars centralis of the nucleus tractus spinalis nervi trigemini and in the nucleus ventralis raphae. Cell bodies containing SOM were found in six nuclei/regions of the brainstem: nucleus ambiguus, nucleus dorsalis motorius nervi vagus, formatio reticularis, nucleus parabrachialis medialis, nucleus reticularis lateralis and nucleus ventralis raphae. According to the observed anatomical distribution of the immunoreactive structures containing neurotensin or SOM, the peptides could be involved in sleep-waking, nociceptive, gustatory, motor, respiratory and autonomic mechanisms.

Mapping of somatostatin-28 (1-12) in the alpaca (Lama pacos) brainstem

Using an indirect immunoperoxidase technique, we studied the distribution of cell bodies and fibers containing somatostatin-28 (1-12) in the alpaca brainstem. Immunoreactive fibers were widely distributed throughout the whole brainstem: 34 brainstem nuclei/regions showed a high or a moderate density of these fibers. Perikarya containing the peptide were widely distributed throughout the mesencephalon, pons and medulla oblongata. Cell bodies containing somatostatin-28 (1-12) were observed in the lateral and medial divisions of the marginal nucleus of the brachium conjunctivum, reticular formation (mesencephalon, pons and medulla oblongata), inferior colliculus, periaqueductal gray, superior colliculus, pericentral division of the dorsal tegmental nucleus, interpeduncular nucleus, nucleus of the trapezoid body, vestibular nucleus, motor dorsal nucleus of the vagus, nucleus of the solitary tract, nucleus praepositus hypoglossi, and in the substantia nigra. This widespread distribution indicates that somatostatin-28 (1-12) is involved in multiple physiological actions in the alpaca brainstem.

Mapping of somatostatin-28 (1-12) in the alpaca diencephalon

Using an immunocytochemical technique, we report for the first time the distribution of immunoreactive cell bodies and fibers containing somatostatin-28 (1-12) in the alpaca diencephalon. Somatostatin-28 (1-12)-immunoreactive cell bodies were only observed in the hypothalamus (lateral hypothalamic area, arcuate nucleus and ventromedial hypothalamic nucleus). However, immunoreactive fibers were widely distributed throughout the thalamus and hypothalamus. A high density of such fibers was observed in the central medial thalamic nucleus, laterodorsal thalamic nucleus, lateral habenular nucleus, mediodorsal thalamic nucleus, paraventricular thalamic nucleus, reuniens thalamic nucleus, rhomboid thalamic nucleus, subparafascicular thalamic nucleus, anterior hypothalamic area, arcuate nucleus, dorsal hypothalamic area, around the fornix, lateral hypothalamic area, lateral mammilary nucleus, posterior hypothalamic nucleus, paraventricular hypothalamic nucleus, suprachiasmatic nucleus, supraoptic hypothalamic nucleus, and in the ventromedial hypothalamic nucleus. The widespread distribution of somatostatin-28 (1-12) in the thalamus and hypothalamus of the alpaca suggests that the neuropeptide could be involved in many physiological actions.

Organization of the human medial preoptic nucleus

The organization of the adult human medial preoptic nucleus was studied by using chemoarchitectonic markers for acetylcholinesterase, nonphosphorylated neurofilament protein (SMI-32), calbindin-D28k, neuropeptide Y (NPY), melanin-concentrating hormone (MCH), cocaine- and amphetamine-regulated transcript (CART), and 3-fucosyl-N-acetyl-lactosamine (CD15) to establish human homologs to the subnuclei making up MPO in the rat, where their connections and functional significance are better understood. The human MPO comprises three subnuclei, the medial MPO, the lateral MPO, and the dorsomedially positioned uncinate subnucleus. As in the rat, the human medial MPO is magnocellular and contains numerous NPY- and CART-immunoreactive fibers and terminals as well as calbindin-positive neurons. The human lateral MPO, like its homolog in the rat, distinctively features numerous MCH-positive fibers and terminals as well as SMI-32-immunoreactive fibers. The uncinate subnucleus is wedged between the lateral surface of the paraventricular nucleus and the medial MPO and is characterized by variable NPY- and CART-immunoreactive fibers and terminals, also seen in the rat central MPO, suggesting that the subnuclei are homologues. The intermediate nucleus was distinguished by CD15-positive neuronal staining, whereas the majority of its neurons also contained acetylcholinesterase. The human intermediate nucleus is positioned on the lateral surface of MPO and by its chemo- and cytoarchitecture constitutes a distinct nucleus of the preoptic area characterized by close structural association with the MPO complex. These findings demonstrate that the human MPO is organized similarly to the rat MPO, in chemo- and cytoarchitectonically distinct subnuclei, which implies differences in their functional specialization, as seen in the rat.

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.

Distribution of somatostatin immunoreactivity in the brain of the snake Bothrops jararaca

The distribution of perikarya and fibers containing somatostatin was studied in the brain of the snake Bothrops jararaca by means of immunohistochemistry using an antiserum against synthetic somatostatin. Immunoreactive perikarya and fibers were localized in telencephalic, diencephalic and mesencephalic areas. In the telencephalon, numerous immunoreactive perikarya were found in the medial, dorsomedial, dorsal and lateral cortex, mainly in the deep plexiform layer, less so in the cellular layer, but not in the superficial plexiform layer. Immunoreactive perikarya were also observed in the dorsal ventricular ridge, the nucleus of the diagonal band of Broca, amygdaloid complex, septum and lamina terminalis. In the diencephalon, labelled cells were observed in the paraventricular, periventricular hypothalamic and in the recessus infundibular nuclei. In the mesencephalon, immunoreactive perikarya were seen in the mesencephalic reticular formation, reticular nucleus of the isthmus and torus semicircularis. Labelled fibers ran along the diencephalic floor and the inner zone of the median eminence, and ended in the neural lobe of the hypophysis. Other fibers were observed in the outer zone of the median eminence close to the portal vessels and in the septum, lamina terminalis, retrochiasmatic nucleus, deep layers of the tectum, periventricular gray and granular layer of the cerebellum. Our data suggest that somatostatin may function as a mediator of adenohypophysial secretion as well as neurotransmitter and/or neuromodulator which can regulate the neurohypophysial peptides in the snake B. jararaca.

Neuronal projections to the lateral retrochiasmatic area of sheep with special reference to catecholaminergic afferents: immunohistochemical and retrograde tract-tracing studies

The retrochiasmatic area contains the A15 catecholaminergic group and numerous monoaminergic afferents whose discrete cell origins are unknown in sheep. Using tract-tracing methods with a specific retrograde fluorescent tracer, fluorogold, we examined the cells of origin of afferents to the retrochiasmatic area in sheep. The retrogradely labeled cells were seen by observation of the tracer by direct fluorescence or by immunohistochemistry with specific antibodies raised in rabbits or horses. Among the retrogradely labeled neurons, double immunohistochemistry for tyrosine hydroxylase, dopamine-beta-hydroxylase, and serotonin were used to characterize catecholamine and serotonin FG labeled neurons. The retrochiasmatic area, which included the A15 dopaminergic group and the accessory supraoptic nucleus (SON), received major inputs from the lateral septum (LS), the bed nucleus of the stria terminalis (BNST), the thalamic paraventricular nucleus, hypothalamic paraventricular and supraoptic nuclei, the perimamillary area, the amygdala, the ventral part of the hippocampus and the parabrachial nucleus (PBN). Further, numerous scattered retrogradely labeled neurons were observed in the preoptic area, the ventromedial part of the hypothalamus. the periventricular area, the periaqueductal central gray (CG), the ventrolateral medulla and the dorsal vagal complex. Most of the noradrenergic afferents came from the ventro-lateral medulla (Al group), and only a few from the locus coeruleus complex (A6/A7 groups). A few dopaminergic neurons retrogradely labeled with flurogold were observed in the periventricular area of the hypothalamus. Rare serotoninergic fluorogold labeled neurons belonged to the dorsal raphe nucleus. Most of these afferents came from both sides of the brain, except for hypothalamic supraoptic and paraventricular nuclei. In the light of these anatomical data, we compared our results with data obtained from rats, and we discussed the putative role of these afferents in sheep in the regulation of several specific functions in which the retrochiasmatic area may be involved, such as reproduction.

Neurochemical compartments in the human forebrain: evidence for a high density of secretoneurin-like immunoreactivity in the extended amygdala

Secretoneurin is a 33-amino acid neuropeptide produced by endoproteolytic processing from secretogranin II, which is a member of the chromogranin/ secretogranin family. In this immunocytochemical study we investigated the localization of secretoneurin-like immunoreactivity in the human substantia innominata in relation to the ventral striatopallidal system, the bed nucleus-amygdala complex and the basal nucleus of Meynert. A high density of secretoneurin immunostaining was found in the medial part of the nucleus accumbens. All subdivisions of the bed nucleus of the stria terminalis displayed a very prominent immunostaining for secretoneurin, whereas substance P and enkephalin showed a more restricted distribution. A high concentration of secretoneurin immunoreactivity was also observed in the central and medial amygdaloid nuclei. In the lateral bed nucleus of the stria terminalis and the sublenticular substantia innominata, the appearance of secretoneurin immunoreactivity was very similar to that of enkephalin-like immunoreactivity, exhibiting mostly peridendritic and perisomatic staining. The ventral pallidum and the inner pallidal segment displayed strong secretoneurin immunostaining. Secretoneurin did not label cholinergic neurons in the basal forebrain. This study demonstrates that secretoneurin-like immunoreactivity is prominent in the bed nucleus-amygdala complex, referred to as extended amygdala. The distribution of secretoneurin-like immunoreactivity in comparison with that of other neuroanatomical markers suggests that this forebrain system is a discret compartment in the human forebrain.

Substantia innominata: a notion which impedes clinical-anatomical correlations in neuropsychiatric disorders

Comparative neuroanatomical investigations in primates and non-primates have helped disentangle the anatomy of the basal forebrain region known as the substantia innominata. The most striking aspect of this region is its subdivision into two major parts. This reflects the fundamental organizational scheme for this portion of the forebrain. According to this scheme, two major subcortical telencephalic structures, i.e. the striatopallidal complex and extended amygdala, form large diagonally oriented bands. The rostroventral extension of the pallidum accounts for a large part of the rostral subcommissural substantia innominata, while the sublenticular substantia innominata is primarily occupied by elements of the extended amygdala. Also dispersed across this region is the basal nucleus of Meynert, which is part of a more or less continuous collection of cholinergic and non-cholinergic corticopetal and thalamopetal cells, which stretches from the septum diagonal band rostrally to the caudal globus pallidus. The basal nucleus of Meynert is especially prominent in the primate, where it is sometimes inappropriately applied as a synonym for the substantia innominata, thereby tacitly ignoring the remaining components. In most mammals, the extended amygdala presents itself as a ring of neurons encircling the internal capsule and basal ganglia. The extended amygdala may be further subdivided, i.e. into the central extended amygdala (related to the central amygdaloid nucleus) and the medial extended amygdala (related to the medial amygdaloid nucleus), which generally form separate corridors both in the sublenticular region and along the supracapsular course of the stria terminalis. The extended amygdala is directly continuous with the caudomedial shell of the accumbens, and to some extent appears to merge with it. Together the accumbens shell and extended amygdala form an extensive forebrain continuum, which establishes specific neuronal circuits with the medial prefrontal-orbitofrontal cortex and medial temporal lobe. This continuum is particularly characterized by a prominent system of long intrinsic association fibers, and a variety of highly differentiated downstream projections to the hypothalamus and brainstem. The various components of the extended amygdala, together with the shell of the accumbens, are ideally structured to generate endocrine, autonomic and somatomotor aspects of emotional and motivational states. Behavioral observations support this proposition and demonstrate the relevance of these structures to a variety of functions, ranging from the various elements of the reproductive cycle to drug-seeking behavior. The neurochemical and connectional features common to the accumbens shell and the extended amygdala are especially relevant to understanding the etiology and treatment of neuropsychiatric disorders. This is discussed in general terms, and also in specific relation to the neurodevelopmental theory of schizophrenia and to the neurosurgical treatment of neuropsychiatric disorders.

Quantitative autoradiographic study of somatostatin receptors in the adult human cerebellum

The evolution of the distribution and density of somatostatin receptors was studied in the human cerebellum during ageing. The brain tissues were collected 3-30 h after death from 20 individuals aged from 28 to 86 years. In vitro autoradiographic experiments were performed on blocks of vermis and of right and left cerebellar hemispheres, using [125I-Tyr0,DTrp8]S14 as a radioligand. In the vermis, the mean concentrations of somatostatin receptors in the molecular layer, the granular layer and the medulla were 140 +/- 9, 150 +/- 22 and 61 +/- 13 fmol/mg proteins, respectively. For each individual, the density of sites in the two lateral lobes was similar. The mean concentrations of somatostatin receptors in the molecular layer, the granular layer and the medulla were 152 +/- 17, 190 +/- 20 and 56 +/- 11 fmol/mg proteins, respectively. The mean level of somatostatin receptors and the type of distribution of the receptors were not correlated to the age of the patients. Different distribution patterns of somatostatin receptors were noted among the patients studied. In the majority of patients (11/20), the density of somatostatin receptors was higher in the granular layer than in the molecular layer. Conversely, in four patients, the density of somatostatin receptors was higher in the molecular layer. The other individuals exhibited similar concentrations of somatostatin receptors in the granular and molecular layers. The present study indicates that the adult human cerebellum contains a high concentration of somatostatin receptors (> 100 fmol/mg proteins) and that the receptor level does not decline during ageing.(ABSTRACT TRUNCATED AT 250 WORDS)

The monoclonal antibody Alz-50, used to reveal cytoskeletal changes in Alzheimer's disease, also reacts with a large subpopulation of somatostatin neurons in the normal human hypothalamus and adjoining areas

The monoclonal antibody Alz-50 is directed against Alzheimer's disease-related modified tau proteins and reveals cytoskeletal changes, i.e. neurofibrillary tangles and dystrophic neurites. The present study shows that, in the hypothalamus of non-demented control subjects, this same antibody gives a distinctive staining pattern of a subpopulation of somatostatin neurons and beaded fibres. Furthermore, Alz-50 occasionally recognizes somatostatin-containing cell bodies and dystrophic neurite-like fibers in the (neuritic) senile plaques of AD patients. These observations have direct consequences for the interpretation of Alz-50 staining in diagnostic usage and for the assessment of Alzheimer's disease-like changes induced by beta-amyloid in experimental animal brains. On dot spotting, Alz-50 was found to bind to a number of fragments from the somatostatin precursor, of which somatostatin 15-28 stained best. Preadsorption of Alz-50 by somatostatin 15-28, as well as other specificity tests, failed, however, to provide any clue to the nature of the unknown compound(s) stained in the control hypothalamus.

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.

Somatostatin receptors in the human cerebellum during development

The ontogeny of somatostatin receptors (SRIF-R) was studied in the human cerebellum from mid-gestation to the 15th month postnatal. The brains were collected 3-26 h after death, from 18 fetuses and infants, and from 4 adults aged from 48 to 82. SRIF-R were characterized by membrane-binding assay and their localization was determined by in vitro autoradiography. Both techniques were conducted with two radio-ligands: [125I-Tyr0, DTrp8]S14 and D-Phe-Cys-125I-Tyr-DTrp-Lys-Thr- ol (125I-SMS 204-090). Membrane-binding studies carried out with each radioligand showed the presence of a single population of saturable, high affinity binding sites. Neither were the Kd values for either ligand (assessed by Scatchard analysis) changed appreciably during development, mean Kd values being 0.36 +/- 0.04 nM and 0.56 +/- 0.11 nM for [125I-Tyr0,DTrp8]S14 and 125I-SMS 204-090, respectively. Although inter-individual fluctuations of the Bmax were observed, the concentration of SRIF-R in the cerebellum of fetuses and infants up to 8 months appeared to be at least 2- to 10-fold higher than in the adult cerebellum. No appreciable differences in the Bmax values were found using either radioligand. The highest density of SRIF-R was observed in the cerebellar cortex of fetuses, in particular in the external granule cell layer (EGC), where stem cells of the granule cells are generated and enter the differentiation process. A high density of SRIF-R also occurred in the internal granule cell layer.(ABSTRACT TRUNCATED AT 250 WORDS)

Light microscopic radioautographic localization of somatostatin binding sites in the brainstem of the rat

The distribution of somatostatin binding sites was investigated by light microscopic radioautography in the brainstem of the rat following in vitro labeling with 125I-Tyr0-DTrp8-somatostatin14. Moderate to high labeling densities were detected within the superior colliculus, the locus coeruleus and subcoeruleus, the parabrachial complex, the nucleus of the solitary tract and the dorsal motor nucleus of the vagus. Most of the white matter was devoid of specific somatostatin binding except for fibers of the glossopharyngeal nerve and the spinal trigeminal tract. In most of the labeled areas, 125I-somatostatin binding was evenly distributed between neuropil and perikarya. In a few instances, however, the binding clearly predominated over nerve cell bodies: namely in the dorsal motor nucleus of the vagus and in the pontine and medullary tegmentum. In the latter two regions, the labeled neurons were identified in adjacent sections by tyrosine hydroxylase immunohistochemistry as belonging to the A5 and A1 catecholamine cell groups, respectively. These findings, together with the confirmed association of somatostatin binding sites with noradrenergic neurons in the locus coeruleus, suggest that interactions with catecholaminergic systems may represent a major mode of action for somatostatin in the brainstem.

Distribution of somatostatin-28 (1-12) in the cat brainstem: an immunocytochemical study

We studied the distribution of somatostatin-28 (1-12)-immunoreactive fibers and cell bodies in the cat brainstem. A moderate density of cell bodies containing the peptide was observed in the ventral nucleus of the lateral lemniscus, accessory dorsal tegmental nucleus, retrofacial nucleus and in the lateral reticular nucleus, whereas a low density of such perikarya was found in the interpeduncular nucleus, nucleus incertus, nucleus sagulum, gigantocellular tegmental field, nucleus of the trapezoid body, nucleus praepositus hypoglosii, lateral and magnocellular tegmental fields, nucleus of the solitary tract, nucleus ambiguous and in the nucleus intercalatus. Moreover, a moderate density of somatostatin-28 (1-12)-immunoreactive processes was found in the dorsal nucleus of the raphe, dorsal tegmental nucleus, accessory dorsal tegmental nucleus, periaqueductal gray and in the marginal nucleus of the brachium conjunctivum. Finally, few immunoreactive fibers were visualized in the interpeduncular nucleus, cuneiform nucleus, locus coeruleus, nucleus incertus, superior and inferior central nuclei, nucleus sagulum, ventral nucleus of the lateral lemniscus, nucleus praepositus hypoglosii, medial vestibular nucleus, Kölliker-Fuse area, nucleus ambiguous, retrofacial nucleus, postpyramidal nucleus of the raphe, nucleus of the solitary tract, dorsal motor nucleus of the vagus, lateral reticular nucleus and laminar and alaminar spinal trigeminal nuclei.

The bed nucleus-amygdala continuum in human and monkey

The cytoarchitecture and distributions of seven neuropeptides were examined in the the bed nucleus of the stria terminalis (BST), substantia innominata (SI), and central and medial nuclei of the amygdala of human and monkey to determine whether neurons of these regions form an anatomical continuum in primate brain. The BST and centromedial amygdala have common cyto- and chemo-architectonic characteristics, and these regions are components of a distinct neuronal complex. This neuronal continuum extends dorsally, with the stria terminalis, from the BST and merges with the amygdala; it extends ventrally from the BST through the SI to the centromedial amygdala. The cytoarchitectonics of the BST-amygdala complex are heterogeneous and compartmental. The BST is parcellated broadly into anterior, lateral, medial, ventral, supracapsular, and sublenticular divisions. The central and medial nuclei of the amygdala are also parcellated into several subdivisions. Neurons of central and medial nuclei of the amygdala are similar to neurons in the lateral and medial divisions of the BST, respectively. Neurons in the SI form cellular bridges between the BST and amygdala. The BST, SI, and amygdala share several neuropeptide transmitters, and patterns of peptide immunoreactivity parallel cytological findings. Specific chemoarchitectonic zones were delineated by perikaryal, peridendritic/perisomatic, axonal, and terminal immunoreactivities. The results of this investigation demonstrate that there is a neuronal continuity between the BST and amygdala and that the BST-amygdala complex is prominent and discretely compartmental in forebrains of human and monkey.

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.

Somatostatin-like immunoreactivity in the brain of an electric fish (Apteronotus leptorhynchus) identified with monoclonal antibodies

The immunohistochemical localization of somatostatin-like immunoreactive (SSir) cells and fibers in the brain of the gymnotiform teleost (Apteronotus leptorhynchus) was investigated using well-characterized monoclonal antibodies directed against somatostatin-14 and -28. Large populations of SSir neurons occur in the basal forebrain, diencephalon and rhombencephalon and a dense distribution of fibers and terminal fields is found in the ventral, dorsomedial and dorsolateral telencephalon, hypothalamus, centralis posterior thalamus, subtrigeminal nucleus, the motor nucleus of vagus and in the ventrolateral medulla. Immunoreactive neurons in the forebrain are concentrated mainly in the ventral telencephalic areas, the region of the anterior commissure and entopeduncular nucleus. In a fashion similar to the large basal telencephalic cells of other species, the cells of the rostral nucleus entopeduncularis have a significant projection to the dorsal telencephalon. The preoptic region and the peri- and paraventricular hypothalamic nuclei are richly endowed with SSir cells; some of these cells contribute fibres to the pituitary stalk and gland. In the thalamus, only the n. centralis posterior stands out for the density of SSir cells and terminals; these cells appear to project to the prepacemaker nucleus, thus suggesting an SS influence on electrocommunication. In the mesencephalon most SSir cells occur in the optic tectum, torus semicircularis and interpeduncular nucleus. The rhombencephalic SSir cells have a wider distribution (central gray, raphe, sensory nuclei, reticular formation, electrosensory lateral line lobe and surrounding the central canal). The results of this study show the presence of SS in various sensory systems, electromotor system and specific hypothalamic nuclei, suggesting a modulatory role in the processing of sensory information, electrocommunication, endocrine and motor activities.

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)

Distribution of 125I-neurotensin binding sites in human forebrain: comparison with the localization of acetylcholinesterase

The distribution of 125I-neurotensin binding sites was compared with that of acetylcholinesterase reactivity in the human basal forebrain by using combined light microscopic radioautography/histochemistry. High 125I-neurotensin binding densities were observed in the bed nucleus of the stria terminalis, islands of Calleja, claustrum, olfactory tubercle, and central nucleus of the amygdala; lower levels were seen in the caudate, putamen, medial septum, diagonal band nucleus, and nucleus basalis of Meynert. Adjacent sections processed for cholinesterase histochemistry demonstrated a regional overlap between the distribution of labeled neurotensin binding sites and that of intense acetylcholinesterase staining in all of the above regions, except in the bed nucleus of the stria terminalis, claustrum, and central amygdaloid nucleus, where dense 125I-neurotensin labeling was detected over areas containing only weak to moderate cholinesterase staining. At higher magnification, 125I-neurotensin-labeled binding sites in the islands of Calleja, supraoptic nucleus of the hypothalamus, medial septum, diagonal band nucleus, and nucleus basalis of Meynert were selectively associated with neuronal perikarya found to be cholinesterase-positive in adjacent sections. Moderate 125I-neurotensin binding was also apparent over the cholinesterase-reactive neuropil of these latter three regions. These data suggest that neurotensin (NT) may directly influence the activity of magnocellular cholinergic neurons in the human basal forebrain, and may be involved in the physiopathology of dementing disorders such as Alzheimer's disease, in which these neurons have been shown to be affected.

Developmental expression of somatostatin in mouse brain. I. Immunocytochemical studies

The postnatal development of the distribution of somatostatin immunoreactive (SOMLI) neurons and fibers in the forebrain of the Balb/C mouse and their relationship to cholinergic afferents have been examined. SOMLI was first discernable in the hypothalamus on postnatal day (PND) 3 and increased gradually to reach adult levels by PND 30. In the limbic system, SOMLI is detectable at birth. In all other structures of the forebrain, SOMLI could be observed by PND 3 but the distribution, density and morphology of the immunoreactive neurons evolved over the following 2-3 weeks. In general, SOMLI cells and fibers increased for 1-3 weeks after their initial appearance and subsequently declined to achieve adult levels. The distribution pattern of SOMLI elements in adult mouse brain was similar to previous reports in rat with a few notable differences in thalamus, olfactory structures and, to a lesser degree, cortex and hippocampus. The temporal pattern of SOMLI expression in extrahypothalamus forebrain regions, during development, suggests a role of this peptide in differentiation and synapse formation. Such an hypothesis receives further support from neonatal lesions of the basal forebrain which resulted in transient cortical cholinergic deafferentation, a delay of cortical differentiation and a transient increase in the number of SOMLI cells in cortex.

Localization of somatostatin-like immunoreactive fibres in the trigeminal principal sensory nucleus of the cat

The location and distribution of nerve fibres and terminals displaying somatostatin-(SOM)-like immunoreactivity (LI) has been examined in cat trigeminal principal sensory nucleus (Vp) using the peroxidase-antiperoxidase technique. The varicose SOM-LI nerve fibres form a fine network in the Vp. SOM-positive terminals are distributed throughout Vp but they are particularly abundant in the ventral subdivision of the nucleus (Vpv). The labelled terminals make predominantly asymmetric axodendritic synaptic contacts. SOM-LI terminals only rarely form symmetrical synapses with non-reactive neuronal elements and are also present free in the neuropil. No SOM-LI perikarya are detected in the Vp. The results of the present study suggest that the majority, if not all, of SOM-LI fibres in the Vp are probably of primary afferent origin and may be involved in relaying trigeminal sensation to neuron located in this brain area.

Peptidergic neurons in the basal forebrain magnocellular complex of the rhesus monkey

The basal forebrain magnocellular complex of primates is defined by the presence of large, hyperchromic, usually cholinergic neurons in the nucleus basalis of Meynert and nucleus of the diagonal band of Broca. Because there is growing evidence for noncholinergic neuronal elements in the basal forebrain complex, five neuropeptides and the enzyme choline acetyltransferase were studied immunocytochemically in this region of rhesus monkeys. Galaninlike immunoreactivity coexists with choline-acetyl-transferase-like immunoreactivity in most large neurons and in some smaller neurons of the primate nucleus basalis and nucleus of the diagnonal band. Four other peptides show immunoreactivity in more limited regions of the basal forebrain complex, usually in separate smaller, noncholinergic neurons. Numerous small, somatostatinlike-immunoreactive neurons occupy primarily anterior and intermediate segments of the nucleus basalis, especially laterally and ventrally. Somewhat fewer, small neuropeptide Y-like-immunoreactive somata are found in the same regions. Neurons that show neurotensinlike immunoreactivity are slightly larger than cells that contain immunoreactivity for somatostatin or neuropeptide Y, but these neurons also occur mainly in anterior and intermediate parts of the nucleus basalis. Overall, the usually small, leucine-enkephalin-like-immunoreactive neurons are infrequent in the basal forebrain complex and are most abundant in the rostral intermediate nucleus basalis. Thus, neurons that appear to contain somatostatin, neuropeptide Y, neurotensin, or enkephalin mingle with cholinergic/galaninergic neurons only in some subdivisions of the nucleus basalis/nucleus of the diagonal band, and their distributions suggest that some of these small neurons could be associated with structures that overlap with cholinergic neurons of the labyrinthine basal forebrain magnocellular complex. We also have found light microscopic evidence for innervation of basal forebrain cholinergic neurons by boutons that contain galanin-, somatostatin-, neuropeptide Y-, neurotensin-, or enkephalinlike immunoreactivity. The origins and functions of these putative synapses remain to be determined.

Chemoanatomic compartments in the human bed nucleus of the stria terminalis

Recent studies have indicated that peptidergic inputs to the bed nucleus of the stria terminalis are more developed in man than in rodents. To facilitate interspecies comparisons, the definition of the chemoanatomical subdivisions of the human bed nucleus of the stria terminalis was attempted. The immunocytochemistry of synenkephalin, [Met]enkephalin, somatostatin, and tyrosine hydroxylase was analysed on four verticofrontal levels in five control subjects. Four principal sectors were identified in the bed nucleus of the stria terminalis: (1) lateral, displaying an irregular patchy terminal innervation overlapping for the four markers studied; (2) central, characterized by a high density of somatostatin neurons, by pericellular basket-like formations for all markers, and by a shell of dense somatostatin innervation; (3) medial, characterized by a less dense aminergic and peptidergic innervation; and (4) lateroventral, where peptidergic (somatostatin and enkephalin) peridendritic plexuses were prominent. Double-labeling analyses showed that the somatostatin, enkephalin and tyrosine hydroxylase-like immunoreactive terminals rarely converged on the same soma or dendrite even in areas where they appeared closely interdigitated. The differences and similarities of these sectors with those defined in the rat are discussed; a marked development of the lateral and ventral bed nucleus of the stria terminalis is emphasized in man. Islands with dense peptidergic innervation, similar to the ventral bed nucleus of the stria terminalis, extended into the sublenticular substantia innominata (intercalated between the ventral pallidum and the basal magnocellular nucleus). This supports the existence of an extended amygdaloid complex from the amygdala to the bed nucleus of the stria terminalis in the human brain, as has been proposed in the rat. In relation to the literature, the present findings suggest the increasing importance of the central and lateral amygdaloid-bed nucleus of the stria terminals components and of their cortical connections in man while the medial amygdala-bed nucleus of the stria terminalis nuclei, which are preferentially connected to the olfactory system, appear less developed.

Further studies of the effects of somatostatin and related peptides in area CA1 of rabbit hippocampus

1. In slice studies of mature and immature CA1 hippocampal pyramidal cells from rabbit, somatostatin 14 (SS14), the related peptide somatostatin 28(1-12) [SS(1-12)], and the synthetic analogue of somatostatin 14, SMS-201995 (SMS), had similar effects. When pressure-ejected onto cell somata, these peptides elicited depolarizations, often accompanied by action potential discharge. When applied to dendrites, the peptides produced depolarizations or hyperpolarizations. 2. When a large amount of one of the three somatostatin-related (SS) peptides was applied to the slice at some distance from the impaled cell, hyperpolarizations were observed that were not always blocked by tetrodotoxin (TTX) or low Ca2+. Since SS peptides were also found to depolarize interneurons in area CA1, it seems likely that the hyperpolarizations that were blocked by TTX or low Ca2+ were mediated via excitation of interneurons that in turn hyperpolarized pyramidal cells. 3. All SS peptides also had long-lasting effects on CA1 pyramidal cells that led to spontaneous firing of action potentials and an increase in the number of action potentials discharged in response to a given depolarizing current pulse; the spontaneous discharge effect was blocked by TTX or low Ca2+ plus Mn2+ and, thus, appeared to have a presynaptic mechanism. However, the increase in discharge in response to a constant depolarizing current pulse was not dependent on intact synaptic transmission and, therefore, was attributable to a direct postsynaptic effect of the SS peptides.

New perspectives in basal forebrain organization of special relevance for neuropsychiatric disorders: the striatopallidal, amygdaloid, and corticopetal components of substantia innominata

The basal forebrain is critically involved in functions representing the highest levels of integration. Only recently has a relatively clear anatomical picture of this important area begun to emerge. The territory that has generally been referred to as the "substantia innominata" appears to be composed of portions of three recognizable forebrain structures: the ventral striatopallidal system, the extended amygdala and the magnocellular corticopetal system. (1) Rostrally, the striatopallidal system reaches ventrally to the base of the brain. (2) Caudal to the ventral extension of the striatopallidal system elements of the centromedial amygdala and bed nucleus of the stria terminalis are merged so that these two areas together with this subpallidal corridor form a large forebrain unit that might be described as an "extended amygdala". (3) Large cholinergic and non-cholinergic corticopetal neurons form a more or less continuous aggregate that is interwoven with the striatopallidal and extended amygdala systems in basal forebrain. Consideration of morphological and connectional characteristics of basal forebrain suggests that the corticopetal cell groups, together with magnocellular elements of the striatum, serve similar functional roles for the striatopallidal system, the extended amygdala, and the septal-diagonal band complex. Specifically, the output of medium spiny neurons in striatum, extended amygdala, and lateral septum are directed toward somewhat larger sparsely or moderately spiny neurons with radiating dendrites which in turn project to diencephalon and brainstem or provide either local feedback (e.g. in striatum) or distal feedback to cortex. The functional implications of this parallel processing of descending forebrain afferents are discussed.