Somatostatinlike immunoreactive neurons in the hedgehog (Erinaceus europaeus) and the sheep (Ovis aries) central nervous system

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.

Somatostatin-14 neurons in the ovine hypothalamus: colocalization with estrogen receptor alpha and somatostatin-28(1-12) immunoreactivity, and activation in response to estradiol

Pituitary gland growth hormone (GH) secretion is influenced by two hypothalamic neuropeptides: growth hormone-releasing hormone (GHRH) and somatostatin. Recent data also suggest that estrogen modulates GH release, particularly at the time of the preovulatory luteinizing hormone surge, when a coincident surge of GH is observed in sheep. The GHRH neurons do not possess estrogen receptor alpha (ERalpha), suggesting that estrogen does not act directly on GHRH neurons. Similarly, few somatotropes express ERalpha, suggesting a weak pituitary effect of estradiol on GH. It was hypothesized, therefore, that estradiol may affect somatostatin neurons to modulate GH release from the pituitary. Using immunocytochemical approaches, the present study revealed that although somatostatin neurons were located in several hypothalamic sites, only those in the arcuate nucleus (13% +/- 2%) and ventromedial nucleus (VMN; 29% +/- 1%) expressed ERalpha. In addition, we found that all neurons immunoreactive for somatostatin-14 were also immunoreactive for somatostatin-28(1-12). To determine whether increased GH secretion in response to estradiol is through modulation of GHRH and/or somatostatin neuronal activity, a final study investigated whether c-fos expression increased in somatostatin- and GHRH-immunoreactive cells at the time of the estradiol-induced LH surge in intact anestrous ewes. Estradiol significantly (P < 0.05) increased the percentage of GHRH (estradiol, 75% +/- 3%; no estradiol, 19% +/- 2%) neurons expressing c-fos in the hypothalamus. The percentage of somatostatin-immunoreactive neurons coexpressing c-fos in the estradiol-treated animals was significantly (P < 0.05) higher (periventricular, 44% +/- 3%; arcuate, 72% +/- 5%; VMN, 81% +/- 5%) than in the control animals (periventricular, 22% +/- 1%; arcuate, 29% +/- 3%; VMN, 31% +/- 3%). The present study suggests that estradiol modulates the activity of GHRH and somatostatin neurons but that this effect is most likely mediated through an indirect interneuronal pathway.

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.

Distribution of galanin immunoreactivity in the sheep diencephalon

Although the physiological role of galanin has been demonstrated in several endocrine regulations in sheep, the anatomical characteristics of this neuronal system has never been studied. The distribution of galanin-containing neurones was described by immunohistochemistry using galanin antiserum in the diencephalon of adult ewes, both ovariectomized or treated with colchicine. Galanin-immunoreactivity was found throughout the diencephalon. In the ovariectomized ewes, galanin-immunoreactive neurones were mainly observed in the medial preoptic area and the infundibular nucleus. The highest density of immunoreactive fibres was found in the external layer of the median eminence. Numerous galanin-immunoreactive fibres were also observed in the preoptic area, the mediobasal hypothalamus, the periphery of the supraoptic and the paraventricular nuclei. With colchicine treatment, the number of labelled neurones increased, and additional galanin-immunoreactive perikarya were observed in the bed nucleus of the stria terminalis, the lateral septum, the supraoptic, the paraventricular and the periventricular nuclei and the paraventricular nucleus of the thalamus. In the caudal part of the diencephalon, the density of labelled neurones was lower in both groups of animals than in other species studied. Regardless of treatment, labelling was not seen in the suprachiasmatic nucleus and only rarely in the ventromedial nucleus. These results describe, for the first time, the distribution of galanin-immunoreactive neurones in the sheep diencephalon. Compared to other species studied, distribution in the sheep diencephalon has several distinct differences. In ovariectomized animals, the medial preoptic area presents more labelled neurones in sheep than in monkeys, whereas in the supraoptic nucleus the density of labelled neurones is lower in sheep than in humans or opossums. After colchicine treatment only very few differences were observed between sheep and rats, but in contrast to other species, the suprachiasmatic nucleus of the sheep does not contain labelled neurones.

Localization of the preprosomatostatin-mRNA by in situ hybridization in the ewe hypothalamus

The peptidergic neurohormone somatostatin (SRIF) derives from a precursor called preprosomatostatin (PPS) by proteolysis. We have isolated by RT-PCR and sequenced a partial cDNA coding for the ovine PPS. It contains a 348 base pairs coding sequence that shares strong similarities with previously cloned mammalian cDNAs. The ovine cDNA was used to synthesize radiolabeled cRNA to probe the PPS mRNA in the ewe hypothalamus by in situ hybridization. The PPS mRNA-containing cells are widely distributed in the hypothalamus. According to the number of silver grains over a cell, they show various staining intensities. The distribution of the PPS mRNA is in good agreement with that of the peptide previously determined using immunohistochemistry. The strongest labeled areas include the periventricular region of the paraventricular nucleus and the lateral division of the ventromedial nucleus. The difference in labeling intensity observed in the diverse populations of labeled neurons could reflect various levels of neuronal activity.

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.

Distribution and pharmacological characterization of somatostatin receptor binding sites in the sheep brain

Somatostatin binding sites have been localized and quantified in the sheep brain using 125I-Tyr0-DTrp8-somatostatin, by quantitative high resolution light microscopic autoradiography. Sections were analyzed by densitometry on radioautographic film, and subsequently on slides coated with photoemulsion. Specific somatostatin binding sites were concentrated in the medial habenula, superior colliculus, dorsal motor nucleus of the vagus nerve, inferior olive, spinal trigeminal nucleus, and cerebellum. In competition experiments, octreotide, a sst2/sst3/sst5 selective agonist only partially displaced 125I-Tyr0-DTrp8-somatostatin in the three cerebellar layers while it was fully active as compared to somatostatin 14 and 28 in the deeper layers of the parietal cortex. Moderate to low somatostatin receptor densities were present in the mesencephalic periaqueductal gray, dorsal raphe, thalamic paraventricular nucleus, interpeduncular nucleus, pineal gland, dorsal tegmental, dorsolateral tegmental and parabrachial nuclei, nucleus of the solitary tract. The distribution of somatostatin binding sites generally correlates with the data obtained on slides dipped in photoemulsion which provided better resolution and more precise localization. In most of the labeled areas, 125I-Tyr0-DTrp8-somatostatin receptor binding was distributed between both neuropil and perikarya. Perikarya bearing 125I-Tyr0-DTrp8-somatostatin receptors were observed in areas which did not display detectable binding sites on film such as the preoptic-anterior hypothalamic complex and arcuate nucleus and in the locus coeruleus. In conclusion, the distribution of 125I-Tyr0-DTrp8-somatostatin binding sites in sheep brain is very reminiscent of other mammals being closer to the human than to rodents.

Distribution of melanin-concentrating hormone (MCH)-like immunoreactivity in neurons of the diencephalon of sheep

An immunohistochemical study with an antiserum raised against salmon melanin concentrating-hormone has demonstrated the presence of numerous melanin concentrating-hormone-immunoreactive neurons in the lateral hypothalamic areas of the sheep. The pattern of distribution of these perikarya is similar to that of rodents and primates. In sheep, however, melanin concentrating-hormone-immunoreactive neurons appeared to form two gatherings: the first is situated ventromedially to the internal capsule and the second in the dorsolateral hypothalamus. In these areas, numerous immunostained perikarya are observed. Compared to the rats, labelled neurons extended more caudally in the ventral tegmental area and more rostrally above the optic chiasma. Compared to primates, these neurons are less numerous in the periventricular area. In our study, dense networks of melanin concentrating-hormone-immunoreactive varicose fibers were observed in the supramamillary nucleus, the lateral hypothalamus, the nucleus medialis thalami and nucleus reuniens and in the bed nucleus of the stria terminalis.

Localization of molluscan R15 alpha 2 peptide immunoreactivity in the mammalian brain

The R15 neuropeptides have been identified in the marine mollusc Aplysia californica. They compose a new family of neuropeptides acting on the cardiovascular, digestive, respiratory, reproductive and nervous systems. In this report we show that one of the members of the R15 neuropeptide family, the alpha 2 peptide is conserved in lower mammals. We have identified R15 alpha 2 immunoreactive neurons in the neurosecretory cell groups of the hypothalamus and in the brainstem of the hedgehog (Erinaceus europaeus). The majority of labeled cells were localized to the anterior periventricular part of the paraventricular nucleus and the accessory neurosecretory cell groups in the lateral hypothalamus as well as to the dorsal part of the nucleus tractus solitarii. In the paraventricular nucleus, R15 alpha 2 immunoreactive neurons also exhibit immunoreactivity for oxytocin, corticotropin releasing factor, vasoactive intestinal polypeptide and for the FMRFamide-related peptide which we found to be conserved in the hedgehog brain as well. No complete colocalization of R15 alpha 2 with any of the neuroactive substances tested, is observed. The highest degree of coexistence occurs with FMRFamide-related peptide, followed by vasoactive intestinal polypeptide, oxytocin and corticotropin releasing factor.

Somatostatin-immunoreactivity in the hippocampus of mouse, rat, guinea pig, and rabbit

The hippocampi of species commonly used for in vitro physiologic studies were examined to determine if there were species-specific and regional differences in somatostatin immunoreactivity. The distributions of somatostatin-immunoreactive somata and fiber plexuses were determined, and the concentration of somatostatin along the septotemporal axis of the hippocampus was measured using a radioimmunoassay. There are many similarities in the patterns of somatostatin immunoreactivity in the hippocampi of mice, rats, guinea pigs, and rabbits. All species had a relatively even distribution of somatostatin-positive perikarya across three fields of the hippocampus (dentate gyrus, CA3, and CA1-2), a similar distribution of somatostatin-immunoreactive perikarya across the strata of the CA1-2 field and the dentate gyrus; and more somatostatin-positive cells in temporal than in septal hippocampus. However, there are species-specific differences in the distribution of somatostatin-immunoreactive perikarya across the strata of CA3. In addition, unlike the other species examined, mice appeared not to have a somatostatin-immunoreactive fiber plexus in the molecular layer of the dentate gyrus. The functional significance of these differences remains to be determined.

Presence of C-flanking peptide of neuropeptide Y(C-PON)-immunoreactive neurons in the olfactory cortex of the hedgehog (Erinaceus europaeus)

Although the presence of the neuropeptide C-terminal flanking peptide of neuropeptide Y, C-PON, has been described in the central nervous system (CNS) of mammals, to date there is no information related with its involvement in brain functions. An analysis of the location of C-PON in specific neuronal circuits of known anatomy and physiological action should provide light on its physiological role. The presence, distribution and morphology of C-PON-containing neurons in the olfactory cortex of the hedgehog was studied by immunocytochemistry. Immunoreactive neurons to C-PON were widely distributed in the three layers of the olfactory cortex of this primitive mammal. These neurons were medium sized and showed two or three immunostained, poorly branched, dendrites. In some positive neurons, a fine, beaded axon-like process was also immunostained. Although direct evidence of a physiological function of C-PON in the olfactory cortex of the hedgehog cannot be accurately stated from our findings, the morphology of C-PON neurons and their distribution in the deep cortical layers, where the majority of pyramidal neurons are located, suggest that this neuropeptide may play a role in the intrinsic neuronal circuitry of the relatively well-developed hedgehog paleocortex. A regulatory vascular role of some peptide-immunoreactive neurons can be inferred since occasional C-PON-positive neurons have been located near blood vessels.

Acute changes in growth hormone-releasing hormone secretion after injection of BIM 23014, a long acting somatostatin analog, in rams

BIM 23014 is a somatostatin analog displaying an increased biological half life due to resistance to enzymatic degradation. This peptide inhibits GH release directly at the level of pituitary somatotrophs. In addition, an action of BIM 23014 at the level of the hypothalamus is possible since somatostatinergic fibers and receptors have been identified on GH-RH neurons. To evaluate the effect of BIM 23014 on GH-RH secretion, hypophysial portal blood (HPB) was continuously collected in conscious sheep. Twelve rams (40-45 kg, 9-month-old) with chronically implanted perihypophysial cannulae were i.v. injected with BIM 23014 (1 mg) or saline. HPB and jugular blood were collected for 3-5 hours before and after the injection for the determinations of GH-RH and GH concentrations respectively. The acute injection of BIM 23014 induced a rapid decrease of plasma GH within the first two hours. Simultaneously, GH-RH in HPB decreased significantly. After reaching a nadir, GH concentrations increased to values greater than baseline. A similar rebound in GH-RH levels in HPB was also observed. These data indicate that BIM 23014 acts at the level of GH-RH hypothalamic neurons, in addition to its well-know effect on the pituitary gland.

Somatostatin- and neuropeptide Y-like immunoreactivity in the dentate area, hippocampus, and subiculum of the domestic pig

With the principal aim of providing baseline observations for future experimental studies, the distribution of somatostatin-like and neuropeptide Y-like immunoreactivities is described in the dentate area, hippocampus, and subiculum of the domestic pig (Sus scrofa domesticus) and compared with the distribution described in other mammals. Intensely stained somatostatin-like immunoreactive nerve cell bodies were present throughout the region, with highest densities in the dentate hilus, stratum radiatum and stratum oriens of the hippocampal regio inferior, stratum oriens of the hippocampal regio superior, and in the subicular cell layer. Somatostatin-like immunoreactive terminals were represented by both stained fibers and stained puncta. Scattered somatostatin-like immunoreactive nerve fibers were seen in most areas, but regular fiber plexuses were present in the dentate molecular layer and dentate hilus, stratum moleculare of the hippocampus, and in the subicular plexiform layer. Somatostatin-like immunoreactive puncta were seen in the dentate molecular layer, stratum moleculare of the hippocampus, and in the subicular plexiform layer. Neuropeptide Y-like immunoreactive nerve cell bodies were less numerous than somatostatin-like immunoreactive ones. They were mainly seen in the dentate granule cell layer and dentate hilus, stratum radiatum and stratum oriens of the hippocampus, and in the subicular cell layer. Intensely stained neuropeptide Y-like immunoreactive fibers were numerous, and present in all areas examined. They formed fiber plexuses in the dentate molecular layer and dentate hilus, stratum moleculare of the hippocampal regio superior, and in the subicular plexiform layer. Neuropeptide Y-like immunoreactive puncta were present in the dentate molecular layer, stratum moleculare of the hippocampus, and in the subicular plexiform layer. Consistent and very characteristic variation in the distribution of somatostatin-like and neuropeptide Y-like immunoreactivity was found along the septotemporal axis of the hippocampus. The distribution of somatostatin-like and neuropeptide Y-like neurons and terminals in the domestic pig displayed striking similarities with the basic pattern of organization of these neuropeptides in other species, although more subtle species-specific characteristics were also observed in the pig.

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)

Claustrum in the hedgehog (Erinaceus europaeus) brain: cytoarchitecture and connections with cortical and subcortical structures

The cytoarchitecture of the claustrum in the hedgehog (Erinaceus europaeus) brain, the morphology of its neurons, and the efferent connections with cortical and subcortical structures were studied with the Nissl and Klüver-Barrera, the Golgi, and the horseradish peroxidase methods. It was found that the claustrum is a well developed nucleus in the hedgehog telencephalon and, as in other mammals, is divided into dorsal and ventral parts. In Golgi-stained sections, spiny multipolar cells are the predominant neurons of both the dorsal and the ventral claustrum and are projection neurons. Aspiny multipolar neurons with fewer, often beaded, dendrites constitute a minority in both divisions and are interneurons. Injections of wheat germ agglutinin-horseradish peroxidase (WGA-HRP) in the prefrontal, motor, somatosensory, auditory and visual areas, and HRP or WGA-HRP injections in the thalamus showed that: (1) the claustroneocortical projections originate in the dorsal claustrum and are distributed to the entire neocortex; these projections are mainly ipsilateral but some also originate contralaterally; (2) the claustroneocortical projections show a rough topographic organization; there exists a substantial degree of overlap; and (3) the claustrothalamic projection, arising throughout the dorsal claustrum, is strictly ipsilateral. No evidence of a thalamoclaustral projection was found. The present results suggest that, although the hedgehog has been referred to as a "paleocortical mammal" owing to the great development of its rhinencephalic structures in comparison with its small neocortex, the dorsal claustrum is well developed and is connected with all neocortical areas as well as with the thalamus, establishing it as a key structure in the hedgehog forebrain.

Coexistence of neuropeptides in the hypothalamic paraventricular nucleus of the sheep

The chemical organization of the hypothalamic paraventricular nucleus (NPV) of the sheep was studied immunocytochemically by using antisera raised against oxytocin (OXY), ovine corticotropin releasing factor (CRF), somatostatin (SRIF), neurotensin (NT) and vasoactive intestinal polypeptide (VIP). Examination of immunocytochemically stained frozen, 30-40 microns thick, and paraffin serial, 6 microns thick, sections has shown that chemically specified subsets of neurons are not strictly demarcated anatomically and that OXY and SRIF or CRF and VIP are jointly expressed by certain subpopulations of neurons which are different from that producing both OXY and CRF.

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.

Anatomy of somatostatin-immunoreactive fibres and cell bodies in the rat trigeminal subnucleus caudalis

The distribution of somatostatin-immunoreactive fibres and cells has been analysed in the rat spinal trigeminal subnucleus caudalis. Immunoreactive fibres are most concentrated in lamina II outer but fibres and terminals occur also in lamina I, lamina II inner, and scattered in the magnocellular region and neighbouring lateral reticular area. Immunoreactive cells occur in laminae I and II and in the magnocellular region of the nucleus but are most abundant in lamina II inner. The lamina II immunoreactive cells are morphologically heterogeneous and include types which are similar to cells described in Golgi studies such as stalked and islet cells. In order to distinguish somatostatin-immunoreactive primary afferents from intrinsic sources of somatostatin such as the lamina II neurons, we have used a monoclonal antibody (LD2) which is specific for primary afferents. Using dual-colour immunofluorescence we have shown that all somatostatin-immunoreactive cells in the trigeminal ganglia express LD2 immunoreactivity. Quantitative immunostaining density profiles indicate that LD2- and somatostatin-immunoreactive fibres overlap mainly in lamina II outer and dual-colour immunofluorescence confirms that this region contains somatostatin and LD2 double-labelled fibres. In contrast, lamina I contains more somatostatin- than LD2-immunoreactive fibres and fewer double-labelled fibres. The presence of double-labelled fibres in outer lamina II indicates that somatostatin-immunoreactive primary afferents terminate largely in this sublamina. However, the small number of double-labelled fibres found suggests that somatostatin-immunoreactive fibres in laminae I and II are derived mainly from intrinsic sources such as the various types of lamina II neurons.

Ultrastructural localization of somatostatin-like immunoreactivity in the rat dentate gyrus

Neurons containing somatostatin (SOM) are enriched in the dentate gyrus. We sought to establish the ultrastructural localization of this peptide in the dentate gyrus of the rat brain with a double-bridged peroxidase-antiperoxidase (PAP) method localizing antisera directed against somatostatin (SOM)-28 and SOM-28. Initial light microscopic observations confirmed that the majority of perikarya and thick varicose processes with intense SOM-like immunoreactivity (SOM-LI) were observed in the hilus. Fine varicose processes with SOM-LI were found throughout all layers of the dentate gyrus but were most intense in the outer third of the molecular layer (ML), where an occasional perikaryon with SOM-LI was seen. By electron microscopy, SOM-LI was found in neuronal perikarya, dendrites, axons, and axon terminals. Two types of SOM-containing perikarya were observed. The first type was small (6-10 microns), round or avoid, and had a labeled cytoplasma with abundant Golgi complexes and a dense accumulation of PAP-reaction product. The second type of perikarya was larger (11-16 microns) and had a more abundant cytoplasm than the first type, but the Golgi complexes did not appear labeled. Most (96% of 374) of the synapses on the SOM-labeled perikarya and dendrites were from terminals without SOM-LI which formed nearly equal proportions of asymmetric and symmetric junctions. The remainder of the presynaptic terminals contained SOM-LI and made primarily symmetric synapses. Synaptic junctions from both unlabeled and labeled terminals were primarily on the shafts of the small (0.5-1.5 microns) SOM-immunoreactive dendrites. The terminals with SOM-LI (0.25-1.3 microns) contained many small, clear vesicles and from zero to four large dense-core vesicles. Terminals with SOM-LI were associated 1) with one unlabeled perikaryon or dendrite (49% of 215 in the hilus; 76% of 326 in the ML); 2) with two unlabeled perikarya or dendrites simultaneously (5% hilus; 4% ML); and 3) with one SOM-containing perikaryon or dendrite (6% hilus; 3% ML). In all three types of associations, synaptic contacts on perikarya were few while the majority were with small (distal) dendrites. Moreover, most of the terminals with SOM-LI formed symmetric junctions or lacked membrane specializations but were without any apparent glial intervention in the plane of section analyzed. The remaining SOM-labeled terminals (40% hilus; 17% ML) were without any apparent synaptic relations. However, a few of these terminals were in direct apposition to other terminals, some of which were also SOM-immunoreactive.(ABSTRACT TRUNCATED AT 400 WORDS)

Distribution of neuropeptides in the infundibular nucleus of the sheep

The distribution of neurons exhibiting somatostatin (SRIF)-, neuropeptide Y (NPY)-, beta-endorphin- and neurotensin (NT)-like immunoreactivity within the infundibular nucleus (NI) of the sheep, and the extent of coexistence of the above peptides within individual neurons of the NI were investigated with immunocytochemical techniques. Our results show that the above neurochemical types of neurons exhibit specific and largely non-overlapping patterns of distribution within the NI of the sheep. Furthermore, the coexistence of these peptides within neurons of the NI is very limited, as from all possible permutations checked, only SRIF and NPY were found together in a small number of cells.

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.

An electron microscopic study of somatostatin immunoreactive structures in lamina II of the rat spinal cord

We are reporting the results of a light and electron microscopic study of somatostatin (SOM) immunoreactive (I) structures in lamina II of the lumbar spinal cord of the rat. At the light microscopic level, the observed distribution and morphology of SOM-I cell bodies and fibers confirmed published studies. At the electron microscopic level, SOM immunostaining in perikarya was localized to the golgi region. Immunostaining in cell bodies could be enhanced by colchicine treatment and after such treatment, it was noticeably increased in the cytoplasm. Synaptic contacts on SOM-I cell bodies were rare and SOM-I axons contacted unlabeled somata in lamina II. Some SOM-I dendrites participate in glomerular arrangements and they exhibited postsynaptic densities adjacent to the central profile of the glomerulus. Nonglomerular SOM-I dendrites and spines were postsynaptic to vesicles containing axons. Vesicle containing SOM-I axons presynaptic to larger dendrites were also observed in the outer portion of lamina II. Somatostatin has been implicated in nociception and some of the SOM-I structures reported here may be the anatomical substrates for SOM-induced analgesia.

Anatomical distribution of somatostatin immunoreactivity in the infant brainstem

The distribution of somatostatin-immunoreactive structures in the infant brainstem was investigated using the peroxidase-antiperoxidase technique. A wide distribution of somatostatin-immunoreactive cell bodies and fibers was observed throughout the brainstem. Numerous somatostatin-immunoreactive cell bodies and fibers were present in several areas of the brainstem including the substantia grisea centralis and the reticular formation. Some immunoreactive cell bodies were seen in cranial nerve nuclei such as the nucleus praepositus, the nucleus nervi hypoglossi and the vestibular nuclei. Immunoreactive fibers were seen in the nucleus cuneatus, the locus coeruleus, the nucleus tractus solitarius, the nucleus ambiguus, the nucleus tractus spinalis nervi trigemini and the dorsal horn of the spinal cord. These data were in agreement with previous works on the human adult. However, a high density of somatostatin-immunoreactive cell bodies and fibers in the interpeduncular nucleus and in the nucleus centralis superior, and a dense network of somatostatin-immunoreactive fibers in the dorsal part of the nucleus inferior olivarius, were also observed. The role of somatostatin in some brainstem nuclei and its probable implication in some specific neuropathological diseases of the infant brainstem is discussed.

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.

Somatostatin immunoreactive structures in the developing rat spinal cord

Somatostatin immunoreactive (SOM-I) perikarya were first observed in the ventral horn at E12, in the presumptive intermediate gray area at E14, and in the alar plate of the rostral spinal cord at E14. In general, after their initial appearance, their density increased and then decreased during development. A moderate density of SOM-I varicosities became obvious in the superficial laminae of the E20 dorsal horn. By E12 a few SOM-I perikarya, interpreted to be dorsal root ganglia, were observed lateral to the spinal cord, and by E13, SOM immunoreactivity was visualized within the central and peripheral processes of dorsal root ganglion axons. In the marginal zone, SOM-I fibers were first demonstrable in the ventral funiculus at E14, and in the lateral funiculus at E15. After their initial appearance, their density increased and then decreased with age, with the exception of the dorsal part of the lateral funiculus where it increased at the early stages of development to an apparently stable level. The early detection of SOM immunoreactivity in specific spinal regions corresponds well with the birth dates of cells in those regions. This indicates that the SOM-I cells are capable of synthesizing the substance at least as early as they have entered their final cell division.

Somatostatin and neuropeptide Y are almost exclusively found in the same neurons in the telencephalon of turtles

In mammals, somatostatin and neuropeptide Y (NPY) are largely found in the same neurons of the telencephalon. To determine if this is a phylogenetically ancient feature of telencephalic organization, the brain of red-eared turtles was examined using immunofluorescence double-labeling procedures. The results showed that somatostatin and NPY are found almost exclusively in the same neurons in the telencephalon of turtles, but these neuropeptides rarely co-occur in neurons outside the telencephalon. Thus, the extensive co-occurrence of NPY and somatostatin appears to be a feature of telencephalic organization that was present in the reptilian common ancestors of mammals and modern reptiles.

Distribution of somatostatinlike immunoreactivity in the brain of the little brown bat (Myotis lucifugus)

The distribution of somatostatinlike immunoreactive (SLI) perikarya, axons, and terminals was mapped in subcortical areas of the brain of the little brown bat, Myotis lucifugus, using light microscopic immunocytochemistry. A preponderance of immunoreactivity was localized in reticular, limbic, and hypothalamic areas including: 1) in the forebrain: the bed nucleus of the stria terminalis; lateral preoptic, dorsal, anterior, lateral and posterior hypothalamic areas; amygdaloid, periventricular, arcuate, supraoptic, suprachiasmatic, ventromedial, dorsomedial, paraventricular, lateral and medial mammillary, and lateral septal nuclei; the nucleus of the diagonal band of Broca and nucleus accumbens septi; 2) in the midbrain: the periaqueductal gray, interpeduncular, dorsal and ventral tegmental, pretectal, and Edinger-Westphal nuclei; and 3) in the hindbrain: the superior central and parabrachial nuclei, nucleus incertus, locus coeruleus, and nucleus reticularis gigantocellularis. Other areas containing SLI included the striatum (caudate nucleus and putamen), zona incerta, infundibulum, supramammillary and premammillary nuclei, medial and dorsal lateral geniculate nuclei, entopeduncular nucleus, lateral habenular nucleus, central medial thalamic nucleus, central tegmental field, linear and dorsal raphe nuclei, nucleus of Darkschewitsch, superior and inferior colliculi, nucleus ruber, substantia nigra, mesencephalic nucleus of V, inferior olivary nucleus, inferior central nucleus, nucleus prepositus, and deep cerebellar nuclei. While these results were similar in some respects to those previously reported in rodents, they also provided interesting contrasts.

Immunohistochemical distribution of cholecystokinin, dynorphin A and Met-enkephalin neurons in sheep hypothalamus

The distribution of cholecystokinin (CCK)-, Met-enkephalin (M-ENK)- and dynorphin (DYN)-like immunoreactive perikarya were examined in the sheep hypothalamus using the peroxidase-anti-peroxidase technique. CCK- and DYN-containing neurons were found primarily in the suprachiasmatic nucleus (SCH) and supraoptic nucleus (SO). No CCK- or DYN-containing neurons were found in the paraventricular nucleus (PVN). M-ENK-containing neurons were found mainly in the PVN of the hypothalamus. In addition, M-ENK neurons were found in the dorsomedial (DMH), lateral (LH), anterior (AH) and periventricular hypothalamic areas. The distribution of these neuropeptides may provide a basis for understanding differences in responsiveness to centrally administered peptides.

VIP- and CCK-like-immunoreactive neurons in the hedgehog (Erinaceus europaeus) and sheep (Ovis aries) brain

The distribution pattern and the morphology of vasoactive intestinal polypeptide (VIP)- and cholecystokinin (CCK)-like-immunoreactive neurons were studied in the brain of the hedgehog and the sheep by means of the peroxidase-antiperoxidase immunocytochemical method. A total of 34 hedgehogs and 26 sheep of both sexes were used. Fourteen hedgehogs and 13 sheep received an intracerebroventricular injection of colchicine that enhanced the immunostaining and revealed "new" immunoreactive cell bodies. VIP-immunoreactive bipolar and multipolar neurons were observed in both species in the cerebral cortex, hippocampal formation, amygdaloid complex, hypothalamus, and central gray substance of the midbrain. CCK-immunoreactive bipolar, bitufted, and multipolar neurons displayed a broader distribution in both mammals than VIP neurons and were found in the cerebral cortex, the hippocampal formation, the amygdaloid complex, the hypothalamus, the mesencephalon, and the pons. In the cortex, in both the hedgehog and the sheep, VIP neurons were located in all layers but were concentrated in layers II and III, with the majority being typical bipolar. CCK neurons were more numerous in the superficial layers (I-III) but were found in the deep layers as well. They were bipolar, bitufted, or multipolar in morphology. From these neurons a small percentage, which were located almost exclusively in layers II and III of the visual cortex, exhibited also VIP immunoreactivity. Perikarya of such double-labeled cells were ovoid or round in shape with one or two main processes emanating from each pole of the cell body and oriented perpendicularly to the pia. The coexistence of the two peptides within individual neurons of the cortex has not been reported in other species and its physiological significance is discussed in relation to the GABAergic neurons of the cortex.

Somatostatin 28 and neuropeptide Y innervation in the septal area and related cortical and subcortical structures of the human brain. Distribution, relationships and evidence for differential coexistence

Somatostatin 28- and neuropeptide Y-containing innervations were mapped in the human medial forebrain (eight control brains) with immunohistochemistry, using the sensitive avidin-biotin-peroxidase method. Peptidergic perikarya and fibers had an extensive distribution: they were densest in the ventral striatum (nucleus accumbens, olfactory tubercle and bed nucleus of the stria terminalis) and infralimbic cortex, of intermediate density in the medial septal area and of lowest density in the dorsal and caudal lateral septal nucleus. Somatostatin-like immunoreactive perikarya and fibers were generally more numerous than the neuropeptide Y-like immunoreactive ones, but more faintly labeled. Their pattern of distribution was strikingly similar in some of the limbic structures studied but clearly distinct in others. Excellent overlap of neuropeptide Y and somatostatin-like immunoreactivity was detected in: (1) the medial septal area, where innervation occasionally formed perivascular clusters; (2) the nucleus accumbens and olfactory tubercle, characterized by dense patchy innervation; and (3) the laterodorsal septal nucleus, scarcely innervated. In the latter structures, most peptidergic neurons were double-labeled. On the other hand, both peptidergic innervations clearly differed in the lateroventral septal nucleus and the bed nucleus of the stria terminalis which contained distinct clusters of somatostatin-like immunoreactive neurons devoid of neuropeptide Y-like immunoreactivity. Also, the perineuronal and peridendritic axonal plexuses ('woolly fibers') present in these structures were only labeled with somatostatin. In the infralimbic cortex, the relation between the peptides varied according to the cortical laminae. Coexistence of somatostatin and neuropeptide Y frequently occurred in layer VI and in the subcortical white matter, whereas layer V and particularly layers II and III contained a contingent of neurons labeled only with somatostatin. Dense horizontal terminal networks in layers I and VI however were similar for both peptides. These findings support the existence of two different types of somatostatin-like immunoreactive perikarya as regards colocalization with neuropeptide Y. Their particular topographical segregation within the cortical and subcortical structures analysed suggest that they could have different connections and functional properties.(ABSTRACT TRUNCATED AT 400 WORDS)

Somatostatin-like immunoreactivity in the midbrain of the cat

Somatostatin (SS) immunoreactivity was localized in cat brain sections with an immunoperoxidase technique. Cell bodies in the midbrain containing SS immunoreactivity were found in the superficial and intermediate gray layers of the superior colliculus, the interpeduncular nucleus, the raphe, the inferior colliculus and nucleus of its brachium, the nucleus of the optic tract, and the lateral tegmental field. Additional positive neurons were seen in the parabigeminal nucleus and in the dorsal periaqueductal gray in kitten material. Immunoreactive fibers were observed in the periaqueductal gray and in the midbrain tegmentum, with particularly dense labeling just dorsal to the substantia nigra and in the parabrachial nuclei. This is the first report of the distribution of SS immunoreactivity in the midbrain of the cat. It is concluded that somatostatin has a distribution compatible with a role as a major neurotransmitter/neuromodulator within certain midbrain nuclei, especially the interpeduncular nucleus and the superior colliculus.

Retinal projections in the hedgehog (Erinaceus europaeus). An autoradiographic and horseradish peroxidase study

The retinal projections of the hedgehog were studied using tritiated leucine and horseradish peroxidase as orthograde tracers. In both series of experiments labeling was seen bilaterally in the suprachiasmatic nucleus, the dorsal and the ventral lateral geniculate nucleus, the superior colliculus, and the pretectal area and contralaterally in the terminal nuclei (dorsal, lateral and medial) of the accessory optic system. A retino-intergeniculate leaflet projection is described for the first time in this species, and its significance is discussed.

Neurotensinlike immunoreactive neurons in the hedgehog (Erinaceus europaeus) and the sheep (Ovis aries) central nervous system

Neurotensin-containing neurons in the hedgehog and sheep central nervous system were studied immunohistochemically. In both species, mapping of neurotensin neurons was achieved only after pretreatment with colchicine injected intracerebroventricularly 2 days prior to perfusion. Bipolar or multipolar neurotensin neurons, 10-30 micron in diameter, were observed in the following regions of the central nervous system of both species: medial amygdaloid nucleus, lateral septal nucleus, interstitial nucleus of the stria terminals, caudate nucleus, preoptic area, and hypothalamus. On the contrary, while immunoreactive neurons were found in the central amygdaloid nucleus, nucleus accumbens, nucleus of the diagonal band, subthalamus, superior central nucleus, dorsal raphe nucleus, central gray substance of the pons, and dorsal horn of the spinal cord of the hedgehog, respective regions of the sheep appeared to be devoid of immunoreactive perikarya. Also, in some regions, namely the hippocampal formation, the central gray substance of the midbrain, the locus coeruleus, and the nucleus of the solitary tract, neurotensin neurons were found exclusively in the latter species. The existence of these differences in the distribution pattern of neurotensin-immunoreactive neurons between the two species as well as between them and others already examined is briefly discussed.