Immunohistochemical distribution of somatostatin in the infant hypothalamus

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.

Beta-protein/A4 deposits are not associated with hyperphosphorylated tau in somatostatin neurons in the hypothalamus of Alzheimer's disease patients

With respect to the pathogenesis of Alzheimer's disease (AD), it has been hypothesized that amorphous plaques containing beta-protein/A4 (Abeta) would locally induce cytoskeletal changes, and that neurons affected by neurofibrillary tangles (NFTs) lose their neuropeptide concentration and eventually die. To test this presumed cascade of events, the hypothalami of 14 non-demented subjects (Braak 0-III) and 28 AD patients (Braak IV-VI) aged 40-98 years were selected. The subject of our study was the nucleus tuberalis lateralis (NTL), which harbors a subpopulation of somatostatinergic neurons with extensive intrinsic interconnectivity. We used Gallyas silver staining, Congo staining, single- and double-staining with monoclonal antibody AT8 and polyclonal antibody anti-Abeta, and double-immunolabeling with AT8 and anti-somatostatin(1-12) with the following results: (1) Significant amounts of silver-staining NFTs were present in only three AD patients. (2) High densities of AT8-stained cytoskeletal changes were mainly found in aged, demented patients. (3) In contrast, large amounts of Abeta deposits were mainly observed in young and middle-aged (40-59 years) AD patients, and were very low or absent mainly in the older non-demented subjects and in AD patients. (4) Reduced anti-somatostatin staining was observed in the NTL of most AD patients, but anti-somatostatin/AT8 double-stained neurons were found virtually exclusively in aged AD patients. Thus, the occurrence of Abeta deposits and hyperphosphorylated tau formation in somatostatin cells are basically independent events, while decreased somatostatin staining only partly goes together with cytoskeletal changes in somatostatin cells in the NTL of AD patients. These observations cannot be explained by the amyloid cascade hypothesis.

Metabolic activity of the human ventromedial nucleus neurons in relation to sex and ageing

The ventromedial nucleus (VMN) in animals is involved in a number of sexually dimorphic behaviors, including reproduction, and is a well-documented target for sex steroids. In rats and in lizards, it is also characterized by the presence of structural sexual dimorphisms. In the present study, we determined whether the metabolic activity of human ventromedial nucleus neurons was sex- or age-related. The size of the immunocytochemically defined Golgi apparatus (GA) and cell profiles were determined as measures for neuronal metabolic activity in 12 male and 16 female control brains sub-divided into four groups with the dividing line being the age of 50. It appeared that the size of the GA relative to cell size was 34% larger in young women (<50 years old) than in young men and was 25% larger in elderly men (> or = 50 years old) than in young men. In addition, the GA/cell size ratio correlated significantly with age in men and not in women. Our data suggest that androgens play an inhibitory role with respect to the metabolic activity of the human VMN neurons.

Somatostatin 1-12 immunoreactivity is decreased in the hypothalamic lateral tuberal nucleus of Huntington's disease patients

The hypothalamic lateral tuberal nucleus (NTL) can be recognized in man and higher primates, only. The function of this nucleus is unknown, but the NTL is affected in a variety of human neurodegenerative diseases, including Huntington's disease (HD) and Alzheimer's disease. In the present study we demonstrate an abundant presence of somatostatin 1-12 (SST1-12) immunoreactivity in both neurites and perikarya of the NTL. This immunoreactivity could be visualized best after microwave pretreatment. In HD brains, NTL SST1-12 immunoreactivity was greatly reduced, providing further evidence of the presence of SST1-12 as an intrinsic neuropeptide in the NTL. Although striatal SST neurons escape destruction in HD, our study demonstrates that not all SST neurons are resistant to the degenerative process in this disease.

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.

Localization and developmental pattern of vasoactive intestinal polypeptide binding sites in the human hypothalamus

Using a quantitative in vitro autoradiographic approach, vasoactive intestinal polypeptide (VIP) binding site densities were compared in the post-mortem hypothalamus of human neonate/infant and adult. The densities were similar during development in most of the hypothalamic nuclei and areas examined underlying the stability of 125I-VIP binding sites in the post-mortem hypothalamus of young and adult individuals. However, the ventral part of the medial preoptic area, the medial, lateral, and supramammillary nuclei were characterized by an increase of 125I-VIP binding with age. In young and adult individuals, the highest densities of hypothalamic 125I-VIP binding sites were detected in the supraoptic and infundibular nuclei; the ependyma; the organum vasculosum of the lamina terminalis; the horizontal limb of the diagonal band of Broca; the ventral part of the medial preoptic area (in adult); the suprachiasmatic, paraventricular, and periventricular nuclei; and the medial and lateral mammillary nuclei in adult. Moderate densities were found in the vertical limb of the diagonal band of Broca, the bed nucleus of the stria terminalis, the ventral part of the medial preoptic area in neonate/infant, the medial and lateral mammillary nuclei in neonate/infant, the supramammillary nucleus in adult, the dorsal hypothalamic area, and the ventromedial nucleus. Low to moderate binding site densities were observed in the other hypothalamic regions of young or adult individuals. The nonspecific binding ranged from 15% of the total binding in the anterior hypothalamus to 20% in the mediobasal and posterior hypothalamic levels. Taken together, these results provide evidence for a large distribution of VIP binding sites in neonate/infant and adult human hypothalamus suggesting the implication of VIP in the development of this brain structure and the maintenance of its various functions.

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)

Chapter 17 The hypothalamic lateral tuberal nucleus: normal anatomy and changes in neurological diseases

The lateral tuberal nucleus is a circumscribed cell mass in the lateral posterior part of the hypothalamus, containing about 60000 neurons. It can be recognized in man and higher primates, probably not in other mammals. Its neurotransmitter content and connections with other parts of the brain are as yet unknown. But receptors for corticotropin-releasing factor and somatostatin, as well as muscarinic cholinergic receptors, benzodiazepine receptors and N-methyl-D-aspartate receptors have been localized within the confines of the nucleus. The lateral tuberal nucleus is affected in a number of human neurodegenerative diseases. Changes in Parkinson's disease are the least obvious: Lewy bodies appear in small amounts, the majority of them apparently lying outside a neuronal perikaryon. Neuronal loss does not occur. In Alzheimer's disease the number of neurons seems to be normal as well. Rarely silver staining tangles occur, and the deposition of A4/beta-protein in amorphous plaques is moderate. Yet, NTL neurons stain heavily in Alz-50 immunocytochemistry, while Alz-50 staining in NTL neurites is very dense. These changes are interpreted as indicating early Alzheimer-related pathology. In Huntington's disease the NTL loses neurons. This loss is related to the severity of the disease: patients who first display motor disturbances at an early age will lose more neurons than those who start later. The relation between these clinical characteristics and the severity of neuronal loss is such, that it seems likely that NTL neurons possess a special vulnerability for the effect of the Huntington gene. This could be related to their NMDA-receptor content. It is hypothesized that the NTL is involved in a neuronal network that regulates feeding and metabolism. NTL pathology may explain the peculiar catabolic state of many patients with Alzheimer's or Huntington's diseases.

Ontogeny of peptides in human hypothalamus in relation to sudden infant death syndrome (SIDS)

The brains of mammals are not mature at birth, in particular in humans. Growth and brain development are influenced by the hormonal state in which the hypothalamus plays the major regulatory role. The maturation of the hormonal patterns leads to the physiological establishment of chronological variations as revealed by the circadian variations of both hypothalamic peptides and pituitary hormones (as illustrated for hypothalamic-pituitary-thyroid axis by the determination of thyro-stimulating hormone (TSH) and thyrotropin-releasing hormone (TRH) circadian rhythms in the rat (Jordan et al., 1989)). It has been established that hypothalamic peptide variations are regulated by hormonal feed-back and amine systems, with the maturation of the latter also being dependent upon the whole functional maturation of the brain. Though these systems have been studied in the rat, very little information is currently available with regard to the human brain. The only biochemical or immunohistochemical information published to date concerns either the fetus or the adult. We have studied four main peptidergic systems (somatostatin-releasing inhibiting factor (SRIF), thyrotropin-releasing hormone (TRH), luteinizing hormone-releasing hormone (LHRH) and delta sleep inducing peptide (DSIP) in post-mortem adults and infants and in sudden infant death syndrome (SIDS) brains either by autoradiography and/or immunochemistry of radioimmunology. From a technical point of view, human brain studies display certain pitfalls not present in animal studies. These may be divided into two subclasses: ante- and post-mortem. Ante-mortem problems concern mainly sex, laterality, nutritional and treatment patterns while post-mortem problems concern post-mortem delay and conditions before autopsy and hypothalamic dissection. This might induce dramatic changes in morphological, immunochemical and autoradiographic evaluations. The matching of pathological subjects with controls is particularly difficult in the case of SIDS because of the rapid changes which take place in physiological regulatory processes during the first year of life. Thus, the treatment of hypothalamic tissue samples both for immunochemistry, radioimmunology and autoradiographic studies required techniques which must be rigorously controlled. For example, SRIF studies were carried out with three different antibodies, which gave similar results. The use of different technical procedures as well as different antibodies is discussed. These types of differences might explain, at least in part, the discrepancy observed until now. As previously described in the fetus (Bugnon et al., 1977b; Bouras et al., 1987), we confirmed that in the infant hypothalamic SRIF immunoreactive cell bodies are present in the paraventricular and suprachiasmatic nuclei and in the periventricular area.(ABSTRACT TRUNCATED AT 400 WORDS)

Autoradiographic distribution of TRH binding sites in the human hypothalamus

Using in vitro quantitative autoradiography and [3H]3MeTRH, a selective high affinity radioligand, we examined the rostrocaudal distribution of TRH binding sites in both the infant and the adult human hypothalamus. The saturation curve shows that the [3H]3MeTRH binds with high affinity to a single class of TRH binding sites and is saturable, the apparent constant of dissociation is in the namomolar range. TRH binding sites showed a wide distribution, principally in the anterior and mediobasal levels of the hypothalamus. TRH binding site concentration was highest within the diagonal band of Broca, the lateral preoptic area, the infundibular and the tuberal nuclei. TRH binding site concentration was moderate in the ventromedial nucleus and the medial preoptic area, whereas we observed low densities in the periventricular, paraventricular and mammillary nuclei. The distribution in the infant and the adult is generally similar. However, it is noteworthy that the infant tuberal nuclei displayed a lower binding site density when compared to the adult. On the other hand, the diagonal band of Broca is relatively more labeled in infant. The analysis of the whole hypothalamus allows us to ascertain the absence of lateral asymmetric distribution both in the infant and the adult. No significant difference is noticed when considering as parameters of variation age, sex or post mortem delay.

Transient expression of somatostatin messenger RNA and peptide in the hypoglossal nucleus of the neonatal rat

The postnatal developmental expression of somatostatin mRNA and peptide in the rat hypoglossal nucleus was analyzed using immunocytochemical and in situ hybridization techniques. Both the neuropeptide and its cognate mRNA were found to be transiently present within a subpopulation of hypoglossal motoneurons during the neonatal period. At the day of birth, a large population of perikarya situated in caudal, ventral regions of the hypoglossal nucleus expressed somatostatin. By postnatal day 7, the number of hypoglossal somata which expressed somatostatin had diminished considerably, and by 2 weeks postnatal, only few such cell bodies were found. By 3-4 weeks postnatal, somatostatin peptide- and mRNA-containing hypoglossal motoneurons were rarely observed, and in the adult, they were never detected, despite the use of colchicine. A double-labeling co-localization technique was used to demonstrate that somatostatin, when present perinatally, always coexisted with calcitonin gene-related peptide in hypoglossal motoneurons. The latter peptide, in contrast to somatostatin, was expressed in large numbers of somata throughout the entire hypoglossal nucleus and persisted within the motoneurons throughout development into adulthood. These results demonstrate that somatostatin is transiently expressed in motoneurons of the caudal, ventral tier of the hypoglossal nucleus in the neonatal rat. The developmental disappearance of somatostatin is most likely not due to cell death; hypoglossal somata continue to express calcitonin gene-related peptide, with which somatostatin coexisted perinatally, a high levels throughout development. Thus, it appears that the regulation of somatostatin expression in hypoglossal neurons occurs at the level of gene transcription or mRNA stability/degradation.(ABSTRACT TRUNCATED AT 250 WORDS)

Regional distribution of somatostatin binding sites in the human hypothalamus: a quantitative autoradiographic study

Using in vitro quantitative autoradiography and [125I]Tyr0-D-Trp8SRIF 14 as radioligand, we characterized the detailed distribution of somatostatin binding sites in human hypothalamus of both infants and adults. Guanosine triphosphate pretreatment, before incubation, allowed us to detect higher [125I]Tyr0-D-Trp8SRIF 14 binding site densities in hypothalamic structures such as preoptic and anterior hypothalamic areas and ventromedial and dorsomedial nuclei. In contrast, guanosine triphosphate was without effect in the other hypothalamic regions. The regional effects of guanosine triphosphate pretreatment were not different in infant and adult hypothalamus. Scatchard analysis showed that in a guanosine triphosphate-sensitive region (preoptic area) and a guanosine triphosphate-insensitive area (infundibular nucleus), [125I]Tyr0-D-Trp8SRIF 14 bound to a single class of binding sites. Affinities were similar in both regions, not modified by guanosine triphosphate pretreatment and not different in the adult (1.5 +/- 1.2 nM vs 3.2 +/- 2.1 nM for preoptic area and infundibular nucleus, respectively) and infant (0.9 +/- 0.5 nM vs 2.4 +/- 1.7 nM for preoptic area and infundibular nucleus). [125I]Tyr0-D-Trp8SRIF 14 binding sites were widely distributed in the anterior, mediobasal and posterior hypothalamus. Somatostatin 28 was twice as potent as somatostatin 14 to displace [125I]Tyr0-D-Trp8SRIF 14 binding in the preoptic area and infundibular nucleus. However, IC50s were 30 times lower in the preoptic area as compared with the infundibular nucleus. In adult as well as in infant, high densities were found mainly in the diagonal band of Broca, preoptic area and infundibular nucleus. Intermediate densities were localized in the anterior hypothalamic area, ventromedial, dorsomedial and lateral mammillary nuclei. The dorsal hypothalamic area, the paraventricular and medial mammillary nuclei displayed low but measurable densities. The only marked difference in the distribution of [125I]Tyr0-D-Trp8SRIF 14 binding sites in adult vs infant was observed in the medial and tuberal nuclei where the concentrations were seven-fold higher in adult hypothalamus.

Functional maturation of somatostatin neurons and somatostatin receptors during development of mouse hypothalamus in vivo and in vitro

Ontogenesis of somatostatin (SRIF) neurons and receptors was studied in fetal hypothalamic cell cultures kept in serum-free medium, and compared to the in vivo developmental pattern. Initial rise in neuronal content of SRIF occurred later in vitro than in vivo. In vitro, K(+)-induced SRIF release was only present after synaptogenesis. SRIF binding sites were measurable as early as 1 day after birth and at an equivalent time in culture, after 6 days in vitro (DIV); their affinity was in the nanomolar range. In cultured cells, binding reached a maximum at two weeks in vitro and decreased sharply thereafter as a consequence of binding site occupancy by the endogenous ligand. Indeed, pretreatment with cysteamine decreased SRIF concentration in the neuronal cultures and twice as many binding sites as in control cultures of 21 DIV were measured. Competition kinetics using unlabelled SMS 201-995 to displace [125I]SRIF revealed two distinct binding sites in the neuronal preparations (IC50 = 11 +/- 3 pM and 4.5 +/- 0.8 nM). In contrast, only the lower affinity site was present on glial cell preparations (1.7 +/- 0.4 nM). SRIF inhibited adenylate cyclase activity in glia and neurons, and the onset of SRIF coupling to the second messenger occurred earlier in vitro than in vivo. Pertussis toxin pretreatment was equally effective in neuronal and glial cell preparations to decrease SRIF binding and to inhibit adenylate cyclase activity.

Anatomical distribution of LHRH-immunoreactive neurons in the human infant hypothalamus and extrahypothalamic regions

The morphological features and distribution of luteinizing hormone-releasing hormone (LHRH)-immunoreactive cell bodies and fibers of the hypothalamic and the neighboring mesencephalic regions were studied in the normal newborn infant by immunohistochemistry. Within the hypothalamus, numerous LHRH-immunoreactive like (IL) cell bodies were found mainly in the ventral portion of the infundibular nucleus close to the median eminence and at a lower extent in the medial preoptic area. In addition, sparse immunoreactive cell bodies were displayed in the paraventricular and medial mammillary nuclei. The mesencephalon also exhibited rare immunoreactive cell bodies in the periaqueductal gray. LHRH-IL fibers, predominantly varicose, formed a continuum from the septo-preoptico level to the mesencephalon. In the hypothalamus, the median eminence exhibited the highest LHRH innervation. LHRH-IL fibers are also observed in the lamina terminalis, the medial preoptic area, the suprachiasmatic, the supraoptic, the peri- and the paraventricular nuclei. In the last two nuclei, some fibers projected to the dorsomedial and ventromedial nuclei whereas others were in close relation with the ependyma. The mesencephalon displayed low LHRH-IL fibers, present essentially in the raphe and interpeduncular nuclei and around the ependyma. When compared with data obtained in other mammals, the present findings agree well with the general distribution and morphological features of LHRH-IL neuronal structures reported elsewhere.