Ontogeny of somatostatin-containing neuron system of the rat: immunohistochemical analysis. II. Forebrain and diencephalon

Molecular characterization and expression of three preprosomatostatin genes and their association with growth in common carp (Cyprinus carpio)

Somatostatins (SSs) are a structurally diverse family of peptides that play important roles in the regulation of growth, development and metabolism in vertebrates. In this study, three preprosomatostatin genes (PSSs) in the common carp, Cyprinus carpio (Cc) were identified and characterized. Based on cloned sequences and genome BLAST, six isoforms of the PSS gene in C. carpio (CcPSS) were identified and included CcPSS1a and CcPSS1b, CcPSS2a and CcPSS2b, and finally, CcPSS3a and CcPSS3b. The open reading frames (ORF) of CcPSS1a, CcPSS2a and CcPSS3a consist of 345, 336 and 363 nucleotides. During embryonic development, the expressions of CcPSS2 and CcPSS3 were first observed at the stage of optic vesicle, and CcPSS1 mRNA was initially detected at the stage of muscular effect. The highest mRNA levels of CcPSS1, CcPSS2 and CcPSS3 were observed at 1-day post-hatch (dph), 2-dph and the stage of heart beating, respectively. In the adult brain, the distributions of three CcPSS mRNAs were differential but overlapping in the hypothalamus, telencephalon and medulla oblongata. For peripheral tissues, all three CcPSS mRNAs were detected in the mid-intestine, and CcPSS1 and CcPSS3 mRNAs were also expressed in the liver. Owing to the importance of somatostatins on regulating growth, functional mutations of CcPSSs were identified in a C. carpio population. A total of 23 polymorphic sites were detected in CcPSS1a and CcPSS3a. Of them, two SNPs (CcPSS1a-g.922C>T, and CcPSS3a-g.1125C>A) were significantly associated with growth traits, indicating their potential applications in gene (marker)-assisted selective breeding in C. carpio.

Topography of Somatostatin Gene Expression Relative to Molecular Progenitor Domains during Ontogeny of the Mouse Hypothalamus

The hypothalamus comprises alar, basal, and floor plate developmental compartments. Recent molecular data support a rostrocaudal subdivision into rostral (terminal) and caudal (peduncular) halves. In this context, the distribution of neuronal populations expressing somatostatin (Sst) mRNA was analyzed in the developing mouse hypothalamus, comparing with the expression pattern of the genes Orthopedia (Otp), Distal-less 5 (Dlx5), Sonic Hedgehog (Shh), and Nk2 homeobox 1 (Nkx2.1). At embryonic day 10.5 (E10.5), Sst mRNA was first detectable in the anterobasal nucleus, a Nkx2.1-, Shh-, and Otp-positive basal domain. By E13.5, nascent Sst expression was also related to two additional Otp-positive domains within the alar plate and one in the basal plate. In the alar plate, Sst-positive cells were observed in rostral and caudal ventral subdomains of the Otp-positive paraventricular complex. An additional basal Sst-expressing cell group was found within a longitudinal Otp-positive periretromamillary band that separates the retromamillary area from tuberal areas. Apart of subsequent growth of these initial populations, at E13.5 and E15.5 some Sst-positive derivatives migrate tangentially into neighboring regions. A subset of cells produced at the anterobasal nucleus disperses ventralward into the shell of the ventromedial hypothalamic nucleus and the arcuate nucleus. Cells from the rostroventral paraventricular subdomain reach the suboptic nucleus, whereas a caudal contingent migrates radially into lateral paraventricular, perifornical, and entopeduncular nuclei. Our data provide a topologic map of molecularly defined progenitor areas originating a specific neuron type during early hypothalamic development. Identification of four main separate sources helps to understand causally its complex adult organization.

Growth hormone-releasing hormone activates sleep regulatory neurons of the rat preoptic hypothalamus

We examined whether growth hormone-releasing hormone (GHRH) may promote non-rapid eye movement (NREM) sleep via activation of GABAergic neurons in the preoptic area. Male Sprague-Dawley rats were implanted with EEG, EMG electrodes and a unilateral intracerebroventricular cannula. Groups of rats received injections (3 microl icv) with gonadotropin-releasing hormone (GHRH) (0.1 nmol/100 g body wt) or equal volume of physiological saline at the onset of the dark period and were permitted spontaneous sleep for 90 min. Separate groups of rats were sleep deprived by gentle handling for 90 min, beginning at the time of GHRH or saline injection, at the onset of the dark period. Other groups of rats received intracerebroventricular octreotide (somatostatin analog OCT) injections, intracerebroventricular injection of one of two doses of competitive GHRH antagonist, or intracerebroventricular saline injection at light onset and were then permitted 90 min spontaneous sleep-waking. Rats were killed immediately after the 90-min sleep/wake monitoring period. Brain tissue was processed for immunohistochemistry for c-Fos protein and glutamic acid decarboxylase (GAD). Single c-Fos and dual Fos-GAD cell counts were determined in the median preoptic nucleus (MnPN), and in the core and the extended parts of the ventrolateral preoptic nucleus (cVLPO and exVLPO). Intracerebroventricular GHRH elicited a significant increase in NREM sleep amount. Double-labeled Fos+GAD cell counts were significantly elevated after GHRH injection in the MnPN and VLPO in both undisturbed and sleep-deprived groups. OCT and GHRH antagonist significantly decreased NREM sleep amount compared with control rats. OCT injection increased single c-Fos-labeled cell counts in the MnPN, but not in the VLPO. Double-labeled cell counts were significantly reduced after OCT and the high dose of GHRH antagonist injection in all areas examined. These findings identify GABAergic neurons in the MnPN and VLPO as potential targets of the sleep-regulatory actions of GHRH.

The somatostatin 2A receptor is enriched in migrating neurons during rat and human brain development and stimulates migration and axonal outgrowth

The neuropeptide somatostatin has been suggested to play an important role during neuronal development in addition to its established modulatory impact on neuroendocrine, motor and cognitive functions in adults. Although six somatostatin G protein-coupled receptors have been discovered, little is known about their distribution and function in the developing mammalian brain. In this study, we have first characterized the developmental expression of the somatostatin receptor sst2A, the subtype found most prominently in the adult rat and human nervous system. In the rat, the sst2A receptor expression appears as early as E12 and is restricted to post-mitotic neuronal populations leaving the ventricular zone. From E12 on, migrating neuronal populations immunopositive for the receptor were observed in numerous developing regions including the cerebral cortex, hippocampus and ganglionic eminences. Intense but transient immunoreactive signals were detected in the deep part of the external granular layer of the cerebellum, the rostral migratory stream and in tyrosine hydroxylase- and serotonin- positive neurons and axons. Activation of the sst2A receptor in vitro in rat cerebellar microexplants and primary hippocampal neurons revealed stimulatory effects on neuronal migration and axonal growth, respectively. In the human cortex, receptor immunoreactivity was located in the preplate at early development stages (8 gestational weeks) and was enriched to the outer part of the germinal zone at later stages. In the cerebellum, the deep part of the external granular layer was strongly immunoreactive at 19 gestational weeks, similar to the finding in rodents. In addition, migrating granule cells in the internal granular layer were also receptor-positive. Together, theses results strongly suggest that the somatostatin sst2A receptor participates in the development and maturation of specific neuronal populations during rat and human brain ontogenesis.

Dopamine release in the nucleus accumbens (shell) of two lines of rats selectively bred to prefer or avoid ethanol

Lower tissue levels of dopamine and 5-hydroxytryptamine (5-HT) have been found in the nucleus accumbens of alcohol-naïve rats selectively bred to prefer ethanol than in rats bred to avoid it. These findings have led to the hypothesis that differences in the dopamine and 5-HT tone may be linked to ethanol preference. In the present study we used the in vivo microdialysis technique to determine the actual extracellular levels of dopamine, its metabolites 3,4-dihydroxyphenyl acetaldehyde (DOPALD), 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and 5-HT and 5-hydroxyindolacetic acid (5-HIAA) in the shell of nucleus accumbens of rat lines selectively bred as either high-ethanol (UChB) or low-ethanol (UChA) drinkers. Basal extracellular levels of dopamine, DOPALD, DOPAC and HVA were lower in the shell of nucleus accumbens of ethanol-naïve UChB than in UChA rats. In agreement, when perfused with 100 microM d-amphetamine or 100 mM KCl lower dopamine increases were observed in nucleus accumbens of UChB rats compared to UChA rats, indicating lower cytosolic (d-amphetamine releasable) and vesicular (KCl releasable) dopamine pools in UChB animals. Since the experiments were performed in ethanol-naïve rats, the present results suggest an innate deficiency in the mesolimbic dopamine system of UChB rats. There were no line differences in basal, d-amphetamine or KCl stimulated 5-HT levels. Thus, the present findings support a role of dopamine, but not of 5-HT, as predictor of ethanol preference in UChB rats. Overall, data obtained are in agreement with previous reports in other rat lines showing that lower dopamine levels and its metabolites are associated with a genetic predisposition to ethanol preference.

The development of hippocampal interneurons in rodents

Interneurons are GABAergic neurons responsible for inhibitory activity in the adult hippocampus, thereby controlling the activity of principal excitatory cells through the activation of postsynaptic GABAA receptors. Subgroups of GABAergic neurons innervate specific parts of excitatory neurons. This specificity indicates that particular interneuron subgroups are able to recognize molecules segregated on the membrane of the pyramidal neuron. Once these specific connections are established, a quantitative regulation of their strength must be performed to achieve the proper balance of excitation and inhibition. We will review when and where interneurons are generated. We will then detail their migration toward and within the hippocampus, and the maturation of their morphological and neurochemical characteristics. We will finally review potential mechanisms underlying the development of GABAergic interneurons.

Ontogeny of the somatostatin variant [Pro2,Met13]somatostatin-14 in the brain, pituitary, and sensory organs of the frogRana esculenta

Two forms of somatostatin are expressed in the frog brain, i.e., somatostatin-14 (SS1) and the [Pro(2), Met(13)]somatostatin-14 variant (SS2). We have previously described the ontogeny of SS1-immunoreactive cells in the brain of Rana esculenta. In the present study, we have investigated the distribution of prepro-SS2 (PSS2)-expressing neurons in the brain of the same species during development by using antibodies directed against the N-flanking region of SS2 (PSS2(54-66)). Immunoreactive perikarya first appeared in the ventral hypothalamus at stages IV-VII. Subsequently, positive neurons were seen in the nucleus of the diagonal band of Broca, the anterior preoptic area, the posterior tuberculum (stages VIII-XII), as well as the dorsal (stages XIII-XV) and medial (stages XIX-XX) periventricular preoptic nucleus. At metamorphic climax and in newly metamorphosed frogs, positive perikarya were found in the striatum and in the interpeduncular nucleus. PSS2(54-66)-immunoreactive fibers were already widely distributed during the first stages of development, indicating that SS2 may act as a neuromodulator and/or neurotransmitter during ontogeny. The presence of PSS2(54-66)-positive nerve fibers in olfactory structures suggests that, in tadpoles, SS2 may be involved in the processing of olfactory information. The occurrence of PSS2(54-66)-like immunoreactivity in taste buds, and in the olfactory and vomeronasal organs indicates that SS2 may mediate the unconditioned and reinforcing properties of natural chemicals. Finally, the intenseexpression of PSS2(54-66)-like immunoreactivity in melanotrope cells of the pituitary suggests that SS2 may diffuse toward the pars distalis to regulate the activity of adenohypophysial cells during tadpole development.

Sim2 contributes to neuroendocrine hormone gene expression in the anterior hypothalamus

Paraventricular (PVN) and supraoptic nuclei of the hypothalamus maintain homeostasis by modulating pituitary hormonal output. PVN and supraoptic nuclei contain five major cell types: oxytocin-, vasopressin-, CRH-, somatostatin-, and TRH-secreting neurons. Sim1, Arnt2, and Otp genes are essential for terminal differentiation of these neurons. One of their common downstream genes, Brn2, is necessary for oxytocin, vasopressin, and CRH cell differentiation. Here we show that Sim2, a paralog of Sim1, contributes to the expression of Trh and Ss genes in the dorsal preoptic area, anterior-periventricular nucleus, and PVN. Sim2 expression overlaps with Trh- and Ss-expressing cells, and Sim2 mutants contain reduced numbers of Trh and Ss cells. Genetically, Sim1 acts upstream of Sim2 and partially compensates for the loss of Sim2. Comparative expression studies at the anterior hypothalamus at early stages reveal that there are separate pools of Trh cells with distinctive molecular codes defined by Sim1 and Sim2 expression. Together with previous reports, our results demonstrate that Sim1 and Otp utilize two common downstream genes, Brn2 and Sim2, to mediate distinctive sets of neuroendocrine hormone gene expression.

Effects of subchronic and chronic melatonin treatment on somatostatin binding and its effects on adenylyl cyclase activity in the rat frontoparietal cortex

Melatonin and somatostatin are known to exert similar effects on locomotor activity. We have previously demonstrated that acute melatonin treatment regulates somatostatin receptor function in the rat frontoparietal cortex. However, the effects of subchronic and chronic melatonin treatment on the somatostatin receptor-G protein-adenylyl cyclase system in the rat frontoparietal cortex are unknown. Melatonin was administered subcutaneously at a daily dose of 25 microg/kg for 4 days, 1 wk or 2 wk. Twenty-four hours after the last injection, the animals were sacrificed. Melatonin did not alter the somatostatin-like immunoreactivity content in the frontoparietal cortex from control and melatonin-treated rats during any of the previously indicated periods. Four days of melatonin administration induced both an increase in the number of [(125)I]-Tyr11-somatostatin receptors and a decrease in the affinity of somatostatin for its receptors in frontoparietal cortical membranes. The increased number of somatostatin receptors in the melatonin-treated rats was associated with an increased capacity of somatostatin to inhibit basal and forskolin-stimulated adenylyl cyclase activity. Melatonin administration for 4 days induced a higher adenylyl cyclase activity both under basal conditions and after direct stimulation of the enzyme with forskolin. No significant differences were observed in the function of Gi proteins in the 4-day melatonin-treated rats. Western blot analyses showed that the 4-day melatonin treatment reduced Gialpha(2) levels, without altering the amount of Gialpha(1). These melatonin-induced changes reverted to control values after 7 or 14 days of treatment. Altogether, the present findings suggest that subchronic melatonin treatment modulates the somatostatin receptor/effector system in the rat frontoparietal cortex.

Differential expression of two somatostatin genes during zebrafish embryonic development

We have identified the cDNAs of two new zebrafish preprosomatostatins, PPSS1 and PPSS3, in addition to the previously cloned PPSS2 (Argenton et al., 1999). PPSS1 is the orthologue of mammalian PPSSs, with a conserved C-terminal SS-14 sequence, PPSS2 is a divergent SS precursor and PPSS3 is a cortistatin-like prohormone. Using whole-mount in situ hybridisation, we have analysed the expression of PPSS1 and PPSS2 in zebrafish embryos up to 5 days post fertilisation. PPSS1 was expressed in the developing pancreas and central nervous system (CNS), whereas PPSS2 expression was exclusively pancreatic. In the CNS, PPSS1 was detected in several areas, in particular in the vagal motor nucleus and in cells that pioneer the tract of the postoptic commissure. PPSS1 was also expressed transiently in the telencephalon and spinal motor neurons. In all areas but the telencephalon PPSS1 was coexpressed with islet-1.

Glial somatostatin-14 expression in the rat pituitary intermediate lobe: a possible neurotrophic function during development?

Somatostatin-14 was first detected on gestational day 17 in radially-oriented, bipolar cells spanning the width of the intermediate lobe of the rat pituitary. Cells were prominent, and constituted approximately 50% of the lobe area. The presence of vimentin, the cellular shape, and the localization identified these cells as glia. At postnatal day 6, somatostatin-14 and vimentin staining appeared in stellate-shaped cells. This is in agreement with the change from bipolar to stellate shape these glia undergo after the onset of innervation ([13] Gary et al. Int. J. Devl. Neurosci. 13, 555-565, 1995). Glia were more abundant, relative to melanotropes, throughout embryonic and early postnatal development compared to adulthood. Reverse transcription-polymerase chain reaction data showed a high level of prosomatostatin mRNA in the intermediate lobe, compared to the anterior and neural lobes from postnatal day 2 animals, and a significant drop in intermediate lobe content in the adult. The correlation between the number of glia and high expression of somatostatin in neonatal relative to adult tissue, together with the close apposition of incoming axons to the abundant, radially oriented glia during innervation of the lobe, support a neurotrophic function of glia-derived somatostatin.

Pancreatic homeodomain transcription factor IDX1/IPF1 expressed in developing brain regulates somatostatin gene transcription in embryonic neural cells

Hox-like homeodomain proteins play a critical role during embryonic development by regulating the transcription of genes that are important for the generation of specific organs or cell types. The homeodomain transcription factor IDX1/IPF1, the expression of which was thought until recently to be restricted to the pancreas and foregut, is required for pancreas development and for the expression of genes controlling glucose homeostasis. We report that IDX1/IPF1 is also expressed in embryonic rat brain at a time coincident with active neurogenesis. Electrophoretic mobility shift assays with nuclear extracts of embryonic brains indicated that IDX1/IPF1 binds to two somatostatin promoter elements, SMS-UE-B and the recently discovered SMS-TAAT3. The requirement of these elements for IDX1/IPF1 transactivation of the somatostatin gene in neural cells was confirmed in transfection studies using embryonic cerebral cortex-derived RC2.E10 cells. Immunohistochemical staining of rat embryos showed IDX1/IPF1-positive cells located near the ventricular surface in germinative areas of the developing central nervous system. Cellular colocalization of IDX1/IPF1 and somatostatin was found in several areas of the developing brain, including cortex, ganglionic eminence, hypothalamus, and inferior colliculus. These results support the notion that IDX1/IPF1 regulates gene expression during development of the central nervous system independent of its role on pancreas development and function.

Identification of multiple somatostatin receptors in the rat somatosensory cortex during development

The present study was aimed at identifying somatostatin receptor subtypes on the basis of their ligand-binding properties in the rat somatosensory cortex during fetal and postnatal development. Characterization of somatostatin-binding sites was performed in individual cortical layers by using three radioligands and eight competitors with known selectivities for the five somatostatin receptor subtypes. Binding sites sensitive to sst2-selective ligands were detected with high densities in the intermediate zone of the fetal cortex. From embryonic day 21 to 21 days postnatal (P21), mixed populations of receptors were detected in the cortical plate and emerging layers I-VI. Putative sst2 receptors were detected throughout the entire period but displayed different affinities for somatostatin and analogs, and a different sensitivity to GTP, depending on the developmental stage and the cortical layer considered. High densities of binding sites exhibiting characteristics of the sst1, sst3/5, and sst4 receptor subtypes were observed from P4 to P7, P7 to P14, and P7 to P21, respectively. In addition, each type of site exhibited a particular distribution pattern across the cortical layers that varied during the development. In the adult cortex, binding sites with sst1 and sst2 receptor characteristics were predominant. This study provides evidences of developmental expression windows of four sst receptor subtypes in selected areas of the rat cerebral cortex.

Ontogeny of (D-Ala(2))-deltorphin I-like immunoreactive neurones in foetal rat brain

Foetal rat brain from embryonic day (ED) 12-22 was immunohistochemically studied to describe the time of first appearance and further distribution patterns of (D-Ala(2))-deltorphin-I-immunoreactive (DADTI-IR) nerve elements. The primary antiserum used in this study was a polyclonal antibody against DADTI previously used in adult and postnatal rat brain mapping. DADTI-IR nerve elements first appeared in the neuroepithelium of ventral mesencephalon on ED 13. From there, positive cell bodies migrated towards the mantle layer until they invaded the whole ventral mesencephalic tegmentum. They then reached their definitive position, corresponding to a subpopulation of the A8, A9 and A10 dopaminergic neurones that had been constantly observed also in the adult age. From ED 15-17, DADTI-positive nerve fibres appeared in the medial forebrain bundle, the neostriatum anlage, the accumbens nucleus, the olfactory tubercle, the fasciculus retroflexus, and the prefrontal cortex. All these locations have also been found in adult rats. From ED 14 onwards, transient DADTI-IR somata and nerve fibres were observed in retinal neuroepithelium, optic pathways as far as the superior colliculus, CA3 hippocampal field, reticular formation in the medulla oblongata. All these locations gradually disappeared either before birth (medulla oblongata) or within the first 3 weeks after birth. These results suggest that the DADT-like molecule recognised by our antibody has during the embryonic development a regulatory function in neuronal growth and differentiation.

Ontogeny and sexual differentiation of somatostatin biosynthesis and secretion in the hypothalamic periventricular-median eminence pathway

The biosynthesis of somatostatin (SRIH) in the hypothalamic periventricular nucleus (PeN) is sexually differentiated in neonatal and adult rats by virtue of the organizational and activational actions, respectively, of sex steroid hormones. Little information exists, however, on the normal pattern of maturation of these neurones or on how the sexually differentiated biosynthesis may relate to ontogenetic changes in somatostatin secretion during the neonatal and pubertal periods of development. Hence in the present study we determined the postnatal developmental profile of SRIH mRNA and peptide levels in the PeN-median eminence (ME) pathway as well as SRIH secretion, using an acute explant preparation, from the day of birth, through puberty and into adulthood in male and female rats. The results demonstrate that: (1) developmental sex differences in SRIH biosynthesis in PeN neurones occurred in an orderly cascade with differences observed for mRNA expression at postnatal day 5, for peptide content in the perikarya at postnatal day 10 and for peptide content in the nerve terminal (ME) by postnatal day 25; (2) sex differences in SRIH release were not evident prior to postnatal day 40; and (3) the developmental profile of SRIH biosynthesis in PeN neurones is unique compared with other hypothalamic (ventromedial nucleus) and extrahypothalamic (parietal cortex) populations. Specific developmental changes in the biosynthetic and secretory activity of the hypothalamic SRIH PeN-ME pathway may have a functional importance in the maturation of hypothalamic SRIH pathways involved in the regulation of GH secretion.

Differential regulation of basal and cyclic adenosine 3',5'-monophosphate-induced somatostatin gene transcription in neural cells by DNA control elements that bind homeodomain proteins

A number of genes encoding neuropeptides are expressed in the peripheral and central nervous systems, in different endocrine organs, and in specialized cells distributed along the gastrointestinal tract. Whether expression of the same neuropeptide gene in different tissues is regulated by similar transcriptional mechanisms or by mechanisms that differ in a cell-specific manner remains unclear. We report on promoter studies on the regulation of the somatostatin gene in immortalized neural precursor cells derived from developing rat forebrain. Expression of the somatostatin gene in these cells was determined by RT-PCR/Southern blot analysis, by immunocytochemistry, and by RIA. We show that in cerebrocortical and hippocampal cells, expression of the somatostatin gene is regulated by several negative and positive DNA cis-regulatory elements located throughout the promoter region. The somatostatin cAMP-response element appears to play a prominent role in neural somatostatin gene expression by acting as a strong enhancer even in the absence of cAMP stimulation. Site-directed mutagenesis followed by transient transfection assays indicated that SMS-TAAT1, SMS-TAAT2, and SMS-UE, three previously identified homeodomain protein-binding regulatory elements that enhance transcription in pancreatic cells, act as repressors of transcription in neural cells. Electrophoretic mobility shifts assays indicate that those elements bind protein complexes that differ between neural and pancreatic cells. Our results support the notion that expression of the somatostatin gene in neural cells occurs via transcriptional mechanisms that are different from those regulating expression of the same gene in pancreatic cells.

Distribution of somatostatin-like immunoreactivity in the brain of the frog, Rana esculenta, during development

The anatomical distribution of somatostatin-like immunoreactivity in the central nervous system of the frog, Rana esculenta, during development and in juvenile specimens was investigated by indirect immunofluorescence. Soon after hatching, at stages II-III, somatostatin-like immunoreactive structures were found in the preoptic-median eminence complex. In stage VI tadpoles, new groups of immunopositive perikarya and nerve fibers appeared in the diencephalon, within the ventral infundibular nucleus and in the ventral area of the thalamus, as well as in the medial pallium. In stages XII-XIV of development, immunopositive perikarya were also present in the dorsal infundibular nucleus of the hypothalamus and ventrolateral area of the thalamus. A small group of somatostatin-like immunoreactive neurons appeared in the posteroventral nucleus of the rhombencephalon. However, these neurons were not seen in later stages of development. Tadpoles in stages XVIII, XXI-XXII and in juveniles were characterized by a wider distribution of immunoreactive cell bodies and fibers in the pallium. New groups of immunoreactive neurons were found in the dorsal and lateral pallium. The presence of positive perikarya in the lateral pallium is a transient expression found only in these stages. The organization of the somatostatinergic system was most complex during the metamorphic climax, with the appearance of positive cell bodies in the posterocentralis area of the thalamus, and in juvenile animals with the presence of perikarya in the ventral part of the medial pallium and within the central grey rhombencephali. In contrast to the adult frog, somatostatin neurons were not observed in the mesencephalon of tadpoles and juveniles.

Estrogen-dependent ontogeny of sex differences in somatostatin neurons of the hypothalamic periventricular nucleus

The sexually dimorphic profile of GH secretion is thought to be engendered by gonadal steroids acting in part on hypothalamic periventricular somatostatin (SOM) neurons. The present study set out to examine and characterize the development of sex differences in these SOM neurons. In the first series of experiments, we used in situ hybridization to examine SOM messenger RNA (mRNA) expression within the periventricular nucleus (PeN) of male and female rats on postnatal day 1 (P1), P5, and P10. Cellular SOM mRNA content was found to increase from P1 to P10 in both sexes (P < 0.01), but was 24% (P < 0.05) and 38% (P < 0.01) higher in males on P5 and P10, respectively. A second series of experiments examined the SOM peptide content of the PeN in developing rats and found increasing levels from P1 to P10, with a 44% higher SOM content in males compared with females on P10 (P < 0.05). The third series of experiments questioned the role of gonadal steroids in engendering sex differences in SOM mRNA expression by determining the effects of neonatal gonadectomy (GDX) and replacement of dihydrotestosterone or estradiol benzoate. The SOM mRNA content of PeN neurons in P5 males gonadectomized on the day of birth was the same as that in P5 females and was significantly reduced compared with that in sham-operated P5 males (P < 0.05). Male rats GDX on P1 and treated with estradiol benzoate from P1 to P5 had cellular SOM mRNA levels similar to those in intact males on P5, whereas dihydrotestosterone treatment had no effect. Treatment of intact males with an androgen receptor antagonist, cyproterone acetate, on P1 had no effect on cellular SOM mRNA on P5, whereas male rats given the aromatase inhibitor 1,4,6-androstatriene-3,17-dione from P1 to P5 had lower (P < 0.05) SOM mRNA levels than controls. In the final set of experiments, dual labeling immunocytochemistry showed that SOM neurons in the PeN of P5 rats did not contain estrogen receptor-alpha, but expressed androgen receptors in a sexually dimorphic manner. These results demonstrate that a sex difference in SOM biosynthesis, which persists into adulthood, develops between P1 and P5 in PeN neurons. Despite the absence of estrogen receptor-alpha in these neurons, the organizational influence of testosterone only occurs after its aromatization to estrogen.

Postnatal development of somatostatin- and neuropeptide Y-immunoreactive neurons in rat cerebral cortex: a double-labeling immunohistochemical study

The postnatal development of somatostatin (SOM)- and neuropeptide Y (NPY)-immunoreactive (ir) neurons was examined in rat cerebral cortex, while considering their coexistence in cortical neurons. Using double immunohistochemical staining for SOM and NPY with diaminobenzidine and benzidine dihydrochloride as chromogens, we subdivided immunoreactive cells into double-labeled SOM/NPY-, SOM only-, and NPY only-ir neurons. SOM/NPY- and SOM only-ir neurons were detectable even at the day of birth, in contrast on NPY only-ir cells which first appeared in most cortices from week two. The morphological features of double-labeled SOM/NPY neurons differed with those of SOM only- and NPY only-ir neurons. No apparent changes in the shape and size of single-labeled neurons occurred with age; throughout their postnatal life they were round and ovoid, had a thin rim of perinuclear cytoplasm, and short processes. However, the features of SOM/NPY-ir neurons were not consistent according to postnatal age; by day P7, these neurons showed immature features and they began to show more advanced neuronal characteristics by week P2, when they had a larger and more intensely-stain cytoplasm. In addition, their processes were longer, thicker and more complex than at earlier ages. At this age, SOM/NPY-ir somata were close to their near maximum size. From week P4, they became smaller and were lightly labeled. SOM/NPY-ir somata were larger than SOM only- and NYP only-ir somata at and after two weeks of age. The present results, showing different postnatal maturation patterns such as time of appearance and morphological features, raise the possibilities that double-labeled SOM/NPY and single-labeled immunoreactive neurons may be different populations regulated by different mechanisms in their development, and with different functional properties during development.

The serotonin innervation of the basal forebrain shows a transient phase during development

The serotonergic innervation of the adult and developing basal forebrain nuclei of the rat was studied with immunocytochemical techniques at the light and electron microscopic levels. A substantial number of relatively thick serotonergic fibers with few varicosities and random orientation were observed at the time of birth. During the subsequent weeks, the serotonergic fibers increased in number and became thinner with many varicosities. They were also re-oriented, and around the end of the third postnatal week they exhibited the pattern of distribution and density seen in the adult. Electron microscopic analysis revealed that serotonin varicosities formed symmetrical or asymmetrical synapses mainly with dendritic shafts throughout postnatal life. Stereological extrapolation from single sections to the whole volume of varicosities showed that the percentage of serotonin varicosities engaged in synaptic junctions varied according to age. The proportion of labelled varicosities forming synapses increased from birth (21.3%) to the end of the second postnatal week (42.5%), then declined markedly in the following week (17.1%) before increasing again to an adult value of 46%. These findings suggest that the formation of synaptic connections by serotonin axons in the basal forebrain shows two distinct phases in postnatal development: exuberant synapses present in the first two weeks of life may be related to the involvement of serotonin in the maturation of this area, whereas synapses formed later in development may affect the functional state of basal forebrain projections to the neocortex and hippocampus. Thus, at these late stages of development and in the adult, serotonin may influence the activity of these forebrain structures both directly and indirectly.

Transient expression of neuropeptide Y (NPY) immunoreactivity in the developing hamster paraventricular thalamic area is due to apoptosis

1. A new population of neurons with transient expression of NPY immunoreactivity was described in the developing hamster paraventricular thalamic area. The present study was performed to discover whether this phenomenon is due to programmed cell death or apoptosis. 2. Toward this aim, immunocytochemical and electron microscopic examination of the paraventricular thalamic region, as well as DNA electrophoresis of tissue extracted from the described area, was performed on different stages of embryonic and postnatal development. 3. A sudden increase in neuropeptide Y immunoreactivity (NPY-IR) in the paraventricular thalamic area at embryonic day 14 (E14) was the first symptom of neuronal degeneration. 4. Electron microscopy revealed many neurons with large masses of condensed chromatin within nuclei and extracellular bodies. The affected cells had a convoluted shape and condensed cytoplasm. 5. DNA electrophoresis revealed a ladder of bands between 150 and 1000 bp that is specific for internucleosomal DNA fragmentation. 6. The data strongly suggest that developmental disappearance of NPY-IR neurons within the hamster dorsal thalamic area is due to apoptosis.

Ontogeny of somatostatin immunoreactive neurons in the medial cerebral cortex and other cortical areas of the lizard Podarcis hispanica

The ontogeny of somatostatin immunoreactive interneurons in the cerebral cortex of the lizard Podarcis hispanica has been studied in histological series of embryos, perinatal specimens, and adults. Somatostatin immunoreactive interneurons appear in the early stages of lizard cerebral cortex ontogeny, their number increases during embryonary development, reaches a peak in early postnatal life, and decreases in adult lizards. The first somatostatin immunoreactive somata in the lizard forebrain appeared on E36, and they were located in non cortical areas. Then, on E39 and later, somatostatin immunoreactive neurons were seen in the lizard cortex in a rostral-to-caudal spatial gradient, which parallels that of the normal histogenesis of the lizard cerebral cortex. On E39, labelled somata were seen in the medial and dorsal cortex inner plexiform layers; immunoreactive puncta and dendritic processes were detectable in the inner plexiform layer of the medial cortex. On E40, labelled neurons were observed in the inner plexiform layer of the lateral cortex; labelled processes were found in the inner plexiform layers (dorsomedial, dorsal, and lateral cortices) and the outer plexiform layers (medial and dorsomedial cortices). At hatching (P0), some somatostatin immunoreactive neurons populated the external plexiform layer of the dorsomedial cortex. On P28, groups of labelled neurons appeared in the cell layer of dorsal and lateral cortices, reaching the adult-mature pattern of somatostatin immunoreactivity in the lizard cerebral cortex, i.e., labelled somata and dendritic processes populating the inner plexiform layers in addition to an axonic labelled plexus in the outermost part of the outer plexiform layers. Immunoreactive somata and processes occupied all the cortical areas, but they were especially abundant in the dorsomedial cortex. Proliferating Cell Nuclear Antigen (PCNA) immunostaining in the same histological series revealed that the number of PCNA immunoreactive nuclei in the subjacent proliferative neuroepithelium followed an inverse-complementary evolution to somatostatin, suggesting some temporal relationship between somatostatin immunoreactive cells and neurogenesis in the lizard cerebral cortex.

The prepubertal ontogeny of galanin-like immunoreactivity in the male Meishan pig brain

Galanin (GAL) is a neuropeptide found in the mammalian brain and is involved in numerous functions including the control of feeding, growth and reproduction, and therefore may be an important peptide to study in agricultural species. We describe the immunohistochemical localization of GAL throughout prepubertal development in the Meishan pig, a Chinese breed known for its superior reproductive characteristics, but slow growth rate and abundant adipose tissue. Brains of animals from gestational day (g) 30, 50, 70, 90 and 110 and postnatal day (pn) 1, 10, 20 and 50 (duration of pregnancy averaged 114 days) were processed using a standard immunohistochemical technique utilizing a commercially available rabbit anti-porcine GAL antibody. Galanin-like immunoreactivity (GAL-IR) in cell bodies and fibers was evident in the brain at g30, primarily in the hypothalamus. Throughout prenatal development, cell bodies containing GAL-IR generally increased in number and distribution in the brain. During postnatal development, the number of cell bodies displaying GAL-IR decreased, particularly in hypothalamic areas. The distribution of GAL-IR in fibers became more widespread throughout gestational development, showing a pattern by pn1 that continued during later postnatal ages. The intensity of GAL-IR in fibers also increased throughout gestation. Some additional increases in immunoreactivity occurred postnatally, especially in the periventricular hypothalamus. The results of this study indicate that the distribution of GAL-IR in cell bodies and fibers in the Meishan pig brain was similar to that seen in other species, including the rat. These results support the hypothesis that GAL participates in the control of feeding, growth and reproduction in the pig.

Peptidergic transmission: from morphological correlates to functional implications

Like non-peptidergic transmitters, neuropeptides and their receptors display a wide distribution in specific cell types of the nervous system. The peptides are synthesized, typically as part of a larger precursor molecule, on the rough endoplasmic reticulum in the cell body. In the trans-Golgi network, they are sorted to the regulated secretory pathway, packaged into so-called large dense-core vesicles, and concentrated. Large dense-core vesicles are preferentially located at sites distant from active zones of synapses. Exocytosis may occur not only at synaptic specializations in axonal terminals but frequently also at nonsynaptic release sites throughout the neuron. Large dense-core vesicles are distinguished from small, clear synaptic vesicles, which contain "classical' transmitters, by their morphological appearance and, partially, their biochemical composition, the mode of stimulation required for release, the type of calcium channels involved in the exocytotic process, and the time course of recovery after stimulation. The frequently observed "diffuse' release of neuropeptides and their occurrence also in areas distant to release sites is paralleled by the existence of pronounced peptide-peptide receptor mismatches found at the light microscopic and ultrastructural level. Coexistence of neuropeptides with other peptidergic and non-peptidergic substances within the same neuron or even within the same vesicle has been established for numerous neuronal systems. In addition to exerting excitatory and inhibitory transmitter-like effects and modulating the release of other neuroactive substances in the nervous system, several neuropeptides are involved in the regulation of neuronal development.

The prepubertal ontogeny of neuropeptide Y-like immunoreactivity in the male Meishan pig brain

Neuropeptide Y (NPY) is widely distributed in the mammalian brain and is involved in numerous functions including the control of feeding, growth and reproduction. Therefore, NPY may be an important peptide to study in agricultural species. This study describes the immunohistochemical localization of NPY throughout prepubertal development in the Meishan pig, a Chinese breed known for its superior reproductive characteristics. Brains of animals from gestational day (g) 30 through postnatal day (pn) 50 (duration of pregnancy averaged 114 days) were processed using a standard immunohistochemical technique utilizing a commercially available rabbit anti-porcine NPY antibody. Neuropeptide Y-like immunoreactivity (NPY-IR) in cell bodies and fibers is evident in many areas of the brain at g30, including the basal telencephalon, hypothalamus, mesencephalon, pons, and medulla. Throughout prenatal development, cell bodies containing NPY-IR generally increase in number and distribution in the brain. During postnatal development the number of cell bodies displaying NPY-IR decreases. The arcuate nucleus of the hypothalamus, shows a dramatic reduction in the number of immunoreactive cell bodies between pn1 (day of birth) and pn20, just before weaning. The distribution of NPY-IR in fibers becomes more widespread throughout gestational development, showing a pattern by g110 that was characteristic of postnatal ages. The intensity of NPY-IR in fibers also increases throughout gestation. Some additional increases in immunoreactivity occur postnatally, especially in the periventricular hypothalamus and the hippocampus. Other brain areas like the caudate nucleus and putamen show decreases in immunoreactivity postnatally. The distribution of NPY-IR in cell bodies and fibers is similar to that seen in other species, including the rat, and supports the hypothesis that NPY participates in controlling feeding, growth and reproduction in the pig.

A confocal approach to the morphofunctional characterization of the transient tyrosine hydroxylase system in the rat suprachiasmatic nucleus

The suprachiasmatic nucleus (SCN) of the neonatal rat is transiently innervated by tyrosine hydroxylase (TH) fibers of unknown origin and whose catecholaminergic nature is rather doubtful. In order to characterize this system morphofunctionally, immunocytochemical double labelling and confocal laser scanning microscopy analysis were employed on cryostat brain sections of 10-day-old rats. Simultaneous stainings for neuropeptide Y (NPY) and tyrosine hydroxylase (TH) immunoreactivity showed that they are not colocalized, neither in the SCN fibers nor in the intergeniculate leaflet (IGL) neurons, site of origin of the NPY projection to the SCN. Therefore, the possibility that SCN transient TH fiber system originates from the IGL could be excluded. Double labelling for TH and aromatic L-aminoacid decarboxylase (AADC) demonstrated that transient SCN TH immunoreactive (IR) fibers are AADC negative, thus supporting the hypothesis of their non-catecholaminergic nature. Moreover two new group of cells which are TH positive and AADC negative were found: one in the SCN and the other in the periventricular hypothalamic nucleus (PHN). The presence of somatostatin (SRIF) and TH in PHN neurons and SCN fibers suggested their possible colocalization, but double immunolabellings gave negative results. Simultaneous immunocytochemical staining for vasoactive intestinal polypeptide (VIP) and TH showed that TH fibers may interact with ventrolateral SCN VIP neurons. This result suggests a possible involvement of TH fibers in regulating VIP cells activity in the entrainment of circadian rhythms.

Postnatal development of [D-Ala2]deltorphin-I-like immunoreactive structures in the rat brain

[D-Ala2]deltorphin-I, a highly selective ligand for delta opioid receptors, is a heptapeptide originally purified from frog skin. Previous immunohistochemical studies indicate that [D-Ala2]deltorphin-I-like molecule(s) may be present in adult rat brain, including specific neuronal cells and fibers partially overlapping with the mesocortical and nigrostriatal dopaminergic systems. Here, we examined the developmental aspect of such immunoreactive brain structures in early postnatal rats. In newborn to 21-day-old rats, positive staining in the brain occurred mainly in subpopulations of neurons and occasionally in tanycytes. On postnatal day 0, neuronal cell bodies containing [D-Ala2]deltorphin-I-like immunoreactivity were found in various brain regions, including the olfactory tubercle, ventral pallidum, hippocampus, ventral tegmental area, pars compacta of the substantia nigra, supramammillary nucleus, and dorsal raphe nucleus. Immunoreactive nerve fibers were observed in the main and accessory olfactory bulbs, olfactory tubercle, prelimbic area, anterior cingulate cortex, neostriatum, accumbens, lateral septal nucleus, lateral habenular nucleus, and superior colliculus. As pups grew, positive staining of cell bodies decreased gradually in both density and intensity, and those in the olfactory tubercle and ventral pallidum were no longer visible on postnatal day 14. On postnatal day 21, positive cells were found only in the ventral midbrain, including the pars compacta of the substantia nigra, ventral tegmental area, A8 region, and supramammillary nucleus. Positive fibers also decreased in density with age except in the accessory olfactory bulb, olfactory tubercle, prelimbic area, and anterior cingulate cortex.

Developmental patterns of somatostatin-receptors and somatostatin-immunoreactivity during early neurogenesis in the rat

The temporal pattern of distribution of somatostatin receptor was investigated using the somatostatin analogue [125I]Tyr0-DTrp8-somatostatin14 as a ligand and compared with that of somatostatin immunoreactivity during early developmental stages in the spinal cord and the sensory derivatives in rat fetuses. Qualitative and quantitative analysis showed that somatostatin receptors were detected in a transient manner. In the neural tube, they were clearly associated with immature premigratory cells and with the developing white matter. During the time-period examined (from day 10.5 to 16.5), the disappearance of somatostatin receptors followed a ventro to dorsal gradient probably linked to the regression of the ventricular zone. In sensory derivatives, they were expressed in the forming ganglia and their central and peripheral nerves from embryonic day 12.5 to 16.5 inclusive, with a peak around day 14.5 and low levels observed at day 16.5. Competition experiments performed at embryonic day 14.5 demonstrated that somatostatin1-14, somatostatin1-28, and Octreotide displaced specific binding with nanomolar affinities while CGP 23996 was only active at micromalar doses. Such displacements are compatible with the SSTR2 and/or SSTR4 pharmacology. During the time period examined, some transient somatostatin immunoreactive cell bodies and fibers were detected in the neural tube and in the sensory derivatives. These results demonstrate the existence, in neuronal derivatives, of a complex temporal and anatomical pattern of expression of somatostatin receptors, from the SSTR2/SSTR4 subtype(s), and somatostatin immunoreactivity. It appears that the transient expression of somatostatin receptors and/or somatostatin immunoreactivity characterizes critical episodes in the development of a cohort of neurons; a fact that unequivocally reinforces the notion that somatostatin plays a fundamental role during neurogenesis in vertebrates.

Ontogeny of somatostatin gene expression in rat forebrain

With hybridization histochemistry, somatostatin (SRIF) mRNA was detected in several neuronal populations of the basal diencephalon (anterior and posterior) and basal telencephalon (lateral) for the first time on the 14th day of gestation (E14). On E16, a large increase of the extent of expression was found in these populations. In addition, cells in the medial telencephalon and a few cells in the future allocortex also contained SRIF mRNA for the first time. In the prenatal period, the expression in the above populations continued to mature and individual nuclei with SRIF mRNA began to be recognizable. At birth, the overall pattern of SRIF gene expression was established but the ventral portions (hypothalamus, amygdala, allocortical areas) had higher levels of expression than the more dorsal ones (striatum and neocortex). Over the first 2 wk of life, this difference decreased and an adult-like pattern was found at postnatal day 21. We demonstrate that most of SRIF gene expression development takes place before birth. This description may serve as a basis for studies on the putative functions of SRIF during brain ontogeny.

Neuroendocrine regulation of thyrotropin-releasing hormone (TRH) in the tuberoinfundibular system

[...] It is now required to list each part needed for mucous excretion. They are two ducts in the brain substance, then a thin portion of membrane shaped as the infundibulum, then the gland that receives the tip of this infundibulum and the ducts that drive the mucus (pituita) from this gland to the palate and nares. [...] and I said that one (duct) [...] from the middle of the common cavity (third ventricle) descends [...] into the brain substance, and the end of this duct is [...] the sinus of the gland where the brain mucus is collected [...].

Neurotransmitter regulation of somatostatin secretion by fetal rat cerebral cortical cells in culture

Extensive studies exploring the regulation of hypothalamic somatostatin GHRIH release have been reported, but the factors regulating GHRIH release in the cerebral cortex have not been well defined. We have studied the effects of central neurotransmitters on GHRIH secretion by cultured fetal rat cerebral cortical cells and on intracellular GHRIH levels. Cells maintained in vitro for 15-20 days were incubated with dopamine (DA), acetylcholine (ACh), gamma-aminobutyric acid (GABA), norepinephrine (NE), serotonin (SE) or histamine (His) (10(-11) M to 10(3) M) for 30 minutes. Following incubation, immunoreactive GHRIH was measured by RIA in cell extracts and incubation media. DA increased intracellular GHRIH content but have no effect on GHRIH in the media. Both media and intracellular GHRIH content were significantly reduced by GABA and SE. The effect of NE was stimulatory at low (10(-9) M) and inhibitory at high (10(-5) M to 10(-3) M) concentrations. ACh was found to increase media GHRIH and to decrease intracellular GHRIH content; 30 min exposure to His did not significantly modify either media or intracellular GHRH. Our findings with fetal rat cerebral cortical cells in culture demonstrate that endogenous neurotransmitters do have the capacity to directly influence GHRIH regulation.

Neurochemical development of the hippocampal region in the fetal rhesus monkey. I. Early appearance of peptides, calcium-binding proteins, DARPP-32, and monoamine innervation in the entorhinal cortex during the first half of gestation (E47 to E90)

Although the entorhinal cortex is a key structure connecting the hippocampal formation with the rest of the cerebral cortex, little is known about its early chemoanatomical development in primates. In the present study, a cytoarchitectonic analysis and immunocytochemical detection of somatostatin, neurotensin, parvalbumin, calbindin-D 28K, DARPP-32, as well as tyrosine hydroxylase, dopamine-beta-hydroxylase, and serotonin, were carried out on serial sections of the entorhinal cortex of six rhesus monkey fetuses aged E47 to E90 (gestation period 165 days). At E56 the cortical plate of the entorhinal cortex already exhibited a sublamination; at E64 the lamina dissecans was partly formed, allowing the emergence of the lamina principalis externa and interna, and at E83 most of the regional and laminar subdivisions characteristic of the adult cortex could be identified, except for the rhinal sulcus restricted to a small dimple. The neurochemical development paralleled the early cytoarchitectonic differentiation, both largely preceding that of the neighboring cortical areas. The somatostatin-like immunoreactive innervation, first detected at E56, was very dense as early as E64 and displayed by E83 a laminar distribution similar to that found in the adult. Labeled neurons indicated an intrinsic origin for this innervation but an extrinsic connection might be present as labeled fibers in the subplate of the entorhinal cortex were in continuity with positive fibers in the intermediate zone of the hippocampal formation. A faint neurotensin-like immunoreactivity first detected at E64 became prominent at E83 in the entorhinal cortex but stopped abruptly at the anlage of the rhinal sulcus. The lack of neurotensin-labeled neurons contrasted with their presence in other parts of the hippocampal region and suggested a precocious extrinsic connection. Only rare parvalbumin-LIR neurons were detected at midgestation, whereas calbindin-D 28K was expressed from E47 on in Cajal-Retzius cells and from E56 on in various types of neurons in the cortical plate and subplate. Most characteristic was a category of medium-sized, deeply stained calbindin-LIR neurons, present only in the lamina principalis externa and possibly corresponding to the population of large neurons described by Kostovic et al. (1990, Soc Neurosci Abstr 16:846) in early developing entorhinal cortex of human fetuses. These and probably other neurons were also DARPP-32-positive, suggesting the possibility of an early dopaminergic regulation. Indeed, the monoaminergic innervation of the entorhinal cortex was detected from E56 on and gradually increased in density, displaying areal and laminar differences in the distribution of the dopaminergic, noradrenergic, and serotoninergic afferents.(ABSTRACT TRUNCATED AT 400 WORDS)

Ontogenesis of NADPH-diaphorase neurons in the mouse forebrain

Demonstration of NADPH diaphorase (NADPH-d) activity in the nervous system has recently gained considerable interest since it has been shown that this enzyme is a nitric oxide synthase (NOS). Therefore, histochemical staining of NADPH-d activity provides a specific labelling of neurons that use nitric oxide (NO). In this work, spatiotemporal distribution of NADPH-d neurons has been determined during forebrain ontogenesis. NADPH-d neurons first appeared between embryonic days 15 and 16 and were confined to the fronto-lateral aspect of the incipient corpus striatum and cortical subplate but were not present in the cortical plate. Until birth, NADPH-d neurons differentiated progressively in cortical subplate and striatum in rostro-caudal and latero-medial directions. For both regions, the adult cortical pattern was established during the first postnatal week. The pattern of genesis of NADPH-d neurons might be related to the spatiotemporal ontogenesis of catecholaminergic afferents to the forebrain described previously in the literature.

Low levels of somatostatin-like immunoreactivity in neocortex resected from presumed seizure foci in epileptic patients

The concentration of somatostatin-like immunoreactivity (SS-LI) was determined by radioimmunoassay in neocortical tissue resected from 20 patients with pharmacologically intractable complex partial seizures. Most resections included either the anterior temporal pole neocortex (15 cases) or cingulate gyrus neocortex (3 cases). The concentration of SS-LI was lowest in cortical tissue immediately adjacent to cortical tumors. Preoperative electrical recordings suggested that this tissue was the seizure focus. In vitro recordings showed that this tissue also exhibited abnormal hyperexcitable synaptic responses. Higher levels of SS-LI, similar to normal values previously reported in human cortex, were present in non-focal temporal neocortical tissue (resected from patients in whom the seizure focus was in the ipsilateral hippocampus) in which no hyperexcitable synaptic activity was present in vitro. The functional loss of inhibitory transmitters suggested by the low SS-LI levels might provide a theoretical basis for the hyperexcitability observed in vivo and in vitro.

Early transient expression of somatostatin (SRIF) immunoreactivity in dorsal root ganglia during ontogenesis in the rat

Immunofluorescence was used in the rat to study the early ontogenetic expression of somatostatin (SRIF) in the dorsal root ganglia (DRGs) from gestational day 10.5 to day 15.5. SRIF-immunoreactivity (IR) was not detectable in day-10.5 embryos, was first observed in DRGs at day 11.5, reached a peak in intensity and distribution at around day 13.5 and thereafter decreased to become undetectable by day 15.5 in the DRGs of the trunk region. The dynamic expression of SRIF-IR in DRG perikarya could be correlated with its expression in nerve fibers located in the limbs and the abdominal mesenchyme. Thus, SRIF-IR is expressed at a time when sensory fibers could have established connections with their embryonic targets and when DRG neurons could have undergone their final mitotic phase. These data showing the earliest and transient expression of a neuropeptide in developing DRGs confirm and extend the notion that SRIF plays an important role in developmental processes.

Induction of somatostatin by kainic acid in pyramidal and granule cells of the rat hippocampus

Seizures were induced in rats by systemic administration of kainic acid and, 1.5-12 h after, expression of preprosomatostatin and c-fos mRNAs in 9 hippocampal areas and in the cerebral perirhinal cortex was investigated using in situ hybridization histochemistry. Immunohistochemistry was also performed to study somatostatin peptide. In the control animals preprosomatostatin mRNA was expressed in some cells in the dentate hilus, the stratum oriens and the stratum radiatum of Ammon's horn, the subiculum and the cortex. Starting 3 h after kainic acid administration preprosomatostatin mRNA was expressed in a subpopulation of granule and pyramidal cells which did not normally express it. Preprosomatostatin mRNA-positive cells were markedly increased in the subiculum. Immunohistochemical examination confirmed that preprosomatostatin mRNA in granule and pyramidal cells was translated into peptide. In contrast, c-fos mRNA was induced in most hippocampal and cortical neurons starting 1.5 h after the kainic acid injection. When diazepam was injected to suppress the generalized seizures, preprosomatostatin mRNA was still expressed in pyramidal and subicular cells but not in granule cells.

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)

Differential ontogenetic expression and regulation of proenkephalin and preprosomatostatin mRNAs in rat caudate-putamen as studied by in situ hybridization histochemistry

Specific oligonucleotide probes and in situ hybridization histochemistry were used to study the ontogeny and regulation of the mRNAs for proenkephalin A and preprosomatostatin in rat brain. In adult brain the most intense hybridization signal for the proenkephalin A mRNA was in caudate putamen, nucleus accumbens and olfactory tubercle. By contrast, the hybridization signal for preprosomatostatin mRNA was more diffusely scattered throughout the brain, with high signals in the neocortex, olfactory bulb and hippocampal formation. Studies of the ontogeny of these mRNAs revealed a different pattern of ontogenetic expression and differential regulation by dopaminergic input. The mRNA for preposomatostatin reached the highest level within the first postnatal week, whereas proenkephalin A mRNA progressively increased throughout the entire period studied. In addition the proenkephalin A mRNA showed a medial to lateral gradient in 2-day-old rat striatum which disappeared with increasing age, whereas preprosomatostatin mRNA increased in most brain areas in fairly uniform fashion with increasing age. Treatment of newborn rats with 6-hydroxydopamine increased the expression of proenkephalin A mRNA by 1.6 fold but had no effect on the expression of preprosomatostatin mRNA. The 6-hydroxydopamine-induced change in proenkephalin A mRNA expression was not observed until postnatal day 32, indicating that enkephalin-containing neurons of the developing striatum are relatively insensitive to dopamine input and that they cannot compensate for the neonatal lesion, despite the fact that the insult was given in a period of high plasticity of the neural tissue.

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.

Ontogeny of somatostatin receptors in the rat somatosensory cortex

The distribution and density of SRIF receptors (SRIF-R) were studied during development in the rat somatosensory cortex by in vitro autoradiography with monoiodinated [Tyr0-DTrp8]S14. In 16-day-old fetuses (E16), intense labeling was evident in the intermediate zone of the cortex while low concentrations of SRIF-R were detected in the marginal and ventricular zones. The highest density of SRIF-R was measured in the intermediate zone at E18. At this stage, labeling was also intense in the internal part of the developing cortical plate; in contrast, the concentration of binding sites associated with the marginal and ventricular zones remained relatively low. Profound modifications in the distribution of SRIF-R appeared at birth. In particular, a transient reduction of receptor density occurred in the cortical plate. During the first postnatal week, the density of receptors measured in the intermediate zone decreased gradually; conversely, high levels of SRIF-R were observed in the developing cortical layers (II to VI). At postpartum day 13 (P13), a stage which just precedes completion of cell migration in the parietal cortex, the most intensely labeled regions were layers V-VI and future layers II-III. From P13 to adulthood, the concentrations of SRIF-R decreased in all cortical layers (I to VI) and the pattern of distribution of receptors at P21 was similar to that observed in the adults.(ABSTRACT TRUNCATED AT 250 WORDS)

Ontogeny of somatostatin mRNA-containing perikarya in the rat central nervous system

The distribution of neuronal perikarya containing somatostatin mRNA in the developing rat brain was investigated with in situ hybridization histochemistry. This study describes the expression of somatostatin mRNA during selected perinatal stages and demonstrates regional changes in somatostatin mRNA expression at the single cell level. The mRNA expression closely parallels previously reported developmental localization of the peptide (Inagaki et al., 1982; Shiosaka et al., 1982). As early as embryonic day 13 (E13), somatostatin mRNA was observed in discrete spinal cord and brainstem regions. At birth, densely hybridized somata could be seen primarily in ventral and caudal brain areas with small scattered neurons in the hippocampus and dorsal neocortex. After birth, somatostatin mRNA increased in forebrain regions, such as the hippocampus, dorsal neocortex, and caudate. By postnatal day 14 (P14), the distribution in the telencephalic and diencephalic regions approached that of the adult brain. Several brain regions manifested large changes in the density of somatostatin mRNA hybridization during development. For example, the cerebellar vermis and brainstem contained somatostatin mRNA perikarya during early postnatal development but decreased in these regions in the adult. During perinatal development, increases in somatostatin mRNA content were the results of increases in both the number of neurons containing somatostatin mRNA as well as in the amount of this mRNA expressed in each cell. As the brain differentiates, the apparent numbers of somatostatin mRNA containing neurons in certain brain regions are reduced. These data provide evidence for transient somatostatinergic neurons during early development in discrete areas of the occipital cortex, pyriform cortex, cerebellum, and brainstem and suggest that this peptide may play a role in the development of these regions.

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

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

Transient expression of somatostatin receptors in the rat visual system during development

The ontogeny of somatostatin receptors in the rat visual system was studied by auto-radiography, using [125I-Tyr0,DTrp8]S14 as a radioligand. The binding sites showed high affinity for somatostatin and somatostatin analogues, and were regulated by GTP as early as day 16 of fetal life (E16), indicating that they represent functional somatostatin receptors. The density of somatostatin receptors was quantified by computerized image-analysis of film autoradiograms, and by grain counting on emulsion-coated slides. During fetal life, somatostatin receptors were observed in the retina, optic nerve, optic chiasma, optic tract, and lateral geniculate nucleus. The highest densities of somatostatin receptors were measured from E16 to E18 in the retina and primary optic pathways. During the first postnatal days, the density of somatostatin receptors decreased dramatically in the retina. In both the optic pathways and dorsal lateral geniculate nucleus, somatostatin receptors gradually disappeared, and the levels of somatostatin receptors were almost undetectable at postnatal day 21 (P21). Conversely, the density of somatostatin receptors remained stable in the ventral lateral geniculate nucleus during the early postnatal life (P0-P7). The timing of expression and the localization of somatostatin receptors in the developing visual system suggest that the immature ganglion cells are responsible for the expression of these evanescent somatostatin receptors. After eye opening, the distribution patterns of somatostatin receptors in the retina and the lateral geniculate nucleus were similar to those observed in adults. In particular, from P14 onwards, somatostatin receptors were concentrated in the inner plexiform layer and, to a lesser extent, in the ganglion cell and photoreceptor layers. In the ventral lateral geniculate nucleus, a heterogeneous distribution of somatostatin receptors was noted, the highest densities being found in the intergeniculate leaflet and the medial zone limiting the parvo-magnocellular interface. The distribution of somatostatin receptors in the retina and the ventral lateral geniculate nucleus after the second postnatal week, together with the presence of somatostatin-like immunoreactive elements in these structures, provide support for the involvement of somatostatin as a neurotransmitter or neuromodulator in the visual system of the adult rat. Conversely, the transient expression of somatostatin receptors observed before maturation and complete organization of the optic pathways suggests that somatostatin plays a trophic role during development of the visual system.

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.