Phylogenetic and anatomical distribution of somatostatin in vertebrates

An immunohistochemical study of somatostatin in the stomach and the small intestine of the African ostrich (Struthio camelus)

The aim of the present study was to clarify the distribution and relative frequencies of somatostatin (SST)-producing cells in the stomach and the small intestine of the ostrich by using immunohistochemistry. The results indicated that somatostatin-immunoreactive (SST-IR) cells were distributed in mucosal layers of the proventriculus, duodenum, jejunum and ileum. However, no immunoreactivity was observed in the gizzard. SST-IR cells were found at the lower part of glandular lobule in the proventriculus, which were oval and round generally. SST-IR cells were present in the mucous membrane of entire small intestine of the ostrich. SST-IR cells had round and spherical shapes (closed-type cells), or spindle and pyriform shapes (open-type cells) in the small intestine. SST-positive cells were localized preferentially in the proventriculus of the 60-day-old ostrich. These results indicated that SST might be involved in functional and developmental regulation of gastrointestinal tract of the ostrich.

Adrenomedullin in nonmammalian vertebrate pancreas: an immunocytochemical study

Adrenomedullin (AM) immunoreactive cells have been identified, by immunocytochemical methods, in the endocrine pancreas of seven nonmammalian vertebrate species, belonging to the cartilaginous and bony fish, amphibian, reptilian, and bird classes. The frequency and distribution of the pancreatic AM cells vary among the different animals. In most species, these cells are found scattered mainly among the exocrine component, with a few present in the islet-like structures. The distribution of AM cells in both fish species and Xenopus shows an inverse pattern, since almost every AM cell is located in the islets. In addition, the colocalization of AM with other classical pancreatic peptide immunoreactivities has been analyzed. In numerous cells, AM immunoreactivity did not colocalize with the other hormones, suggesting that AM-producing cells might constitute a new endocrine cell type in the pancreas of many species. Nevertheless, in other cells a species-specific pattern of colocalizations with insulin, somatostatin, glucagon, and pancreatic polypeptide was found, indicating that complex interactions among all these hormones may occur. In conclusion, AM represents a new regulatory peptide of the endocrine nonmammalian vertebrate pancreas, which is possibly involved in the modulation of insulin secretion and other pancreatic functions.

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.

Antisomatostatin-induced growth acceleration in chinook salmon (Oncorhynchus tshawytscha)

Since somatostatin (SRIF) inhibits the release of growth hormone (GH), its immunoneutralization may provide an alternative to GH therapy as a means of enhancing somatic growth in fish. The present study examined the feasibility of accelerating growth in juvenile chinook salmon by means of antiSRIF administration. Yearling salmon of Nicola River stock (BC, Canada) were injected intraperitoneally every 5 days, for a total of 40 days, with either SRIF (1 μg g-1 body wt.), antiSRIF (SOMA-10, 1 μg g(-1)), recombinant bovine GH (rbGH, 2.5 μg g(-1)), recombinant porcine GH (rpGH, 2.5 μg g(-1)) or saline (controls). No significant differences were observed in length, weight or final condition factor (k) between the SRIF-treated and control fish over the experimental period. However, the fish treated with the antiSRIF were significantly (p ≤ 0.05) longer and heavier than the control salmon after 25 and 30 days respectively. Furthermore, antiSRIF treatment caused a lowering in k when compared to the control salmon. Fish injected with rbGH or rpGH were significantly longer and heavier than all other groups (p ≤ 0.05), after only 5 days. GH treated groups also returned higher k when compared against all other treatments (p ≤ 0.05). No differences were observed in growth between the two rGH treatments over the experimental period.

Measurement of somatostatin release in rat brain by microdialysis

We determined the most suitable conditions for measuring the somatostatin (SRIF) level by brain microdialysis and investigated its release from the hypothalamus. The relative recovery rate of SRIF was 8.4 +/- 0.5% (mean +/- SE) using a polycarbonate (PC) membrane with the push-pull method at a flow rate of 2 microliters/min. Using tubes with an internal diameter of 0.28 mm and lengths of 5, 25, 50 and 100 cm, the relative recovery rates using a PC membrane with the push method were 8.2 +/- 0.5%, 7.3 +/- 0.6%, 6.2 +/- 0.5% and 4.1 +/- 0.6%, respectively. When using tubes with an internal diameter of 0.1 mm and lengths of 5, 25, 50 and 100 cm, the relative recovery rates were 7.3 +/- 0.7%, 5.6 +/- 1.0%, 3.5 +/- 1.1% and 1.4 +/- 0.7%, respectively. The relative recovery rate was 5.2 +/- 0.5% with a polysulfone (PS-F, Fresenius) membrane, 4.5 +/- 0.4% with a PS-H (Hospal) membrane, 2.6 +/- 0.2% with an ethylenevinyl alcohol membrane (EVAL), 5.1 +/- 0.8% with a polyvinyl alcohol (PVA) membrane and 10.4 +/- 0.8% with a PS-K (Kaneka) membrane. With the push method, the extracellular SRIF level in rat pituitary was 42.8 +/- 1.8 pg/ml with a PC membrane, 23.1 +/- 2.9 pg/ml with an EVAL membrane at a flow rate of 2 microliters/min. With the push-pull method, it was 52.7 +/- 5.2 pg/ml using a PC membrane, 33.5 +/- 2.8 pg/ml using a PVA membrane and 54.4 +/- 3.2 pg/ml using a PS-K membrane.(ABSTRACT TRUNCATED AT 250 WORDS)

Distribution of somatostatin-immunoreactivity in the brain of the larval lamprey (Petromyzon marinus)

The detailed distribution of somatostatinergic neurons and fibre tracts in the brain of larval lamprey was studied in serially sectioned material using immunocytochemical techniques. Neurons were found to be arranged in four nuclei: a hypothalamic nucleus consisting of both small cerebrospinal fluid-contacting neurons and larger non-contacting neurons, a thalamomesencephalic nucleus and two isthmotrigeminal reticular nuclei. The hypothalamic nucleus is the first to differentiate. Analysis of young larvae showed that somatostatin-immunoreactivity first appeared in hypothalamic cells (12 mm larvae), while it appeared later in the other nuclei. The different somatostatin-immunoreactive fibre tracts innervate different regions of the brain. In addition, somatostatin-immunoreactive fibres originating from hypothalamic neurons were found in the anterior neurohypophysis, which suggests the presence of a hypothalamohypophysial somatostatinergic system in lampreys.

Co-localization of tyrosine hydroxylase, GABA and neuropeptide Y within axon terminals innervating the intermediate lobe of the frog Rana ridibunda

Possible co-existence of gamma-aminobutyric acid (GABA), catecholamines, and neuropeptide Y (NPY) in the same nerve terminals of the frog intermediate lobe was investigated by immunocytochemistry at the electron microscopic level. Co-localization of GABA and tyrosine hydroxylase (TH) was studied by using a double immunogold labeling procedure. Co-localization of glutamate decarboxylase (GAD) and NPY was studied by combining, respectively, the peroxidase-antiperoxidase method and a radioimmunocytochemical labeling procedure. Catecholamines and GABA were systematically co-localized in nerve endings of the pars intermedia. Most of the NPY-immunoreactive fibers also contained GAD-like immunoreactivity. However, a few NPY-positive nerve terminals were not immunoreactive for GAD. These data provide evidence for co-existence of a regulatory peptide (NPY) and several neurotransmitters (i.e., GABA and catecholamines) within the same axon terminals in the intermediate lobe. Since GABA, dopamine, and NPY have all been shown to inhibit the activity of frog melanotrope cells, the present findings suggest that these neuroendocrine factors may interact either at the pre-synaptic or post-synaptic level.

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)

Radioimmunoassay for salmon pancreatic somatostatin-25

A specific and sensitive radioimmunoassay (RIA) for the measurement of plasma levels of somatostatin-25 (SS-25) in salmon was developed using antisera raised against coho salmon (Oncorhynchus kisutch) SS-25. Somatostatin-25 was iodinated by the chloramine-T method and repurified on Sephadex G-25. The RIA was performed using a double antibody (goat anti-rabbit gammaglobulin as second antibody) method under disequilibrium conditions. Plasma from several salmonids (coho, chinook, rainbow trout, brook trout, arctic char, lake trout, and whitefish) as well as plasma from some nonsalmonids (sucker, bluegill) cross-reacted with the antisera; serial dilutions of plasma from rainbow trout, brook trout, chinook salmon, and coho salmon were parallel to the SS-25 standard curve. Plasma from catfish showed negligible cross-reactivity. None of the mammalian somatostatins (somatostatin-14, somatostatin-28). U II, or other pancreatic hormones (insulin, glucagon) tested showed significant cross-reactivity with the antibody in the assay system. The lowest detectable level of SS-25 was 5 pg/tube; especially reproducible results were obtained in the range of 0.15-1.20 ng/ml, which appears to be the normal range of SS-25 circulating in the plasma of salmonids. Intra- and interassay coefficients of variation were 5.7 and 12.6%, respectively. Injection of glucose into chinook salmon resulted in an elevation of plasma SS-25 titers within 30 min and was coincident with hyperglycemia.

Immunocytochemical and ultrastructural characterization of endocrine cells in chicken proventriculus

The endocrine cells of the chicken proventriculus were investigated immunocytochemically, using the peroxidase-antiperoxidase technique on paraffin and semithin sections for light microscopy, and immunogold staining in osmium-fixed material for electron microscopy. The fixation procedure also allowed a detailed ultrastructural investigation. Twenty-three antisera were tested and 7 immunoreactive cell-types were identified: D-cells containing somatostatin-like peptide; EG-cells immunoreactive to anti-glucagon, anti-GLP1 and anti-neurotensin; NT-cells labelled only with anti-neurotensin; BN-cells containing bombesin-like material; ENK-cells showing met-enkephalin immunoreactivity; EC-cells reactive to anti-serotonin; and APP-cells positive to anti-avian pancreatic polypeptide. In addition, enterochromaffin-like (ECL) cells, were also detected by electron microscopy. The presence of ENK-cells and the ultrastructure of these and NT-cells are described for the first time in chicken proventriculus, and glucagon. GLP1 and neurotensin are shown to be colocalized in the EG-cells.

Distribution of somatostatin-14 and somatostatin-28 gastrointestinal-pancreatic cells of rats and humans

Somatostatin-14 and somatostatin-28 are biologically active peptides derived from the posttranslational cleavage of prosomatostatin. Because both peptides are found in variable concentrations in the gastrointestinal (GI) tract and pancreas, it has been contended that somatostatin-28 is either an intermediate in the processing to somatostatin-14 or a terminal product derived from prosomatostatin. To address this question, two antisera were used to recognize epitopes in two regions of somatostatin-14; one with high specificity for somatostatin-14 and the other interacting with prosomatostatin, somatostatin-28, and somatostatin-14. Distribution of these peptides was measured in extracts of pancreas and mucosa and submucosa/muscularis from the rat and human GI mucosal biopsies; the antisera were used to immunostain cells in these tissues. Extracts of human and rat intestinal mucosa contained both somatostatin-28 and somatostatin-14. By immunocytochemistry, D cells in stomach and pancreas and neural processes in the intestine, extending into the mucosal villi adjacent to endocrine cells, stained with both antisera indicating the presence of somatostatin-14, prosomatostatin, and possibly somatostatin-28. In contrast, endocrine cells in the gut reacting with antisera against somatostatin-28 did not immunostain with somatostatin-14-specific antisera. Thus, these data suggest that somatostatin-28 is the terminal peptide processed from prosomatostatin in intestinal mucosal cells, whereas somatostatin-14 is the major final product in gastric and pancreatic D cells and neurons. The localization of somatostatin-28 and somatostatin-14 in different cells in the pancreas and GI tract implies that they serve different functions.

Distribution and relative abundance of neurons in the pigeon forebrain containing somatostatin, neuropeptide Y, or both

Immunohistochemical studies in several mammalian species and in red-eared turtles have shown that somatostatin (SS) and neuropeptide Y (NPY) co-occur in a substantial proportion of the telencephalic neurons containing either. To explore further the possibility that telencephalic neurons co-containing SS and NPY may be evolutionarily conserved among amniotes, we determined the distribution and co-occurrence of SS and NPY in forebrain neurons in pigeons. Single-label immunohistochemical studies revealed the presence of overlapping populations of SS+ neurons and NPY+ neurons in most of the major subdivisions of the telencephalon. Double-label immunofluorescence studies revealed that in subdivisions of the telencephalon that are comparable to mammalian cortex (i.e., those dorsal and lateral to the basal ganglia), the vast majority of NPY+ neurons were also SS+, whereas a major and regionally variable percentage of the SS+ neurons were not NPY+. In contrast, within the basal telencephalon (including the basal ganglia and several other structures) neurons labeled only for NPY or only SS were more abundant than those containing both neuropeptides. Outside the telencephalon, the only forebrain cell group containing neurons in which SS and NPY were co-localized was in the lateral hypothalamus. A series of double- and triple-label immunohistochemical studies was undertaken to determine the extent of co-occurrence of SS and NPY in striatal neurons and the relationship of these neurons to striatal neurons containing other neuropeptides. In addition, immunohistochemical single- and double-label techniques were employed in conjunction with retrograde-labeling by fluorogold to determine the projections of SS+ and NPY+ striatal neurons. The results indicate that: 1) a population of striatal interneurons containing both SS and NPY exists in pigeons and constitutes approximately the same fraction of all striatal neurons as reported in mammals, 2) neurons containing NPY (but not SS) form a second, larger population of striatal interneurons, 3) neurons containing SS (but not NPY) form a third population of striatal interneurons that is approximately half as abundant as the NPY+ interneuron population, and 4) one-third of the substance P-containing striatonigral projection neurons also contain SS. The existence in pigeons of a major population of neurons containing both SS and NPY throughout the telencephalon, the existence of a population of neurons containing only SS in cortex-equivalent parts of the telencephalon, and the existence of a population of interneurons containing only NPY in the striatum is consistent with findings in mammals and turtles.(ABSTRACT TRUNCATED AT 400 WORDS)

Modulation of neuropeptide-stimulated pituitary hormone secretion in hatchling turtles

Neuropeptides that have relatively narrow actions on mammalian pituitary secretion may have divergent effects on pituitary hormone secretion in ectothermal vertebrates. In turtles, secretion of both thyrotropin (TSH) and growth hormone (GH) can be stimulated in vitro by thyrotropin-releasing hormone (TRH) and by members of corticotropin-releasing hormone (CRH) and growth hormone-releasing hormone (GHRH) peptide families. To determine if these neuropeptides share common modes of action, and to study other potential regulators of the turtle pituitary, somatostatin-14 (SRIH) and monoamines were tested for direct effects on in vitro basal and neuropeptide-stimulated TSH and GH secretion. Pituitary glands from young turtles (Pseudemys scripta) were cultured in the presence of 25 nM TRH, ovine CRH, or rat GHRH with or without SRIH. Glands were incubated for several 2-hr periods in medium alone or in medium containing peptides. Preincubation for 4 hr with SRIH (6 or 60 nM) significantly reduced basal and TRH-stimulated TSH and GH output (SRIH present during entire incubation). In another experiment, basal hormone secretion was reduced when SRIH (60 nM) was present only during the 2-hr basal period; however, reduction of TSH and GH responses to TRH required the presence of SRIH (60 nM) during the basal period and the period of stimulation. TSH responses to 25 nM oCRH and rGHRH and GH responses to rGHRH were significantly reduced by preincubation with 60 nM SRIH. The biogenic amines, dopamine (DA), serotonin (5HT), and norepinephrine (NE) (50 or 500 nM) were tested for possible direct actions on basal and neuropeptide-stimulated pituitary TSH and GH secretion.(ABSTRACT TRUNCATED AT 250 WORDS)

Relationship between serum growth hormone levels and the brain and pituitary content of immunoreactive somatostatin in the goldfish, Carassius auratus L

In this study, the relationships between endogenous brain and pituitary immunoreactive somatostatin (irSRIF) and circulating growth hormone (GH) levels in the goldfish were examined using two approaches. First, the amount of irSRIF in extracts of the pituitary gland and various brain regions was measured by radioimmunoassay several times throughout the year and was compared to serum GH levels at each time. The amounts of irSRIF in extracts of the pituitary gland, hypothalamus, and telencephalon were found to be inversely related to seasonal changes in serum GH levels, such that irSRIF was highest in these regions when serum GH levels were lowest (November and February). Conversely, irSRIF in these regions was lower in May, June, and July when serum GH levels were highest. These results suggest that endogenous irSRIF in the pituitary and forebrain may participate in the regulation of seasonal changes in serum GH levels in the goldfish. In extracts from other brain regions (thalamus + midbrain and cerebellum + medulla), some changes in the amount of irSRIF were observed among the various sample times, but these variations were not related to changes in serum GH levels. In a second set of experiments, the origin of irSRIF fibers innervating the goldfish pituitary gland was examined by using brain lesioning techniques to destroy regions of the forebrain known to contain irSRIF perikarya and fibers, and subsequently measuring the amount of irSRIF in the pituitary gland. Lesions in the preoptic area of the forebrain resulted in increased serum GH levels concomitant with a decrease in pituitary irSRIF content. This provides direct evidence that the preoptic area is the origin of a somatostatinergic projection inhibiting GH secretion from the goldfish pituitary. Lesions centered in the nucleus lateral tuberis (NLT) pars anterioris did not influence serum GH levels or the pituitary content of irSRIF. In contrast, more posterior lesions centered in the NLT pars posterioris (NLTp) resulted in a dramatic reduction in the amount of irSRIF in the pituitary. This suggests that the majority of irSRIF projections to the goldfish pituitary pass through the area destroyed by the lesion centered in the NLTp; it is also possible that perikarya within this area may be the origin of at least some of the irSRIF-containing fibers in the goldfish pituitary. Together, results from the present study provide evidence of a functional relationship between circulating levels of GH and endogenous brain and pituitary irSRIF in the goldfish.

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

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

Different cellular distributions of two somatostatins in brain and pancreas of salmonids, and their associations with insulin- and glucagon-secreting cells

Invariant somatostatin-14 (SST-14) and somatostatin-25 (SST-25), isolated from coho salmon pancreas (Plisetskaya et al., 1986a) are likely coded by two distinct somatostatin genes. The present study was undertaken to investigate whether these genes are expressed in the same or in different cell types in the pancreatic islets and in the brain of two salmonids: rainbow trout and coho salmon. Antibodies generated against SST-14, mammalian (m) SST-28(1-14), salmon (s) SST-25, salmon insulin, and salmon glucagon were used as immunocytochemical probes. Two distinct cell types containing SSTs were revealed in the pancreas of both salmonid species: one cell type immunoreactive to both SST-14 and mSST-28(1-14) and the other cell type immunoreactive only to sSST-25. The SST-14/mSST-28(1-14)-positive cells were limited to the more central parts of the islets, in apposition to the insulin-positive cells: sSST-25-positive cells were located more peripherally and were associated topographically with the glucagon-positive cells. In contrast to the pancreas, neurons in the neurohypophysis and hypothalamus of the rainbow trout and coho salmon contained only SST-14-like and mSST-28(1-14)-like immunoreactivities, while immunoreactivity to sSST-25 was completely absent. These results suggest that differentiation in the pancreas and brain of salmonid fishes results in cell types in which SST genes are separately expressed. The close topographical association of sSST-25 with glucagon cells, and of SST-14 with insulin cells, in the pancreatic islets implies yet unknown functional regulatory relationships that require detailed study.

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

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

Sexually dimorphic age-related differences in the immunocytochemical distribution of somatostatin in the platyfish

Somatostatin (SRIF) was localized by immunocytochemistry in the brains and pituitary glands of male and female platyfish (Xiphophorus maculatus) between the ages of 8 and 30 months (average life span is 30 months). In the brain, immunoreactive (ir-) SRIF is found in the perikarya of the ventrobasal hypothalamus (nucleus lateralis tuberis, nucleus anterior tuberis), dorsomedial hypothalamus, dorsal thalamus, ventral tegmentum and rhombencephalic basal plate; in the pituitary it is localized surrounding the ir-growth hormone containing cells of the caudal pars distalis, and in older fish it is also found within certain cells of the pars intermedia. We have demonstrated that there are consistent, sexually dimorphic, age-related changes in the intensity and/or distribution of ir-SRIF. The sexual dimorphism of the changes in SRIF immunoreactivity during the aging of platyfish may be related to the different patterns of growth observed in males and females.

The distribution of proenkephalin-derived peptides in the central nervous system of turtles

The present study was carried out to examine if peptides similar to the various opioid peptide products of mammalian proenkephalin are present in the turtle central nervous system and to determine their distribution. Antisera against several enkephalin peptides were used: leucine-enkephalin (LENK), methionine-enkephalin (MENK), methionine-enkephalin-arg6-phe7 (MERF), methionine-enkephalin-arg6-gly7-leu8 (MERGL), Peptide E (PEPE), and BAM22P. Their specificity and cross-reactivity were carefully examined. The results indicated that LENK, MENK, and MERF (or highly similar peptides) are present in the turtle central nervous system, and that a peptide showing immunological similarity to BAM22P and PEPE also appeared to be present. In contrast, MERGL did not appear to be present. The distributions of the immunoreactive labeling for LENK, MENK, MERF, BAM22P, and PEPE were indistinguishable, and double-label studies showed that LENK, MERF, and BAM22P were colocalized within individual neurons and fibers. Although all of the above substances were observed in the same cell groups, there was some regional variation, in terms of which enkephalin peptide appeared to be most abundant. The distributions of these enkephalin peptides were very similar to those previously described in mammals and birds. Enkephalin was more abundant in the basal ganglia than in overlying telencephalic regions. Within the basal ganglia, enkephalin was present in striatal neurons and fibers and in pallidal fibers, thereby suggesting the existence of an enkephalinergic striatopallidal projection. Sensory relay nuclei of the thalamus were generally poor in enkephalinergic fibers, whereas the hypothalamus was rich in enkephalinergic neurons and fibers. Enkephalinergic neurons and fibers were present in the midbrain central gray. As is true of neurons of the nucleus spiriformis lateralis of the avian pretectum, the neurons of the homologous cell group in turtles, the dorsal nucleus of the posterior commissure of the pretectum, were found to contain enkephalin and have an enkephalinergic projection to the deep layers of the ipsilateral tectum. Enkephalinergic neurons and fibers were also abundant in the entry zones of the trigeminal nerve and dorsal root fibers of the spinal cord.(ABSTRACT TRUNCATED AT 400 WORDS)

Characterization of coho salmon (Oncorhynchus kisutch) islet somatostatins

Three different somatostatins have been isolated from the pancreatic islet tissue of the coho salmon (Oncorhynchus kisutch) by gel filtration and HPLC. Two of these peptides contain 14 amino acids and the larger third peptide consists of 25 amino acids. The sequence of the salmon SST-25 is Ser-Val-Asp-Asn-Leu-Pro-Pro-Arg-Glu-Arg-Lys-Ala-Gly -Cys-Lys-Asn-Phe-Tyr-Trp-Lys-Gly-Phe-Thr-Ser-Cys. The sequence of the salmon SST-14-I is Ala-Gly-Cys-Lys-Asn-Phe-Phe-Trp-Lys-Thr-Phe-Thr-Ser-Cys. The other small somatostatin (SST-14-II) which was not sequenced has an amino acid composition identical to the C-terminal 14 amino acids of the SST-25 and it is probably derived from this larger form. Evidence for low levels of a somatostatin containing 28 amino acids is also presented. This SST-28 appears to be an N-terminal extended precursor of SST-25 or a peptide derived via alternative processing of a common preprosomatostatin. Injected into juvenile salmon, SST-25 caused a decline in circulating levels of plasma insulin, depletion of liver glycogen, and activation of lipolytic pathways. Juvenile salmon treated with anti-SST-25 serum revealed elevated levels of plasma insulin as well as an increase of the glycogen content of the liver.

Somatostatin stimulates ACTH release in brown trout (Salmo trutta L.)

Injections of somatostatin (SRIF) produced small but significant increases in the serum cortisol concentration of brown trout in which endogenous ACTH secretion was suppressed with dexamethasone. SRIF did not stimulate in vitro secretion of cortisol by trout interrenal tissue. These results suggest that SRIF may play a minor role in ACTH secretion in salmonids.

Gastrointestinal somatostatin: distribution, secretion and physiological significance

Somatostatin-like immunoreactivity (SLI) has been found throughout the gastrointestinal tract in all species examined. In the stomach it is mainly present in endocrine-type D-cells whereas in the intestine there is also an extensive distribution in enteric neurones. In all regions of the gastrointestinal tract multiple forms of somatostatin exist. A precursor (prosomatostatin) has been partially sequenced, three forms with 20 (SS-20), 25 (SS-25) and 28 (SS-28) amino acids completely sequenced, and somatostatin-14 (SS-14) demonstrated by radioimmunoassay. Both SS-14 and SS-28 exert a wide range of actions on the gastrointestinal tract and there is strong supportive evidence for a role in the regulation of gastric acid and gastrin secretion, gastrointestinal motility and intestinal transport. Both in vivo and in vitro studies on the secretion of gastric SLI into the vasculature have shown that nutrients initiate the process but that subsequent events are regulated by a complex interplay between hormonal and neuronal pathways. GIP is one of the most potent hormonal secretagogues. In the stomach, acetylcholine, opioid peptides and substance P are probably involved in parasympathetic inhibitory pathways and gastrin releasing peptide in stimulatory pathways. The sympathetic nerves are also stimulatory. Regulation of secretion of intestinal SLI has not been so extensively studied. Although SLI is also found in the gastrointestinal lumen the significance is unclear. Despite these advances the exact route of delivery of somatostatin to its target organs is uncertain and paracrine, endocrine and neural pathways may all be involved.

An elasmobranchian somatostatin: primary structure and tissue distribution in Torpedo marmorata

Extracts of brain, stomach, pancreas, and intestine from Torpedo marmorata, an elasmobranchian cartilaginous fish, contained somatostatin-like immunoreactivity. Gel filtration studies demonstrated that material with the elution volume of somatostatin-14 was the only component detected in all tissue extracts. This result contrasts with the situation in mammals where prosomatostatin is processed to multiple molecular forms in a tissue-specific manner. Somatostatin from pancreas and gut was purified to homogeneity and amino acid sequence analysis indicated that T. marmorata somatostatin from both tissues has the same structure as somatostatin-14 isolated from the higher vertebrates. Further examination of other lower vertebrate species is required in order to test the hypothesis that the ability to regulate the production of multiple forms of a regulatory peptide from a single precursor molecule developed only relatively late in evolution.

Localization and identification of neuropeptide Y (NPY)-like immunoreactivity in the frog brain

The distribution of neuropeptide Y (NPY) in the central nervous system of the frog Rana ridibunda was determined by immunofluorescence using a highly specific antiserum. NPY-like containing perikarya were localized in the infundibulum, mainly in the ventral and dorsal nuclei of the infundibulum, in the preoptic nucleus, in the posterocentral nucleus of the thalamus, in the anteroventral nucleus of the mesencephalic tegmentum, in the part posterior to the torus semicircularis, and in the mesencephalic cerebellar nucleus. Numerous perikarya were also distributed in all cerebral cortex. Important tracts of immunoreactive fibers were found in the infundibulum, in the preoptic area, in the lateral amygdala, in the habenular region, and in the tectum. The cerebral cortex was also densely innervated by NPY-like immunoreactive fibers. A rich network of fibers was observed in the median eminence coursing towards the pituitary stalk. Scattered fibers were found in all other parts of the brain except in the cerebellum, the nucleus isthmi and the torus semicircularis, where no immunoreactivity could be detected. NPY-immunoreactive fibers were observed at all levels of the spinal cord, with particularly distinct plexus around the ependymal canal and in the distal region of the dorsal horn. At the electron microscope level, NPY containing perikarya and fibers were visualized in the ventral nuclei of the infundibulum, using the peroxidase-antiperoxidase and the immunogold techniques. NPY-like material was stored in dense core vesicles of 100 nm in diameter. A sensitive and specific radioimmunoassay was developed. The detection limit of the assay was 20 fmole/tube. The standard curves of synthetic NPY and the dilution curves for acetic acid extracts of cerebral cortex, infundibulum, preoptic region, and mesencephalon plus thalamus were strictly parallel. The NPY concentrations measured in these regions were (pmole/mg proteins) 163 +/- 8, 233 +/- 16, 151 +/- 12 and 60 +/- 13, respectively. NPY was not detectable in cerebellar extracts. After Sephadex G-50 gel filtration of acetic acid extracts from whole frog brain, NPY-like immunoreactivity eluted in a single peak. Reverse phase high performance liquid chromatography (HPLC) and radioimmunoassay were used to characterize NPY-like peptides in the frog brain. HPLC analysis revealed that infundibulum, preoptic area and telencephalon extracts contained a major peptide bearing NPY-like immunoreactivity. The retention times of frog NPY and synthetic porcine NPY were markedly different. HPLC analysis revealed also the existence, in brain extracts, of several other minor components cross-reacting with NPY antibodies.(ABSTRACT TRUNCATED AT 400 WORDS)

In vitro release of growth hormone from the pituitary gland of tilapia, Oreochromis mossambicus

The release of growth hormone from the proximal pars distalis of the tilapia, Oreochromis mossambicus, was significantly stimulated by cortisol (1 microgram/ml) in an in vitro system. Growth hormone released into the medium and remaining in the tissue was measured by densitometry after gel electrophoresis. Neither triiodothyronine (6.7 ng/ml) nor equimolar concentrations of thyroxin altered the release of growth hormone. In combination with cortisol, triiodothyronine did not alter the effect of cortisol alone.

Immunoreactive and bioactive somatostatin-like material is present in tobacco (Nicotiana tabacum)

Immunoreactive and biologically active somatostatin-like material is present in extracts of tobacco plants (Nicotiana tabacum). Comparative chromatographic and immunological characterization of this peptide along with synthetic (hypothalamic-like) somatostatin-14 and -28, indicates that both molecular forms are present in the plant. Tobacco-somatostatin inhibits the prostaglandin E2-induced release of growth hormone from cultured anterior pituitary cells. This finding raises questions concerning the evolutionary mechanisms responsible for the presence of this neuropeptide in plants, and the physiological significance of this phenomena.

Somatostatin-like immunoreactivity in the pituitary and brain of three teleost fish species: somatostatin as a potential regulator of prolactin cell function

Somatostatin-like immunofluorescence occurs in the hypothalamus and neurohypophysis of three euryhaline teleosts: tilapia, killifish, and mudsucker. This immunofluorescence was eliminated by incubating the primary antibody with excess somatostatin or somatostatin-28 but not with urotensin II, a partial analogue of somatostatin. In all three fishes, the strongest reaction was seen in the proximal pars distalis and parts of the pars intermedia. Strongly fluorescing processes from cells of the preoptic nucleus extend toward the pituitary. Distinct fluorescence was also associated with the neurohypophysis penetrating into the rostral pars distalis in the tilapia but not in the killifish or mudsucker. In the tilapia, an extensive network of immunofluorescent fibers and small cells were present in the anterior dorsolateral telencephalon, in addition to a moderately fluorescing group of cells anterolateral to the preoptic nucleus. A small area of diffuse fluorescence was also seen in the anterior dorsolateral midbrain tegmentum. Previous physiological studies have implicated somatostatin as a regulator of prolactin cell activity in tilapia. The present study demonstrates the route by which somatostatin may be delivered to the rostral pars distalis to inhibit prolactin secretion.

Difference in dose-response curves for glucose-induced insulin and somatostatin release in rat pancreas

We studied the glucose dependence of insulin and somatostatin release from rat pancreata, which were perfused in vitro in the presence of 3-isobutyl-1-methylxanthine (IBMX; 0.5 mM). Half-maximal insulin release occurred at approx. 12 mM glucose, and half-maximal somatostatin release at approx. 7 mM glucose.

Bacillus subtilis contains multiple forms of somatostatin-like material

Extracts of B. subtilis contain somatostatin-like immunoactivity (1-20 pg per g wet weight cells). Two major forms were detected, one with reactivity in both N- and C-terminal immunoassays similar to somatostatin-28 and a second form reactive only in the C-terminal specific immunoassay similar to somatostatin-14. Both forms were active in a bioassay and the bioactivity was neutralized in the presence of antibody to the central, biologically active part of somatostatin-14. Preconditioned medium contained no detectable somatostatin whereas conditioned medium had 80-380 pg per liter.

Gastrointestinal hormones in birds: morphological, chemical, and developmental aspects

Historically, the enterochromaffin cell was the first endocrine cell type detected in avian gut; subsequently, a number of types of such cells were distinguished on the basis of the ultrastructural features of the secretory granules. More recently, immunocytochemical procedures have revealed somatostatin-, pancreatic polypeptide (PP)-, polypeptide YY-, glucagon-, secretin-, vasoactive intestinal peptide (VIP)-, gastrin-, cholecystokinin-, neurotensin-, bombesin-, substance P-, enkephalin-, motilin-, and FMRFamide-like immunoreactivity in avian gastrointestinal endocrine cells. Most endocrine cells are located in the antrum; there are a number in the proventriculus and small intestine but few in the gizzard, cecum, and rectum. Several avian gastroenteropancreatic hormones, including glucagon, VIP, secretin, bombesin, neurotensin, and PP, have been isolated and sequenced. They resemble the equivalent mammalian peptides in terms of molecular size but differ in amino acid composition and sequence; some (e.g., VIP) differ only in minor respects, others (e.g., secretin) more radically. Gastrointestinal endocrine cells appear late in development; available data indicate that few types are recognized by either immunocytochemistry or electron microscopy before 16 days of incubation. Experimental evidence has shown that at least the majority of gut endocrine cells are of endodermal origin and are not derived from the neural crest or neuroectoderm as earlier proposed. In early embryos, the progenitors of gastrointestinal endocrine cells are more widespread than are the differentiated cells in chicks at hatching. This, along with other observations, raises the question of factors that might influence the differentiation of gut endocrine cells.

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

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

In vitro effects of thyrotropin-releasing hormone and somatostatin on prolactin and growth hormone release by the pituitary of Poecilia latipinna. I. An electrophoretic study

Pituitary glands were removed from Poecilia latipinna which had been maintained in one-third seawater and were incubated for 18 hr in media of either 300 mosmol/kg (OP300) or 340 mosmol/kg (OP340) osmotic pressure for measurement of both total and newly synthesised prolactin (PRL) and growth hormone (GH) release. Thyrotropin-releasing hormone (TRH) at 100 ng/ml increased release of total and newly synthesised PRL into OP340, but not into OP300, medium. Conversely, 300 ng/ml of somatotropin-release-inhibiting factor (SRIF) inhibited total and newly synthesised PRL release into OP300, but not OP340, medium. At 1000 ng/ml, SRIF inhibited total PRL release into both media, but newly synthesised PRL release was reduced significantly only in OP300 medium. The release of GH was unaffected by 100 ng/ml TRH in OP300 medium, but both total and newly synthesised GH release were enhanced by this dose in OP340 medium. SRIF at 300 ng/ml reduced total GH release into OP300 medium, whereas the release of newly synthesised GH was inhibited in OP340 medium. At 1000 ng/ml, SRIF inhibited total GH release into both media, but release of the newly synthesised hormone was not significantly altered. These results suggest that TRH can stimulate and SRIF inhibit both PRL and GH release by Poecilia pituitaries, but that these effects may be modulated by plasma osmotic pressure.

Isolation and structure of guinea pig gastric and pancreatic somatostatin

Somatostatin-14 has been isolated from guinea pig pancreas and stomach and purified to homogeneity by gel filtration, ion-exchange chromatography and reverse phase HPLC. Amino acid composition and sequence analysis indicated that guinea pig somatostatin from both tissues has the same structure as somatostatin-14 from all other mammalian species yet studied. The study has demonstrated that somatostatin-14 from gastric tissue has the same structure as the peptide from hypothalamus and pancreas.

In vitro study of frog (Rana ridibunda Pallas) interrenal function by use of a simplified perifusion system. VII. Lack of effect of somatostatin on angiotensin-induced corticosteroid production

Somatostatin (SRIF), the somatotropin release inhibiting factor of the hypothalamus, has been reported to inhibit the production of angiotensin II (AII)-stimulated aldosterone in the rat adrenal glomerulosa cells. Since the interrenal of the frog is the homolog of mammalian adrenal zona glomerulosa, the effect of synthetic SRIF on perifused dice of Rana ridibunda was tested. Graded doses of SRIF did not modify the spontaneous production of corticosterone and aldosterone. The highest concentration of SRIF (10(-5) M) did not alter the stimulatory effect of the AII agonist [Sar1-Val5] AII upon corticosteroidogenesis. Thus, in apparent contradiction to recent findings in mammals, SRIF did not alter the effect of AII in the frog interrenal cell.

The effects of somatostatin on serum growth hormone levels in the goldfish, Carassius auratus

In the present study the effects of somatostatin on serum growth hormone (GH) levels in the goldfish, Carassius auratus, were investigated. A single intraperitoneal injection of either 0.1 or 1.0 micrograms somatostatin/g body wt caused a significant decrease in serum GH levels at 1 h postinjection compared to vehicle-injected controls. Two intraperitoneal injections of somatostatin (1.0 micrograms/g body wt), given 12 hr apart, caused a significant decrease in serum GH levels, compared to both presample and vehicle-injected control groups at 1.5 and 6 hr following the second injection. In fish given two injections of somatostatin, a post inhibitory rebound in serum GH levels occurred by 24 hr following the second injection. Thyrotropin-releasing hormone (1 micrograms/g body wt), given as a control peptide, caused a significant increase in serum GH levels at 24 hr, but no significant changes were found at 1.5 or 6 hr following the second of two intraperitoneal injections given 12 hr apart. The increases in serum GH at 24 hr may be due to stress. The results demonstrate that somatostatin causes a transient decrease in blood GH levels in goldfish.

Differential secretion of glucagon-like and somatostatin-like immunoreactivity from the perfused eel pancreas in response to D-glucose

The effects of D-glucose on the differential secretion of glucagon-like (GLI) and somatostatin-like (SLI) immunoreactivity have been studied using the perfused eel pancreas. During control perfusions with 2.7 mM glucose, basal secretion of GLI and SLI remained essentially stable for a period of 46 min, with an overall mean rate of 381 +/- 20 and 268 +/- 23 pg/min/100 mg dry wt of pancrease, respectively. An acute increase in perfusate glucose to 8.3, 16.7, and 33.3 mM resulted in a monophasic, dose-dependent decline in GLI secretion over 30 min. However, acute return of control glucose concentrations (2.7 mM) from 16.7 or 33.3 mM did not result in return of GLI to control levels, whereas from 8.3 mM glucose this was achieved slowly. By contrast, 8.3 mM glucose was without effect on SLI secretion, but at 16.7 and 33.3 mM a dose-dependent, biphasic pattern of release was evident, with a rapid return to control SLI levels during the terminal perfusion period with 2.7 mM glucose. The results suggest that the A and D cells of teleosts are sensitive to changes in glucose concentration, and, in terms of secretory profiles, release of GLI, and SLI, are qualitatively similar to those of mammals.

Effects of hypothalamic lesions on serum growth hormone levels and growth rates in goldfish, Carassius auratus

Serum growth hormone (GH) levels and growth rates of goldfish were measured concurrently following discrete electrothermic lesions of a number of hypothalamic nuclei. Following lesions of the nucleus preopticus periventricularis (NPP), significant increases in serum GH levels were evident at 4 weeks postlesioning in comparison to both sham-operated and normal control groups. In addition, the NPP-lesioned fish showed significant increases in both total body weight and standard length increments compared to control groups. Lesions in other hypothalamic areas including the nucleus anterior tuberis, nucleus lateralis tuberis and the nucleus recessus lateralis had no consistent effect on growth rates or serum GH levels. The present results suggest that the NPP is concerned with the inhibition of GH secretory function in the goldfish.

Somatostatin-like immunoreactivity in the forebrain of Pseudemys turtles

Previous investigations of cortical organization in the brain of the turtle have revealed many features typical of mammalian neocortex. Recent evidence suggests that many neocortical neurons contain neuroactive peptides. The possibility that one such peptide, somatostatin, is found in the turtle brain was tested using immunocytochemical techniques. Intense somatostatin-like immunoreactivity was observed in many neurons and fibers in turtle cortex, as well as in several forebrain nuclei. Cortical neurons with several different dendritic configurations showed immunoreactive labelling, including bipolar, stellate and pyramidal cell types. In addition, stained cells and processes were observed in close association with the ependyma of the lateral ventricle. Other forebrain regions containing immunoreactive neurons included the dorsal ventricular ridge, the basal telencephalic nuclei and the hypothalamus. These data support the idea that peptidergic neurons existed in the pallium of an ancestor common to modern mammals and reptiles. We speculate that somatostatin plays a similar role in the normal function of all types of cortex and suggest that turtle cortex may provide a useful model for the study of this cortical neuropeptide.

Regional distribution of somatostatin-like immunoreactivity in the human brain

The regional distribution and chromatographic characteristics of somatostatin-like immunoreactivity (SLI) were studied in autopsy specimens of 8 human brains. SLI concentrations in 8 different regions of these brains ranged from (mean +/- S.E.) 756.3 +/- 363.4 pmol/g tissue in anterior hypothalamus to 1.6 +/- pmol/g in cerebellum. Chromatography of the extracts of human brain cortex, anterior hypothalamus, thalamus and amygdala on Sephadex G-50 disclosed one major peak which corresponded to the elution peak of synthetic somatostatin. Since the human brains were obtained at autopsy 11-36 h after death, the effects of temperature and time lapse between death and tissue extraction on SLI concentration and chromatographic pattern in rat brain were examined. After storage at 4 degrees C or 23 degrees C for 2 h and 8 h, a significant increase in SLI concentration was noted, although by 24 h in increase was no longer observed. A gradual loss in the eluting forms of SLI on gel chromatography was observed with storage at 4 degrees C or 23 degrees C.