Neurotransmitter candidates in the retina of the mudpuppy,Necturus maculosus

Summary Neurons accumulating (³H)-glycine and (³H) GABA were demonstrated with the use of autoradiography. Both were accumulated by different types of amacrine cells, similar those of goldfish. (³H)-GABA was also accumulated by horizontal cells, again similar to the goldfish. These results and physiological studies from other laboratories suggest that GABA and glycine are neurotransmitter candidates in amacrine cells of the mudpuppy.Immunoreactive neuropeptide Y (NPY), glucagon, vasoactive intestinal peptide (VIP), somatostatin, substance P, and neurotensin were found in different types of stratified amacrine cells. Weakly immunoreactive enkephalin and bombesin processes were also seen in the inner plexiform layer. Gastrin-immunoreactive neurons were not detectable.Endogenous 5-hydroxytryptamine was visualized immunohistochemically in a population of diffuse amacrine cells and some cells in the ganglion cell layer. This suggests that 5-hydroxytryptamine may be a neurotransmitter in the retina of the mudpuppy.     

Retinal neuropeptides in the skates,Raja clavata,R. radiata,R. oscellata (Elasmobranchii)

Summary The distribution of immunoreactive neuropeptides was investigated in the retina of three species of skates (Raja clavata, R. radiata, R. oscellata), elasmobranch fish often used in electrophysiological work on the retina. Enkephalins, neuropeptide Y (NPY), substance P and glucagon were found in different types of amacrine cells.All four peptides appeared in cell bodies in the innermost part of the inner nuclear layer. Processes from the cells containing enkephalins were numerous and ramified throughout the inner plexiform layer. Processes from the cells containing glucagon were thick and rare, and were found throughout the inner plexiform layer, at times with a predominance in sublaminae 1 and 4. NPY-immunoreactive fibres appeared mainly in sublamina 1 but also in 2 or 3, and substance-P-immunoreactive fibres in sublaminae 1,4 and 5.Antisera against somatostatin, VIP or neurotensin did not show any immunoreactivity in the skate retina.     

The distribution and colocalization of neuropeptides and 5-hydroxytryptamine in pelvic nerves supplying the posterior large intestine of the toad,Bufo marinus

The distribution and colocalization of neuropeptides and 5-hydroxytryptamine in the posterior portion of the large intestine of the toad was studied using single- and dual-label immunohistochemistry. Neurons containing colocalized galanin/somatostatin or vasoactive intestinal peptide alone were observed along intramural pelvic nerves. Some of the galanin/somatostatin neurons also contained 5-hydroxytryptamine. Synaptic boutons containing colocalized calcitonin gene-related peptide/vasoactive intestinal peptide were associated with the galanin/somatostatin neurons. The muscle of the large intestine was also innervated by axons containing galamin/somatostatin, vasoactive intestinal peptide/calcitonin gene-related peptide or vasoactive intestinal peptide alone. Nerve fibres containing calcitonin gene-related peptide/substance P, probably representing primary afferent nerves, were also associated with muscle bundles. Submucosal blood vessels carried dense plexuses of fibres containing vasoactive intestinal peptide alone or and calcitonin gene-related peptide/substance P. Adrenergic perivascular nerves also contained galanin and neuropeptide Y.     

Immunohistochemical study of the developing endocrine pancreas of the opossum (Didelphis virginiana)

Cells immunoreactive for insulin, glucagon, somatostatin, bovine pancreatic polypeptide and 5-hydroxytryptamine are found in the pancreas of the newborn opossum and of all later stages examined. All immunoreactive cell types are present in primary and secondary islets and within elements of the exocrine pancreas. Cells immunoreactive for glucagon, bovine pancreatic polypeptide, somatostatin and 5-hydroxytryptamine generally are confined to the periphery of secondary (intralobular) islets, whereas insulin-immunoreactive cells occupy the central region. Endocrine cells within primary (interlobular) islets are randomly scattered. A small number of pancreatic-polypeptide-immunoreactive cells are reactive for the amine 5-hydroxytryptamine also, but the reverse is not observed. The endocrine pancreas continues to differentiate and develop throughout postnatal life and into adulthood. Little difference was observed between the head and tail regions of the opossum pancreas for the measurements made.     

Somatostatin: peripheral venoconstrictive activity and interaction with monoamines in man

The mechanism of somatostatin venoconstriction and tachyphylaxis in the human hand vein in vivo has been investigated. No cross-tachyphylaxis was observed between somatostatin and 5-hydroxytryptamine, noradrenaline, adrenaline, dopamine or tyramine-induced venoconstriction. Somatostatin potentiates the venoconstrictive activity of noradrenaline, adrenaline and dopamine, but not that of 5-hydroxytryptamine and tyramine. Phentolamine antagonizes the somatostatin-induced venoconstriction, whereas methysergide, haloperidol and morphine do not. It is suggested that somatostatin could act on specific receptors in the hand vein, but the mechanism of somatostatin venoconstriction and interaction with vasoactive monoamines remains to be defined.     

Pulses of somatostatin release are slightly delayed compared with insulin and antisynchronous to glucagon

It was early proposed that somatostatin-producing delta-cells in pancreatic islets have local inhibitory effects on the release of insulin and glucagon. Recent observations that pulses of insulin and glucagon are antisynchronous make it important to examine the temporal characteristics of glucose-induced somatostatin release. Analysis of 30 s fractions from the perfused rat pancreas indicated that increase of glucose from 3 to 20 mmol/l results in initial suppression of somatostatin release followed by regular 4-5 min pulses. During continued exposure to 20 mmol/l glucose, the pulses of somatostatin overlapped those of insulin with a delay of 30 s. Somatostatin and glucagon pulses were coupled in antisynchronous fashion (phase shift 2.4+/-0.2 min), supporting the idea that the delta-cells have a local inhibitory effect on glucagon release. It was possible to remove the pulses of somatostatin and glucagon with maintenance of the insulin rhythmicity by addition of 1 micromol/l of the P2Y(1) receptor antagonist MRS 2179.     

Somatostatin release from isolated perfused rat stomach.

Gastric somatostatin release from the isolated rat stomach was studied using a perfusion technique. Somatostatin released from the isolated perfused rat stomach was found to be identical in molecular size and immunoreactively with synthetic somatostatin. Infusion of glucagon (10^?7 M) caused biphasic increase of gastric somatostatin release. Gastric somatostatin release was also stimulated by infusion of theophylline (10^?3 M) and dibutyryl cyclic AMP (10^?3 M). These results indicate the possible involvement of adenylate cyclase-cyclic AMP system in the regulatory mechanism of gastric somatostatin release.     

Differential localization of lectin binding sites and neuropeptides in human dorsal root ganglia

The subpopulations were compared of neurons in human dorsal root ganglia (DRG), as substance P, identified by somatostatin, Glycine max lectin (SBA) specific to terminal N-acetylgalactosamine, and Ulex europaeus I agglutinin (UEA-I) specific to l-fucose. The lectins and neuropeptides all bound to neurons of small diameter. Furthermore, the majority of the SBA binding neurons or somatostatin positive neurons were also UEA-I binding neurons. However, SBA binding neurons were not colocalized with somatostatin or substance P. Less than 20% of substance P positive neurons showed colocalization with l-fucosyl residues, and approximately 10% of l-fucosyl residues showed colocalization with substance P. Our results suggest that both l-fucose and terminal N-acetylgalactosamine containing neurons in the human DRG are subjected to different subpopulations from substance P or somatostatin positive neurons.     

Adaptive changes of gastro-entero-pancreatic system endocrine cells in the black-spotted pond frog Rana nigromaculata after fasting

Changes in distribution density,morphology and secretory content of endocrine cells in the gastro-entero-pancreatic system of black-spotted frogs Rana nigromaculata before and after fasting were investigated using immunohistochemistry and antisera to six gut hormones.Six types of endocrine cells were detected in the digestive tract of Rana nigromaculata,including 5-hydroxytryptamine(5-HT),gastrin(GAS),somatostatin(SOM),glucagon(GLU),pancreatic polypeptide(PP)and vasoactive intestinal polypeptide(VIP)cells.A...     

Effects of aspartate,substance P,and serotonin on neuronal activity in the central gray substance:In vitro experiments

Effects of aspartate (2 · 10^–5 M), substance P (10^–7–10^–8 M), and serotonin (5-hydroxytryptamine, 5-HT; 5 · 10^–5 M) on the background activity of neurons in the central gray substance (CGS) were studied on slices of the rat midbrain. Aspartate and substance P (transmitters of nociceptive signals), and 5-HT (modulator of transmission of nociceptive influences) were found either to facilitate or to depress the activity of CGS neurons. The predominant effect of substance P or 5-HT applications to neurons of the dorsal CGS part was facilitation, and to neurons of the ventral CGS part, inhibition. The effects of aspartate application on studied CGS neurons were of varying nature, but inhibitory effects were found to prevail.The findings support our earlier hypothesis that assigned the studied neurons to spontaneously discharging inhibitory CGS interneurons, which control the activity of efferent CGS neurons. The role of tested substances in the regulation of CGS neuronal activity and the antinociceptive CGS effects is discussed.Neirofiziologiya/Neurophysiology, Vol. 25, No. 5, pp. 354–362, September–October, 1993.     

Exocrine pancreas under experimental conditions

Summary At least four types of endocrine-like cells have been detected histochemically in the mucosa of the human colon and rectum, i.e. argentaffin cells storing 5-hydroxytryptamine (5 HT) and non-argentaffin cells reacting with glucagon, somatostatin and bovine pancreatic peptide (BPP) antibodies. Ultrastructurally, four main types and three rare types of endocrine-like cells have been identified. Among the former cells were: (1) argentaffin EC₁ cells, known to store 5 HT and substance P, (2) poorly argyrophil L cells, corresponding to the glucagon-immunoreactive cells storing enteroglucagon or glucagon-like immunoreactivity (GL1), (3) inconstantly argyrophil F-like cells, possibly corresponding to BPP-immunoreactive cells, and (4) fairly argyrophil H cells of unknown function. Rare D cells, corresponding to somatostatin cells, N cells, corresponding to neurotensin cells, and P cells, of unknown function, have been also found.Supported in part by the Italian National Research Council (Grant N. 76.01558.04)     

Effect of gastrointestinal hormones on choleresis from the isolated perfused rat liver

Using isolated perfused rat liver, the direct effect of secretin, glucagon, caerulein, insulin and somatostatin on choleresis was investigated. When the liver was perfused in the absence of sodium taurocholate, the bile volumes were: control, 0.33 +/- 0.01 (mean +/- S.E.M.) ml/10 g liver per 50 min; secretin 0.05 U/ml, 0.39 +/- 0.01 (P less than 0.01); glucagon 10(-10) M, 0.44 +/- 0.02 (P less than 0.01); caerulein 10(-8) M, 0.34 +/- 0.03 (n.s.); insulin 1 mU/ml, 0.35 +/- 0.02 (n.s.); glucagon plus somatostatin 10(-7) M, 0.46 +/- 0.03 (n.s. vs. glucagon alone), respectively. When 10(-5) M sodium taurocholate was present in the perfusate, the bile volumes were: control, 0.61 +/- 0.03; secretin, 0.63 +/- 0.01 (n.s.); glucagon, 0.70 +/- 0.01 (P less than 0.05); caerulein, 0.55 +/- 0.01 (n.s.); insulin, 0.62 +/- 0.04 (n.s.); somatostatin, 0.59 +/- 0.01 (n.s.); respectively. Glucagon increased glucose output and cyclic AMP in the effluent from the liver neither of which were suppressed by somatostatin. Secretin increased cyclic AMP but not glucose output. These results indicate that glucagon has the most potent action on bile acid-independent canalicular bile, that caerulein and insulin do not act on canalicular bile production directly and that somatostatin does not directly suppress canalicular bile production nor hepatic glucose output produced by glucagon in rats.     

Effect of somatostatin and two of its analogues on basal and arginine-stimulated insulin and glucagon secretion in the dog

Two analogues of somatostatin (d-Trp⁸,d-Cys¹⁴-somatostatin, and the octapeptide DesAA^{1,2,3,4,13,14},d-Trp⁸,GABA¹²-somatostatin) were compared with somatostatin using infusions, of 0.1 and 0.5 μg · kg^?1 · min^?1 in conscious dogs. Basal concentrations of insulin and glucagon were markedly and similarly lowered by all three somatostatin (SRIF) compounds at either dose. Arginine stimulation of insulin and glucagon secretion was entirely abolished by SRIF and by the octapeptide during infusion at 0.1 μg · kg^?1 · min^?1 but both hormones were only partly inhibited by d-Trp⁸,d-Cys¹⁴-SRIF. The higher dose (0.5 μg · kg^?1 · min^?1) of all three SRIF peptides lowered plasma insulin and glucagon before and during arginine stimulation. The recovery of plasma insulin and glucagon was delayed after discontinuation of the d-Trp⁸,d-Cys¹⁴-SRIF, and particularly after the octapeptide when compared with SRIF suggesting a longer duration of action of the analogues.The results did not confirm the previously suggested selective suppression of glucagon by d-Trp⁸,d-Cys¹⁴-SRIF. The new octapeptide appears to be promising for future clinical studies due to its potent inhibitory effect on insulin and glucagon, and its prolonged duration of action.     

Synthesis and biological activity of glycosylated analogs of somatostatin

The synthesis by solid-phase methodology of two glycosylated analogs of somatostatin [Glc-Asn⁵]-SS and [NAcGlc-Asn⁵]-SS is described. These two analogs have been biologically tested on the secretion of pituitary growth hormone, pancreatic glucagon and insulin. The results show that glycosylation of somatostatin on the Asn⁵ residue decreases by a hundred fold the inhibition activity on GH release when tested $\text{in}$$\text{vitro}$. $\text{In}$$\text{vivo}$, since the activity is similar to somatostatin the carbohydrates are probably removed by some enzymatic reaction and thus liberate the full activity of somatostatin.     

Effect of starvation of gastric somatostatin release

The present study is an investigation of the effects of 16 and 48 hours starvation on gastric somatostatin release using the isolated perfused rat stomach. Before sacrifice the body weights and blood glucose levels of fasted rats were significantly lower than fed rats. In the presence of 4.4 mM glucose, basal somatostatin concentrations in the stomach perfusate of fasted rats were also significantly lower. Gastric somatostatin release was stimulated in all three groups similarly by 5 × 10^?8 M glucagon when the decrease in basal levels is considered. These results suggest that gastric somatostatin as well as pancreatic somatostatin contributes to nutrient homeostasis and that nutrient homeostasis influences somatostatin levels in turn.     

Insulin and glucagon secretion in rats: effects of calcitonin gene-related peptide

Immunoreactive calcitonin gene-related peptide (CGRP) has been shown to occur in intrapancreatic nerves and islet somatostatin cells in the rat. Therefore, we investigated the effects of CGRP on insulin and glucagon secretion in the rat. CGRP was infused i.v. at one of 3 dose levels (4.3, 17 or 68 pmol/min). Infusion of CGRP alone was found to elevate basal plasma levels of both insulin and glucagon. In contrast, CGRP impaired the plasma insulin responses to both glucose (7 mg/min; P less than 0.001) and arginine (8.5 mg/min; P less than 0.001), and inhibited the arginine-induced increase in plasma glucagon concentrations (P less than 0.001). Since CGRP and somatostatin are colocalized within the D-cells, we also infused CGRP and somatostatin together at equimolar dose levels (17 pmol/min), with glucose (7 mg/min). By that, the increase in plasma insulin concentrations decreased more rapidly than during infusion of either peptide alone. Since alpha 2-adrenoceptor activation is known to inhibit glucose-stimulated insulin secretion, we also infused CGRP together with the specific alpha 2-adrenoceptor antagonist yohimbine (37 nmol/min). In that way, the plasma insulin-lowering effect of CGRP was prevented. We have shown in the rat: (1) that CGRP stimulates basal insulin and glucagon secretion; (2) that CGRP inhibits stimulated insulin and glucagon secretion; (3) that CGRP and somatostatin more rapidly induce a potent inhibitory action on glucose-stimulated insulin secretion when given together; and (4) that the alpha 2-adrenoceptor antagonist, yohimbine, counteracts the inhibitory action of CGRP on glucose-stimulated insulin secretion. We suggest that CGRP is of importance for the regulation of insulin and glucagon secretion in the rat. The mechanisms behind the islet effects of CGRP can not be established by the present results, though they apparently require intact alpha 2-adrenoceptors.     

Neuropeptides and retinal development

Different peptidergic systems have been investigated with some detail during retinal development, including substance P (SP), vasoactive intestinal polypeptide (VIP), pituitary adenylate cyclase activating polypeptide (PACAP) and somatostatin (SRIF). Concerning possible developmental actions of neuropeptides, VIP and PACAP exert protective and growth-promoting actions that may sustain retinal neurons during their development. In addition, the presence of transient SRIF expressing cells and recent observations in SRIF receptor knock out mice indicate variegated roles of this peptide in the development of the retina and of retinofugal projections. Finally, recent studies have shown that, in the developing rabbit retina, changes in the expression pattern of SP receptors are accompanied by modifications of SP physiological effects, indicating that retinal circuits where SP is involved are likely to function in a substantially different manner before the retina becomes involved in the processing of visual stimuli. SP neurotransmission in the immature retina may subserve developmental events, and SP is likely to represent an important developmental factor for the maturation of retinal neurons and circuitries.     

3H-imipramine binding in membrane preparations from brains of insects (Periplaneta americana,Locusta migratoria) and mollusc (Helix pomatia)

1. The binding of [³H]-imipramine to brain membrane preparations of the insects, Periplaneta americana, Locusta migratoria and the mollusc, Helix pomatia was investigated.2. [³H]-Imipramine binding is similar in invertebrates and vertebrates although, in insects, the binding is independent of sodium.3. In the three invertebrate systems studied, [³H]-imipramine binding was inhibited by 5-hydroxytryptamine (5-HT) only at high concentrations (100 μM 5-HT caused 20–30% inhibition in insects and 10% inhibition in snail).4. Studies on binding and incorporation of [³H]-imipramine and [³H]-5-hydroxytryptamine indicate that the imipramine binding site differs from the 5-hydroxytryptamine recognition site of uptake.5. The [³H]-imipramine binding sites are not specific for 5-hydroxytryptamine and have similar affinity for dopamine.     

Turnover of Acinar and Islet Cells in the Pancreas of Monosodium Glutamate‐Treated Obese Mice

Objective: Subcutaneous administrations of monosodium glutamate (MSG) to neonatal animals result in obesity and induce the toxicity on the central nervous system, and furthermore, have an effect on entero‐pancreatic hormone. The effect of MSG on the cell turnover of organs, especially the pancreas, has received little attention until now. This study was designed to examine the effect of MSG on pancreatic cell turnover by immunohistochemistry and [³H]thymidine autoradiography. Research Methods and Procedures: Male JcI‐ICR strain mice were SC injected with MSG (2 mg/g body weight daily) for 5 days after birth, received 112 repeated injections of [³H]thymidine at 6‐hour intervals for 28 days after birth, and then were killed immediately thereafter, or 30, 60, or 120 days after the last injection. Autoradiography was performed on sections immunostained for glucagon, insulin, and somatostatin. Results: After continuous labeling, most pancreatic cells were labeled, and thereafter, labeling of cells decreased in control and MSG‐treated mice. The mean grain counts of acinar cells in MSG‐treated mice decreased more slowly than those in control mice. On the other hand, those of islet cells, including glucagon, insulin, and somatostatin cells, decreased more rapidly in MSG‐treated mice than those in control mice. Discussion: Cell turnover of acinar cells was decelerated and that of islet cells including glucagon, insulin, and somatostatin cells was accelerated in MSG‐treated mice pancreas. MSG‐induced hypothalamic lesions exert the contrary influences on the cell turnover of acinar and islet cells.     

Subcellular localization and some properties of the adenylate cyclase activity of the yeast, Saccharomyces cerevisiae

Saccharomyces cerevisiae was grown in the presence of 5% (w.v) Glucose and converter to protoplasts. The total particulate material obtained from lysed protoplasts was fractionated by sucrose density gradient ultracentrifugation and the distribution of adenylate cyclase throughout the gradient determined. Adenylate cyclase activity was found to be larger associated whith intracellular particulate fractions. Little activity was found in the plasma membrane-rich fraction.The adenylate cyclase activity was found to be inhibited by F^?, pyrophosphate and aminophylline, whereas glucagon, 5-hydroxytryptamine and concanavalin A were without effect.The enzymic activity appeared to be modulated by “catabolite repressors” (glucose, fructose and α-methylglucoside) as well as by acetate. A possible role for adenylate cyclase in regulating the levels of cyclic AMP in the cell during glucose repression is suggested.