Immunohistochemical evidence for synaptic connections between neuropeptide Y-containing axons and periventricular somatostatin neurons in the anterior hypothalamus in rats

doi:10.1016/0006-8993(90)91703-J

Brain Research

Volume 520, Issues 1–2, 18 June 1990, Pages 170-177

https://doi.org/10.1016/0006-8993(90)91703-J Get rights and content

Abstract

By employing a pre-embedding double immunolabeling technique, we examined light and electron microscopically synaptic associations between neuropeptide Y (NPY)-containing axons and somatostatin (SRIH)-containing neurons in the anterior periventricular area (APV) of the rat hypothalamus. For light microscopy, the immunoreactions for NPY and SRIH were visualized with silver-gold and diaminobenzidine (DAB), respectively, and the reverse labeling was used for electron microscopy. Light microscopy disclosed many brown SRIH perikarya surrounded by several black beads of NPY fibers in the APV. In electron microscopy, immunoreactive SRIH neurons revealed silver-gold particles scattered throughout the cytoplasm and accumulated in the Golgi area and the secretory granules. SRIH perikarya and dendritic processes indicated synaptic associations with DAB-labeled NPY fiber terminals and immunonegative fibers. NPY presynaptic terminals possessed numerous small clear vesicles and a few dense core visicles; vesicular membranes and cores were labeled with DAB chromogen. Both the pre- and postsynaptic membranes were thickened equally to be a symmetric synapse. These findings suggest that NPY neurons are involved in the regulation of growth hormone secretion from the pituitary by affecting periventricular SRIH neurons.

References (28)

AlonsoG. et al.
Electron microscopic immunocytochemical study of somatostatin neurons in the periventricular nucleus of the rat hypothalamus with special reference to their relationships with homologous neuronal processes
Neuroscience
(1985)
BaiF.L. et al.
An arcuato-paraventricular and -dorsomedial hypothalamic neuropeptide Y-containing system which lacks noradrenaline in the rat
Brain Research
(1985)
ChronwallB.M.
Anatomy and physiology of the neuroendocrine arcuate nucleus
Peptides
(1985)
ChronwallB.M. et al.
The anatomy of neuropeptide-Y-containing neurons in rat brain
Neuroscience
(1985)
EpelbaumJ.
Somatostatin in the central nervous system: physiology and pathological modifications
Prog. Neurobiol.
(1986)
EverittB.J. et al.
Differential co-existence of neuropeptide Y (NPY)-like immunoreactivity with catecholamines in the central nervous system of the rat
Neuroscience
(1984)
HisanoS. et al.
Suprachiasmatic nucleus neurons immunoreactive for vasoactive intestinal polypeptide have synaptic contacts with axons immunoreactive for neuropeptide Y: an immunoelectron microscopic study in the rat
Neurosci. Lett.
(1988)
HisanoS. et al.
Localization of glucocorticoid receptor in neuropeptide Y-containing neurons in the arcuate nucleus of the rat hypothalamus
Neurosci. Lett.
(1988)
HorváthS. et al.
Electron microscopic immunocytochemical evidence for the existence of bidirectional synaptic connections between growth hormone-releasing hormone- and somatostatin-containing neurons in the hypothalamus of the rat
Brain Research
(1989)
OhtsukaM. et al.
Electron microscopic study of somatostatin-containing neurons in rat arcuate nucleus with special reference to neuronal regulation
Brain Research
(1983)

BrazeauP. et al.

Hypothalamic polypeptide that inhibits the secretion of immunoreactive pituitary growth hormone

Science

(1973)

DaikokuS. et al.

Ultrastructural evidence for neuronal regulation of growth hormone secretion

Neuroendocrinology

(1988)

EldeR.P. et al.

Immunocytochemical localization of somatostatin in cell bodies of the rat hypothalamus

Am. J. Anat.

(1975)

FuxeK. et al.

Central glucocorticoid receptor immunoreactive neurons: new insights into the endocrine regulation of the brain

Ann. N.Y. Acad. Sci.

(1987)

Cited by (54)

Endocrine rhythms of growth hormone release: Insights from animal studies
2017, Best Practice and Research: Clinical Endocrinology and Metabolism
Citation Excerpt :
Most NPY neurons within the ARC express GH receptors [82], and GH treatment induces cFos expression in two thirds of NPY expressing neurons within the ARC [81]. In the rat [83], mouse [84] and in sheep [85], projections from NPY neurons in the ARC pass through the PeVN, where they surround somatostatin expressing neurons. These observations not only suggest interactions between NPY-neurons and the GH axis, but more importantly, that NPY neurons might selectively modulate GH release via somatostatin.
Growth hormone (GH) secretory patterns emerge following birth, and changes in patterning occur throughout life. These secretory patterns are coupled to growth, reproduction and metabolism. Comparing human and animal studies, this review will highlight ultradian patterning of GH release and the mechanisms that contribute to this. Discussions will focus on the emergence in variations in the number and frequency of GH secretory events, and the amounts of GH released (peak and basal). Animal studies have contributed significantly to our understanding of the processes that regulate GH release. However, translation of knowledge from animal models to benefit our understanding of human physiology is sometimes limited. To overcome these limitations, it is critical that we reconcile the cause and consequences of differences in GH release between humans and model organisms. In doing so, we can embrace emerging technologies that will rapidly advance our knowledge of endogenous process that control GH release.
Juxtapositions between the somatostatinergic and growth hormone-releasing hormone (GHRH) neurons in the human hypothalamus
2015, Neuroscience
Citation Excerpt :
NPY stimulates hypophysiotropic somatostatin release and thereby inhibits GH secretion (Rettori et al., 1990). The indirect inhibitory role of NPY is also supported by the demonstration of synaptic connections between NPY-positive axon terminals and somatostatin-IR neurons in the periventricular nucleus (Hisano et al., 1990). GH is thought to exert a short-loop feedback action on the hypothalamic somatostatin- and GHRH-containing neurons.
Somatostatin is a 14–28 amino acid peptide that is located not only in the gastrointestinal system but also in multiple sites of the human brain. The inhibitory effect of somatostatin on the growth hormone (GH) secretion of the pituitary gland is a well-established phenomenon. There is a general consensus that somatostatin is released into the hypophysial portal blood and modulates GH secretion by hormonal action. In the present study, we explored the possibility that in addition to the hormonal route, somatostatin may also influence GH secretion via influencing the growth hormone-releasing hormone (GHRH) secretion by direct contacts that may be functional synapses.
Since the verification of these putative synapses by electron microscopy is virtually impossible in humans due to the long post mortem time, in order to reveal the putative somatostatinergic-GHRH juxtapositions, light microscopic double-label immunohistochemistry was utilized.
By examining the slides with high magnification, we observed that the vast majority of the GHRH perikarya received contacting somatostatinergic axonal varicosities in the arcuate nucleus. In contrast, GHRH axonal varicosities rarely contacted somatostatinergic perikarya.
The morphology and the abundance of somatostatin to GHRH juxtapositions indicate that these associations are functional synapses, and they represent, at least partially, the morphological substrate of the somatostatin-influenced GHRH secretion. Thus, in addition to influencing the GH secretion directly via the hypophysial portal system, somatostatin may also modulate GH release from the anterior pituitary by regulating the hypothalamic GHRH secretion via direct contacts. The rare GHRH to somatostatin juxtapositions indicate that the negative feedback effect of GH targets the somatostatinergic system directly and not via the GHRH system.
The effect of intracerebroventricular infusions of ghrelin or short fasting on the gene expression and immunoreactivity of neuropeptide Y in the hypothalamic neurons in prepubertal female lambs: A morphofunctional study
2012, Journal of Chemical Neuroanatomy
Citation Excerpt :
This suggest that NPY terminals located in this area can be involved in the regulations associated with the somatotrophic axis (Gładysz et al., 2001; Polkowska and Gładysz, 2001). Immunohistochemical studies have demonstrated synaptic connections between NPY containing axons and somatostatin perikarya in the PEV nucleus of rats (Hisano et al., 1990) and sheep (Iqbal et al., 2005). The direct morphological connections between NPY fibres and somatostatin perikarya are increased, during the period of the enhanced GH release due to decrease of the somatostatin output (Tillet et al., 2010).
The role of exogenous ghrelin in the regulation of neuropeptide Y (NPY) neuronal system in the hypothalamus of intact lambs has not been yet determined. The aim of present study was to investigate the effects of intracerebroventricular infusion of ghrelin or short fasting on the secretory activity of the NPY neurons in the hypothalamus of prepubertal female sheep. Animals (n = 30) were randomly divided into three groups, two groups were fed standard diet and one group was fasted for 72 h. One group fed standard diet and fasted group were infused to the 3rd ventricle of the brain with vehicle, while the remaining group fed standard diet was infused with ghrelin (25 μg/120 μl/h) for 6 h during three consecutive days. Immediately after the treatment, tissues were collected. Parts of the brains were fixed in situ for further immunohistochemical analysis, and remaining parts were frozen for RT-PCR analysis. Both, fasting and ghrelin infusion elicited the same kind of changes in the mRNA and intra-neuronal levels of the NPY hypothalamic neurons. Namely, the expression of NPY mRNA in the medial basal hypothalamus and immunoreactivity of NPY in the arcuate and periventricular nuclei increased in fasted and standard fed with ghrelin's infusion groups compared to standard fed sheep (P < 0.05). These data demonstrate that ghrelin takes part in the mechanisms linking the nutritional status with an activity of the hypothalamic NPY at the level of the central nervous system by stimulating NPY secretion in sheep.
Inhibitory effect of somatostatin on the NPY response to insulin-induced hypoglycemia and the role of endogenous opioids
2011, Regulatory Peptides
Citation Excerpt :
Reduction of growth hormone (GH), adrenocorticotropin (ACTH), cortisol, arginine-vasopressin (AVP), and oxytocin (OT) response to hypoglycemia has been described after administration of SRIH in humans [6–8,15,16]. SRIH containing perikarya are widely distributed throughout the brain, but most prominent concentration of SRIH have been localized in the preoptic area and the anterior hypothalamus where NPY is also present [9–12]. In light of these observations we questioned whether NPY response to insulin induced hypoglycemia involves a somatostatinergic pathway.
The present study was undertaken in order to establish whether somatostatin (SRIH) is able to modify the neuropeptide Y (NPY) response to insulin-induced hypoglycemia during insulin tolerance test (ITT) in man. In addition, the possible involvement of opioid peptides in the mediation of hypoglycemia and/or SRIH action was investigated. Subjects were injected intravenously with 0.15 IU/kg insulin alone (control test) or with SRIH (4.1 μg/min/90 min), naloxone (10 mg in an iv bolus) or the combination of the two substances. Plasma NPY concentrations rose significantly during ITT. The NPY response was significantly reduced by the treatment with SRIH. The administration of naloxone did not modify NPY levels whereas when both SRIH and naloxone were given, NPY response to hypoglycemia did not differ from that observed in the control test. These data demonstrate that SRIH inhibits the NPY response to hypoglycemia. Naloxone-sensitive endogenous opiates do not seem to be involved in the control of hypoglycemia-induced NPY release. In contrast, since naloxone reversed the inhibiting effect of SRIH, an involvement of opioid peptides in the SRIH action may be supposed.
Role of endogenous somatostatin in regulating GH output under basal conditions and in response to metabolic extremes
2008, Molecular and Cellular Endocrinology
Somatostatin (SST) was first described over 30 years ago as a hypothalamic neuropeptide which inhibits GH release. Since that time a large body of literature has accumulated describing how endogenous SST mediates its effects on GH-axis function under normal conditions and in response to metabolic extremes. This review serves to summarize the key findings in this field with a focus on recent progress, much of which has been made possible by the availability of genetically engineered mouse models and SST receptor-specific agonists.
Glutamatergic innervation of growth hormone-releasing hormone-containing neurons in the hypothalamic arcuate nucleus and somatostatin-containing neurons in the anterior periventricular nucleus of the rat
2006, Brain Research Bulletin
Growth hormone-releasing hormone (GHRH) and somatostatin are the two main hypothalamic neurohormones, which stimulate or inhibit directly hypophysial growth hormone (GH) release. Majority of the GHRH neurons projecting to the median eminence is situated in the arcuate nucleus and the somatostatin neurons in the anterior periventricular nucleus. Data suggest that the excitatory amino acid glutamate may play an important role in the control of hypothalamic neuroendocrine neurons and processes including the control of GH. There is a dense plexus of glutamatergic fibres in the hypothalamic arcuate and anterior periventricular nucleus. The aim of the present studies was to examine the relationship of these fibres to the GHRH neurons in the arcuate nucleus and to somatostatin neurons in the anterior periventricular nucleus. Double-labelling immuno-electron microscopy was used. Glutamatergic structures were identified by the presence of vesicular glutamate transporter 2 (VGluT2) (a selective marker of glutamatergic elements) immunoreactivity. A significant number of VGluT2-immunoreactive boutons was observed to make asymmetric type of synapses with GHRH-immunostained nerve cells in the arcuate and with somatostatin neurons in the anterior periventricular nucleus. A subpopulation of somatostatin-immunoreactive neurons displayed also VGluT2 immunoreactivity. Our findings provide direct neuromorphological evidence for the view that the action of glutamate on GH release is exerted, at least partly, directly on GHRH and somatostatin neurons releasing these neurohormones into the hypophysial portal blood.

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Immunohistochemical evidence for synaptic connections between neuropeptide Y-containing axons and periventricular somatostatin neurons in the anterior hypothalamus in rats

Abstract

Neuroscience

Brain Research

Peptides

Neuroscience

Prog. Neurobiol.

Neuroscience

Neurosci. Lett.

Neurosci. Lett.

Brain Research

Brain Research

Hypothalamic polypeptide that inhibits the secretion of immunoreactive pituitary growth hormone

Science

Ultrastructural evidence for neuronal regulation of growth hormone secretion

Neuroendocrinology

Immunocytochemical localization of somatostatin in cell bodies of the rat hypothalamus

Am. J. Anat.

Central glucocorticoid receptor immunoreactive neurons: new insights into the endocrine regulation of the brain

Ann. N.Y. Acad. Sci.