Pancreatic polypeptides affect luteinizing and growth hormone secretion in rats

Neuropeptide Y induces gonadotropin-releasing hormone gene expression directly and through conditioned medium from mHypoE-38 NPY neurons

Neuropeptide Y (NPY) regulates reproductive function at the level of the hypothalamus through control of GnRH secretion. However, the direct control of GnRH gene expression by NPY has not yet been studied. GT1-7 neurons were treated with 100 nM of NPY over a 36 h time course. GnRH mRNA levels were significantly increased by NPY up to 12 h. We determined that GT1-7 neurons expressed Y1, Y2, and Y4 NPY receptors, but not Y5. Functional analysis of NPY receptor activation indicated that the Y1/Y4/Y5 receptor agonist [Leu31, Pro34] significantly induced cAMP accumulation in the GT1-7 neurons. Western blot studies demonstrated changes in the phosphorylation status of AKT, ERK1/2, CREB and ATF-1 after NPY exposure. Pharmacological inhibitors of the MAPK and PKA signal transduction pathways attenuated the NPY-mediated increase in GnRH transcription. This NPY-mediated increase in GnRH mRNA was also inhibited with the Y1-receptor specific antagonist BIBP-3226. The mHypoE-38 neurons secrete detectable levels of NPY and can be used as an endogenous source of NPY. Conditioned medium from mHypoE-38 neurons induced an increase in GnRH mRNA, which was inhibited by the Y1 receptor antagonist BIBP-3226. Together, these studies strengthen the evidence for the importance of NPY in the regulation of reproductive function.

Neuropeptide Y in the primate model of subarachnoid hemorrhage

The cause of cerebral vasospasm after subarachnoid hemorrhage (SAH) remains unknown. Recently, an association between the potent vasoconstricting peptide, neuropeptide Y, and delayed cerebral vasospasm after SAH has been postulated. This was based on the findings of increased neuropeptide Y levels in the cerebrospinal fluid (CSF) and plasma after SAH in animals and humans. For this study, the primate model of SAH was used to assess the possible role of neuropeptide Y in delayed vasospasm after SAH. Fifteen cynomolgus monkeys underwent placement of a clot of either whole blood or red blood cells in the subarachnoid space around the middle cerebral artery (MCA). Sequential arteriography for assessment of MCA diameter and sampling of blood and CSF for neuropeptide Y were performed: before SAH (Day 0); 7 days after SAH, when signs of delayed cerebral vasospasm peak in this model and in humans; 12 days after SAH; and 28 days after SAH. Subarachnoid hemorrhage did not evoke changes in CSF or plasma levels of neuropeptide Y. Nine monkeys had arteriographic evidence of vasospasm on Day 7, but no change in neuropeptide Y levels occurred in plasma or CSF. In addition, neuropeptide Y levels did not change, even after resolution of vasospasm on Day 12 or Day 28. Neuropeptide Y levels were substantially higher in CSF than in arterial plasma (p less than 0.003 at each interval). No correlation was found between neuropeptide Y levels in CSF and in plasma. These results do not confirm a relationship between neuropeptide Y levels in the CSF or peripheral plasma and delayed cerebral vasospasm in SAH.

Role of neuropeptide Y in reproductive function

NPY acts both at the hypothalamus and the anterior pituitary gland to modulate reproductive hormone secretion. Within the hypothalamus, NPY stimulates LHRH secretion in the presence of physiological levels of estrogen and suppresses pulsatile LHRH release following ovariectomy. Intracerebroventricular injection of NPY antiserum blocks or delays the LH surge in steroid-primed ovariectomized rats, thereby adding support for a physiological role of NPY in the neuroendocrine events preceding ovulation. Blockade of alpha 2 adrenergic receptors decreases NPY-stimulated LH release in steroid-primed rats implying a potential noradrenergic mediation of NPY activity. Physiological levels of progesterone do not augment, and may actually suppress NPY-induced LHRH secretion in vitro from median eminences obtained from estrogen-primed ovariectomized rats. The physiological role of progesterone, if any, in modulating NPY effects on LHRH release remains to be determined. Little, if anything, is known about the NPY receptor in the median eminence or the intracellular mechanisms which transduce the NPY signal into activation of LHRH release in estrogen-treated ovariectomized rats although translocation of intracellular calcium is required. Equally puzzling is the mechanism of desensitization of the LHRH-releasing mechanisms of the median eminence of ovariectomized rats or the specific site of NPY suppression of pulsatile LHRH secretion. NPY is released into the hypothalamo-hypophysial portal circulation and this appears correlated with LHRH secretion before the LH surge. NPY affects LH and FSH release from anterior pituitary cells in vitro and enhances LHRH-induced LH secretion. Taken together, the studies described above suggest an important physiological role for NPY as a modulator of neuroendocrine activity which culminates in the preovulatory surge of LH.

The role of neuropeptide Y (NPY) in control of gonadotropin and prolactin release in the rat

Neuropeptide Y is a peptide found in a variety of hypothalamic loci which is frequently colocalized with catecholamines. It is also secreted into hypophyseal portal vessels. We have previously evaluated the effects of this peptide on FSH, LH and prolactin release. In ovariectomized females neuropeptide Y inhibits LH release. It has similarly been reported to inhibit LH release in intact males; however, estrogen priming of ovariectomized animals converts this inhibitory action into a stimulatory effect. In ovariectomized animals the peptide has a direct stimulatory effect on perifused pituitary cells, enhancing the release of both FSH and LH, an effect which is contrary to that obtained with LH release after intraventricular injection of the peptide. In the present experiments the physiological significance of these effects has been evaluated by the intraventricular injection (3V) of highly specific antiserum directed against the peptide. In ovariectomized and in ovariectomized, estrogen-primed rats, the third ventricular injection of antiserum had no effect on gonadotropin release. In male rats intraventricular injection of the antiserum elevated LH, which indicates that the inhibitory action of the peptide seen in intact males is of physiological significance. However, it has been reported by others that the proestrous type discharge of LH-RH is blocked by intraventricular injection of neuropeptide Y antiserum. Neuropeptide Y might therefore play an essential role in the preovulatory release of LH. On the other hand, others have shown that intraventricular injection of neuropeptide Y in male rats can either stimulate, at low doses, or inhibit, at high doses, the release of prolactin. We have confirmed the inhibitory action, which appears to be of physiological significance since antisera directed against the peptide injected intraventricularly resulted in an elevation of prolactin release. The results of these studies indicate that neuropeptide Y plays a very important and often physiologically significant role in the control of LH and prolactin release by hypothalamic action.

Localization and characterization of neuropeptide Y in the brain of Microcebus murinus (Primate, Lemurian)

The distribution of neuropeptide Y (NPY) in the brain of the lemur Microcebus murinus was determined by immunocytochemistry with the aid of a highly specific antiserum against synthetic porcine NPY. When compared with previous immunohistochemical data obtained in primates and other mammalian species, the localization of NPY-immunoreactive (IR) structures in the Microcebus murinus brain revealed particular features. (1) Numerous NPY-IR perikarya and a dense network of IR nerve terminals were found in the supraoptic and suprachiasmatic nuclei, respectively. The occurrence of NPY-IR perikarya in the supraoptic nucleus, also reported in the squirrel monkey, seems to be specific to primates. In the squirrel monkey, the suprachiasmatic nucleus exhibits only a moderate innervation, whereas in humans it appears totally devoid of NPY-IR fibers. (2) IR perikarya and axon processes were observed in many upper brainstem areas, in particular in the interpeduncular, raphe pontine, dorsal tegmental, parabrachial, and dorsal raphe nuclei, in the locus coeruleus, the nucleus of the solitary tract, and the reticular formation; in this latter area, the occurrence of two categories of NPY-IR neurons was demonstrated on the basis of their morphology and localization, suggesting that they may play distinct roles. (3) NPY-IR nerve processes could be traced over a long distance. (4) For the first time, numerous NPY-IR terminals were observed close to the lumen of the various cerebral ventricles. The immunoreactive NPY-like peptide was characterized by combining high performance liquid chromatography (HPLC) analysis and radioimmunoassay quantification. The dilution curves obtained with synthetic porcine NPY and serial dilutions of occipital cortex, paraventricular and supraoptic hypothalamus, posterior hypothalamus, medulla oblongata, or preoptic area extracts were parallel. The highest amounts of NPY were measured in the hypothalamus and telencephalon. HPLC analysis resolved a single peak of NPY-like immunoreactivity that exhibited the same retention time as synthetic porcine NPY. The distribution of NPY in the lemurian brain is discussed with respect to phylogeny and putative functions.

Neuropeptide Y: an overview of central distribution, functional aspects, and possible involvement in neuropsychiatric illnesses

Neuropeptide Y (NPY) was first discovered and characterized as a 36-amino-acid peptide neurotransmitter in 1982. It is widely distributed in the central nervous system, with particularly high concentrations within several limbic and cortical regions. A number of co-localizations with other neuromessengers such as noradrenaline, somatostatin, and gamma-aminobutyric acid have been demonstrated. A large number of physiological and pharmacological actions of NPY have been suggested. Recent clinical data also suggest the involvement of NPY in several neuropsychiatric illnesses, particularly in depressive and anxiety states. This article gives a comprehensive review of central distribution of NPY and its receptors, co-localizations and interactions with other neuromessengers, genetic aspects, pharmacological and physiological actions, influence on neuroendocrine functions, and possible involvement in various neuropsychiatric illnesses.

Multifactorial control of pituitary hormone secretion: the "wheels" of the brain

An attempt is made to deal with the complexity of the nerve fibers in the median eminence. Visual aids are presented in the shape of "wheels" that depict a dynamic interplay of neurochemicals which result in the release of hormones from the anterior pituitary gland. The multiplicity of neurochemicals in the median eminence is perceived to be responsible for the integrated control of pituitary hormone releasing factors.

Central nervous system effects of peptides, 1980-1985: a cross-listing of peptides and their central actions from the first six years of the journal Peptides

A tabular synopsis is presented for articles concerned with the effects of peptides on the central nervous system that appeared in the journal Peptides from 1980-1985. A table arranged alphabetically by peptide and one arranged by effects, both listing routes of injection, species, direction of change, and qualifying notes, provides easy cross-referencing of peptides and their effects. Over 80 peptides and over 135 effects are listed. The list of peptides includes, but is not limited to: ACTH, angiotensin, bombesin, bradykinin, calcitonin, casomorphin, CCK, ceruletide, CGRP, CRF, dermorphin, DSIP, dynorphin, endorphins, enkephalins, GRF, gastrin, LHRH, litorin, metkephamid, MIF-l, motilin, MSH, NPY, NT, oxytocin, ranatensin, sauvagine, substances P and K, somatostatin, TRH, VIP, vasopressin, and vasotocin. The list of effects includes, but is not limited to: aggression, alcohol, analgesia, attention, avoidance, behavior, cardiovascular regulation, catalepsy, conditioned behavior, convulsions, dopamine binding and metabolism, discrimination, drinking, EEG, exploration, feeding, fever, gastric secretion, GI motility, grooming, learning, locomotor behavior, mating, memory, neuronal activity, open field, operant behavior, rearing, respiration, satiety, scratching, seizure, sleep, stereotypy, temperature, thermoregulation and tolerance.

Neuropeptide Y and peptide YY neuronal and endocrine systems

An extensive system of neuropeptide Y (NPY) containing neurons has recently been identified in the central and peripheral nervous system. In addition, NPY and a structurally related peptide, peptide YY (PYY), containing endocrine cells have been identified in the periphery. The NPY system is of particular interest as the peptide coexists with catecholamines in the central and sympathetic nervous system and adrenal medulla. Evidence has been presented which indicates that NPY may play important roles in regulating autonomic function.