Hypothalamic Vasoactive Intestinal Polypeptide Research Articles

Prior Experience with Photostimulation Enhances Photo-Induced Reproductive Response in Female House Finches

In vertebrates, reproductive output often increases with age. Unlike older birds, first-year photoperiodic birds lack experience with the reproductively stimulatory effects of long day lengths (photostimulation). We examined whether age-related differences in annual reproductive development could be partially attributed to previous experience with photostimulation in the photoperiodic house finch (Carpodacus mexicanus). By manipulating photoperiod, we generated 2 groups of first-year females: a photo-experienced group that underwent 1 photoperiodically induced cycle of gonadal development and regression and a photo-naïve group exposed to long days since hatch. We transferred both groups from long to short days and then photostimulated and exposed them to male birdsong prior to sacrifice. Following concurrent photostimulation, both groups exhibited similar plasma luteinizing hormone surges and hypothalamic vasoactive intestinal polypeptide immunoreactivity. In contrast, hypothalamic gonadotropin-releasing hormone immunoreactivity and circulating vitellogenin levels were higher in photo-experienced birds, and yolk deposition occurred in only 2 females, both of which were photo-experienced. Our results demonstrate that photo-experience enhances some aspects of early photo-induced reproductive development and raise the hypothesis that photo-experience may account for at least some age-related variation in reproductive output.

Pituitary adenylate cyclase-activating polypeptide does not colocalize with vasoactive intestinal polypeptide in the hypothalamic magnocellular nuclei and posterior pituitary of cats and rats.

Pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal polypeptide (VIP) immunoreactive cells were demonstrated in the hypothalamic magnocellular nuclei in cats and rats. In cats these immunoreactive cells were stained without any treatment or intervention; however, in rats we had to use the pituitary stalk section to enhance the amount of PACAP and VIP for successful immunostaining. In both species the regions occupied by PACAP and VIP immunoreactive cells partially overlap each other in the paraventricular and supraoptic nuclei. Nevertheless, in either cats or rats PACAP and VIP immunoreactivities do not colocalize in the same cells studied by double labeling immunohistochemistry (IHC) or by the combination of immunohistochemistry and in situ hybridization. As was expected, PACAP and VIP immunoreactive materials were stored in different fibers of the posterior pituitary where the distribution of PACAP and VIP fibers also showed different patterns: PACAP fibers form a dense plexus at the periphery of the posterior lobe, in the vicinity of the intermediate lobe; however, the VIP fibers were evenly distributed mainly in the center of the posterior lobe. In spite of the high sequence homology of PACAP and VIP, the two peptides are synthesized in different subpopulations of hypothalamic neurons. This different distribution correlates well with the different role of the hypothalamic PACAP and VIP in the biologic clock and in the functions of the anterior and posterior pituitary.

Changes in basal hypothalamic chicken gonadotropin-releasing hormone-I and vasoactive intestinal polypeptide associated with a photo-induced cycle in gonadal maturation and prolactin secretion in intact and thyroidectomized starlings (Sturnus vulgaris).

Chicken gonadotropin-releasing hormone-I (GnRH-I) and the avian prolactin-releasing hormone, vasoactive intestinal polypeptide (VIP), were measured in the basal hypothalamus in male starlings during photo-induced gonadal growth and the subsequent development and maintenance of reproductive photorefractoriness. Comparisons were made with thyroidectomized birds, which maintain breeding condition irrespective of changes in photoperiod. In intact birds, basal hypothalamic GnRH-I increased four-fold after photostimulation and then decreased 115-fold over 12 weeks to values characteristic of long-term photorefractoriness. Pituitary and plasma prolactin increased after photostimulation, reaching peak values when the testes were regressing, and returned to low values in long-term photorefractory birds. Basal hypothalamic VIP did not change after photostimulation in intact birds. In photostimulated thyroidectomized birds, values for basal hypothalamic GnRH-I and VIP, and for pituitary and plasma prolactin, remained no different to those of nonphotostimulated intact birds. These observations confirm that reproductive photorefractoriness is related to a decrease in hypothalamic GnRH-I. However, photorefractoriness in terms of prolactin secretion is not similarly related to a decrease in basal hypothalamic VIP. The mechanisms responsible for the decrease in prolactin in long-term photorefractory birds and for the total lack of photoperiodic responses in thyroidectomized birds remain unresolved.

Possible involvement of vasoactive intestinal polypeptide in the central stimulating action of pituitary adenylate cyclase-activating polypeptide on prolactin secretion in the rat

Effect of pituitary adenylate cyclase-activating polypeptide (PACAP) on prolactin (PRL) secretion was studied in Wistar strain male rats in vivo. Intravenous injection of PACAP-38 and PACAP-27 resulted in a dose-related increase in plasma PRL levels both in conscious rats and in urethane-anesthetized rats. In anesthetized animals, i.c.v. injection of PACAP-38 and PACAP-27 also elicited a dose-related increase in plasma PRL. The PRL secretion induced by i.c.v. injection of PACAP-38 was attenuated by pretreatment with rabbit antiserum to vasoactive intestinal polypeptide (VIP). These findings suggest that PACAPs stimulate PRL secretion in the rat by acting not only directly on the pituitary but also indirectly through the central nervous system, at least partly, via hypothalamic VIP.

Chronic but not Acute Exposure to Stress is Associated with Hypothalamic Vasoactive Intestinal Polypeptide (VIP) Release into Median Eminence

The influence of stress on hypothalamic VIP release into the pituitary portal blood has not been assessed at present despite the fact that this peptide has been implicated in the control of several pituitary hormones and especially in the release of prolactin (PRL) caused by stress. In the present work the effect of stress on the in vivo release of VIP into the pituitary portal blood of male rats was evaluated by means of push-pull perfusion (PPP) of median eminence (EM). VIP content in the PPP liquid was successfully measured and their levels agree well with pituitary portal blood levels measured by other authors. Whereas plasma PRL levels strongly increased during acute immobilization (IMO), no changes in VIP secretion into the ME were observed. VIP release into the ME was also unaffected by exposure to ether. In contrast, in chronically immobilized rats a significant increase in VIP release into the ME was obtained in response to acute IMO. The present data argue against a major role of hypothalamic VIP in PRL release caused by acute stress and show that chronic stress qualitatively alters the signal of hypothalamic VIP to the pituitary.

Pituitary Prolactin Messenger Ribonucleic Acid Levels in Incubating and Laying Hens: Effects of Manipulating Plasma Levels of Vasoactive Intestinal Polypeptide

Pituitary PRL messenger RNA levels in hens, measured by dot-blot hybridization, correlated directly with concentrations of plasma PRL, being 3-fold higher in incubating than in laying birds. Nest deprivation of incubating hens for 24 h caused a rapid decrease in both plasma PRL and pituitary PRL mRNA, which remained depressed thereafter. A single injection of vasoactive intestinal polypeptide (VIP) in laying hens resulted in an increase (P less than 0.05) in pituitary PRL mRNA whereas passive immunoneutralization of VIP in incubating hens resulted in a decrease (P less than 0.001) in pituitary PRL mRNA. The rapid decrease in pituitary PRL mRNA after nest deprivation or passive immunoneutralization of VIP was associated with a significant increase in pituitary PRL content, presumably a consequence of the decreased PRL secretion. In situ hybridization showed PRL mRNA to be localized in the cephalic lobe of the anterior pituitary gland in which most PRL cells, identified immunocytochemically, were found. Northern blotting studies showed that the pituitary gland contains a single 860 base(s) mature PRL mRNA transcript irrespective of physiological state or VIP manipulation. Both in situ and Northern hybridization studies confirmed that the amount of pituitary PRL mRNA was related directly to the concentration of plasma PRL. These observations are consistent with the view that in incubating hens hypothalamic VIP, in addition to acting as a PRL releasing hormone, also plays a major role in the regulation of the amount of PRL mRNA in the anterior pituitary gland.

Age-Related Changes in Rates of Basal Secretion of Immunoreactive Vasoactive Intestinal Polypeptide and Dopamine into Pituitary Stalk Blood from the Hypothalamus in Anesthetized Male Rats.

Age-related changes in prolactin (PRL) in systemic blood plasma, and in secretions of hypothalamic vasoactive intestinal polypeptide (VIP), an important candidate for PRL-releasing factor, and dopamine, a PRL-inhibiting factor, into the pituitary stalk blood were investigated. The experiments were performed on male urethane-chloralose-anesthetized Wistar rats of three different ages, i.e., (1) adult rats 5-8 months old, (2) middle-aged rats 12-15 months old, and (3) aged rats 24-26 months old. The concentration of immunoreactive PRL (iPRL) in systemic blood plasma of the aged rats was significantly higher than that of the adult rats (p less than 0.01). The secretion rate of hypothalamic immunoreactive VIP (iVIP) into the pituitary stalk blood was unchanged during aging, while that of dopamine was markedly increased in the aged rats in comparison with the value in both adult and middle-aged rats (p less than 0.01). These results indicate that the basal secretion of hypothalamic VIP is well maintained, while that of hypothalamic dopamine is augmented in aged rats with hyperprolactinemia. It can be assumed that the increase in the pituitary PRL secretion is a primary event during aging in rats, and that a high circulating level of PRL may facilitate the hypothalamic dopamine secretion through the activation of a negative feedback system of the hormone.

Suckling Stimulates the Expression of Vasoactive Intestinal Polypeptide Gene in Rats.

The effect of suckling on vasoactive intestinal polypeptide (VIP) gene expression in the hypothalami was studied during the postpartum period in rats. Female rats were divided into two groups immediately after delivery. In one group, a mother was housed with 8 pups, and in the other, without any pups. The former group was named S(+) and the latter S(-). On days 0, 3, 6, 9 and 12 after delivery, the mothers were killed by decapitation. Hypothalamic VIP mRNA was measured by RNA dot hybridization. Although the VIP mRNA level showed no significant change after delivery in the S(-) group, VIP mRNA in the S(+) group on days 6, 9 and 12 increased to 1.6, 3.5 and 2.1 times higher than the level observed on day 0, respectively. These results suggest that suckling induces the synthesis of VIP after 6 postpartum days.

The role of hypothalamic vasoactive intestinal polypeptide in the maintenance of prolactin secretion in incubating bantam hens: observations using passive immunization, radioimmunoassay and immunohistochemistry.

The role of chicken vasoactive intestinal polypeptide (cVIP) as a prolactin-releasing factor was investigated in incubating bantam hens. Specific antibodies were raised against cVIP (anti-cVIP) for passive immunization studies, to develop a radioimmunoassay and to localize VIP neurones immunohistochemically in the hypothalamus. The concentration of plasma prolactin decreased after i.v. injection of anti-cVIP: this low concentration being maintained by daily injection of anti-cVIP. Incubating hens injected daily with anti-cVIP deserted their nests after 4.5 +/- 0.6 days and returned to lay after 20 +/- 1 days. This disruption of incubation behaviour with anti-cVIP was prevented by concomitant, twice daily, injections of 30 IU ovine prolactin. The concentration of plasma LH was not immediately affected after injection of anti-cVIP but increased when the hens deserted their nests. The amount of cVIP, measured by radioimmunoassay, was significantly higher in the median eminence (P less than 0.01) and medial basal hypothalamus (P = 0.05) in incubating than in laying hens. No differences were seen in the amounts of cVIP in the preoptic hypothalamus or in a part of the forebrain including the nucleus accumbens, between laying and incubating hens. Morphological observations were made on immunohistochemically identified cVIP cell bodies in the medial basal hypothalamus. These showed that cVIP cell number, cell area and density of immunoreactive product were significantly (P less than 0.05) greater in incubating than in laying hens. Further, the density of cVIP reaction product in the anterior median eminence was also significantly (P less than 0.01) greater in incubating than in laying hens.(ABSTRACT TRUNCATED AT 250 WORDS)

Reduced vasoactive intestinal polypeptide immunoreactivity in the pituitaries of hormone-deficient mutant mice.

The prolactin-producing cells of the bovine anterior pituitary were found to contain a vasoactive intestinal polypeptide (VIP) immunoreactive substance, thus suggesting a role for VIP in the regulation of prolactin release. The pituitaries of the dw and lit strains of mutant mice, congenitally deficient in prolactin-producing cells, and hyt mice, which were found to have reduced numbers of prolactin-producing cells, showed a markedly reduced VIP immunoreactivity. Hypothalamic VIP immunoreactivity, however, was found to be unchanged in the three strains of mutant mice, indicating that the high concentration of VIP in the hypothalamus does not derive from the adenohypophysis through retrograde flow. The deficiency in the mutant mice seems to be due to the lack of prolactin target cells in the pituitary.

Galanin stimulates the release of vasoactive intestinal polypeptide from perifused hypothalamic fragments in vitro and from periventricular structures into the cerebrospinal fluid in vivo in the rat

Intracerebroventricular injection of galanin (2 micrograms/rat) raised plasma prolactin (PRL) levels in the rat, which was accompanied by an increase in immunoreactive vasoactive intestinal polypeptide (VIP) in the cerebrospinal fluid (CSF). Immunoreactive VIP release from superfused rat hypothalamic fragments in vitro was dose-relatedly stimulated by galanin (10(-7) and 10(-8) M). PRL release from superfused rat anterior pituitary cells was stimulated by TRH (10(-8) M) but not affected by galanin (10(-7) to 10(-5) M). These findings indicate that central galanin has a stimulating role in the release of hypothalamic VIP, which results in pituitary PRL secretion in the rat.

Central galanin stimulates pituitary prolactin secretion in rats: Possible involvement of hypothalamic vasoactive intestinal polypeptide

The effect of galanin, a newly identified neuropeptide, on pituitary prolactin (PRL) secretion was examined in the rat. Intracerebroventricular (i.c.v.) injection of all 5 doses of galanin (0.4, 1, 2, 5 and 10 micrograms/rat) raised plasma PRL levels in urethane-anesthetized rats. Galanin injection (2 micrograms/rat, i.c.v.) also increased plasma PRL levels in conscious rats. The intermediate dose of galanin (2 micrograms/rat, i.c.v.) produced a greater response in plasma PRL levels than either smaller or larger doses of galanin. Intravenous injection of galanin did not affect plasma PRL levels. Passive immunization with specific anti-vasoactive intestinal polypeptide (VIP) rabbit serum suppressed plasma PRL response to galanin (2 micrograms/rat, i.c.v.) in anesthetized rats. These findings indicate that central galanin has a stimulatory role in pituitary PRL secretion via the hypothalamus in the rat and that VIP may be involved in rat PRL release induced by galanin.

Inhibition by antiserum to Vasoactive Intestinal Polypeptide (VIP) of prolactin secretion induced by serotonin in the rat

Intraventricular (i.c.v.) injection of serotonin (5HT) or intravenous (i.v.) injection of 5-hydroxytryptophan (5HTP), a precursor of 5HT, raised plasma prolactin (PRL) levels in urethane-anesthetized rats pretreated with normal rabbit serum. When the animals were injected i.c.v. or i.v. with specific anti-VIP rabbit serum, the plasma PRL responses to 5HT and 5HTP were blunted. These findings suggest that hypothalamic VIP is involved, at least in part, in PRL secretion induced by central serotonergic stimulation in the rat.

Involvement of hypothalamic vasoactive intestinal polypeptide (VIP) in prolactin secretion induced by serotonin in rats.

To study the possible involvement of hypothalamic vasoactive intestinal polypeptide (VIP) in regulating the secretion of prolactin (PRL), the effect of anti-VIP rabbit serum on serotonin (5-HT)-induced PRL release was examined in urethane-anesthetized male rats. Anti-VIP serum (AVS) or normal rabbit serum (NRS) was infused into a single hypophysial portal vessel of the rat for 40 min at a rate of 2 microliters/min with the aid of a fine glass cannula and 5-HT was injected into a lateral ventricle 10 min after the start of the infusion. Intraventricular injection of 5-HT (10 micrograms/rat) caused an increase in plasma PRL levels in control animals infused with NRS and 5-HT-induced PRL release was blunted in animals infused with AVS (mean +/- SE peak plasma PRL: 118.9 +/- 19.8 ng/ml vs 54.7 +/- 16.2 ng/ml, p less than 0.05). These findings suggest that the secretion of PRL induced by 5-HT is mediated, at least in part, by hypothalamic VIP release into the hypophysial portal blood in the rat.