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J P Advis

Publications and source records attributed to J P Advis.

At least 19 recordsLinked to original sources
PubMed2003

Regulation of gonadotropin releasing hormone release by neuropeptide Y at the median eminence during the preovulatory period in ewes.

The median eminence (ME) of the hypothalamus is known to be an important brain site where hypophysiotropic release might be regulated by excitatory and inhibitory signals impinging on their neuronal terminals. Since a role for neuropeptide Y (NPY) on preovulatory luteinizing hormone (LH) release has been suggested, we hypothesized that NPY might act at the ME to control preovulatory gonadotropin-releasing hormone (GnRH) release and thus the onset of the preovulatory surge of LH. To examine this possibility, we used the ewe as an animal model to determine: (a) immunocytochemical distribution of GnRH and NPY in the ewe ME; (b) changes in in vivo release of NPY and GnRH using ME push-pull cannula (PPC) perfusate samples, as well as in plasma LH, during the luteal, follicular and preovulatory phases of a synchronized estrous cycle, and (c) effects of ME perfusion of NPY or a Y1-NPY antagonist, or an NPY antiserum on in vivo release of ME-GnRH and plasma LH during a synchronized follicular phase. Immunolocalization reveals a dense plexus of beaded GnRH-containing neurites in the arcuate nucleus and in its vicinity, the pituitary stalk and the palisade. In contrast, a dense plexus of NPY-containing neurites occurs in the internal layer, with occasional fibers found in the intermediate and lateral external zone of the ME. In the area between the lateral internal and lateral external layers, both NPY and GnRH-containing processes were found, thus providing opportunities for synaptic and/or paracrine interactions between NPY- and GnRH-containing neurons. Hormonal analysis indicated that a synchronized preovulatory surge of LH is elicited within a 2-hour window by the sequential implantation and removal of silastic-encased estradiol (E2) or progesterone (P4) implants. In this paradigm, there was a parallel increase in ME release of both NPY and GnRH preceding the synchronized LH surge. The onset of this synchronized LH surge was advanced by ME perfusion of exogenous NPY and was both delayed and blunted by ME perfusion with the NPY antagonist (both were perfused through the PPC probe for 2 h, starting 2-3 h before the expected onset of the LH surge). In addition, NPY perfusion in the ME increases, while perfusion of the Y1-NPY antagonist or of the NPY antiserum decreases ME-PPC GnRH content and plasma levels of LH in early follicular ewes. Finally, perfusion of NPY antiserum during an ongoing LH surge disrupted LH release. These results suggest that interactions between NPY and GnRH neurons are important in controlling the timing, magnitude and maintenance of the preovulatory LH surge.

Animals↗
PubMed2001

Chronic ethanol inhibits NK cell cytolytic activity: role of opioid peptide beta-endorphin.

The role of beta-endorphin (beta-EP) in ethanol-altered NK cell cytolytic activity is studied using male Fischer-344 rats as an animal model. Ethanol was administered for 1, 2, 3, or 4 wk in a liquid diet containing 8.7% ethanol (v/v), which means that 37% of the total calories were derived from ethanol. Rats treated with ethanol for 1 wk showed an increase in hypothalamic and plasma levels of immunoreactive (IR)-beta-EP, but displayed no significant effect on NK cell activity determined by (51)Cr release assay, as compared with those in pair-fed and ad libitum-fed animals. However, animals treated with ethanol for 2, 3, or 4 wk showed decreased hypothalamic and plasma levels of IR-beta-EP and decreased splenic NK cell activity. No significant decrease in the number of splenocytes and NK cells or in the percentage of NK cells was seen until after 3 and 4 wk of ethanol treatment. Exposure in vitro of splenic lymphocytes obtained from control animals to various concentrations of beta-EP increased NK cell activity. The opiate antagonist naltrexone blocked the beta-EP-stimulated effect. The in vitro NK cell response to beta-EP was reduced in the splenocytes obtained from animals treated with ethanol for 2 wk, but not in those obtained from animals treated with ethanol for 1 wk as compared with those in control animals. Additionally, beta-EP administration into the paraventricular nucleus of the hypothalamus stimulated NK cell cytolytic activity, whereas the opiate blocker administration reduced NK cell activity. The NK cell responses to paraventricular nucleus beta-EP were reduced in the animals treated with ethanol for 2 wk. These data provide evidence for the first time that ethanol inhibits NK cell cytolytic activity, possibly by reducing beta-EP-regulated splenic NK cell function.

Animals↗
PubMed1999

An analysis of physiological mechanisms underlying the antigonadotropic action of intracranial prolactin in ring doves.

Intracerebroventricular (ICV) injections of prolactin (PRL) exert potent antigonadal and antigonadotropic effects in ring doves (Streptopelia risoria) at doses that are insufficient to stimulate prolactin-dependent crop growth. To explore the physiological basis of these effects, we tested the ability of ICV-injected PRL to influence pituitary responsiveness to chicken gonadotropin-releasing hormone-I (cGnRH-I) and to alter GnRH content and concentration in the preoptic area (POA) and median eminence (ME). cGnRH-I-induced changes in plasma LH were monitored by radioimmunoassay (RIA) in photostimulated male doves after they received five daily ICV injections of ovine PRL (1 microg/2 microl) or saline vehicle. Although PRL treatment reduced basal plasma LH levels and testes weight, it did not reduce the amount or alter the pattern of LH released in response to a bolus injection of cGnRH-I. This suggests that ICV PRL does not suppress LH by reducing pituitary responsiveness to GnRH. In two subsequent studies, GnRH content (ng/region) and concentration (pg/microg protein) in the POA and ME were measured in male doves by RIA and by competitive enzyme immunoassay after 5 days of ICV PRL or vehicle treatment. Although ICV PRL reduced plasma LH levels in both studies, no significant PRL-induced alterations in GnRH content or concentration were apparent. In a final study, PRL-treated female doves had lower plasma LH levels than vehicle-treated control females at 12 and 24 h after a single ICV injection. GnRH content of the POA was also lower in PRL-treated females than in controls at 24 h. However, the two treatment groups did not differ in POA or ME GnRH content at earlier postinjection sampling intervals. Analysis of GnRH concentration data revealed no treatment group differences in either region at any sampling interval (1, 6, 12, or 24 h post-PRL injection). Collectively, these results are consistent with the idea that ICV-injected PRL acts at the level of the CNS to inhibit the reproductive system. However, the nature of the alterations involved remains to be clarified. Plausible hypotheses are (1) that ICV PRL suppresses the gonadal axis by influencing the activity of GnRH neurons at brain sites other than the POA or ME or (2) that PRL alters the synthesis, storage, degradation, and/or release of GnRH in the POA or ME, but the dynamic changes involved are not reflected in integrated, steady-state measures such as peptide content or concentration in tissue.

Animals↗
PubMed1993

Neuropeptide Y regulation of LHRH release in the median eminence: immunocytochemical and physiological evidence in hens.

It has been suggested that hypothalamic median eminence (ME) might be a control site for luteinizing hormone-releasing hormone (LHRH) release. Thus, stimulatory and/or inhibitory inputs acting at this site might be involved in regulating LHRH release from the ME and, therefore, luteinizing hormone (LH) release from the anterior pituitary. Since a role for neuropeptide Y (NPY) on LH release has been suggested, we have hypothesized that NPY might act in the ME to control preovulatory LHRH release in hens. To examine this possibility we have determined: (a) the immunocytochemical distribution of LHRH and NPY in the ME of the hen, (b) the basal and NPY-stimulated release of LHRH in vitro from the ME of hens undergoing a natural or a premature preovulatory surge of LH, and (c) the tissue content of LHRH and NPY in microdissected MEs, at various times before and during a natural or a premature preovulatory surge of LH. A potential role for NPY on LHRH release in the ME is suggested for the following reasons. (a) There are opportunities for synaptic interactions between NPY and LHRH-containing axons at this site. LHRH-containing cell bodies localized in the anterior hypothalamus/medial preoptic area project to the ME. NPY-containing perikarya, concentrated in the ventromedial aspect of the arcuate nucleus, might contact LHRH processes going to the ME and/or might themselves send axons to the ME, (b) Addition of NPY to the incubation media increases LHRH release from microdissected ME tissue of hens killed at the time of the natural preovulatory surge of LH, but not in hens killed 7 h before the occurrence of this surge. However, the stimulatory effect of NPY on LHRH release can be induced at this latter time when a premature LH surge is elicited. While the natural preovulatory surge of LH occurs 4 h before the second ovulation in a sequence (C2 ovulation), administration of progesterone (P4) 10-14 h before the expected natural C2 ovulation advances the natural LH surge by 7-8 h. Thus, NPY might act as a physiological stimulus of LHRH release at the ME during the preovulatory surge of LH. This is suggested since in vitro basal LHRH release from denervated ME tissue does not change before and during the natural or the premature LH surge. Therefore, preovulatory release of LHRH in vivo might be under a continuous drive from stimulatory inputs to the LHRH neuron and NPY might be one of these stimulating factors.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1993

Beta-endorphin regulation of LHRH release at the median eminence level: immunocytochemical and physiological evidence in hens.

We studied the effect that beta-endorphin (beta END) might have at the median eminence (ME) on luteinizing hormone (LH)-releasing hormone (LHRH) during the ovulatory cycle of domestic hens. Thus, we assessed (a) the immunocytochemical distribution of beta END and LHRH in the hen ME, (b) the temporal changes in ME and preoptic area (POA) LHRH and beta END content, in both a spontaneous and a premature C2 ovulatory model. The premature C2 ovulation occurs 6-7 h after the administration of progesterone (P4) injected 14 h before the spontaneous second (C2) ovulation of a sequence and therefore 7-8 h earlier than expected, (c) the ME in vitro release of beta END in both models, and (d) the effect of beta END and naloxone on in vitro ME-LHRH release in the two models. In the hen, beta END cell bodies are located in the periarcuate area with axons projecting to both the ME and the POA. LHRH perikarya are located in the medial POA and anterior hypothalamus and project to the ME and infundibulum through the ventrolateral hypothalamus. In the spontaneous C2 ovulatory model, both beta END and LHRH content in the ME remained unchanged during the 14 h preceding the C2 ovulation. However, POA-LHRH content was increasing at the time of the LH surge (4 h before the expected C2 ovulation) and remained elevated until the C2 ovulation occurred. In contrast, POA-beta END content was lowest at the time of the LH surge and remained low until the C2 ovulation occurred.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Serial long-term assessment of in vivo LHRH release from a discrete area of the ewe median eminence using multiple guide cannula assembly and removable push-pull cannulae.

Analysis of neuronal interactions at the median eminence (ME) that control anterior pituitary function requires sampling of in vivo release of specific hypophysiotropic components and of putative inputs that might regulate such a release. We developed a multiple guide cannula assembly (MGCA) to sample repetitively discrete areas of the ewe ME, using removable push-pull cannula (PPC) probes. The MGCA is attached to the skull over the ME using stereotaxic surgery. A specific guide cannula of the assembly (1 of 48 guides) located on the midline and directly on top of the central portion of the ME is selected based on roentgenograms obtained after infusion of radiopaque contrast material into the third ventricle. The MGCA and the large size of the ewe brain allows the simultaneous positioning of a PPC probe, an infusion cannula or another removable probe in additional discrete hypothalamic and extrahypothalamic areas. To determine the capabilities of this sampling technique, we assessed in vivo release of LHRH from the extracellular space at the posterior-lateral ME, under various reproductive conditions that have well-defined LH-secretory patterns. The pulsatile profile of both LHRH and LH was significantly lower in anestrus than during the follicular phase of cycling ewes. In vivo pulsatile release of LHRH was higher in the follicular than in the midluteal phase of ewes sampled repetitively from the same ME site during three consecutive estrous cycles. All ewes showed increased midluteal progesterone levels. In vivo LHRH release, as determined by PPC sampling of the extracellular fluid at the posterior-lateral ME, probably reflects a mix of hypophysiotropic and nonhypophysiotropic LHRH components. Histological analysis revealed a well-organized, pallisade-like array of astroglial processes along the track of chronically implanted cannulae. This glial scar is disrupted along the tracks of acutely reimplanted cannulae but without apparent difference in the yield of the method. Our method increases the efficiency and versatility of ME PPC sampling providing an additional tool to assess the role of the ME as the final neuroendocrine control site of anterior pituitary function.

Animals↗
PubMed1993

Feed restriction in prepubertal lambs: effect on puberty onset and on in vivo release of luteinizing-hormone-releasing hormone, neuropeptide Y and beta-endorphin from the posterior-lateral median eminence.

The exact nature of the interaction between energy balance and reproduction is still elusive. Theoretically, nutrition-related variables must reach the hypothalamic luteinizing-hormone-releasing hormone (LHRH) network and/or its neuronal inputs, to alter plasma luteinizing hormone (LH) and therefore reproductive activity. In an attempt to assess the potential mechanism of such interaction at the median eminence (ME) level, the area of hypophysiotropic LHRH neuronal terminals and release, we used a decreased caloric intake lamb model which delays the onset of puberty. Thus, we determined the in vivo release of neuropeptides, by push-pull cannula (PPC) sampling from the posterior-lateral ME, in feed-restricted (FR) ewe lambs and in full-fed (FF), age-matched, contemporary control animals. Specifically, we assessed: (1) serum LH and ME in vivo release of LHRH, beta-endorphin (beta-END) and neuropeptide Y (NPY); beta-END and NPY are two putative neuronal inputs to LHRH neuronal terminals at the ME, reported to be involved in the control of both reproduction and feed intake; (2) the effect that exogenous infusion of beta-END through the PPC might have on the release of ME LHRH and NPY, and on plasma LH. In contrast to other works, the present results were obtained in lambs with intact ovaries. Furthermore, FR lambs were always compared statistically with FF contemporary paired controls that had attained puberty. Feed restriction decreased ME LHRH release, lowered plasma LH and prevented the onset of puberty. The changes induced by feed restriction in both LHRH and LH release were associated predominantly with decreases in pulse amplitude, rather than alterations in pulse frequency. The decreased LHRH and LH release occurred in the presence of a decreased beta-END but unchanged NPY release from the ME. Exogenous infusion of beta-END into the posterior-lateral ME decreased both LHRH and NPY release from this site and decreased plasma LH. In conclusion, decreased caloric intake lowers LH release and prevents puberty onset by decreasing the amplitude of the LHRH output from the hypothalamic hypophysiotropic network. A compensatory but unsuccessful mechanism for the FR status might be a lower beta-END-inhibitory tone on ME LHRH neuronal terminals. The unchanged release of NPY at this site supports the specificity of the changes induced by feed restriction on LHRH and beta-END in vivo release.

Animals↗
PubMed1993

Beta-endorphin regulation of luteinizing hormone-releasing hormone release at the median eminence in ewes: immunocytochemical and physiological evidence.

Beta-endorphin (beta-END) is an inhibitory factor in the neuroendocrine control of luteinizing hormone (LH) release and thus, presumably also of hypophysiotropic luteinizing hormone-releasing hormone (LHRH) release. In order to address if the median eminence (ME) is a site of beta-END action, we studied its functional role in ewes by assessing: (a) the hypothalamic distribution of beta-END using immunolabeling and by comparing this distribution with our data on the localization of LHRH; (b) the ME in vivo release of LHRH and beta-END during the luteal (day 12) and the follicular (day 15) phases of the estrous cycle; (c) the in vivo release of LHRH from the posterior-lateral ME, as assessed by push-pull cannula (PPC) sampling, before, during, and after infusion of increasing doses of beta-END or naloxone through the PPC, during the follicular phase; and (d) the in vivo release of ME-LHRH and serum LH, before, during, and after infusion of beta-END or naloxone in luteal and follicular ewes. In the ewe, beta-END-containing perikarya are located in and around the arcuate nucleus. Their processes are also present in the diagonal band, medial septal nucleus, and medial and lateral hypothalamic areas, including the preoptic region and posterior ME. Perikarya containing LHRH are located in the preoptic area and project also to the ME, providing opportunities for synaptic interactions between beta-END and LHRH-containing perikarya and processes at these levels. ME in vivo release of LHRH and beta-END increase from the luteal (low LH/high progesterone, P4) to the follicular phase (high LH/low P4). In follicular ewes, in vivo LHRH and LH release is decreased, in a dose-dependent manner, by beta-END infused through the PPC probe into the posterior-lateral ME. In contrast, infusion of naloxone under similar conditions increases LHRH and LH release, also in a dose-dependent fashion. The inhibitory effect of beta-END on LHRH and LH, as well as the stimulatory effect of naloxone on LHRH and LH, were only marginally apparent in luteal ewes. These results suggest that the ME is a major control site where beta-END exerts its influence on hypophysiotropic LHRH release. The strength of this inhibitory effect apparently increases throughout the follicular phase, and might prevent the premature onset of the preovulatory surge of LHRH and LH.

Animals↗
PubMed1993

The median eminence as a site for neuroendocrine control of reproduction in hens.

Based on events occurring during the genesis of a preovulatory surge of luteinizing hormone (LH) and an ovulatory failure of central origin, the hypothalamic median eminence (ME) is probably a major neuroendocrine control site for reproductive activity in the hen. The ratio of facilitatory to inhibitory (F:I) inputs on LH-releasing hormone (LHRH) neuronal terminals is an important determinant of the ME control site. The word "facilitatory" is defined as "stimulatory or increasing responsiveness to inputs". A relative increase in the F:I ratio of inputs on LHRH neuronal terminals at the ME is apparently involved in the genesis of the preovulatory surge of LH. Both an increase in neuropeptide Y (NPY) facilitatory inputs and a decrease in beta-endorphin (beta END) inhibitory inputs to ME-LHRH neuronal terminals are involved in the increase in the F:I ratio preceding the preovulatory surge of LH. Although the NPY component of this ratio (F) is apparently driven by the preovulatory surge of progesterone (P4) itself, its beta END component (I) might be related to the preovulatory surge of estradiol accompanying or preceding that of P4. As the egg-producing life of the hen progresses, a relative decrease in the F:I ratio on ME-LHRH neuronal terminals occurs. As a consequence of this decrease, stress-related inputs (e.g., feed restriction) can induce an hypothalamic failure of central origin in laying hens ending their 1st yr of production, but not in birds at the start of their egg-laying life. An increase in ME dopaminergic inhibitory inputs (I) on LHRH neuronal terminals is an apparent cause of the ovulatory failure induced by feed restriction.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Median eminence and anterior pituitary degradation of luteinizing hormone releasing hormone in hens undergoing changes in luteinizing hormone secretion.

Studies described in this report provide physiological evidence for a possible involvement of median eminence (ME) and anterior pituitary (AP) luteinizing hormone releasing hormone degrading activity (LHRH-DA) in the genesis of the hen's preovulatory surge of luteinizing hormone (LH). Serum LH and progesterone (P4), ME LHRH content and LHRH-DA, and AP LHRH-DA were determined in laying hens in the following reproductive conditions: 1) a "spontaneous" preovulatory LH surge; 2) a "premature" preovulatory LH surge; and 3) an ovulatory failure induced by feed withdrawal. The premature preovulatory surge of LH occurred 3 h after P4 administration and was preceded by an increase in both ME and AP LHRH-DA and by a decrease in ME LHRH content 1 h after P4 administration. However, the premature preovulatory LH surge was associated with a decrease in LHRH-DA back to control levels as ME LHRH content increased, even though LHRH was presumably being released from the ME at this time to maintain the preovulatory surge of LH. Although similar changes in LHRH-DA (an increase in both ME and AP LHRH-DA, followed by a decrease) also preceded the spontaneous preovulatory surge of LH, its profile was significantly blunted and no changes in ME LHRH content were associated with this LH surge. In contrast, ovulatory failure was correlated with a decrease in ME LHRH content but no changes in LHRH-DA. Therefore, in the hen, ME and AP enzymatic degradation of LHRH I might be involved in the genesis of a premature preovulatory surge of LH.

Animals↗
PubMed1992

Dopaminergic regulation of luteinizing hormone-releasing hormone release at the median eminence level: immunocytochemical and physiological evidence in hens.

Theoretically, the most effective inhibitory control of hypophysiotropic luteinizing hormone-releasing hormone (LHRH) release might occur through a presynaptic inhibition of LHRH neuronal terminals at the median eminence (ME) level. Since: (a) we have recently reported the existence of synaptic contacts between dopamine- and LHRH-containing processes in the ewe ME, and (b) nutritional deprivation induces an ovulatory failure in both birds and mammals, we have assessed the possibility that the anovulatory state induced by feed withdrawal (FW) in laying hens, might be caused by a dopaminergic inhibition of LHRH release at the ME level. Laying hens at the start (35 weeks old) and end (75 weeks old) of their commercial egg-laying life were killed at 0, 1, 2 and 4 days after FW. Serum luteinizing hormone (LH) and progesterone (P4), in vitro release of LHRH by isolated ME, and LHRH content in ME and preoptic area (POA) were determined by RIA. ME content of dopamine (DA) and its main metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) were assessed by LCED. The distribution of LHRH and tyrosine hydroxylase (TH)-containing processes at the ME level of the hen was determined immunocytochemically. In the hen, LHRH-containing cell bodies are localized in the anterior hypothalamus and medial POA. LHRH-containing axons project toward the ME and infundibulum through the ventral-lateral hypothalamus. TH-containing perikarya are concentrated in the arcuate nucleus and in the adjacent part of the periventricular nucleus, dorsal to the arcuate. TH-containing axons converge toward the ME and descend into the infundibulum. Dense concentrations of TH- and LHRH-containing processes are located in the lateral and mediobasal portions of the external layer of the ME, providing opportunities for synaptic interactions between them. Ovulatory failure and regression of the ovary and reproductive tract occurred 2-3 days after FW at the end, but not at the beginning of the hen's commercial egg-laying life. After FW, hens at the end of their productive life had higher (p less than 0.01) tuberoinfundibular DA turnover, produced less LHRH, and had lower serum LH and P4 than hens undergoing FW at the beginning of their productive life. In addition, in vitro release of HRH from denervated ME tissue of hens undergoing FW at the end of their commercial egg-laying life was higher and was reversed in a dose-dependent fashion by DA, but not by serotonin. Thus, the ovulatory failure associated with FW in laying hens might be caused by a presynaptic inhibition of in vivo LHRH release at the level of ME hypothalamic neuronal terminals.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1990

Norepinephrine-stimulated in vitro release of luteinizing hormone-releasing hormone (LHRH) from median eminence tissue is facilitated by inhibition of LHRH-degrading activity in hens.

We and others have previously reported the existence of hypothalamic and anterior pituitary (AP) enzymes that degrade luteinizing hormone (LH)-releasing hormone (LHRH). We have further characterized these LHRH-degrading activities (LHRH-DA) and in addition assessed the role of LHRH-DA in LHRH release from median eminence (ME) tissue in vitro. Major LHRH-DA components were separated and their molecular weights were estimated by gel filtration chromatography. The role of LHRH-DA in LHRH release was determined by release studies from isolated ME, in the presence and absence of N-tosyl L-phenylalanine chloromethyl ketone (TPCK) and/or norepinephrine (NEpi). Degradation and in vitro release studies were performed by using LHRH analogs with amino acid substitutions at their 5-6 bond. Biological activity of these analogs was assessed by measuring in vitro LH release from dispersed anterior pituitary cells. LHRH-DA was determined by high-performance liquid chromatography; LH and LHRH were measured by radioimmunoassay. Separation of LHRH-DA by gel filtration chromatography yielded two major enzymatic activities: a Tyr5-Gly6 cleaving endopeptidase and a post-proline cleaving enzyme. Although LHRH-DA from AP and ME produced identical degradation fragments, the former had 3-fold greater specific activity than the latter. LHRH moieties with a Tyr5-Gly6 bond substitution were more resistant to enzymatic degradation and had greater biological activity than LHRH moieties with a Tyr5-Gly6 bond. TPCK decreased LHRH-DA and increased NEpi-stimulated in vitro release of LHRH from isolated ME.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Direct hypothalamic control of vasoactive intestinal peptide (VIP) levels in the developing rat ovary.

We have previously identified the neurotransmitter vasoactive intestinal peptide (VIP) in nerve fibers of the immature rat ovary and showed that it stimulates steroid release by a mechanism involving increased synthesis of the components of the cholesterol side-chain cleavage enzyme complex. The present experiments were undertaken to study the ontogeny of ovarian VIP levels and to determine if they change in relation to the initiation of puberty. VIP was already detected in 2-day-old ovaries; levels remained constant at approximately 4.5 pg/mg ovary until the end of juvenile development (day 30). Thereafter, and preceding the peripubertal activation of the ovary, VIP levels increased two-fold, decreased gradually towards the first proestrus, and returned to juvenile values after the first ovulation. Transection of the ovarian nerves eliminated radioimmunoassayable VIP levels in both intact and hypophysectomized rats, indicating that ovarian VIP derives mostly from the extrinsic innervation of the gland. Treatment of hypophysectomized immature female rats with human chorionic gonadotropin (hCG), follicle stimulating hormone (FSH), growth hormone (GH), prolactin (Prl), estradiol, or their combination, failed to reproduce the peripubertal increase in VIP. In contrast, unilateral direct anodal current lesions of the left preoptic-anterior hypothalamic area (POA-AHA) of hypophysectomized juvenile rats led to a significant increase in VIP in the ipsilateral ovary. Surprisingly, both bilateral lesions and lesions of the right POA-AHA also increased VIP levels in the left ovary suggesting the existence of a marked asymmetry in the hypothalamic control of ovarian VIP. Lesions of the ventromedial nucleus, dorsal AHA or small lesions of the AHA were ineffective.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1989

Immunocytochemical and physiological evidence of a synapse between dopamine- and luteinizing hormone releasing hormone-containing neurons in the ewe median eminence.

Immunocytochemical labeling revealed that the arcuate nucleus (ARN) of the ewe's hypothalamus contains numerous tyrosine hydroxylase (TH)-positive neurons, that appear to lack dopamine-beta-hydroxylase (DBH)-like immunoreactivity. Axons of these presumed dopaminergic neurons converge in the median eminence (ME) with Luteinizing Hormone Releasing Hormone (LHRH)-containing axons originating mostly from neurons situated in the medial preoptic area. Electron microscopic double labeling revealed synaptic contacts between TH-positive presynaptic profiles and LHRH-containing postsynaptic elements. Samples of ME, ARN, paraarcuate and lateral hypothalamus were dissected and incubated to assess LHRH release and tissue content. Only ME-LHRH release was significantly reduced in the presence of dopamine (DA). All other regions released equal amounts with and without DA. Thus, a presynaptic dopaminergic inhibition of LHRH-containing axons at the level of the ME might contribute to the regulation of LHRH release into the portal vessels.

Animals↗
PubMed1988

N-tosyl-L-phenylalanine chloromethyl ketone inhibits LHRH-degrading activity and increases in vitro LHRH release from the immature rat median eminence.

Median eminence (ME) luteinizing-hormone-releasing hormone (LHRH)-degrading activity (LHRH-DA) may play a role in regulating the availability of releasable LHRH. Incubation of LHRH with ME tissue supernatant yields LHRH(1-5) and LHRH(6-10) degradation fragments, as detected by high-performance liquid chromatography (HPLC) analysis, suggesting a 5-6 cleavage of the decapeptide. Since these fragments are also present after incubation of LHRH with alpha-chymotrypsin (alpha-CH), we examined the possibility that the irreversible inhibitor of alpha-CH, N-tosyl-L-phenylalanine chloromethyl ketone (TPCK), might inhibit LHRH-DA and affect LHRH release. Irreversible inhibitors of trypsin-like proteases [N-alpha-p-tosyl-L-lysine chloromethyl ketone (TLCK), and phenylmethylsulfonylfluoride (PMSF)] were used as controls. LHRH-DA was determined by HPLC estimation of the loss of synthetic LHRH incurred when the peptide was incubated with aliquots of ME supernatant in the presence or absence of the inhibitors. LHRH release from ME fragments was assessed by radioimmunoassay after incubating the tissue with the inhibitors in Krebs-Ringer bicarbonate buffer. The LHRH-DA in both the incubation medium and the ME tissue was determined at the end of the incubation. TPCK (0.5-100 microM) added to ME tissue supernatant inhibited LHRH-DA in a dose-dependent manner. In contrast, when TPCK was added to medium in which intact ME were being incubated to assess LHRH release, the LHRH-DA of these ME was inhibited only at the 25-, 50- and 100-microM doses of TPCK, suggesting a relative inability of the inhibitor to reach endopeptidase pools in intact tissue. These same doses of TPCK increased LHRH release from the incubated ME.(ABSTRACT TRUNCATED AT 250 WORDS)

Age Factors↗
PubMed1985

Changes in luteinizing hormone-releasing hormone content of discrete hypothalamic areas associated with spontaneous and induced preovulatory luteinizing hormone surges in the domestic hen.

It is widely assumed that luteinizing hormone-releasing hormone (LHRH) neuronal activation is involved in the preovulatory surge of LH in the hen. In addition, this LH surge may be initiated by ovarian progesterone (P4) release. Thus, spontaneous and P4-induced LH surges should be associated with acute changes in LHRH content of discrete hypothalamic areas associated with LHRH cell bodies and/or LHRH axon terminals. Medial preoptic area (mPOA) and infundibulum (INF) LHRH content was measured by radioimmunoassay at intervals before, at, and following peak LH levels of a spontaneous preovulatory surge of LH, as well as when this surge was advanced by P4 administration in laying hens. Nonlaying birds served as additional controls. Levels of serum LH, P4, 17 beta-estradiol and pituitary LH were also measured. Increased (P less than 0.05) LHRH content in mPOA without changes in the INF are associated with peak serum LH levels of the spontaneous LH surge. By contrast, decreased (P less than 0.05) LHRH content in both mPOA and INF is associated with peak serum LH levels when the spontaneous surge was advanced 8 h by P4 administration to laying hens. Medial preoptic area and INF LHRH contents were significantly lower (P less than 0.05) in nonlaying than in laying hens.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Discrete hypothalamic distribution of luteinizing hormone-releasing hormone (LHRH) content and of LHRH-degrading activity in laying and nonlaying hens.

Hypothalamic enzymatic luteinizing hormone-releasing hormone (LHRH)-degrading activity (LHRH-DA) may play a physiologic role in the neuroendocrine control of LHRH in mammals. The present study analyzes the existence and possible physiologic role of LHRH-DA in birds. The LHRH content in discrete hypothalamic samples of laying and nonlaying hens was correlated to their LHRH-DA. Degrading activity was assessed by high-performance liquid chromatography (HPLC) of chicken LHRH and of its degradation fragments. Luteinizing hormone-releasing hormone content was estimated by radioimmunoassay. Luteinizing hormone-releasing hormone content of discrete medial preoptic, infundibulum, and arcuate samples, as well as serum LH and progesterone levels, were higher (P less than 0.05) in laying than in nonlaying hens. The LHRH content of these hypothalamic areas was also higher (P less than 0.05) than those of immediately adjacent areas, in both animal groups. Luteinizing hormone-releasing hormone-degrading activity, which generates LHRH1-5 as the main degradation fragment, was higher (P less than 0.01) in the infundibulum of laying than in nonlaying hens. It was also higher (P less than 0.01) in samples from the infundibulum and medial preoptic area than in immediately adjacent lateral samples. Finally, LHRH-DA, showing a similar HPLC profile of degradation fragments, was also present in areas of low or undetectable LHRH content.(ABSTRACT TRUNCATED AT 250 WORDS)

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