Changes in plasma gonadotrophins, 17ß-oestradiol, progesterone, prolactin, thyroxine and triiodothyronine concentrations in female Japanese quail (Coturnix coturnix japonica) of a heavy body weight line during photo-induced ovarian growth and regression.

1. Simultaneous changes of the width of the cloacal opening and plasma luteinising hormone (LH), follicle stimulating hormone (FSH), 17ß-oestradiol, progesterone, prolactin, thyroxine (T(4)) and triiodothyronine (T(3)) during photo-induced ovarian growth and regression were measured in commercially bred Japanese quail from a heavy body weight line. 2. Somatically mature female Japanese quail were transferred from short days (light:dark 8L:16D) at 10°C to long days (16L:8D) at 20°C, and sexually mature female Japanese quail were transferred from long to short days. All variables were measured at transfer and every five days thereafter (except for a measurement at 12 instead of 10 d) for 35 d. 3. Transfer from short to long days caused significant increases in LH, FSH, 17ß-oestradiol, ovary weights and oviduct weights after five days, and in the cloacal opening after 12 d. T(3) decreased after five days, whereas no significant changes were observed in T(4) concentrations. Progesterone and prolactin both decreased after 25 long days. 4. The transfer of quail from long to short days caused significant decreases in LH, FSH, 17ß-oestradiol, progesterone, prolactin, ovary and oviduct weights after 12 d and an increase in T(3). There was no significant change in T(4) concentrations. The cloacal opening decreased after 25 short days. 5. These results are the first to show simultaneous changes in gonadotrophins, sex steroids, thyroid hormones and prolactin during photo-induced gonadal growth and regression in female Japanese quail.

Changes in plasma gonadotrophins, testosterone, prolactin, thyroxine and triiodothyronine concentrations in male Japanese quail (Coturnix coturnix japonica) of a heavy body weight line during photo-induced testicular growth and regression.

1. Simultaneous changes of cloacal gland area (CGA) and plasma luteinising hormone (LH), follicle stimulating hormone (FSH), testosterone (T), prolactin (PRL), thyroxine (T(4)) and triiodothyronine (T(3)) during photo-induced testicular growth and regression were measured in commercially bred Japanese quail from a heavy body weight line. 2. Somatically mature male Japanese quail were transferred from short days (light:dark 8L:16D) at 10°C, to long days (16L:8D) at 20°C; and sexually mature male Japanese quail were transferred from long to short days. All variables were measured at transfer and every 5 d thereafter for 35 d. 3. Transfer from short to long days caused significant increases in LH, FSH, T and testis weight (TW) after 5 d, and in CGA after 10 d. T(3) decreased after 5 d, whereas T(4) increased significantly after 25 long days and PRL did not undergo any consistent change. The testicular growth rate was k = 0·1146. 4. Transferring quail from long to short days caused significant decreases in LH and FSH after 5 d, and decreases in T, TW and CGA after 10 d. T(4) decreased after 5 d whilst T(3) increased significantly by day 15. PRL decreased significantly after 10 d then rose before declining again. The testicular regression rate was k = 0·0582. 5. The rates of photo-induced testicular development and regression in a strain of large Japanese quail did not differ from rates reported for other strains of quail. CGA was a better indicator of TW than plasma T concentrations during growth and regression. The role of PRL in photo-induced reproductive cycles in male Japanese quail remains to be determined. 6. The photoperiod-induced changes in gonad size and hormone concentrations, together provide valuable information that can be used in future studies of the endocrinology and neuroendocrinology of photoperiodism in birds.

New hypotheses on the function of the avian shell gland derived from microarray analysis comparing tissue from juvenile and sexually mature hens.

Activation of the shell gland region of the avian oviduct is mediated by ovarian steroids. To understand more extensively how shell glands are maintained and function, we have compared gene expression in the shell glands from juvenile and laying hens using a chicken cDNA microarray. Average expression profiles of juvenile and sexually mature shell glands were compared resulting in the identification of 266 differentially regulated genes. Reverse transcription quantitative polymerase chain reaction confirmed expression differences. The differentially expressed genes included several with known involvement in shell gland function, including ion transport and shell matrix proteins. There were also many unpredicted differentially expressed genes, and for some we propose hypotheses for their functions. These include those encoding (a) osteoprotegerin, a decoy death receptor for receptor activator of nuclear factor NFkB ligand (RANKL) and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), that in the shell gland, may prevent apoptosis and/or may have an endocrine effect by preventing RANKL's action on bone osteoclasts that mobilize stored calcium; (b) prostatic acid phosphatase (ACPP) and prostate stem cell antigen (PSCA) that could play a role in sperm physiology within the shell gland; (c) urea transporter (SLC14A2) that could provide a novel anti-microbial defence; (d) bactericidal/permeability-increasing protein-like 2 (BPIL2), and other potential anti-microbials that have not previously been documented in the chicken. These new hypotheses, if borne out experimentally, will lead to a greater understanding of shell gland function including the processes involved in eggshell formation and anti-microbial activity.

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.

Sites of gene expression for vasoactive intestinal polypeptide throughout the brain of the chick (Gallus domesticus).

The peptide neurotransmitter vasoactive intestinal polypeptide (VIP) has several important functions in vertebrates, particularly, influencing the neuroendocrine and autonomic nervous systems both in developing and in adult animals. To document potential brain areas that might play significant functional roles, the distribution of VIP mRNA was examined throughout the entire chick brain by using in situ hybridization histochemistry (ISHH). In addition, a VIP binding-site study was completed that focused on the lateral septal organ (LSO), a circumventricular organ of potential significance in avian species. The areas where VIP message was found included the olfactory bulbs, posterior hippocampus, parahippocampal area, hyperstriatum, archistriatum/nucleus (n.) taenia (amygdala), medial part of the LSO, organum vasculosum of the lamina terminalis, medial preoptic region, bed n. of the pallial commissure, anterior hypothalamic (hypo.) n., lateral hypo. area (most extensive and dense message), periventricular hypo. n., lateral to the paraventricular n., ventromedial hypo. n., stratum cellulare externum, inferior hypo. n., infundibular hypo. n., median eminence, three layers within the stratum griseum et fibrosum superficiale, area ventralis of Tsai, n. tegmenti pedunculopontinus pars compacta (substantia nigra), intercollicular n., central gray, locus ceruleus, parabrachial n., ventrolateral medulla, reticular pontine area, in and about the n. vestibularis descendens. When compared with immunocytochemistry that detected the presence of the peptide product VIP, more areas of the brain were found to contain perikarya expressing VIP by using ISHH, particularly in the telencephalon and the mesencephalon. VIP binding sites were found in the lateral portion of the LSO where the blood-brain barrier is not fully developed. Hence, the LSO was found to contain neural elements that synthesize as well as bind VIP. VIP appears to be a useful peptide for defining major components of the visceral forebrain system in birds.

Expression of biologically active recombinant-derived chicken prolactin in Escherichia coli.

The putative chicken prolactin (chPRL) cDNA clone PRL101 was manipulated in vitro and cloned into the Escherichia coli expression vector pKK2332 to produce a plasmid coding for recombinant-derived mature chPRL (R-chPRL). Expression of this manipulated cDNA sequence in E. coli resulted in the production of a 23 kDa protein which cross-reacted with specific chPRL antisera in Western blots. The partially purified protein stimulated ring dove crop sac mucosa to proliferate in a PRL bioassay, demonstrating that the R-chPRL was biologically active. R-chPRL was expressed at a level of approximately 1.5% of total cell protein.

Evidence for alternative splicing of the chicken vasoactive intestinal polypeptide gene transcript.

Two forms of chicken vasoactive intestinal polypeptide (VIP) mRNA have been identified by reverse transcription (RT)-PCR and RNase protection assay. The shorter form of chicken VIP mRNA encodes a protein that does not contain an analogue of rat peptide histidine isoleucine (PHI) 1-27 or human peptide histidine methionine 1-27. The larger form encodes both VIP and a chicken analogue of PHI 1-27 in the same protein product. Three VIP cDNAs isolated from a chicken hypothalamic cDNA library were derived from the shorter mRNA. Sequence analysis of the longest clone identified an open reading frame that codes for a 165 amino acid preproVIP protein and contains two polyadenylation signals. In situ hybridisation with an oligonucleotide probe from the VIP cDNA sequence showed that VIP-encoding mRNA occurs in cells in the basal hypothalamus, an area of the brain known to contain VIP neurosecretory neurones. RT-PCR of total RNA from liver, kidney, gut, pancreas, pituitary, cerebellum, forebrain and hypothalamus, using primers derived from the VIP cDNA sequence, showed that the shorter form of VIP mRNA is present in all of these tissues. The sequence of the longer form of VIP mRNA was obtained by sequencing a portion of the VIP gene from genomic DNA. This revealed a potential exon that was not represented in the VIP cDNA clones analysed. RT-PCR with primers from this sequence showed that it was expressed in the gut and hypothalamus. RNase protection assays confirmed the presence of the two forms of mRNA in gut and hypothalamus. The relative proportions of the two mRNA forms were: 97.8% VIP only, 2.2% PHI/VIP in the hypothalamus and 98.5% VIP only, 1.5% PHI/VIP in the gut. In conclusion, chicken VIP mRNA is alternatively spliced. The shortest form, which encodes a preproprotein containing only the VIP peptide, is the most abundant. The longer form of chicken VIP mRNA encodes a preproprotein containing sequences for both VIP and a chicken form of PHI.

Sex differences in the LH responses to chicken LHRH-I and -II in the domestic fowl.

Maximal incremental changes in plasma LH were compared in adult hens and cockerels after i.v. injection of chicken (c) LHRH-I (pGlu1-His2-Trp3-Ser4-Tyr5-Gly6-Leu7-Gln8-Pro9-Gly10-N H2) or cLHRH-II (pGlu1-His2-Trp3-Ser4-His5-Gly6-Trp7-Tyr8-Pro9-G ly10-NH2). The LH response to cLHRH-I and -II was more rapid and greater in cockerels than in hens. The potencies of the two decapeptides were the same in cockerels but different in hens. Relative to cLHRH-I, the potency of cLHRH-II was 0.91 (0.6-1.2; 95% confidence limits) in cockerels and 36.5 (16.8-128.6) in hens. The greater potency of cLHRH-II relative to cLHRH-I in the hen than in the cockerel could not be accounted for by sex differences in the half-lives of the decapeptides in the peripheral circulation. The half-lives of both decapeptides in hens and cockerels ranged between 2.42 and 3.77 min. It is concluded that the interaction between LHRH-I and -II and the gonadotrophs is sexually differentiated in the domestic fowl. A new homologous radioimmunoassay was established for cLH. As in other chicken LH radioimmunoassays, there was evidence of cross-reactivity with TSH.

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)

Physiological roles of chicken LHRH-I and -II in the control of gonadotrophin release in the domestic chicken.

The physiological roles of chicken LHRH-I and -II (cLHRH-I and -II) in the regulation of gonadotrophin release were investigated in the domestic chicken. Measurements of the neuropeptides, using specific radioimmunoassays, in brain sections cut in three planes or in grossly dissected brain areas, showed that cLHRH-II occurs in low amounts throughout the brain whereas cLHRH-I is most abundant in the diencephalon. Within the diencephalon, the largest amount of cLHRH-I occurred in the median eminence of the hypothalamus. The amount of cLHRH-I in the median eminence was higher (P less than 0.05) in laying than in out-of-lay hens. No cLHRH-II was detected in the median eminence in either reproductive state. The amount of cLHRH-I in the hypothalamus was increased (P less than 0.05) in cockerels at the onset of puberty and in somatically immature birds after castration. There were no correlated changes in the amounts of hypothalamic cLHRH-II measured in the same experimental samples. Active immunization of laying hens against cLHRH-I but not against cLHRH-II resulted in the complete regression of the reproductive system and a depression in the concentration of plasma LH. These observations, taken together, suggest that gonadotrophin secretion in the hen is more likely to be directly regulated by cLHRH-I than by cLHRH-II.

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.

Photoperiodic control of the concentration of luteinizing hormone, prolactin and testosterone in the male emu (Dromaius novaehollandiae), a bird that breeds on short days.

The objective of this study was to establish, for a short-day breeding bird, the male emu, whether the breeding season is principally controlled by changes in photoperiod, and to investigate the endocrine mechanisms involved. Two groups of adult males were subjected to three alternating periods of 150-185 days of 14 h light/day (LD) and 10 h light/day (SD) terminating in a 360-day period of LD or SD. Transfer from LD to SD led to increases in plasma concentrations of luteinizing hormone (LH) and testosterone, after 82 +/- 8 and 73 +/- 3 (SEM) days, and an increase in prolactin concentrations after 115 +/- 12 days. Concentrations of LH and testosterone began to decrease before transfer back to LD, at a time when prolactin concentrations were approaching peak values. Transfer from LD to 360 days of SD resulted in increases in LH and testosterone concentrations, and these terminated after an increase in prolactin concentrations. After transfer from SD to 360 days of LD, plasma concentrations of LH and testosterone began to increase, after delays of 222 +/- 24 and 225 +/- 13 days, and were high at the end of the study, while prolactin values remained depressed throughout. These observations clearly show that seasonal breeding in the emu is directly controlled by changes in photoperiod. The dynamics of the hormonal responses to change of photoperiod suggest that, despite being short-day breeders, the photoregulation of breeding in emus involves mechanisms that are currently accepted for birds, rather than mechanisms that have been proposed for short-day breeding mammals. The initiation of breeding in emus is due to dissipation of photorefractoriness by short days which leads to an increase in the secretion of gonadotrophins to levels that are sufficient to support full reproductive condition. The termination of breeding, while days are still short, is due to the antigonadotrophic action of prolactin which, unusually for birds, increases while the days are still short. In conclusion, breeding activity in male emus is strongly controlled by photoperiod. Emus are short-day breeders, but the central mechanisms that regulate the secretion of reproductive hormones seem to be similar to those previously proposed for long-day breeding birds. The pattern of prolactin secretion in emus suggests an important role for this hormone in the termination of the breeding cycle.

Distribution and regulation by oestrogen of fully processed and variant transcripts of gonadotropin releasing hormone I and gonadotropin releasing hormone receptor mRNAs in the male chicken.

The aim of this study was to increase understanding of the occurrence and regulation of chicken gonadotropin releasing hormone I (cGnRH I) and chicken gonadotropin releasing hormone receptor (cGnRH-R) mRNA variants in the hypothalamic-pituitary-testicular axis (HPTA). The study was carried out in the cockerel. Fully processed cGnRH I mRNA (cGnRH Ia) and a variant transcript (cGnRH Ib) with a retained intron 1 were observed in the preoptic/anterior hypothalamus (POA), the basal hypothalamus, anterior pituitary gland, and testes. Fully processed cGnRH-R mRNA (cGnRH-Ra) and a variant transcript (cGnRH-Rb) with a deletion were detected in the same tissues. In juvenile cockerels, concentrations of cGnRH Ia and b in the POA increased after castration, and this was prevented by oestrogen treatment. In the anterior pituitary gland, the concentration of cGnRH-Ra increased after castration and this was reversed by oestrogen treatment. In intact adult cockerels, oestrogen treatment depressed plasma luteinizing hormone but did not affect concentrations of cGnRH I and cGnRH-R mRNAs in the POA, basal hypothalamus, and anterior pituitary gland, suggesting that locally produced oestrogen, by aromatization, may exert maximal suppression on cGnRH I and GnRH-R mRNAs. In intact adult cockerels, the concentrations of cGnRH Ia and b in the testis, but not cGnRH-Ra and b, were depressed by oestrogen treatment. It was concluded that fully processed and variant cGnRH I and cGnRH-R mRNAs occur in all components of the HPTA. Oestrogen appears to play a role in the regulation of cGnRH Ia and b in the POA and testes, and of cGnRH-Ra in the POA and anterior pituitary gland.

Endocrine and testicular changes in a short-day seasonally breeding bird, the emu (Dromaius novaehollandiae), in southwestern Australia.

Seasonal changes in testicular morphology and blood plasma concentrations of LH, testosterone, and prolactin are described for captive male emus in southwestern Australia. Testicular mass and testicular testosterone did not differ between the non-breeding (spring-summer) and the breeding (autumn-winter) seasons. Nevertheless, the testes obtained in the breeding season (May and August) were nearly two fold greater in mass than those collected in the non-breeding season (October and February). The highest testicular concentrations of testosterone were observed in February and lowest in October, while the values during the breeding season were intermediate. The patterns of histological changes in the testes also indicate that emus breed over the autumn-winter months. Tubule diameter was larger in the breeding season than in the non-breeding season, whereas the relative volume of the interstitium was larger in the non-breeding and smaller in the breeding season. Moreover, during the autumn and winter months, plasma LH and testosterone concentrations were high. Outside this period, in spring and summer, the concentrations of these hormones were low. Prolactin concentrations rose around the winter solstice, after the initial increases in plasma LH and testosterone. The end of the breeding season, in early spring, was marked by a gradual decrease in plasma LH concentrations but a rapid fall in testosterone concentrations. Prolactin concentrations continued to increase and peaked near the spring equinox, several weeks after the breeding season ended, and then decreased to reach baseline values by mid-summer. These testicular and endocrine changes are consistent with observations that the emu is a short-day breeder in southwestern Australia. Reproductive activity in the male begins soon after the summer solstice, well in advance of the development of suitable breeding conditions, and is then terminated in spring before food resources become limited by the onset of the dry season.

Effect of delayed step-up lighting on plasma luteinizing hormone and reproductive function in broiler breeders.

The aim of the study was to establish, in contemporary broiler breeders, whether delayed photostimulation at 313 d results in a reproductive response similar to that after photostimulation at 134 d (standard practice). The standard lighting program was compared with a novel program in which daily hours of light were reduced to 3 h during rearing and kept at 3 h until photostimulation at 264 d (8 h) or at 313 d (16 h). This experiment was done with hens fed ad libitum or feed-restricted hens. In photostimulated and nonphotostimulated hens, feed restriction delayed the onset of egg production and enhanced the subsequent rate of laying. Standard photostimulation advanced the onset of lay and increased the subsequent rate of lay in hens fed ad libitum and feed-restricted hens. Delayed photostimulation of hens did not impair the photoinduced increase in the concentration of plasma luteinizing hormone (LH) or egg production. Delayed photostimulation in cockerels failed to stimulate LH secretion. Unexpectedly, for feed-restricted hens, transfer from 3 to 8 h light/d at 264 d resulted in an increased in plasma LH and increased egg production. A similar increase in plasma LH was observed for cockerels subjected to the same lighting treatment. We concluded that, in broiler breeder hens, the reproductive response to photostimulation is not impaired if photostimulation is delayed for up to 313 d. Cockerels may not respond well to delayed photostimulation.

Genetic control of incubation behavior in the domestic hen.

The genetic control of incubation behavior was investigated in the domestic hen by analysis of the incidence of the behavior in reciprocal crosses between nonbroody White Leghorn (WL) and broody Bantam (B) lines and in a backcross of F1 males (WL male x B female) and WL females. The hypothesis tested was that a sex-linked gene (or genes) plays a dominant role in the expression of incubation behavior. The incidence of incubation behavior was tested in hens held in floor pens with access to nests containing hard-boiled eggs during a 28-wk photoinduced laying cycle. The cycle was repeated if the behavior was not observed during the first cycle. The incidence of incubation behavior in B and WL hens was 78.6% (n = 28) and 0% (n = 28), respectively. Contrary to prediction, the incidence of incubation behavior in the WL male x B female and the B male x WL female crosses were not significantly different (61.6%, n = 73; and 56.8%, n = 37, respectively). The incidence of incubation behavior in the F1 backcross was 5.8% (n = 103), which was significantly less (P < 0.001) than predicted (39.3%). It was concluded that incubation behavior was not controlled by major genes on the Z chromosome. It was hypothesized that at least two dominant autosomal genes are involved, one causing and the other inhibiting the behavior with equal influence.

A radioimmunoassay for recombinant-derived chicken prolactin suitable for the measurement of prolactin in other avian species.

A homologous radioimmunoassay for chicken prolactin is described. The assay is based on recombinant-derived chicken prolactin that has been used to raise an antibody and produce 125I-labeled tracer and assay standards. The radioimmunoassay measures a minimum of 0.03 +/- 0.01 ng of the recombinant prolactin with 50% displacement of binding by 0.6 +/- 0.1 ng. Chicken plasma and pituitary immunoreactivity dilute in parallel with the standard curve. The mean (+/- SE) concentrations of plasma prolactin were 12.1 +/- 1.5, 433.2 +/- 5.5, and 1609.8 +/- 18.5 ng/ml in out-of-lay, laying, and incubating bantam hens, respectively. The binding of recombinant prolactin was not displaced by extracts of neural lobe or plasma from a hypophysectomized hen. Plasma prolactin concentrations were increased after intravenous administration of chicken vasoactive intestinal polypeptide or quipazine, a 5-HT agonist. The assay measures immunoreactive prolactin in other birds. Plasma from quail, turkey, great tit, and wryneck displaced the 125I-labeled prolactin tracer parallel to the standard curve. Starling, ring dove, and penguin plasma displaced the binding in a nonparallel manner.

Passive immunization against chicken vasoactive intestinal polypeptide suppresses plasma prolactin and crop sac development in incubating ring doves.

Passive immunization of incubating ring doves with daily injections of sheep anti-chicken vasoactive intestinal polypeptide (cVIP) serum prevented the proliferation of crop sac tissue observed in control doves given nonimmune serum. Daily injections of anti-cVIP serum did not prevent crop sac development in nonbreeding doves simultaneously treated with ovine prolactin. The concentrations of plasma prolactin were significantly depressed in birds given anti-cVIP serum although this effect became progressively less pronounced during the course of the 7- or 14-day treatment periods. Body weights and weights of regressed reproductive organs were unaffected by treatment with anti-cVIP serum and did not differ significantly from control birds. Doves showing a decreased prolactin response to anti-cVIP serum treatment developed an immune response to sheep serum which may have immunoneutralized the administered antibody. Concentrations of plasma LH were not consistently affected by anti-cVIP serum administration and were low throughout the study. The depression in plasma LH normally seen in females after their young hatch was not observed in females treated with anti-cVIP serum. No effect of treatment was observed upon the birds' incubation behavior or in their readiness to feed and brood their young. These results suggest that in the ring dove, VIP is the physiological prolactin-releasing factor responsible for stimulating prolactin secretion and consequently the development of the crop sac, during incubation. They further indicate that increased concentrations of plasma prolactin may not be essential for gonadal regression or the maintenance of full incubation and brooding behavior in ring doves under laboratory conditions.

Evidence for the involvement of dopamine and 5-hydroxytryptamine in the regulation of the preovulatory release of luteinizing hormone in the domestic hen.

Injections of the dopamine (DA) precursor L-dopa and the 5-hydroxytryptamine (5-HT) precursor 5-hydroxytryptophan, beginning 6 hr before the predicted preovulatory release of LH, abolished the LH surge and blocked ovulation. The inhibitory effect of the drugs on the preovulatory release of LH was not reversed by injection of progesterone. This showed that the drugs inhibited LH release by acting on the central nervous system rather than peripherally, by inhibiting the release of progesterone from the ovary. The turnover rates of DA and 5-HT were estimated during the ovulatory cycle in the median eminence, the posterior hypothalamus, and the anterior hypothalamus. The turnover rates of the two monoamines were estimated from their rates of accumulation after inhibiting their catabolism with the monoamine oxidase inhibitor pargyline. Turnover of DA and 5-HT in the median eminence was depressed during the preovulatory release of LH and decrease in the anterior hypothalamus when preovulatory LH levels were increasing. Observations were also made of changes in the concentrations of hypothalamic DA, 5-HT, noradrenaline (NA), and adrenaline (A) during the ovulatory cycle. Concentrations of DA, 5-HT, and NA increased in the anterior hypothalamus and decreased in the posterior hypothalamus during the 4 hr before the peak of the preovulatory release of LH. These results strengthen the view that hypothalamic DA and 5-HT play a role in the regulation of the preovulatory release of LH by a reduction in inhibitory inputs on LHRH neurones.

Absence of an effect of naloxone, an opioid antagonist, on luteinizing hormone release in vivo and luteinizing hormone-releasing hormone I release in vitro in intact, castrated, and food restricted cockerels.

The possibility that the tonic secretion of luteinizing hormone (LH) and chicken luteinizing hormone-releasing hormone I (LHRH-I) is regulated by an inhibitory action of endogenous opioid peptides was investigated in cockerels using the opiate receptor antagonist, naloxone. Baseline concentrations of plasma LH in the experimental cockerels were increased by surgical castration or reduced by limiting food intake. Baseline and K(+)-induced releases of LHRH-I from perifused mediobasal-preoptic hypothalami from castrated cockerels were higher than those from hypothalami from intact cockerels. Similarly, baseline and K(+)-induced releases of LHRH-I from perifused mediobasal hypothalami from fully fed cockerels were higher than those from the hypothalami from fasting cockerels. Intravenous injections of 0.1, 1, or 10 mg naloxone/kg body weight failed to increase the concentration of plasma LH in castrated, intact, fully fed, or fasted cockerels. Perifusion of mediobasal-preoptic hypothalami from castrated or intact cockerels with 200 microM naloxone or mediobasal hypothalami from fully fed or fasted cockerels with 10 microM naloxone failed to stimulate the release of LHRH-I. These observations suggest in the cockerel that endogenous opioid peptides may not play an obligatory role in the inhibitory control of the tonic secretion of luteinizing hormone.