Biomedical subjects

P J Sharp

Publications and source records attributed to P J Sharp.

At least 91 records · Page 5Linked to original sources

PubMed1994

Aromatase-immunoreactive neurons in the adult female chicken brain detected using a specific antibody.

Estrogen formation in the brain catalysed by the cytochrome P450arom is required for the control of estrogen-dependent neural mechanisms regulating reproductive behaviour. A polyclonal antibody was raised against a 15-amino acid fragment of the chicken ovarian P450arom protein, to localise aromatase-immunoreactive (AR-IR) cells in the adult female chicken brain. Specificity of antibody reaction was established by Western blot and by inhibition of aromatase activity in homogenates of chicken ovarian follicles determined by a radiometric assay. The AR-IR material in the brain was localised in the perikarya and some of their adjacent cytoplasmatic processes. Intense immunoreactivity was observed in the preoptic region as well as in other hypothalamic nuclei. AR-IR cells were also found in extrahypothalamic areas; in particular, in the area entorhinalis and hippocampus. These results confirm histologically that aromatization of testosterone in the adult female chicken brain occurs in preoptic nuclei closely associated with the regulation of reproductive behaviour. The mapping of AR-IR cells in the female chicken brain now allows study of its regulation under different physiological and environmental conditions, and its relation to classic target areas expressing estrogen receptors.

Amino Acid Sequence↗

PubMed1994

Effect of active immunization against recombinant-derived chicken prolactin fusion protein on the onset of broodiness and photoinduced egg laying in bantam hens.

The hypothesis that the onset of incubation behaviour (broodiness) in the domestic hen is induced by an increase in prolactin secretion was investigated by actively immunizing bantam hens against recombinant-derived chicken prolactin. A second objective was to establish whether active immunization against prolactin affects photoinduced onset of egg laying and the rate of egg production. The immunogen was a fusion protein (beta gals-prolactin, 23 kDa) produced in Escherichia coli, comprising chicken prolactin (without the nine amino-terminal amino acids) fused to 18 amino acids of E. coli beta-galactosidase. A control immunogen was produced in the same strain of E. coli harbouring the same plasmid vector used to produce beta gals-prolactin minus the prolactin gene sequence. Hens were immunized i.m. with 1 mg of protein containing 0.8-0.9 mg of fusion protein in Freund's incomplete adjuvant at 4-8 week intervals beginning before or after egg laying, which was induced by increasing the daily photoperiod. The beta gals-prolactin immunogen, but not the control immunogen, stimulated the production of antibodies to chicken prolactin. In Expts 1, 2 and 3, hens were placed in floor pens with nest boxes after photostimulation to induce broodiness. In these experiments, immunization with beta gals-prolactin reduced the incidence or delayed the development of broodiness. This effect was more pronounced if immunization was initiated before, rather than after, the onset of egg laying. In Expts 1 and 2 hens were immunized with beta gals-prolactin before photostimulation. The presence of antibodies to prolactin in their blood did not affect photoinduced onset of egg laying.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1993

Ultrastructure of lipid-containing cells of the anterior pituitary gland of the domestic chicken, Gallus domesticus.

A combination of light and electron microscopy techniques was applied to characterize a luteinizing hormone (LH)-gonadotroph-like cell in the anterior pituitary gland of the adult domestic chicken. This cell type (mean +/- sem, 91 +/- 8 microns2) was larger than typical LH-gonadotrophs (71 +/- 5 microns2, p < 0.01) and seen in pituitary glands from adult males but not those from adult females of the same age. The ultrastructural features of these cells were similar to typical LH-gonadotrophs in the same section, except for the presence of large (1,126 +/- 77 nm diameter), round, or polymorphic electron-dense inclusions (14 +/- 3 per cell) in the cisternae of the endoplasmic reticulum. When resin sections of anterior pituitary gland were stained with the vapours from the fixative osmium tetroxide and a solution of potassium ferricyanide, inclusions were found that appeared to be lipid in nature and were circumscribed by the cisternal membranes of the endoplasmic reticulum. These lipid inclusions were associated occasionally with acid phosphatase and lysosome-like bodies. The cellular pigment, lipofuscin, considered to be a marker of aging, was absent from the anterior pituitary glands from these adult chickens. These observations suggest that the appearance of lipid in LH-gonadotrophs is unlikely to be age-related and an alternative explanation is discussed in relation to a sex difference in the LH response of adult chickens to gonadotrophin-releasing hormone (GnRH).

Acid Phosphatase↗

PubMed1993

Plasma prolactin during the breeding season in adult and immature macaroni (Eudyptes chrysolophus) and gentoo (Pygoscelis papua) penguins.

Plasma prolactin levels were measured in free-living breeding adult and immature (pre-breeding) macaroni (Eudyptes chrysolophus) and gentoo (Pygoscelis papua) penguins at Bird Island, South Georgia (54 degrees S, 38 degrees W). Macaroni and gentoo penguins first breed at 5-6 and 2 years of age, respectively. In adult birds, of both species, prolactin was low (< 1.0 microgram. liter-1) during the courtship period and then increased during early (gentoo) to mid (macaroni) incubation (to 3.9-4.7 and 2.4-3.5 micrograms.liter-1, respectively), remaining elevated until the creche period, by which time continuous nest attendance by the adults had ceased. This pattern is similar to that seen in other altricial species and is consistent with delayed onset of brood patch development and full incubation efficiency, which has been previously reported in penguins. Adult female macaroni penguins showed a marked, but transient, increase in prolactin concentrations within 24 hr of the first egg being laid (from 1.7 to 7.0 micrograms.liter-1), plasma levels decreasing following clutch completion (to prelaying levels) before increasing again during incubation. Elevated plasma prolactin levels occurred in all age classes of immature (nonbreeding) birds in both macaroni (1- to 5 year-olds) and gentoo (1-year-olds) penguins. However, compared to that in adult birds, the increase in prolactin was more transient in immatures, a smaller proportion of immatures had detectable prolactin levels at each stage of the breeding cycle, and, at least in 1- and 2-year-olds, absolute levels of prolactin were lower.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1993

Mate choice and reproductive success in the red-legged partridge (Alectoris rufa).

Behavioral patterns, reproductive success, and concentrations of plasma-luteinizing hormone, testosterone, and estrogen were compared in pairs of red-legged partridges which had either selected their own mates or had been randomly paired. Males in self-selected pairs called more frequently than males in non-self-selected pairs. Females in self-selected pairs but not those in non-self-selected pairs guarded their nests. Females in self-selected pairs had a greater egg production and laid more of their eggs in nests than females in non-self-selected pairs. There was a significant difference between the two groups in the concentration of plasma testosterone in males, which was higher in males from self-selected pairs prior to the onset of egg laying. These results are consistent with the hypothesis that mate choice affects both reproductive parameters and nest defense in monogamous birds.

Animals↗

PubMed1993

Brood size affects behavior, interclutch interval, LH levels, and weight in ring dove (Streptopelia risoria) breeding pairs.

This study examines the effects of experimental manipulation of brood size (one or two squabs) on the behavior, interclutch interval, plasma LH concentrations, and weights of ring dove parents. Twelve dove pairs were observed, sampled, and weighed over a cycle with one and a cycle with two squabs. Before hatch, no parameter showed any difference between pairs which would subsequently have one or have two squabs. After hatch, males and females having one squab fed less, while males showed more perch-, bow-, and nest-cooing over the 2 weeks after hatch. Females also showed more nest-cooing with one squab and a shorter interclutch interval. For both sexes the plasma LH concentrations were higher when rearing a single squab, showed a lesser decrease after hatch, and increased more rapidly. Both sexes also showed a smaller weight loss when rearing a single squab. The results show that the intricate relationships between behavior, physiology, and reproduction in the ring dove are tuned to brood size and emphasize the latter factor as an important and meaningful variable in the doves' reproductive cycle.

Animals↗

PubMed1993

Precocious puberty in tamoxifen-treated cockerels: hypothalamic gonadotrophin-releasing hormone-I and plasma luteinising hormone, prolactin, growth hormone and testosterone.

1. The administration of the anti-oestrogen, tamoxifen (TAM) to juvenile chicks results in precocious puberty. In the present study the effects of TAM administration (1 mg/kg body weight on alternate days from 12 d of age) on testicular function, hypothalamic chicken gonadotropin-releasing hormone (cGn-RH-I), plasma luteinising hormone (LH), growth hormone (GH), prolactin (PRL) and testosterone were studied in juvenile White Leghorn cockerels. 2. The increase in hypothalamic GnRH-I content which occurs during sexual development was advanced in TAM-treated birds, in association with precocious testicular development, an early rise of plasma testosterone content and enhanced comb growth. 3. Plasma LH concentrations behaved similarly and were higher in the TAM-treated than in control birds, during most of the experimental period. Plasma PRL concentration, which is high at hatching, decreased more quickly in TAM-treated than in control birds; plasma GH values were not consistently affected by TAM treatment. 4. Both the growth and the involution of the bursa of Fabricius in the TAM-treated cockerels preceded that in the control chicks. 5. It is concluded that TAM treatment induces precocious puberty in the cockerel by blocking the negative feedback action of aromatised testicular androgens on the hypothalamus.

Animals↗

PubMed1993

Characterization of the chicken preprogonadotrophin-releasing hormone-I gene.

Partial cDNA clones for chicken gonadotrophin-releasing hormone (GnRH)-I were isolated by reverse transcription-polymerase chain reaction using total RNA from the hypothalami of domestic chickens. Primers for amplification were based on the nucleotide sequence of the mammalian GnRH genes. These amplified clones were used to screen a genomic library from which a series of overlapping clones was isolated. A 6.3 kb EcoRI fragment containing all the exons and 3.0 kb of the 5' upstream region was sequenced. The exon-intron structure of the gene was found to be of a similar configuration to those of the mammalian and osteichthyes GnRH genes analysed so far. Individual domains of the predicted prepropeptide are similar to those of mammalian GnRH prepropeptides, comprising a 23 amino acid signal peptide, the decapeptide hormone and a Gly-Lys-Arg cleavage site, followed by a 56 amino acid GnRH-associated peptide. The nucleotide sequence coding for the decapeptide hormone translates into the amino sequence for chicken GnRH-I. The prepropeptide has approximately 50% identity with mammalian prepropeptides and 25% identity with the teleost prepropeptides.

Amino Acid Sequence↗

PubMed1993

Photoperiodic control of reproduction in the domestic hen.

Egg laying in domestic hens exposed to natural lighting begins shortly after the winter solstice, peaks in early spring, begins to decrease before the fall equinox, and is at its lowest during the late fall and early winter. The seasonal cycle of egg production phase-leads that of the changes in day length. This seeming anomaly can be explained if it is accepted that 1) short days are photoperiodically neutral and do not actively inhibit gonadotropin-releasing hormone (GnRH)-I neurons; and 2) long days are photoperiodically active, transducing both stimulatory and inhibitory inputs to GnRH-I neurons. The development of a long day-induced inhibitory input results in a form of photorefractoriness. Around the winter solstice, photorefractoriness is dissipated by prolonged exposure to short days, allowing GnRH-I neurons to express a photoperiodic-independent, genotype-dependent, level of activity. This is sufficient to stimulate egg laying before the minimum photoperiod for photoinduced gonadotropin release is reached in early spring. When day length begins to decrease after the summer solstice, the photoinduced stimulatory input to GnRH-I neurons is reduced, unmasking the photoinduced inhibitory input. As a consequence, the activity of GnRH-I neurons decreases rapidly and the intensity of egg laying decreases. The minimum and maximum day lengths required to stimulate reproductive function in short-day hens, calculated from the photoperiodic response curves (PRC) for luteinizing hormone release are about 10 and 13 h, respectively, depending on genotype.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

Neuroendocrine control of reduced persistence of egg-laying in domestic hens: evidence for the development of photorefractoriness.

Egg-laying in hens exposed for more than 11 months to photostimulatory daylengths was intermittent and associated with a reduction in numbers of yellow-yolky ovarian follicles. Old laying hens (105 weeks) had lower concentrations of luteinizing hormone (LH) in the pituitary gland and plasma and reduced pituitary gland responsiveness to chicken LH-releasing-hormones (LHRH-I and II) in vivo when compared with young laying hens (28 weeks). Four weeks after transfer from 14 to 8 h light/day, egg production almost stopped in old, but not in young hens, although plasma LH concentrations decreased in all birds. After transfer from 14 to 20 h light/day, plasma LH increased in young, but not in old, hens, without a change in the rate of egg production. Reproductive function was enhanced in old hens returned to long days after induction of a moult and ovarian regression by reducing daylength and dietary restriction. Moulted hens had a greater rate of egg production, higher concentrations of plasma LH and a greater pituitary-gland responsiveness to LHRH-II in vivo than unmoulted control hens. After transfer from 14 to 8 h light/day, egg-laying decreased more rapidly in unmoulted than in moulted hens; transfer to 17 h light/day increased egg production in moulted, but not in unmoulted, birds. Induction of ovarian regression in old hens by dietary restriction alone also enhanced reproductive function after the dietary restriction was relaxed. Egg-laying was more persistent in hens brought into lay for a second year by transferring them from 3 to 11 h light/day than in hens transferred from 3 to 20 h light/day. Egg production was stimulated in hens maintained on 3 or 11 h light/day for 42 weeks, after transfer to 20 h light/day. Egg production ceased in hens maintained on 20 h light/day for 46 weeks, after transfer to 3 h light/day. These observations are consistent with the view that poor persistence of laying in hens less than 2 years old and exposed continuously to long days is caused, in part, by a reduction in hypothalamic-gonadotroph function. This reduction in neuroendocrine function may be due, in part, to the development of relative photorefractoriness.

Aging↗

PubMed1992

The effect of photoperiodic history on egg laying in dwarf broiler hens.

An experiment was conducted in dwarf broiler breeders to determine whether the decrease in egg production towards the end of a laying year is due to the development of photorefractoriness or to age per se. The birds were reared on short days (8 h light/day) and subjected to dietary restriction to prevent BW exceeding the minimum required to support egg production. They were transferred at 22 wk of age to long days (20 h light/day) while controls were maintained on short days for a further 2, 14, or 30 wk. At the end of these periods, dietary restriction was relaxed to stimulate egg production, and the control short-day birds were transferred to long days. The number of days to the onset of egg laying after lifting dietary restriction was less in short-day controls than in hens exposed to long days for 14 wk [19.5 +/- .5 (SE) versus 24.0 +/- 1.1 days, P < .01] or 30 wk (26.4 +/- 1.3 versus 41.2 +/- 1.1 days, P < .001). The number of eggs laid during the 12 wk after first oviposition in hens exposed to long days for 2, 14, or 30 wk before relaxing dietary restriction was not significantly different from that of the short-day controls. The numbers of eggs laid during the 12 wk after first oviposition decreased (P < .001) as the hens became older irrespective of photoperiodic history. These observations indicate that in dwarf broiler breeders, photoperiodic history, and therefore the development of photorefractoriness, is less important than age per se in maintaining intensity of egg laying in the 1st laying yr.

Aging↗

PubMed1991

Effects of presence of squabs upon plasma concentrations of prolactin and LH and length of time of incubation in ringdoves on "extended" incubatory patterns.

The effects of a brief exposure to newly hatched squabs upon the concentrations of plasma prolactin and LH secretion and length of incubation time in ring doves were investigated using a novel experimental procedure. After 5 days of incubation birds were deprived of their nests for 3 days. On return to their nests, the birds immediately resumed incubation and laid a second clutch of eggs after 5 days at which time the first clutch was removed. A consequence of this procedure was that at the time of hatching, concentrations of plasma prolactin had passed their peaks and were falling to baseline values, while concentrations of plasma LH were beginning to increase. This experimental manipulation made it possible to demonstrate that brief exposure to newly hatched squabs significantly affects the concentration of plasma prolactin, an effect which was more pronounced in females than in males. This increased secretion of prolactin was associated with a reduction of plasma LH which reached significance in females but not in males. Birds exposed to squabs spent a significantly longer period of time on their nests as compared to those birds not exposed to squabs. This observation is consistent with a role for prolactin in maintaining readiness to incubate.

Animals↗

PubMed1991

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.

Animals↗

PubMed1991

Purified glutathione S-transferases from parasites as candidate protective antigens.

Glutathione S-transferase (GST) activity was detected in larvae of the Australian sheep blowfly Lucilia cuprina, and in the nematode Haemonchus contortus. A specific inhibitor of the enzyme was shown to affect survival of both species of parasite in vitro. GST from both parasites has been purified and partially characterized. Antisera raised to the purified enzymes were shown to inhibit the enzyme activity in vitro. However, the antisera had no effect on the survival of either parasite.

Amino Acid Sequence↗

PubMed1991

Plasma concentrations of luteinising hormone and body weights during somatic maturation in intact and castrated Australorp cockerels from a line of hens selected for increased ovulation rate.

1. Plasma concentrations of luteinising hormone (LH), comb size and body weight were measured between 46 and 208 d of age in intact and castrated cockerels from lines of selected and control Australorp domestic chickens. The selected line had been selected for increased rate of lay by reducing oviposition intervals within sequences. The cockerels were reared and maintained on 15.25 h light/d. 2. Concentrations of plasma LH in the intact control cockerels were low in the 'immature' phase (less than 100 d old) and increased during the 'mature' phase (older than 175 d) with a peak occurring when the testes are beginning to grow at the onset of the 'mature' phase. In comparison with the control line of cockerels, the selected line had significantly higher plasma LH concentrations at the onset of the 'mature' phase. Selection had no effect on the mean concentration of plasma LH in either the immature phase or a few weeks after the onset of the mature phase. 3. There was no effect of selection in sibling females for higher rates of lay on changes in comb size or body weight during sexual maturation in the intact cockerels. 4. Castration at 45-46 d of age resulted in increased plasma LH concentrations and no comb growth. Plasma LH concentration increased progressively between 40-208 d. There was no difference between the two lines of cockerels in plasma LH concentration or rate of body growth after castration. 5. It is concluded that selection of females for a change in the rate of egg production has resulted in increased plasma LH concentrations in sibling males around the onset of sexual maturation. Selection appears to have caused this effect by altering an unidentified component of the inhibitory feedback mechanism which controls the tonic secretion of LH.

Animals↗

PubMed1991

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.

Animals↗

PubMed1990

Chromatography and generation of specific antisera to synthetic peptides from a protective Boophilus microplus antigen.

Four oligopeptides corresponding to predicted antigenic regions of the protective Bm86 glycoprotein of the cattle tick Boophilus microplus were synthesized and purified. Three were conjugated to carrier proteins and antisera raised in rabbits and cows. All elicited antipeptide antibodies that recognized Bm86 and recombinant derived products in Western blots; however, only one produced antiserum capable of recognizing native Bm86 in an indirect immunofluorescence assay. Ticks fed in vitro on this antiserum showed no obvious gut damage.

Amino Acid Sequence↗

PubMed1990

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.

Animals↗