Biomedical subjects

A J Douglas

Publications and source records attributed to A J Douglas.

At least 19 recordsLinked to original sources

PubMed2006

Effects of alpha-melanocyte-stimulating hormone on magnocellular oxytocin neurones and their activation at intromission in male rats.

The peptides alpha-melanocyte-stimulating hormone (alpha-MSH) and oxytocin have very similar effects on several behaviours, including male sexual behaviour. Both induce penile erection and enhance copulatory behaviour when given centrally, suggesting that their central actions are not independent. Here, we used intromission as a physiological stimulus to investigate whether some central effects of alpha-MSH during male sexual behaviour are mediated by oxytocin neurones. We used the expression of the immediate-early gene product Fos to investigate oxytocin neurone activation at intromission and after intracerebroventricular (i.c.v.) administration of alpha-MSH (1 microg/5 microl) and studied the effects of i.c.v. administration of a MC4 receptor antagonist on Fos expression and on the latency of male rats to exhibit sexual behaviour in the presence of a receptive female. In rats that showed intromission, Fos was expressed in magnocellular oxytocin neurones in both the paraventricular nucleus (PVN) and the supraoptic nucleus (SON), but there was no significant activation of parvocellular oxytocin neurones of the PVN. Similarly, alpha-MSH increased Fos expression in magnocellular oxytocin neurones but had little or no effect in parvocellular oxytocin neurones. In male rats that achieved intromission, central injection of a MC4 receptor antagonist significantly attenuated the increase in Fos expression in magnocellular oxytocin neurones in both the PVN and the SON and increased mount and intromission latencies compared to vehicle-injected controls. Together, the results indicate that magnocellular oxytocin neurones are involved in the central regulation of male sexual behaviour, and that some of the central effects of alpha-MSH are likely to be mediated by magnocellular oxytocin neurones.

Animals↗

PubMed2005

Reduced activity of the noradrenergic system in the paraventricular nucleus at the end of pregnancy: implications for stress hyporesponsiveness.

We investigated whether changes in noradrenaline neurotransmission in the hypothalamus could explain the hyporesponsiveness of the hypothalamic-pituitary-adrenal (HPA) axis in late pregnancy. Noradrenaline release within the hypothalamic paraventricular nucleus in response to swim stress, as estimated by microdialysis and high-performance liquid chromatography, was lower in 20-day pregnant rats compared to virgin rats. Driving a central noradrenergic pathway using intravenous cholecystokinin increased adrenocorticotropic hormone (ACTH) secretion in virgin rats, but the response was significantly less in 16-day and 20-day pregnant rats. Thus, the activity of noradrenergic inputs to the paraventricular nucleus and the HPA axis is attenuated in late pregnancy. The sensitivity of the HPA axis to noradrenaline in pregnancy was investigated by intracerebroventricular administration of an alpha1-receptor antagonist, benoxathian, before and during exposure to swim stress. In virgin rats, benoxathian increased basal and stress-induced ACTH secretion, but in late pregnant rats the benoxathian effects were attenuated, indicating reduced sensitivity of the HPA axis to noradrenaline neurotransmission and/or the inability of the system to become disinhibited at this time. alpha1A-adrenoreceptor mRNA expression in the parvocellular and magnocellular paraventricular nucleus, measured by in situ hybridisation, was decreased in late pregnant compared to virgin rats. Additionally, blocking endogenous opioid inhibition with naloxone pretreatment restored the ACTH secretory response to cholecystokinin in pregnant rats. Thus, in late pregnancy, there is reduced noradrenergic input to the paraventricular nucleus and reduced alpha1A-receptor expression in the paraventricular nucleus, both of which may contribute to the reduced responsiveness of the HPA axis in pregnancy.

Adrenergic alpha-Antagonists↗

PubMed2003

No stress response of the hypothalamo-pituitary-adrenal axis in parturient rats: lack of involvement of brain oxytocin.

During parturition, the basal activity of the hypothalamo-pituitary-adrenal (HPA) axis of Wistar rats is strongly attenuated, whereas the oxytocin system is activated. We investigated the secretory responses of the HPA axis and oxytocin to exposure to a mild emotional stressor (airpuff) comparing virgin female, d 22 pregnant, and parturient rats. Furthermore, as the brain oxytocin system is activated in parturition and oxytocin has been shown to inhibit HPA axis responses in virgin rats, the role of brain oxytocin in the regulation of stress responses during parturition was investigated by intracerebroventricular administration of an oxytocin receptor antagonist before stressor exposure (0.75 micro g/5 micro l). In virgin female rats, exposure to airpuff increased ACTH (2.5 +/- 0.34-fold) and corticosterone (5.1 +/- 2.3-fold) secretion, but in late pregnancy and parturition, the stress-induced increase in ACTH (pregnancy: 1.9 +/- 0.41-fold; parturition: 1.3 +/- 0.13-fold) and corticosterone secretion (parturition: 1.8 +/- 0.40-fold) were strongly attenuated. Oxytocin secretion remained unchanged in response to airpuff in both virgin and parturient rats despite higher overall plasma concentrations in the latter. Oxytocin receptor blockade in the brain elevated basal and stress-induced ACTH secretion in virgin but not pregnant or parturient rats and had no effect on oxytocin secretion either in virgin or parturient rats. We conclude that the reactivity of the HPA axis to external stressors is strongly attenuated during parturition, and this cannot be disinhibited by blocking the receptor-mediated action of brain oxytocin.

Adrenocorticotropic Hormone↗

PubMed2002

Beta-endorphin cells in the arcuate nucleus: projections to the supraoptic nucleus and changes in expression during pregnancy and parturition.

Supraoptic nucleus oxytocin neurone activity and secretion are inhibited in late pregnancy and parturition by endogenous opioids. Here, we investigated alterations in the projections and gene expression of beta-endorphin/pro-opiomelanocortin neurones in the arcuate nucleus in the pregnant rat. All regions of the arcuate nucleus were found to contain cells immunoreactive for beta-endorphin fluorescent microbeads retrogradely transported from the supraoptic nucleus, and double-labelled neurones (beta-endorphin plus microbeads), showing that beta-endorphin neurones throughout the arcuate nucleus project to the supraoptic nucleus. There was an increase in the number of beta-endorphin-immunoreactive cells in the arcuate nucleus and an increase in the density of beta-endorphin fibres within the supraoptic nucleus and peri-supraoptic region in late pregnancy and parturition, suggesting enhanced expression of beta-endorphin and increased beta-endorphin innervation of the supraoptic nucleus. Pro-opiomelanocortin mRNA expression in the arcuate nucleus increased in late compared to early pregnancy: the number of positive neurones significantly increased in the caudal region. Fos expression (an indicator of neuronal activation) in the arcuate nucleus was colocalized in beta-endorphin neurones in both proestrus and parturient rats, but the number of positive cells did not increase during parturition, suggesting lack of activation of beta-endorphin neurones at birth. Thus, beta-endorphin cells in the arcuate nucleus project to the supraoptic nucleus and increased innervation during pregnancy may explain the enhanced endogenous opioid inhibition of oxytocin neurones.

Animals↗

PubMed2002

The importance of oxytocin mechanisms in the control of mouse parturition.

The role of oxytocin in parturition in mice was investigated. Pup birth profiles, blood samples and brains were collected from parturient mice observed under red light conditions in a reversed light:dark photoperiod. Peripheral administration of an oxytocin antagonist in a dose-dependent manner delayed the birth of subsequent pups, indicating that oxytocin is required for a normal pup birth profile. Oxytocin neurones were activated during birth as shown by both increased immediate early gene ( Fos) expression in oxytocin neurones in the supraoptic nucleus and increased plasma oxytocin concentrations during birth. In addition, the nucleus of the tractus solitarius and the olfactory bulbs, sites that process inputs to oxytocin neurones, become activated during parturition. Exposure to stress during parturition halted subsequent deliveries; at this stage plasma oxytocin concentrations were not higher than those of virgin mice, and birth was restored by administration of oxytocin. Administration of beta-adrenergic antagonist (propranolol) also restored stress-delayed birth, whereas administration of ritrodrine (beta-agonist) delayed birth in non-stressed mice, indicating that adrenergic mechanisms contribute to stress-delayed births in mice. Administration of morphine (mu-opioid agonist) delayed births transiently, but naloxone (opioid antagonist) did not prevent stress-delayed birth, indicating that endogenous opioids do not appear to contribute to neuroendocrine or uterine mechanisms that promote birth in mice. Therefore, despite evidence in oxytocin knockout mice that oxytocin is not essential for parturition in this species, the results of the present study indicate that oxytocin neurone activity and secretion contribute to the birth process in normal mice.

Adrenergic beta-Agonists↗

PubMed2001

Brain preparations for maternity--adaptive changes in behavioral and neuroendocrine systems during pregnancy and lactation. An overview.

Pregnancy, parturition and lactation comprise a continuum of adaptive changes necessary for the development and maintenance of the offspring. The endocrine changes that are driven by the conceptus and are essential for the maintenance of pregnancy and are involved in the preparations for motherhood are outlined. These changes include large increases in the secretion of sex steroid hormones, and the secretion of peptide hormones that are unique to pregnancy. The ability of these pregnancy hormones to alter several aspects of brain function in pregnancy is considered, and the adaptive importance of some of these changes is discussed, for example in metabolic and body fluid adjustments, and the induction of maternal behavior. The importance of sex steroids in determining the timing of the various adaptive changes in preparing for parturition and maternal behavior is emphasized, and the concept that the actions of prolactin and oxytocin, quintessential mammalian motherhood neuropeptides, can serve to coordinate a spectrum of adaptive changes is discussed. The part played by oxytocin neurons and their regulatory mechanisms is reviewed to illustrate how neural systems involved in maternity are prepared in pregnancy via changes in phenotype, synaptic organization and in the relative importance of their different inputs, to function optimally when needed. For oxytocin neurons secreting from the posterior pituitary, important in parturition and essential in lactation, these changes include mechanisms to restrain their premature activation, and adaptations to support synchronized burst firing for pulsatile oxytocin secretion in response to stimulation via afferents from the birth canal, olfactory system or suckled nipples. Within the brain, expression of oxytocin receptors permits centrally released oxytocin to facilitate the expression of maternal behavior. Changes in other neuroendocrine systems are similarly extensive, leading to lactation, suppression of ovulation, reduced stress responses and increased appetite; these changes in lactation are driven by the suckling stimulus. The possible link between these adaptations and changes in cognition and mood in pregnancy and post partum are considered, as well as the dysfunctions that lead to common problems of depression and puerperal psychoses.

Adaptation, Physiological↗

PubMed2001

Endogenous opioid regulation of oxytocin and ACTH secretion during pregnancy and parturition.

Progress of parturition in the rat is optimal when there is increased oxytocin secretion, thus ensuring quick birth and otherwise risking adverse neonatal health. To ensure that the mechanisms for this are available, oxytocin neurons adapt in pregnancy and this includes development of a tonic inhibition by endogenous opioids. Endogenous opioid inhibition of oxytocin secretion increases in pregnancy, initially acting on the nerve terminals in the posterior pituitary and later on oxytocin cell bodies and their inputs. This inhibition enhances stores of oxytocin and enables restraint of oxytocin neuron responsiveness to selected excitatory inputs. The hypothalamic neurons which mediate stress also adapt in late pregnancy so that hypothalamo-pituitary-adrenal axis and oxytocin secretory responses to stressor exposure are attenuated. This is also partly due to endogenous opioid inhibition. Thus, in pregnancy oxytocin and hypothalamo-pituitary-adrenal axis secretion in response to stimulation is restrained, protecting the unborn fetus(es) from premature delivery and glucocorticoid exposure and preparing the oxytocin neurons for their important secretory role during parturition. In parturition itself, endogenous opioids continue to inhibit these neurons. Stress exposure during parturition delays births, probably due to endogenous opioid inhibition of pulsatile oxytocin secretion. On the other hand, basal ACTH and corticosterone secretion are reduced in parturition through inhibition by endogenous opioids. So, opioids continue to regulate the activity of oxytocin and hypothalamo-pituitary-adrenal mechanisms in labor; inhibition of oxytocin neurons at this time may control the spacing of pup births.

Adrenocorticotropic Hormone↗

PubMed2001

The N-terminal region of the VP1 protein of swine vesicular disease virus contains a neutralization site that arises upon cell attachment and is involved in viral entry.

The N-terminal region of VP1 of swine vesicular disease virus (SVDV) is highly antigenic in swine, despite its internal location in the capsid. Here we show that antibodies to this region can block infection and that allowing the virus to attach to cells increases this blockage significantly. The results indicate that upon binding to the cell, SVDV capsid undergoes a conformational change that is temperature independent and that exposes the N terminus of VP1. This process makes this region accessible to antibodies which block virus entry.

Amino Acid Sequence↗

PubMed2000

Single amino acid differences are sufficient for CD4(+) T-cell recognition of a heterologous virus by cattle persistently infected with bovine viral diarrhea virus.

Cattle that are persistently infected (PI) with one strain of bovine viral diarrhea virus (BVDV) can resolve infection with a second, antigenically heterologous strain but not the homologous strain. Since CD4(+) T cells are thought to be critical for the resolution of acute BVDV infection (Howard et al., 1992, Vet. Immunol. Immunopathol. 32, 303-314), we have examined the recognition of a heterologous virus (NADL) by CD4(+) T cells from Pe515-PI animals. The immune response of non-PI control cattle challenged with NADL or Pe515ncp was strain cross-reactive, whereas Pe515-PI animals responded to NADL only. The immune repertoire of both groups included NS3, which differs by approximately 1% (9/683) amino acids between these two viruses. Lymphoproliferative responses to proteins and synthetic peptides corresponding to three nonconservative differences in NS3 demonstrated that CD4(+) T cells from non-PI control animals responded well to proteins but poorly to the peptides from both viruses. In contrast, PI animals were responsive to heterologous proteins and peptides but nonresponsive to the homologous equivalents. A single amino acid difference between the two sequences was sufficient to allow responsiveness.

Amino Acid Sequence↗

PubMed2000

Nitric oxide and the oxytocin system in pregnancy.

We examined the functional role of the nitric oxide (NO)-producing system in magnocellular neurons and how this changes at the end of pregnancy, using a combination of blood sampling and oxytocin radioimmunoassay, electrophysiology, immunocytochemistry for Fos expression, and in situ hybridization histochemistry. In urethane-anesthetized virgin rats, systemic administration of NO synthase (NOS) inhibitors led to a facilitation of oxytocin release evoked by hyperosmotic stimulation. Direct application of the NO donor sodium nitroprusside to the supraoptic nucleus by in vivo microdialysis inhibited the electrical activity of both oxytocin neurons and vasopressin neurons, whereas direct application of an NOS inhibitor increased electrical activity, indicating that endogenous NO acts within the supraoptic nucleus to inhibit neuronal activity. However, during late pregnancy, the influence of endogenous NO is dramatically downregulated, reflected by a reduced expression of neuronal NOS mRNA in these neurons and a loss of efficacy of NOS inhibitors on stimulus-evoked oxytocin release. This downregulation may cause the oxytocin system to become more excitable at term, resulting in the capacity for greater release of oxytocin during parturition.

Animals↗

PubMed2000

Sex-steroid induction of endogenous opioid inhibition on oxytocin secretory responses to stress.

In pregnancy, endogenous opioids inhibit enhanced basal and stressor-stimulated oxytocin neurone activity and secretion. By contrast, stress responses of the hypothalamo-pituitary-adrenal (HPA) axis are reduced in pregnancy. We investigated whether the high levels of oestradiol and progesterone of pregnancy could induce these changes. Silastic capsules containing oestradiol or progesterone (or control capsules) were implanted s.c. in virgin female rats for 16 or 17 days, with or without progesterone removal on day 15 to mimic the progesterone withdrawal seen at the end of pregnancy. Plasma concentrations of oxytocin, adrenocorticotrophic hormone (ACTH) and corticosterone were measured in jugular vein blood samples from conscious rats. Under basal conditions, naloxone (5 mg/kg) increased oxytocin secretion in all groups, but had no greater effect in sex-steroid treated rats, and did not induce Fos expression in the supraoptic nucleus. Forced swimming, a stressor, increased oxytocin secretion at 5 min in vehicle-injected controls, and this response was slightly attenuated in the sex-steroid treated groups. Pretreatment with naloxone greatly enhanced the response in the sex-steroid treated rats, and was less effective in the controls. In rats treated with oestradiol alone, naloxone prolonged the response. Thus, the combined sex-steroid treatment enhanced the responsiveness of oxytocin neurones to the stressor, while simultaneously restraining oxytocin secretion via endogenous opioid inhibition. In the same rats, ACTH and corticosterone secretion was also stimulated by the stressor, but the hypothalamo-pituitary-adrenal (HPA) axis response was not attenuated in sex-steroid treated rats. Naloxone weakly reduced the HPA axis response in controls and was ineffective in the sex-steroid treated rats. We conclude that oestradiol and progesterone may be responsible for inducing the opioid restraint and enhanced oxytocin neurone responsiveness in pregnancy.

Animals↗

PubMed2000

Attenuation of hypothalamic-pituitary-adrenal axis stress responses in late pregnancy: changes in feedforward and feedback mechanisms.

The hypothalamic-pituitary-adrenal axis is hyporesponsive to stress in late pregnancy, exemplified as reduced adrenocorticotropic hormone (ACTH) and corticosterone responses to restraint, but the mechanisms are unknown. We investigated forward drive and negative feedback upon the hypothalamic-pituitary-adrenal axis in pregnant rats. Corticotropin-releasing hormone (CRH) and vasopressin mRNA expression in the parvocellular paraventricular nucleus and mineralocorticoid and glucocorticoid receptor expression in the paraventricular nucleus and hippocampus were quantified with in situ hybridization. Because it can enhance the corticosterone negative feedback signal, 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) bioactivity in these brain regions and anterior pituitary was measured in vitro, and ACTH and corticosterone stress responses were measured after intracerebroventricular glycyrrhetinic acid, an 11beta-HSD inhibitor. Changes in corticosterone feedback on ACTH secretion were examined after pharmacological adrenalectomy by metyrapone and aminoglutethimide. Parvocellular paraventricular nucleus CRH mRNA content was reduced on day 21 and the CRH mRNA : vasopressin mRNA ratio was unaltered, indicating decreased production of both CRH and vasopressin. An increase in glucocorticoid receptor mRNA expression in the dentate gyrus (mineralocorticoid receptor mRNA expression was unaltered) and increased 11beta-HSD1 activity in the paraventricular nucleus and anterior pituitary suggest an increase in slow negative feedback mechanisms in pregnancy, but glycyrrhetinic acid did not modify the stress response. After metyrapone/aminoglutethimide treatment, corticosterone decreased ACTH secretion more slowly in pregnancy, indicating a decrease in rapid feedback sensitivity. Thus, reduced forward drive rather than increased effectiveness of glucocorticoid negative feedback may underlie stress hyporesponsiveness of the hypothalamic-pituitary-adrenal axis in pregnancy.

11-beta-Hydroxysteroid Dehydrogenase Type 1↗

PubMed2000

Quo vadis neurohypophysial hormone research?

Here we highlight just a few of the outstanding questions in the field of neurohypophysial hormones that we envisage will be addressed successfully in the new millennium. To begin, we focus on the regulation of receptors. Despite intensive investigation with new drugs, molecular modelling and transgenic models, the determinants of receptor selectivity remain elusive; there may even be more vasopressin or oxytocin receptor subtypes to be discovered. We discuss the controversy over the interesting studies that indicate modulation of oxytocin receptor-binding by steroids. Oxytocin and vasopressin release and action in the brain are discussed from several aspects. Dendritically released oxytocin acting locally is important for the milk ejection reflex, and similarly released vasopressin is important in regulating patterning of vasopressin neurone activity. Such dendritically released oxytocin and vasopressin is likely to be important in paracrine modulation of neural circuitry involved in neuroendocrine control, and for a range of behaviours. Is it possible that the whole range of behaviours that comprise 'social' (or 'anti-social') or 'maternal' behaviour can be engineered by modifying the expression of just these one or two peptides and their receptors? However, whether gene expression and knockout approaches will answer all the open questions about the real functions of oxytocin and vasopressin remains to be shown.

Animals↗

PubMed2000

Effect of progesterone on the activation of neurones of the supraoptic nucleus during parturition.

Parturition is driven by a pulsatile pattern of oxytocin secretion, resulting from burst firing activity of supraoptic oxytocin neurones and reflected by induction of Fos expression. Rats were injected with progesterone on day 20 of pregnancy to investigate the role of the decreasing progesterone:ratio oestrogen ratio, which precedes delivery, in the activation of supraoptic neurones. Progesterone delayed the onset of birth by 28 h compared with vehicle (control) and prolonged the duration of delivery, which was overcome by pulsatile injections of oxytocin, indicating that the slow delivery may reflect impaired oxytocin secretion. Parturient rats pretreated with progesterone had fewer Fos immunoreactive nuclei in the supraoptic nucleus than did parturient rats pretreated with vehicle. The number of Fos immunoreactive nuclei was not restored after oxytocin injection, indicating that appropriate activation of oxytocin neurones is impaired by progesterone and also that there is a lack of stimulatory afferent drive. Fos expression increased in the nucleus of the tractus solitarius during parturition in rats pretreated with either vehicle or progesterone, but not in rats that had been pretreated with progesterone and induced with oxytocin, indicating that this input was inhibited. Endogenous opioids inhibit oxytocin neurones in late pregnancy and the opioid antagonist, naloxone, increases Fos expression in supraoptic nuclei by preventing inhibition. However, progesterone attenuated naloxone-induced Fos expression in the supraoptic nucleus in late pregnancy and naloxone administered during parturition did not accelerate the duration of births delayed by progesterone administration, indicating that progesterone does not act by hyperactivation of endogenous opioid tone. RU486, a progesterone receptor antagonist, enhanced supraoptic neurone Fos expression in late pregnancy, indicating progesterone receptor-mediated actions. Thus, progesterone withdrawal is necessary for appropriate activation of supraoptic and tractus solitarius neurones during parturition.

Analysis of Variance↗

PubMed1999

Discrimination of granulocyte colony-stimulating factor isoforms by high-performance capillary electrophoresis.

Granulocyte colony-stimulating factor (G-CSF) is a glycoprotein which acts primarily to stimulate the proliferation, differentiation and activation of committed progenitor cells of the neutrophil-granulocyte lineage into functionally mature neutrophils. The traditional biological assays employed to detect G-CSF are a myeloid bone marrow colony assay, a factor-dependent cell line specific for G-CSF and commercially available immunoassays. However, these methods will not distinguish between glycosylated and non-glycosylated forms of the molecule. In this study high-performance capillary electrophoresis (HPCE) was used to analyse glycosylated and non-glycosylated recombinant human granulocyte colony-stimulating factor (r-met-hG-CSF). Glycosylated G-CSF preparations contained human serum albumin (HSA), added as a protein carrier. Glycosylated and non-glycosylated G-CSFs were prepared in 40 mM Na2HPO4 buffer, pH 2.5, containing hydroxypropylmethylcellulose (HPMC) or 50 mM Na2HPO4 buffer, pH 9.0. Glycosylated G-CSF could be separated into two distinct glycoform populations at the lower pH studied. Differences in migration time and peak shape between glycosylated and non-glycosylated G-CSF were demonstrated. HPCE analysis of G-CSF produced using a baculovirus expression vector system revealed a further distinct G-CSF glycoform and demonstrated the resolving power of the technique.

Electrophoresis, Capillary↗

PubMed1998

Attenuated neuroendocrine responses to emotional and physical stressors in pregnant rats involve adenohypophysial changes.

1. The responsiveness of the rat hypothalamo-pituitary-adrenal (HPA) axis and hypothalamo-neurohypophysial system (HNS) to emotional (elevated plus-maze) and physical (forced swimming) stressors and to administration of synthetic corticotrophin-releasing hormone (CRH) was investigated during pregnancy and lactation. In addition to pregnancy-related adaptations at the adenohypophysial level, behavioural responses accompanying the neuroendocrine changes were studied. 2. Whereas basal (a.m.) plasma corticosterone, but not corticotrophin (adrenocorticotrophic hormone; ACTH), levels were increased on the last day (i.e. on day 22) of pregnancy, the stress-induced rise in both plasma hormone concentrations was increasingly attenuated with the progression of pregnancy beginning on day 15 and reaching a minimum on day 21 compared with virgin control rats. A similar attenuation of responses to both emotional and physical stressors was found in lactating rats. 3. Although the basal plasma oxytocin concentration was elevated in late pregnancy, the stress-induced rise in oxytocin secretion was slightly lower in day 21 pregnant rats. In contrast to vasopressin, oxytocin secretion was increased by forced swimming in virgin and early pregnant rats indicating a differential stress response of these neurohypophysial hormones. 4. The blunted HPA response to stressful stimuli is partly due to alterations at the level of corticotrophs in the adenohypophysis, as ACTH secretion in response to CRH in vivo (40 ng kg-1, i.v.) was reduced with the progression of pregnancy and during lactation. In vitro measurement of cAMP levels in pituitary segments demonstrated reduced basal levels of cAMP and a lower increase after CRH stimulation (10 nM, 10 min) in day 21 pregnant compared with virgin rats, further indicating reduced corticotroph responsiveness to CRH in pregnancy. 5. The reduced pituitary response to CRH in late pregnancy is likely to be a consequence of a reduction in CRH receptor binding as revealed by receptor autoradiography. [125I] CRH binding in the anterior pituitary was significantly reduced in day 11, 17 and 22 pregnant rats compared with virgin controls. 6. Anxiety-related behaviour of the animals as revealed by the time on and entries into the open arms of the elevated plus-maze was different between virgin and pregnant rats with decreased number of entries indicating increased anxiety with the progression of pregnancy (except on pregnancy day 18). The emotional behaviour, however, was not correlated with the neuroendocrine responses. 7. The results indicate that the reduced response of the HPA axis to stressors described previously during lactation is already manifested around day 15 of pregnancy in the rat and involves physiological adaptations at the adenohypophysial level. However, alterations in stressor perception at higher brain levels with the progression of pregnancy may also be involved.

Acclimatization↗

PubMed1998

Stimulation of expression of the oxytocin gene in rat supraoptic neurons at parturition.

We measured expression of the oxytocin gene in the supraoptic nucleus (SON) during pregnancy, parturition and lactation to examine its relationship to states of accumulation or depletion of oxytocin stores and to conditions of strong excitation of oxytocin neurons. The primary transcript (heterogeneous nuclear RNA, hnRNA) of the oxytocin gene was measured using a 3H-cDNA probe against intron 1 for in situ hybridisation. Autoradiographs of the SON showed the hnRNA as discrete clumps of silver grains within the nucleus of each neuron. The number of cells expressing oxytocin hnRNA did not change during pregnancy but increased during parturition; 10-day lactating animals showed similar increases. Oxytocin mRNA was also measured by in situ hybridisation using a 3H- or 35S-labelled oligonucleotide probe against exon C: hybridisation was seen over the cytoplasm of supraoptic neurons, but no differences were measured between virgin, mid-pregnant, preparturient, parturient or 2-day lactating rats. The data suggest that enhanced oxytocin gene transcription is not necessary to increase oxytocin stores in pregnancy. However, acute stimulation of magnocellular oxytocin neurons at parturition, which strongly increases neuron activity and secretion, results in a rapid increase in the number of cells expressing oxytocin hnRNA, and increased expression is sustained in lactation.

Animals↗

PubMed1998

Serological evidence for pneumovirus infections in pigs.

A serological survey was carried out on pig sera from herds in Northern Ireland to investigate the incidence of reactivity to bovine respiratory syncytial virus (BRSV) antigens. A total of 529 pig sera from 61 herds were tested and 219 (41 per cent) were found to be reactive with BRSV-infected cell cultures in an indirect immunofluorescence test. None of the BRSV-reactive sera immunostained turkey rhinotracheitis virus-infected cell cultures, indicating specificity for BRSV epitopes. The specificity of this reactivity for BRSV antigen was confirmed by double immunolabelling, using monoclonal antibodies to BRSV and two pig sera with different reactivities to BRSV antigens. A longitudinal serological investigation of two litters of pigs indicated that BRSV-serum reactivity developed between six and 11 weeks after birth. The immunofluorescent staining pattern observed with the majority (73 per cent) of the BRSV-reactive pig sera was typical of that observed with known BRSV-reactive bovine sera. The other immunoreactive pig sera stained BRSV-infected cell cultures in an atypical staining pattern. These different reactivity patterns, combined with the results of the serum neutralisation tests, suggest that more than one serotype of a porcine pneumovirus may exist.

Animals↗