Peripubertal GnRH and testosterone co-treatment leads to increased familiarity preferences in male sheep.

Chronic gonadotropin-releasing hormone agonist (GnRHa) treatment is effective for the medical suppression of the hypothalamic-pituitary-gonadal axis in situations like central precocious puberty and gender dysphoria. However, its administration during the peripubertal period could influence normal brain development and function because GnRH receptors are expressed in brain regions that regulate emotions, cognition, motivation and memory. This study used an ovine model to determine whether chronic peripubertal GnRHa-treatment affected the developmental shift from preference of familiarity to novelty. Experimental groups included Controls and GnRHa-treated rams. To differentiate between effects of altered GnRH signaling and those associated with the loss of sex steroids, a group was also included that received testosterone replacement as well as GnRHa (GnRHa + T). Preference for a novel versus familiar object was assessed during 5-min social isolation at 8, 28 and 46 weeks of age. Approach behavior was measured as interactions with and time spent near the objects, whereas avoidance behavior was measured by time spent in the entrance zone and attempts to escape the arena via the entry point. Emotional reactivity was measured by the number of vocalizations, escape attempts and urinations. As Control and GnRHa-treated rams aged, their approach behaviors showed a shift from preference for familiarity (8 weeks) to novelty (46 weeks). In contrast, relative to the Controls the GnRHa + T rams exhibited more approach behaviors towards both objects, at 28 and 46 weeks of age and preferred familiarity at 46 weeks of age. Vocalisation rate was increased in GnRHa treated rams in late puberty (28 weeks) compared to both Control and GnRHa + T rams but this effect was not seen in young adulthood (46 weeks). These results suggest that the specific suppression of testosterone during a developmental window in late puberty may reduce emotional reactivity and hamper learning a flexible adjustment to environmental change. The results also suggest that disruption of either endogenous testosterone signalling or a synergistic action between GnRH and testosterone signalling, may delay maturation of cognitive processes (e.g. information processing) that affects the motivation of rams to approach and avoid objects.

Circadian rhythms of melatonin and behaviour in juvenile sheep in field conditions: Effects of photoperiod, environment and weaning.

Entrainment of circadian rhythms (CR) to the light dark cycle has been well described under controlled, experimental conditions. However, studies in rodents have reported that rhythms in the laboratory are not always reproduced under field conditions. The aim of this study was to characterise the CR of sheep maintained under conditions of standard UK farm animal husbandry and to investigate the effects of environmental challenges presented by season, weaning and changes in housing on CR. Male sheep (n = 9) were kept at pasture, or group housed in barns, under natural photoperiod for one year. CR in locomotor activity were monitored using accelerometry, and 24 h patterns in plasma cortisol and melatonin were measured every 4 h by ELISA. CR was measured before and after weaning, in summer and winter, and at pasture and by barn housing. Cosinor analysis revealed high amplitude, diurnal rhythms in locomotor activity that were disrupted by weaning and by barn housing. Rhythms in winter showed an interrupted night time activity pattern, but only when the sheep were kept at pasture. Cortisol and melatonin secretion followed typical circadian patterns in winter and summer. The CR of the sheep under the field conditions of this study were strikingly robust under basal conditions, but easily disrupted by environmental challenges. Interrupted patterns of activity during the long nights of wintertime, not previously reported for sheep kept in experimental conditions were recorded. Based on these findings, we propose that animals require exposure to more complex environments than the laboratory in order to exhibit their true circadian phenotype.

A reduction in long-term spatial memory persists after discontinuation of peripubertal GnRH agonist treatment in sheep.

Chronic gonadotropin-releasing hormone agonist (GnRHa) administration is used where suppression of hypothalamic-pituitary-gonadal axis activity is beneficial, such as steroid-dependent cancers, early onset gender dysphoria, central precocious puberty and as a reversible contraceptive in veterinary medicine. GnRH receptors, however, are expressed outside the reproductive axis, e.g. brain areas such as the hippocampus which is crucial for learning and memory processes. Previous work, using an ovine model, has demonstrated that long-term spatial memory is reduced in adult rams (45 weeks of age), following peripubertal blockade of GnRH signaling (GnRHa: goserelin acetate), and this was independent of the associated loss of gonadal steroid signaling. The current study investigated whether this effect is reversed after discontinuation of GnRHa-treatment. The results demonstrate that peripubertal GnRHa-treatment suppressed reproductive function in rams, which was restored after cessation of GnRHa-treatment at 44 weeks of age, as indicated by similar testes size (relative to body weight) in both GnRHa-Recovery and Control rams at 81 weeks of age. Rams in which GnRHa-treatment was discontinued (GnRHa-Recovery) had comparable spatial maze traverse times to Controls, during spatial orientation and learning assessments at 85 and 99 weeks of age. Former GnRHa-treatment altered how quickly the rams progressed beyond a specific point in the spatial maze at 83 and 99 weeks of age, and the direction of this effect depended on gonadal steroid exposure, i.e. GnRHa-Recovery rams progressed quicker during breeding season and slower during non-breeding season, compared to Controls. The long-term spatial memory performance of GnRHa-Recovery rams remained reduced (P<0.05, 1.5-fold slower) after discontinuation of GnRHa, compared to Controls. This result suggests that the time at which puberty normally occurs may represent a critical period of hippocampal plasticity. Perturbing normal hippocampal formation in this peripubertal period may also have long lasting effects on other brain areas and aspects of cognitive function.

Spatial memory is impaired by peripubertal GnRH agonist treatment and testosterone replacement in sheep.

Chronic gonadotropin-releasing hormone agonist (GnRHa) is used therapeutically to block activity within the reproductive axis through down-regulation of GnRH receptors within the pituitary gland. GnRH receptors are also expressed in non-reproductive tissues, including areas of the brain such as the hippocampus and amygdala. The impact of long-term GnRHa-treatment on hippocampus-dependent cognitive functions, such as spatial orientation, learning and memory, is not well studied, particularly when treatment encompasses a critical window of development such as puberty. The current study used an ovine model to assess spatial maze performance and memory of rams that were untreated (Controls), had both GnRH and testosterone signaling blocked (GnRHa-treated), or specifically had GnRH signaling blocked (GnRHa-treated with testosterone replacement) during the peripubertal period (8, 27 and 41 weeks of age). The results demonstrate that emotional reactivity during spatial tasks was compromised by the blockade of gonadal steroid signaling, as seen by the restorative effects of testosterone replacement, while traverse times remained unchanged during assessment of spatial orientation and learning. The blockade of GnRH signaling alone was associated with impaired retention of long-term spatial memory and this effect was not restored with the replacement of testosterone signaling. These results indicate that GnRH signaling is involved in the retention and recollection of spatial information, potentially via alterations to spatial reference memory, and that therapeutic medical treatments using chronic GnRHa may have effects on this aspect of cognitive function.

Epigenetics and developmental programming of welfare and production traits in farm animals.

The concept that postnatal health and development can be influenced by events that occur in utero originated from epidemiological studies in humans supported by numerous mechanistic (including epigenetic) studies in a variety of model species. Referred to as the 'developmental origins of health and disease' or 'DOHaD' hypothesis, the primary focus of large-animal studies until quite recently had been biomedical. Attention has since turned towards traits of commercial importance in farm animals. Herein we review the evidence that prenatal risk factors, including suboptimal parental nutrition, gestational stress, exposure to environmental chemicals and advanced breeding technologies, can determine traits such as postnatal growth, feed efficiency, milk yield, carcass composition, animal welfare and reproductive potential. We consider the role of epigenetic and cytoplasmic mechanisms of inheritance, and discuss implications for livestock production and future research endeavours. We conclude that although the concept is proven for several traits, issues relating to effect size, and hence commercial importance, remain. Studies have also invariably been conducted under controlled experimental conditions, frequently assessing single risk factors, thereby limiting their translational value for livestock production. We propose concerted international research efforts that consider multiple, concurrent stressors to better represent effects of contemporary animal production systems.

Effects of season on the reproductive organs and steroid hormone profiles in guinea hens (Numida meleagris).

The study documented gross anatomical and histological differences in the reproductive organs of 28 breeding and non-breeding female guinea fowls. Peripheral progesterone and 17ß-oestradiol concentrations were also compared in breeding and non-breeding hens. In non-breeding females, all ovarian and oviducal gross anatomical features had significantly regressed. Histologically, some of the changes in a regressing oviduct include systematic changes in height and size of all epithelial cells in all regions of the duct, absence/sparse ciliation of portions of surface epithelium in the magnum, isthmian and uterine regions, general loss of cytoplasmic mass, reduction in size and degeneration of tubular glands. Mucosal folds in all regions of the oviduct except the infundibular lip were higher in breeding females. No difference was found between the two groups in plasma progesterone concentrations. Breeding females, however, had higher peripheral oestradiol concentrations than non-breeding females. About 2 h prior to oviposition, plasma oestradiol concentrations peaked at 2.4-fold (230 pg/ml) compared with baseline concentration and plasma progesterone concentrations by nearly 9-fold (5.29 ng/ml) of baseline. Significant regression and changes in the histological structure of the ovary and oviduct had occurred in non-breeding females, and lower peripheral oestrogen concentrations may be responsible for this phenomenon.

ADAR-mediated RNA editing suppresses sleep by acting as a brake on glutamatergic synaptic plasticity.

It has been postulated that synaptic potentiation during waking is offset by a homoeostatic reduction in net synaptic strength during sleep. However, molecular mechanisms to support such a process are lacking. Here we demonstrate that deficiencies in the RNA-editing gene Adar increase sleep due to synaptic dysfunction in glutamatergic neurons in Drosophila. Specifically, the vesicular glutamate transporter is upregulated, leading to over-activation of NMDA receptors, and the reserve pool of glutamatergic synaptic vesicles is selectively expanded in Adar mutants. Collectively these changes lead to sustained neurotransmitter release under conditions that would otherwise result in synaptic depression. We propose that a shift in the balance from synaptic depression towards synaptic potentiation in sleep-promoting neurons underlies the increased sleep pressure of Adar-deficient animals. Our findings provide a plausible molecular mechanism linking sleep and synaptic plasticity.

Effects of season on the reproductive organ and plasma testosterone concentrations in guinea cocks (Numida meleagris).

The physiological basis of seasonal breeding in the guinea fowl (Numida meleagris) still remains unknown, despite the socioeconomic importance of these birds, particularly in Ghana. A study involving a total of 50 local guinea cocks was conducted, and documented gross anatomical and histological differences in the reproductive organs of breeding and non-breeding male guinea fowls. The study also compared peripheral testosterone concentrations in breeding and non-breeding cocks. Seasonal differences in variables measured were determined using two-tailed t-test/Mann-Whitney U-test. All comparisons were made at 5% level of significance. Breeding males had significantly (P = 0.000) higher anatomical biometric parameters than their non-breeding counterparts. Also, breeding birds had thicker (P = 0.000) phalli than their non-breeding counterparts. Histologically, regressing testis was characterized by the presence of sloughed off cells and increased debris in the tubular lumen and within the excurrent duct system, collapsed tubules and reduction in tubular lumen. Germ and Sertoli cell populations and nuclear diameters and actual seminiferous tubular diameter and length in regressing testes were significantly (P = 0.000) lower than in active testes. Leydig cell nuclear diameters and populations were also significantly (P = 0.000) reduced. Relative volume of seminiferous tubules in the testis, testicular sperm production/mg testis and per testis and peripheral testosterone concentrations were all higher (P < 0.05) in breeding than non-breeding testis. The ducts in the epididymal region also saw significant (P < 0.05) reductions in luminal diameters in non-breeding birds. Significant regression in anatomical and histological structures of the guinea cock reproductive tract occurred during the non-breeding season, and lower peripheral testosterone concentrations may be responsible for this phenomenon.

Disrupted seasonal biology impacts health, food security and ecosystems.

The rhythm of life on earth is shaped by seasonal changes in the environment. Plants and animals show profound annual cycles in physiology, health, morphology, behaviour and demography in response to environmental cues. Seasonal biology impacts ecosystems and agriculture, with consequences for humans and biodiversity. Human populations show robust annual rhythms in health and well-being, and the birth month can have lasting effects that persist throughout life. This review emphasizes the need for a better understanding of seasonal biology against the backdrop of its rapidly progressing disruption through climate change, human lifestyles and other anthropogenic impact. Climate change is modifying annual rhythms to which numerous organisms have adapted, with potential consequences for industries relating to health, ecosystems and food security. Disconcertingly, human lifestyles under artificial conditions of eternal summer provide the most extreme example for disconnect from natural seasons, making humans vulnerable to increased morbidity and mortality. In this review, we introduce scenarios of seasonal disruption, highlight key aspects of seasonal biology and summarize from biomedical, anthropological, veterinary, agricultural and environmental perspectives the recent evidence for seasonal desynchronization between environmental factors and internal rhythms. Because annual rhythms are pervasive across biological systems, they provide a common framework for trans-disciplinary research.

Aging causes a slowing in ciliary beat frequency, mediated by PKCε.

The elderly are at much higher risk for developing pneumonia than younger individuals. Pneumonia is a leading cause of death and is the third most common reason for hospitalization in the elderly. One reason that elderly people may be more susceptible to pneumonia is a breakdown in the lung's first line of defense, mucociliary clearance. Cilia beat in a coordinated manner to propel out invading microorganisms and particles. Ciliary beat frequency (CBF) is known to slow with aging, however, little is known about the mechanism(s) involved. We compared the CBF in BALB/c and C57BL/6 mice aged 2, 12, and 24 mo and found that CBF diminishes with age. Cilia in the mice at age 12 and 24 mo retained their ability to be stimulated by the ß2 agonist procaterol. To help determine the mechanism of ciliary slowing, we measured protein kinase C alpha and epsilon (PKCα and PKCε) activity. There were no activity differences in PKCα between the mice aged 2, 12, or 24 mo. However, we demonstrated a significantly higher PKCε activity in the mice at 12 and 24 mo than the in the mice 2 mo of age. The increase in activity is likely due to a nearly threefold increase in PKCε protein in the lung during aging. To strengthen the connection between activation of PKCε and ciliary slowing, we treated tracheas of mice at 2 mo with the PKCε agonist 8-[2-(2-pentylcyclopropylmethyl)-cyclopropyl]-octanoic acid (DCP-LA). We noted a similar decrease in baseline CBF, and the cilia remained sensitive to stimulation with ß2 agonists. The mechanisms for the slowing of baseline CBF have not been previously determined. In this mouse model of aging we were able to show that decreases in CBF are related to an increase in PKCε activity.

Reasons for recall following conditional discharge: explanations given by male patients suffering from dual diagnosis in a London Forensic Unit.

Patients who have been discharged from forensic services often have conditions they have to abide by as part of their discharge, and failure to do so leads to recall. We interviewed six men who had been conditionally discharged from forensic services and then been recalled into hospital to find out what they thought went wrong. The reasons they gave for why things went wrong included feeling that the system was unfair and made them feel like criminals even though they did not feel they had put anyone at risk. Some of them were not fully aware of the conditions they needed to adhere to, and some of them had breached the conditions but did not take responsibility for what had happened. In addition, supervision was felt to be very controlling and disruptive rather than supportive when patients were often lonely, bored and needing support. Most participants reported that they experienced poor standards of aftercare in hostels they were required to reside in. In the future, care of patients after conditional discharge should include better communication between patients and their supervisory team, recognition of the need for more support and improvements in the standards of care in hostels, as well as a collaborative approach to risk assessment that might reduce the frequency of relapse and readmission. This study explores how male patients suffering from dual diagnosis in a forensic unit perceive being recalled and readmitted following conditional discharge and their views about how services might be improved. A qualitative approach was used drawing on grounded theory techniques. Audiotaped semistructured interviews collected data from a purposefully selected sample of six participants who had been recalled and met the inclusion criteria of the study. Data were analysed using the constant comparative method. Most participants perceived the recall system as unfair, inappropriately criminalized their behaviour and was based on an assessment of risk that they did not understand or accept. Participants were not fully aware of the conditions of their discharge, and most did not accept responsibility for their role in being recalled and blamed the system. Care following discharge was rarely seen as positive, and poor standards in hostels were reported by most participants. Supervision was often seen as disruptive and controlling, and focused more on surveillance rather than support. Better communication might have helped them understand and adhere to the conditions of their discharge. Participants identified the importance of family and friends to their recovery, the importance of having their own accommodation, and the need to be more independent.

Potentiation of brain stimulation reward by morphine: effects of neurokinin-1 receptor antagonism.

RATIONALE: The abuse potential of opioids may be due to their reinforcing and rewarding effects, which may be attenuated by neurokinin-1 receptor (NK1R) antagonists. OBJECTIVE: This study was conducted to measure the effects of opioid and NK1R blockade on the potentiation of brain stimulation reward (BSR) by morphine using the intracranial self-stimulation method. METHODS: Adult male C57BL/6J mice (n = 15) were implanted with unipolar stimulating electrodes in the lateral hypothalamus and trained to respond for varying frequencies of rewarding electrical stimulation. The BSR threshold (θ(0)) and maximum response rate (MAX) were determined before and after intraperitoneal administration of saline, morphine (1.0-17.0 mg/kg), or the NK1R antagonists L-733,060 (1.0-17.0 mg/kg) and L-703,606 (1.0-17.0 mg/kg). In morphine antagonism experiments, naltrexone (0.1-1.0 mg/kg) or 10.0 mg/kg L-733,060 or L-703,606 was administered 15 min before morphine (1.0-10.0 mg/kg) or saline. RESULTS: Morphine dose-dependently decreased θ(0) (maximum effect = 62% of baseline) and altered MAX when compared to saline. L-703,606 and L-733,060 altered θ(0); 10.0 mg/kg L-733,060 and L-703,606, which did not affect θ(0) or MAX, attenuated the effects of 3.0 and 10.0 mg/kg morphine, and 1.0 and 0.3 mg/kg naltrexone blocked the effects of 10.0 mg/kg morphine. Naltrexone given before saline did not affect θ(0) or MAX. CONCLUSIONS: The decrease in θ(0) by morphine reflects its rewarding effects, which were attenuated by NK1R and opioid receptor blockade. These results demonstrate the importance of substance P signaling during limbic reward system activation by opioids.

Masculinization of the distal tubular and external genitalia in female sheep with prenatal androgen exposure.

Prenatal exposure to endogenous or exogenous androgens alters the development of the female reproductive tract. Although lesions in ovaries and external genitalia of androgenized female sheep have been reported, lesions of the tubular genitalia have not. Testosterone propionate (TP) or dihydrotestosterone (DHT) was administered by intramuscular injection twice weekly to 32 ewes from 30 to 90 days of pregnancy. The ewes lambed normally. The reproductive tracts from 24 treated and 13 control postpubertal female offspring were examined at 10 months of age. The ovaries, oviducts, and uteri were grossly and histologically normal in both TP- and DHT-exposed sheep. However, in the DHT-treated sheep, the uterus connected to a misshapen, saccular vagina that opened into the urethra; in the TP-treated sheep, it ended in a blind sac. In both TP- and DHT-treated sheep, the urethra was approximately 5 times longer than that of control sheep, and it resembled a male urethra with bilateral male accessory genital glands. The urethra terminated in a fully developed penis in both TP- and DHT-treated sheep, and a scrotal sac was present (without testes). These results show that prenatal exposure of female sheep to exogenous androgens results in masculinization of the tubular and external genitalia.

Developmental programming: prenatal androgen exposure alters the gonadotroph population of the ovine pituitary gland.

In utero exposure of the female foetus to androgens during development disrupts the reproductive axis and results in hypersecretion of luteinising hormone (LH) (but not follicle-stimulating hormone) in postnatal life. Abnormalities in the neural circuits controlling hypothalamic gonadotrophin-releasing hormone have been documented; however, androgens could also programme abnormalities in the pituitary gland. Ovine foetuses were exposed to either testosterone propionate or the non-aromatisable androgen dihydro-testosterone from days 30-90 of gestation (term 147 days) and the effects on the functional morphology of the pituitary were determined. Exogenous testosterone propionate exposure resulted in pituitary glands in adult male and female sheep that were 40% heavier than controls. Because this effect was not observed in the dihydro-testosterone-exposed animals, these actions are mediated via the oestrogen receptor (ER). No significant differences were apparent in 90- or 140-day foetuses. There was no difference between control and androgen-exposed animals in the density of LHß or ERα immunoreactive cells in the pituitary although the density of follicle-stimulating hormone-ß immunoreactive cells was lower in the testosterone-treated animals. The percentage of cells co-localising LHß and ERα was lower in the testosterone-treated ewes and this may, in part, explain a reduced ability to respond to steroid feedback. Thus, enlargement of the pituitary gland, coupled with a reduced sensitivity to oestrogen negative-feedback, may contribute to the hyper-secretion of LH observed in animals that have been exposed to excess androgens during foetal life.

Older men's experiences of community-based health checks in Knowsley, UK.

A study using both qualitative and quantitative methods was undertaken to examine the impact of community-based health checks on men in Knowsley, UK. The main objective was to understand whether community-based health checks targeted at specific geographical and age groups were an effective way of improving health in men. Interviews were conducted with 50 service users, and a completed postal questionnaire was received from 178 men who had attended during the service's pilot period. Results indicated that men were generally satisfied with both the content and structure of the health checks. Men spoke favourably of the service they had received, particularly in comparison to their previous experiences of primary care. They reported enjoying using a service that allowed them to examine their own health in a comfortable environment. Knowledge was provided to a group whose awareness of health matters was often poor, and the vast majority of men reported making a variety of positive lifestyle changes as a result of attending. Reported improvements to health included giving up smoking, reducing alcohol consumption, increasing exercise and eating more healthily. The study suggests that services of this nature deserve careful consideration by health care professionals and policy-makers.

Distribution of galanin receptor-2 immunoreactive neurones in the ovine hypothalamus: no evidence for involvement in the control of gonadotrophin-releasing hormone secretion.

Galanin is a small neuropeptide that mediates its effects via three receptor isoforms: galanin receptor-1, galanin receptor-2 and galanin receptor-3 (Gal-R1, Gal-R2 and Gal-R3). Galanin is thought to be an important intermediate in signalling in the hypothalamic-pituitary-gonadal axis and has been widely detected in the ovine hypothalamus. The expression of galanin and Gal-R1 has been reported to fluctuate during the reproductive cycle. Although the distribution of Gal-R1 has been determined in the ovine hypothalamus, the distribution of Gal-R2 was hitherto unknown. Using immunohistological and immunofluorescence techniques, we have mapped the distribution of Gal-R2 in the ovine hypothalamus, collected during the follicular phase of the oestrous cycle and examined colocalisation of Gal-R2 with oestrogen receptor alpha (ERalpha) and gonadotrophin-releasing hormone (GnRH). Gal-R2 was expressed in several regions of the hypothalamus (supraoptic nucleus, paraventricular nucleus, ventromedial nucleus, arcuate nucleus) but not as widely expressed as Gal-R1. Areas of Gal-R2 expression overlapped with those reported for Gal-R1. We observed that, in certain defined regions of the hypothalamus, up to 50% of neurones that express Gal-R2 also express ERalpha. No neurones coexpressed Gal-R2 and GnRH. Thus, we conclude that, in follicular phase animals, this receptor plays little or no role in direct intermediary signal transmission in GnRH-mediated control of the reproductive cycle.

Progesterone can block the preovulatory gonadotropin-releasing hormone/luteinising hormone surge in the ewe by a direct inhibitory action on oestradiol-responsive cells within the hypothalamus.

Elevated oestradiol concentrations during the follicular phase stimulate a surge in gonadotropin-releasing hormone (GnRH) and luteinising hormone (LH) concentrations, which leads to ovulation. Progesterone can block the oestradiol-induced GnRH/LH surge, but the mechanism that is involved is unclear. We examined the effect of progesterone on oestradiol-induced activation of cells within the ovine hypothalamus/preoptic area (POA) to determine: (i) in which regions progesterone acts to block the GnRH/LH surge and (ii) whether progesterone directly or indirectly prevents activation of oestradiol-responsive cells. Cellular activation was assessed by measuring the number of cells that expressed Fos (an immediate early gene). Exposure to increased oestradiol concentrations in the absence of progesterone (which normally stimulates a LH surge) did not cause any region-specific changes in hypothalamic Fos expression during the activation stage of the LH surge-induction process (Experiment 1). The same treatment significantly increased cellular activation within the POA, lateral septum (LS), and arcuate nucleus at the time of surge onset (Experiment 2). Concurrent exposure to increased oestradiol and progesterone concentrations during the activation stage of the surge-induction process (which normally blocks the LH surge) was associated with significantly reduced cellular activation within the ventromedial hypothalamus and anterior hypothalamic area, relative to the positive controls (oestradiol increment alone) and arcuate nucleus relative to the negative controls (no increment in oestradiol) during the activation stage (Experiment 1). At the time of surge onset (Experiment 2), exposure to progesterone during the activation period prevented the oestradiol-induced increase in cellular activation that occurred in the POA, LS and arcuate nucleus of the positive controls. These results demonstrated that oestradiol and progesterone induced differential region- and time-specific effects on cellular activation within the regions of the ovine brain that generate the preovulatory GnRH/LH surge. Moreover, the lack of cellular activation within the POA, LS and arcuate nucleus at the time of surge onset in animals exposed to progesterone during the activation stage is consistent with the hypothesis that progesterone can block the preovulatory surge by direct inhibition of oestradiol-induced cellular activation in these areas.

Impacts of aggregate dredging on sediment composition and associated benthic fauna at an offshore dredge site in the southern North Sea.

Dredging and associated screening at a dredge site in the southern North Sea (Area 408) is associated with areas of well-sorted fine sand that extend for up to 3 km to the south-east of the dredged area and overlay sediments with a more variable particle size composition. This well-sorted fine sand may reflect deposition and transport of material mobilised by the dredging and screening processes at the dredge site. Multivariate analysis of the benthic community structure suggests that marine aggregate dredging, at the level of intensity employed in the study area prior to sample collection, has had a limited impact on benthic community composition compared with that reported from studies elsewhere. This is ascribed to the likely rapid rates of recolonisation by the mobile opportunistic polychaetes and crustaceans that dominate the macrofauna of the sandy gravel deposits at this particular dredge site. Analysis of variance showed, however, that significant differences existed between the sample treatments in terms of species evenness (Pielou's J). Dredged samples were found to have the lowest mean species evenness (0.71) when compared to controls (0.77). The present study highlights the inherent difficulties in the application of general impact/recovery predictions to dredged sites with varying environmental characteristics.

Sexually differentiated regulation of gnRH release by gonadal steroid hormones in sheep.

Exposure of the sheep fetus to testosterone from day 30 to day 90 of a 147 day gestation causes the neurones that control GnRH secretion, the GnRH neuronal network, to become organized in a sex-specific manner. After androgen exposure in utero, GnRH neurones are activated in a sexually differentiated pattern by gonadal steroid hormones. Specifically, follicular phase concentrations of oestrogen trigger a GnRH 'surge' in ewes, but not in rams or females treated with androgen during fetal life. Furthermore, progesterone is a less potent inhibitor of GnRH release in rams or females treated with androgen during fetal life. The reasons for the sexual differentiation of these steroid feedback mechanisms probably reside in a dimorphism in steroid-sensitive neural inputs to GnRH neurones. The density of neurones containing oestrogen receptor alpha is sexually differentiated in areas of the ovine brain that are known to be involved in the steroidal regulation of GnRH. Furthermore, neurones in these regions are activated in a gender-specific pattern. A determination of the neural phenotype of these steroid-sensitive cells will form a basis for understanding the mechanisms by which the GnRH neuronal network is organized and activated in a sexually differentiated manner.

Antigenic variations in the CD4 induced sites of the CCR5-tropic, pathogenic SHIVsf162p3 gp120 variants.

In vivo passage of non-pathogenic, CCR5-tropic simian/human immunodeficiency virus (SHIV) - SHIVsf162 resulted in a pathogenic isolate, SHIVsf162p3. In an attempt to characterize envelope (Env)-mediated properties that may contribute to its pathogenicity, major (P3 major) and minor (P3 minor) Env gp120 variants were cloned from the plasma of a SHIVsf162p3-infected animal, and expressed in the context of luciferase reporter viruses. Entry mediated by these envelopes and susceptibility to neutralization by CD4 induced-site (CD4i) antibodies (MAbs) was analyzed in comparison to parental SF162. Sequence analysis revealed that the P3 major and minor variant Envs contained 14 and 17 amino acid changes, respectively, compared with SF162. The rank order of entry mediated by the three envelopes was P3 major > SF162 > P3 minor, whereas the reverse order was observed for susceptibility to neutralization by CD4i MAbs. Since CD4i epitopes overlap the coreceptor (CoR) binding site, these findings suggest that the amino acid changes accumulated upon in vivo passage of SHIVsf162 result in Env gp120 structural rearrangements that modulate the exposure and/or conformation of the CoR binding site. This, in turn, led to increased entry and infectivity of the P3 major variant and may be responsible, in part, for the enhanced pathogenicity of SHIVsf162p3.