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Biomedical subjects

R J Rodgers

Publications and source records attributed to R J Rodgers.

195 records · Page 11Linked to original sources
PubMed1980

Plasma LH and FSH in ewes that were either fertile or infertile after long-term grazing of oestrogenic pasture.

The levels of plasma LH and FSH were measured in serial blood samples taken at 15-min intervals for 6 h from ewes that had remained fertile after grazing oestrogenic pasture (clover-fertile ewes), from ewes that were permanently affected by clover disease (clover-infertile ewes) and from normal ewes. Two flocks of ewes from different locations were studied. In flock 1, tonic LH secretion (total area under the curve of LH concentration versus time, 1 area unit = 1 ng ml-1 x 1 h) was significantly (P < 0.05) greater in clover-infertile ewes (10.4 area units) during anoestrus than in ewes that had remained fertile after prolonged grazing of oestrogenic clover (5.4 area units). Tonic LH and FSH secretions during the bleeding season and FSH secretion during anoestrus were not significantly different. In flock 2, LH levels during the breeding season were significantly (P < 0.05) elevated in clover-infertile ewes (10.9 area units) compared to normal ewes (5.4 area units) that had never grazed oestrogenic clover. LH secretion in clover-infertile ewes (7.8 area units) was intermediate to that found in infertile and control ewes. Concentrations of FSH, progesterone and ovarian vein oestradiol-17 beta (E2) during the breeding season were similar in the three groups. In another experiment, the positive feedback release of LH following administration of E2 (12.5, 25 or 50 micrograms per ewe) was measured in anoestrous ewes of flock 2. Significantly (P < 0.01) more clover-infertile ewes demonstrated a positive feedback effect than control ewes when given 12.5 micrograms E2 but not when given higher doses. The elevation of LH secretion in permanently affected clover-infertile ewes is inconsistent with the hypothesis that the hypothalamo-pituitary axis of these ewes is less responsive to the negative feedback effect of oestrogen. Furthermore, the patency of the positive feedback loop is consistent with the ability to ovulate.

Animal Feed↗
PubMed1979

Effects of nicotine, mecamylamine, and hexamethonium on shock-induced fighting, pain reactivity, and locomotor behaviour in rats.

Three series of experiments were performed to evaluate possible nicotinic cholinergic influences on fighting behaviour in rats. Each series consisted of three tests (naive animals in each test); shock-induced fighting, pain threshold estimation and locomotor activity. In the first series, nicotine (0.25 -- 1.00 mg/kg) was found to produce a dose-dependent inhibition of fighting without altering shock thresholds. However, the highest dose used also significantly reduced rearing in the activity test. In the second series, mecamylamine (a centrally active antinicotinic) produced a facilitation of fighting at low doses (2.5 mg/kg) and an inhibition at higher doses (10 mg/kg). Whilst these effects were unrelated to changes in shock thresholds, the high dose resulted in a reduction in both horizontal activity and rearing. Finally, as a control for possible peripheral effects of nicotinic blockage, a third series examined the behavioural effects of hexamethonium. Low doses of this compound (2.25 -- 4.5 mg/kg) had little effect on fighting whilst higher doses (9 -- 18 mg/kg) attenuated these responses. Interestingly, although hexamethonium had no effect on shock thresholds, the highest dose (18 mg/kg) produced a facilitation of horizontal activity. Results are discussed in relation to the hypothesis of central nicotinic cholinergic inhibition of agonistic behaviour.

Aggression↗
PubMed1979

Effect of naloxone on the behaviour of rats exposed to a novel environment.

It has recently been suggested that endogenous opiates may play a general role in stress responding. To test this hypothesis, naloxone hydrochloride (0.5-4.0 mg/kg SC) was administered to rats exposed to an open field situation. Naloxone treatment produced a decrease in locomotor activity and rearing, and an increase in defaecation. A simple dose-response relationship was not observed, with the most potent effects exerted by the 1 mg/kg dose. Nvertheless, these results indicate that naloxone increases emotionality in the rat and suggest that opioid peptides may be released under conditions of nonpainful stress.

Animals↗
PubMed1979

Exploratory behaviour and aversive thresholds following intra-amygdaloid application of opiates in rats.

Rats were bilaterally implanted with guide cannulae aimed at the central or medial nucleus of the amygdala. Microinjections of morphine (10 microgram) at both sites significantly elevated the threshold of response in the flinch-jump test; but only at medial sites did naloxone (1 microgram) antagonise this effect. However, in the hole-board test, an opposite pattern of results emerged. Morphine injections into the central nucleus produced naloxone-reversible reductions in both exploration and activity whilst, in the medial nucleus, the morphine-induced decrease in exploration was not reversed by naloxone. It is concluded that (1) the presence or absence of naloxone-sensitive opiate receptors cannot always be deduced on the basis of a single behavioural test and (2) within the amygdaloid complex, two distinct naloxone-sensitive opiate systems appear to be involved in the modulation of behavioural responses to different forms of stimulation.

Amygdala↗
PubMed1979

Partial anxiolytic action of morphine sulphate following microinjection into the central nucleus of the amygdala in rats.

In the social interaction test of anxiety, bilateral microinjections of morphine sulphate (10 microgram) into the central nucleus of the amygdala counteracted the reduction in social interaction normally seen when the test arena is unfamiliar to rats. However, these injections did not counteract the decrease in social interaction that is observed as illuminance of the arena is increased. Morphine injections into the medial site depressed social interaction below the levels shown by control animals. In the open field test, morphine produced a facilitation of peripheral activity when injected into the central nucleus whilst a decrease in rearing was observed following similar injections into the medial nucleus. Overall, these data indicate a partial anxiolytic action of morphine in the central amygdaloid nucleus. Results are discussed in relation to possible differences in opioid peptide innervation of these two amygdaloid nuclei.

Amygdala↗
PubMed1977

Elevation of aversive threshold in rats by intra-amygdaloid injection of morphine sulphate.

Bilateral micro-injection of morphine sulphate (10 microgram, 20 microgram) into the cortico-medial amygdala produced a dose-dependent increase in aversive threshold. Similar injections into the basolateral amygdala or caudate-putamen failed to have any consistent effect on aversive thresholds. Whilst overall activity levels remained unaffected by morphine injection into either amygdaloid site, caudate animals exhibited a significant decrement in total activity in response to both morphine and control injections. Results are discussed with reference to a possible role for limbic mechanisms in morphine analgesia.

Amygdala↗
PubMedDate not supplied

Corticosterone response to the plus-maze: high correlation with risk assessment in rats and mice.

Exposure to the elevated plus-maze induces behavioural and physiological effects in rodents consistent with fear/anxiety. Maze-naive animals display high levels of risk assessment towards the open arms, and explore these areas less extensively than other parts of the maze while, immediately following the test, pain latencies, skin conductance levels, and plasma corticosterone titres (CORT) are significantly elevated. Although previous research has suggested a link between the plasma CORT response and open-arm exploration, significant elevations in CORT have also been found with restricted exposure to the closed arms. The present study employed ethological measures in an attempt to further characterise the relationship between behavioural and CORT responses to this widely used animal model of anxiety. Our results confirm that, relative to home-cage controls, 5-min exposure to the plus-maze significantly increases plasma CORT levels in test-naive male Wistar rats and male Swiss-Webster mice. Furthermore, in both species, the CORT response was found to be highly correlated with measures of risk assessment (mice: rs = +0.87; rats: rs = +0.58), but not with measures of open-arm activity (entries, time), general locomotor activity, rearing, or head dipping. Findings are discussed in relation to the functional significance of risk assessment in potentially dangerous situations and the potential involvement of glucocorticoids in this process. All rights reserved.

Animals↗
PubMedDate not supplied

Behavioural effects in mice of subchronic chlordiazepoxide, maprotiline and fluvoxamine. II. The elevated plus-maze.

In view of apparent commonalities in the aetiology, symptomatology, and pharmacotherapy of anxiety and depressive disorders, the present study compares the effects of the benzodiazepine, chlordiazepoxide (1.0-8.0 mg/kg), the selective noradrenaline (NA) reuptake inhibitor, maprotiline (0.5-10.0 mg/kg), and the serotonin (5-HT)-selective reuptake inhibitor, fluvoxamine (2.0-8.0 mg/kg), on the behaviour of mice in the elevated plus-maze test of anxiety. To more accurately reflect the clinical situation, subjects were treated daily for 21 days prior to testing, and comprehensive behavioural profiles were obtained through the application of an ethological scoring technique. Results show that subchronic treatment with chlordiazepoxide produced clear anxiolytic-like effects at the highest dose tested, coupled with an inhibition of risk assessment over the entire dose range. With the exception of risk assessment measures, anxiolytic-like effects were also seen with a low dose (0.5 mg/kg) of maprotiline: these effects were lost at higher doses. In contrast to these data, fluvoxamine produced minimal behavioural change under present test conditions. Findings are discussed in relation to the relative efficacy of selective monoamine. reuptake inhibitors in the treatment of anxiety disorders, and the nature of anxiety evoked in mice by exposure to the elevated plus-maze.

Adrenergic Uptake Inhibitors↗
PubMedDate not supplied

Behavioural effects in mice of subchronic chlordiazepoxide, maprotiline, and fluvoxamine. I. Social interactions.

The present study compares the effects of subchronic administration (daily. 21 days) of chlordiazepoxide (CD), maprotiline and fluvoxamine on the behavior of male mice during dyadic social interactions. Maprotiline like chlordiazepoxide, stimulated aggression at 4 mg/kg and 2 mg/kg respectively (intermediate dose levels), whereas effects of fluvoxamine (3-8 mg/kg) were mainly sedative. Non-social activity was reduced by CD at 4 and 8 mg/kg and by maprotiline at 0.5 mg/kg. At the highest dose tested (10 mg/kg), maprotiline increased immobility, resembling the effects of fluvoxamine, while at 2 mg/kg, it reduced social investigation. Thus, despite some commonalities, there were several differences in behavioral profile of the compounds tested. Data are discussed in relation to the efficacy of each of these compounds in treating anxiety and depressive disorders.

Adrenergic Uptake Inhibitors↗