Biomedical subjects

R J Rodgers

Publications and source records attributed to R J Rodgers.

At least 109 records · Page 6Linked to original sources

PubMed1994

Anchorage-independent culture of bovine granulosa cells: the effects of basic fibroblast growth factor and dibutyryl cAMP on cell division and differentiation.

During ovarian folliculogenesis granulosa cells divide while in contact with stromal cells and other granulosa cells. Following ovulation, however, they cease dividing and differentiate into large luteal cells. When cultured in monolayer, granulosa cells spontaneously differentiate into luteal cells, thus confounding the study of the follicular functions of granulosa cells in vitro, such as cell division. We have found that bovine granulosa cells were able to divide in an anchorage-independent culture system consisting of soft agar and an overlay of methylcellulose. The cells grew in colonies and retained the ultrastructural features of follicular granulosa cells. They also secreted an extracellular matrix with features of basal lamina. The granulosa cells responded to basic fibroblast growth factor (bFGF) in a dose- and time-dependent manner, with a three- to five-fold increase (at 50 ng bFGF/ml for 14 days) in the level of DNA per dish. This mitogenic effect was inhibited by dibutyryl cAMP (dbcAMP) (1 mM). In the presence of dbcAMP the cells hypertrophied considerably, did not secrete extracellular matrix, and developed the ultrastructural features of luteal cells. They also secreted threefold more progesterone. This system offers the ability to study the follicular functions of granulosa cells in culture.

Animals↗

PubMed1994

Ethological evaluation of the effects of acute and chronic buspirone treatment in the murine elevated plus-maze test: comparison with haloperidol.

Buspirone is renowned for its highly inconsistent effects in animal models of anxiety. In the present study, the effects of acute (0.63-5.0 mg/kg) and chronic (1.25-5.0 mg/kg, daily, 15 days) buspirone treatment on the behaviour of mice in the elevated plus-maze test were assessed using a recently developed ethological scoring method. On acute administration, a selective reduction in risk assessment behaviours was observed at 1.25 mg/kg; these mild anxiolytic-like effects were maintained at higher doses (2.5-5.0 mg/kg) which also reduced measures of general activity. Similar, though more potent, effects were observed with chronic administration; the lowest dose tested (1.25 mg/kg) reduced open arm entries and total stretch attend postures while higher doses profoundly reduced all major indices of anxiety (traditional and novel) and, concomitantly, suppressed total entries and rearing. Acute administration of haloperidol (0.0125-0.1 mg/kg) appeared to mimic the behavioural suppressant effects of buspirone without selectively affecting anxiety-related measures at any dose. It is suggested that the anti-anxiety and behavioural suppressant profile of buspirone may reflect combined action at 5-HT1A and D2 receptors, respectively. Results are discussed in relation to the utility of risk assessment as a sensitive index of anxiety in models based upon unconditioned behaviour.

Animals↗

PubMed1994

"Cohort removal" induces hyperthermia but fails to influence plus-maze behaviour in male mice.

Mice removed last from their home cage display elevated body temperature compared with those removed first. This stress-induced hyperthermia (SIH) response has been reported for Swiss and NMRI mice and has been forwarded as a model of anticipatory anxiety. In the present study, the effects of order of removal from the home cage (cohort removal) on body temperature and behaviour in the elevated plus maze have been examined in group-housed male DBA/2 mice. Results confirm the basic phenomenon of SIH in this strain, with mice removed from the home cage in positions 4-10 displaying a significantly higher mean rectal temperature compared with those removed in positions 1-3. Despite this observation, however, detailed ethological analysis failed to reveal any significant effect of cohort removal on behaviour displayed in the elevated plus-maze paradigm. Data are discussed in relation to variations in the nature of reactions evoked in different animal models of anxiety.

Animals↗

PubMed1994

Antianxiety and behavioral suppressant actions of the novel 5-HT1A receptor agonist, flesinoxan.

Flesinoxan is a potent and selective 5-HT1A receptor agonist. In this study, the effects of this compound on behavior in the murine elevated plus-maze have been assessed using a recently developed ethological scoring method. Results show that, at low doses (0.1-0.5 mg/kg), flesinoxan inhibited risk assessment behaviors (stretched attend postures and closed arm returns) indicative of a reduction in anxiety. These effects were maintained at a higher dose of 1.0 mg/kg, which also increased percent open entries and time spent on the central platform and open arms. However, this more convincing anxiolytic profile was associated with significant reductions in total arm entries and rearing, suggesting a combination of anxiolysis and behavioral suppression at high doses. The plus-maze profile observed with flesinoxan is very similar to that previously reported for 8-OH-DPAT in the same test but, despite superficial similarities, can be distinguished from that seen with buspirone. Data are discussed in relation to behavioral similarities and differences between 5-HT1A receptor agonists, and the advantages of a more detailed approach to the analysis of plus-maze behavior.

Animals↗

PubMed1994

Dopamine D1 and D2 receptor ligands modulate the behaviour of mice in the elevated plus-maze.

To further our understanding of the potential role of dopamine in mechanisms of anxiety, the effects of four dopamine receptor ligands were examined in an ethological version of the murine elevated plus-maze test. The D1 receptor partial agonist, SKF 38393 (2.5-20.0 mg/kg), had minimal behavioural activity in this test, whereas the selective D1 receptor antagonist, SCH 23390 (0.025-0.2 mg/kg), had dose-dependent but behaviourally nonspecific effects. Quinpirole (0.0625-0.5 mg/kg), a D2 receptor agonist, had no effects at low doses but severely disrupted locomotion and exploration at the highest doses tested. In marked contrast to the lack of effect or nonspecific effects seen with the other ligands tested, the D2 receptor antagonist, sulpiride (2.5-20.0 mg/kg), produced an unambiguous anxiolytic-like profile under present test conditions. Although none of the doses tested adversely affected general activity, clear antianxiety effects were observed on both traditional and novel (i.e., risk assessment) behavioural measures. Data are discussed in relation to the relative importance of D1 and D2 receptor mechanisms in plus-maze anxiety, and the need to further assess D2 involvement through the use of more selective compounds.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗

PubMed1994

Characterization and relative abundance of alternatively spliced luteinizing hormone receptor messenger ribonucleic acid in the ovine ovary.

Complementary DNA (cDNA) clones encoding the LH receptor (LHR) were recently isolated from pig, rat, mouse, and human testes or ovaries. Many of the LHR cDNAs isolated from these species encoded incomplete and, therefore, possibly inactive forms of the LHR. The four major incomplete cDNAs, designated B, C, D, and E, were due to alternative splicing of the full-length cDNA, designated the A form. Northern analyses of messenger RNA (mRNA) encoding LHR in these species and in sheep revealed multiple mRNA species in ovarian tissue, but were unable to distinguish between the full-length (functional) form and the splice variants. We have used reverse transcription of mRNA, amplification via the polymerase chain reaction, and cDNA sequencing to determine which alternatively spliced mRNA species were present in ovine ovarian follicles and corpora lutea, and ribonuclease protection assays to confirm these results and determine the relative abundance of these splice variants. Ovine LHR cDNAs of the full-length A form, B form, and two novel splice forms, designated F and G, were isolated and sequenced. By using LHR cDNAs that spanned the regions of the gene in which the majority of splicing variation occurred, ribonuclease-protected fragments of different sizes were generated depending on which mRNA species (A-G) were present. It is estimated that the ratios of the steady state mRNA levels of the splice variant B form/full-length A form/G form/F form were 5-3.5:1:1:0.3. The E, C, and D forms were not detected, even when using the sensitive method of reverse transcription-polymerase chain reaction for the latter two forms. The overall level of expression of LHR mRNA was greater in corpora lutea than follicles, but the relative abundance of the splice variants was similar in follicles and corpora lutea.

Alternative Splicing↗

PubMed1993

Defense system psychopharmacology: an ethological approach to the pharmacology of fear and anxiety.

Defensive behaviors comprise a set of flexible and adaptive responses to threatening situations and stimuli. In semi-natural situations affording a wide variety of responses, defensive behaviors change over time in response to information about the presence of danger, acquired through risk assessment activities. Two test batteries, a Fear/Defense Test Battery (F/DTB) measuring defensive behaviors to present, approaching predators, and an Anxiety/Defense Test Battery (A/DTB) measuring reactions to potential threat, have been used in conjunction with administration of potentially anxiolytic drugs. Results suggest that the F/DTB behaviors are not systematically responsive to anxiolytics. However, on the A/DTB, anxiolytic benzodiazepines produce a profile of effects primarily involving risk assessment activities. Very similar profiles of effect are seen also with some 5-HT1A compounds, alcohol, imipramine and MK-801, but not for a variety of additional compounds. A consistent pattern of gender differences are obtained with the A/DTB, with females more defensive than males. These results indicate that particular patterns of defensive behaviors may provide a very appropriate animal model for the analysis of pharmacological effects on anxiety.

Animals↗

PubMed1993

Influence of prior maze experience on behaviour and response to diazepam in the elevated plus-maze and light/dark tests of anxiety in mice.

A single prior undrugged exposure to the elevated plus-maze has been reported to reduce open arm activity on retest and to attenuate/abolish the anxiolytic response to benzodiazepines at retest intervals ranging from 48 h to 14 days. The present study was designed to examine the generality of these findings by comparing the effects of prior maze experience on baseline behaviour and response to diazepam in two murine models of anxiety. Parallel experiments were conducted in which DBA/2 mice were exposed/not exposed to the plus-maze, treated daily with saline or diazepam (2-4 mg/kg daily for 8 days) and then tested on either the elevated plus-maze or in the light/dark test of exploration. Results show that, in both tests, diazepam reduced behavioural indices of anxiety in maze-naive mice only. However, interpretation of this apparent loss of diazepam efficacy is at least partially confounded by the observation that maze experience per se altered baseline behaviour in both procedures, reducing open arm activity in the plus-maze and increasing light compartment activity in the light/dark test. The apparent elimination of an anxiolytic response to diazepam in two animal models of anxiety by prior plus-maze experience is discussed in relation to experience-related baseline shifts in behaviour.

Animals↗

PubMed1993

Attenuation of antipredator defensive behavior in rats following chronic treatment with imipramine.

The anxiety/defense test battery has been developed to assess defensive reactions in rats to situations associated with a natural predator, the domestic cat. This comprises three paradigms designed to study the effects of cat exposure on general activity and location with respect to the cat (proxemic avoidance), the effects of cat exposure on non-defensive consummatory behavior, and the behavioral response to cat odor. In the present study subjects were exposed to 21 days pretreatment with imipramine (0, 5, and 15 mg/kg), before being assessed in the three experimental paradigms (carried out over a total period of 7 days). Imipramine treatment was maintained on a daily basis during the 7 days taken to complete the series of tests. The data indicated a behaviorally specific profile consistent with anxiety/fear reduction, but not with sedation, in three different paradigms, following treatment with 15 mg/kg imipramine. These behavioral changes included a reduction in freezing, proxemic avoidance and a disinhibition of suppressed feeding in response to cat presentation. Similarly, imipramine treatment (15 mg/kg) significantly reduced behaviors associated with risk assessment (e.g. flat back approach, stretch attend) during presentation of a cat odor stimulus. This behavioral profile suggests that chronic pretreatment with imipramine produces an attenuation of antipredator defensive behavior.

Aggression↗

PubMed1993

Influence of social isolation, gender, strain, and prior novelty on plus-maze behaviour in mice.

Behavioural baseline is a critical determinant of response to drugs and other manipulations. In the present study, the influence of several organismic and procedural variables on basal plus-maze profiles in mice were examined. The methodology incorporated traditional behavioural parameters as well as novel measures derived from ethological analysis. Experiment 1 showed that social isolation for 1-3 weeks enhanced aggression in male DBA/2 mice but did not substantially alter their behaviour on the maze. A reduction in stretch attend postures did, however, suggest a minor reduction in anxiety in socially isolated animals. In Experiment 2, males of both DBA/2 and T1 strains exhibited higher levels of general activity on the maze than their female counterparts. Although additional evidence suggested that DBA/2 (but not T1) females were less anxious than males, no major sex differences were noted. Experiment 3 revealed a significant strain difference in plus-maze profiles, with T1 males showing a lower basal level of anxiety than DBA/2 males. This study also demonstrated that DBA/2 and T1 males react very differently to prior novelty experience, with enhanced anxiety evident in the former and reduced anxiety in the latter. Together, these findings point to a range of organismic and procedural variables that may account for inconsistencies in the literature on the elevated plus-maze.

Aggression↗

PubMed1993

Anxiety enhancement in the murine elevated plus maze by immediate prior exposure to social stressors.

Anxiety has been implicated in the acute nonopioid analgesic reaction seen in defeated mice. In the present study, behavioural responses to the elevated plus-maze test were examined in male DBA/2 mice immediately following defeat by an experienced aggressive conspecific. Compared to home-cage controls, defeat reduced total arm entries and rearing, although anxiety enhancement was indicated by decreases in percent open-arm entries and percent time spent on the open arms. These effects were accompanied by significant increases in nonexploratory behaviour (movement arrest and grooming) and risk assessment (closed arm returns, protected head dipping, and stretch-attend postures). This anxiogenic effect of social defeat was partially replicated in mice merely exposed to the scent of an aggressive male conspecific. The specificity of present findings to socially relevant stressors was confirmed by the general lack of effect on plus-maze behaviour of prior exposure to a novel cage or to interaction with a nonaggressive male. Present results are not only consistent with the anxiety hypothesis of defeat analgesia but also show that the elevated plus-maze test is sensitive to alterations in anxiety produced by ecologically relevant stimuli. Possible implications for pharmacological studies are discussed.

Agonistic Behavior↗

PubMed1993

Yohimbine potentiates active defensive responses to threatening stimuli in Swiss-Webster mice.

Yohimbine HCl, an antagonist at alpha 2-noradrenaline receptors with putative panicogenic effects in human subjects, was administered to Swiss-Webster mice at doses of 0.5, 1.0, and 2.0 mg/kg. Animals were then tested in two defense test batteries. Yohimbine produced increases in flight from an approaching/contacting human and potentiated animals' reactions to dorsal contact. During a 5-min exposure to a cat (separated from the mouse by a wire-mesh screen) and the 15-min period thereafter, yohimbine produced a dose-dependent pattern of changes in defensive behaviors that included increases in locomotion, transits from one segment of the test chamber to another, fore- and hindpaw wall climbing, screen climbing and hanging, and roof pushing. Crouching (relative immobility while in a hunched-back posture) was notably decreased at all doses. During the postcat period, two different response patterns, "high-escape" and "low-escape," characterized in part by high and low frequencies of wall climbing, were observed in cat-exposed groups. In yohimbine-injected mice, the low-escape behavior pattern also included a tendency to avoid the segment of the test chamber closest to the cat compartment. Both patterns differed from the crouching and immobility generally exhibited by vehicle-injected, cat-exposed controls. It was suggested that yohimbine effected these behavioral changes by either potentiating neural mechanisms mediating flight or inhibiting mechanisms mediating freezing. This model may have some utility for the investigation of panicogenic and antipanic compounds and may contribute insights into the etiology of panic disorder.

Aggression↗

PubMed1992

Evidence for differential effects of 8-OH-DPAT on male and female rats in the Anxiety/Defense Test Battery.

The Proxemics/Activity test and the Eat/Drink test, two components of the Anxiety/Defense Test Battery, were developed to measure defensive reactions to situations associated with a natural predator (cat). In the present studies the behavioral effects of 8-OH-DPAT treatment (0.01-1.0 mg/kg, SC) were entirely consistent with anxiety/fear reduction. These effects included an increase in time spent near the cat compartment, and a complimentary decrease in time spent farthest from this compartment, together with an increase in transits and locomote behavior. 8-OH-DPAT (1.0 mg/kg) also increased eat frequencies and durations (highly preferred food) both during and following cat presentation, without influencing drinking. This finding is discussed with reference to previous findings with 8-OH-DPAT in studies assessing both food intake and anxiolysis. Interestingly, 8-OH-DPAT was more potent in a majority of its effects in female subjects, a finding consistent with recent neurochemical data. These findings provide important behavioral evidence for a sexual differentiation in 5-HT function, and support the case for greater emphasis on female subjects in animal models of anxiety.

8-Hydroxy-2-(di-n-propylamino)tetralin↗

PubMed1992

MK-801 produces a reduction in anxiety-related antipredator defensiveness in male and female rats and a gender-dependent increase in locomotor behavior.

The present study investigated the effects of the non-competitive NMDA antagonist MK-801 (0.04-0.16 mg/kg), on antipredator defensive reactions of male and female rats in three paradigms comprising the Anxiety/Defense Test Battery (A/DTB). In order to facilitate interpretation of data from the above study, the behavioral effects of the compound were also assessed in the non-threatening environment of the home cage. The data indicate a marked gender difference in the locomotor effects of the compound with females, but not males, showing a dose-dependent increase in general locomotor activity, a decrease in freezing, and a loss of balance at the highest dose, in both non-threatening and threatening contexts. The behavioral profile for males in the A/DTB included decreased orientation to and proxemic avoidance of the cat stimulus or stimulus site, and increased transits and eating in the cat situation. Contacts with the cat odor stimulus were increased, as was normal, curved back, locomotion in this test. In the absence of non-specific locomotor effects for males, this profile for the A/DTB provides convincing evidence for anxiety/fear reduction with MK-801. While locomotor effects tended to mask the putative anxiolytic properties of the compound in females, evidence remains from behavioral changes not attributable to a locomotor influence to indicate anxiety/fear reduction in this sex.

Aggression↗

PubMed1992

Effects of diazepam on behavioural and antinociceptive responses to the elevated plus-maze in male mice depend upon treatment regimen and prior maze experience.

Recent studies have shown that brief exposure to an elevated plus-maze (EPM) produces non-opioid antinociception in male mice. The present experiments were designed to assess the effects of diazepam on this phenomenon. When acutely administered, low doses (0.5-1.0 mg/kg) of diazepam failed to produce an anxiolytic profile and exerted rather inconsistent effects on EPM-induced elevations in tail-flick latencies. In EPM-experienced mice, chronic treatment with higher doses of diazepam (2-4 mg/kg, 8 days) produced a weak anxiolytic action and inhibited the early phase of EPM antinociception only. However, in EPM-naive mice, 8-day diazepam pretreatment exerted a marked anxiolytic effect and completely eliminated the antinociceptive response to the maze. Together, these data support the view that anxiety is a key factor in certain forms of adaptive pain inhibition and suggest a possible mediational role for benzodiazepine receptors. Our findings also show that prior exposure to the EPM, rather than chronic handling/injection, greatly reduces the anti-anxiety effect of diazepam. Furthermore, since re-exposure to the maze, per se, decreased time spent on the open arms and central platform, a shift in behavioural baseline ("retest anxiogenesis") may have contributed to the weak behavioural effects of diazepam in test-experienced animals. Importantly, as chronic treatment with diazepam did not influence this anxiogenic-like retest profile, our data suggest that a single prior experience of the EPM may radically alter the nature of the anxiety reaction provoked by this test.

Analgesia↗

PubMed1992

Attenuation of defensive analgesia in male mice by 5-HT3 receptor antagonists, ICS 205-930, MDL 72222, MDL 73147EF and MDL 72699.

Recent studies have shown that non-opioid defensive analgesia in male mice is potently inhibited by the 5-HT3 receptor antagonist, ondansetron. The present series of experiments was conducted to further explore the involvement of 5-HT3 receptor mechanisms in this particular form of adaptive inhibition of pain. The drug ICS 205-930 significantly attenuated the reaction at 1.25-2.5 micrograms/kg, with smaller and larger doses being ineffective. Both MDL 72222 and MDL 73147EF produced flat dose-response curves, with significant inhibition of defensive analgesia at minimum effective doses of less than or equal to 10 and 300 micrograms/kg, respectively. Although MDL 72699, the quaternary salt of MDL 72222, also inhibited the reaction, this effect was seen at comparatively large doses (0.5-1.0 mg/kg) only. None of the compounds tested had significant intrinsic effects of tail-flick latencies, over the dose ranges tested. These findings indicate that 5-HT3 receptor mechanisms may have an important modulatory role in certain forms of "stress" analgesia. Data are discussed in relation to the consistent profile of partial inhibition produced by 5-HT3 receptor antagonists in this model.

Analgesia↗

PubMed1992

The anxiety/defense test battery: influence of gender and ritanserin treatment on antipredator defensive behavior.

The anxiety/defense test battery has been developed to measure defensive reactions in laboratory rats to both direct exposure to, and stimuli associated with, a natural predator, the domestic cat. The present investigation confirmed earlier findings with each test providing a distinct behavioral profile following exposure to predator stimuli. In addition, the data showed a consistent gender difference in a number of these behavioral measures, indicating that females are more defensive than males. These effects included reliability higher levels of cat avoidance and crouching, with lower levels of transits, lying and drinking for cat-exposed females. Similarly, females exposed to a cat odor stimulus showed a reliably higher level of stretch attend and flat back approach behaviors (risk assessment) towards the stimulus block. The 5-HT2 antagonist, ritanserin, failed to provide significant indication of anxiolytic activity, and had minimal influence on antipredator defensive behavior. An important exception to this profile was a reliable decrease in stretch attend behavior to a cat odor stimulus in females but not males. Overall, these findings suggest a complex relationship between gender, antipredator defensive behavior, and anxiolytic drug treatment.

Animals↗

PubMed1992

The role of bovine lipoproteins in the regulation of steroidogenesis and HMG-CoA reductase in bovine adrenocortical cells.

The sources of cholesterol for steroid hormone production were examined using bovine adrenocortical (BAC) cells in primary culture. The experiments were designed to determine the effects of lipoproteins on cortisol production and the level of BAC cell 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase. Most studies on BAC cell lipoprotein requirements have been conducted using human low-density lipoprotein (hHDL); none have used the homologous bovine lipoproteins. BAC cells treated with corticotropin (ACTH) in a medium devoid of lipoproteins increased and maintained cortisol production 7- to 20-fold above basal levels. Under such conditions ACTH also increased the rate of HMG-CoA reductase activity. Inhibition of HMG-CoA reductase with mevinolin inhibited cortisol production by 85%, indicating that the cells were using cholesterol synthesized de novo for steroid production. Cortisol production was increased almost 40-fold above basal levels if hLDL (100 micrograms/ml) was included in the incubation medium. Human LDL also suppressed the levels of HMG-CoA reductase in a concentration-dependent fashion. Human HDL was without effect on either BAC cell steroidogenesis of HMG-CoA reductase. Addition of bovine LDL (bLDL) to the incubation medium also caused an increase in cortisol production and inhibited cholesterol synthesis. By contrast to hHDL, bHDL (100 micrograms/ml) increased the ability of BAC cells to produce cortisol production. Bovine HDL (bHDL) also was able to decrease HMG-CoA reductase, but not to the extent caused by hLDL or bLDL. These data demonstrate that bovine adrenal cells can use bHDL as a source of cholesterol for steroid hormone production. These findings may be of particular importance when one considers that in vivo, the bHDL content of bovine serum greatly surpasses the level of bLDL.

Adrenal Cortex↗