FG 7142- and restraint-induced alterations in the ataxic effects of alcohol and midazolam in rats are time dependent

Environmental and immune stressors enhance alcohol-induced motor ataxia in rat

Infection is now accepted as a stressor, consequently we sought to compare the short- and longer-term consequences of several environmental stressors versus an endotoxin challenge on alcohol-induced motor ataxia. The present set of studies examined the impact of intermittent electric shock (SHOCK), intermittent cold water swim (ICWS), or lipopolysaccharide (LPS) administration on the motor ataxic effects of an intraperitoneal (i.p.) injection of alcohol (ETOH). In Experiment 1 SHOCK, but not ICWS, enhanced the motor ataxic effects of ethanol at both 2 and 24 h post-stress. In Experiment 2 administration of LPS did not affect the motor ataxic effects of ETOH 4 h later, but enhanced the ataxic potency of ETOH 24 h later. The results indicate that certain environmental and immune stressors have the potential to alter the long-term behavioral reactivity to alcohol. These examples of stress-induced enhancement of the motor ataxic effects of ETOH may have important implications for the development of alcohol dependence.

Differential effects of midazolam and pentylenetetrazole on behavioral repetition and variation

The present study investigated the effects of midazolam and pentylenetetrazole upon repeating and varying sequences of responses. Rats were exposed to a multiple schedule with two components. Under the VARY component, water was provided if the current sequence of four responses differed from each of the five previous ones; under the REPEAT component, water delivery was contingent upon a particular four-response sequence. Each component was signaled by specific exteroceptive stimuli. Overall, sequence variability was affected by midazolam, and to a lesser degree, by pentylenetetrazole. With the REPEAT contingency, drug administration increased behavior variation, thus reducing accuracy; with the VARY contingency, behavior variation and accuracy were not altered. These results were explained on the basis of the disruptive effects of both drugs upon the discriminative control exerted by previous responses within a sequence and by exteroceptive stimuli.

Neural correlates of cat odor-induced anxiety in rats: region-specific effects of the benzodiazepine midazolam

Cat odor elicits a profound defensive reaction in rats that is reduced by benzodiazepine drugs. The neural correlates of this phenomenon were investigated here using Fos immunohistochemistry. Rats received either midazolam (0.75 mg/kg, s.c.) or vehicle and were exposed to pieces of a collar that had been worn by a domestic cat or an unworn (dummy) collar. Cat odor caused midazolam-sensitive defensive behavioral responses, including avoidance of collar contact, inhibition of grooming, and prolonged rearing. Cat odor exposure induced Fos expression in the posterior accessory olfactory bulb (glomerular, mitral, and granule cell layers), with granule cell layer activation attenuated by midazolam. High basal Fos expression, and some cat odor-associated Fos expression, was evident in the main olfactory bulb (glomerular cell layer), and midazolam exerted a strong inhibitory effect in this region. Midazolam inhibited Fos expression in key limbic regions involved in pheromone transduction (medial amygdala and bed nucleus of the stria terminalis) and defensive behavior (prelimbic cortex, lateral septum, lateral and medial preoptic areas, and dorsal premammillary nucleus). However, midazolam failed to affect cat odor-related Fos expression in a range of key defense-related sites, including the ventromedial hypothalamic nucleus, paraventricular nucleus of the hypothalamus, periaqueductal gray, and cuneiform nucleus. These results indicate that midazolam exerts a region-specific effect on the neural substrates activated by predator odor, with effects in the lateral septum and dorsal premammillary nucleus likely to be of major importance. These findings also suggest the intriguing hypothesis that cat odor is processed by rats as a "pheromone-like" stimulus.

A comparison of female and male rats' ETOH-induced ataxia and exploration following restraint or swim stress

Animal models of stress reactivity are often employed in developing treatments for humans. Many studies use shock stress, and most use male rats. These experiments compare female and male rats exposed to either restraint stress (RS) or ambient-temperature swim stress (SS), using two durations of each stressor and naive controls. The ataxic effects of a 0.6 g/kg i.p. dose of ethanol (ETOH) were measured. Females exhibited less ataxia than males following ETOH administration. There were no significant effects of stress on ETOH-induced ataxia. Exploration was also measured in an open-field test (OFT) both pre- and poststress. In the prestress OFT, females were more active than males. For the no-stress groups and the shorter-duration stress groups, exploration decreased between the first and second OFTs. However, the groups exposed to the longer-duration stress did not show this expected decrease in exploration. A key finding of this research is that while sex differences may be present at baseline, the sexes may react similarly to stress. These data extend knowledge on sex differences in stress, alcohol reactivity and exploratory behavior.

Not all 'predator odours' are equal: cat odour but not 2,4,5 trimethylthiazoline (TMT; fox odour) elicits specific defensive behaviours in rats

The behavioural responses to two commonly used 'predator odours' were assessed in male Wistar rats. Cat odour was presented to rats in the form of a piece of collar that had been worn by a domestic cat. Fox odour was presented in an equivalent piece of (unworn) collar that had been impregnated with 2,4,5 Trimethylthiazoline (TMT)-an extract of fox faeces. Other rats were exposed to collars containing Triethylamine (TEA), a putrid fishy smell, or formaldehyde, which has an acrid irritating smell. Experiment 1 showed that rats approached cat odour, TMT and TEA significantly less than they did an unworn collar. However, only cat odour increased retreat to the hide box, reduced locomotor activity and elicited 'head out' behaviour. When tested immediately after odour exposure, only cat odour exposed rats showed increased anxiety in the elevated plus maze and suppressed activity in a 90-min general activity test. When returned to the odour-paired environment 24 h later in the absence of test odours, only rats that had previously received cat odour showed evidence of conditioned fear. Experiment 2 showed that rats given the benzodiazepine drug midazolam (0.5 mg/kg) display increased approach and decreased defensiveness towards a cat odour impregnated collar. In contrast, midazolam accentuated the avoidance of TMT and formaldehyde containing collars. Experiment 3 showed that when cat odour was presented in a small, enclosed environment, rats display increased body immobility, decreased grooming and increased orientation towards the odour-exuding stimulus. These responses were not seen with TMT or TEA containing collars. Taken together, these results suggest that while cat odour strongly elicits specific defensive behaviours in rats, TMT has effects that are more characteristic of an aversive odour. We suggest that the results of some previous studies using TMT may need to be reassessed.

Behavioral analysis of stress controllability effects in a new swim stress paradigm

Previous animal stress studies have illustrated the marked impact of coping on subsequent behavior and physiology by using shock as the stressor. The current study evaluates the generality of shock stress controllability effects in a new swim stress paradigm on several dependent measures: behavioral despair, analgesia, shuttlebox escape, and alcohol reactivity. In this new paradigm, rats in the escape group are able to learn the behavioral response as evidenced by significant reduction in the acquisition of a lever press response. Both escape and yoked subjects showed "behavioral despair" in comparison to both restrained and home cage controls when tested 24 h later. In the standard shuttlebox escape task 24-h post-stress, no group differences emerged, although a trend for poorer performance in the yoked subjects was evident. No group differences were observed in pain sensitivity after the first or second forced swim exposure. Finally, stress controllability effects were observed in behavioral reactivity to alcohol 2-h post-stress as measured by rotarod performance. This effect is opposite to the previous observations with the tailshock stress controllability paradigm. These results suggest that (1) there are certain similarities, but some fundamental differences between the behavioral endpoints measured following intermittent swim stress in comparison to the well-established effects of the intermittent tailshock stress model and (2) the qualitative nature of a stressor may markedly influence the behavioral and physiological consequences of stress and coping.

Post-injection delays in experimental chambers, but not in home cages, produce both sensitization and tolerance of operant behaviour to midazolam: relation to pharmacokinetics

The effects of post-injection delay time and environmental context on behaviour after subcutaneous administration of 3 mg/kg midazolam were investigated under a differential reinforcement of low rate schedule (i.e. DRL 45 s) in 3 h sessions. Post-injection delays were varied (0-120 min) for two groups of rats placed in either the experimental chamber (group 1) or home cage (group 2) during the pre-session delay times. Midazolam increased shorter-response (inter-response times < 45 s) rates and decreased reinforcement rates in a time-related manner. Reinforcement rate-time profiles were also integrated with parallel pharmacokinetics. Post-injection delays in either environment yielded performances that mirrored the pharmacokinetic profile operative at the corresponding time-delay points. At higher concentrations (> 0.12 microg/ml) the pharmacokinetics of midazolam largely determined the behavioural effects in both groups, regardless of post-injection delays. However, at lower drug concentrations, longer post-injection delays (> 60 min) in the experimental chamber produced both sensitization and tolerance, as measured by greater increases in shorter-response rates and a more rapid return of the reinforcement rate, respectively. Interaction of the discriminative stimulus effects of midazolam with the context probably alters the magnitude of behavioural effects when the delay occurs in the experimental chambers, whereas no such interaction is present in group 2. The DRL schedule with post-injection delays in experimental chambers provides a useful behavioural paradigm for studying both sensitization and tolerance.