The effects of repeated pentylenetetrazol administration on rat emotional behavior

Abstract

Interictal behavioural disorder belongs to the specific syndromes observed in epilepsy and involves, among others, anxiety and depression. In the present study we investigated the influence of repeated administration of a proconvulsive agent, pentylenetetrazol (PTZ), at the subtreshold dose (30 mg/kg i.p.) gradually leading to seizures, on rat emotional behaviour. The animals were considered to be kindled after reaching at least the stage 4 or 5 (maximum) of seizures, on two consecutive test days. Rats were tested in several tests of anxiety-like behaviour: the open field test of neophobia, the Vogel test of conflict behaviour, step-down avoidance test of learning and memory, conditioned fear test (treezing reaction of rats in a context conditioned to the aversive stimulation), and ultra-vocalization test (USV) (reaction of animals to the acute or conditioned aversive stimuli). In the Vogel, open field, and step-down avoidance tests there were no significant differences in behaviour between the kindled and control rats. However, in the conditioned fear test, kindled rats expressed the reduced number of freezing episodes. In the USV test kindled animals exhibited also decreased basal, and enhanced shock-induced conditioned vocalization. The kindled rats did not differ from controls in their reactivity to the painful stimuli (flinchjump test), and motor activity. A challenge dose of yohimbine (a fear-evoking drug, given at the dose of 2.5 mg/kg, i.p.) produced a clear tendency to enhance thigmotaxis in the kindled rats only. These data suggest that pentylenetetrazol kindling is associated with behavioural changes in rats, indicative of increased emotionality and disturbances in the processes of selective attention. The pentylenetetrazol kindled rats may be a useful model to study the mechanisms contributing to the interictal disorders in emotional behaviour, similar to those observed in epileptic patients.