APPLICATION OF NOSE-POKE HABITUATION VALIDATION WITH POSTTRIAL DIAZEPAM-INDUCED AND CHOLECYSTOKININ-INDUCED HYPOMNESIA AND HYPERMNESIA

The present study describes the use of nose-poke habituation as a memo ry task and demonstrates that it is sensitive to hypo- and hypermnesti c pharmacological treatments administered post-trial. Habituation of n ose-poke behavior of rats was defined as a reduction in number of nose -pokes compared to baseline. It was measured using a board with 16 hol es, to which animals were exposed on 2 consecutive days (baseline and test) for 10 min, respectively. After the first exposure, rats were in jected intraperitoneally (i.p.) immediately or with a delay of 2.5 h w ith doses of diazepam (0.9-4.5 mg/kg) known to be hypomnestic, or chol ecystokinin (CCK-8S; 0.2-25 mu g/kg), which was reported to have memor y facilitating effects. An enhancement of habituation in comparison wi th vehicle controls was interpreted in terms of a hypermnestic effect of the treatment. Conversely, hypomnestic action of the drug treatment was inferred from a reduced habituation. The results show that when d iazepam was injected immediately post-trial, the normal reduction in n umber of nose-pokes during test was prevented, indicative of a failure to habituate presumeably due to an amnesia for the baseline/training trial. In contrast, enhanced habituation (facilitation of memory) was induced when CCK-8S was injected immediately post-trial, as reflected by a decrease in number of nose-pokes during test compared to control animals. The effects were not due to enduring proactive effects of the compounds on performance during test, since post-trial injections of diazepam or CCK-8S with a delay of 2.5 h did not have the effects that immediate post-trial injection had. These results show that nose-poke habituation learning can be a suitable method to investigate hypo- an d hypermnestic effects of drugs in addition to the conventionally used inhibitory avoidance paradigms or appetitively motivated tasks.