EFFECTS OF POSTNATAL STIMULATION ON THE PASSIVE-AVOIDANCE BEHAVIOR OFYOUNG-RATS

We examined the effects of stimulation on either postnatal days 1-7 or 21-27 on passive avoidance reaction (PAR) of young rats. Animals rece ived tactile or visual stimulation for 10 min each day, and were train ed on postnatal day 28 in a step-through apparatus using a footshock o f 0.75 mA for 2 s. Retention was tested on five consecutive days begin ning on day 29. Memory retention was measured for each rat 24, 48, 72, 96 and 120 h after the acquisition trial. Step-through latencies to e nter the dark compartment, time spent in the illuminated compartment a nd number of crossings of the light beam were recorded up to 200 s. Ra ts that received tactile or visual stimulation during the 4th postnata l week displayed significantly lower PAR latencies, a shorter stay in the illuminated compartment and a higher number of crossings of the li ght beam compared to rats treated during the 1st postnatal week. The u ntreated control group showed a rapid decline of PAR latencies, All ex perimental groups remained in the illuminated compartment longer and s howed PAR latencies well above those of the control group. The differe nces became more pronounced when visual stimulation in the first postn atal week was used. The number of crossings of the light beam was sign ificantly reduced by the treatment, with the exception of the experime ntal group stimulated visually in the 4th week. The behavioural change s induced by tactile or visual stimulation have a long-lasting effect in coping with a stressful task.