AVERSIVE AND APPETITIVE PROPERTIES OF LATERAL HYPOTHALAMIC-STIMULATION IN MICE - POSSIBLE DIFFERENTIAL EFFECTS ON LONG-TERM-MEMORY

Mice of the BALB/c strain were bilaterally implanted in the lateral hypothalamus (LH) in order to study the influence of post-trial LH stimulation on learning and memory. In the first experiment, the learning task was food-reinforced operant conditioning. Thirty seconds after a 15-min learning session, the experimental groups received a bilateral LH discontinuous stimulation for 80 sec. Five current intensities were used: 0, 2, 4, 8, and 20 μA. Testing was carried out 24 hr later. Compared to the 0-μA group performance, results showed an impairment for the 2-μA group and an improvement for the three other groups. In the second experiment, the self-stimulation thresholds were individually determined. An energizing effect of stimulation on behavior was observed for the 4-μA intensity and the threshold values ranged from 6 to 9 μA. In the third experiment the effects of 80 sec discontinuous stimulation were tested using a switch on-switch off paradigm. Then, the 2-μA current intensity induced an aversive reaction in stimulated animals, whereas no such effect was observed at 4 μA intensity; only appetitive reactions were observed for higher current intensities. These data indicate a possible relationship (i) between the 2-μA aversive properties of hypothalamic stimulation and the 24-hr delayed impairment of performance, and (ii) between the energizing effect of 4 μA LH stimulation and the retention facilitation. © 1979 Academic Press, Inc.