Isolation rearing enhances acquisition in a conditioned inhibition paradigm

Isolation rearing from weaning has been reported to enhance excitatory cond itioning. The present study employed a conditioned inhibition procedure to examine whether this result was attributable to locomotor hyperactivity. Ra ts were raised from 21 days old in isolation or in groups of five. In Phase 1, presentation of stimulus A+ was followed immediately by sucrose availab ility (excitatory conditioning). In Phase 2, sucrose was again presented af ter A+ alone, but not after a compound presentation of A+ with a second sti mulus, B-. Thus, B is believed to acquire conditioned inhibitory properties , countering the excitatory impact of A, and reducing responding specifical ly to this stimulus compound. Isolates showed enhanced excitatory condition ing in Phase 1. Furthermore, acquisition of conditioned inhibition in Phase 2 was also facilitated by isolation rearing. In Phase 3, B- was paired wit h a period of sucrose availability. Isolation rearing initially retarded re sponding to B-, confirming that this stimulus possessed a greater degree of behavioural inhibition in these animals. Later in training, isolates showe d enhanced excitatory conditioning to B-, as shown previously to A+ in Stag e 1. These results suggest that isolation rearing enhances the acquisition of appetitive Pavlovian associations, independently of locomotor hyperactiv ity. (C) 1998 Elsevier Science Inc.