Involvement of the parafascicular nucleus in the facilitative effect of intracranial self-stimulation on active avoidance in rats

To evaluate whether parafascicular nucleus (PF) is involved in the facilitative effect of lateral hypothalamic intracranial self-stimulation (LH-ICSS) on two-way active avoidance acquisition (5 sessions, 10 trials each, one daily) and long-term retention (10 days), rats were lesioned bilaterally at the PF and implanted with an electrode aimed at the LH to obtain ICSS behavior. After each acquisition session rats were allowed to self-administer 2500 trains of LH-ICSS. The main results were: (1) LH-ICSS facilitated the acquisition and retention of conditioning; (2) PF lesions impaired both acquisition and retention of two-way active avoidance; (3) there was a positive relationship between PF lesions size and learning disruption, and (4) LH-ICSS failed to facilitate learning when PF was lesioned. We concluded that the lesion size is a critical variable to evaluate the effects of PF lesions on learning and memory, and that LH-ICSS treatment may exert their effects through the PF nucleus or, at least, the integrity of PF is required for LH-ICSS to improve clearly the task.