The effect of unilateral 6-hydroxydopamine lesions in the substantia nigra on hippocampal noradrenaline-induced feeding and other behaviour in the rat.
Introduction: Given that administration of noradrenaline (NA) to the cerebral ventricles or into the hippocampus can elicit feeding, and that lesion the the dopaminergic (DA) substantia nigra (SN) can bring about aphagia, the present report considers the interaction of these two manipulations. Methods: Cannulae were implanted into the SN and the dorsal hippocampus of rats kept on a normal food and water regimen. One week after surgery 13 µg NA in 0.6 µl were administered to the hippocampus and the animals were observed for 20 minutes or until 3 minutes had elapsed after feeding had stopped. The behavioural effects of 6-hydroxydopamine lesions of the SN were recorded from a circular open arena. Results: 1/ Feeding in short bouts was elicited after NA injection to 25/30 sites in the hippocampus 2/ More feeding was observed from sites where later histology suggested there had been no leakage to the ventricles (88%). The feeding behavior did not result from spreading depression (<7 shakes recorded on 3% of tests). 3/ After SN lesion, NA still elicited feeding from all hippocampal sites (on two or more occasions). 4/ The SN lesion did not alter the latency to feed, the duration of feeding or the intake of food. (A temporary decrease of body weight was registered on the third postoperative day, only). 5/ NA treatment did not affect locomotion (pre- or post-lesion) although the lesion on its own increased the latency to move and rotation in the open field. Conclusions: Unilateral SN-6-OHDA treatment did not affect feeding elicited by ipsi- or contralateral hippocampal teatment with NA. It is suggested that 6-OHDA induced hypophagia may result from non-specific effects of treatment as the latencies to rest, the duration of grooming increased and feeding bout-duration decreased following the injection of vehicle or toxin.