Turning behavior, barrel rolling, and sensory neglect induced by picrotoxin in the thalamus

Microinjections of picrotoxin in the ventromedial thalamic nucleus (VMT) in the rat elicited a slow contralateral turning plus a stereotyped upward sniffing. The animals showed a tendency to stand on the hind legs, increased grooming, and a tilt of the head toward the injected side. Similar injections in the parafascicular nuclear complex (Pf) initiated a faster ipsilateral turning and all the behaviors described plus another motor component: an ipsilateral barrel rolling. A 6-OHDA lesion did not impair the barrel rolling induced by picrotoxin injection in the Pf nucleus. Animals injected with picrotoxin in the Pf and VMT showed a marked increase in the current needed to evoke an orienting response after stimulation of the contralateral flank. Unlike rats treated with 6-OHDA, this response to ipsilateral stimulation was also reduced.