Chlorpromazine methiodide acts at the vestibular nuclear complex to induce barrel rotation in the rat

Barrel rotation is a unique motor response observed in rats in which, following an intracerebral injection, the animal develops a twist about the long axis and rolls laterally repeatedly. The response was first described following injection of somatostatin. We have previously shown that 'experimental dystonia' in rats induced by intraventricular chlorpromazine methiodide (CPZMI) is identical to barrel rotation, and that it is due to an antimuscarinic effect. The purpose of the present study was to investigate the neuroanatomical basis of CPZMI-induced rotation. We injected CPZMI in 3 microliters into right lateral and IVth ventricle and found that IVth ventricle injections were significantly more likely to induce rotation. Nuclear groups adjacent to the IVth ventricle, which are rich in muscarinic cholinergic receptors, include locus coeruleus and vestibular nuclear complex (VNC). We found that only VNC injections induced rotation. Only certain control compounds injected into VNC elicited the response. We conclude that barrel rotation has a specific neuroanatomical basis, involving central vestibular mechanisms, and that it has a specific pharmacologic basis.