Enhanced GABA function in the angular complex (lateral periaqueductal grey matter and adjacent reticular formation) alters the postural component of striatal- or nigral-derived circling

Summary Unilateral injection of muscimol into the angular complex (lateral periaqueductal grey matter and adjacent reticular formation) caused ipsiversive rotation. Focal injection of picrotoxin into the same site produced contraversive rotation. Administration of apomorphine to animals with a unilateral 6OHDA lesion of the left medial forebrain bundle caused contraversive rotation. Focal injection of muscimol into the angular complex reversed the direction of rotation such that apomorphine administration now produced ipsiversive circling. Unilateral injection of muscimol into substantia nigra zona reticulata caused contraversive rotation. Focal injection of picrotoxin into the same site produced ipsiversive rotation. The prior injection of muscimol into the ipsilateral angular complex prevented the contraversive rotation induced by intranigral administration of muscimol such that animals now showed ipsiversive circling. In both 6-OHDA-lesioned animals and animals receiving intranigral muscimol, focal injection of muscimol into the angular complex caused a reversal in the direction of circling through loss of the postural component with no obvious change in locomotor activity. Bilateral electrolytic lesions of the angular complex overall had no effect on amphetamine-induced locomotion. Manipulation of GABA function in the angular complex alters circling behaviour initiated from the striatum or substantia nigra by altering the postural component without affecting the locomotor response of the animals. The data suggest a critical role for the angular complex as an outflow station from basal ganglia.