Alterations of neuronal activity in the superior colliculus of rotating animals

We have investigated the relationship between alterations in neuronal activ ity in the superior colliculus and behavioral responses which occur followi ng disruption of basal ganglia circuitry. These changes were analysed follo wing unilateral suppression of the immediate early genes, c-fos and ngfi-a, in the striatum and/or the globus pallidus. Animals with unilateral suppre ssion of immediate early gene expression in the striatum exhibited robust c ircling activity, following administration of D-amphetamine, that was direc ted towards the side of suppression. The intensity of rotation was inversel y related to the length of the recovery period following antisense infusion and increased significantly when the globus pallidus was infused simultane ously with the striatum. The difference between ipsiversive (towards the an tisense-infused hemisphere) and contraversive rotations was calculated and animals were grouped by number according to their ipsiversive bias: I, <50 turns; II, 50-500 turns; III, 500-1000 turns; IV, >1000 turns. Immunohistoc hemical localization of Fos was used as an indicator of neuronal activity i n the superior colliculus. While group I animals showed diffuse Fos-like im munoreactivity throughout the intermediate layers of the superior colliculu s, those animals in groups II-IV showed increasing suppression of Fos-like immunoreactivity in the stratum album intermediale and marked enhancement i n the stratum griseum intermediale. Correlation and regression analysis rev ealed a significant positive relationship between the number of ipsiversive rotations and the number of Fos-positive nuclei in the stratum griseum int ermediale of the ipsilateral superior colliculus. These data suggest that the degree of rotation elicited in an animal may de pend on reciprocal suppression/stimulation of adjacent intermediate strata of the superior colliculus. This study provides the first demonstration, us ing Fos immunohistochemistry, of changes in tectal activity produced by alt erations in basal ganglia function. These findings support previous electro physiological studies in this region and suggest that the nigrotectal proje ction may be an important site of altered basal ganglia output. (C) 1999 IB RO. Published by Elsevier Science Ltd.