Alterations of striatal cholinergic receptors after lesioning of the substantia nigra

Abstract

Dopamine deficiency syndrome is known to cause cholinergic hyperactivity. Therefore, it was hypothesized that the said phenom- enon may be due to enhanced cholinergic receptor functions. In the present study we examined the changes in striatal dopa- minergic and cholinergic receptors in unilateral substantia nigra lesioned rats that showed vigorous ipsilateral rotation (total turns >300) in response to apomorphine (1 mg kg -1 ip). [ 3H] Spiperone ( 3H -SP) and [ 3 H]-quinuclidinyl benzilate ( 3H -QNB) bindings were performed in the striata of the lesioned animals. There was no significant difference in the dissociation equilibrium constant values (K d) between the lesioned and non-lesioned sides. However, a significant difference in the maximum receptor density (B max ) of both [ 3H]-SP and [ 3H]-QNB bindings was observed between the lesioned and non-lesioned sides. The B max of [ 3H]-SP binding was significantly decreased on the lesioned side, whereas the B max of the [ 3H]-QNB binding was significantly increased. These results support the hypothesis that deficiencies of the dopaminergic system cause overactivity of the cholinergic system in the striatum.