Characterization of benzodiazepine receptor changes in substantia nigra, globus pallidus and entopeduncular nucleus after striatal lesions.

This study explored the character and time course of benzodiazepine (BDZ) receptor changes in substantia nigra pars reticulata, globus pallidus and entopeduncular nucleus after striatal kainate lesions in the rat. Receptor levels at the lesion site and striatal projection areas were measured at 1 week, 1 month and 2 to 3 months after the lesion. One week after the lesion, no receptor changes in substantia nigra pars reticulata, globus pallidus, or entopeduncular nucleus were detected. There were small but insignificant increases in BDZ binding in striatal projection sites 1 month after the lesion. At the 2- to 3-month time point, BDZ binding increased in substantia nigra pars reticulata (44%, P less than .01), globus pallidus (43%, P less than .02) and entopeduncular nucleus (54%, P less than .05). At all time points, the binding affinities of BDZ receptors were unchanged in the denervated and corresponding intact structures. Likewise, BDZ binding was enhanced to a similar extent by gamma-aminobutyric acid on both sides of the brain. CL 218,872, a triazolopyridazine and ethyl beta-carboline-3-carboxylate were used to delineate BDZ receptor subtypes involved in the receptor increase. Deafferented areas were less sensitive to triazolopyridazine and ethyl beta-carboline-3-carboxylate when compared to the corresponding intact areas. This suggests that a proliferation of the triazolopyridazine-insensitive BDZ receptor subtype (BDZ2 receptors) has taken place.