DECREASE OF SOMATOSTATIN RECEPTOR-BINDING IN THE RAT CEREBRAL-CORTEX AFTER IBOTENIC ACID LESION OF THE NUCLEUS BASALIS MAGNOCELLULARIS - A QUANTITATIVE AUTORADIOGRAPHIC STUDY

The specific binding of I-125-Tyr11-somatostatin-14 (I-125-Tyr11-SS-14 ) was measured in different cortical regions after unilateral ibotenic acid lesion of the rat nucleus basalis magnocellularis (NBM). A marke d loss of acetylcholinesterase-positive fibers was observed in the fro ntal, parietal, temporal and occipital cortices ipsilateral to the les ion. The loss of cholinergic cell bodies in the NBM was further invest igated with cholineacetyltransferase (ChAT) immunohistochemistry which indeed demonstrated a loss of ChAT-positive magnocellular perikarya. Autoradiographic analyses of specific binding of I-125-Tyr11-SS-14 dem onstrated a significant reduction in binding density in the denervated parts of the neocortex. The decrease in specific binding was most pro nounced (40-50%) in the superficial layers (I-III) of the frontal, par ietal and temporal cortices 2 and 4 weeks after lesion. A significant loss in I-125-Tyr11-SS-14 binding in the deeper layers was only observ ed in the frontal cortex after 2 and 4 weeks. In the occipital cortex a significant decrease was measured in the superficial layers only aft er 4 weeks. The specific binding in all cortical regions returned to n ormal after 6 weeks. The results suggested that I-125-Tyr11-SS-14 bind ing sites are localized on cholinergic afferents in the rat neocortex and that an up-regulation of number of binding sites, alternatively an increased binding affinity occured with time after lesion.