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 ¹²⁵I-Tyr¹¹-somatostatin-14 (¹²⁵I-Tyr¹¹-SS-14) was measured in different cortical regions after unilateral ibotenic acid lesion of the rat nucleus basalis magnocellularis (NBM). A marked loss of acetylcholinesterase-positive fibers was observed in the frontal, parietal, temporal and occipital cortices ipsilateral to the lesion. The loss of cholinergic cell bodies in the NBM was further investigated with cholineacetyltransferase (ChAT) immunohistochemistry which indeed demonstrated a loss of ChAT-positive magnocellular perikarya. Autoradiographic analyses of specific binding of ¹²⁵I-Tyr¹¹-SS-14 demonstrated a significant reduction in binding density in the denervated parts of the neocortex. The decrease in specific binding was most pronounced (40-50%) in the superficial layers (I-III) of the frontal, parietal and temporal cortices 2 and 4 weeks after lesion. A significant loss in ¹²⁵I-Tyr¹¹-SS-14 binding in the deeper layers was only observed in the frontal cortex after 2 and 4 weeks. In the occipital cortex a significant decrease was measured in the superficial layers only after 4 weeks. The specific binding in all cortical regions returned to normal after 6 weeks. The results suggested that ¹²⁵I-Tyr¹¹-SS-14 binding 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.