Characterization of Receptor‐Coupled Phosphoinositide Hydrolysis in the Rat Hippocampus After Intradentate Colchicine

Abstract: Lesions produced by intradentate hippocampal administration of colchicine have been reported to produce several time‐dependent behavioral and neurochemical changes, including a possible change in the signal transduction process for the cholinergic muscarinic receptor. To characterize further the effects of colchicine on receptor‐coupled hydrolysis of phosphoinositides, colchicine was injected ste‐reotaxically into the dentate gyrus of rats at a dose of 2.5 μg/ site. The animals were killed 1, 3, or 12 weeks after injection and the hippocampi removed and sliced. [3H]Inositol was incorporated into slices, and various receptor agonists known to stimulate inositol phosphate (IP) metabolism were studied. Colchicine administration altered agonist‐stimulated turnover in the hippocampus in a time‐dependent manner. This hy‐perstimulation was receptor‐mediated, because it was blocked by pirenzepine. The hyperstimulation of turnover was observed also with norepinephrine and serotonin. Colchicine had no effect on IP turnover in vitro. The effect of the colchicine lesion was observed only in the hippocampus, because no change in cholinergic muscarinic receptor‐stimulated phosphatidylinositol turnover was observed in the cortex. These studies indicate that intradentate administration of colchicine produces a compensatory change in the signal transduction process in the hippocampus detectable 12 weeks after the lesion.