EFFECT OF AMMONIUM ACETATE ON THE SOMATOSTATINERGIC SYSTEM IN THE RATFRONTOPARIETAL CORTEX

Short (90 min)-, mid (5 days)-, and long-term (15 days) ammonium aceta te (5 mmol/kg IP) administration decreased the number of specific [I-1 25][Tyr11]somatostatin receptors in synaptosomes from the frontopariet al cortex without changing the affinity constant. Administration of am monium acetate did no affect the levels of somatostatin-like immunorea ctivity in the frontoparietal cortex. The administration of a single d ose of N-carbamyl-L-glutamate (1 mmol/kg) plus L-arginine(1 mmol/kg) 1 h before the last administration of ammonium acetate totally blocked the inhibitory effects of the latter on somatostatin receptor number i n the frontoparietal cortex synaptosomes. N-Carbamyl-L-glutamate plus L-arginine alone had no observable effect on the somatostatinergic sys tem. The decrease in the number of somatostain receptors induced by am monium acetate might reflect decreased target cell sensitivity to soma tostatin, a phenomenon that could contribute to the depressed neuronal excitability induced by ammonia in the rat frontoparietal cortex.