Kainic acid induced seizures: changes in somatostatin, substance P and neurotensin

The neuropeptides somatostatin, neurotensin and substance P were investigated in rats during and after limbic seizures induced by systemic injection of kainic acid (10 mg/kg, i.p.). Three hours after injection of the toxin, pronounced decreases (40-50%) in somatostatin-like immunoreactivity in frontal cortex, striatum, dorsal hippocampus and amygdala/pyriform cortex were observed. Concomitantly, neurotensin-like and substance P-like immunoreactivities were also reduced in the frontal cortex and the hippocampus. These early decreases in peptide levels may result from increased release and subsequent inactivation of the peptides during acute seizures. At later time intervals, 3, 10 and 30 days after injection of kainic acid, the initially decreased peptide levels were partially normalized. However, the reduction in somatostatin-like immunoreactivity in amygdala/pyriform cortex and striatum persisted up to 30 days. Neurotensin-like immunoreactivity remained decreased in the frontal cortex. On the other hand, neurotensin- and substance P-like immunoreactivities were increased in the striatum and substantia nigra 10-30 days after injection of kainic acid. These late changes in peptide levels may suggest destruction of peptidergic neurons or adaptive changes induced by the convulsions. Pretreatment of rats with cysteamine (100 mg/kg, i.p.), an agent which decreases brain somatostatin levels, had no effect on the intensity of kainic acid induced convulsions, although a slightly earlier onset of seizures was observed. The changes in peptide levels, especially the marked decreases in somatostatin content after systemic injection of kainic acid, suggest considerable acute and chronic alterations in peptidergic systems caused by limbic convulsions.