Changes in immunoreactive somatostatin in brain following lidocaine-induced kindling in rat

The kindling phenomenon has become a useful model for studying epileptogenesis. The present authors have previously reported increased levels of immunoreactive somatostatin (IR-SRIF) in various regions of the brain of electrically-amygdaloid kindled (EAK) rats. In this study, an examination was made of immunoreactive somatostatin in pharmacologically-kindled (PK) rats. Sixteen male Sprague-Dawley rats were injected intraperitoneally (i.p.) with a subthreshold dose of lidocaine (60 mg/kg), once daily. Once the kindling phenomenon was established, kindled rats (7), non-kindled rats (9) and controls (6) were sacrificed by microwave irradiation. Another group of 5 rats was injected with a single suprathreshold dose of lidocaine (110 mg/kg) and killed 10 min after the resultant seizure. Various brain areas were removed and assayed for immunoreactive somatostatin in kindled rats. Immunoreactive somatostatin was significantly greater than in controls in the amygdala (56%; P less than 0.02), entorhinal + piriform cortex (50%; P less than 0.05) and hypothalamus (29%; P less than 0.02). In non-kindled rats, immunoreactive somatostatin increased only in the amygdala (58%; P less than 0.02). No difference was found in the immunoreactive somatostatin content of rats injected with an suprathreshold dose of lidocaine compared to controls. The alteration of immunoreactive somatostatin, in both lidocaine-kindled and electrically-amygdaloid kindled rats suggests a possible role of this neuropeptide in kindling.