DIFFERENTIAL SPATIAL PATTERNS OF FOS INDUCTION FOLLOWING GENERALIZED CLONIC AND GENERALIZED TONIC SEIZURES

The expression of generalized clonic and generalized tonic seizures ha s been suggested to result from the activation of different and indepe ndent neuronal circuits. Using the induction of the c-fos protein (Fos ) as a marker of neuronal activity, we identified brain structures tha t are differentially associated with the expression of electroconvulsi ve shock-induced generalized clonic and generalized tonic seizures. Ex pression of either seizure phenotype resulted in a similar bilaterally symmetrical increase in Fos immunoreactivity in many forebrain struct ures, including the bed nucleus of the stria terminalis, hippocampal d entate gyrus, amygdala, and piriform cortex, compared to controls. How ever, following tonic hindlimb extension (THE), the degree of labeling in specific thalamic, hypothalamic, and brain stem areas was signific antly greater than that of either controls or animals exhibiting cloni c seizures. While a greater number of neurons in the hypothalamus (e.g ., ventromedial nucleus), subparafascicular thalamic nucleus, peripedu ncular area, deep medial superior colliculus, dorsal and lateral centr al gray, and paralemniscal nuclei were robustly labeled following THE, noticeably fewer cells were immunoreactive following face and forelim b clonic seizure behaviors. These differences were also found to be in dependent of the stimulus magnitude. In animals stimulated with the sa me current intensity but expressing either of the two seizure phenotyp es, the pattern of Fos induction was consistent with the seizure pheno type expressed. These results demonstrate that specific subsets of neu rons are differentially activated following the expression of differen t generalized seizure behaviors and that activity in discrete mesencep halic and diencephalic structures is more frequently associated with t he expression of generalized tonic seizures than with the expression o f generalized clonic seizures. (C) 1997 Academic Press.