Possible involvement of brainstem norepinephrine in pentylenetetrazol convulsions in rats

The thresholds of twitch and clonic convulsion induced by intravenous infusion of pentylenetetrazol (PTZ) were measured in rats treated with 6-hydroxydopamine (6-OHDA). In adult rats, intraventricularly applied 6-OHDA increased susceptibility to PTZ convulsions and decreased norepinephrine (NE) contents of the cortex, hypothalamus and brainstem. When 6-OHDA was applied intraventricularly at 8 days after birth, PTZ convulsion susceptibility was slightly decreased and brainstem NE content was significantly increased. However, the effects of 6-OHDA given at 20 days after birth were similar to those observed in adults. Significant decrease of cortical and hypothalamic NE contents, but no change in PTZ convulsion susceptibility, occurred following 6-OHDA injections into the dorsal and ventral NE bundles. These results suggest that the brainstem NE neurons play an inhibitory role on the development of PTZ convulsions.