The role of the locus coeruleus in regulation of seizure susceptibility in rats.

When studying the role of the locus coeruleus (LC) in the regulation of seizure susceptibility in rats, we found that bilateral LC lesion significantly lowered the electroshock seizure threshold for the tonic extension of forelegs. The pattern of maximal electroshock seizure was not affected by LC lesion, although the recovery time was slightly prolonged. In the pentylenetetrazol (PTZ) seizure threshold test, LC lesion significantly elevated the twitch threshold, but did not affect the threshold for the generalized clonic seizure or clonic convulsion. Incidence of the tonic extension in the PTZ seizure test tended toward an increase with LC lesion. Biochemical determinations revealed that LC lesion significantly decreased the norepinephrine contents in various brain regions as well as the 5-hydroxytryptamine contents of some brain regions, but not the 5-hydroxyindoleacetic acid contents. These results suggest that while the LC is involved in the regulation of seizure susceptibility, the involvement differs with various types of seizures.