Modification by drugs used in anaesthesia of CNS stimulation induced in mice by laudanosine and strychnine.

We have investigated in mice the effects of several drugs which may be administered as part of an anaesthetic technique on the convulsive threshold to laudanosine and to strychnine, which is reported to have a similar mechanism of action. I.v. administered propofol, thiopentone and midazolam increased the dose of convulsant necessary to produce seizure when administered 2 min before the convulsive stimulus. In contrast, methohexitone and etomidate exhibited a proconvulsant effect, although with the latter this was significant only in laudanosine-treated mice. Pethidine was proconvulsant in both laudanosine- and strychnine-treated mice, but morphine was proconvulsant only in strychnine-treated mice. The effects of morphine, but not pethidine, were antagonized by naloxone 1 mg kg-1. Laudanosine, but not strychnine caused arousal from anaesthesia in subconvulsive doses. This and other evidence suggests that the mechanism of the CNS excitation produced by strychnine and laudanosine are not the same.