Head twitches induced by benzodiazepines and the role of biogenic amines

Clonazepam, one of the benzodiazepines, induced head twitches in mice in a dose-dependent manner and sustained them for at least 120 min. Some of the benzodiazepines such as nitrazepam, fludiazepam, and nimetazepam also significantly induced head twitches at doses higher than 10 mg/kg, but other benzodiazepines like diazepam, flurazepam, oxazepam, medazepam, and chlordiazepoxide did not significantly induce head twitches at doses up to 60 mg/kg. The head twitches induced by clonazepam were more strongly blocked by a n antiserotonin drug, cyproheptadine than catecholamine receptor blocking drugs, haloperidol, propranolol, and phentolamine, and were not blocked by GABA receptor blocking drugs, bicuculline and picrotoxin, as well as by a glycine receptor blocking drug, strychnine. Clonazepam also increased the head twitches induced by mescaline, a serotonin receptor stimulant. These results indicate that the head twitches induced by clonazepam might be mediated via serotonergic neuron systems.