Action of clonidine on centrally evoked salivation in anaesthetized cats.

1. Clonidine (4 microgram/kg) given intracisternally to anaesthetized cats inhibited brain stem-evoked parasympathetic submaxillary or parotid salivation by 62% at 5 Hz and 44% at 15 Hz. 2. The inhibitory action of clonidine on salivation was equally prevented by pretreatment with either intracisternal yohimbine (175 microgram/kg) or phentolamine (250 microgram/kg), used as preferential pre- and post-synaptic alpha-adrenoreceptor-blocking drugs respectively. 3. the inhibition of centrally evoked salivation by clonidine is due to an action on alpha-adrenoreceptors but no clear evidence was obtained to indicate whether these were located pre- or post-synaptically. This is in contrast to the preferential presynaptic action of clonidine in reducing peripheral parasympathetic nerve-evoked salivation.