On the mechanism of action of clonidine: effects on single central neurones.
1 Noradrenaline and clonidine were applied by microiontophoresis to single neurones in the cerebral cortex and medullary reticular formation of anaesthetized rats.2 Of a total of 247 neurones studied, 79% of medullary units and 60% of cortical units responded in the same manner to both noradrenaline and clonidine. The usual response was a depression of neuronal firing rate.3 It proved possible to antagonize some responses to both substances by the microiontophoresis of bulbocapnine, whilst leaving unaffected similar responses to 5-hydroxytryptamine.4 On 13% of the cells, clonidine produced an increase of firing rate. This effect could not be attributed to a post-synaptic antagonism of tonically released endogenous noradrenaline, but may indicate a presynaptic action of clonidine, reducing noradrenaline release.5 These observations are thought to support the idea that clonidine may have an agonist action on noradrenaline receptors in the brain.
D000818:Animals; D002540:Cerebral Cortex / Q000187:drug effects; D003000:Clonidine / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D004566:Electrodes; D066298:In Vitro Techniques; D007478:Iontophoresis; D008297:Male; D008526:Medulla Oblongata / Q000187:drug effects; D009474:Neurons / Q000187:drug effects*; D009638:Norepinephrine / Q000037:antagonists & inhibitors / Q000494:pharmacology; D051381:Rats; D012154:Reticular Formation / Q000187:drug effects; D012701:Serotonin / Q000494:pharmacology
D012701:Serotonin; D003000:Clonidine; D009638:Norepinephrine