Brain noradrenaline and anaesthesia: behavioural and electrophysiological evidence

Neonatal administration of 6-hydroxydopamine to rat pups was used to deplete brain noradrenaline in the locus coeruleus projection system to less than 5% of normal and the response to barbiturate and non-barbiturate anaesthetics examined. The sleeping time in response to administration of thiopentone, pentobarbitone, methohexitone or hexobarbitone was markedly increased in 6-hydroxydopamine-treated rats, as it was for the non-barbiturates chloral hydrate and diisopropylphenol. The sleeping time for other non-barbiturates such as althesin, ketamine and ethyl carbamate (urethane) was not affected in noradrenaline-depleted rats. Similarly, an index of the evoked potential, recorded in the primary somatosensory cortex to supramaximal electrical stimulation of the forepaw, decreased more markedly with increasing doses of thiopentone in 6-hydroxydopamine-treated rats than in controls. Potentiation of the effect of diisopropylphenol on the evoked cortical response was also seen in noradrenaline-depleted rats while the effect of althesin did not differ. It is suggested that brain noradrenaline pathways originating from the locus coeruleus may play an important role in the duration and depth of anaesthesia resulting from barbiturate and some related agents.