Central monaminergic neuronal effects on minimum alveolar concentrations (MAC) of halothane and cyclopropane in rats

The effect of interference with central catecholamine- or serotonin-containing neurons on the response of rats to inhalation anesthetics were explored. Interference with catecholaminergic function by inhibition of amine synthesis with alpha-methyltyrosine alone or combined with destruction of these neurons by 6-hydroxydopamine reduced brain concentrations of norepinephrine and dopamine without altering serotonin concentrations. These alterations decreased the minimum alveolar concentration (MAC) of halothane when tail-clamping was used as the test stimulus. Similar small reductions of halothane MAC were produced in rats given 5,6-dihydroxytryptamine and p-chlorophenylalanine, which decreased brain serotonin without altering noreopinephrine or doapamine concentrations. When catecholaminergic or serotoninergic neuronal function was similarly disrupted in rats later exposed to cyclopropane, no alternation in MAC was observed. It is suggested that disruption of central amine-containing neurons may lower the MAC's of depressant anesthetics only, and not excitatory anesthetics.