Effects of baclofen and gamma-aminobutyric acid on different types of medullary respiratory neurons.

Effects of baclofen and gamma-aminobutyric acid on medullary respiratory neurons were investigated. Medullary inspiratory neurons of the dorsal and ventral respiratory groups were stimulated by baclofen, 0.5-2 mg/kg, and depressed by doses greater than 4-6 mg/kg. Expiratory neurons were depressed by doses of baclofen which increased phrenic nerve activity. Microelectrophoresis of baclofen (5 mM, pH 3) depressed medullary inspiratory neurons. It is suggested that low i.v. doses of baclofen increase inspiratory activity by disinhibition of medullary neurons whereas higher doses directly depress medullary inspiratory neurons.