Action of baclofen on mammalian synaptic transmission

Microiontophoretic and systemic injections were used to investigate the mechanism of baclofen's powerful depressant action on transmission at primary afferent synapses in the cat. Iontophoretic applications depressed the spontaneous and evoked activity of cuneate cells and reduced the excitability and input resistance of spinal motoneurones. These effects, which were quick to reverse, resemble those of γ-aminobutyrate and may be due to activation of γ-aminobutyrate receptors by high concentrations of baclofen. Systemic doses of baclofen (0.1–5 mg/kg i.V.), which are known to give only a very low tissue concentration (