What is the mechanism of action of the muscle relaxant baclofen?

Baclofen functions primarily as a GABA-B receptor agonist. The mechanism is centered on its action in the central nervous system, where it binds to GABA-B receptors. Activation of these receptors leads to increased potassium conductance, resulting in hyperpolarization of the neuronal membrane and a subsequent decrease in the release of excitatory neurotransmitters. This action ultimately contributes to muscle relaxation and reduction of spasticity, making baclofen effective in managing conditions such as multiple sclerosis and spinal cord injury.

The other options describe different mechanisms and receptors that are not involved in baclofen's action. For instance, GABA-A receptor agonists primarily function by enhancing the effects of GABA, leading to increased chloride ion influx and neuronal inhibition, but this is not the action of baclofen. NMDA receptor antagonists block excitatory glutamate receptors and are typically used for different therapeutic purposes, such as managing neuropathic pain. Muscarinic receptor antagonists primarily affect the parasympathetic nervous system, influencing actions such as glandular secretion and smooth muscle contraction, and do not play a role in baclofen's muscle relaxant properties.