A 41-year-old man suffering from amyotrophic lateral sclerosis presented to his
physician with muscle fasciculations, spasticity of limbs, hyperactive deep tendon
reflexes and extensor plantar reflexes. Baclofen was prescribed to reduce spasticity and
cramps. Which of the following actions most likely mediated the therapeutic effect of the
drug in the patient’s disease?
A. Activation of GABA B receptors in the spinal cord B. Blockade of Nm receptors of motor end plate C. Increased substance P release in the spinal cord D. Blockade of CA++ channels in the skeletal muscle membrane E. Increased K+ conductance in the skeletal muscle membrane
Activation of gaba b receptors in the spinal cord-learning objective: describe the mechanism of action of baclofen.answer: abaclofen is an agonist at gaba b receptors. activation of these receptors by baclofen results inhyperpolarization of presynaptic terminals, probably by increased k+ conductance. thishyperpolarization reduces the release of excitatory transmitters in both the brain and the spinalcord. baclofen is at least as effective as diazepam in reducing spasticity and is frequently usedfor this purpose.b) this would be the action of nondepolarizing neuromuscular blockers.c) actually baclofen can cause blockade of substance p release from spinal cord and this seemone of the reasons of its analgesic activity in patients with spasticity.d, e) baclofen can indirectly block ca++ channels as a consequence of membranehyperpolarization, and can increase k+ conductance, but these actions occur in neuronal, nor inskeletal muscle membrane.