Which mechanism of action is expected to decrease spasticity in a patient with upper motor neuron dysfunction?

To decrease spasticity in a patient with upper motor neuron dysfunction, the mechanism involving the activation of GABA receptors in muscle spindle afferents is particularly effective. GABA (gamma-aminobutyric acid) is an inhibitory neurotransmitter in the central nervous system. When GABA receptors are activated, they promote hyperpolarization of neurons, leading to a decrease in excitatory output from those neurons.

In the context of muscle spindle afferents, this action leads to reduced excitability and consequently lowers the reflexive muscle contractions that characterize spasticity. Spasticity often arises from an imbalance between excitatory and inhibitory signals in the nervous system due to upper motor neuron lesions. Thus, enhancing GABAergic activity helps to restore this balance and provides relief from spasticity.

This mechanism is a fundamental therapeutic target in conditions like multiple sclerosis, cerebral palsy, and stroke where spasticity is a common feature. By focusing on enhancing inhibitory pathways, we can effectively manage the symptoms and improve the quality of life for patients suffering from such conditions.