Depression of h-reflex following carbonic anhydrase inhibition appears unrelated to changes in synaptic effectiveness.
Presynaptic inhibition (PI) of Ia afferents was examined as a possible contributor to the depression of the soleus H-reflex following carbonic anhydrase (CA) inhibition with Acetazolamide (ACZ). Ten males (aged 22-32) were studied in two randomized conditions, control and ACZ administration (250 mg 14, 8, and 2 h before testing) separated by at least one week. PI of soleus Ia afferents was indirectly assessed two ways: a conditioning stimulus of Ia afferents in the common peroneal nerve (N = 6), and heteronymous Ia facilitation from the quadriceps to soleus muscle (N = 4). Conditioning (C) of the soleus H-reflex (common peroneal nerve stimulation protocol) resulted in depression of the H-reflex in the supine and standing position compared to the test (T, unconditioned) H-reflex in the same position. This result was unaltered following ACZ treatment. C (heteronymous facilitation protocol) resulted in facilitation of the H-reflex in the supine, but not the standing position. This result was unaltered following ACZ treatment. It was concluded that the depression of the H-reflex following CA inhibition (present study; Brechue et al., 1997) appears to be unrelated to changes in the tonic level of PI of Ia afferents. The best hypothesis for the reduction in the H-reflex appears to be conduction block of the primary afferent fibers secondary to local increases in PCO2.
Beekley
Matthew D
MD
United States Military Academy, West Point, New York, USA.
Brechue
William F
WF
D000086:Acetazolamide / Q000008:administration & dosage / Q000494:pharmacology*; D000328:Adult; D002257:Carbonic Anhydrase Inhibitors / Q000008:administration & dosage / Q000494:pharmacology*; D004576:Electromyography; D006181:H-Reflex / Q000187:drug effects*; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000187:drug effects; D009475:Neurons, Afferent / Q000187:drug effects; D010543:Peroneal Nerve / Q000187:drug effects; D011187:Posture; D016683:Supine Position; D013569:Synapses / Q000187:drug effects*
D002257:Carbonic Anhydrase Inhibitors; D000086:Acetazolamide