Actions of immobilizing drugs on synaptic transmission

Abstract

Because some immobilizing agents reportedly have a central action, we investigated the effects of gallamine (Flaxedil) and decamethonium (Syncurine) on synaptic transmission. In spinal cats, ventilated with oxygen, we stimulated a lumbar dorsal root and recorded the compound reflex action potential in the ipsilateral ventral root. Gallamine, 6.25 mg/kg, had no discernible effect on the ventral root reflex. Gallamine, 12.5 mg/kg, affected neither the height of the monosynaptic spike nor the latency to its onset; but the polysynaptic response (area under the multiphasic portion of the potential curve) was increased in the first 5 min, then returned to baseline. These changes were associated with moderate hypertension. Decamethonium, 0.5 mg/kg, profoundly depressed the monosynaptic and polysynaptic ventral root responses, and increased the latency to onset of the reflex. These changes were associated with a marked hypotension. Gallamine given in customary paralyzing doses (1–2 mg/kg) has virtually no effect on synaptic transmission in the spinal cord, whereas decamethonium depresses transmission.