Effects of acetaldehyde on the monosynaptic reflex pathway in the cat spinal cord

The effects of acetaldehyde on monosynaptic reflexes were investigated in the cat spinal cord. Intravenous injection of lower doses of acetaldehyde (0.1-0.5 mg/kg) increased the amplitude of the ventral root monosynaptic reflex potentials elicited by the dorsal root stimulation; the amplitude was decreased at higher doses (1.0-10.0 mg/kg). Acetaldehyde hyperpolarized the motoneuron at lower and depolarized it at higher doses. In some cells, however, acetaldehyde induced an initial, brief depolarization and subsequent hyperpolarization. Depolarization increased with increasing the dose of acetaldehyde. Hyperpolarization was always associated with an increased amplitude of the monosynaptically-induced action potentials. Depolarization was accompanied by a decreased amplitude or block of the action potentials. During aldehyde-induced depolarization, antidromic action potentials were more severely depressed than orthodromic ones. The present results suggest that acetaldehyde acts predominantly on the motoneuron membrane resulting in hyperpolarization at relatively lower doses and in depolarization at higher doses.