Facilitation of spinal synaptic transmission by catechol

Abstract

In spinal unanaesthetized cats, intravenously administered catechol (2.5–5.0 mg/kg) produced an immediate increase in the size of the monosynaptic and polysynaptic responses, the dorsal root potential and reflex, and in spontaneous ventral and dorsal root activity. Presynaptic as well as postsynaptic inhibition was not reduced. Catechol produced a differential effect on paired, maximal, dorsal root stimuli, increasing the discharging zone evoked by the initial stimulus significantly more than that evoked 400 msec later. Furthermore, repeated administration of equal doses at regular intervals produced progressively decreasing facilitatory effects on the monosynaptic response. Catechol did not modify the focally recorded initial spike representing the activity of afferent terminals after peripheral stimulation, nor did it alter the excitability of these terminals or of motoneuronal somas. The possibility that catechol may increase transmitter release from afferent terminals is discussed.