Latency of the nictitating membrane response to periocular electro-stimulation in unanesthetized rabbits

The latency of the nictitating membrane response (NMR) in rabbit (Oryctolagus cuniculus) to periocular electro-stimulation is a negative exponential function of stimulus current with an asymptote of approximately 17 msec. The NMR was recorded by means of a precision low-torque potentiometer like that employed in previous studies of NMR latency, and the criterion of response initiation employed here was similar to that employed in studies of classical conditioning in this preparation. Using estimates from physiological studies on surgically acute preparations, the minimum latency of the NMR of 17 msec can be decomposed as follows: 4 msec to fire motoneurons of the accessory abducens nucleus; 9 msec for conduction, synaptic transmission, and recruitment of retractor bulbi muscle fibers; 4 msec for the nictitating membrane to initiate its sweep after eyeball retraction. The implications of these estimates for chronic unit-recording studies of the conditioned NMR are discussed.