[Neurophysiological mechanisms of the reflex lacrimation].

Neurophysiological mechanisms of the reflex lacrimation were analyzed in anesthetized rabbits. The secretory pattern of the lacrimation elicited by stimulation of the cornea consisted of two phases, that is, a rapid flow phase during stimulation and the subsequent slow flow phase in post-stimulus time. Parasympathetic nerve activities are closely related to the secretory volume in the rapid flow phase of the reflex lacrimation. On the other hand, excitation of the sympathetic nerve depressed the secretion in the rapid flow phase, while it facilitated slightly the secretion in the slow flow phase. The postganglionic parasympathetic fibers innervating the lacrimal gland showed two responses, i.e., the early and late discharges, when a single electrical shock was applied to the cornea. Their latencies were 68.7 +/- 8.7 msec and 173.3 +/- 14.2 msec, respectively. The threshold of the late response was about 10 times greater than that of the early one. With moderate anesthesia by pentobarbital or with transection of lateral 1/3 of medulla oblongata at the rostral level of the subnucleus caudalis of the spinal trigeminal nucleus, the late response was abolished whereas the early one was left almost unaffected. It is assumed that the early response is elicited by afferent impulses transmitted via the rostral part of the trigeminal sensory nuclear complex and the late one via the caudal part of the complex and also possibly the reticular formation.