The interaction between the central and peripheral nervous systems in the mediation of gill withdrawal reflex behavior inAplysia

Abstract

We studied the relationship between the peripheral and central nervous system in mediating the gill withdrawal reflex. The central and peripheral nervous systems which mediate the gill withdrawal reflex interact and are parts of an integrated nervous system. The PNS initiates and mediates the behavior in the absence of the CNS. When the CNS is present, it bestows greater adaptability to the reflex evoked by peripheral stimulation. 1. Interposition of PNS activity affected the CNS mediated response. Tactile stimuli applied to the gill and siphon resulted in enhancement of the CNS mediated response (Fig. 2A). 2. Interposition of activity in the CNS affected the PNS mediated reflex. Branchial nerve stimulation resulted in suppression, while ctenidial nerve stimulation resulted in enhancement of the reflex (Fig. 2B). 3. Repeated depolarization of L7 (ISI 30 s) resulted in response decrement of its elicited gill withdrawal response (Fig. 3). 4. Repeated depolarization of LDG 1 (ISI 30 s) resulted in enhancement of its elicited gill withdrawal response (Fig. 10). These adaptive changes in L7 and LDG 1 occur at their peripheral terminations in the gill (Fig. 7). 5. Interposition of the PNS activity resulted in enhancement of the effectiveness of L7 and LDG 1 to elicit a gill withdrawal response (Figs. 4, 5, 11). 6. Activity in L7 and LDG 1 dishabituates the gill withdrawal reflex evoked by tactile stimulation of the gill and siphon (Fig. 6, 12). 7. Tonic activity in L7 and LDG 1 (1–3 spikes/s) enhances the amplitude of the gill withdrawal reflex (Fig. 13). 8. There are functional differences in the peripheral terminations of L7 and LDG 1 and the nature of the CNS-PNS interaction is pathway dependent. Branchial nerve terminations mediate decrement and suppression (Figs. 2, 8, 11); ctenidial nerve terminations mediate response increment and enhancement (Figs. 2, 8, 11). 9. The interaction takes place peripherally (Figs. 2, 7). We suggest that it occurs in the gill ganglion.