Egg laying in Aplysia. I. Behavioral patterns and muscle activity of freely behaving animals after selectively elicited bag cell discharges.

Aplysia egg laying is a complex sequence of head and neck movements initiated by the release of ovulatory and neuroactive hormones from the neurosecretory bag cells. This behavioral pattern is difficult to study in reduced preparations, because they do not show ovulation or egg laying behaviors. This paper describes the use of chronically implanted electrodes to elicit normal neurosecretory activity and provides an analysis of egg laying behaviors and the underlying muscle activity in intact, freely behaving A. californica and A. brasiliana. 1. Bag cell discharges elicited with a fine wire electrode implanted in the connective tissue sheath above the cell bodies were typically without noxious behavioral side effects. 2. Following selectively elicited bag cell discharges, egg laying consisted of four rhythmic head and neck movements that were separated functionally into appetitive behaviors ('waves' and 'undulations') used to explore and prepare the substrate and consummatory behaviors ('weaves' and 'tamps') used to distribute and attach the egg string. The amount of time an animal performed consummatory behaviors was positively related to the amount of eggs deposited. By contrast, the appetitive phase of egg laying was independent of the size of the egg mass. 3. The individual behaviors and their temporal sequence were similar following selectively elicited bag cell discharges, spontaneous discharges of animals with implanted electrodes and during normal egg laying of unoperated animals. 4. Three longitudinal muscle systems occurred within the head and neck. Following a selectively elicited bag cell discharge, spatially and temporally coordinated patterns of EJP bursts of different durations were recorded chronically from each muscle group. These EJP patterns were characteristic for specific head and neck movements used in appetitive and consummatory egg laying behaviors.