G. P. Ferguson

Spontaneous and induced egg laying behavior of the pond snail lymnaea-stagnalis

SummaryInLymnaea egg laying is initiated by the discharge of the neurosecretory caudodorsal cells (CDCs), which release an ovulatory hormone (caudodorsal cell hormone; CDCH) and other peptides. Egg laying is a complex behavioral pattern composed of various postures and action patterns. This paper describes the egg laying behavior of intact and freely behaving animals as it occurs spontaneously after an environmental stimulus (clean water stimulus; CWS), and following injections of highly purified CDCH. CDC discharges were monitored in vivo with chronically implanted electrodes. In these animals the egg laying behavior following spontaneous and electrically elicited CDC discharges was analyzed.1.The egg laying behavior induced by the CWS consisted of three separate phases that occurred in a fixed temporal sequence. Shortly after transferral to clean water, animals became quiescent (resting). This was followed by an active phase (turning) during which behaviors were performed to prepare the substrate for the subsequent oviposition phase. Following oviposition, animals examined the deposited egg mass.2.After spontaneous CDC discharges and CDC discharges elicited by selective electrical stimulation of the CDCs (with a chronically implanted fine wire electrode) the egg laying behavior was the same as that following the CWS. All phases of egg laying behavior followed the CDC discharge.3.In contrast, the egg laying behavior following injections of highly purified CDCH was different to that following the CWS. These animals showed no resting phase. Instead, they continued locomoting and entered directly into the turning phase. The animals that did not lay eggs after injection because they were refractory did not show egg laying behavior.4.The durations of the joint turning and oviposition phases depended strongly on clutch size, suggesting that the ovulated eggs are instrumental in causing this behavior.5.We conclude that whenever egg laying is preceded by a CDC discharge, either occurring spontaneously or induced by CWS or electrical stimulation, the behavior differs from that following injections of CDCH directly into the blood. This demonstrates that the presence of CDCH in the blood is not sufficient to produce the full complement of egg laying behaviors and suggests that CDCH, or one of the other peptides released during a CDC discharge, has important local effects within the CNS.

Egg laying inAplysia

SummaryAplysia 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 behavingA. californica andA. 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.

Control of egg laying behaviour patterns in Lymnaea stagnalis

Publisher Summary This chapter discusses the egg laying behavior of Lymnaea, which is initiated by the discharge of the neurosecretory caudodorsal cells (CDCs). These cells are electronically coupled and have their somata in the cerebral ganglia. The egg laying behavior of Lymnaea is observed under five different conditions: (1) spontaneous egg laying of unoperated animals, (2) induced egg laying after clean water stimulus, (3) spontaneous egg laying of animals where the CDCs are monitored using fine wire electrodes, (4) egg laying elicited by electrical stimulation of the CDCs through fine wire electrodes, and (5) induced egg laying following the injection of purified and synthetic CDCH. The neuroendocrine system controlling egg laying behavior in Lymnaea is similar to systems controlling the reproductive behavior of a wide range of animals. Egg laying behavior involves both the neuroendocrine system and a number of motor routines borrowed from other behaviors, including locomotion, feeding, and shell twisting. These routines are clearly modified during egg laying behavior, and this raises the question of how these motor routines are reorganized depending on the behavior in which they occur.