HABITUATION IN LIMULUS ABDOMINAL GANGLIA

¹ Division of Biopsychology, University of Waterloo, Waterloo, Ontario

1. Extracellular recordings were made from dorsal root units in the abdominal ganglia of Limulus. These units are activated by tactile stimulation of the gill book covers.

2. The response in these units to repeated puffs of air directed on a gill book is a rapid decline in activity. The response "spontaneously recovers" with time when the stimulus is withheld. Stronger stimuli or different stimuli (water drops) produce an immediate recovery of the diminished responsivity; this recovery is similar to "dishabituation" noted in other studies and rules out fatigue as an explanation for the dorsal root response decrement. Sensory fatigue or adaptation are ruled out by the demonstration that repeated puffs of air do not produce any response decrement in the nerves (ventral roots) which carry the afferent tactile information.

3. The relationship between the number of ganglia and the acquisition of habituation was examined and no differences were found. However, during retests the Intact and Isolated Ventral Cord preparations demonstrated a better persistence of the response decrement.

4. These findings are discussed with respect to habituation data obtained by others in invertebrates.