Defense reaction in the pond snail Planorbis corneus. III. Response to input from statocysts

Abstract

1. In the intact pond snail Planorbis corneus, a rapid tilt in any plane evoked a defense reaction consisting of a fast movement of the shell towards the head, shortening of the foot, inhibition of locomotion and of rhythmical feeding movements. This reaction was similar to the first phase of the general defense reaction of Planorbis to cutaneous stimulation. 2. A method has been developed for inclination of the isolated CNS in space (up to 90 degrees) and simultaneous intracellular recordings from different neurons. 3. The statocyst receptor cells (SRCs) responded both phasically and tonically to the tilt. The SRCs differ in their spatial zones of sensitivity. 4. Essential manifestations of the defense reaction to the input from statocysts could be observed in the in vitro preparation of the CNS isolated with statocysts. Both tilting of the CNS and electrical stimulation of individual SRCs elicited an excitatory response in numerous neurons from different ganglia, including motor neurons (MNs) of the columellar muscle. This response was of "all-or-none" nature, and could be evoked by electrical stimulation of any SRC. The response was followed by a long (10-20 s) period of refractoriness. 5. Activation of SRCs resulted also in excitation of the giant dopaminergic cell in the left pedal ganglion (related to the control of respiration), in inhibition of the feeding rhythm generator, and in inhibition of the pedal neurons responsible for activation of the ciliary locomotor system. 6. Combined stimulation of two inputs able to evoke a defense reaction, i.e., those from the statocyst and from cutaneous nerve, revealed a strong interdependence of their central effects.(ABSTRACT TRUNCATED AT 250 WORDS)

Network interneurons underlying ciliary locomotion inHermissenda

“…Graviceptive stimulation of Hermissenda in a horizontal orientation produces a shortening of the foot and an inhibition of forward ciliary locomotion (Lederhendler et al 1986;Matzel et al 1990). A similar defensive response is elicited in the pond snail Planorbis, where the activation of statocyst receptor cells by rapid tilting evokes foot shorting and inhibition of ciliary locomotion (Arshavsky et al 1994). In contrast, Hermissenda placed in a vertical orientation exhibit a gravitactic reponse that involves the initiation of ciliary locomotion in the direction opposite the gravitational force vector.…”