Control of Locomotion in Marine Mollusk Clione Limacina. IX. Neuronal
Mechanisms of Spatial Orientation.
Panchin, Y. V., Y. I. Arshavsky, T. G. Deliagina, L. B. Popova, and G. N.
Orlovsky.
Institute of Problems of Information Transmission, Academy of Sciences of
Russia, Moscow 101447; Department of Biology, University of California, San
Diego, La Jolla, California 92093; Nobel Institute for Neurophysiology,
Department of Neuroscience, Karolinska Institutet, 17177 Stockholm, Sweden; A.
N. Belozersky Institute of Physico-Chemical Biology, Moscow State University,
Moscow 119899, Russia.
APStracts 2:0044N, 1995.
SUMMARY AND CONCLUSIONS
1. When swimming freely, the pteropod mollusk Clione limacina actively
maintains a vertical orientation, with its head up. Any deflection from the
vertical position causes a correcting motor response, i.e., bending of the
tail in the opposite direction, and an additional activation of the locomotor
system. Clione can stabilize not only the vertical orientation with its head
up, but also the posture with its head down. This is observed at higher water
temperature, as well as at a certain stage of hunting behavior. The postural
control is absent in some forms of behavior (vertical migrations, defensive
reactions, "looping" when hunting). The postural reflexes are driven
by input from the statocysts. After removal of the statocysts, Clione was
unable to maintain any definite spatial orientation. 2. Activity of the
neuronal mechanisms controlling spatial orientation of Clione was studied
in in vitro experiments, with the use of a preparation consisting of the CNS
and statocysts. Natural stimulation (tilt of the preparation up to 90 degrees
) was used to characterize responses in the statocyst receptor cells (SRCs).
It was found that the SRCs depolarized and fired (10_20 Hz) when, during a
tilt, they were in a position on the bottom part of the statocyst, under the
statolith. Intracellular staining has shown that the SRC axons terminate in
the medial area of the cerebral ganglia. Electrical connections have been
found between some of the symmetrical SRCs of the left and right statocysts.
3. Gravistatic reflexes were studied by using both natural stimulation (tilt
of the preparation) and electrical stimulation of SRCs. The reflex consisted
of three components: 1 ) activation of the locomotor rhythm generator located
in the pedal ganglia; this effect of SRCs is mediated by previously identified
CPA1 and CPB1 interneurons that are located in the cerebral ganglia and send
axons to the pedal ganglia; 2 ) bending the tail evoked by differential
excitation and inhibition of different groups of tail muscle motor neurons;
this effect is mediated by CPB3 interneurons; and 3 ) modification of wing
movements by differential excitation and inhibition of different groups of
wing motor neurons; this effect is mediated by CPB2 interneurons. 4.
Gravistatic reflexes in the tail motor neurons were inhibited or reversed at a
higher water temperature. 5. The SRCs are not $QUOTpure$QUOT gravitation
sensory organs because they are subjected to strong influences from the CNS.
In particular, CPC1 interneurons, participating in coordination of different
aspects of the hunting behavior, exert an excitatory action on some of the
SRCs, and inhibitory actions on others. It seems likely that, via these
central influences on SRCs, the spatial orientation of Clione can be
changed in relation to different forms of behavior.
Received 6 June 1994; accepted in final form 9 January 1995.
APS Manuscript Number J322-4.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 3 April 1995.