IN VITRO APPETITIVE CLASSICAL CONDITIONING OF THE FEEDING RESPONSE IN THE
POND SNAIL LYMNAEA STAGNALIS.
Gyrgy Kemenes, Kevin Staras and Paul R. Benjamin.
Sussex Centre for Neuroscience, School of Biological Sciences, University
of Sussex, Falmer, Brighton, United Kingdom, BN1 9QG.
APStracts 4:141N, 1997.
ABSTRACT
An in vitro preparation was developed that allowed electrophysiological
analysis of appetitive conditioning of feeding in the model molluscan system,
Lymnaea. The network generating the feeding motor program (fictive feeding) is
well-characterized at the cellular level and consists of identified central
pattern generator (CPG) interneurons, motoneurons and modulatory interneurons.
Activation of a modulatory interneuron, the Slow Oscillator (SO), evokes the
three-phase fictive feeding rhythm in the same semi-intact preparations where
tactile stimuli can be applied to the lips. By pairing touch as a conditioned
stimulus (CS) with stimulation of the SO as an unconditioned stimulus (US) we
established an effective in vitro paradigm for appetitive conditioning. Before
training, touch to the lips evoked only brief and weak activity in the feeding
interneurons and motoneurons. After 6 to 10 conditioning trials, there was a
significant enhancement in the fictive feeding response to CS alone. This was
not seen in controls (CS only, US only, random CS and US) and in preparations
where there was no initial brief response to touch prior to conditioning.
Following training, the CS activated the fictive feeding without an increased
activation of the SO or the serotonergic modulatory interneuron CGCs. Direct
recordings from the protraction phase N1M interneurons during in vitro
conditioning indicated that the enhancement of the fictive feeding is due to
an increased activation of these CPG cells by mechanosensory inputs from the
lips. We also found that the conditioned response was not due to a facilitated
activation of modulatory neurons in the feeding network, such as the Slow
Oscillator (SO) or the Cerebral Giant Cells (CGCs), because the activity of
these cells remained unchanged following conditioning.
Received 27 March 1997; accepted in final form 30 June 1997.
APS Manuscript Number J256-7.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 27 August 1997