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First published online January 31, 2006
Journal of Experimental Biology 209, 766-779 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02049

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Classical conditioning of activities of salivary neurones in the cockroach

Hidehiro Watanabe and Makoto Mizunami^*

Graduate School of Life Sciences, Tohoku University, Katahira 2-1-1, Sendai 980-8577, Japan

^* Author for correspondence (e-mail: makoto{at}biology.tohoku.ac.jp)

Accepted 20 December 2005

Secretion of saliva to aid swallowing and digestion is a basic physiological function found in many vertebrates and invertebrates. For mammals, classical conditioning of salivation in dogs was reported by Pavlov a century ago. However, conditioning of salivation or of related neural activities in non-mammalian species has not been reported. In many species of insects, salivation is regulated by salivary neurones. In this study, we found that salivary neurones of the cockroach Periplaneta americana exhibited a strong response to sucrose solution applied to the mouth and a weak response to odours applied to an antenna, and we studied the effect of conditioning on the activities of salivary neurones. After three sets of differential conditioning trials in which an odour was presented just before the presentation of sucrose solution and the other odour was presented alone, the response of salivary neurones to sucrose-associated odour significantly increased but that to the odour presented alone was unchanged. Backward pairing trials in which an odour was presented after the presentation of sucrose solution were not effective in achieving conditioning. Our study of the change in the level of saliva secretion in response to electrical stimulation of salivary neurones suggested that the magnitude of increase in odour response of salivary neurones by conditioning is sufficient to lead to an increased level of salivation. This study suggests classical conditioning of salivation in an insect.

Key words: learning, memory, olfaction, taste, salivary neurones, insect

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