Conditioned cardiac reflexes in fish after stimulation of the surface of the head with varied sugar solutions

Abstract

Comparative physiological investigations suggest that spatial orientation in fish results from combined activity of several analyzers (2, 4). Less attention has been paid to the study of chemical perception in adaptive behavior than of other sensory systems. Data on the physiology and structure of the chemical analyzer have been obtained in higher animals in studies of interoceptive stimulation (1, 3, 10, 11, 13).

Chemical analysis, as a factor in adaptation, is particularly important in aquatic animals, especially in fish. Experiments to study the responses of fish to chemical agents have shown that they can perceive sweet, bitter, sour, and salt sensations (5, 19, 20, 23, 25–27); these findings relate to both receptors of the oral cavity and chemoreceptors on the outer surface of the body. A conditioned-reflex technique has determined the degree of discrimination of salt concentration and pH in seawater (18) and the ability of fish to form conditioned reflexes to very low concentrations of carbon dioxide (14, 15).

Recent electrophysiological investigations have shown responses in the nerve fibers supplying chemoreceptors of the oral cavity, the body surface and its appendages (17, 21, 22).

The investigation described below (part of a series of investigations of peripheral and central mechanisms of nonolfactory chemical reception in fish) was designed to study 1) the ability of fish to form conditioned cardiac reflexes to chemical stimulation of the skin on the surface of the head, 2) the degree and range of analysis of different sugars and their concentrations, 3) the role of the forebrain in these responses.