The electrical responses of the olfactory epithelium of some fishes.

The electrophysiological studies on the olfactory nervous system have been very few compared with those on the other sensory organs. It is well known that the fish can well smell out odorous substances in water. By observing the behaviour of fishes, Parker (1910, 1911) made it clear that the catfish and the killifish are able to smell odorous materials in water, and provided evidence that gustatory and olfactory perceptions are not the same in these fish. Olmsted (1918) observed that the catfish could not respond to olfactory stimulation when the olfactory organ was eliminated, and that blinded fishes found foods as readily as normal fishes did. Adrian and Ludwig (1938) recorded the discharges produced by olfactory stimulation in the olfactory nerve of the catfish, carp and tench. The discharges increased rapidly to maximum after a latency of 0.5 to 5 sec., and then decreased very slowly. When a decoction of aniseed was used as stimulus, discharges appeared not only when it was given, but also when it was washed out with water ('off-effect'). It was suspected that this 'off-effect' might be due to mechanical stimulation of flowing water. Gasser (1956) studied the structure of the olfactory nerve fiber of the pike by means of an electron-microscope, and recorded the action potential of the nerve produced by electrical stimulation. The electrical activity of the olfactory epithelium, however, has not been studied in fish, though it has in the dog (Hosoya and Yoshida, 1937 a, b) and in the frog (Ottoson, 1956, 1958; Takagi and Shibuya, 1959, 1960 a). Takagi and Shibuya (1959, 1960 a, b, c) recently found that there are three types of responses, that is, the on-, the on-offand the offresponses in the olfactory epithelium of the frog and the toad. Thus, studies on the olfactory nervous system of fishes have been limited only to the activity of the olfactory nerve. In oder to clarify the function of the olfactory nervous system, it seems necessary to study the activity of the olfactory epithelium first, and then that of the higher olfactory pathway. It also seems important to compare these activities in the fish with those in the terrestrial animals. This paper is concerned with the responses of the olfactory epithelium of some fishes. The results are compared with the olfactory responses in the frog and the toad.