TOSHIAKI J. HARA
94
mus was 17.8, 19.1, and 53.0 sec, respectively. No direct correlation between chemical structure and sensitivity was ascertained. According to
Humbach (1960), taste sensitivity of Anoptichthys for four basic taste
qualities was several thousands times better than that of Phorinus.
IV. ELECTROPHYSIOLOGICAL STUDIES OF CHEMORECEPTOR
RESPONSES
A. Olfactory System
Electrophysiological studies of the chemoreceptive functions of fishes
have not been extensive-partly because of small size of the structure
and partly because fish live in water. Adrian and Ludwig (1938) who
initiated analysis of the olfactory system in fishes with electrophysiological techniques recorded continuous impulse discharges in the olfactory
tract of the catfish, carp, and tench. Such a resting discharge with low
frequency and amplitude shifted to a maximum after a latency of 0.5-5
sec in response to mechanical as well as to chemical stimulation of the
olfactory sac. The response gradually decreased during stimulation ( adaptation) and was then followed by a refractory period lasting 5-20 sec
during which the organ was insensitive to a second stimulus. There has
been a marked increase in the number of electrophysiological studies of
fish olfactory system in the last few years.
1. MUCOSAL POTENTIALS
Resting potentials of the olfactory epithelium were recorded in some
teleost fishes with glass microelectrodes (Shibuya, 1960). They were
12.4 mV in Anguilla japonica, 8.7 mV in Misgurnus, 8.6 mV in Parasilurus,
and 7.6 mV in Channa, Cyprinus, and Entosphenus. Slow negative potentials were induced in the mucosa during stimulation with odorous fluids
such as butyric acid or extract of silkworm pupae (Fig. 6). The shape of
the potentials were different in different species of fishes. Generally, however, the potentials showed a fast-rising phase with a slower exponential
fall. The potential increased in time with increasing stimulus durations.
In Parasilums and Anguilla, it had a short duration (0.4-0.7 sec) with a
rapid decline. In the eel it always had a duration of about 0.4 sec regardless of stimulus duration ( Fig. 6e). Corresponding potentials were
simultaneously recorded in the olfactory nerves.
In addition to the “on-response” (appearing at the onset of stimulation), a distinct shift in potential appeared when stimulus ceased (“off-
94
mus was 17.8, 19.1, and 53.0 sec, respectively. No direct correlation between chemical structure and sensitivity was ascertained. According to
Humbach (1960), taste sensitivity of Anoptichthys for four basic taste
qualities was several thousands times better than that of Phorinus.
IV. ELECTROPHYSIOLOGICAL STUDIES OF CHEMORECEPTOR
RESPONSES
A. Olfactory System
Electrophysiological studies of the chemoreceptive functions of fishes
have not been extensive-partly because of small size of the structure
and partly because fish live in water. Adrian and Ludwig (1938) who
initiated analysis of the olfactory system in fishes with electrophysiological techniques recorded continuous impulse discharges in the olfactory
tract of the catfish, carp, and tench. Such a resting discharge with low
frequency and amplitude shifted to a maximum after a latency of 0.5-5
sec in response to mechanical as well as to chemical stimulation of the
olfactory sac. The response gradually decreased during stimulation ( adaptation) and was then followed by a refractory period lasting 5-20 sec
during which the organ was insensitive to a second stimulus. There has
been a marked increase in the number of electrophysiological studies of
fish olfactory system in the last few years.
1. MUCOSAL POTENTIALS
Resting potentials of the olfactory epithelium were recorded in some
teleost fishes with glass microelectrodes (Shibuya, 1960). They were
12.4 mV in Anguilla japonica, 8.7 mV in Misgurnus, 8.6 mV in Parasilurus,
and 7.6 mV in Channa, Cyprinus, and Entosphenus. Slow negative potentials were induced in the mucosa during stimulation with odorous fluids
such as butyric acid or extract of silkworm pupae (Fig. 6). The shape of
the potentials were different in different species of fishes. Generally, however, the potentials showed a fast-rising phase with a slower exponential
fall. The potential increased in time with increasing stimulus durations.
In Parasilums and Anguilla, it had a short duration (0.4-0.7 sec) with a
rapid decline. In the eel it always had a duration of about 0.4 sec regardless of stimulus duration ( Fig. 6e). Corresponding potentials were
simultaneously recorded in the olfactory nerves.
In addition to the “on-response” (appearing at the onset of stimulation), a distinct shift in potential appeared when stimulus ceased (“off-