4. CHEMORECEPTION
101
sponses to sucrose, levulose, and glycine increased asymptotically with
increasing concentrations, while that for dextrose was sigmoid. Inhibitory
interactions may occur when two chemicals are presented to the taste
receptors simultaneously or successively. Competitive actions were observed among dextrose, sucrose, and levulose. Mercuric chloride ( 1c4 M )
reversibly blocked the taste responses to dextrose, sucrose, and levulose,
but not to glycine and NaCl. These results suggest the existence of at
least two different kinds of receptors in the palatal organ of carp; one is
commonly responsive to all four substances and the other only to glycine.
The existence of palatal chemoreceptors responding specifically to
dilute solutions (O.OOS0.0005 M for NaC1) of salts with monovalent
cations (Konishi and Niwa, 1964; Konishi, 1967) and of various organic
compounds (Konishi and Hidaka, 1969) has been demonstrated in carp.
Strong responses were produced by various chemicals with polyvalent
anions such as Na-citrate, Na2HP0,, Na,Fe( CH) 6 , tetramethylammonium-C1, choline-C1, Na-glutamate, glucose, and glycine. The response
decreased with increasing concentration, then increased again at much
higher concentrations. In general, the higher the valency of the anion
of the compounds, the larger the responses induced. Applications of
distilled water, immediately after stimulation with a salt solution at concentrations (O.OOl-O.05 A4 for NaCl) where responses were depressed,
elicited a marked integrated response (distilled water effect). The effect
has been ascribed to the activity of the same receptor as in the response
to dilute salt solutions. By analyzing the effects of acid, alkali, and dye
salts, a hypothesis which explains underlying mechanism in terms of an
interfacial electrokinetic process has been presented ( Konishi, 1967).
Such responses to dilute solutions are not restricted to freshwater fishes.
Similar responses were also observed in the facial nerves innervating the
upper lip of sea catfish Plotosus anguillaris (Konishi and Hidaka, 1967).
The biological significance of the response to dilute solution and distilled
water is unknown. Similar effects of highly diluted solutions and distilled
water on the olfactory bulbar responses have often been observed (Hara,
unpublished data).
The palatal chemoreceptors of the carp were found to be highly sensitive to carbon dioxide. No detectable responses to oxygen, nitrogen or
air were obtained ( Konishi et al., 1969). The responses were confirmed to
be independent of pH of the solutions applied. Avoidance behaviors to
CO, and/or pH were studied in Atlantic salmon parr, minnow, and roach,
in connection with water pollution (Hoglund, 1961; Hoglund and Hardig,
1969). The removal of olfactory tissues and the sectioning of the nerves
innervating the lateral line organs did not essentially change the reactions
of the fish.
101
sponses to sucrose, levulose, and glycine increased asymptotically with
increasing concentrations, while that for dextrose was sigmoid. Inhibitory
interactions may occur when two chemicals are presented to the taste
receptors simultaneously or successively. Competitive actions were observed among dextrose, sucrose, and levulose. Mercuric chloride ( 1c4 M )
reversibly blocked the taste responses to dextrose, sucrose, and levulose,
but not to glycine and NaCl. These results suggest the existence of at
least two different kinds of receptors in the palatal organ of carp; one is
commonly responsive to all four substances and the other only to glycine.
The existence of palatal chemoreceptors responding specifically to
dilute solutions (O.OOS0.0005 M for NaC1) of salts with monovalent
cations (Konishi and Niwa, 1964; Konishi, 1967) and of various organic
compounds (Konishi and Hidaka, 1969) has been demonstrated in carp.
Strong responses were produced by various chemicals with polyvalent
anions such as Na-citrate, Na2HP0,, Na,Fe( CH) 6 , tetramethylammonium-C1, choline-C1, Na-glutamate, glucose, and glycine. The response
decreased with increasing concentration, then increased again at much
higher concentrations. In general, the higher the valency of the anion
of the compounds, the larger the responses induced. Applications of
distilled water, immediately after stimulation with a salt solution at concentrations (O.OOl-O.05 A4 for NaCl) where responses were depressed,
elicited a marked integrated response (distilled water effect). The effect
has been ascribed to the activity of the same receptor as in the response
to dilute salt solutions. By analyzing the effects of acid, alkali, and dye
salts, a hypothesis which explains underlying mechanism in terms of an
interfacial electrokinetic process has been presented ( Konishi, 1967).
Such responses to dilute solutions are not restricted to freshwater fishes.
Similar responses were also observed in the facial nerves innervating the
upper lip of sea catfish Plotosus anguillaris (Konishi and Hidaka, 1967).
The biological significance of the response to dilute solution and distilled
water is unknown. Similar effects of highly diluted solutions and distilled
water on the olfactory bulbar responses have often been observed (Hara,
unpublished data).
The palatal chemoreceptors of the carp were found to be highly sensitive to carbon dioxide. No detectable responses to oxygen, nitrogen or
air were obtained ( Konishi et al., 1969). The responses were confirmed to
be independent of pH of the solutions applied. Avoidance behaviors to
CO, and/or pH were studied in Atlantic salmon parr, minnow, and roach,
in connection with water pollution (Hoglund, 1961; Hoglund and Hardig,
1969). The removal of olfactory tissues and the sectioning of the nerves
innervating the lateral line organs did not essentially change the reactions
of the fish.