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TOSHIAKI J. HAM
Central regulation of afferent transmission within the nervous system
may be a common process in neural integration. Particularly in fishes,
such a mechanism of central regulation, including interbulbar connections,
may play an important role in the orientation toward or away from a
stimulus source by simultaneous bilateral equating of stimulation.
B. Gustatory Receptors
1. PALATAL ORGAN OF CARP
Unlike the olfactory system, taste receptors of fishes are scattered
widely over the body surface. For this reason electrophysiological studies
on taste function in fishes have mainly involved the recording of potential
discharges from the nerve fibers innervating taste buds. Hoagland (1933)
first recorded electrical responses from the facial nerve innervating the
taste buds on the barbels of the catfish exposed to various taste solutions.
Subsequently a more thorough investigation of the electrical responses of
the taste receptors was undertaken by Konishi and Zotterman (1961a,b)
in carp.
Integrated electrical responses to various taste substances were recorded from the glossopharyngeal, facial, and branchial nerves innervating the palatal organ, barbels, and gill rakers. The findings suggest that
the palatal organ plays the principal role in gustation in the carp although
certain differences exist between Swedish and Japanese carps (Konishi
and Zotterman, 1961a,b, 1963). Swedish carp showed a large gustatory
response to sucrose (0.5 M ) and acetic acid (0.005 M , pH 3.8) and a
weak response to quinine (0.01 M ) , while Japanese carp show low sensitivity to sucrose and high sensitivity to quinine. Responses to human
saliva were much larger than those to NaCl (0.5 M ) . Single taste fibers
from the glossopharyngeal nerve could be qualitatively classified into
seven groups according to their response patterns to four basic taste substances and saliva. Acetic acid (0.005 M ) stimulated all taste fibers, except for salt fibers which were specifically responsive only to NaCI. The
fibers responsive to human saliva were also stimulated by sucrose. Extract
of silkworm pupa also induced a marked gustatory response. The final
gustatory active compound could not be identified either in saliva or in
extract of silkworm pupae. Lytic agents produced an irreversible depression of taste responses. Thus, treatment with 0.3% sodium cholate depressed the response to sucrose while treatment with 0.005% digitonin
immediately reduced the responsiveness of the taste receptors.
Furthermore, the taste responses of the carp to sucrose, dextrose,
levulose, and glycine were analyzed (Hidaka and Yokota, 1967). Re-
TOSHIAKI J. HAM
Central regulation of afferent transmission within the nervous system
may be a common process in neural integration. Particularly in fishes,
such a mechanism of central regulation, including interbulbar connections,
may play an important role in the orientation toward or away from a
stimulus source by simultaneous bilateral equating of stimulation.
B. Gustatory Receptors
1. PALATAL ORGAN OF CARP
Unlike the olfactory system, taste receptors of fishes are scattered
widely over the body surface. For this reason electrophysiological studies
on taste function in fishes have mainly involved the recording of potential
discharges from the nerve fibers innervating taste buds. Hoagland (1933)
first recorded electrical responses from the facial nerve innervating the
taste buds on the barbels of the catfish exposed to various taste solutions.
Subsequently a more thorough investigation of the electrical responses of
the taste receptors was undertaken by Konishi and Zotterman (1961a,b)
in carp.
Integrated electrical responses to various taste substances were recorded from the glossopharyngeal, facial, and branchial nerves innervating the palatal organ, barbels, and gill rakers. The findings suggest that
the palatal organ plays the principal role in gustation in the carp although
certain differences exist between Swedish and Japanese carps (Konishi
and Zotterman, 1961a,b, 1963). Swedish carp showed a large gustatory
response to sucrose (0.5 M ) and acetic acid (0.005 M , pH 3.8) and a
weak response to quinine (0.01 M ) , while Japanese carp show low sensitivity to sucrose and high sensitivity to quinine. Responses to human
saliva were much larger than those to NaCl (0.5 M ) . Single taste fibers
from the glossopharyngeal nerve could be qualitatively classified into
seven groups according to their response patterns to four basic taste substances and saliva. Acetic acid (0.005 M ) stimulated all taste fibers, except for salt fibers which were specifically responsive only to NaCI. The
fibers responsive to human saliva were also stimulated by sucrose. Extract
of silkworm pupa also induced a marked gustatory response. The final
gustatory active compound could not be identified either in saliva or in
extract of silkworm pupae. Lytic agents produced an irreversible depression of taste responses. Thus, treatment with 0.3% sodium cholate depressed the response to sucrose while treatment with 0.005% digitonin
immediately reduced the responsiveness of the taste receptors.
Furthermore, the taste responses of the carp to sucrose, dextrose,
levulose, and glycine were analyzed (Hidaka and Yokota, 1967). Re-