4. THYROID FUNCTION AND ITS CONTROL IN FISHES
265
ginning has been made in studies by Hara et al. (1965, 1966; Hara and
Gorbman, 1967) and by Oshima and Gorbman (1966a,b). These workers
have selected particular sensory-evoked ( optic, olfactory) electrical
events in the goldfish brain and have analyzed them in some detail, in
terms of pattern, amplitude, threshold, and other properties. Optically
evoked (by light flashes) midbrain potentials are sensitized by prior
thyroxine treatment of the fish, and recovery time between stimuli is
shortened. Electrical potential patterns in the olfactory bulb evoked by
chemical stimulation of the olfactory organ of goldfish are affected by
thyroxinization in a more complex way. Apparently, reactivity of neurons
in the olfactory bulb is potentiated by thyroxine, but centrifugal impulses
from the posterior brain to the bulb are inhibited by thyroxine treatment.
Thyroxinization of goldfish also produces changes in spontaneous and
injury-evoked electrical activity in the forebrain and diencephalon. It
seems remarkable so far in this analysis that the influences of thyroxine
and other hormones on central nervous functions in fishes are so widespread, and the implications of these influences are many. Unfortunately,
the significance of these thyroxine-influenced neuroelectrophysiological
changes in terms of particular behavioral or neurosecretory events remains to be defined. One suggestion has been made by Godet and Dupe
( 1965), who have studied the relation of thyroid state to cerebral electrogenesis, particularly with respect to olfaction, in the lungfish, Protopterus
annectens. On the basis of their work they have developed a neuroendocrine hypothesis which explains the awakening of the lungfish from the
dry state when moistened, causing him to excyst from the cocoon to resume aquatic phase activity. Their data, at least in part, support a hypothesis requiring that increasing humidity activates the thyroid, presumably through a hypothalamic mechanism. Thyroid hormones, acting upon
cerebral centers, increase sensitivity of an olfactory center, and this, in
turn, evokes normal feeding and other behavior. Data supporting this
interesting idea are incomplete, but at least they illustrate how an eventual piecing together of nervous and endocrine phenomena will serve to
explain endocrine and neuroendocrine regulation of behavior.
REFERENCES
Aloj, S., Roche, J., and Salvatore, G. (1967). Isolation and properties of a thyroglobulin subunit from lamprey thyroid gland. Gen. Comp. Endocrinol. 9, 429.
Arvy, L., Fontaine, M., and Gabe, M. (1956). Fonction thyroidienne et complexe
hypothalamo-hypophysaire chez la truite. Compt. Rend. SOC. B i d . 150, 625627.
Arvy, L., Fontaine, M., and Gabe, M. (1957). Fonctionnement thyroidien et neurosbcr6tion hypothalamique chez la truite ( Salmo gairdnerii). J . Physio2. (Paris)
49, 685.
265
ginning has been made in studies by Hara et al. (1965, 1966; Hara and
Gorbman, 1967) and by Oshima and Gorbman (1966a,b). These workers
have selected particular sensory-evoked ( optic, olfactory) electrical
events in the goldfish brain and have analyzed them in some detail, in
terms of pattern, amplitude, threshold, and other properties. Optically
evoked (by light flashes) midbrain potentials are sensitized by prior
thyroxine treatment of the fish, and recovery time between stimuli is
shortened. Electrical potential patterns in the olfactory bulb evoked by
chemical stimulation of the olfactory organ of goldfish are affected by
thyroxinization in a more complex way. Apparently, reactivity of neurons
in the olfactory bulb is potentiated by thyroxine, but centrifugal impulses
from the posterior brain to the bulb are inhibited by thyroxine treatment.
Thyroxinization of goldfish also produces changes in spontaneous and
injury-evoked electrical activity in the forebrain and diencephalon. It
seems remarkable so far in this analysis that the influences of thyroxine
and other hormones on central nervous functions in fishes are so widespread, and the implications of these influences are many. Unfortunately,
the significance of these thyroxine-influenced neuroelectrophysiological
changes in terms of particular behavioral or neurosecretory events remains to be defined. One suggestion has been made by Godet and Dupe
( 1965), who have studied the relation of thyroid state to cerebral electrogenesis, particularly with respect to olfaction, in the lungfish, Protopterus
annectens. On the basis of their work they have developed a neuroendocrine hypothesis which explains the awakening of the lungfish from the
dry state when moistened, causing him to excyst from the cocoon to resume aquatic phase activity. Their data, at least in part, support a hypothesis requiring that increasing humidity activates the thyroid, presumably through a hypothalamic mechanism. Thyroid hormones, acting upon
cerebral centers, increase sensitivity of an olfactory center, and this, in
turn, evokes normal feeding and other behavior. Data supporting this
interesting idea are incomplete, but at least they illustrate how an eventual piecing together of nervous and endocrine phenomena will serve to
explain endocrine and neuroendocrine regulation of behavior.
REFERENCES
Aloj, S., Roche, J., and Salvatore, G. (1967). Isolation and properties of a thyroglobulin subunit from lamprey thyroid gland. Gen. Comp. Endocrinol. 9, 429.
Arvy, L., Fontaine, M., and Gabe, M. (1956). Fonction thyroidienne et complexe
hypothalamo-hypophysaire chez la truite. Compt. Rend. SOC. B i d . 150, 625627.
Arvy, L., Fontaine, M., and Gabe, M. (1957). Fonctionnement thyroidien et neurosbcr6tion hypothalamique chez la truite ( Salmo gairdnerii). J . Physio2. (Paris)
49, 685.