Thyrotropin Releasing Hormone (TRH) in Pineal and Hypothalamus of the Frog: Effect of Season and Illumination1 IVOR M. D. JACKSON, RICHARD SAPERSTEIN,2 AND SEYMOUR REICHLIN Endocrine Division, Department of Medicine, New England Medical Center, Tufts University School of Medicine, Boston, Massachusetts 02111 ABSTRACT. The influence of photo-illumination and season on the pineal and hypothalamic content of TRH in the leopard frog (Rana pipiens) was studied. Animals (4-6 in each group) were exposed to constant light or darkness for 72 h and then sacrificed. The pineal and hypothalamus from each frog were extracted for TRH measurement by radioimmunoassay. The experiment was performed in spring, autumn, early winter and mid-winter. In early winter, mid-winter and spring the pineal content of TRH ranged from 0.14-0.70 ng. Significant differences between groups due to season and illumination were recorded. In autumn, mean levels
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URING the course of studies of the anatomical and phylogenetic distribution of thyrotropin releasing hormone (TRH), we observed, by use of a specific radioimmunoassay, that the pineal gland of the leopard frog (Rana pipiens) contained relatively large concentrations of this substance (1). First identified in the mammalian hypothalamus, where it plays an important role in the regulation of the pituitarythyroid axis (2,3), TRH has also been found to have an extensive extrahypothalamic distribution (1), especially so in submammalian forms such as amphibians, fish, and lamprey (1) in which this hormone has no apparent effect on thyroid function. TRH has also been demonstrated in the head region of the provertebrate amphioxus (1) and the ganglia of several species of snails (4). Its function in these animals is not known, but recent studies of the effects of TRH on behavior (5), and on electrical activity of nerve cells Received April 19, 1976. 1 Presented in part at the 56th Annual Meeting of The Endocrine Society in Atlanta, Georgia, June, 1974. Supported in part by U.S.P.H.S. Grant No. AM 16684. 2 Present address: Merck Institute for Therapeutic Research, Rahway, New Jersey.
of TRH were 12.95 ng (dark exposed) and 4.19 ng (light exposed)—values 10-20 times higher than at other times of the year (P < 0.001). The hypothalamic content of TRH ranged from 11.4 ng in spring to 19.5 ng in autumn. Seasonal differences were present, but no effect of light or darkness was found. There was no definite relation between the TRH levels in hypothalamus and pineal. The alteration in pineal and hypothalamic TRH produced by season, and the effect of illumination on pineal TRH content, support the view that TRH has a neuronal function in vertebrates, possibly as a neurotransmitter. (Endocrinology 100: 97, 1977)
(6), suggest that this peptide may act as a neurotransmitter. The role of TRH in the function of the frog pineal is also unknown. The pineal of the frog, derived embryologically from the epithalamic recess of the diencephalon, contains photoreceptor cells, supporting cells and nerve cells that conduct impulses to the diencephalon (7). Electrical activity in the pineal body of some anuran species is modified by light of characteristic wave length (8). Like the mammalian and avian pineal gland, the anuran pineal contains norepinephrine and serotonin; unlike the mammalian or avian pineal, the concentration of the melatonin forming enzyme, hydroxyindole o-methyl transferase (HIOMT), is not modified by altered lighting (7). The evidence that pineal function in the frog is light-related led us to study the effects on frog pineal TRH concentration of constant light and constant darkness. Hypothalamic TRH concentration was also determined since there is some evidence that the pineal gland may influence the hypothalamus in mammalian (9) and avian species (10,11). The role of environmental lighting on 97
The Endocrine Society. Downloaded from press.endocrine.org by [${individualUser.displayName}] on 14 November 2015. at 12:39 For personal use only. No other uses without permission. . All rights reserved.
JACKSON, SAPERSTEIN AND REICHLIN
98 20 —
A fats T
108 = 64— CONSTANT 2 -
1 — .8: .6.4-
.2-
LIGHT \ / # P
D
URING the course of studies of the anatomical and phylogenetic distribution of thyrotropin releasing hormone (TRH), we observed, by use of a specific radioimmunoassay, that the pineal gland of the leopard frog (Rana pipiens) contained relatively large concentrations of this substance (1). First identified in the mammalian hypothalamus, where it plays an important role in the regulation of the pituitarythyroid axis (2,3), TRH has also been found to have an extensive extrahypothalamic distribution (1), especially so in submammalian forms such as amphibians, fish, and lamprey (1) in which this hormone has no apparent effect on thyroid function. TRH has also been demonstrated in the head region of the provertebrate amphioxus (1) and the ganglia of several species of snails (4). Its function in these animals is not known, but recent studies of the effects of TRH on behavior (5), and on electrical activity of nerve cells Received April 19, 1976. 1 Presented in part at the 56th Annual Meeting of The Endocrine Society in Atlanta, Georgia, June, 1974. Supported in part by U.S.P.H.S. Grant No. AM 16684. 2 Present address: Merck Institute for Therapeutic Research, Rahway, New Jersey.
of TRH were 12.95 ng (dark exposed) and 4.19 ng (light exposed)—values 10-20 times higher than at other times of the year (P < 0.001). The hypothalamic content of TRH ranged from 11.4 ng in spring to 19.5 ng in autumn. Seasonal differences were present, but no effect of light or darkness was found. There was no definite relation between the TRH levels in hypothalamus and pineal. The alteration in pineal and hypothalamic TRH produced by season, and the effect of illumination on pineal TRH content, support the view that TRH has a neuronal function in vertebrates, possibly as a neurotransmitter. (Endocrinology 100: 97, 1977)
(6), suggest that this peptide may act as a neurotransmitter. The role of TRH in the function of the frog pineal is also unknown. The pineal of the frog, derived embryologically from the epithalamic recess of the diencephalon, contains photoreceptor cells, supporting cells and nerve cells that conduct impulses to the diencephalon (7). Electrical activity in the pineal body of some anuran species is modified by light of characteristic wave length (8). Like the mammalian and avian pineal gland, the anuran pineal contains norepinephrine and serotonin; unlike the mammalian or avian pineal, the concentration of the melatonin forming enzyme, hydroxyindole o-methyl transferase (HIOMT), is not modified by altered lighting (7). The evidence that pineal function in the frog is light-related led us to study the effects on frog pineal TRH concentration of constant light and constant darkness. Hypothalamic TRH concentration was also determined since there is some evidence that the pineal gland may influence the hypothalamus in mammalian (9) and avian species (10,11). The role of environmental lighting on 97
The Endocrine Society. Downloaded from press.endocrine.org by [${individualUser.displayName}] on 14 November 2015. at 12:39 For personal use only. No other uses without permission. . All rights reserved.
JACKSON, SAPERSTEIN AND REICHLIN
98 20 —
A fats T
108 = 64— CONSTANT 2 -
1 — .8: .6.4-
.2-
LIGHT \ / # P
