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Effect of long or short photoperiod on pineal melatonin content in the white-footed mouse, Peromyscus leucopus
Life Sciences, Vol. 29, pp. 1623-1627 Printed in the U.S.A.
Pergamon Press
EFFECT OF LONG OR SHORT PHOTOPERIOD ON PINEAL MELATONIN CONTENT IN THE WHITE-FOOTED MOUSE, PEROMYSCUS LEUCOPUS i L. J. Petterborg,
B. A. Richardson,
and R. J. Reiter
Department of Anatomy, The University of Texas Health Science at San Antonio, 7703 Floyd Curl Drive, San Antonio, Texas 78284
Center
(Received in final form August 13, 1981) S Llmma r~ Adult white-footed mice were maintained under either a long photoperiod (LP, LD 16:8, lights out at 2100) or a short photoperiod (SP, LD 8:16, lights out at 1700) for six weeks. Subgroups from each lighting regime were killed at specific times over a 24 hour period. Pineal radioimmunoassayable melatonin levels were significantly elevated at night compared to daytime values. Pineal melatonin content appears to be elevated for a longer period of time in the SP mice than in the LP animals. The apparent increased melatonin production observed in white-footed mice maintained under short and reproductively repressive daylengths may help to explain the ability of chronically available exogenous melatonin to cause gonadal atrophy in this species. The white-footed mouse, Perom~scus leucopus, is a native North American rodent. In this species photoperiod plays a significant role in the regulation of reproductive processes (I-6). Mice kept under daylengths of less than 12 hours of light per day undergo gonadal involution while animals kept in photoperiods exceeding 12 hours of light per day maintained functional reproductive organs. That the pineal gland plays a role in photoperiod-mediated processes in Peromyscus is supported by the observation of Quay (7) that pineal glands from white-footed mice kept in darkness appeared to be more active than glands from mice exposed to increasing daylengths. Additionally, it has recently been shown that pineal removal prevents the reduction in ovarian weight which results from exposure of mice to a naturally short winter photoperiod (8). In mammals, the daily cycle of light and darkness appears to regulate the biosynthetic activity and endocrine functions of the pineal gland (9). The most studied product of pineal biosynthetic activity is the indole melatonin; melatonin levels become greatly elevated at night compared to daytime values. Syrian hamsters are highly susceptible to the reproductively repressive effects of short photoperiod, their annual rhythm of heightened sexual activity during the spring and summer (long daylengths) is followed by gonadal regression in the winter (short daylengths). The annual reproductive cycle of this species can be mimiced by giving hamsters melatonin injections late in the light phase of a long photoperiod (9). Circadian pineal melatonin levels have been determined for the hamster under a variety of lighting schedules (10-13). Pineal melatonin
iSupported by NSF grant # PCM 8003441. 0024-3205/81/161623-05502.00/0 Copyright (c) 1981 Pergamon Press Ltd.
1624
Pineal Melatonin Content in
Peromyscus
Vol. 29, No. 16, 1981
content is low during the day and begins to rise during the night after a variable lag period (which depends on the length of the dark cycle) to reach peak values around 0400. The reproductive system of P. leucopus is also very sensitive to photoperiodic manipulation and melatonin injections (3, 4, 14). In addition, the chronic administration of melatonin through a subcutaneous implant causes profound inhibition of reproductive processes in both juvenile and adult mice (5, 6, 15). In the hamster, melatonin implants not only fail to exhibit inhibitory properties, but such treatment interferes with the normally repressive effects of short photoperiod and afternoon melatonin injections (16, 17). Since the effects of subcutaneous melatonin depots are diametrically opposed in these two species the intriguing possibility exists that the control of melatonin production and/or release differs between them. The purpose of the following experiment was the determination of the daily pineal melatonin rhythms of white-footed mice exposed to long or short photoperiod.
Materials
and Methods
Colony-derived adult white-footed mice of both sexes were divided into two groups; one group was kept in normal colony lighting of 16 h of light per day (lights on at 0500, LP) while the other group was placed in a light tight cabinet and received 8 h of light per day (lights on at 0900, SP). After six weeks of treatment, subgroups of animals were killed at either I000, 1600, 2200, 2400, 0200, or 0400. The mice were exposed to dim red light (25 watt tungsten bulb behind a No. IA Safe Light Filter, Kodak) immediately prior to decapitation. Pineal glands were removed from the brains, placed in 1 ml of sodium phosphate buffer (pH 7.0) at 4°C, disrupted by sonification and stored frozen. Pineal melatonin content was determined in 400 using the radioimmunoassay of Rollag and Niswender were subjected to a one way analysis of variance and multiple comparisons among groups. Data points were cantly different if P
N1 aliquots of homogenate (18). The resulting data the Newman-Kuels test for considered to be signifi-
Results The daily pineal melatonin rhythm in the white-footed mouse appears to be similar to other animals which exhibit a significant nighttime elevation over daytime values. Mice maintained in long photoperiod (LP) had significantly greater pineal melatonin levels at 0200 (for males) and 0400 (for females) compared to all other time points (fig. l). Nighttime pineal melatonin levels in mice subjected to short photoperiod (SP) for six weeks were also greatly elevated over daytime values (fig. 2). However, unlike LP values, peak melatonin levels for SP males at 0200 and females at 0400 were only significantly greater than the two daytime points. Discussion The effect of different photoperiods on hamster pineal melatonin content have recently been examined (II, 19). These studies have shown that under short photoperiodic conditions, the nocturnal rise in pineal melatonin levels occurred well into the dark phase after a variable lag period depending on the length of darkness. Under long photoperiod the daily profile of pineal melatonin in Peromyscus leucopus appears similar to other rodent species. Daytime values are
Vol. 29, No. 16, 1981
Pineal Melatonin Content in Perormjsous
1625
low with peak levels coming toward the end of the dark phase of the photoperiodic cycle. White-footed mice exposed to SP for six weeks (which is sufficient time to cause gonadal atrophy in this species, 6) e x h i b i t what appears to be a pineal melatonin rhythm which may be characterized by a prolonged peak duration.
120"~
IO0"
• Moles o Femoles I B Period of Oorkness
80E
/
LD 16:8
Q_ ""E 60" tO
o(D 4 0 "~ 2 0
Oj. I000
,I,
L 1860
' 02'00 Time
FIG.
Jo6o
1
Mean (±SEM) pineal melatonin content of glands collected from whitefooted mice kept in long photoperiod (LP). Values at 0200 for males and 0400 for females are significantly elevated. N=7 at each point for each sex.
The white-footed mouse also differs significantly from the hamster in its response to exogenous melatonin. Subcutaneous melatonin implants have been shown to repress sexual development in young mice (5) and cause gonadal atrophy in adults (6). In the Syrian hamster, melatonin administered as a subcutaneous deposit is not only ineffective in causing gonadal regression but actually prevents the inhibitory effects of short photoperiod (16) and afternoon melatonin injections (]7). The observed differences in the reproductive consequences produced by chronically available melatonin in Syrian hamsters and white-footed mice might be explained on the basis of the respective pineal melatonin rhythms of these species in short photoperiod. Pineal melatonin profiles in the hamster do not appear to vary to any great extent between animals exposed to long or short photoperiod. Panke et al. (ll) have suggested that short photoperiod causes gonadal regression in the hamster because the nocturnal melatonin surge coincides with the animal's period of sensitivity to the indole. This explanation depends on the coordination of the melatonin peak and the circadian
1626
Pineal Melatonin Content in
Perom~jseus
Vol. 29, No. 16, 1981
rhythm of sensitivity to melatonin rather than on any alterations of duration or magnitude of the melatonin peak. Chronically available melatonin from a subcutaneous reservoir presumably fails to cause gonadal atrophy since under conditions of continuous melatonin availability the receptors to the indole are believed to be down regulated (9). In contrast to the Syrian hamster, under a short daylength the pineal melatonin peak of the white-footed mouse seems to be prolonged to fill the dark phase of the light-dark cycle rather than rising sharply towards the end of the darkness as in long photoperiod. The difference in the melatonin profiles between mice kept in long or short photoperiod suggests an increased production of melatonin in animals in LD 8:16 over those in LD 16:8. The fact that chronic melatonin availability produces gonadal atrophy in Perom scys!u~ supports the supposition that regulation of the reproductive status in this species is dependent on the quantity of melatonin produced subject to photoperiodic regulation rather than to the timing of the nocturnal melatonin surge. In the Syrian hamster then, it appears that the timing of the melatonin peak relative to the period of sensitivity must coincide to elicit the negative influence of short days. The white-footed mouse on the other hand, may respond to the increased period of dark in short photoperiod by increasing melatonin production and thereby inhibiting the reproductive system.
,2o1 '°°l 80
• Moles o Females
I
Period of Darkness
LD 816
¢-
4o-
20 ~ O-
o~oo
~86o
,obo
Time
FIG.
2
Mean (±SEM) pineal melatonin content of glands collected from whitefooted mice kept in short photoperiod (SP) for six weeks. Values at 0200 for males and 0400 for females are significantly evaluated over values at I000 and 1600. N=7 at each point for each sex except females at I000, 1600 and 2200 where N=6.
Vol. 29, No. 16, 1981
Pineal Melatonin Content in
Peromyscu8
1627
References
I. 2. 3. 4. 5. 6. 7. 8.
W. L. WHITAKER, J. Exp. Zool. 83 33-59 (1940). G. R. LYNCH, Comp. Biochem. Physiol. 44A 1373-1376 (1973). P.G. JOHNSTON and I. ZUCKER, Biol. Reprod. 22 983-989 (1980). P. G. JOHNSTON and I. ZUCKER, Biol. Reprod. 23 859-866 (1980). L. J. PETTERBORG and R. J. REITER, J. Reprod. Fert. 60 209-212 (1980). L. J. PETTERBORG and R. J. REITER, J. Andrology in press (1981). W. B. QUAY, J. Morph. 98 471-495 (1956). L. J. PETTERBORG, R. J. PELTER and G. C. BRAINARD, Experientia 37 247
9.
(1981). R. d. REITER, Prog. P s y c h o b i o l . P h y s i o l . Psych. 9 323-356 (1980).
I0. II. 12. 13. 14. 15. 16. 17. 18. 19.
E. S. PANKE, M. D. ROLLAG and R. J. PELTER, Endocrinology 104 194-197 (1979). E. S. PANKE, M. D. ROLLAG and R. J. REITER, Comp. Biochem. Physiol. 66A 691-693 (1980). M. D. ROLLAG, E. S. PANKE and R. J. PELTER, Proc. Soc. Exp. Biol. Med° 165 330-334 (1980). M. D. ROLLAG, E. S. PANKE, W. TRAKULRUNGSI, C. TRAKULRUNGSI and R. J. REITER, Endocrinology 106 231-236 (1980). P. G. JOHNSTON and I. ZUCKER, Biol. Reprod. 23 1069-1074 (1980). G. R. LYNCH and A. L. EPSTEIN, Comp. Biochem. Physiol. 53C 67-68 (1976). R. J. PELTER, M. K. VAUGHAN, D. E. BLASK and L. Y. JOHNSON, Science 185 1169-1171 (1974). R. J. REITER, P. K. RUDEEN, J. W. SACKMAN, M. K. VAUGHAN, L. Y. JOHNSON and J. C. LITTLE, Endocrine Res. Comm. 4 35-44 (1977). M. D. ROLLAG and G. D. NISWENDER, Endocrinology 98 482-489 (1976). L. TAMARKIN, S. M. REPPERT, D. C. KLEIN, B. PRATT and B. D. GOLDMAN, Endocrinology 107 1525-1529 (1980).
Pergamon Press
EFFECT OF LONG OR SHORT PHOTOPERIOD ON PINEAL MELATONIN CONTENT IN THE WHITE-FOOTED MOUSE, PEROMYSCUS LEUCOPUS i L. J. Petterborg,
B. A. Richardson,
and R. J. Reiter
Department of Anatomy, The University of Texas Health Science at San Antonio, 7703 Floyd Curl Drive, San Antonio, Texas 78284
Center
(Received in final form August 13, 1981) S Llmma r~ Adult white-footed mice were maintained under either a long photoperiod (LP, LD 16:8, lights out at 2100) or a short photoperiod (SP, LD 8:16, lights out at 1700) for six weeks. Subgroups from each lighting regime were killed at specific times over a 24 hour period. Pineal radioimmunoassayable melatonin levels were significantly elevated at night compared to daytime values. Pineal melatonin content appears to be elevated for a longer period of time in the SP mice than in the LP animals. The apparent increased melatonin production observed in white-footed mice maintained under short and reproductively repressive daylengths may help to explain the ability of chronically available exogenous melatonin to cause gonadal atrophy in this species. The white-footed mouse, Perom~scus leucopus, is a native North American rodent. In this species photoperiod plays a significant role in the regulation of reproductive processes (I-6). Mice kept under daylengths of less than 12 hours of light per day undergo gonadal involution while animals kept in photoperiods exceeding 12 hours of light per day maintained functional reproductive organs. That the pineal gland plays a role in photoperiod-mediated processes in Peromyscus is supported by the observation of Quay (7) that pineal glands from white-footed mice kept in darkness appeared to be more active than glands from mice exposed to increasing daylengths. Additionally, it has recently been shown that pineal removal prevents the reduction in ovarian weight which results from exposure of mice to a naturally short winter photoperiod (8). In mammals, the daily cycle of light and darkness appears to regulate the biosynthetic activity and endocrine functions of the pineal gland (9). The most studied product of pineal biosynthetic activity is the indole melatonin; melatonin levels become greatly elevated at night compared to daytime values. Syrian hamsters are highly susceptible to the reproductively repressive effects of short photoperiod, their annual rhythm of heightened sexual activity during the spring and summer (long daylengths) is followed by gonadal regression in the winter (short daylengths). The annual reproductive cycle of this species can be mimiced by giving hamsters melatonin injections late in the light phase of a long photoperiod (9). Circadian pineal melatonin levels have been determined for the hamster under a variety of lighting schedules (10-13). Pineal melatonin
iSupported by NSF grant # PCM 8003441. 0024-3205/81/161623-05502.00/0 Copyright (c) 1981 Pergamon Press Ltd.
1624
Pineal Melatonin Content in
Peromyscus
Vol. 29, No. 16, 1981
content is low during the day and begins to rise during the night after a variable lag period (which depends on the length of the dark cycle) to reach peak values around 0400. The reproductive system of P. leucopus is also very sensitive to photoperiodic manipulation and melatonin injections (3, 4, 14). In addition, the chronic administration of melatonin through a subcutaneous implant causes profound inhibition of reproductive processes in both juvenile and adult mice (5, 6, 15). In the hamster, melatonin implants not only fail to exhibit inhibitory properties, but such treatment interferes with the normally repressive effects of short photoperiod and afternoon melatonin injections (16, 17). Since the effects of subcutaneous melatonin depots are diametrically opposed in these two species the intriguing possibility exists that the control of melatonin production and/or release differs between them. The purpose of the following experiment was the determination of the daily pineal melatonin rhythms of white-footed mice exposed to long or short photoperiod.
Materials
and Methods
Colony-derived adult white-footed mice of both sexes were divided into two groups; one group was kept in normal colony lighting of 16 h of light per day (lights on at 0500, LP) while the other group was placed in a light tight cabinet and received 8 h of light per day (lights on at 0900, SP). After six weeks of treatment, subgroups of animals were killed at either I000, 1600, 2200, 2400, 0200, or 0400. The mice were exposed to dim red light (25 watt tungsten bulb behind a No. IA Safe Light Filter, Kodak) immediately prior to decapitation. Pineal glands were removed from the brains, placed in 1 ml of sodium phosphate buffer (pH 7.0) at 4°C, disrupted by sonification and stored frozen. Pineal melatonin content was determined in 400 using the radioimmunoassay of Rollag and Niswender were subjected to a one way analysis of variance and multiple comparisons among groups. Data points were cantly different if P
N1 aliquots of homogenate (18). The resulting data the Newman-Kuels test for considered to be signifi-
Results The daily pineal melatonin rhythm in the white-footed mouse appears to be similar to other animals which exhibit a significant nighttime elevation over daytime values. Mice maintained in long photoperiod (LP) had significantly greater pineal melatonin levels at 0200 (for males) and 0400 (for females) compared to all other time points (fig. l). Nighttime pineal melatonin levels in mice subjected to short photoperiod (SP) for six weeks were also greatly elevated over daytime values (fig. 2). However, unlike LP values, peak melatonin levels for SP males at 0200 and females at 0400 were only significantly greater than the two daytime points. Discussion The effect of different photoperiods on hamster pineal melatonin content have recently been examined (II, 19). These studies have shown that under short photoperiodic conditions, the nocturnal rise in pineal melatonin levels occurred well into the dark phase after a variable lag period depending on the length of darkness. Under long photoperiod the daily profile of pineal melatonin in Peromyscus leucopus appears similar to other rodent species. Daytime values are
Vol. 29, No. 16, 1981
Pineal Melatonin Content in Perormjsous
1625
low with peak levels coming toward the end of the dark phase of the photoperiodic cycle. White-footed mice exposed to SP for six weeks (which is sufficient time to cause gonadal atrophy in this species, 6) e x h i b i t what appears to be a pineal melatonin rhythm which may be characterized by a prolonged peak duration.
120"~
IO0"
• Moles o Femoles I B Period of Oorkness
80E
/
LD 16:8
Q_ ""E 60" tO
o(D 4 0 "~ 2 0
Oj. I000
,I,
L 1860
' 02'00 Time
FIG.
Jo6o
1
Mean (±SEM) pineal melatonin content of glands collected from whitefooted mice kept in long photoperiod (LP). Values at 0200 for males and 0400 for females are significantly elevated. N=7 at each point for each sex.
The white-footed mouse also differs significantly from the hamster in its response to exogenous melatonin. Subcutaneous melatonin implants have been shown to repress sexual development in young mice (5) and cause gonadal atrophy in adults (6). In the Syrian hamster, melatonin administered as a subcutaneous deposit is not only ineffective in causing gonadal regression but actually prevents the inhibitory effects of short photoperiod (16) and afternoon melatonin injections (]7). The observed differences in the reproductive consequences produced by chronically available melatonin in Syrian hamsters and white-footed mice might be explained on the basis of the respective pineal melatonin rhythms of these species in short photoperiod. Pineal melatonin profiles in the hamster do not appear to vary to any great extent between animals exposed to long or short photoperiod. Panke et al. (ll) have suggested that short photoperiod causes gonadal regression in the hamster because the nocturnal melatonin surge coincides with the animal's period of sensitivity to the indole. This explanation depends on the coordination of the melatonin peak and the circadian
1626
Pineal Melatonin Content in
Perom~jseus
Vol. 29, No. 16, 1981
rhythm of sensitivity to melatonin rather than on any alterations of duration or magnitude of the melatonin peak. Chronically available melatonin from a subcutaneous reservoir presumably fails to cause gonadal atrophy since under conditions of continuous melatonin availability the receptors to the indole are believed to be down regulated (9). In contrast to the Syrian hamster, under a short daylength the pineal melatonin peak of the white-footed mouse seems to be prolonged to fill the dark phase of the light-dark cycle rather than rising sharply towards the end of the darkness as in long photoperiod. The difference in the melatonin profiles between mice kept in long or short photoperiod suggests an increased production of melatonin in animals in LD 8:16 over those in LD 16:8. The fact that chronic melatonin availability produces gonadal atrophy in Perom scys!u~ supports the supposition that regulation of the reproductive status in this species is dependent on the quantity of melatonin produced subject to photoperiodic regulation rather than to the timing of the nocturnal melatonin surge. In the Syrian hamster then, it appears that the timing of the melatonin peak relative to the period of sensitivity must coincide to elicit the negative influence of short days. The white-footed mouse on the other hand, may respond to the increased period of dark in short photoperiod by increasing melatonin production and thereby inhibiting the reproductive system.
,2o1 '°°l 80
• Moles o Females
I
Period of Darkness
LD 816
¢-
4o-
20 ~ O-
o~oo
~86o
,obo
Time
FIG.
2
Mean (±SEM) pineal melatonin content of glands collected from whitefooted mice kept in short photoperiod (SP) for six weeks. Values at 0200 for males and 0400 for females are significantly evaluated over values at I000 and 1600. N=7 at each point for each sex except females at I000, 1600 and 2200 where N=6.
Vol. 29, No. 16, 1981
Pineal Melatonin Content in
Peromyscu8
1627
References
I. 2. 3. 4. 5. 6. 7. 8.
W. L. WHITAKER, J. Exp. Zool. 83 33-59 (1940). G. R. LYNCH, Comp. Biochem. Physiol. 44A 1373-1376 (1973). P.G. JOHNSTON and I. ZUCKER, Biol. Reprod. 22 983-989 (1980). P. G. JOHNSTON and I. ZUCKER, Biol. Reprod. 23 859-866 (1980). L. J. PETTERBORG and R. J. REITER, J. Reprod. Fert. 60 209-212 (1980). L. J. PETTERBORG and R. J. REITER, J. Andrology in press (1981). W. B. QUAY, J. Morph. 98 471-495 (1956). L. J. PETTERBORG, R. J. PELTER and G. C. BRAINARD, Experientia 37 247
9.
(1981). R. d. REITER, Prog. P s y c h o b i o l . P h y s i o l . Psych. 9 323-356 (1980).
I0. II. 12. 13. 14. 15. 16. 17. 18. 19.
E. S. PANKE, M. D. ROLLAG and R. J. PELTER, Endocrinology 104 194-197 (1979). E. S. PANKE, M. D. ROLLAG and R. J. REITER, Comp. Biochem. Physiol. 66A 691-693 (1980). M. D. ROLLAG, E. S. PANKE and R. J. PELTER, Proc. Soc. Exp. Biol. Med° 165 330-334 (1980). M. D. ROLLAG, E. S. PANKE, W. TRAKULRUNGSI, C. TRAKULRUNGSI and R. J. REITER, Endocrinology 106 231-236 (1980). P. G. JOHNSTON and I. ZUCKER, Biol. Reprod. 23 1069-1074 (1980). G. R. LYNCH and A. L. EPSTEIN, Comp. Biochem. Physiol. 53C 67-68 (1976). R. J. PELTER, M. K. VAUGHAN, D. E. BLASK and L. Y. JOHNSON, Science 185 1169-1171 (1974). R. J. REITER, P. K. RUDEEN, J. W. SACKMAN, M. K. VAUGHAN, L. Y. JOHNSON and J. C. LITTLE, Endocrine Res. Comm. 4 35-44 (1977). M. D. ROLLAG and G. D. NISWENDER, Endocrinology 98 482-489 (1976). L. TAMARKIN, S. M. REPPERT, D. C. KLEIN, B. PRATT and B. D. GOLDMAN, Endocrinology 107 1525-1529 (1980).