Jul 23, 1982 - in Male Deer Mice: Involvement of the Circadian. System. J. MAL. WHITSETT,'. HERBERT. UNDERWOOD and JAMES. CHERRY. Department.
OF REPRODUCTION
BIOLOGY
Photoperiodic
28,
652-656
(1983)
Stimulation
of Pubertal
Involvement J. MAL
WHITSETT,’
of the Circadian
HERBERT
North
Development
Raleigh,
System and JAMES
UNDERWOOD
Department Carolina
in Male Deer Mice:
CHERRY
of Zoology State University
North
Carolina
27650
ABSTRACT prairie deer mice (Peromyscus maniculatus bairdii) is accelerated by exposure of juveniles to a long-day photoperiod, and, conversely, retarded by exposure to short days. The purpose of the present study was to evaluate the possible involvement of the circadian system in the photoperiodic regulation of puberty. Weanling males, previously housed on a short-day light cycle of 6L:18D, were subjected to a “resonance” protocol in which they received one of the following light cycles: 6L:18D, 6L:30D, 6L:42D, 6L:54D, or 16L:8D. Postweaning exposure to cycles of 16L:8D, 6L:30D, and 6L:54D stimulated reproductive organ growth as measured at 6 weeks of age. Exposure to cycles of 6L:18D and 6L:42D failed to stimulate reproductive development. These data support the hypothesis that young male deer mice use a circadian rhythm of responsiveness to light to measure photoperiodic time and, consequently, regulate pubertal development. Pubertal
development
in
INTRODUCTION
Day length or photoperiod lished as an important factor in of seasonal cycles of reproduction of many species of vertebrates fishes (de Vlaming, 1972) (Boissin-Agasse et al., 1982)
is well estab the regulation in adults ranging from to carnivores and ungulates (Karsch et a!., 1980) among the mammals. Although less is known of the control of the initial transition from immaturity to a breeding state during puberty, recent evidence indicates that day length can influence pubertal development in several species of mammals including sheep (Foster, 1981), Djungarian hamsters (Hoffmann, 1981), voles (Grocock, 1981), white-footed mice (Johnston and Zucker,
1980;
and
prairie
1982; A
Whitsett central
periodism time general of
an
first,
Petterborg
deer issue the
nature
measurement. hypotheses
of
to as
the
measure
accumulates
proposed
measurement sumes a light. gered in the other 1971)
circadian sensitivity;
-
day
length.
day
or
Thus, a photoperiodic by the presence of circadian cycle, times. Pittendrigh emphasized the
light but
rhythm second,
not and
dual
response at certain by Minis role of
Zoology, Raleigh,
November 18, 1982. July 23, 1982. requests: 3. Mal
North Carolina NC 27650.
State
Whitsett, University,
is
trigtimes
light at (1964, light in
system: first, light for the organism’s including the
of photoperiodic photo light is photoperiodically
The
hypothesis,
-
Accepted Received 1Reprint
night.
amount of the then triggers the photoperiodic The second hypothesis, originally by Bunning (1936) to explain the of photoperiod in plants, ascircadian rhythm in sensitivity to critical
inductive only if the rhythm of photoperiodic photosensitivity is entrained in such a way that the photosensitive portion of the rhythm is illuminated. This kind of circadian mechanism has been termed the “external coincidence” model because it demands the coincidence of an external stimulus light with an internal rhythm of photosensitivity. More recently, Pittendrigh (1972) has propounded an “internal coincidence” model in which the internal coincidence of two or more
there are two for the ability
“hourglass”
the
a
kind of photoperiodic as an entraining agent many circadian rhythms,
Miller,
of photo
of
this acts
1980),
and
throughout
Accumulation product response.
photoperiodic
Currently, to account
organism known
Reiter,
mice (Whitsett Lawton, 1982). in the physiology
and is
and
holds that an organism does, quite literally, measure the length of the light (or dark) period. Presumably, some reaction product
-
Dept. of Box 5577,
652
-
-
SYSTEM
CIRCADIAN
24
PUBERTY
___
94
___
___________ ___________
0
653
72
___
___
00%
AND
___
___________
6 LIeD 6
each
EJ
L300
6L.42D
LJ
6L540
EEJ
FIG. 1. A hypothetical cycle (i.e., h 0-12,
night”
or photosensitive
circadian not
oscillators
induction
in
the
coincidence position, the
correct
phase
however, researchers in experimentally internal of
and
external
was
young
deer
to we
measure determined
to
several
day the ahemeral
This “resonance” in Fig. 1, involves (6 h) tervals
pulses such
the uses
(non-24 protocol, exposing
of light spaced that, for some
or light
To
date,
been successful between the mechanism during of this that the system
accomplish of juvenile h)
light
this, males cycles.
which is depicted deer mice to short at different individuals,
inthe
pulse recurs with a period of 24 h or a multiple thereof, and for other individuals, the pulse recurs with a period that is 12 h more (or less) than a multiple of 24 h. The former condition results in pulses always occurring during the
individual’s “subjective day,” whereas in the latter condition, one pulse falls during the subjective day and the alternating pulse falls during the “subjective night.” Assuming that a photosensitive phase of a circadian rhythm of photoperiodic photosensitivity occurs during the subjective night of an individual, light cycles of 6L:18D and 6L:42D should not stimulate development, but cycles of 6L:30D and 6L: 54D should be stimulatory. Light will fall in the light-sensitive portion of the circadian day every 3 or 5 calendar days for individuals on the 6L:30D and 6L:54D schedules, respectively. This general protocol has been used repeatedly in investigations of photoperiodic time measuring systems
photosensitivity and the remainder
day”
in adult mammals 1972; Grocock and deer
Enright, mouse
accordance no treatment should
of
models.
The purpose hypothesis its circadian
length. To response
photoperiodic
“subjective
is simply oscillators
is known of the time measurement
mouse
of
relationship.
coincidence
development. to test
study
of
whether role
system internal
have not discriminating
As yet, nothing photoperiodic
pubertal
determines occur. The
will
in an internal to entrain, or
circadian rhythm 24-36, etc.) is the phase of an individual.
light
in deer
in deer
and and
cycle
birds Clarke,
The first half of the “subjective
(Elliott 1974;
with
the involving
et al., Hamner
If the
1967; Turek, 1974). measures photoperiodic
young time in
hourglass hypothesis, 6-h pulses of light
stimulate development, because 6 are less than the critical photoperiod mice (Whitsett et a!., in preparation).
MATERIALS
AND
Prairie deer mice bairdii) were maintained polypropylene cages on
They
mice.
of the
were provided
METHODS
(Peromyscus in 28.5 X a
with
Blox
h
18.5
maniculatus X 12.0 cm
bedding of shredded aspen. tap water and Wayne F -6 Blox (during pregnancy
and Wayne Breeder lactation) ad lib. Adult male and female deer mice, housed previously on a light:dark cycle of 15L:9D, were paired for breeding in a room having a cycle of 6L:18D. Males were removed from the cages 5 days later. Females and offspring remained on the 6L:18D schedule until weaning. Male offspring were weaned at 20-2 3 days of age. Between 21 and 24 days of age, they were moved to a separate research facility where they were assigned, on a random basis, to one of 10 light-tight wooden chambers. Each chamber, measuring 1.21 X 0.45 X 0.61 m, was lighted by one fluorescent bulb controlled by a timer. The 30-W bulb (Sylvania F30T12 -CW-RS) produced an average intensity of 1100 lux at the level of the deer mice. Fresh
and
air
was
continuously.
the
supplied
Lights
by
were
a
ventilation
off
in the
fan
room
that
ran
in which
chambers were located. Each chamber, which held 9 cages of individuallyhoused deer mice, received one of the following treatments: 6L:18D, 6L:30D, 6L:42D, 6L:54D or 16L:8D. There were two replicate chambers per experimental treatment condition; thus 18 males received each treatment. Only males weighing between 8.4 and 10.9 g at weaning were used in the study. Light:dark cycles with a period of 24 h were controlled by electromechanical timers; ahemeral cycles were controlled by programmable electronic timers. On the first day of the treatments, lights were activated at 0600 h, the time at which the
654
WHITSETT
6
-
2
-
ET AL.
II
160
*
E
E 120
C,
U)
w
Ui
6
60
0 0
UI
I
>-
4
I40
I .
*
E
E
.
4o-
32
U)
0
z
Iii -J
4
24
C)
.
30
*
(I) Ui
>
C,
-
* 16
4
U,
20
-
-J
#
0 UI C)
z
a
10
U U,
Iii U,
TT LO
FIG.
2. Influence
6:18
630
6:42
654
of light:dark
cycles
LD
168
on reproductive
extension of bar represents median and right extension group is significantly different from 6L:18D control, 16L:8D control (Duncan’s multiple range test, o=0.05).
males
had
experienced
the
Consequently, introduction chambers occurred during The
onset the
into light
of
light
the period.
since
birth.
photoperiod
males
remained in the chambers from 3 until 6 weeks of age, at which time they were removed, killed, and frozen at -20#{176}C. At a later date the deer mice were thawed and weighed. The area of the androgen -dependent ventral sebaceous gland (Doty and Kart, 1972) was measured, and testes and seminal vesicles were removed and weighed (Lawton and Whitsett, 1979). The design of the experiment was a single classification analysis of variance. The F tests were calculated using the General Linear Models procedure of the SAS computer program (Helwig and Council, 1979). As the distributions of responses to the various light cycles were sometimes highly skewed, results have been described by both means and medians in Fig. 2. This permits a simple evaluation of the direction and degree of skew and substitutes partially
for standard errors, which have little meaning for the highly skewed distributions. Prior to the calculation of F tests, a logarithmic transformation was applied to the data for testis and seminal vesicle weights. RESULTS
As ment
illustrated influenced
in Fig. 2, photoperiod reproductive organ
treatgrowth
618
630
642
6:8
6:54
organs in male deer mice at 6 weeks of age. Left represents mean. An asterisk (‘) indicates that treatment a pound sign (4fr) that it is significantly different from Sample size=18 per treatment group.
(testes,
F
vesicles,
F (4,85)2055,
gland, general 2.28,
(4,85)15.04,
P
