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It seems that experiments have been done to demonstrate
CR-like behavior and
physiology in mice by deletion of a gene controlling their
day versus night
synchrony. Much of the paper examines the brain region that
controls the
synchrony and the messages emanated from this region, but
other features of
the experiments may bear our consideration. Our
http://en.wikipedia.org/wiki/Circadian_rhythm may be
governed by our CR
pattern, regarding our meal timing. From the abstract of
the paper below,
comes: "a clock-controlled gene- ... null mice showed
accelerated
acquisition of food anticipatory activity during a daytime food
restriction."

For Fig. 4, the cortisol concentrations were higher at ZT 1
about 3-fold and
at ZT 11 about 5-fold for the null mice, compared with
control mice. At ZT
1, the glucose concentrations in the blood were little
different for both
types of mice, but for ZT 11 they were about 45% lower.

For Fig. 7, the food anticipatory [locomotor] activity was
about twice as
high for the null mice, compared with the control mice.

Li JD, Hu WP, Boehmer L, Cheng MY, Lee AG, Jilek A, Siegel
JM, Zhou QY.
Attenuated Circadian Rhythms in Mice Lacking the
Prokineticin 2 Gene.
J Neurosci. 2006 Nov 8;26(45):11615-11623.
PMID: 17093083

Circadian clocks drive daily rhythms in virtually all
organisms. In mammals,
the suprachiasmatic nucleus (SCN) is recognized as the
master clock that
synchronizes central and peripheral oscillators to evoke
circadian rhythms
of diverse physiology and behavior. How the timing
information is
transmitted from the SCN clock to generate overt circadian
rhythms is
essentially unknown. Prokineticin 2 (PK2), a
clock-controlled gene that
encodes a secreted protein, has been indicated as a
candidate SCN clock
output signal that regulates circadian locomotor rhythm.
Here we report the
generation and analysis of PK2-null mice. The reduction of
locomotor rhythms
in PK2-null mice was apparent in both hybrid and inbred
genetic backgrounds.
PK2-null mice also displayed significantly reduced
rhythmicity for a variety
of other physiological and behavioral parameters, including
sleep-wake
cycle, body temperature, circulating glucocorticoid and
glucose levels, as
well as the expression of peripheral clock genes. In
addition, PK2-null mice
showed accelerated acquisition of food anticipatory activity
during a
daytime food restriction. We conclude that PK2, acting as a
SCN output
factor, is important for the maintenance of robust circadian
rhythms.

... Reduced circadian rhythms of locomotor activity in
PK2-/- mice
Locomotor activity, a commonly used index for circadian
rhythmicity, can be
monitored by either running wheels (e.g., voluntary
activity) or
interruption of infrared beams (e.g., spontaneous activity).
... running
wheels. PK2-/- mice and their WT littermates were initially
entrained to LD
for 3 weeks, followed by 4-8 weeks in DD. In the C57BL/6 x
129/Ola mixed
genetic background, all WT and the majority of PK2-/- mice
were entrained to
the LD and exhibited an identical free-running period under
constant
darkness (Table 1). However, a small number of PK2-/- mice
(4 of 34) did not
display discernible locomotor rhythm under both LD and DD.
The amplitude of
locomotor rhythmicity of PK2-/- mice, shown by the relative
power of FFT,
was significantly reduced under both LD and DD conditions
(Table 1).
Furthermore, the daily wheel-running counts of PK2-/- mice were
significantly lower than that of WT mice under both LD and
DD (Table 1). The
PK2-/- mice in the C57BL/6 inbred background consistently
showed
significantly lower relative FFT power and wheel-running
counts than WT mice
under both LD and DD (Table 1). One of five PK2-/- mice in
inbred C57BL/6
background was arrhythmic under DD. Furthermore,, PK2-/-
mice (C57BL/6)
showed a longer free-running period than WT mice (Table 1).
Because PK2-/-
mice (C57BL/6) displayed very low running counts
(supplemental Fig. S1A,
available at www.jneurosci.org as supplemental material),
for comparison of
the activity pattern between WT and PK2-/- mice under LD,
hourly running
counts were normalized to the percentage of 24 h total
activity. As shown in
Figure 2C, the percentage distribution of wheel-running
activity showed
significant difference in genotype x time interaction (F(1)
= 20.10; p <
0.0001). Especially, the peak activity of PK2-/- mice
occurred at the late
night compared with early night in the WT mice (Fig. 2C). It
should also be
noted that PK2-/- mice showed apparently reduced
consolidation in the
wheel-running activity (Fig. 2A,B).

[...]

Attenuated circadian rhythms of body temperature and sleep
in PK2-/- mice
The body temperature in mammals also exhibits a circadian
rhythm, which is
at least in part controlled by signals from the SCN (Moore,
1997; Schibler
and Sassone-Corsi, 2002; Nagashima et al., 2005). The core
body temperature
is higher in the active phase than inactive phase even under
constant
darkness. It has been proposed that behavioral or
physiological rhythms such
as locomotor activity and/or food intake may account for
body temperature
rhythms. However, the SCN is also able to modulate
thermoregulation that
results in body temperature rhythm, because the circadian
body temperature
rhythm persists in completely bed-rested humans, fasting
humans and rats,
and hibernating squirrels (Nagashima et al., 2005). We
implanted body
temperature probes (Mini-Mitter) into the abdominal cavities
of PK2-/- and
WT mice (n = 5 mice per group), and the core body
temperature was monitored
continuously under LD conditions. As shown in Figure 3A,
both PK2-/- and WT
mice showed circadian rhythms in the body temperature.
However, the
oscillation amplitudes of PK2-/- mice were significantly
smaller than WT
mice (supplemental Fig. S3, available at www.jneurosci.org
as supplemental
material). Specifically, the main difference in body
temperature occurred
during the dark period, when PK2-/- mice could not reach
high peaks as WT
mice (Fig. 3A). The oscillation amplitude of body
temperature in PK2-/- mice
was also reduced under the DD condition (supplemental Fig.
S3B,C, available
at www.jneurosci.org as supplemental material).

[...]

It is well known that SCN plays an important role in
circadian regulation of
sleep-wakefulness. In rats and mice, SCN lesions affect
sleep onset and
timing but have no significant effect on either the total
amount of sleep or
the amount of recovery sleep after sleep deprivation
(Mistlberger et al.,
1983). In contrast, lesions in the SCN of squirrel monkeys
result not only
in the loss of sleep circadian rhythm but there is also a 4
h increase in
the amount of sleep, leading to the hypothesis that the
output from the SCN
enhances wakefulness in diurnal animals (Edgar et al.,
1993). The observed
attenuation in the rhythmicity of locomotor and the body
temperature in
PK2-/- mice may reflect fundamental alterations in the
rhythm of sleep-wake
cycle (Dijk and Czeisler, 1995; Naylor et al., 2000; Dudley
et al., 2003;
Shiromani et al., 2004). We directly analyzed the sleep-wake
rhythms of
PK2-/- and WT mice by implanting EEG and EMG electrodes to
monitor the sleep
and wake patterns during 2 d of LD, followed by 2 d of DD.
As shown in
Figure 3B, the sleep patterns of PK2-/- and WT mice were
significantly
different under both LD and DD. Compared with WT mice,
PK2-/- mice slept 85
min less during each LD cycle (total sleep time: WT,
706.0±14.3 min vs
PK2-/-, 621.3±28.2 min; n = 11 mice per group; p < 0.01 by
unpaired t test).
Most of the sleep reduction occurred during the light period
(total sleep
time at light period: WT, 488.0±8.0 min vs PK2-/-,
423.2±16.0 min; n = 11
mice per group; p < 0.01 by unpaired t test) (Fig. 3C).
There was no
significant difference in total sleep time between PK2-/-
and WT mice during
the dark period (WT, 218.0±12.4 min vs PK2-/-, 198.1±16.1
min; n = 11 mice
per group). Because of the reduction of sleep during the
light period, the
amplitudes of sleep rhythm of PK2-/- mice were significantly
smaller than WT
controls under LD, as analyzed by cosine simulation
(supplemental Fig.
S4A,C, available at www.jneurosci.org as supplemental
material). Under DD,
the amplitudes of sleep oscillation were also significantly
reduced in
PK2-/- mice (supplemental Fig. S4B,C, available at
www.jneurosci.org as
supplemental material). Thus, PK2 contributes significantly
to the magnitude
of circadian sleep-wake rhythmicity.

Altered circadian rhythms of circulating corticosterone and
glucose levels
in PK2-/- mice
The circadian clock plays an essential role in controlling
the daily rhythm
of circulating hormones (Moore and Eichler, 1972; Buijs et
al., 1993; Buijs
and Kalsbeek, 2001; Dubocovich and Markowska, 2005) and
energy metabolites
(La Fleur et al., 1999; Rudic et al., 2004). In rodents, the
plasma
corticosterone and glucose levels peak around the onset of
the active period
(Moore and Eichler, 1972; Buijs et al., 1993; La Fleur et
al., 1999). SCN
lesion results in the disruption of the glucocorticoid
rhythms in rats,
specifically the morning glucocorticoid levels are elevated,
leading to the
hypothesis that SCN output signals function as suppressors
for the
glucocorticoid level (Moore and Eichler, 1972; Buijs et al.,
1993). We
investigated the role of PK2 in the circadian regulation of
glucocorticoid
by measuring the levels of plasma corticosterone in PK2-/-
and WT mice at ZT
1 and ZT 11, time points that approximately correspond to
the reported peak
and trough times of circulating corticosterone. As shown in
Figure 4A, WT
mice showed a significantly higher corticosterone level at
ZT 11 than at ZT
1, whereas there was no significant oscillation of
corticosterone level in
PK2-/- mice (p = 0.11; n = 8-10 mice per time point).
Particularly, the
PK2-/- mice had significantly higher corticosterone levels
than WT controls
at ZT 1, indicating a possible negative regulation of
corticosterone level
by PK2 signaling.
[...]

Maintaining glucose levels within a narrow range is
essential for daily
function. Controlled by the SCN, a clear circadian rhythm in
blood glucose
levels is present (La Fleur et al., 1999; Rudic et al.,
2004). Recently, two
major clock genes, Clock and Bmal1, were shown to be
critical for the
glucose homeostasis (Rudic et al., 2004). As a target gene
of these two
transcription factors in the SCN, it is likely that a
deficiency in PK2 will
affect glucose rhythms. We measured the blood glucose
concentrations of
PK2-/- and WT mice at approximately peak and trough times,
ZT 1 and ZT 11.
As shown in Figure 4B, glucose level displayed an obvious
circadian
oscillation in WT mice, with a higher level at ZT 11 than at
ZT 1. However,
the oscillation rhythm of blood glucose was abolished in
PK2-/- mice.

Normal rhythm of clock genes expression in the SCN of PK2-/-
mice
The PK2-/- mice showed identical free-run period as WT mice
suggests that
PK2 may not be involved in the central clockwork regulation.
To further
analyze the effect of PK2 deficiency on the clockwork
function, we examined
the expression of core clockwork genes in the SCN of PK2-/-
and WT mice by
using in situ hybridization. As shown in Figure 5, the
oscillation of all
clock genes examined were essentially normal in the SCN of
PK2-/- mice,
indicating that loss of the PK2 gene had minimal influence
on the function
of core clockwork in the SCN. It should also be noted that
temporal profiles
of vasopressin in the SCN of WT and PK2-/- mice were
indistinguishable (Fig.
5). These molecular studies confirm that PK2 acts as an
output factor
downstream of the core oscillator to regulate circadian rhythms.

[...]

Attenuated circadian oscillation in the liver of PK2-/- mice
Circadian oscillations of clockwork and clock-controlled
genes also occur in
a variety of peripheral organs. It has been established that
the SCN clock
is critical in synchronizing these peripheral clocks (Buijs
and Kalsbeek,
2001; Reppert and Weaver, 2002; Yoo et al., 2004; Guo et
al., 2005). To
investigate whether a deficiency in PK2 affects the
synchronization of
peripheral clocks, we examined the molecular oscillation of
the clockwork
and clock-controlled genes in the liver, a peripheral organ
that does not
express detectable PK2 or PK receptor 2 (PKR2) mRNA (data
not shown). The
mRNA levels of Bmal1 and Dbp in the liver were measured by
real-time PCR.
Bmal1 and Dbp were chosen because they peak at different
phases and are
regulated by different transcription factors, Rora
(RAR-related orphan
receptor A) and Bmal1/Clock, respectively (Ripperger et al.,
2000; Sato et
al., 2004). As shown in Figure 6, A and B, Bmal1 and Dbp
displayed circadian
rhythms in both WT and PK2-/- mice. However, the amplitudes
of oscillation
for Bmal1 and Dbp mRNAs were significantly smaller in PK2-/-
mice, reflected
by a 40% reduction in the peak levels.

[...]

Accelerated adaptation of PK2-/- mice to daytime restricted
feeding
Our observations indicate that the control of SCN over
diverse circadian
processes is weakened in PK2-/- mice. To further investigate
the deficit in
the SCN control of circadian rhythms, we challenged PK2-/-
mice with a
scheduled daytime RF, which can entrain the circadian
rhythms independent of
the SCN (Damiola et al., 2000; Stokkan et al., 2001). In
response to a
daytime RF, rodents will feed at unusual period for the sake
of survival and
gradually become active before the food is made available, a
phenomenon
called FAA. FAA is an rhythmic event associated with the
food entrained
oscillators (FEO). During RF, the FEO competes with the
light entrained
oscillator (LEO) (i.e., SCN) for the control of activity and
physiological
events. Thus, the higher FAA has been interpreted as a
relatively stronger
FEO control (Dudley et al., 2003; Pitts et al., 2003). The
FAAs of PK2-/-
and WT mice were monitored when the food was available
between ZT 3 to ZT 7
of LD cycles. As shown in Figure 7, A and B, PK2-/- mice
displayed
significantly higher FAA during days 3-6 of RF, confirming a
weaker SCN
control in PK2-/- mice for the locomotor activity.

[...]