Pharmacological
and environmental regulation on yawning in the
high-yawning (HY) subline of
Sprague&endash;Dawley rats.
Eguibar José
R., Cortés Ma del Carmen, and Uribe
Carlos.
Institute of
Physiology and Secretarìa General.
Benemérita Universidad Autónoma de
Puebla. México.
The high-yawning (HY)
subline was obtained at the Institute of
Physiology in the Benemérita Autonomous
University of Puebla through a strict inbreeding
process along 75 generations. This group of rats
showed a spontaneous yawning frequency more than
20 times/h. On the other hand, low-yawning (LY)
rats have a mean yawning frequency around 2
times/h, and were selected from another stock of
Sprague-Dawley by inbreeding process through 60
generations.
The availability of HY
rats allows us to analyze the environmental
influences that regulated yawning expression.
So, we demonstrated that yawning showed a
circadian oscillation with a clear peak before
darkness. This circadian rhythm did not show a
free running under constant light conditions,
but it is possible to synchronize it whit a
restricted availability of food or water, which
produced a clear peak of yawning that predicts
their presentation.
On the other hand, HY
rats are more sensible to presynaptic
dopaminergic D2/D3 agonist such as: apomorphine,
3-PPP, quinpirole or 7-OH-DPAT. Central
administration of adrenocorticotropin hormone
(ACTH1-24) no clear effect were obtained on
yawning frequency in the HY subline, probably
due to displacement produced by the increase in
frequency and duration of grooming bouts. On the
other hand, central administration of bombesin,
a gastrointestinal peptide, inhibits yawning in
HY rats. Also is the case with GABAa and GABAb
agonists which inhibits spontaneous and
cholinergic-induced yawning. In the case of
cholinergic agonists such as physostigmine or
pilocarpine produced larger increase on yawning
frequency in HY respect to LY rats.
HY rats showed different
responses in the elevated plus maze and burying
test. In fact, HY subline showed lower
corticosterone level after immobilization in a
cylinder respect to LY ones. These results
clearly indicate that stress induced different
responses in hypothalamus-pituitary-adrenal
glands in both sublines.
In conclusion, HY subline
allows us to analyze with detail pharmacological
and environmental factors that modulate yawning
frequency. It is clear that the behavioural and
environmental differences in HY rats are due to
differences in the biochemical pathways involved
in synthesis, release or metabolism of
neurotransmitters and modulators involved in the
regulation of yawning.
This work is partly
supported by VIEP-BUAP SAL/G/2009 and CONACYT
106,694 grants to JRE and by Dr. E.
Agüera-Ibañez,
Rector-BUAP.
