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28 janvier 2010
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Première conférence internationale sur le bâillement
First International Conference on Yawning
Paris 24 - 25 juin 2010
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jose eguibar 
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.