Apomorphine-induced yawning in the rat: influence of fasting and time of day.
Yawning behavior is an experimental tool to study physiological responses, to elucidate the mechanisms of action of some drugs and hormones, and it is also a paradigm for some diseases and for dopamine (DA) agonists' clinical use. In this study, the effects of 24- and 48-h fasting as well as the influence of the light-dark cycle on apomorphine (APO)-induced yawning were evaluated. Initially, control and 48-h-fasted adult male rats were tested for yawning induced by APO (50, 100, 150 micrograms/kg, SC). The most effective dose tested was 100 micrograms/kg. Fasting significantly lowered yawning in all doses tested. Comparison between 24- and 48-h-fasted rats for APO (100 micrograms/kg)-induced yawning showed no significant difference between groups. Ad lib-fed groups were tested for APO (100 micrograms/kg)-induced yawning in both the light and in the dark phases of the cycle. Total number of yawnings increased significantly in the dark period. The present data show that fasting reduces and dark period increases APO-induced yawning in rats, suggesting that these conditions modulate the expression of this behavior.
Nasello
A G
AG
Medical School of Santa Casa, São Paulo, Brazil.
Tieppo
C A
CA
Felicio
L F
LF
D000818:Animals; D001058:Apomorphine / Q000494:pharmacology*; D002940:Circadian Rhythm / Q000187:drug effects / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D005215:Fasting / Q000502:physiology*; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D011954:Receptors, Dopamine / Q000187:drug effects / Q000502:physiology; D015000:Yawning / Q000187:drug effects* / Q000502:physiology
D011954:Receptors, Dopamine; D001058:Apomorphine