Abstract
Apomorphine-induced yawning was completely suppressed in animals treated with 5 nmol [D-Pro 4]casomorphin (CM) (ICV), 10 nmol [D-Phe 3]CM (ICV) or 10 nmol [D-Pip 4]CM (ICV). The apomorphine-induced yawning was also decreased, by des-Tyr analogs, but only by about 50%. Physostigmine (0.15 mg/kg, IP) induced yawning. The physostigmine-induced yawning was suppressed by 5 nmol [D-Pro 4]CM and 10 nmol [D-Phe 3]CM. Both [des-Tyr-D-Phe 3]CM and [des-Tyr-D-Pip 4]CM were without effect, whereas [des-Tyr-D-Pro 4]CM increased significantly the physostigmine-induced yawning. The results suggest that dopaminergic transmission can be modulated by β-casomorphin derivatives, thus resulting in a decrease in yawning. In the case of the des-tyrosine derivatives, we can assume a dopaminergic modulation, too. An increase in serotonergic activity might be supposed for [des-Tyr-D-Pro 4]CM.
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