The chick has a practical advantage in the screening process in that chicks require only small quantities of drugs. The chick separation stress paradigm has traditionally been recognized as a valid form of anxiolytic screening. Further, chick behavior involving standing motionless with eyes closed or sitting motionless with head drooped is nearly always associated with electrophysiological sleep. When centrally administered, some DNA-encoded L-α-amino acids, as well as some DNA-non-encoded amino acids, such as metabolites of L-α-amino acids, D-amino acid and β-amino acid, have shown sedative and/or hypnotic effects in chicks. The effects of some of these amino acids have subsequently been confirmed in humans. In conclusion, the chick model is convenient and useful for screening central functions of amino acids and their metabolites for hypnosis and sedation.
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