N-Methyl-d-aspartate and α-amino-3-hydroxy-5-methyl-4- isoxazolepropionate receptors involved in the induction of sedative effects under an acute stress in neonatal chicks

Glutamate, an excitatory amino acid, acts at several glutamate receptor subtypes. Recently, we reported that central administration of glutathione induced hypnosis under stressful conditions in neonatal chicks. Glutathione appears to bind to the N-methyl-d-aspartate (NMDA) receptor. To clarify the involvement of each glutamate receptor subtype during stressful conditions, intracerebroventricular (i.c.v.) injection of several glutamate receptor agonists was given to chicks under social separation stress. Glutamate dose-dependently induced a hypnotic effect. NMDA, α-amino-3-hydroxy-5- methyl-4-isoxazolepropionate (AMPA) and kainate are characterized as ionotropic glutamate receptors (iGluRs). Although NMDA also induced sleep-like behavior or sedative effects, the potency of NMDA was less than that of glutamate. AMPA tended to decrease distress vocalizations induced by acute stress and brought about a sedative effect. Kainate and (S)-3, 5-dehydroxyphenylglycine, which is a metabotropic glutamate receptor agonist, had no influence on chick behavior. Thus, it is suggested that the iGluRs, NMDA and AMPA, are important in inducing hypnosis and sedation under acute stress in chicks.