Passive avoidance learning in the day-old chick is modulated by GABAergic agents.

Injection of drugs directly into the intermediate medial hyperstriatum ventrale (IMHV) of day-old chicks, prior to training on a chrome bead dipped in either the strong aversant methyl anthranilate (MeA), or the weak aversant quinine, allows investigation of the effects of potential amnestic and memory-enhancing agents on retention of a passive avoidance task. Chicks were injected into the left and right IMHV, with either saline or muscimol (GABA agonist), 30 minutes before training on an MeA-coated bead. On test, either 10 min, 30 min or 24 h after training, birds were presented with a dry chrome bead. Normally, trained birds will avoid the test bead; however, significantly more muscimol-injected birds pecked the dry bead than did saline-injected chicks, indicating amnesia in the muscimol-injected birds. In chicks injected bilaterally into the IMHV with bicuculline, a GABAA antagonist, 30 minutes prior to training on a quinine-coated bead, avoidance scores were significantly improved on testing at 24 h compared with saline-injected control chicks, indicating enhanced retention in bicuculline-treated birds. These results suggest a role for the GABAergic system in the acquisition and retention of passive avoidance learning in the day-old chick.