INCREASES IN NMDA RECEPTOR-BINDING ARE SPECIFICALLY RELATED TO MEMORYFORMATION FOR A PASSIVE-AVOIDANCE TASK IN THE CHICK - A QUANTITATIVE AUTORADIOGRAPHIC STUDY

One-day-old chicks (Gallus domesticus) were trained on a one-trial pas sive avoidance task in which the aversive stimulus was an unpleasant t asting substance, methylanthranilate (MeA). Control birds were present ed with a water (W) coated bead. Five minutes after training a group o f MeA-trained chicks were given a brief sub-convulsive trans-cranial e lectric shock, which rendered half amnesic whilst the remainder were a ble to show recall for the aversive stimulus. Thirty minutes after tra ining birds were killed and quantitative receptor autoradiography was used to determine NMDA sensitive [H-3]L-glutamate binding in specific regions of the forebrain of: (i) MeA-trained chicks; (ii) water-contro l chicks; (iii) MeA-trained electroshocked chicks showing recall; and (iv) MeA-electroshocked chicks amnesic for the aversive stimulus. Incr eases (80% in the left lobus parolfactorius and 67% in the left interm ediate medial hyperstriatum ventrale) in NMDA sensitive [H-3]L-glutama te binding occurred in electro-shocked chicks which showed recall of t he aversive experience but were absent in MeA-trained chicks rendered amnesic by electro-shock. The increased binding in electroshocked MeA- trained birds which showed recall was similar to that observed previou sly in MeA-trained birds (without electroshock), compared to water con trol birds, whereas binding levels in MeA-trained electroshocked amnes ic birds were not different from those of water control birds. These d ata argue strongly that alterations in binding to glutamate receptor s ub-types are specific to memory formation for the passive avoidance ta sk.