AGE AND THE EFFECTS OF 2-D,L-AMINO-5-PHOSPHONOVALERATE IN AN AREA OF THE CHICK FOREBRAIN WHICH IS ESSENTIAL FOR EARLY LEARNING

The intermediate, medial part of the hyperstriatum ventrale (IMHV) is a region of the avian forebrain which is known to be essential for ear ly learning in the domestic chick. The IMHV in an in vitro slice prepa ration displays two forms of synaptic plasticity. The incidence of bot h varies with age and is maximal between 3 and 5 days post-hatch. Sinc e NMDA receptors are critical for at least one of these plasticities, we have investigated the relationship between age and the contribution of NMDA receptors to the field response evoked by local, low-frequenc y stimulation and have found that the magnitude of the NMDA-dependent component of the response varies with age, peaking between 3 and 5 day s post-hatch. Spontaneous neural activity, recorded intracellularly, c an be completely and reversibly silenced by NMDA receptor blockade and the incidence of spontaneous activity also varies with age, peaking b etween 3 and 5 days. These results suggest that the IMHV contains NMDA receptors which can be activated near resting membrane potential. Eit her the efficiency or the numbers of these receptors is maximal at a s pecific point in development and their peak activity coincides with a peak in synaptic plasticity. These characteristics are similar to thos e reported for young mammals.