Enhanced responses to NMDA receptor activation in the developing cat caudate nucleus.

An in vitro slice preparation was used to assess the effects of N-methyl-D-aspartate (NMDA) receptor activation in the developing cat caudate nucleus. Removal of Mg2+ from the bathing medium, in the presence of 10 microM bicuculline, increased the amplitude and duration of the excitatory postsynaptic potential induced by local extracellular stimulation at all ages tested. In neurons younger than 35 days of age, removal of Mg2+ in the presence of bicuculline produced an increase in excitatory postsynaptic potential amplitude and duration as well as bursts of action potentials when local extracellular stimulation was applied. The effects of Mg2+ removal were reversibly attenuated by the specific NMDA receptor antagonist DL-2-amino-5-phosphonovaleric acid. These findings are important because they demonstrate that NMDA receptor-mediated responses can be induced in developing caudate neurons by local extracellular stimulation and these responses are enhanced in early postnatal periods at ages when motor control is being established.