Role of NMDA receptors in lesion-induced plasticity.

The effect of the N-methyl-D-aspartate (NMDA) receptor antagonist MK-801 on the acquisition and maintenance of a compensated state following unilateral labyrinthectomy was investigated in two species, grass frog and goldfish. MK-801: 1) inhibits the acquisition of a compensated state, and 2) causes a loss of compensation in early phases of the compensation process, but 3) has no such effect to the long-term maintenance of compensation. It is concluded that NMDA receptors perform a transient function by inducing a sensory or functional substitution process in the deafferented vestibular system. A hypothesis is presented explaining the lesion-induced adaptive process as a result of a self-organizing process in a neural net using Hebb-like algorithms to organize the strength of connections.