d-Cycloserine, A Positive Modulator of the NMDA Receptor, Enhances Acquisition of a Conditioned Taste Aversion

Pharmacological manipulations using agents that affect the action of the N-methyl-D-aspartate (NMDA) receptor have been demonstrated to modulate acquisition and retention in experimental animals. Although it is well established that antagonists of this receptor debilitate acquisition of many experimental tasks, the effects of agonists of the receptor site have not been thoroughly examined, except for those of D-cycloserine (DCS), a partial agonist of the NMDA receptor. In the present study, DCS is demonstrated to enhance acquisition of a conditioned taste aversion (CTA) in rats, extending the findings of facilitation of learning with this agonist to a CTA paradigm. DCS itself did not cause a taste aversion nor did it summate with lithium chloride, the unconditioned stimulus, to increase avoidance of the conditioned stimulus in experimental animals. It appears that modulation of the NMDA receptor can affect gustatory learning.