Effects of D-cycloserine on extinction of conditioned freezing.

The present study tested the prediction that D-cycloserine (DCS), a partial N-methyl-D-aspartate agonist, would facilitate extinction of conditioned freezing in male Sprague-Dawley rats. Rats received 5 light-shock pairings (conditioning). The following day, rats received 6 light-alone presentations (extinction training). Twenty-four hours later, rats received 1 light-alone presentation (test). Subcutaneous DCS injection before or after extinction training significantly enhanced extinction, and the dose-response curve for this effect was linear. Increasing the delay of DCS administration after extinction training led to a linear decrease in the facilitatory effect. The effect of systemic administration was replicated by intra-basolateral amygdala infusion. These results suggest that DCS facilitates extinction of conditioned freezing by acting on consolidation processes partly mediated by the basolateral amygdala.