Effects of D-cycloserine on the extinction of appetitive operant learning

Abstract

Four experiments with rat subjects examined whether D-cycloserine (DCS), a partial NMDA agonist, facilitates the extinction of operant lever-pressing reinforced by food. Previous research has demonstrated that DCS facilitates extinction learning with methods that involve Pavlovian extinction. In the current experiments, operant conditioning occurred in Context A, extinction in Context B, and then testing occurred in both the extinction and conditioning contexts. Experiments 1A and 1B tested the effects of three doses of DCS (5, 15, and 30 mg/kg) on the extinction of lever pressing trained as a free operant. Experiment 2 examined their effects when extinction of the free operant was conducted in the presence of nonresponse-contingent deliveries of the reinforcer (that theoretically reduced the role of generalization decrement in suppressing responding). Experiment 3 examined their effects on extinction of a discriminated operant, that is, one that had been reinforced in the presence of a discriminative stimulus, but not in its absence. A strong ABA renewal effect was observed in all four experiments during testing. However, despite the use of DCS doses and a drug administration procedure that facilitates the extinction of Pavlovian learning, there was no evidence in any experiment that DCS facilitated operant extinction learning assessed in either the extinction or the conditioning context. DCS may primarily facilitate learning processes that underlie Pavlovian, rather than purely operant, extinction.

Figure 1

Results of Experiment 1a. Left: Mean responding (plus or minus standard errors of the mean) during each 30-min session of acquisition. Center: Mean responding (plus or minus standard errors) during 5-min bins of the two extinction sessions. Right: Mean responding (plus or minus standard errors) during the 10-min test sessions in the extinction context (Context B) and the original acquisition (renewal) context (Context A). Note the change in y-axis between panels. 0, 5, 15, and 30 = doses (in mg/kg) of DCS.

Figure 2

Results of Experiment 1b. Left: Mean responding (plus or minus standard errors of the mean) during each 30-min session of acquisition. Center: Mean responding (plus or minus standard errors) during 5-min bins of the single extinction session. Right: Mean responding (plus or minus standard errors) during the 10-min test sessions in the extinction context (Context B) and the the original acquisition (renewal) context (Context A). Note the change in y-axis between panels. 0, 5, 15, and 30 = doses (in mg/kg) of DCS.

Figure 3

Results of Experiment 2. Left: Mean responding (plus or minus standard errors of the mean) during each 30-min session of acquisition. Center: Mean responding (plus or minus standard errors) during 5-min bins of the single extinction session (which also involved noncontingent presentations of the pellet reinforcer). Right: Mean responding (plus or minus standard errors) during the 10-min test sessions in the extinction context (B) and the renewal context (A) in test sessions where noncontingent pellets (Pellet) or no pellets (No Pellet) were delivered. Note the change in y-axis between panels. 0, 5, 15, and 30 = doses (in mg/kg) of DCS.

Figure 4

Results of Experiment 3. Left: Mean elevation scores (plus or minus standard errors of the mean) during each 16-trial session of discriminated operant training (acquisition). Center: Mean responding (plus or minus standard errors) during successive 4-trial blocks of the single extinction session. Right: Mean elevation scores (plus or minus standard errors) during the 10-min test sessions in the extinction context (B) and the renewal context (A). Note the change in y-axis between panels. 0, 5, 15, and 30 = doses (in mg/kg) of DCS.