Figure 3: Intra-VTA SB-334867 (3 and 6g) fails to affect reinstatement elicited by presentation of cues predictive of sweetened condensed milk (SCM) availability. Male (n=20) Sprague Dawley rats were trained to respond for SCM in the presence of discriminative stimuli predictive of reward availability or nonavailability. A constant 70dB white noise (S+) indicated availability of SCM, whilst constant illumination of a 2.8W house light (S-) in the top corner of the operant chamber indicated non-availability of SCM (i.e. lever responses resulted in no consequence). Sessions were initiated by extending two retractable levers into the chamber that coincided with the presentation of either the S+ or S- discriminative cues. During S+ conditioning sessions, responses on the active lever (under a fixed ratio 1 schedule of reinforcement) resulted in a delivery of (0.1 ml) SCM into a receptacle positioned between the two levers. Rewarded responses were followed by a 20-sec timeout period signaled by the illumination of a cue light above the lever. During S- conditioning sessions, responses on the active lever resulted in no reward and was followed by an intermittent beeping tone that lasted for 20 sec. In both S+ and S- sessions, responses on the left (inactive) lever were recorded but responses were inconsequential as per training conditions. Following lever training, animals were exposed to 8 S+ conditioning sessions and 8 S- conditioning sessions over eight days (2 sessions per day, in random sequence, 20 minutes/session). Lever pressing was then extinguished in 1-hour sessions during which reinforcers and discriminative stimuli were withheld, until a criterion of < 6 active lever responses over three consecutive days was reached. One day following extinction, animals were exposed to the S- cue and lever responding was recorded for two hours. The following day, animals received unilateral intra-VTA injections of either SB- 334867 (3g or 6g/0.5l) or vehicle (equivolume) 15 minutes before being presented with the S+ cue in the absence of SCM reward, and reinstatement responding was recorded over two hours. Presentation of S+ stimuli resulted in a robust reinstatement of responding on the active lever in all animals but had no effect on inactive lever responding. A one-way ANOVA revealed that there were no significant differences in active lever responding between treatment groups (p>.05). No differences were observed across groups in terms of inactive lever responding (data not shown). Together, these data indicate that intra-VTA SB-334867 (3 and 6g) has no affect on cue-induced reinstatement of SCM-seeking.
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