Figure 1.
Cartoon depictions of the main procedural elements of the reward-related paradigms studied.
(A) Pavlovian-instrumental transfer. Mice were first trained to discriminate between one auditory cue (CS+) which was predictive of the delivery of a food reward and a second auditory cue (CS−) not associated with reward. Instrumental training, starting with a continuous schedule of reinforcement, progressed through increasingly sparse variable interval schedules of reinforcement to increase the rate of pressing on the active lever (AL) delivering food reward. Presses on a second, inactive (control) lever (IL) had no programmed consequences. During the PIT probe test, lever presses during presentations of the CS+, CS− and inter-trial interval (ITI) periods were recorded as well as Pavlovian approach behavior (head-entries (HE) into the magazine). (B) Acquisition, extinction and reinstatement of an instrumental response. Mice were trained to respond to a visual stimulus on a touchscreen to obtain a food reward (delivery of which was concomitant with a compound light/tone stimulus to serve as a conditioned reinforcer). During extinction training, responses produced no reward or conditioned reinforcement. Response were subsequently reinstated either by non-contingent delivery of reward and conditioned reinforcers (CR) during the first six of thirty trials (Reward6+CR6), delivery of the CRs during all thirty trials (CR30), or a combination of these two procedures (Reward6+CR30). (C) Malaise-induced reinforcer devaluation. During instrumental training, mice were trained to lever press on a random ratio reinforcement schedule for food reward. Next, on separate session conducted in the home cage, free availability of food pellet was paired with LiCl-induced malaise (Devalued group) or Food and LiCl injections were given unpaired (Non-devalued group). The effect of US-devaluation on lever pressing and magazine head entry was examined in the absence of the primary food reward (i.e. extinction) in the conditioning chambers.
Figure 2.
Reward-related behaviors in the C57BL/6J inbred mouse strain.
(A) Sessions to reach criterion on Pavlovian (PAV) and various schedules of instrumental training prior to the PIT probe (n = 13). (B) During the PIT probe, there were more active lever (AL) presses during the CS+ than the CS− trials, or the ITI periods (*p<.05), and more AL presses than inactive lever (IL) presses during the CS+ and CS− trials, and ITI periods (#p<.05). There were also more IL presses during the ITI periods than the CS+ (‡p<.05). (C) More head entries were made during the CS+ than CS− trials, or ITI periods (*p<.05) (n = 12). (D) Training sessions to acquire and extinguish a simple stimulus-reward instrumental response (n = 31). (E) Percent responding across extinction sessions. (F) Reinstatement of operant behavior by the Reward6+CR30, CR30 and Reward6+CR30 protocols (#p<.05 versus responding on last extinction session) (n = 10/condition). (G) Lever press responding across instrumental training session prior to devaluation (n = 17). (H) Pellets eaten prior to trial 1 and 2 of US-LiCl paired (Devalued) or unpaired (Non-devalued group) session in the home cage, during a context generalization test (GEN) in the conditioning chamber and the home cage retention test (RET) (n = 7–10/group). (I) Lever presses and head-entry responses into the magazine did not differ between devalued (D) and non-devalued (ND) groups. FR = fixed ratio, VI = variable interval, RR = random ratio. Data are Means ±SEM.
Figure 3.
Reward-related behaviors in the DBA/2J inbred mouse strain.
(A) Sessions to reach criterion on Pavlovian (PAV) and various schedules of instrumental training prior to the PIT probe (n = 12). (B) During the PIT probe, there were more active lever (AL) presses during the CS+ than the CS− or ITI (*p<.05), and more AL presses than inactive lever (IL) presses during the CS+, CS− and ITI (#p<.05). There were also more IL presses during the ITI than the CS+ and CS− (‡p<.05). (C) More head entries were made during the CS+ than CS− or ITI (*p<.05) (n = 12). (D) Sessions to acquire and extinguish a simple stimulus-reward operant behavior (n = 21). (E) Percent responding across extinction sessions. (F) Reinstatement of operant behavior by Reward6+CR6 and Reward6+CR30 but not CR6 protocols (#p<.05 versus responding on last extinction session) (n = 6–9/condition). (G) Increasing lever pressing with instrumental training prior to devaluation (n = 18). (H) Pellets eaten prior to trial 1 and 2 of US-sickness pairing, during a context generalization tests (GEN) and a long-term retention test (RET) (n = 9/group). (I) Lever presses and head entries did not differ between devalued (D) and non-devalued (ND) groups. FR = fixed ratio, VI = variable interval, RR = random ratio. Data are Means ±SEM.
Figure 4.
Reward-related behaviors in the BALB/cJ inbred mouse strain.
(A) Sessions to reach criterion on Pavlovian (PAV) and various schedules of instrumental training prior to the PIT probe (n = 12). (B) During the PIT probe, there were more active lever (AL) presses during the CS+ than the CS− or ITI (*p<.05), and more AL presses than inactive lever (IL) presses during the CS+, CS− and ITI (#p<.05). There were also more IL presses during the ITI than the CS+ and CS− (‡p<.05). (C) More head entries were made during the CS+ than CS− or ITI (*p<.05) (n = 12). (D) Sessions to acquire and extinguish a simple stimulus-reward operant behavior (n = 28). (E) Percent responding across extinction sessions. (F) Reinstatement of operant behavior by Reward6+CR6, CR6 and Reward6+CR30 (#p<.05 versus responding on last extinction session) (n = 9–10/condition). (G) Increasing lever pressing with instrumental training prior to devaluation (n = 16). (H) Pellets eaten prior to trial 1 and 2 of US-sickness pairing, during a context generalization tests (GEN) and a long-term retention test (RET) (n = 8/group). (I) Lever presses and head entries did not differ between devalued (D) and non-devalued (ND) groups. FR = fixed ratio, VI = variable interval, RR = random ratio. Data are Means ±SEM.