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The role of the central amygdala (CeA) in the adjustment to a 32-to-2% sucrose downshift in the consummatory successive negative contrast (cSNC) task and in a free-choice 10% alcohol-water preference task (PT) was studied using chemogenetic inactivation. cSNC is a model of frustrative nonreward that enhances alcohol consumption. In Experiment 1, sessions 1-10 involved 5-min access to 32% sucrose and sessions 11-12 involved access to 2% sucrose. Vehicle or clozapine N-oxide (CNO; 1 or 3 mg/kg, ip), used later to activate the inhibitory designer receptor, was administered 30 min before sessions 11-12. There was no evidence that CNO affected consummatory behavior after the sucrose downshift. In Experiment 2, all animals received an infusion of the inhibitory designer receptor hM4D(Gi) into the CeA. After recovery, animals received access to either 32% or 2% sucrose on sessions 1-10, followed by 2% sucrose on sessions 11-12. Immediately after each 5-min sucrose session, animals received a 2-bottle, 1-h PT with 10% alcohol and water. CNO (3 mg/kg, ip) or vehicle was administered 30 min before sessions 11-12. CeA inactivation prior to sucrose downshift eliminated the cSNC effect, which was observed in vehicle controls. However, there was no evidence that CeA inactivation affected preference for 10% alcohol over water. These results support the hypothesis that CeA activity is critical for cSNC effect, an outcome consistent with the view that the amygdala plays a central role in frustrative nonreward., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Successive negative contrast (SNC) involves a disruption of behavior when the paired reward is unexpectedly reduced from a large to a small amount, relative to a control always receiving the small amount. Five experiments with rats explored SNC in the Pavlovian autoshaping procedure in which a retractable lever is paired with the delivery of food pellets. In Experiment 1, a 12-to-2 pellet downshift either early in training (after 3 sessions) or late in training (after 20 sessions) yielded no significant evidence of SNC either in terms of lever pressing or goal entries. Experiment 2 showed that presession feeding (another form of reward devaluation) suppressed lever pressing in nonreinforced tests early in training. However, no statistical evidence of lever pressing suppression was found late in training. Presession feeding also suppressed lever pressing late in training if the test session included reinforcements. Experiment 3, using reward downshift, showed that adding a nontarget lever produced no statistical evidence of response suppression to the target lever during the downshift. Lever pressing to the target lever increased and goal entries tended to decrease after a 12-to-2 pellet downshift. Using a within-subject design and two target levers with distinct reward values (Experiment 4), reward downshift produced evidence of lever pressing enhancement in single-lever trials, but lever pressing suppression and a switch in preference to the unshifted lever in nonreinforced free-choice trials. Experiment 5 replicated these within-subject SNC effects, but found only modest evidence for a successive positive contrast effect in free-choice behavior. These results suggest that autoshaping in rats may induce response invigoration in forced-choice situations, but response suppression in free-choice situations. (PsycINFO Database Record (c) 2018 APA, all rights reserved).

Rats exposed to unexpected reward loss increase voluntary oral consumption of ethanol. Such consumption has been assumed to attenuate loss-induced negative affect (called emotional self-medication). To test this assumption, food-deprived male Wistar rats were exposed to 10 sessions of access to 32% sucrose followed by 5 sessions of access to 4% sucrose (reward downshift). A two-bottle preference test was initiated immediately after each consummatory session to assess ethanol intake. The experimental group received access to 2% ethanol and water, whereas the control group received access to two water bottles. On sessions 11, 12, and 15, immediately after the preference test, animals were tested in the elevated plus maze (EPM) for signs of anxiety. Sucrose consumption was reduced after the 32-to-4% sucrose downshift on sessions 11 and 12, but behavior recovered by session 15. Consummatory suppression was followed by increased ethanol intake in the preference test after sessions 11 and 12, but intake was reduced to preshift levels by session 15; no changes were observed in water controls. Finally, general activity (closed-arm entries and total arm entries) in the EPM increased in the ethanol group on session 12, but not on session 15, relative to water controls. The increase in ethanol consumption induced by reward downshift had measurable effects on activity as assessed in the EPM. These results show that voluntary oral 2% ethanol consumption after reward downshift can affect subsequent behavior, but fall short of providing unambiguous evidence that such ethanol consumption reduces negative affect., (Copyright © 2018 Elsevier B.V. All rights reserved.)

The dorsomedial striatum (DMS) has been implicated in the acquisition of reward representations, a proposal leading to the hypothesis that it should play a role in situations involving reward loss. We report the results of an experiment in which the effects of DMS excitotoxic lesions were tested in consummatory successive negative contrast (reward devaluation), autoshaping training with partial vs. continuous reinforcement (reward uncertainty), and appetitive extinction (reward omission). Animals with DMS lesions exhibited reduced lever pressing responding, but enhanced goal entries, during partial reinforcement training in autoshaping. However, they showed normal negative contrast, acquisition under continuous reinforcement (CR), appetitive extinction, and response facilitation in early extinction trials. Open-field testing also indicated normal motor behavior. Thus, DMS lesions selectively affected the behavioral adjustment to a situation involving reward uncertainty, producing a behavioral reorganization according to which goal tracking (goal entries) became predominant at the expense of sign tracking (lever pressing). This pattern of results shows that the function of the DMS in situations involving reward loss is not general, but restricted to reward uncertainty. We suggest that a nonassociative, drive-related process induced by reward uncertainty requires normal output from DMS neurons., (Copyright © 2016 IBRO. Published by Elsevier Ltd. All rights reserved.)

Exposing rats to an upshift from a small reward to a larger reward sometimes yields evidence of consummatory successive positive contrast (cSPC), an effect that could be a suitable animal model of positive emotion. However, cSPC is an unreliable effect. Ten experiments explored the effects of an upshift in sucrose or saccharin concentration on consummatory behavior under several conditions. There was occasional evidence of cSPC, but mostly a combination of increased consummatory behavior relative to preshift reward concentrations and a reduced behavioral level relative to unshifted controls. Such a pattern is consistent with processes causing opposite changes on behavior. Reward upshift may induce processes that suppress behavior, such as taste neophobia (induced by an intense sucrose taste) and generalization decrement (induced by novelty in reward conditions after the upshift). An experiment tested the role of such novelty-related effects by preexposing animals to either the upshift concentration (12% sucrose) or water during three days before the start of the experiment. Sucrose-preexposed animals drank significantly more than water-preexposed animals during the upshift, but just as much as unshifted controls (i.e., no evidence of cSPC). These results suggest that cSPC may be difficult to obtain reliably because reward upshift induces opposing processes. However, they also seriously question the ontological status of cSPC., (Copyright © 2016 Elsevier B.V. All rights reserved.)