Frustrative nonreward: Chemogenetic inactivation of the central amygdala abolishes the effect of reward downshift without affecting alcohol intake

https://doi.org/10.1016/j.nlm.2020.107173Get rights and content

Highlights

  • The central amygdala (CeA) was inactivated with the inhibitory designer receptor hM4D(Gi).

  • CeA inactivation eliminated the effects of reward downshift in consummatory behavior.

  • CeA inactivation did not alter preference for 10% alcohol over water.

  • Clozapine-N-oxide (3 mg/kg, ip) by itself did not affect consummatory behavior.

  • Vehicle in animals that received the hM4D(Gi) designer receptor had no effect.

Abstract

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.

Section snippets

Experiment 1

The DREADDs procedure involves infusing an engineered G protein-coupled muscarinic receptor modified to respond only to the synthetic compound clozapine N-oxide (CNO) (Urban & Roth, 2015). The infusion is done before training starts and, once the receptor is genetically expressed within the target area, a systemic administration of CNO activates the receptor. CNO activates the DREADD producing either neural excitation or inhibition, depending on the type of engineered receptor infused. CNO can

Subjects

Fifty-two male Wistar rats, experimentally naïve and 90 days old at the start of the experiment served as subjects. The mean (SEM) ad lib weight of the 30 animals selected for analysis (see below) was 515.6 g (13.3 g). The maintenance conditions were the same described for Experiment 1.

Surgery

All animals were subjected to the surgical procedure. In preparation for surgery, animals were food deprived to 90% of their average free-food weights and anesthetized with inhalation isoflurane (5% for

Discussion

Chemogenetic inactivation of the CeA on sessions involving reward downshift eliminated the cSNC effect. This effect of CeA inactivation is in line with the results of previous experiments using permanent lesions (Becker et al., 1984) and reversible lidocaine inactivation (Kawasaki et al., 2015). In these previous experiments, the lesion and inactivation were not as restricted to the CeA as in the present case. This confirms that neurons located in this output nucleus from the amygdala are

Acknowledgments

The National Institute on Drug Abuse (NIDA) provided the clozapine N-oxide (CNO) used in this study. This research was partially funded by TCU/SERC grants received by S. Guarino (#17005) and Z. Wade (# 180329). The authors thank I. Muzzio and K. C. Leong for their help with the understanding of the DREADD technique, Y. Liu for providing access to the fluorescence microscope for processing images, C. Torres for comments on an earlier version of this article, and Z. Wade and Q. Nguyen for their

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