Basolateral Amygdala to Orbitofrontal Cortex Projections Enable Cue-Triggered Reward Expectations

Abstract

To make an appropriate decision, one must anticipate potential future rewarding events, even when they are not readily observable. These expectations are generated by using observable information (e.g., stimuli or available actions) to retrieve often quite detailed memories of available rewards. The basolateral amygdala (BLA) and orbitofrontal cortex (OFC) are two reciprocally connected key nodes in the circuitry supporting such outcome-guided behaviors. But there is much unknown about the contribution of this circuit to decision making, and almost nothing known about the whether any contribution is via direct, monosynaptic projections, or the direction of information transfer. Therefore, here we used designer receptor-mediated inactivation of OFC→BLA or BLA→OFC projections to evaluate their respective contributions to outcome-guided behaviors in rats. Inactivation of BLA terminals in the OFC, but not OFC terminals in the BLA, disrupted the selective motivating influence of cue-triggered reward representations over reward-seeking decisions as assayed by Pavlovian-to-instrumental transfer. BLA→OFC projections were also required when a cued reward representation was used to modify Pavlovian conditional goal-approach responses according to the reward's current value. These projections were not necessary when actions were guided by reward expectations generated based on learned action-reward contingencies, or when rewards themselves, rather than stored memories, directed action. These data demonstrate that BLA→OFC projections enable the cue-triggered reward expectations that can motivate the execution of specific action plans and allow adaptive conditional responding.SIGNIFICANCE STATEMENT Deficits anticipating potential future rewarding events are associated with many psychiatric diseases. Presently, we know little about the neural circuits supporting such reward expectation. Here we show that basolateral amygdala to orbitofrontal cortex projections are required for expectations of specific available rewards to influence reward seeking and decision making. The necessity of these projections was limited to situations in which expectations were elicited by reward-predictive cues. These projections therefore facilitate adaptive behavior by enabling the orbitofrontal cortex to use environmental stimuli to generate expectations of potential future rewarding events.

Keywords: DREADD; Pavlovian-to-instrumental transfer; chemogenetics; devaluation; hM4Di; reinstatement.

Figure 1.

Effect of CNO-hM4Di inactivation of OFC→BLA or BLA→OFC projections on postsynaptic responses. hM4Di-mCherry and/or ChR2-EYFP were expressed in either the BLA or OFC, and whole-cell patch-clamp recordings in voltage-clamp mode were obtained from postsynaptic BLA (OFC_hM4Di/ChR2→BLA: n = 5 cells; OFC_ChR2→BLA: n = 5) or OFC cells (BLA_hM4Di/ChR2→OFC: n = 7; BLA_ChR2→OFC: n = 5) before and after CNO application. A, Representative fluorescent image of hM4Di-mCherry/ChR2-eYFP expression in OFC cell bodies. Arrows indicate coexpressing cells. B, Representative florescent image of biocytin-filled cell (blue) surrounded by ChR2-eYFP and hM4Di-mCherry terminals in BLA. C, Representative fluorescent image of biocytin-filled cell surrounded by ChR2-eYFP and hM4Di-mCherry terminals in OFC. D, Representative fluorescent image of hM4Di-mCherry/ChR2-eYFP expression in BLA cell bodies. Scale bars, 20 μm. E, Sample traces (average of 2–3 sweeps) of evoked EPSCs in BLA in response to optical stimulation of OFC terminals (blue line, 470 nm, 5 ms pulse, 8 mW) before (black) and after (gray) CNO application. F, Sample traces of evoked EPSCs in OFC in response to optical stimulation of BLA terminals. G, Average optically evoked EPSC response following CNO, expressed as a percentage of pre-CNO baseline responses, compared between subjects expressing hM4Di and ChR2 with ChR2-only controls for recordings made in the BLA or OFC. Error bars indicate SEM. ***p < 0.001.

Figure 2.

Viral expression and cannulae placements. A–D, OFC_hM4Di→BLA rats (n = 10). Bilateral hsyn-hM4Di-mCherry injections were made into the OFC, and guide cannulae were implanted above the BLA, such that CNO infusion would inactivate OFC terminals in the BLA. A, Representative fluorescent image of hM4Di-mCherry expression in the OFC. Scale bars, 100 μm. B, Schematic representation of hM4Di-mCherry maximal viral spread in the OFC for all subjects. Numbers to the bottom right of each section indicate distance anterior to bregma (mm). Coronal section drawings taken from Paxinos and Watson (1998), their Figures 6–9 and 31–33, reprinted with permission. C, Representative immunofluorescent image of hM4Di-mCherry expression in the BLA. Dashed line indicates guide cannula track. D, Schematic representation of microinfusion injector tips in the BLA. E–H, BLA_hM4Di→OFC rats (n = 19). Bilateral hsyn-hM4Di-mCherry injections were made into the BLA, and guide cannulae were implanted above the OFC, such that CNO infusion would inactivate BLA terminals in the OFC. E, Representative immunofluorescent image of hM4Di-mCherry expression in the OFC. F, Schematic representation of microinfusion injector tips in the OFC. G, Representative fluorescent image of hM4Di-mCherry expression in the BLA. H, Schematic representation of hM4Di-mCherry maximal viral spread in the BLA for all subjects.

Figure 3.

Effect of inactivating OFC→BLA or BLA→OFC projections on PIT. A, Task design. O, Outcome/reward; A, action. B, C, Trial-averaged lever presses per 2-min period averaged across both levers during the Baseline periods compared with pressing during the CS periods separated for presses on the lever that, in training, delivered the same outcome as predicted by the CS (CS-Same) and pressing on the other available lever (CS-Diff) for OFC_hM4Di→BLA (B; n = 10) or BLA_hM4Di→OFC (C; n = 10) groups. Inset, CS-induced elevation in responding [CS presses/(CS presses + Baseline presses)] on action Same versus Different for the BLA_hM4Di→OFC group. D, E, Trial-averaged entries into the food-delivery port during the Baseline and CS periods for the OFC_hM4Di→BLA (D) and BLA_hM4Di→OFC (E) groups. Error bars indicate SEM. *p < 0.05. **p < 0.01. ***p < 0.001.

Figure 4.

Effect of CNO infusion in subjects lacking hM4Di receptors. A, B, Trial-averaged lever presses per 2-min period averaged across both levers during the Baseline periods compared with pressing during the CS periods separated for presses on the lever that, in training, delivered the same outcome as predicted by the CS (CS-Same) and pressing on the other available lever (CS-Diff) for OFC_mCherry→BLA (A; n = 11) and BLA_mCherry→OFC (B; n = 12) groups. Error bars indicate SEM. *p < 0.05. **p < 0.01. ***p < 0.001.

Figure 5.

Effect of inactivating BLA→OFC projections on sensitivity to outcome-specific devaluation. A, Task design. Only one devaluation condition shown. B, Average lever-press rate during the devaluation test. Presses separated for those that, in training, earned the currently devalued versus valued reward type. C, Trial-averaged entries into the food-delivery port during the Baseline and CS periods separated by the CS predicted the valued versus devalued reward. Inset, CS-induced elevation in responding [CS entries/(CS entries + Baseline entries)] (n = 9). Error bars indicate SEM. *p < 0.05. **p < 0.01.

Figure 6.

Effect of inactivating BLA→OFC projections on outcome-specific reinstatement. A, Task design. B, Trial-averaged lever presses per 2-min period averaged across both levers during the Baseline periods compared with pressing during the 2-min Reward periods following reward delivery, separated for presses on the lever that, in training, delivered the same outcome as the presented reward (Reinstated) and pressing on the other available lever (Non-reinstated). C, Trial-averaged entries into the food-delivery port during the Baseline and Reward-delivery periods (n = 9). Error bars indicate SEM. **p < 0.01. ***p < 0.001.