Ventral tegmental area GABA neurons mediate stress-induced blunted reward-seeking in mice

ARTICLE https://doi.org/10.1038/s41467-021-23906-2 OPEN Ventral tegmental area GABA neurons mediate stress-induced blunted reward-seeking in mice 1234567890():,; Daniel C. Lowes 1, Linda A. Chamberlin1, Lisa N. Kretsge 1, Emma S. Holt1, Atheir I. Abbas2, Alan J. Park 1,3,4, Lyubov Yusufova1, Zachary H. Bretton1, Ayesha Firdous1, Armen G. Enikolopov5, Joshua A. Gordon6 & Alexander Z. Harris 1,3 ✉ Decreased pleasure-seeking (anhedonia) forms a core symptom of depression. Stressful experiences precipitate depression and disrupt reward-seeking, but it remains unclear how stress causes anhedonia. We recorded simultaneous neural activity across limbic brain areas as mice underwent stress and discovered a stress-induced 4 Hz oscillation in the nucleus accumbens (NAc) that predicts the degree of subsequent blunted reward-seeking. Surprisingly, while previous studies on blunted reward-seeking focused on dopamine (DA) transmission from the ventral tegmental area (VTA) to the NAc, we found that VTA GABA, but not DA, neurons mediate stress-induced blunted reward-seeking. Inhibiting VTA GABA neurons disrupts stress-induced NAc oscillations and rescues reward-seeking. By contrast, mimicking this signature of stress by stimulating NAc-projecting VTA GABA neurons at 4 Hz reproduces both oscillations and blunted reward-seeking. Finally, we find that stress disrupts VTA GABA, but not DA, neural encoding of reward anticipation. Thus, stress elicits VTA-NAc GABAergic activity that induces VTA GABA mediated blunted reward-seeking. 1 Department of Psychiatry, Columbia University, College of Physicians and Surgeons, New York, NY, USA. 2 VA Portland Health Care System, Department of Behavioral Neuroscience and Department of Psychiatry, Oregon Health & Science University, Portland, OR, USA. 3 Division of Systems Neuroscience, New York State Psychiatric Institute, New York, NY, USA. 4 The Mortimer B. Zuckerman Mind Brain Behavior Institute at Columbia University, New York, NY, USA. 5 Department of Neuroscience and Kavli Institute for Brain Science, Columbia University Medical Center, New York, NY, USA. 6 National Institute of Mental Health, Bethesda, MD, USA. ✉email: NATURE COMMUNICATIONS | (2021)12:3539 | https://doi.org/10.1038/s41467-021-23906-2 | www.nature.com/naturecommunications 1 ARTICLE NATURE COMMUNICATIONS | https://doi.org/10.1038/s41467-021-23906-2 I n humans and rodents, acute stress transiently disrupts reward-seeking1,2, and repeated stress exposure produces lasting reward-seeking deficits3,4. Dopamine (DA) transmission between the ventral tegmental area (VTA) and the nucleus accumbens (NAc) lie at the core of reward processing5–7. Yet, despite 40 years of research into the DA anhedonia hypothesis8, we do not fully understand how stress disrupts reward processing and its underlying neural circuitry. Past studies investigating VTA-NAc DA transmission in stress-induced blunted rewardseeking have yielded conflicting results9,10. Crucially, these studies relied on indirect measures of reward circuit activity, such as in vitro or baseline in vivo recordings of DA neural firing rates. Here, we record reward circuit activity during both stress and subsequent reward-seeking to directly determine that VTA GABA activity links acute stress and blunted reward-seeking. Results Restraint stress induces low-frequency NAc LFP oscillations and impairs reward anticipation. To screen for the stressinduced neural activity that causes blunted reward-seeking, we recorded local field potentials (LFP)—which reflect local synchronous synaptic activity11,12—across brain areas implicated in depression, including the prefrontal cortex13,14, NAc4,13, dorsal and ventral hippocampus13,15, basolateral amygdala13, and VTA4,13, as mice either explored a familiar environment or underwent 30 mins of acute restraint stress. A prominent lowfrequency (2–7 Hz, henceforth 4 Hz) oscillation of LFP activity emerged in the NAc during restraint stress (Fig. 1a and Supplementary Fig. 1a). A restraint-induced oscillation also appeared in other brain regions, including the prefrontal cortex, where stress has previously been reported to induce low-frequency oscillations (Fig. 1b)16. However, simultaneous recordings revealed that the restraint-induced oscillation was largest in the NAc (Supplementary Fig. 1b). The magnitude of the restraint-induced oscillation did not differ between the core and shell of the NAc (Supplementary Fig. 1c). This restraint-induced oscillation straddles the hippocampal theta frequency range (4–12 Hz), yet simultaneous recordings in the hippocampus and NAc revealed that the restraint-induced oscillation was distinct from hippocampal theta (Supplementary Fig. 1d). We did not observe similar oscillations during periods of voluntary immobility in the familiar environment, suggesting that this neural activity reflects restraint, rather than decreased movement (Supplementary Fig. 1e). As further evidence that this oscillation is a signature of acute stress, it persisted at the same magnitude throughout the restraint session and only abated when the mice were released from restraint (Supplementary Fig. 2a). Restrained mice spent ~5% of their time struggling, and periods of struggling were associated with decreased 4 Hz power (Supplementary Fig. 2b). Moreover, exposure to another stressor (tail suspension) induced a similar magnitude low-frequency oscillation in the NAc that decreased during struggling events (Supplementary Fig. 2c), confirming that passive stressors elicit a 4 Hz NAc oscillation. Although recent work has proposed that respiration-driven oscillations originating in the olfactory bulbs and piriform cortex represent the true source of NAc oscillations17,18, we found only modest coherence between the NAc LFP and respirations, which was not increased by restraint (Supplementary Fig. 2d, e). Thus, rhythmic lowfrequency NAc LFP activity appears to be a neural signature of acute stress. We wondered if this stress-induced NAc activity could cause blunted reward-seeking. To test this hypothesis, we trained mice to collect rewards after hearing a reward-predicting cue (CS+). After a 1.5 s delay from CS+ onset, a reward was available for 5 s. Once the mice reached stable performance, we recorded VTA2 NAc reward circuit activity from them over 2 days as they either explored a familiar environment or underwent acute restraint stress in a counterbalanced order (Fig. 1c). Immediately after undergoing 30 mins of restraint stress, freely moving mice showed increased latency to retrieve rewards and decreased anticipatory (delay period) licking relative to mice exposed to a neutral environment for an equivalent period (Fig. 1d, e). This decreased reward anticipation returned to control levels when measured the following day (Supplementary Fig. 2f). Stress did not significantly decrease general mouse movement (Supplementary Fig. 2g) or non-reward-predicting cue (CS−) associated behavior (Supplementary Fi (...truncated)