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BackgroundAnhedonia is hypothesized to be associated with blunted mesocorticolimbic dopamine (DA) functioning in samples with major depressive disorder. The purpose of this study was to examine linkages between striatal DA binding, reward circuitry functioning, anhedonia, and, in an exploratory fashion, self-reported stress, in a transdiagnostic anhedonic sample.MethodsParticipants with (n=25) and without (n=12) clinically impairing anhedonia completed a reward-processing task during simultaneous positron emission tomography and magnetic resonance (PET-MR) imaging with [11C]raclopride, a DA D2/D3 receptor antagonist that selectively binds to striatal DA receptors.ResultsRelative to controls, the anhedonia group exhibited increased [11C]raclopride binding potential (ΔBPND) in response to rewards, interpreted as decreased task-related DA release, in the left putamen, caudate, and nucleus accumbens and right putamen and pallidum. There were no group differences in task-related brain activation (fMRI) during reward processing after correcting for multiple comparisons. General functional connectivity (GFC) findings revealed blunted fMRI connectivity between PET-derived striatal seeds and target regions (i.e., bilateral caudate, putamen, pallidum, medial prefrontal cortex, anterior cingulate cortex, and thalamus) in the anhedonia group. Associations were identified between anhedonia severity and the magnitude of task-related DA release to rewards in the left putamen, but not mesocorticolimbic GFC. We did not find evidence of associations between self-reported stress and striatal DA response to rewards, mesocorticolimbic fMRI activation or GFC in the anhedonic sample.ConclusionsResults provide evidence for reduced striatal DA functioning during reward processing and blunted mesocorticolimbic network functional connectivity in a transdiagnostic sample with clinically significant anhedonia.

SummaryBackgroundThe impact of COVID-19 on human health extends beyond the morbidity and death toll directly caused by the SARS-CoV-2 virus. In fact, accumulating evidence indicates a global increase in the incidence of fatigue, brain fog and depression, including among non-infected, since the pandemic onset. Motivated by previous evidence linking those symptoms to neuroimmune activation in other pathological contexts, we hypothesized that subjects examined after the enforcement of lockdown/stay-at-home measures would demonstrate increased neuroinflammation.MethodsWe performed simultaneous brain Positron Emission Tomography / Magnetic Resonance Imaging in healthy volunteers either before (n=57) or after (n=15) the 2020 Massachusetts lockdown, using [11C]PBR28, a radioligand for the glial marker 18 kDa translocator protein (TSPO). First, we compared [11C]PBR28 signal across pre- and post-lockdown cohorts. Then, we evaluated the link between neuroinflammatory signals and scores on a questionnaire assessing mental and physical impacts of the pandemic. Further, we investigated multivariate associations between the spatial pattern of [11C]PBR28 post-lockdown changes and constitutive brain gene expression in post-mortem brains (Allen Human Brain Atlas). Finally, in a subset (n=13 pre-lockdown; n=11 post-lockdown), we also used magnetic resonance spectroscopy to quantify brain (thalamic) levels of myoinositol (mIns), another neuroinflammatory marker.FindingsBoth [11C]PBR28 and mIns signals were overall stable pre-lockdown, but markedly elevated after lockdown, including within brain regions previously implicated in stress, depression and “sickness behaviors”. Moreover, amongst the post-lockdown cohort, subjects endorsing higher symptom burden showed higher [11C]PBR28 PET signal compared to those reporting little/no symptoms. Finally, the post-lockdown [11C]PBR28 signal changes were spatially aligned with the constitutive expression of several genes highly expressed in glial/immune cells and/or involved in neuroimmune signaling.InterpretationOur results suggest that pandemic-related stressors may have induced sterile neuroinflammation in healthy individuals that were not infected with SARS-CoV-2. This work highlights the possible impact of the COVID-19 pandemic-related lifestyle disruptions on human brain health.FundingR01-NS094306-01A1, R01-NS095937-01A1, R01-DA047088-01, The Landreth Family Foundation.

BackgroundThe social motivation hypothesis of autism suggests that autism spectrum disorder (ASD) is characterized by impaired motivation to seek out social experience early in life that interferes with the development of social functioning. This framework posits that impaired mesolimbic dopamine (DA) function underlies compromised responses to social rewards in ASD. Although this hypothesis is supported by functional magnetic resonance imaging (fMRI) studies, no molecular imaging study has evaluated striatal dopamine functioning in response to rewards in ASD.MethodsThis study evaluated striatal dopaminergic functioning during incentive processing in ASD using simultaneous positron emission tomography (PET) and fMRI using the D2/D3 dopamine receptor antagonist [11C]raclopride. Using a bolus + infusion protocol, voxel-wise binding potential (BPND) was compared between groups (Controls=12, ASD=10) in the striatum.ResultsRelative to controls, the ASD group demonstrated relatively decreased phasic DA release to incentives in the right and left putamen and left caudate. Striatal clusters showing significant between-group BPNDdifferences were used as seeds in whole-brain fMRI general functional connectivity analyses. This revealed increased connectivity between the PET-derived right putamen seed and clusters in the precuneus and right insula in the ASD group. Within the ASD group, decreased phasic DA release in the left putamen was related to poorer theory-of-mind skills.ConclusionsASD was characterized by impaired striatal phasic DA release and abnormally increased functional connectivity, providing support for the social motivation hypothesis of autism. PET measures of dopamine receptor target occupancy may be suitable to evaluate novel ASD therapeutics targeting the striatal dopamine system.