Faculty Bibliography

22q11.2 Deletion Syndrome (22q11.2DS) is the strongest known molecular risk factor for schizophrenia. Brain responses to auditory stimuli have been studied extensively in schizophrenia and described as potential biomarkers of vulnerability to psychosis. We sought to understand whether these responses might aid in differentiating individuals with 22q11.2DS as a function of psychotic symptoms, and ultimately serve as signals of risk for schizophrenia. A duration oddball paradigm and high-density electrophysiology were used to test auditory processing in 26 individuals with 22q11.2DS (13-35 years old, 17 females) with varying degrees of psychotic symptomatology and in 26 age- and sex-matched neurotypical controls (NT). Presentation rate varied across three levels, to examine the effect of increasing demands on memory and the integrity of sensory adaptation. We tested whether N1 and mismatch negativity (MMN), typically reduced in schizophrenia, related to clinical/cognitive measures, and how they were affected by presentation rate. N1 adaptation effects interacted with psychotic symptomatology: Compared to an NT group, individuals with 22q11.2DS but no psychotic symptomatology presented larger adaptation effects, whereas those with psychotic symptomatology presented smaller effects. In contrast, individuals with 22q11.2DS showed increased effects of presentation rate on MMN amplitude, regardless of the presence of symptoms. While IQ and working memory were lower in the 22q11.2DS group, these measures did not correlate with the electrophysiological data. These findings suggest the presence of two distinct mechanisms: One intrinsic to 22q11.2DS resulting in increased N1 and MMN responses; another related to psychosis leading to a decreased N1 response.

Lipid-processing mechanisms during demyelination are poorly understood. In this issue of Neuron,Nugent et al. (2020) show by cell-specific lipidomics that Trem2 deficiency leads to cholesterol ester (CE) overload in microglia. This is mediated by misregulation of lipid metabolism genes and is rescued by modulating CE synthesis or efflux.

Coherent neuronal dynamics play an important role in complex cognitive functions. Optogenetic stimulation promises to provide new ways to test the functional significance of coherent neural activity. However, the mechanisms by which optogenetic stimulation drives coherent dynamics remain unclear, especially in the non-human primate brain. Here, we perform computational modeling and experiments to study the mechanisms of optogenetic-stimulation-driven coherent neuronal dynamics in three male non-human primates. Neural responses arise from stimulation-evoked, temporally dynamic excitatory (E) and inhibitory (I) activity. Spiking activity is more likely to occur during E/I imbalances. Thus the relative difference in the driven E and I responses precisely controls spike timing by forming a brief time interval of increased spiking likelihood. Experimental results agree with parameter dependent predictions from the computational models. These results demonstrate that optogenetic stimulation driven coherent neuronal dynamics are governed by the temporal properties of E-I activity. Transient imbalances in excitatory and inhibitory activity may provide a general mechanism for generating coherent neuronal dynamics without the need for an oscillatory generator.SIGNIFICANCE STATEMENTWe examine how coherent neuronal dynamics arise from optogenetic stimulation in the primate brain. Using computational models and experiments, we demonstrate that coherent spiking and local field potential activity is generated by stimulation-evoked responses of excitatory and inhibitory activity in networks, extending the growing literature on neuronal dynamics. These responses create brief time intervals of increased spiking tendency and are consistent with previous observations in the literature that balanced excitation and inhibition controls spike timing, suggesting that optogenetic-stimulation-driven coherence may arise from intrinsic E-I balance. Most importantly, our results are obtained in non-human primates and thus will play a leading role in driving the use of causal manipulations with optogenetic tools to study higher cognitive functions in the primate brain.

BACKGROUND:To assess the effects of eradication of hepatitis C virus (HCV) on cardiovascular risk (CVR) and preclinical atherosclerosis in HIV/HCV-coinfected patients. SETTING/METHODS:Prospective cohort study. METHODS:We assessed serum lipids, 10-year Framingham CVR scores, pulse wave velocity, carotid intima-media thickness, and biomarkers of inflammation and endothelial dysfunction (BMKs) at baseline and 96 weeks (wk) after initiation of anti-HCV therapy (Rx) in HIV/HCV-coinfected patients. RESULTS:A total of 237 patients were included. Anti-HCV therapy comprised pegylated interferon and ribavirin plus 1 direct-acting antiviral in 55.2%, pegylated interferon and ribavirin in 33.8%, and all-oral direct-acting antiviral in 11.0%. A total of 147 (62.0%) patients achieved sustained viral response (SVR). Median increases in low-density lipoprotein cholesterol in patients with and without SVR were 14 mg/dL and 0 mg/dL (P = 0.024), respectively. Increases in CVR categories were found in 26.9% of patients with SVR (P = 0.005 vs. baseline) and 8.1% of patients without SVR (P = 0.433). This resulted in a significant interaction between SVR and CVR over time (P < 0.001). No significant effect of SVR was observed for pulse wave velocity (P = 0.446), carotid intima-media thickness (P = 0.320), and BMKs of inflammation and endothelial dysfunction. CONCLUSIONS:In coinfected patients, eradication of HCV had no effect on markers of preclinical atherosclerosis and BMKs of inflammation and endothelial dysfunction but was associated with a clinically relevant rise in serum low-density lipoprotein cholesterol. Evaluation of CVR should be an integral part of care after the cure of chronic hepatitis C in patients with HIV.

Sudden unexplained death in childhood (SUDC) affects children >1-year-old whose cause of death remains unexplained following comprehensive case investigation and is often associated with hippocampal abnormalities. We prospectively performed systematic neuropathologic investigation in 20 SUDC cases, including (i) autopsy data and comprehensive ancillary testing, including molecular studies, (ii) ex vivo 3T MRI and extensive histologic brain samples, and (iii) blinded neuropathology review by 2 board-certified neuropathologists. There were 12 girls and 8 boys; median age at death was 33.3 months. Twelve had a history of febrile seizures, 85% died during apparent sleep and 80% in prone position. Molecular testing possibly explained 3 deaths and identified genetic mutations in TNNI3, RYR2, and multiple chromosomal aberrations. Hippocampal abnormalities most often affected the dentate gyrus (altered thickness, irregular configuration, and focal lack of granule cells), and had highest concordance between reviewers. Findings were identified with similar frequencies in cases with and without molecular findings. Number of seizures did not correlate with hippocampal findings. Hippocampal alterations were the most common finding on histological review but were also found in possibly explained deaths. The significance and specificity of hippocampal findings is unclear as they may result from seizures, contribute to seizure pathogenesis, or be an unrelated phenomenon.

The population activity of CA1 pyramidal neurons (PNs) segregates along anatomical axes with different behaviors, suggesting that CA1 PNs are functionally subspecialized based on somatic location. In dorsal CA1, spatial encoding is biased towards CA2 (CA1c) and in deep layers of the radial axis. In contrast, non-spatial coding peaks towards subiculum (CA1a) and in superficial layers. While preferential innervation by spatial versus non-spatial input from entorhinal cortex (EC) may contribute to this specialization, it cannot fully explain the range of in vivo responses. Differences in intrinsic properties thus may play a critical role in modulating such synaptic input differences. Here we examine the postsynaptic integrative properties of dorsal CA1 PNs in six subpopulations along the transverse (CA1c, CA1b, CA1a) and radial (deep, superficial) axes. Our results suggest that active and passive properties of deep and superficial neurons evolve over the transverse axis to promote the functional specialization of CA1c versus CA1a as dictated by their cortical input. We also find that CA1b is not merely an intermediate mix of its neighbors, but uniquely balances low excitability with superior input integration of its mixed input, as may be required for its proposed role in sequence encoding. Thus, synaptic input and intrinsic properties combine to functionally compartmentalize CA1 processing into at least three transverse axis regions defined by the processing schemes of their composite radial axis subpopulations.

Over 115 000 people are waiting for life-saving organ transplants, of whom a small fraction will receive transplants and many others will die while waiting. Existing efforts to expand the number of available organs, including increasing the number of registered donors and procuring organs in uncontrolled environments, are crucial but unlikely to address the shortage in the near future and will not improve donor/recipient compatibility or organ quality. If successful, organ bioengineering can solve the shortage and improve functional outcomes. Studying manufactured organs in animal models has produced valuable data, but is not sufficient to understand viability in humans. Before risking manufactured organ experimentation in living humans, study of bioengineered organs in recently deceased humans would facilitate evaluation of the function of engineered tissues and the complex interactions between the host and the transplanted tissue. Although such studies do not pose risk to human subjects, they pose unique ethical challenges concerning the previous wishes of the deceased, rights of surviving family members, effective operation and fair distribution of medical services, and public transparency. This article investigates the ethical, legal and social considerations in performing engineered organ research on the recently deceased.

Auto-reactive T cells are fundamental to many autoimmune processes, including neuromyelitis optica spectrum disorder (NMOSD). Several lines of evidence indicate that an antibody against aquaporin-4 (AQP4) is present in NMOSD patients. Further, this AQP4 antibody is pathogenic and can cause profound neurological damage. T cells are fundamental to many autoimmune processes, including NMOSD. Here we review work from animal models to discuss mechanisms by which auto-reactive T cells modulate the process by which antibodies cross the blood-brain barrier and orchestrate the local inflammatory milieu underlying NMOSD pathophysiology. We also examine clinical studies that document the presence of AQP4-specific T cells and the unique cytokine profile of NMOSD patients. This work encourages a renewed and broadened attention to the fundamental role of T cells in neuroautoimmune conditions which will hopefully lead to new therapies and better patients' outcomes.

BACKGROUND:Endovascular therapy (EVT) for stroke improves outcomes but is time sensitive. OBJECTIVE:To compare times to treatment and outcomes between patients taken to the closest primary stroke center (PSC) with those triaged in the field to a more distant comprehensive stroke center (CSC). METHODS:During the study, a portion of our region allowed field triage of patients who met severity criteria to a more distant CSC than the closest PSC. The remaining patients were transported to the closest PSC. We compared times to treatment and clinical outcomes between those two groups. Additionally, we performed a matched-pairs analysis of patients from both groups on stroke severity and distance to CSC. RESULTS:Over 2 years, 232 patients met inclusion criteria and were closest from the field to a PSC; 144 were taken to the closest PSC and 88 to the more distant CSC. The median additional transport time to the CSC was 7 min. Times from scene departure to alteplase and arterial puncture were faster in the direct group (50 vs 62 min; 93 vs 152 min; p<0.001 for both). Among patients who were independent before the stroke, the OR for less disability in the direct group was 1.47 (95% CI 1.13 to 1.93, p=0.003), and 2.06 (95% CI 1.10 to 3.89, p=0.01) for the matched pairs. CONCLUSIONS:In a densely populated setting, for patients with stroke who are EVT candidates and closest to a PSC from the field, triage to a slightly more distant CSC is associated with faster time to EVT, no delay to alteplase, and less disability at 90 days.