Mechanopathology of biofilm-like Mycobacterium tuberculosis cords.

Mycobacterium tuberculosis (Mtb) cultured axenically without detergent forms biofilm-like cords, a clinical identifier of virulence. In lung-on-chip (LoC) and mouse models, cords in alveolar cells contribute to suppression of innate immune signaling via nuclear compression. Thereafter, extracellular cords cause contact-dependent phagocyte death but grow intercellularly between epithelial cells. The absence of these mechanopathological mechanisms explains the greater proportion of alveolar lesions with increased immune infiltration and dissemination defects in cording-deficient Mtb infections. Compression of Mtb lipid monolayers induces a phase transition that enables mechanical energy storage. Agent-based simulations demonstrate that the increased energy storage capacity is sufficient for the formation of cords that maintain structural integrity despite mechanical perturbation. Bacteria in cords remain translationally active despite antibiotic exposure and regrow rapidly upon cessation of treatment. This study provides a conceptual framework for the biophysics and function in tuberculosis infection and therapy of cord architectures independent of mechanisms ascribed to single bacteria.

cGAS-STING drives ageing-related inflammation and neurodegeneration.

Low-grade inflammation is a hallmark of old age and a central driver of ageing-associated impairment and disease1. Multiple factors can contribute to ageing-associated inflammation2; however, the molecular pathways that transduce aberrant inflammatory signalling and their impact in natural ageing remain unclear. Here we show that the cGAS-STING signalling pathway, which mediates immune sensing of DNA3, is a critical driver of chronic inflammation and functional decline during ageing. Blockade of STING suppresses the inflammatory phenotypes of senescent human cells and tissues, attenuates ageing-related inflammation in multiple peripheral organs and the brain in mice, and leads to an improvement in tissue function. Focusing on the ageing brain, we reveal that activation of STING triggers reactive microglial transcriptional states, neurodegeneration and cognitive decline. Cytosolic DNA released from perturbed mitochondria elicits cGAS activity in old microglia, defining a mechanism by which cGAS-STING signalling is engaged in the ageing brain. Single-nucleus RNA-sequencing analysis of microglia and hippocampi of a cGAS gain-of-function mouse model demonstrates that engagement of cGAS in microglia is sufficient to direct ageing-associated transcriptional microglial states leading to bystander cell inflammation, neurotoxicity and impaired memory capacity. Our findings establish the cGAS-STING pathway as a driver of ageing-related inflammation in peripheral organs and the brain, and reveal blockade of cGAS-STING signalling as a potential strategy to halt neurodegenerative processes during old age.

The cGAS-STING pathway drives type I IFN immunopathology in COVID-19.

COVID-19, which is caused by infection with SARS-CoV-2, is characterized by lung pathology and extrapulmonary complications1,2. Type I interferons (IFNs) have an essential role in the pathogenesis of COVID-19 (refs 3-5). Although rapid induction of type I IFNs limits virus propagation, a sustained increase in the levels of type I IFNs in the late phase of the infection is associated with aberrant inflammation and poor clinical outcome5-17. Here we show that the cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathway, which controls immunity to cytosolic DNA, is a critical driver of aberrant type I IFN responses in COVID-19 (ref. 18). Profiling COVID-19 skin manifestations, we uncover a STING-dependent type I IFN signature that is primarily mediated by macrophages adjacent to areas of endothelial cell damage. Moreover, cGAS-STING activity was detected in lung samples from patients with COVID-19 with prominent tissue destruction, and was associated with type I IFN responses. A lung-on-chip model revealed that, in addition to macrophages, infection with SARS-CoV-2 activates cGAS-STING signalling in endothelial cells through mitochondrial DNA release, which leads to cell death and type I IFN production. In mice, pharmacological inhibition of STING reduces severe lung inflammation induced by SARS-CoV-2 and improves disease outcome. Collectively, our study establishes a mechanistic basis of pathological type I IFN responses in COVID-19 and reveals a principle for the development of host-directed therapeutics.

Applying an evolutionary mismatch framework to understand disease susceptibility.

Noncommunicable diseases (NCDs) are on the rise worldwide. Obesity, cardiovascular disease, and type 2 diabetes are among a long list of "lifestyle" diseases that were rare throughout human history but are now common. The evolutionary mismatch hypothesis posits that humans evolved in environments that radically differ from those we currently experience; consequently, traits that were once advantageous may now be "mismatched" and disease causing. At the genetic level, this hypothesis predicts that loci with a history of selection will exhibit "genotype by environment" (GxE) interactions, with different health effects in "ancestral" versus "modern" environments. To identify such loci, we advocate for combining genomic tools in partnership with subsistence-level groups experiencing rapid lifestyle change. In these populations, comparisons of individuals falling on opposite extremes of the "matched" to "mismatched" spectrum are uniquely possible. More broadly, the work we propose will inform our understanding of environmental and genetic risk factors for NCDs across diverse ancestries and cultures.

Absolute pitch: neurophysiological evidence for early brain activity in prefrontal cortex.

Absolute pitch (AP) is the ability to rapidly label pitch without an external reference. The speed of AP labeling may be related to faster sensory processing. We compared time needed for auditory processing in AP musicians, non-AP musicians, and nonmusicians (NM) using high-density electroencephalographic recording. Participants responded to pure tones and sung voice. Stimuli evoked a negative deflection peaking at ~100 ms (N1) post-stimulus onset, followed by a positive deflection peaking at ~200 ms (P2). N1 latency was shortest in AP, intermediate in non-AP musicians, and longest in NM. Source analyses showed decreased auditory cortex and increased frontal cortex contributions to N1 for complex tones compared with pure tones. Compared with NM, AP musicians had weaker source currents in left auditory cortex but stronger currents in left inferior frontal gyrus (IFG) during N1, and stronger currents in left IFG during P2. Compared with non-AP musicians, AP musicians exhibited stronger source currents in right insula and left IFG during N1, and stronger currents in left IFG during P2. Non-AP musicians had stronger N1 currents in right auditory cortex than nonmusicians. Currents in left IFG and left auditory cortex were correlated to response times exclusively in AP. Findings suggest a left frontotemporal network supports rapid pitch labeling in AP.

Aging Enhances Neural Activity in Auditory, Visual, and Somatosensory Cortices: The Common Cause Revisited.

In humans, age-related declines in vision, hearing, and touch coincide with changes in amplitude and latency of sensory-evoked potentials. These age-related differences in neural activity may be related to a common deterioration of supra-modal brain areas (e.g., PFC) that mediate activity in sensory cortices or reflect specific sensorineural impairments that may differ between sensory modalities. To distinguish between these two possibilities, we measured neuroelectric brain activity while 37 young adults (18-30 years, 18 males) and 35 older adults (60-88 years, 20 males) were presented with a rapid randomized sequence of lateralized auditory, visual, and somatosensory stimuli. Within each sensory domain, we compared amplitudes and latencies of sensory-evoked responses, source activity, and functional connectivity (via phase-locking value) between groups. We found that older adults' early sensory-evoked responses were greater in amplitude than those of young adults in all three modalities, which coincided with enhanced source activity in auditory, visual, and somatosensory cortices. Older adults also showed stronger neural synchrony than young adults between superior prefrontal and sensory cortices; and in older adults, the degree of phase synchrony was positively correlated with the magnitude of source activity in sensory areas. Critically, older adults who showed enhanced neural activity in one sensory domain also showed enhanced activity in other modalities. Together, these findings support the common cause hypothesis of aging and highlight the role of prefrontal regions in exerting top-down control over sensory cortices.SIGNIFICANCE STATEMENT A prominent theory of aging posits that age-related declines in sensory processing across domains are related to a single common neurobiological mechanism. However, the neural evidence supporting this common cause hypothesis has remained elusive. Our study revealed robust age-related changes in three sensory domains across a range of neural metrics. Importantly, older adults who showed increased neural activity within one sensory domain also showed enhanced neural activity in the other two sensory modalities. No such relation among activity in sensory cortices was observed in young adults. Age-related increases in neural activity in sensory cortices coincided with enhanced neural synchrony between the PFC and sensory cortices, underlining the importance of the PFC in regulating sensory processing.

Asymmetric information flow in brain networks supporting expressive language in childhood.

Low-beta (13-23 Hz) event-related desynchrony (ERD), a neural signature of expressive language, lateralizes from bilateral to left hemisphere in development. In contrast, low-beta event-related synchrony (ERS), thought to reflect inhibition, lateralizes from bilateral to the right hemisphere across development. Using whole-brain directed connectivity analyses, we aimed to characterize hemispheric and regional contributions to expressive language, in childhood. We studied 80 children and adolescents, 4 to less than 19 years of age, performing covert auditory verb generation in magnetoencephalography. Outdegree, indegree, and betweenness centrality were used to differentiate regions acting as drivers, receivers, and bridging hubs, respectively. The number of suprathreshold connections significantly increased with age for delta band (p < .01). Delta outflow was mapped to left inferior frontal gyrus (IFG), while regions of right hemisphere, including right IFG, showed significant inflow. The right parietal cortex showed significant ERS, but without corresponding outdegree or indegree. Betweenness mapped to midline cortical and subcortical structures. Results suggest Broca's area develops a driving role in the language network, while Broca's homologue receives information without necessarily propagating it. Subcortical and midline hubs act as intrahemispheric relays. Findings suggest that Broca's homologue is inhibited during expressive language, in development.

Trends in fetal and neonatal outcomes during the COVID-19 pandemic in Alabama.

BACKGROUND: The current study evaluated the hypothesis that the COVID-19 pandemic is associated with higher stillbirth but lower neonatal mortality rates. METHODS: We compared three epochs: baseline (2016-2019, January-December, weeks 1-52, and 2020, January-February, weeks 1-8), initial pandemic (2020, March-December, weeks 9-52, and 2021, January-June, weeks 1-26), and delta pandemic (2021, July-September, weeks 27-39) periods, using Alabama Department of Public Health database including deliveries with stillbirths ≥20 weeks or live births ≥22 weeks gestation. The primary outcomes were stillbirth and neonatal mortality rates. RESULTS: A total of 325,036 deliveries were included (236,481 from baseline, 74,076 from initial pandemic, and 14,479 from delta pandemic period). The neonatal mortality rate was lower in the pandemic periods (4.4 to 3.5 and 3.6/1000 live births, in the baseline, initial, and delta pandemic periods, respectively, p < 0.01), but the stillbirth rate did not differ (9 to 8.5 and 8.6/1000 births, p = 0.41). On interrupted time-series analyses, there were no significant changes in either stillbirth (p = 0.11 for baseline vs. initial pandemic period, and p = 0.67 for baseline vs. delta pandemic period) or neonatal mortality rates (p = 0.28 and 0.89, respectively). CONCLUSIONS: The COVID-19 pandemic periods were not associated with a significant change in stillbirth and neonatal mortality rates compared to the baseline period. IMPACT: The COVID-19 pandemic could have resulted in changes in fetal and neonatal outcomes. However, only a few population-based studies have compared the risk of fetal and neonatal mortality in the pandemic period to the baseline period. This population-based study identifies the changes in fetal and neonatal outcomes during the initial and delta COVID-19 pandemic period as compared to the baseline period. The current study shows that stillbirth and neonatal mortality rates were not significantly different in the initial and delta COVID-19 pandemic periods as compared to the baseline period.

Rapid endotheliitis and vascular damage characterize SARS-CoV-2 infection in a human lung-on-chip model.

Severe cases of SARS-CoV-2 infection are characterized by hypercoagulopathies and systemic endotheliitis of the lung microvasculature. The dynamics of vascular damage, and whether it is a direct consequence of endothelial infection or an indirect consequence of an immune cell-mediated cytokine storm remain unknown. Using a vascularized lung-on-chip model, we find that infection of alveolar epithelial cells leads to limited apical release of virions, consistent with reports of monoculture infection. However, viral RNA and proteins are rapidly detected in underlying endothelial cells, which are themselves refractory to apical infection in monocultures. Although endothelial infection is unproductive, it leads to the formation of cell clusters with low CD31 expression, a progressive loss of barrier integrity and a pro-coagulatory microenvironment. Viral RNA persists in individual cells generating an inflammatory response, which is transient in epithelial cells but persistent in endothelial cells and typified by IL-6 secretion even in the absence of immune cells. Inhibition of IL-6 signalling with tocilizumab reduces but does not prevent loss of barrier integrity. SARS-CoV-2-mediated endothelial cell damage thus occurs independently of cytokine storm.

The Diversity-Innovation Paradox in Science.

Prior work finds a diversity paradox: Diversity breeds innovation, yet underrepresented groups that diversify organizations have less successful careers within them. Does the diversity paradox hold for scientists as well? We study this by utilizing a near-complete population of ∼1.2 million US doctoral recipients from 1977 to 2015 and following their careers into publishing and faculty positions. We use text analysis and machine learning to answer a series of questions: How do we detect scientific innovations? Are underrepresented groups more likely to generate scientific innovations? And are the innovations of underrepresented groups adopted and rewarded? Our analyses show that underrepresented groups produce higher rates of scientific novelty. However, their novel contributions are devalued and discounted: For example, novel contributions by gender and racial minorities are taken up by other scholars at lower rates than novel contributions by gender and racial majorities, and equally impactful contributions of gender and racial minorities are less likely to result in successful scientific careers than for majority groups. These results suggest there may be unwarranted reproduction of stratification in academic careers that discounts diversity's role in innovation and partly explains the underrepresentation of some groups in academia.

Retaining Hückel Aromaticity in the Triplet Excited State of Azobenzene.

The implication of the potential concept of aromaticity in the relaxed lowest triplet state of azobenzene, an efficient molecular switch, using elementary aromaticity indices based on magnetic, electronic, and geometric criteria has been discussed. Azobenzene exhibits a major Hückel aromatic character retained in the diradical lowest relaxed triplet state (T1 ) by virtue of a twisted geometry with partial delocalization of unpaired electrons in the perpendicular p-orbitals of two nitrogen atoms to the corresponding phenyl rings. The computational analysis has been expanded further to stilbene and N-diphenylmethanimine for an extensive understanding of the effect of closed-shell Hückel aromaticity in double-bond-linked phenyl rings. Our analysis concluded that stilbene has Hückel aromatic character in the relaxed T1 state and N-diphenylmethanimine has a considerable Hückel aromaticity in the phenyl ring near the carbon atom while a paramount Baird aromaticity in the phenyl ring near the nitrogen atom of the C=N double bond. The results reveal the application of excited-state aromaticity as a general tool for the design of molecular switches.

Clinical outcomes of bileaflet St. Jude Medical and tilting disc TTK Chitra mechanical heart valve prosthesis: A comparative study.

BACKGROUND: Comparative data on the clinical outcomes of TTK Chitra mechanical heart valve prosthesis (CHVP), an indigenously developed low-cost tilting disc valve and commonly used bileaflet valve, the St. Jude medical (SJM) prosthesis are sparse. METHODS: We conducted a retrospective follow-up study of consecutive patients undergoing mitral (MVR) and aortic valve replacement (AVR) with SJM or CHVP mechanical prostheses over a 6-year period at our institution. RESULTS: Seven hundred and thirty-five patients who underwent isolated MVR (n = 510) or AVR (n = 225) were included in the study. Patients with CHVP were younger and belonged to a lower socioeconomic class. The study cohort was followed-up for 2836 patient-years (SJM: 1865.1, CHVP: 971.0). All-cause mortality (p = 0.894), valve-related mortality (p = 0.681), prosthetic valve thrombosis (p = 0.155), embolism (p = 0.210), hemorrhage (p = 0.959) and infective endocarditis (IE, p = 0.084) were similar between both valve on follow-up. Estimated event free survival was 2302 ± 1 days in SJM as compared to 2484 ± 65 days in CHVP group (p = 0.393). Valve type was not an independent predictor of adverse events after adjusting for baseline data, time in therapeutic range and aspirin use. Subgroup analysis of patients who underwent MVR and AVR showed similar functional improvement and outcomes, except for a higher incidence of IE with SJM at the aortic position (p = 0.041). CONCLUSION: The indigenously developed, low-cost CHVP has comparable midterm clinical performance as SJM in aortic or mitral positions.

Efficacy of Skin-to-Skin Care versus Swaddling for Pain Control Associated with Vitamin K Administration in Full-Term Neonates: A Randomized Controlled Trial.

OBJECTIVE: The objective of the study was to assess the efficacy of immediate skin-to-skin care (SSC) versus swaddling in pain response to intramuscular injection of vitamin K at 30 min of birth in neonates. METHODS: Healthy full-term newborns were enrolled immediately after normal vaginal delivery and randomized in two groups, SSC and swaddling. Neonatal Infant Pain Scale (NIPS) was measured before, immediately after and at 2 min after the injection. RESULTS: Total 100 newborns were enrolled in the study (50 in each group). The mean (SD) birth weight of newborns in the SSC and swaddling group was 2668 (256) and 2730 (348) g, respectively. NIPS was comparable between the SSC and swaddling at before [1.78 (0.58) vs. 1.96 (0.83), p = 0.21], and immediately after the injection [4.82 (0.72) vs. 5.08 (0.75), p = 0.08]. NIPS at 2 min after the injection was significantly low in the SSC group compared to the swaddling group [1.38 (0.70) vs. 2.88 (1.00), p < 0.001]. At 2 min after injection, the NIPS score was significantly lower than baseline in the SSC group (p = 0.002), while it was significantly higher in the swaddling group (p < 0.001). A significantly higher proportion of newborns had a NIPS score of more than three at 2 min after injection in the swaddling group as compared to the SSC group (22% vs. 2%, p < 0.001). CONCLUSION: Immediate SSC was more efficacious as compared to swaddling as a pain control intervention while giving vitamin K injection. CLINICAL TRIAL REGISTRATION: The trial is registered with the Clinical Trial Registry of India with Registration number: CTRI/2020/01/022984.

Skin-to-skin care and swaddling are commonly used non-pharmacological measures to reduce pain perception in neonates for invasive procedures like heel prick, venipuncture and vaccination. We did this randomized control trial to compare the efficacy of immediate skin-to-skin care after birth vs. swaddling for reducing neonatal pain associated with intramuscular injection of vitamin K at 30 min after birth. We observed that the immediate skin-to-skin care, a standard of care, is more efficacious in controlling pain compared to swaddling for giving routine intramuscular vitamin K injection within one hour of birth.

Clinical Profile of Prosthetic Valve Endocarditis due to Candida parapsilosis: An 11-year Retrospective Observational Study from a Quaternary Cardiac Referral Institute in India.

Background: Recent changes in the diagnostic criteria and the introduction of newer technologies like prosthetic valve replacement require the need to identify the changing epidemiology of prosthetic valve endocarditis (PVE). Materials and methods: This is a retrospective, cross-sectional, observational study. Patients diagnosed with Candida parapsilosis definite and possible PVE as per modified Duke's criteria for a period of 11 years from January 2010 to December 2020 were included for the analysis. Results: Twelve of the 47 PVE cases (25.5%) were caused by C. parapsilosis. The median age of the patients was 52 years. Males were predominantly affected (58%). Based on the modified Duke's criteria, eight (67%) were definite infective endocarditis (IE) cases. The single valve was affected in 11 cases (92%) with the mitral valve being the commonest (n = 8, 67%). The type of valve commonly involved was mechanical [n = 10, 83%]. The mean size of the vegetation was 13.15 mm. Most cases (n = 7, 58%) were late-onset PVE. The mean C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), and procalcitonin (PCT) levels for C. parapsilosis PVE were 70.2 mg/L, 51.08 mm/hour, and 0.3 ng/mL, respectively. The rates of complications and in-hospital mortality were 75% each. The most common observed complication was embolic events (n = 8, 67%). Statistical significance (p ≤ 0.05) was observed for mean vegetation size, overall complications, embolic events, and mortality for C. parapsilosis PVE when compared with bacterial PVE. Conclusion: C. parapsilosis was the commonest etiological agent causing PVE. Predominant mitral valve involvement, higher rates of late-onset presentation, complications, and mortality were key differential characteristics observed. Highlights: The manuscript throws light on the changing epidemiology, clinical, and microbiological profile of PVE due to Candida sp., which are scarcely studied and reported in low- and middle-income countries like India. How to cite this article: Ponnambath DK, Gopalakrishnan A, Pillai VV, Kaviyil JE, Raja K. Clinical Profile of Prosthetic Valve Endocarditis due to Candida parapsilosis: An 11-year Retrospective Observational Study from a Quaternary Cardiac Referral Institute in India. Indian J Crit Care Med 2021;25(8):860-865.

Preserving quantifiable ethnographic records of disappearing human lifeways.

The human evolutionary sciences place high value on quantitative data from traditional small-scale societies that are rapidly modernizing. These data often stem from the sustained ethnographic work of anthropologists who are today nearing the end of their careers. Yet many quantitative ethnographic data are preserved only in summary formats that do not reflect the rich and variable ethnographic reality often described in unpublished field notes, nor the deep knowledge of their collectors. In raw disaggregated formats, such data have tremendous scientific value when used in conjunction with modern statistical techniques and as part of comparative analyses. Through a personal example of longitudinal research with Batek hunter-gatherers that involved collaboration across generations of researchers, we argue that quantifiable ethnographic records, just like material artifacts, deserve high-priority preservation efforts. We discuss the benefits, challenges, and possible avenues forward for digitizing, preserving, and archiving ethnographic data before it is too late.

Leopard predation on gelada monkeys at Guassa, Ethiopia.

Predation is widely believed to exert strong selective pressure on primate behavior and ecology but is difficult to study and rarely observed. In this study, we describe seven encounters between lone wild leopards (Panthera pardus) and herds of geladas (Theropithecus gelada) over a 6-year period in an intact Afroalpine grassland ecosystem at the Guassa Community Conservation Area, Ethiopia. Three encounters consisted of attempted predation on geladas by leopards, one of which was successful. All three attacks occurred in low-visibility microhabitats (dominated by tussock graminoids, mima mounds, or tall shrubs) that provided leopards with hidden viewsheds from which to ambush geladas. An additional four encounters did not result in an attempted attack but still document the consistently fearful responses of geladas to leopards. In encounters with leopards, geladas typically gave alarm calls (n = 7 of 7 encounters), reduced interindividual distances (n = 5), and collectively fled towards or remained at their sleeping cliffs (n = 7), the only significant refugia in the open-country habitat at Guassa. Geladas did not engage in mobbing behavior towards leopards. Encounters with leopards tended to occur on days when gelada herd sizes were small, raising the possibility that leopards, as ambush hunters, might stalk geladas on days when fewer eyes and ears make them less likely to be detected. We compare the behavioral responses of geladas to leopards at Guassa with those previously reported at Arsi and the Simien Mountains and discuss how gelada vulnerability and responses to leopards compare with those of other primate species living in habitats containing more refugia. Lastly, we briefly consider how living in multilevel societies may represent an adaptive response by geladas and other open-country primates to predation pressure from leopards and other large carnivores.

Hunter-gatherer residential mobility and the marginal value of rainforest patches.

The residential mobility patterns of modern hunter-gatherers broadly reflect local resource availability, but the proximate ecological and social forces that determine the timing of camp movements are poorly known. We tested the hypothesis that the timing of such moves maximizes foraging efficiency as hunter-gatherers move across the landscape. The marginal value theorem predicts when a group should depart a camp and its associated foraging area and move to another based on declining marginal return rates. This influential model has yet to be directly applied in a population of hunter-gatherers, primarily because the shape of gain curves (cumulative resource acquisition through time) and travel times between patches have been difficult to estimate in ethnographic settings. We tested the predictions of the marginal value theorem in the context of hunter-gatherer residential mobility using historical foraging data from nomadic, socially egalitarian Batek hunter-gatherers (n = 93 d across 11 residential camps) living in the tropical rainforests of Peninsular Malaysia. We characterized the gain functions for all resources acquired by the Batek at daily timescales and examined how patterns of individual foraging related to the emergent property of residential movements. Patterns of camp residence times conformed well with the predictions of the marginal value theorem, indicating that communal perceptions of resource depletion are closely linked to collective movement decisions. Despite (and perhaps because of) a protracted process of deliberation and argument about when to depart camps, Batek residential mobility seems to maximize group-level foraging efficiency.

Development and Validation of HPLC Method for Determination of Sodium Copper Chlorophyllin - A Food Colorant and Its Application in Pharmacokinetic Study.

A simple, accurate, and precise bioanalytical method was developed and validated for the determination of pharmacokinetic parameters of sodium copper chlorophyllin, a USFDA approved food additive and colorant in rat plasma. The column used was Luna® C18 250×4.6 mm, 100 Å, having particle size 4.5 µm, and the mobile phase used was methanol (MeOH), and 10 mM ammonium acetate buffer in the ratio of 90 : 10, the flow rate was 1 ml/min, and the injection volume of 20 µL. The retention time of sodium copper chlorophyllin was obtained at 9 min. The method was found to be linear at the range of 0.50-8.00 µg mL-1 .

Increasing the expression level of ChR2 enhances the optogenetic excitability of cochlear neurons.

Optogenetics comprise a promising alternative to electrical stimulation for characterization of neural circuits and for the next generation of neural prostheses. Optogenetic stimulation relies on expression of photosensitive microbial proteins in animal cells to initiate a flow of ions into the cells in response to visible light. Here, we generated a novel transgenic mouse model in which we studied the optogenetic activation of spiral ganglion neurons, the primary afferent neurons of the auditory system, and showed a strong optogenetic response, with a similar amplitude as the acoustically evoked response. A twofold increase in the level of channelrhodopsin expression significantly increased the photosensitivity at both the single cell and organismal levels but also partially compromised the native electrophysiological properties of the neurons. The importance of channelrhodopsin expression level to optogenetic stimulation, revealed by these quantitative measurements, will be significant for the characterization of neural circuitry and for the use of optogenetics in neural prostheses.NEW & NOTEWORTHY This study reveals a dose-response relationship between channelrhodopsin expression and optogenetic excitation. Both single cell and organismal responses depend on the expression level of the heterologous protein. Expression level of the opsin is thus an important variable in determining the outcome of an optogenetic experiment. These results are key to the implementation of neural prostheses based on optogenetics, such as next generation cochlear implants, which would use light to elicit a neural response to sound.