Neurophysiology of the Superior Laryngeal Nerve in an In Vivo Rat Model.

OBJECTIVE: The superior laryngeal nerve (SLN) is fundamental in laryngeal sensation, cough reflex, and pitch control. SLN injury has substantial consequences including altered sensation, aspiration, and dysphonia. To date, in vivo measurement of the SLN remains elusive. The purpose of this study was to assess the feasibility of recording motor and sensory evoked potentials in a rat SLN model. METHODS: Twenty-two rat hemi-laryngeal preparations (n = 11) were obtained from 4-month-old Sprague-Dawley rats and included in this study. Compound motor action potentials (CMAPs) and motor unit number estimation (MUNE) were calculated by stimulating the SLN at the point of medial extension near the carotid artery and by placing a recording electrode on the cricothyroid muscle. Sensory response was determined through stimulation of the SLN and laryngoscopic visualization of a laryngeal adductor reflex (LAR). SLN and cricothyroid muscle cross-sections were stained and histologic morphometrics were quantified. RESULTS: Laryngeal evoked potentials were successfully obtained in all trials. Mean CMAP latency and negative durations were 0.99 ± 0.57 ms and 1.49 ± 0.57 ms, respectively. The median MUNE was 2.06 (IQR 1.88, 3.51). LAR was induced with a mean intensity of 0.69 ± 0.20 mV. Mean axon count, myelin thickness, and g-ratio were 681 ± 192.2, 1.72 ± 0.26, and 0.45 ± 0.04, respectively. CONCLUSIONS: This study demonstrates the feasibility of recording evoked response potentials following SLN stimulation. We hypothesize that this work will provide a tractable animal model to study changes in laryngeal sensation and cricothyroid motor function with aging, neurodegenerative disease, aspiration, or nerve injury. LEVEL OF EVIDENCE: NA Laryngoscope, 134:1778-1784, 2024.

Quantitative Evaluation of Vocal Bowing Following Bilateral Thyroplasty in Age-Related Vocal Atrophy.

OBJECTIVE: Age-related vocal atrophy (ARVA) is associated with vocal fold bowing, persistent glottal gap during phonation, and dysphonia. Bilateral medialization thyroplasty is sometimes performed in patients with ARVA to improve vocal fold closure and voice. We set out to quantify stroboscopic changes in vocal fold bowing, glottal closure, and abduction angle following bilateral thyroplasty and determine how these changes affect voice quality among patients with ARVA. METHODS: Fifteen individuals with ARVA who underwent bilateral medialization thyroplasty were included in this study. Two independent investigators calculated bowing index (BI), normalized glottal gap area (NGGA), and maximum abduction angle from laryngostroboscopic exams using ImageJ™. Consensus Auditory-Perceptual Evaluation of Voice (CAPE-V) and patient-reported measures were collected before and after thyroplasty. RESULTS: Thyroplasty resulted in a 10-point improvement in overall CAPE-V (Mean dif -10; 95% CI -17, -3.3, p < 0.01) and VHI-10 (mean dif -3.8; 95% CI -9.8, 2.3, p = 0.19, n = 8). NGGA and BI significantly decreased following surgery (mean dif -78; 95% CI -155, -1.5, p = 0.05; and mean dif -2.1; 95% CI -2.4, -0.84, p < 0.01, respectively). BI correlated with CAPE-V scores (r = 0.66, 95% CI 0.22, 0.87, p < 0.01). When considering the normalized combined contributions of both NGGA and BI, there was a stronger correlation in CAPE-V scores (r = 0.87, 95% CI 0.50, 0.97, p < 0.01) compared with either measure alone. CONCLUSIONS: Thyroplasty resulted in a decrease in vocal fold bowing, glottal gap area, and CAPE-V scores in patients with ARVA. Correction of vocal bowing and glottal gap, following bilateral thyroplasty, improved voice measures following surgery. Quantitative evaluation of vocal fold morphology may be valuable when assessing the severity and treatment-response in patients with ARVA following bilateral thyroplasty. Laryngoscope, 134:835-841, 2024.

Recurrent laryngeal motor nerve conduction studies in a rat model: Establishing an objective measure for investigating laryngeal innervation.

INTRODUCTION/AIMS: Disease or injury can cause neuromuscular changes to the larynx that can affect voice, breathing, and swallowing. Motor nerve conduction studies have had limited use in the study of laryngeal neurophysiology, despite their importance in other anatomic sites. The aim of this study was to explore the feasibility of performing recurrent laryngeal motor nerve conduction studies (rlMNCS) in a rat model. METHODS: rlMNCS were performed in 15 rats under anesthesia. A bipolar stimulating electrode was placed on the recurrent laryngeal nerve (RLN) 5 mm below the cricoid cartilage. Via direct laryngoscopy, a recording electrode was placed transorally into the thyroarytenoid muscle. The RLN was maximally stimulated to determine the compound muscle action potential (CMAP). Three consecutive trials were averaged. RESULTS: The mean stimulating threshold to the RLN to achieve a CMAP from the thyroarytenoid was 1.7 ± 0.6 mA. RLN stimulation caused a visible adductor twitch of the vocal fold in all animals. The mean negative amplitude was 2.0 ± 0.8 mV, and the total area was 1.0 ± 0.4 mV ms. The CMAP latency and negative duration were 1.0 ± 0.1 ms and 0.9 ± 0.2 ms, respectively. DISCUSSION: rlMNCS are feasible and may be useful in understanding laryngeal neurophysiology with disease or injury. This work could provide a tractable animal model for studying and monitoring treatment of neuromuscular conditions affecting voice, breathing, and swallowing.

Utilizing novel recurrent laryngeal motor nerve conduction studies to characterize the aging larynx: A pilot study.

Objectives: Age-related changes to the larynx are associated with dysphonia and contribute to reduced quality of life. This study utilizes recurrent laryngeal motor nerve conduction studies (rlMNCS) to determine if neurophysiologic changes occur in the aging larynx using an aging rat model. Study Design: Animal study. Methods: In vivo rlMNCS were performed in 10 young hemi-larynges (3-4 months) and 10 aged hemi-larynges (18-19 months) rats (Fischer 344 × Brown Norway F344BN). Recording electrodes were placed into the thyroarytenoid (TA) muscle through direct laryngoscopy. Recurrent laryngeal nerves (RLNs) were directly stimulated with bipolar electrodes. Compound motor action potentials (CMAPs) were obtained. RLN cross-sections were stained with toluidine blue. Axon count, myelination, and g-ratio were quantified utilizing AxonDeepSeg analysis software. Results: rlMNCS were successfully obtained in all animals. Mean CMAP amplitude and negative durations in young rats were 3.58 ± 2.20 mV and 0.93 ± 0.14 mS (mean dif: 0.17; 95% CI: -2.21 to 2.54), respectively, and 3.74 ± 2.81 mV and 0.98 ± 0.11 mS (mean dif: 0.050; 95% CI: -0.07 to 0.17). No significant differences in onset latency or negative area were observed. Mean axon count in young rats (176 ± 35) was comparable to that in old rats (173 ± 31). Myelin thickness and g-ratio did not differ between groups. Conclusions: There were no statistically significant differences in RLN conduction or axon histology between young and aged rats in this pilot study. This work provides a basis for future, adequately powered studies, and may lead to a tractable animal model to study the aging larynx. Level of Evidence: 5.

Treatments for Age-related Vocal Atrophy: A Systematic Review.

OBJECTIVE: Age-related vocal atrophy (ARVA) can dramatically affect voice, communication, and quality of life. The objectives of this systematic review were to (1) determine whether treatments for ARVA were superior to controls (2) compare the relative efficacy of procedural and behavioral treatments (3) review the various types of outcome measures, and (4) evaluate the quality of studies. REVIEW METHODS: The literature was searched using strategies designed by a medical librarian (2/18/21, updated 3/9/22). Studies investigating treatments for bilateral vocal atrophy were included. Studies involving unilateral atrophy, presbyphonia (without endoscopic findings), or an absent comparator group were excluded. The Preferred Reporting Items for Systematic Reviews and Meta-analyses checklist was used to guide this study. RESULTS: After applying the inclusion/exclusion criteria, 8 articles remained, including 4 randomized trials and 4 cohort studies, and a narrative synthesis was performed. Surgical and behavioral treatments for ARVA appeared to be superior to control groups, based on specific outcome measures. However, the superiority of these treatments over controls was not uniformly observed across multiple outcome measures. When comparing different treatments, superiority could not be established based on the quality and completeness of the studies included in the systematic review. Outcome measures also varied between individual studies. Finally, the risk of bias was analyzed and scored. Consistent point deductions among reviewed studies were noted. CONCLUSIONS: When comparing treatments for ARVA. Surgery and voice therapy were both superior to control groups based on specific outcome measures from different domains. Superiority of one treatment could not be established. LEVEL OF EVIDENCE: N/A Laryngoscope, 133:2846-2855, 2023.

Postmarketing Reporting of Paxlovid-Related Dysgeusia: A Real-World Pharmacovigilance Study.

OBJECTIVE: A novel COVID-19 therapeutic, nirmatrelvir/ritonavir (Paxlovid), is commonly associated with reports of dysgeusia. The Food and Drug Administration Adverse Event Reporting System (FAERS) database was used to determine the real-world reporting of Paxlovid-associated dysgeusia (PAD), identify associated factors, and describe the relative reporting rates of dysgeusia for Paxlovid compared to other COVID-19 therapeutics (OCT), ritonavir alone, and other protease inhibitors (OPI). STUDY DESIGN: Observational retrospective. SETTING: Tertiary academic medical center. METHODS: We collected patient and adverse event characteristics reported in the FAERS database between January 1968 and September 2022. Disproportionality analyses were used to compare the reporting of PAD to dysgeusia reported for OCT, ritonavir, and OPI. RESULTS: 345,229 adverse events were included in the present study. Dysgeusia was a frequently reported Paxlovid-associated adverse event (17.5%) and was associated with nonserious COVID-19 infection (reporting odds ratio [ROR] 1.4; 95% confidence interval [CI] 1.2, 1.7) and female sex (ROR = 1.7; 95% CI 1.6, 1.9). Paxlovid was more likely to be associated with the reporting of dysgeusia compared to OCT (ROR 305.4; 95% CI 164.1, 568.5), ritonavir (ROR 28.0; 95% CI 24.1, 32.7), and OPI (ROR 49.0; 95% CI 42.8, 56.1). CONCLUSION: Dysgeusia is much more likely to be reported by patients receiving Paxlovid than those receiving OCT, ritonavir alone, or OPI. These findings suggest a potential mechanism of dysgeusia that causes distorted taste out of proportion to the background effects of COVID-19 infection and specific to nirmatrelvir. Future studies are needed to determine the underlying pathophysiology and long-term clinical implications for patients who report dysgeusia with Paxlovid.

Quantification of Vocal Fold Atrophy in Age-Related and Parkinson's Disease-Related Vocal Atrophy.

OBJECTIVE: Vocal fold atrophy (VFA) is associated with aging and Parkinson's disease (PD). Clinical diagnosis of VFA depends on several visual-perceptual laryngostroboscopy findings that are inherently subjective. The purpose of this study was to use quantitative measurements to; (1) examine the relationships between VFA and dysphonia severity and (2) evaluate differences in VFA in patients with age-related VFA versus PD. METHODS: Thirty-six patients >60 years of age with VFA were included in this retrospective cohort study. Demographic information, medical history, Consensus Auditory-Perceptual Evaluation of Voice (CAPE-V), Voice Handicap Index-10 (VHI-10), and still images from the stroboscopic exam were obtained. Image J™ was used to measure VFA, including bowing index (BI), normalized glottal gap area, and normalized mucosal wave amplitude. Pearson's correlation was used to evaluate the relationship between VFA, CAPE-V, and VHI-10. t-Tests and multivariate linear regression were used to compare VFA measures by dysphonia severity (CAPE-V <30 vs. >30) and diagnosis (age-related vocal atrophy [ARVA] and PD). RESULTS: BI was positively correlated with CAPE-V. Patients with CAPE-V >30 had a significantly larger BI compared to those with CAPE-V <30. Patients with PD had significantly larger BI than those with ARVA. Diagnosis of PD also predicted a larger BI after controlling for age and CAPE-V. CONCLUSION: Quantitative measures supported an association between bowing severity and dysphonia severity in patients with PD and ARVA. A PD diagnosis significantly predicted more severe BI. These findings demonstrate the potential utility of BI. Quantitative VFA measures might also provide insight into the mechanisms of ARVA and dysphonia. LEVEL OF EVIDENCE: 3 Laryngoscope, 133:1462-1469, 2023.

Long-term outcomes with the pulmonary autograft inclusion technique in adults with bicuspid aortic valves undergoing the Ross procedure.

OBJECTIVE: To compare outcomes with wrapped (pulmonary autograft inclusion) versus unwrapped techniques in adults with bicuspid aortic valves undergoing the Ross procedure. METHODS: Between 1992 and 2019, 129 adults with bicuspid aortic valves (aged ≥18 years) underwent the Ross procedure by a single surgeon. Patients were divided into those without autograft inclusion (unwrapped, n = 71) and those with autograft inclusion (wrapped, n = 58). Median follow-up was 10.3 years (interquartile range, 3.0-16.8 years). Need for autograft reintervention was analyzed using competing risks. RESULTS: Pre- and intraoperative characteristics as well as 30-day morbidity or mortality did not differ between cohorts. Survival at 1, 5, and 10 years, respectively, was 97.2%, 97.2%, and 95.6% in the unwrapped cohort and 100%, 100%, and 100% in the wrapped cohort (P = .15). Autograft valve failure occurred in 25 (35.2%) of the unwrapped and 3 (5.2%) of the wrapped patients. Competing risks analysis demonstrated the wrapped cohort to have a lower need for autograft reintervention (subhazard ratio, 0.28, 95% confidence interval, 0.08-0.91; P = .035). The cumulative incidence of autograft reintervention (death as a competing outcome) at 1, 5, and 10 years, respectively, was 10.2%, 14.9%, and 26.8% in the unwrapped cohort and 4.0%, 4.0%, and 4.0% in the wrapped cohort. CONCLUSIONS: In adults with bicuspid aortic valves, the Ross procedure with pulmonary autograft inclusion stabilizes the aortic root preventing dilatation and reduces the need for reoperation. The autograft inclusion technique allows the Ross procedure to be performed in this population with excellent long-term outcomes.

Air Pollution Particulate Matter Amplifies White Matter Vascular Pathology and Demyelination Caused by Hypoperfusion.

Cerebrovascular pathologies are commonly associated with dementia. Because air pollution increases arterial disease in humans and rodent models, we hypothesized that air pollution would also contribute to brain vascular dysfunction. We examined the effects of exposing mice to nanoparticulate matter (nPM; aerodynamic diameter ≤200 nm) from urban traffic and interactions with cerebral hypoperfusion. C57BL/6 mice were exposed to filtered air or nPM with and without bilateral carotid artery stenosis (BCAS) and analyzed by multiparametric MRI and histochemistry. Exposure to nPM alone did not alter regional cerebral blood flow (CBF) or blood brain barrier (BBB) integrity. However, nPM worsened the white matter hypoperfusion (decreased CBF on DSC-MRI) and exacerbated the BBB permeability (extravascular IgG deposits) resulting from BCAS. White matter MRI diffusion metrics were abnormal in mice subjected to cerebral hypoperfusion and worsened by combined nPM+BCAS. Axonal density was reduced equally in the BCAS cohorts regardless of nPM status, whereas nPM exposure caused demyelination in the white matter with or without cerebral hypoperfusion. In summary, air pollution nPM exacerbates cerebrovascular pathology and demyelination in the setting of cerebral hypoperfusion, suggesting that air pollution exposure can augment underlying cerebrovascular contributions to cognitive loss and dementia in susceptible elderly populations.

Air Pollution Particulate Matter Exposure and Chronic Cerebral Hypoperfusion and Measures of White Matter Injury in a Murine Model.

BACKGROUND: Exposure to ambient air pollution particulate matter (PM) is associated with increased risk of dementia and accelerated cognitive loss. Vascular contributions to cognitive impairment are well recognized. Chronic cerebral hypoperfusion (CCH) promotes neuroinflammation and blood-brain barrier weakening, which may augment neurotoxic effects of PM. OBJECTIVES: This study examined interactions of nanoscale particulate matter (nPM; fine particulate matter with aerodynamic diameter ≤200 nm) and CCH secondary to bilateral carotid artery stenosis (BCAS) in a murine model to produce white matter injury. Based on other air pollution interactions, we predicted synergies of nPM with BCAS. METHODS: nPM was collected using a particle sampler near a Los Angeles, California, freeway. Mice were exposed to 10 wk of reaerosolized nPM or filtered air (FA) for 150 h. CCH was induced by BCAS surgery. Mice (C57BL/6J males) were randomized to four exposure paradigms: a) FA, b) nPM, c) FA + BCAS, and d) nPM + BCAS. Behavioral outcomes, white matter injury, glial cell activation, inflammation, and oxidative stress were assessed. RESULTS: The joint nPM + BCAS group exhibited synergistic effects on white matter injury (2.3× the additive nPM and FA + BCAS scores) with greater loss of corpus callosum volume on T2 magnetic resonance imaging (MRI) (30% smaller than FA group). Histochemical analyses suggested potential microglial-specific inflammatory responses with synergistic effects on corpus callosum C5 immunofluorescent density and whole brain nitrate concentrations (2.1× and 3.9× the additive nPM and FA + BCAS effects, respectively) in the joint exposure group. Transcriptomic responses (RNA-Seq) showed greater impact of nPM + BCAS than individual additive effects, consistent with changes in proinflammatory pathways. Although nPM exposure alone did not alter working memory, the nPM + BCAS cohort demonstrated impaired working memory when compared to the FA + BCAS group. DISCUSSION: Our data suggest that nPM and CCH contribute to white matter injury in a synergistic manner in a mouse model. Adverse neurological effects may be aggravated in a susceptible population exposed to air pollution. https://doi.org/10.1289/EHP8792.

Nanoparticulate matter exposure results in white matter damage and an inflammatory microglial response in an experimental murine model.

Exposure to ambient air pollution has been associated with white matter damage and neurocognitive decline. However, the mechanisms of this injury are not well understood and remain largely uncharacterized in experimental models. Prior studies have shown that exposure to particulate matter (PM), a sub-fraction of air pollution, results in neuroinflammation, specifically the upregulation of inflammatory microglia. This study examines white matter and axonal injury, and characterizes microglial reactivity in the corpus callosum of mice exposed to 10 weeks (150 hours) of PM. Nanoscale particulate matter (nPM, aerodynamic diameter ≤200 nm) consisting primarily of traffic-related emissions was collected from an urban area in Los Angeles. Male C57BL/6J mice were exposed to either re-aerosolized nPM or filtered air for 5 hours/day, 3 days/week, for 10 weeks (150 hours; n = 18/group). Microglia were characterized by immunohistochemical double staining of ionized calcium-binding protein-1 (Iba-1) with inducible nitric oxide synthase (iNOS) to identify pro-inflammatory cells, and Iba-1 with arginase-1 (Arg) to identify anti-inflammatory/ homeostatic cells. Myelin injury was assessed by degraded myelin basic protein (dMBP). Oligodendrocyte cell counts were evaluated by oligodendrocyte transcription factor 2 (Olig2). Axonal injury was assessed by axonal neurofilament marker SMI-312. iNOS-expressing microglia were significantly increased in the corpus callosum of mice exposed to nPM when compared to those exposed to filtered air (2.2 fold increase; p<0.05). This was accompanied by an increase in dMBP (1.4 fold increase; p<0.05) immunofluorescent density, a decrease in oligodendrocyte cell counts (1.16 fold decrease; p<0.05), and a decrease in neurofilament SMI-312 (1.13 fold decrease; p<0.05) immunofluorescent density. Exposure to nPM results in increased inflammatory microglia, white matter injury, and axonal degradation in the corpus callosum of adult male mice. iNOS-expressing microglia release cytokines and reactive oxygen/ nitrogen species which may further contribute to the white matter damage observed in this model.

Increased Incidence of COVID-19 Infections Amongst Interpersonal Violence Patients.

OBJECTIVE: To investigate whether any specific acute care surgery patient populations are associated with a higher incidence of COVID-19 infection. BACKGROUND: Acute care providers may be exposed to an increased risk of contracting the COVID-19 infection since many patients present to the emergency department without complete screening measures. However, it is not known which patients present with the highest incidence. METHODS: All acute care surgery (ACS) patients who presented to our level I trauma center between March 19, 2020, and September 20, 2020 and were tested for COVID-19 were included in the study. The patients were divided into two cohorts: COVID positive (+) and COVID negative (-). Patient demographics, type of consultation (emergency general surgery consults [EGS], interpersonal violence trauma consults [IPV], and non-interpersonal violence trauma consults [NIPV]), clinical data and outcomes were analyzed. Univariate and multivariate analyses were used to compare differences between the groups. RESULTS: In total, 2177 patients met inclusion criteria. Of these, 116 were COVID+ (5.3%) and 2061 were COVID- (94.7%). COVID+ patients were more frequently Latinos (64.7% versus 61.7%, P = 0.043) and African Americans (18.1% versus 11.2%, P < 0.001) and less frequently Caucasian (6.0% versus 14.1%, P < 0.001). Asian/Filipino/Pacific Islander (7.8% versus 7.2%, P = 0.059) and Native American/Other/Unknown (3.4% versus 5.8%, P = 0.078) groups showed no statistical difference in COVID incidence. Mortality, hospital and ICU lengths of stay were similar between the groups and across patient populations stratified by the type of consultation. Logistic regression demonstrated higher odds of COVID+ infection amongst IPV patients (OR 2.33, 95% CI 1.62-7.56, P < 0.001) compared to other ACS consultation types. CONCLUSION: Our findings demonstrate that victims of interpersonal violence were more likely positive for COVID-19, while in hospital outcomes were similar between COVID-19 positive and negative patients.

Complementary and Alternative Medicine for the Treatment of Gliomas: Scoping Review of Clinical Studies, Patient Outcomes, and Toxicity Profiles.

INTRODUCTION: Complementary and alternative medicine (CAM) are highly used among those diagnosed with glioma. Further research is warranted, however, as it remains important to clearly delineate CAM practices that are unproven, disproven, or promising for future research and implementation. METHODS: A systematic review was conducted to identify all articles that investigated the effect of any CAM therapy on survival of patients with newly diagnosed or recurrent glioma. RESULTS: Eighteen papers and 4 abstracts pertaining to the effects of ketogenic diet (4), antioxidants (3), hyperbaric oxygen (4), cannabinoids (2), carbogen and nicotinamide (3), mistletoe extract (2), hypocupremia and penicillamine (1), and overall CAM use (3) on overall and progression-free survival in patients with low- and high-grade glioma were identified (Levels of Evidence I-IV). Ketogenic diets, hyperbaric oxygen therapy, and cannabinoids appear to be safe and well tolerated by patients; preliminary studies demonstrate tumor response and increased progression-free survival and overall survival when combined with standard of care therapies. Antioxidant usage exhibit mixed results perhaps associated with glioma grade with greater effect on low-grade gliomas; vitamin D intake was associated with prolonged survival. Conversely, carbogen breathing and hypocupremia were found to have no effect on the survival of patients with glioma, with associated significant toxicity. Most modalities under the CAM umbrella have not been appropriately studied and require further investigation. CONCLUSIONS: Despite widespread use, Level I or II evidence for CAM for the treatment of glioma is lacking, representing future research directions to optimally counsel and treat glioma patients.

Effects of ambient particulate matter on vascular tissue: a review.

Fine and ultra-fine particulate matter (PM) are major constituents of urban air pollution and recognized risk factors for cardiovascular diseases. This review examined the effects of PM exposure on vascular tissue. Specific mechanisms by which PM affects the vasculature include inflammation, oxidative stress, actions on vascular tone and vasomotor responses, as well as atherosclerotic plaque formation. Further, there appears to be a greater PM exposure effect on susceptible individuals with pre-existing cardiovascular conditions.

The interdependence of excitation and inhibition for the control of dynamic breathing rhythms.

The preBötzinger Complex (preBötC), a medullary network critical for breathing, relies on excitatory interneurons to generate the inspiratory rhythm. Yet, half of preBötC neurons are inhibitory, and the role of inhibition in rhythmogenesis remains controversial. Using optogenetics and electrophysiology in vitro and in vivo, we demonstrate that the intrinsic excitability of excitatory neurons is reduced following large depolarizing inspiratory bursts. This refractory period limits the preBötC to very slow breathing frequencies. Inhibition integrated within the network is required to prevent overexcitation of preBötC neurons, thereby regulating the refractory period and allowing rapid breathing. In vivo, sensory feedback inhibition also regulates the refractory period, and in slowly breathing mice with sensory feedback removed, activity of inhibitory, but not excitatory, neurons restores breathing to physiological frequencies. We conclude that excitation and inhibition are interdependent for the breathing rhythm, because inhibition permits physiological preBötC bursting by controlling refractory properties of excitatory neurons.

Contributions of Rod and Cone Pathways to Retinal Direction Selectivity Through Development.

UNLABELLED: Direction selectivity is a robust computation across a broad stimulus space that is mediated by activity of both rod and cone photoreceptors through the ON and OFF pathways. However, rods, S-cones, and M-cones activate the ON and OFF circuits via distinct pathways and the relative contribution of each to direction selectivity is unknown. Using a variety of stimulation paradigms, pharmacological agents, and knockout mice that lack rod transduction, we found that inputs from the ON pathway were critical for strong direction-selective (DS) tuning in the OFF pathway. For UV light stimulation, the ON pathway inputs to the OFF pathway originated with rod signaling, whereas for visible stimulation, the ON pathway inputs to the OFF pathway originated with both rod and M-cone signaling. Whole-cell voltage-clamp recordings revealed that blocking the ON pathway reduced directional tuning in the OFF pathway via a reduction in null-side inhibition, which is provided by OFF starburst amacrine cells (SACs). Consistent with this, our recordings from OFF SACs confirmed that signals originating in the ON pathway contribute to their excitation. Finally, we observed that, for UV stimulation, ON contributions to OFF DS tuning matured earlier than direct signaling via the OFF pathway. These data indicate that the retina uses multiple strategies for computing DS responses across different colors and stages of development. SIGNIFICANCE STATEMENT: The retina uses parallel pathways to encode different features of the visual scene. In some cases, these distinct pathways converge on circuits that mediate a distinct computation. For example, rod and cone pathways enable direction-selective (DS) ganglion cells to encode motion over a wide range of light intensities. Here, we show that although direction selectivity is robust across light intensities, motion discrimination for OFF signals is dependent upon ON signaling. At eye opening, ON directional tuning is mature, whereas OFF DS tuning is significantly reduced due to a delayed maturation of S-cone to OFF cone bipolar signaling. These results provide evidence that the retina uses multiple strategies for computing DS responses across different stimulus conditions.