Vagal sensory neurons mediate the Bezold-Jarisch reflex and induce syncope

Visceral sensory pathways mediate homeostatic reflexes, the dysfunction of which leads to many neurological disorders1. The Bezold-Jarisch reflex (BJR), first described2,3 in 1867, is a cardioinhibitory reflex that is speculated to be mediated by vagal sensory neurons (VSNs) that also triggers syncope. However, the molecular identity, anatomical organization, physiological characteristics and behavioural influence of cardiac VSNs remain mostly unknown. Here we leveraged single-cell RNA-sequencing data and HYBRiD tissue clearing4 to show that VSNs that express neuropeptide Y receptor Y2 (NPY2R) predominately connect the heart ventricular wall to the area postrema. Optogenetic activation of NPY2R VSNs elicits the classic triad of BJR responses-hypotension, bradycardia and suppressed respiration-and causes an animal to faint. Photostimulation during high-resolution echocardiography and laser Doppler flowmetry with behavioural observation revealed a range of phenotypes reflected in clinical syncope, including reduced cardiac output, cerebral hypoperfusion, pupil dilation and eye-roll. Large-scale Neuropixels brain recordings and machine-learning-based modelling showed that this manipulation causes the suppression of activity across a large distributed neuronal population that is not explained by changes in spontaneous behavioural movements. Additionally, bidirectional manipulation of the periventricular zone had a push-pull effect, with inhibition leading to longer syncope periods and activation inducing arousal. Finally, ablating NPY2R VSNs specifically abolished the BJR. Combined, these results demonstrate a genetically defined cardiac reflex that recapitulates characteristics of human syncope at physiological, behavioural and neural network levels.

Response time and safety profile of pulsed oral methotrexate therapy in idiopathic retinal periphlebitis

PURPOSE

To evaluate the response time and safety profile of low-dose oral methotrexate pulsed therapy in idiopathic retinal periphlebitis (Eales' disease).

METHODS

A tertiary care center-based prospective interventional study, based on visual acuity grading, was undertaken. Twenty-one consecutive patients with idiopathic retinal periphlebitis were administered 12.5 mg methotrexate as a single oral dose, once per week for 12 weeks (cumulative dose = 150 mg). Each patient was assessed for change in visual acuity grades. Time of first therapeutic response was also noted. Drug safety was monitored by laboratory tests that included twice-weekly white blood cells and differential counts, twice-weekly platelet counts, and monthly liver function tests.

RESULTS

Twenty-one eyes were assessed. Mean follow-up period was 6 months. All showed improvement in visual acuity grades. An excellent visual outcome (6/6 or better) was achieved in 18 (69%) eyes. Time of first therapeutic response varied from 2 to 6 weeks with a majority of eyes (80%) showing response by 4 weeks (median = 3 weeks). All the side effects of methotrexate were mild or moderate in severity and rapidly reversible on dose reduction or discontinuation. No patient had any constitutional symptoms severe enough to necessitate cessation of therapy.

CONCLUSIONS

Low dose oral methotrexate pulse therapy (at a dose of 12.5 mg/week) is clinically effective within 4 weeks, and is associated with an acceptable safety profile.