Biology subjects

Ezra, M.

Publications and source records attributed to Ezra, M..

3 recordsLinked to original sources

bioRxiv2026

Breathlessness catastrophising after COVID-19 involves both interoceptive and visceromotor connectivity

Persistent breathlessness is common after COVID-19, yet its severity typically correlates weakly with objective clinical measures. This discordance is often attributed to perceptual inference amplified by anxiety. Because breathing involves a closed perception-action loop, breathlessness may also reflect alterations in interoceptive and visceromotor pathways. We acquired 7-tesla resting-state functional MRI in 53 post-COVID patients with varying breathlessness and estimated functional connectivity across 18 pre-defined interoceptive and visceromotor regions. Linear regression identified two connections associated with breathlessness catastrophising: reduced dorsal periaqueductal grey-posterior insula (dPAG-PoI1) and increased basolateral amygdala-dorsal anterior cingulate (BLA-dACC) connectivity. The dPAG-PoI1 association was stronger in patients who had required mechanical ventilation, whereas the BLA-dACC association was attenuated at higher generalised anxiety. These findings are consistent with two potentially separable contributions to symptom burden: weakened interoceptive signalling between brainstem and sensory cortex, and heightened visceromotor influence of threat processing on autonomic control, rather than anxiety-driven misperception alone.

neuroscience↗

bioRxiv2020

Phase dynamics of cerebral blood flow in subarachnoid haemorrhage in response to sodium nitrite infusion

Aneurysmal subarachnoid haemorrhage (SAH) is a devastating subset of stroke. One of the major determinates of morbidity is the development of delayed cerebral ischemia (DCI). Disruption of the nitric oxide (NO) pathway and consequently the control of cerebral blood flow (CBF), known as cerebral autoregulation, is believed to play a role in its pathophysiology. Through the pharmacological manipulation of in vivo NO levels using an exogenous NO donor we sought to explore this relationship. Phase synchronisation index (PSI), an expression of the interdependence between CBF and arterial blood pressure (ABP) and thus cerebral autoregulation, was calculated before and during sodium nitrite administration in 10 high-grade SAH patients acutely postrupture. In patients that did not develop DCI, there was a significant increase in PSI around 0.1 Hz during the administration of sodium nitrite (33%; p-value 0.006). In patients that developed DCI, PSI did not change significantly. Synchronisation between ABP and CBF at 0.1 Hz has been proposed as a mechanism by which organ perfusion is maintained, during periods of physiological stress. These findings suggest that functional NO depletion plays a role in impaired cerebral autoregulation following SAH, but the development of DCI may have a distinct pathophysiological aetiology.

neuroscience↗

bioRxiv2019

Effect of nitrite on neural activity in the healthy brain

BackgroundNitrite is a major intravascular store for nitric oxide. The conversion of nitrite to the active nitric oxide occurs mainly under hypoxic conditions to increase blood flow where it is needed the most. The use of nitrite is, therefore, being evaluated widely to reduce the brain injury in conditions resulting in cerebral hypoxia, such as cardiac arrest, ischaemic stroke or subarachnoid haemorrhage. However, as it is still unknown how exogenous nitrite affects the brain activity of healthy individuals, it is difficult to clearly understand how it affects the ischaemic brain. ObjectiveHere we performed a double-blind placebo-controlled crossover study to investigate the effects of nitrite on neural activity in the healthy brain. MethodsTwenty-one healthy volunteers were recruited into the study. All participants received a continuous infusion of sodium nitrite (0.6mg/kg/h) on one occasion and placebo (sodium chloride) on another occasion. Electroencephalogram was recorded before the start and during the infusion. We computed the power spectrum density within the conventional frequency bands (delta, theta, alpha, beta), and the ratio of the power within the alpha and delta bands. We also measured peripheral cardiorespiratory physiology and cerebral blood flow. ResultsWe found no significant effect of nitrite on the power spectrum density in any frequency band. Similarly, the alpha-delta power ratio did not differ between the two conditions. However, nitrite infusion decreased the mean blood pressure and increased the methaemoglobin concentration in the blood. ConclusionOur study shows that exogenous sodium nitrite does not alter the electrical activity in the healthy brain. This might be because the sodium nitrite is converted to vasoactive nitric oxide in areas of hypoxia, and in the healthy brain there is no significant amount of conversion due to lack of hypoxia. However, this lack of change in the power spectrum density in healthy people emphasises the specificity of the brains response to nitrite in disease.

neuroscience↗