Biology subjects

Bhandare, A.

Publications and source records attributed to Bhandare, A..

4 recordsLinked to original sources

bioRxiv2025

CO2 sensitive connexin channel synapses in the VTA release 5HT to regulate dopaminergic neurons

Hypercapnic arousal is a life-preserving reflex that promotes awakening in response to elevated PCO2, yet the cellular mechanisms by which CO2 is detected remain incompletely understood. Serotonergic neurons of the dorsal raphe (DR) have been implicated in hypercapnic responses, but the molecular sensor that directly detects CO2 within this circuit is unknown. Here, we show that the CO2-gated connexin 26 (Cx26) hemichannel is expressed on serotonergic terminals projecting from the DR to the ventral tegmental area (VTA). Brief elevations in PCO2 modulated the excitability of VTA dopamine neurons through serotonergic signaling without altering glutamatergic transmission, and these effects were abolished by pharmacological inhibition of hemichannels. By expressing Cx26 and genetically encoded GRAB5HT sensors in cultured cells, we further demonstrate that Cx26 hemichannels opened by elevated PCO2 are directly permeable to serotonin. Selective removal of CO2 sensitivity from Cx26 in DR serotonergic neurons delayed arousal from sleep during transient hypercapnia and reduced activation of VTA dopamine neurons in vivo. Together, these findings identify Cx26 hemichannels as a direct CO2 sensor that enables serotonin release through a channel co-synapse and contributes to hypercapnic arousal.

neuroscience↗

bioRxiv2022

Neural correlate of reduced respiratory chemosensitivity during chronic epilepsy

Central autonomic cardiorespiratory dysfunction underlies sudden unexpected death in epilepsy (SUDEP). Here we used single cell neuronal Ca2+ imaging and intrahippocampal kainic acid (KA)-induced chronic epilepsy in mice to investigate progressive changes in key cardiorespiratory brainstem circuits during chronic epilepsy. Following induction of status epilepticus (SE), adaptive ventilatory responses to hypercapnia were reduced in mice with chronic epilepsy for 5 weeks post-SE with partial recovery at week 7. These changes were paralleled by post-SE alterations in the chemosensory responses of neurons in the retrotrapezoid nucleus (RTN). Neurons that displayed adapting responses to hypercapnia were less prevalent and exhibited smaller responses over weeks 3-5, whereas neurons that displayed graded responses to hypercapnia became more prevalent by week 7. Over the same period, chemosensory responses of the presympathetic rostral ventrolateral medullary neurons showed no change. Mice with chronic epilepsy showed enhanced sensitivity to seizures, which can invade the RTN and possibly impair further the chemosensory circuits. Our work suggests that assessment of respiratory chemosensitivity may have potential for identifying people at risk of SUDEP.

neuroscience↗

bioRxiv2020

Connexin26 mediates CO2-dependent regulation of breathing via glial cells of the medulla oblongata

Breathing is highly sensitive to the PCO2 of arterial blood. Although CO2 is detected via the proxy of pH, CO2 acting directly via Cx26 may also contribute to the regulation of breathing. Here we exploit our knowledge of the structural motif of CO2-binding to Cx26 to devise a dominant negative subunit (Cx26DN) that removes the CO2-sensitivity from endogenously expressed wild type Cx26. Expression of Cx26DN in glial cells of a circumscribed region of the medulla - the caudal parapyramidal area - reduced the adaptive change in tidal volume and minute ventilation by approximately 30% at 6% inspired CO2. As central chemosensors mediate about 70% of the total response to hypercapnia, CO2-sensing via Cx26 in the caudal parapyramidal area contributed about 45% of the centrally-mediated ventilatory response to CO2. Our data unequivocally links the direct sensing of CO2 to the chemosensory control of breathing and demonstrates that CO2-binding to Cx26 is a key transduction step in this fundamental process.

neuroscience↗

bioRxiv2018

Analyzing the brainstem circuits for respiratory chemosensitivity in freely moving mice

The regulated excretion of CO2 during breathing is a key life-preserving homeostatic mechanism. In the rostral medulla oblongata, neurons in two nuclei -the retrotrapezoid nucleus (RTN) and the rostral medullary Raphe -have been proposed as central CO2 chemosensors that mediate adaptive changes in breathing. One such adaptive change is active expiration, thought to be controlled by the lateral parafacial region (pFL). Here we use promoter-driven expression of GCaMP6 and head-mounted mini-microscopes to image the Ca2+ activity in neurons and glia of RTN, Raphe and pFL in awake adult mice during inspiration of elevated CO2 to discriminate their roles in the adaptive response to hypercapnia. While there were multiple types of neuronal response to hypercapnia in both the RTN and the Raphe, a substantial proportion of neurons in the Raphe encoded the inspired level of CO2. By contrast, such responses were very rare in the RTN and the responses of RTN neurons suggest that this nucleus plays an integrative rather than a direct sensing role in the chemosensory reflex. pFL neurons were reliably activated by hypercapnia and their activity preceded active expiration suggesting a key causal link to this aspect of breathing. Our analysis considerably revises understanding of chemosensory control in the adult awake mouse and paves the way to understanding how breathing is coordinated with complex non-ventilatory behaviours such as swallowing and vocalisation.

neuroscience↗