Biology subjects

Rahmati, N.

Publications and source records attributed to Rahmati, N..

3 recordsLinked to original sources

bioRxiv2026

WNK-SPAK/OSR1 signaling pathway facilitates ictal activity via reduced neuronal chloride extrusion rate

Seizures upregulate Na+-K+-2Cl- (NKCC1)-mediated Cl- influx and downregulate K+-Cl- (KCC2)-mediated Cl- efflux via the WNK-SPAK/OSR1 kinases, leading to cytoplasmic chloride ([Cl-]i) accumulation, reduced GABAergic inhibition and anticonvulsant failure. Early studies found that inhibiting WNK-kinase reduced baseline [Cl-]i (ECl) and seizures via increased KCC2 activity. However, increased KCC2 activity alone should not affect ECl whose determinants are more complex. We determined the net effects of WNK-SPAK/OSR1 pathway inhibitor WNK463 on ECl and [Cl-]i transients during spontaneous ictal-like discharges (ILDs). We found that WNK463 reduced interictal [Cl-]i but did not change baseline [Cl-]i measured in the presence of TTX. WNK463 enhanced neuronal Cl- extrusion during and after ILDs, before abolishing ILDs. Pharmacological inhibition and targeted siRNA silencing demonstrated that the anti-ictal effects of WNK463 involved both NKCC1 and KCC2. Our data support a mechanism whereby mutual NKCC1 inhibition and KCC2 activation via the WNK-SPAK/OSR1 pathway exert powerful anti-ictal effects by facilitating [Cl-]i extrusion during ILDs.

neuroscience↗

bioRxiv2023

A dynamic balance between neuronal death and clearance after acute brain injury

After acute brain injury, neuronal apoptosis may overwhelm the capacity for microglial phagocytosis, creating a queue of dying neurons awaiting clearance. The size of this queue should be equally sensitive to changes in neuronal death and the rate of phagocytosis. Using rodent organotypic hippocampal slice cultures as a model of acute perinatal brain injury, serial imaging demonstrated that the capacity for microglial phagocytosis of dying neurons was overwhelmed for two weeks. Altering phagocytosis rates, e.g. by changing the number of microglia, dramatically changed the number of visibly dying neurons. Similar effects were generated when the visibility of dying neurons was altered by changing the membrane permeability for vital stains. Canonically neuroprotective interventions such as seizure blockade and neurotoxic maneuvers such as perinatal ethanol exposure were mediated by effects on microglial activity and the membrane permeability of apoptotic neurons, and had either no or opposing effects on healthy surviving neurons. SignificanceAfter acute brain injury, microglial phagocytosis is overwhelmed by the number of dying cells. Under these conditions, the assumptions on which assays for neuroprotective and neurotoxic effects are based are no longer valid. Thus longitudinal assays of healthy cells, such as assessment of the fluorescence emission of transgenically-expressed proteins, provide more accurate estimates of cell death than do single-time-point anatomical or biochemical assays. More accurate estimates of death rates will increase the translatability of preclinical studies of neuroprotection and neurotoxicity.

neuroscience↗

bioRxiv2020

Unique actions of GABA arising from cytoplasmic chloride microdomains

Developmental, cellular, and subcellular variations in the direction of neuronal Cl- currents elicited by GABAA receptor activation have been frequently reported, and we found a corresponding variance in the reversal potential (EGABA) for individual interneurons synapsing on a single pyramidal cell. These findings suggest a corresponding variance in the cytoplasmic concentration of Cl- ([Cl-i]). We determined [Cl-]i by: 1) two-photon imaging of the Cl- sensitive, ratiometric fluorescent protein SuperClomeleon (sCLM); 2) Fluorescence Lifetime IMaging (FLIM) of the Cl- sensitive fluorophore MEQ; and 3) electrophysiological measurements of EGABA. These methods collectively demonstrated stable [Cl-]i microdomains in individual neurons in vivo. Fluorometric and electrophysiological estimates of local [Cl-]i were highly correlated. [Cl-]i microdomains persisted after pharmacological inhibition of cation-chloride cotransporters (CCCs) but steadily decreased after inhibiting the polymerization of the anionic macromolecule actin. These studies highlight the existence of functionally significant neuronal Cl- microdomains that modify the impact of GABAergic inputs.

neuroscience↗