*2.5. Measurement of Brain Sodium*

Measurement of brain sodium was done with a sodium estimation kit procured from United Diagnostics Industry (UDI, Dammam, KSA), as per the kit protocol procedures. Na+/K+-ATPase is an enzyme found in the cell0 s membrane. It performs several functions in cell physiology. The assay activates the B-galactosidase enzyme by the sodium present in the sample and the consequent enzymatic transformation of o-nitrophenyl-β, D-glactopyranoside (o-NPG) into o-nitrophenol, and galactose. The o-nitrophenol formed was kinetically measured at 405 nm against distilled water every 20 s for two minutes as per the kit protocol. One unit of sodium level was defined as micromoles of o-NPG (o-nitrophenyl-β, D-glactopyranoside) decomposed per minute using molar absorbance of 18.75 <sup>×</sup> <sup>10</sup><sup>3</sup> <sup>M</sup>−<sup>1</sup> Cm−<sup>1</sup> .
