Double-barreled and Concentric Microelectrodes for Measurement of Extracellular Ion Signals in Brain Tissue.

Electrical activity in the brain is accompanied by significant ion fluxes across membranes, resulting in complex changes in the extracellular concentration of all major ions. As these ion shifts bear significant functional consequences, their quantitative determination is often required to understand the function and dysfunction of neural networks under physiological and pathophysiological conditions. In the present study, we demonstrate the fabrication and calibration of double-barreled ion-selective microelectrodes, which have proven to be excellent tools for such measurements in brain tissue.

Dysbalance of astrocyte calcium under hyperammonemic conditions.

Increased brain ammonium (NH4(+)/NH3) plays a central role in the manifestation of hepatic encephalopathy (HE), a complex syndrome associated with neurological and psychiatric alterations, which is primarily a disorder of astrocytes. Here, we analysed the influence of NH4(+)/NH3 on the calcium concentration of astrocytes in situ and studied the underlying mechanisms of NH4(+)/NH3-evoked calcium changes, employing fluorescence imaging with Fura-2 in acute tissue slices derived from different regions of the mouse brain. In the hippocampal stratum radiatum, perfusion with 5 mM NH4(+)/NH3 for 30 minutes caused a transient calcium increase in about 40% of astrocytes lasting about 10 minutes.

Kir4.1 channels mediate a depolarization of hippocampal astrocytes under hyperammonemic conditions in situ.

Increased ammonium (NH(4) (+) ) concentration in the brain is the prime candidate responsible for hepatic encephalopathy (HE), a serious neurological disorder caused by liver failure and characterized by disturbed glutamatergic neurotransmission and impaired glial function. We investigated the mechanisms of NH(4) (+) -induced depolarization of astrocytes in mouse hippocampal slices using whole-cell patch-clamp and potassium-selective microelectrodes. At postnatal days (P) 18-21, perfusion with 5 mM NH(4) (+) evoked a transient increase in the extracellular potassium concentration ([K(+) ](o) ) by about 1 mM.