Locus coeruleus neurones in vitro: pH-sensitive oscillations of membrane potential in an electrically coupled network

The response to hypercapnic acidosis (2-8% CO2, bath pH 7.8-7.2) was examin ed in whole cell recordings from neonatal (P1 to P5) rat Locus coeruleus (L C) neurones in the in vitro brainstem-spinal cord preparation exposed to lo w Ca2+ (0.2 mM)-high Mg2+ (5 mM). This medium suppressed chemical synaptic transmission and resulted in a pattern of subthreshold oscillations of memb rane potential and rhythmic burst discharge which was synchronized througho ut the network. The oscillation was suppressed, and the discharge of indivi dual neurones desynchronized, by the gap junction uncoupler, carbenoxolone, indicating that in low Ca2+-high Mg2+ LC neurones form an electrically cou pled network. Switching from 2 to 8% CO2 decreased the oscillation amplitud e and increased its frequency. The oscillation was suppressed by external C d2+ and by TTX, but persisted during injection into the cell soma of QX-314 . We conclude that in LC neurones acidosis increases the frequency of a Ca2 +- and Na+-dependent dendritic oscillator which is synchronized by gap junc tion coupling throughout the network. This coupling is retained during acid osis. (C) 1999 Elsevier Science B.V. All rights reserved.