Cl − channels are randomly activated by continuous GABA secretion in cultured embryonic rat hippocampal neurons

Throughout the adult vertebrate central nervous system (CNS) γ-aminobutyric acid (GABA) mediates transient Cl − conductances commonly identified as fast, Cl −-dependent inhibitory synaptic signals [Prog. Neurobiol., 36 (1991) 35–92). In the rat hippocampus Cl −-dependent excitatory transients mediated by GABA emerge during the first postnatal week superimposed on a steady-state baseline that is also Cl −- and GABA-dependent [Int. J. Dev. Neurosci., 8 (1990) 481–490]. Here we report that many embryonic rat hippocampal neurons cultured for hours to days exhibit random fluctuations in Cl − channel activity that are mediated by continuous secretion of GABA in the absence of transients. Thus, GABA is broadcast tonically before it is released transiently.