Intracellular effects of QX-314 and Cs+ in hippocampal pyramidal neurons in vivo

The effects of intracellular diffusion of the lidocaine derivative anesthetic QX-314 and of Cs+, which block Na+ and K+ conductances, respectively, were investigated in vivo in rat CA1 and CA3 pyramidal neurons to demonstrate slow Ca(2+)-related events. QX-314 loading prevented fast Na+ spikes, but slower presumably Ca2+ spikes remained. A slower and a faster duration type of QX-314-resistant spikes were observed. The former had high thresholds, while the latter was activated at moderate depolarized levels. The slower and the faster QX-314-resistant spikes fired at frequencies up to 8/s and 35/s and were 35-60 and 5-10 ms in duration, respectively. With Cs+ loading, pyramidal neurons depolarized and slow, presumably Ca2+, and fast Na+ spikes widened. Fast spikes usually showed a prominent shoulder and a slower repolarization. No differences were observed between drug effects in CA1 and CA3 neurons. In terms of their possible participation in theta rhythm genesis the slow QX-314-resistant events display the correct frequency and duration and can oscillate regeneratively.