The effect of propofol on CA1 pyramidal cell excitability and GABA(A)-mediated inhibition in the rat hippocampal slice

An in vitro paired-pulse orthodromic stimulation technique was used to examine the effects of propofol on excitatory afferent terminals, CA1 pyramidal cells and recurrent collateral evoked inhibition in the rat hippocampal slice. Hippocampal slices 400 mu m thick were perfused with oxygenated artificial cerebrospinal fluid, and electrodes were placed in the CAI region to record extracellular field population spike (PS) or excitatory postsynaptic potential (EPSP) responses to stimulation of Schaffer collateral/commissural fibers. Gamma-aminobutyric acid (GABA)-mediated recurrent inhibition was measured using a paired-pulse technique. The major effect of propofol (7-28 mu M) was a dose and time dependent increase in the intensity and duration of GABA-mediated inhibition. This propofol effect could be rapidly and completely reversed by exposure to known GABA(A) antagonists, including picrotoxin, bicuculline and pentylenetetrazol. It was also reversed by the chloride channel antagonist, 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS). It was not antagonized by central (flumazenil) or peripheral (PK11195) benzodiazepine antagonists. Reversal of endogenous inhibition was also noted with the antagonists picrotoxin and pentylenetetrazol. Input/output curves constructed using stimulus propofol caused only a small enhancement of EPSPs at higher stimulus intensities but had no effect on PS amplitudes. These studies are consistent with propofol having a GABA(A)-chloride channel mechanism causing its effect on recurrent collateral evoked inhibition in the rat hippocampal slice.