Systemic diazepam alters local hippocampal CA1 circuits and differentially affects entorhinal and CA3 inputs

The GABAA positive allosteric modulator diazepam is taken systemically by millions of people daily. GABAA signaling is essential for hippocampal circuit function, but the effects of systemic diazepam on hippocampal information processing during behavior has not been studied. To answer this question, large neural ensembles were recorded from rats running a linear track under systemic diazepam administration. A cross-correlation of spiking activity revealed significantly increased inhibition from interneurons, aligned with the timescale of GABAA, suggesting a direct effect on local circuits. Local field potentials (LFP) showed an increase in theta and lo-gamma (30-50 Hz) power but a decrease in hi-gamma (80-120 Hz) power. We also found decreased amplitude and rate of sharp wave ripple (SWR) events and a reduction of firing rate and proportion of cells recruited to the SWRs. An autocorrelation of single-cell spike trains revealed a decrease and shift from shorter to longer timescales, aligning differently with theta frequencies. Phase coupling measurements showed decreased cellular coupling to theta and increased coupling to lo-gamma and hi-gamma. Finally, entropy of decoding along the track was increased, suggesting less precise spatial representations under diazepam. These changes suggest mechanisms that would likely disrupt hippocampal memory storage and consolidation processes under systemic diazepam.