Figure 1.

Recording of EEG and field potentials in the CA3 region. A, Schematic diagram of the intact rodent preparation as used to collect field potentials in the CA3 stratum pyramidale evoked by stimulation of the medial angular bundle (mPP) and the commissural/associational fibers within the contralateral CA3 region (cCA3). B, Graphic representation of responses collected during theta rhythm. Only CA3 responses evoked 30 ms before or after the maximum or minimum points of theta peaks and troughs were measured. Shown are examples of CA3 responses evoked on the peak and trough of theta recorded in the CA3 stratum pyramidale. C, Comparison of theta rhythm recorded at the hippocampal fissure at the dentate/CA1 border, the hilar/CA3 region of the dentate gyrus, and the stratum pyramidale of CA3. Note that at both hilar and CA3 sites, theta is ∼180† out of phase with theta recorded at the fissure. D, Histogram of fast Fourier transforms (frequency vs EEG power shown in squared millivolts ±SEM) of 200 1 s EEG epochs averaged during the first 20 min exploring a novel environment. Shown are the effects of 50 mg/kg atropine sulfate (n = 4, dashed line ± SEM) and water vehicle (n = 4, solid line ± SEM). Atropine-treated animals displayed an increase in the theta frequency of maximum power, and an attenuation of theta power among lower frequencies of the theta (6–8 Hz), although these effects only approached significance (for 6 Hz, p = 0.10; n = 8). However, the total power, total theta power, percent theta power, and normalized power at each frequency (4–12 Hz) all were not altered significantly by atropine when recorded in the CA3 pyramidal cell region (all p > 0.05, RM ANOVA). E, Placement of CA3 recording electrodes for each subject as verified by histological analysis of cresyl-violet-stained sections, with electrode termination sites shown as circles, with termination sites determined by sclerosis, blood tracks, and cell displacement. n = 18.