Shimono K, Brucher F, Granger R, Lynch G, Taketani M (2000). Origins and distribution of cholinergically induced beta rhythms in hippocampal slices. Journal of Neuroscience, 8462-8473.

Shimono, K., Brucher, F., Granger, R., Lynch, G., and Taketani, M.

Abstract

Regional variations and substrates of high-frequency rhythmic activity induced by cholinergic stimulation were studied in hippocampal slices with 64-electrode recording arrays. (1) Carbachol triggered b waves (17.6 6 5.7 Hz) in pyramidal regions of 75% of the slices. (2) The waves had phase shifts across the cell body layers and were substantially larger in the apical dendrites than in cell body layers or basal dendrites. (3) Continuous, twodimensional current source density analyses indicated apical sinks associated with basal sources, lasting ;10 msec, followed by apical sources and basal sinks, lasting ;20 msec, in a repeating pattern with a period in the range of 15–25 Hz. (4) Carbachol-induced b waves in the hippocampus were accompanied by 40 Hz (g) oscillations in deep layers of the entorhinal cortex. (5) Cholinergically elicited b and g rhythms were eliminated by antagonists of either AMPA or GABA receptors. Benzodiazepines markedly enhanced b activity and sometimes introduced a distinct g frequency peak. (6) Twenty Hertz activity after orthodromic activation of field CA3 was distributed in the same manner as carbachol-induced b waves and was generated by a current source in the apical dendrites of CA3. This source was eliminated by high concentrations of GABAA receptor blockers. It is concluded that cholinergically driven b rhythms arise independently in hippocampal subfields from oscillatory circuits involving (1) bursts of pyramidal cell discharges, (2) activation of a subset of feedback interneurons that project apically, and (3) production of a GABAA-mediated hyperpolarization in the outer portions of the apical dendrites of pyramidal neurons