Fast and Slow Gamma Rhythms Are Intrinsically and Independently Generated in the Subiculum

By August 24, 2011

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Jesse Jackson Sylvain Williams
J Neuroscience Acute Rat Sprague Dawley rats Hippocampus Penetrating Electrode A1x16-3mm-100-703 A16

Gamma rhythms are essential for memory encoding and retrieval. Despite extensive study of these rhythms in the entorhinal cortex,
dentate gyrus, CA3, and CA1, almost nothing is known regarding their generation and organization in the structure delivering the most
prominent hippocampal output: the subiculum. Here we show using a complete rat hippocampal preparation in vitro that the subiculum
intrinsically and independently generates spontaneous slow (25–50 Hz) and fast (100 –150 Hz) gamma rhythms during the rising phase
and peak of persistent subicular theta rhythms. These two gamma frequencies are phase modulated by theta rhythms without any form
of afferent input from the entorhinal cortex or CA1. Subicular principal cells and interneurons phase lock to both fast and slow gamma,
and single cells are independently phase modulated by each form of gamma rhythm, enabling selective participation in neural synchrony
at both gamma frequencies at different times. Fast GABAergic inhibition is required for the generation of fast gamma, whereas slow
gamma is generated by excitatory and inhibitory mechanisms. In addition, the transverse subicular axis exhibits gamma rhythm topography
with faster gamma coupling arising in the distal subiculum region. The subiculum therefore possesses a unique intrinsic circuit
organization that can autonomously regulate the timing and topography of hippocampal output synchronization. These results suggest
the subiculum is a third spontaneousgammagenerator in the hippocampal formation (in addition to CA3 and the entorhinal cortex), and
these gamma rhythms likely play an active role in mediating the flow of information between the hippocampus and multiple cortical and
subcortical brain regions.

Jackson, Jesse, Romain Goutagny, and Sylvain Williams. "Fast and slow gamma rhythms are intrinsically and independently generated in the subiculum." Journal of Neuroscience 31.34 (2011) : 12104-12117. August 24, 2011 Douglas Mental Health University Institute, McGill University, Department of Psychiatry, Montre´al, Quebec