Rossi CA, Lehmkhule MJ, Kesner RP, Dudek FE (2010) Evidence that focal hippocampal interneuron loss disrupts theta-rhythm activity in dorsal CA1. Neuroscience 2010 Abstracts 811.1/LLL64. Society for Neuroscience, San Diego, CA.
Summary: Hippocampal theta activity (6-12 Hz) is an oscillatory local field potential that is thought to play a critical role in the encoding and storage of new information. As a hypothetical mechanism for theta rhythm generation, interneurons have been proposed to appropriately time the GABAergic inhibition of principal cells, as a means of organizing the theta pattern; however, little experimental work has been done to test this hypothesis directly. The current study aims to test in a relatively direct manner the hypothesis that interneurons synchronize the activity of pyramidal cells into theta-band oscillations. In the current study, SSP-saporin (a selective interneuron-targeting neurotoxic lesioning agent) was infused into six sites located in dorsal CA1 in order to create an interneuron-only lesion confined to that area. Animals were also implanted with chronic field potential recording electrodes aimed at areas CA1, CA3, and dentate gyrus. All animals were then monitored, using video and EEG recordings, 24 h per day for the next 7 to 10 days. In addition, EEG was recorded while animals were allowed to explore a novel open field for 30 min in order to create a situation where theta rhythm activity is highly likely to occur. Local field potentials from animals that received SSP-Saporin injections into the dorsal CA1 area revealed attenuation of theta rhythm activity in the lesioned area. Recordings from controls, however, showed a robust peak of activity in the theta frequency band, similar to what has been traditionally described in the hippocampus of naive rats. Together, these results suggest that local elimination of interneurons disrupts local theta rhythm without induction of seizure activity. These experiments provide evidence concerning the possible organizational role of GABAergic interneurons in theta rhythm, an important component of normal hippocampal function.
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