Thalamocortical dysrhytmia and the thalamic reticular nucleus in behaving rats

Objective: The aim of the study was to investigate the effects of bilateral chemical lesion of the rostral pole of the thalamic reticular nucleus on EEG activities in freely-moving rats applying quantitative analysis and brain mapping of power spectra distribution. Methods: Ketamine-sedated Sprague Dawley rats were implanted to monitor behavioral states with frontoparietal electrodes in a first series of experiments and with multiple electrodes along the antero-posterior axis (F1, F2, F7, F8, T3, T4, P3, P4) in a second series. Monopolar and bipolar recordings were obtained in animals stereotaxically injected with ibotenic acid into both rostral poles of the thalamic reticular nucleus. Long-term video-EEG recordings and brain mapping based on quantitative spectral analysis were made. Results: Two forms of dysrhythmia gradually emerged in the neocortical EEG at 12-24 h post-injection: potentiation of theta waves and spontaneous High Voltage Spindles (HVS) at 4.5-8 Hz frequency. Brain mapping during these dysrhythmia shows highest power posteriorly (parietotemporal) for theta and mesiofrontally for HVS. Conclusions: Given the lack of inhibitory intrinsic interneurons in the rat thalamus, bilateral destruction of a small part of the solely GABAergic population may promote cortical dysrhythmia (probably by dis- inhibition). The topographic differences in power might indicate different involved structures.