INTRODUCTION: Retinal signals pass through the dorsal lateral geniculate nucleus (dLGN) of the thalamus to target the primary visual cortex. Besides the driver input from the eye, dLGN also receives substantial modulatory projections from layer 6 of cortex and the brainstem, which exert strong influence on the dLGN cells. Thalamic neurons have two switching modes of firing activity: tonic and burst. Bursts comprise a number of closely spaced action potentials, followed by a long refractory period between bursts. AIM(S): The aim of the present study was to determine whether activity of the rat dLGN depends on alternating brain states in terms of its spontaneous activity, firing mode (tonic and bursting) and light-induced responses. METHOD(S): Extracellular single-unit in vivo and EEG recordings combined with white light stimulations were performed in 19 adult Long Evans rats under urethane anaesthesia. Light-induced responses, bursting parameters and correlation between spontaneous neuronal activity and EEG were analysed. RESULTS: In total, 22 light-responsive neurons were recorded and all of them were characterized by burst firing mode detected in both EEG phases. Spontaneous activity of 68% of cells was modulated by EEG changes with significant decrease during the deactivation. Moreover, during that phase the percentage of bursts was higher, while neuronal responses to light were significantly reduced. CONCLUSIONS: The dorsal lateral geniculate nucleus of the thalamus comprises of two subpopulations of light-sensitive cells, which are distinguished by their sensitivity to cyclic brain alternations under urethane anaesthesia. Interestingly, bursting cells within dLGN are involved in visual signal transmission in a state dependent manner. FINANCIAL SUPPORT: Supported by: 2013/08/W/ N23/00700, DS/MND/WBiNoZ/IZ/18/2016.
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