The thalamic dorsal lateral geniculate nucleus (dLGN) serves as a gateway for light information transfer en route to the primary visual cortex (V1). Although the nonretinal modulatory input arising from the deep layer of V1 to the dLGN is well characterized, little is known about its in‑ fluence upon dLGN activity under brain state dependent changes. Urethane anesthesia provides a powerful tool for acute in vivo studies, which allows for the observation of cyclic alternations of REM- and NREM-like stages during electrocorticographic (ECoG) recording, resembling nat‑ ural sleep. Our study aimed to investigate the nature of spontaneous neuronal activity and stimulus responsive‑ ness of the rat dLGN under alternating sleep-like phases with intact and silenced V1. Extracellular multi-unit ac‑ tivity of the dLGN and cortical ECoG signals were record‑ ed in vivo from 48 adult male Long Evans rats under ure‑ thane anaesthesia. All recordings were performed under dark conditions and were combined with white light stim‑ ulations and V1 muscimol application. First, we described different relationships between single-unit dLGN activity and brain state alternations: neurons led by ECoG, neu‑ rons whose spike rate preceded ECoG alternations, and neurons correlated and not correlated with ECoG changes. Silencing cortical input altered relationships with ECoG in all groups, however the most prominent changes were ob‑ served in cells where firing rate preceded ECoG changes. In terms of light-induced activity, we found that the am‑ plitude of light responses did not change between cortical phases before and after muscimol application. However, the type of response was modulated in 25% of neurons, both by the brain state alternations and cortical musci‑ mol application. We demonstrated that spontaneous ac‑ tivity of rat dLGN cells varies in a state-dependent man‑ ner and can be altered by silencing V1. On the other hand, in a majority of cells the amplitude of light-induced re‑ sponses remained constant, suggesting that retinal input has priority over non-retinal cortical influences. Support‑ ed by: 2013/08/W/N23/00700, K/DSC/004648.
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