Modulation of Spontaneous and Light-Induced Activity in the Rat Dorsal Lateral Geniculate Nucleus by General Brain State Alterations under Urethane Anesthesia.

The thalamic dorsal lateral geniculate nucleus (dLGN) serves as a gating station for the transfer of light information en route to the primary visual cortex (V1). Although the modulatory input arising from the V1 and several brainstem nuclei to the dLGN is well characterised in higher mammals, little is known about its influence on dLGN activity in rodents. Using simultaneous recordings of electrocorticogram (ECoG) and single unit neuronal activity under urethane anesthesia in Long Evans rats, we managed to show that cyclic changes in the general brain state strongly affect spontaneous activity and light encoding properties of dLGN neurons. First, we characterised several groups of dLGN cells: neurons led by ECoG, neurons in which the spike rate preceded ECoG changes and neurons co-occurring or not correlated with ECoG signal. Secondly, we verified that although the general light responsiveness of the dLGN is not influenced by the state of the brain, modulation of types of photoresponses and differences in ability to encode ambient light levels were observed. Cells responding to light in a sustained manner encoded light intensity more accurately during the cortical activation phase of urethane anesthesia. On the other hand, isoflurane anesthesia does not induce such rhythmic changes in ECoG and shuts down the spontaneous neuronal activity in the dLGN. Together, these data suggest a greater modulation of spontaneous activity and dLGN neurons function, than it was previously reported for the rodent dLGN and highlight the role of anesthesia in interpretations of findings from ongoing acute experiments.