The cholinergic influence upon rat dorsal lateral geniculate nucleus is dependent on state of arousal

Several lines of evidence suggest a role for acetylcholine (ACh) in mediating the effects of state of arousal on transfer of visual information through the lateral geniculate nucleus (LGN). Local application of cholinergic agonists to geniculate relay cells in anesthetized cats and rats produces predominantly facilitatory effects. This indicates that presynaptic release of ACh may be responsible for the increased excitability of LGN relay cells that is observed during waking and REM sleep. In this study in rats we have examined the influence of cholinergic agonists applied during the 3 natural states of arousal: waking, slow-wave (SW) sleep and rapid eye movement (REM) sleep. Pharmacological agents were iontophoretically administered to identified, single cells in head-restrained, unanesthetized rats free to sleep and wake. Application of cholinergic agonist produced state-dependent differences in response in all geniculate relay-cells studied. During both waking and REM sleep, a facilitatory response was always observed, whereas in SW sleep responses were of three types: no effect (62%), inhibition (24%), and biphasic inhibition followed by facilitation (14%). All response types were antagonized by scopolamine. In contrast to the qualitatively different state-dependent effects of cholinergic agonists, response to application of glutamate, with quantitatite variations, was uniformly facilitatory in all states, though responses in SW sleep tended to be lower in magnitude. The effects of γ-aminobutyric acid (GABA), glycine, and serotonin were inhibitory in all states. These data are consistent with the suggested role of ACh in mediation of increased relay-cell excitability during REM sleep and waking. Our findings, however, also indicate that in the transition from SW sleep to REM or waking, local release of ACh is not solely responsible for alterations in cell excitability.