Ascending, descending and local control of neuronal activity in the rat lateral geniculate nucleus

Mechanisms of control for activities of relay neurons (P-cells) in the rat dorsal lateral geniculate nucleus (LGNd) are surveyed with special reference to ascending projection arising from the locus coeruleus (LC), the local projection from the visual portion of the thalamic reticular nucleus (vTRN) and the descending projection from the visual cortex (VC). Noradrenaline released from terminals of LC neurons exerts a facilitatory influence on P-cell activity via alpha-receptors. A recurrent projection of vTRN neurons on P-cells is inhibitory, utilizing GABA as a transmitter. P-cells receive an excitatory input from corticothalamic neurons of VC. However, in many P-cells the corticofugal excitation is counterbalanced by inhibition arising in vTRN neurons which are invariably exited by the collateral branches of the corticogeniculate axons. Thus, LGNd is not a simple relay station, but various modifications of visual information are made in this nucleus.