MODULATION OF RETINAL INFORMATION STREAMS BY SEROTONIN AND AROUSAL IN THE THALAMUS

Abstract

Retinal ganglion cell (RGC) types relay parallel streams of visual information regarding global luminance, fine details and motion. Previous work has highlighted the role of neuromodulators in shaping sensory processing, as early as the inputs from the retina to the thalamus. We hypothesize that neuromodulators might efficiently control which information streams reach the cortex, by selectively gating transmission from specific RGC axons in thalamus. We here study the complementary and orthogonal effects of high arousal states and serotonin in an awake behaving animal. We find that optogenetic stimulation of serotonergic axons in visual thalamus suppresses ongoing and visually evoked calcium activity and glutamate release from RGC boutons. Two photon calcium imaging revealed that serotonin axon stimulation suppressed RGC boutons preferring global changes in luminance more than those preferring local visual stimuli, while the converse was true for suppression during periods of high arousal. In this latter state we also found that RGC boutons preferring decreases in luminance and posterior motion were more suppressed. Converging evidence suggests that differential expression of the 5-HT1B receptor on RGC presynaptic terminals, but not differential density of nearby serotonin axons, may contribute to the selective serotonergic gating of specific visual information streams before they can activate thalamocortical neurons.