Link to bioRxiv paper: http://biorxiv.org/cgi/content/short/2020.07.09.188615v1?rss=1 Authors: Zeinab Fazlali, Yadollah Ranjbar-Slamloo, Ehsan Arabzadeh Abstract: Locus Coeruleus (LC) noradrenergic system has widespread projections throughout the brain and affects sensory processing in various modalities. Inhibition of both spontaneous and sensory-evoked cortical activity is well-documented in early experiments by either LC electrical micro-stimulation or local application of norepinephrine (NE). However, the temporal profile of LC modulation of sensory response is not well-established. Here, we recorded neuronal activity from the rat barrel cortex under urethane anesthesia and coupled LC micro-stimulation with brief mechanical deflection of whiskers at 10 different time lags (50-500 ms). LC micro-stimulation exhibited a biphasic effect on BC spontaneous activity: a period of suppression (~100 ms) followed by a period of excitation (~200 ms). This profile was highly consistent across BC units: 82% of BC units showed early suppression and 91% of BC units showed late excitation. We observed a similar effect on the sensory-evoked response: at 50-ms lag, the evoked response (1-75 ms after deflection onset) decreased in 77% of units and at 150-ms lag, the early evoked response was facilitated in 85% of units. At 150 to 350-ms time lags, LC micro-stimulation caused a combined facilitation followed by suppression on the evoked response. For lags of 400-ms and higher, the effect was pure facilitation. Additionally, response latency was significantly decreased at 250 ms time lag. In summary, we found that LC modulation affects the cortical processing of sensory inputs in a complex manner which critically depends on the time lag between LC activation and sensory input. These results have clear implications for temporal integration of sensory input and its noradrenergic modulation in a behavioral setting.Competing Interest StatementThe authors have declared no competing interest.View Full Text Copy rights belong to original authors. Visit the link for more info