The effect of norepinephrine release on odor discrimination learning in adult rats

Massaeli, Faghihe (2019) The effect of norepinephrine release on odor discrimination learning in adult rats. Masters thesis, Memorial University of Newfoundland.

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Abstract

The locus coeruleus is the main source of norepinephrine in the brain with extensive projections to many areas throughout the cortex including the olfactory bulb and piriform cortex. It has been shown that noradrenergic receptor blockade in either olfactory bulb or piriform cortex impairs similar odor discrimination. The goal of this thesis is to test whether enhancing locus coeruleus activity using optogenetic stimulation promotes odor discrimination learning. Adult TH-CRE rats were bilaterally infused with adeno-associated virus containing light-excitable channels targeting noradrenergic locus coeruleus neurons (AAV8- Ef1a-DIO-eChR2 (H134R)-EYFP). In vivo electrophysiology revealed neurons transfected with the viral vector were active when blue light (473 nm) was given at a frequency of 10Hz of 150mA laser current. After confirming the excitability response of the neurons, we tested the effect of light on general locomotor activity. Subsequently, we sought to determine the role of locus coeruleus activation on odor discrimination learning. Food-deprived animals were trained to discriminate between two simple odors, one paired with a food reward. This training was followed by a highly similar odor discrimination in which animals were optogenetically stimulated with a phasic pattern of blue laser light. AAV-ChR2 infused rats discriminated the similar odors after 3 days of training, while non-infused control rats reached the learning criteria in 8 days. The enhanced LC activity induced by photostimulation during highly similar odor discrimination training promoted faster learning.

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