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
