Tonic electrical stimulation of the locus coeruleus enhances cortical
sensory-evoked responses via noradrenaline α1 and β receptors
Abstract
The locus coeruleus (LC) neurons send extensive projections to the
somatosensory cortex and release noradrenaline (NA) at synaptic
terminals, which is thought to regulate the activation of
sensory-related cells by acting on three types of receptors (α1, α2 and
β). Although previous studies have examined the effects of LC
stimulation on single-unit sensory neurons, their impact on
somatosensory evoked potentials (SEPs) and their temporal variations, as
well as the specific roles of NA receptors remain unclear. Herein, we
investigated how SEPs are modulated by tonic LC stimulation at
physiological frequencies (0.1, 1 and 4 Hz) and identified the receptors
involved in these changes. Forepaw stimulation-induced amplitudes in SEP
were enhanced in response to 1 Hz stimulation of the LC but not in
response to 0.1 and 4 Hz stimulation. Interestingly, the enhancement of
SEPs after LC stimulation persisted for tens of minutes following the
cessation of stimulation. Optical imaging using a voltage-sensitive dye
showed an increase in the depolarizing response in the somatosensory
cortex after 1 Hz stimulation. Prazosin (α1 receptor antagonist) and
propranolol (β receptor antagonist) inhibited SEP enhancement following
1 Hz LC stimulation, whereas yohimbine (α2 receptor antagonist) had no
effect. This suggests that the observed enhancement in SEP observed is
primarily mediated by the activation of cortical excitatory α1 and β
receptors. These findings provide insight into the impact of the NA
system on sensory information processing as well as the pathophysiology
of sensory disorders related to the disruption of the NA system.