The impact of the locus coeruleus efferent pathway on thalamic and cortical sensory neuron response properties in the awake rat

The nucleus locus coeruleus (LC) and its norepinephrine (NE) containing efferent system have been implicated in modulating arousal states and attentional processes.;The goal of this work was to characterize the impact of tonic and phasic LC system output on simultaneously recorded target neurons of the somatosensory thalamus and cortex in the awake behaving rat. The general hypothesis tested in this dissertation is that electrical or chemical manipulations of LC neuron output over the physiological range of tonic discharge frequencies, alters sensory-evoked response properties of target thalamic and cortical neurons recorded simultaneously in the awake freely moving rat.;The first portion of this research was to develop a set of techniques to record the effects of pharmacological or electrical manipulations of the LC on sensory evoked responses of many simultaneously recorded single neurons along the trigeminal somatosensory system of the awake freely moving rat.;The second portion of this research characterized the effects of tonic LC stimulation on the magnitude and latency of whisker pad stimulus-evoked responses. Target cells at the thalamic and cortical levels of the rat trigeminal somatosensory pathway primarily demonstrated either an augmentation or a suppression of the stimulus-evoked discharge over the range of LC stimulus frequencies tested.;The third portion of this research characterized the effects of systemic and local administration of the alpha-2 adrenergic receptor agonist clonidine on whisker pad stimulus-evoked response firing rates and latencies. These treatments resulted in the preferential augmentation of stimulus-evoked discharge for thalamic and cortical neurons.;The fourth portion of this research characterized the effects of phasic LC electrical stimulation on whisker pad stimulus-evoked response firing rates and latencies. Target somatosensory cells of the thalamus and cortex demonstrated augmentation or a suppression of the stimulus-evoked discharge in equal proportions following phasic LC stimulation.;The results of these studies suggest that LC output mediates changes in sensory information processing at the cellular level and that these changes are likely to enhance sensory signal detection and discrimination in the behaving animal. Moreover, the work provides a perspective on how a broadly projecting brainstem modulatory system can coordinately influence signal transmission at multiple stages of a complex, ascending sensory network. (Abstract shortened by UMI.)...