Chronic cold exposure potentiates CRH-evoked increases in electrophysiologic activity of locus coeruleus neurons.
BACKGROUND
Chronic stress exposure can produce sensitization of norepinephrine release in the forebrain in response to subsequent stressors. Furthermore, the increase in norepinephrine release in response to the stress-related peptide corticotropin-releasing hormone (CRH) is potentiated by prior chronic stress exposure. To explore possible mechanisms underlying these alterations in norepinephrine release, we examined the effect of chronic stress on the electrophysiologic activity of locus coeruleus (LC) neurons in response to centrally applied CRH.


METHODS
Single-unit recordings of LC neurons in halothane-anesthetized rats were used to compare the effect of intraventricular administration of CRH (0.3-3.0 microg) in control and previously cold-exposed (2 weeks at 5 degrees C) rats.


RESULTS
The CRH-evoked increase in LC neuron activity was enhanced following chronic cold exposure, without alteration in basal activity of LC neurons. The enhanced CRH-evoked activation was apparent at higher doses of CRH but not at lower ones, resulting in an increased slope of the dose-response curve for CRH in previously cold-exposed rats.


CONCLUSIONS
These data, in combination with previous data, suggest that the sensitivity of LC neurons to excitatory inputs is increased following chronic cold exposure. The altered functional capacity of LC neurons in rats after continuous cold exposure may represent an experimental model to examine the role of central noradrenergic neurons in anxiety and mood disorders.
Department of Neuroscience, University of Pittsburgh, Pittsburgh, Pennsylvania, USA.
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D000818:Animals; D001008:Anxiety Disorders / Q000523:psychology; D002908:Chronic Disease; D003080:Cold Temperature; D003346:Corticotropin-Releasing Hormone / Q000502:physiology*; D003865:Major Depressive Disorder / Q000523:psychology; D004594:Electrophysiology / Q000379:methods; D006801:Humans; D008125:Locus Coeruleus / Q000502:physiology*; D008297:Male; D009474:Neurons / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013313:Stress Disorders, Post-Traumatic / Q000523:psychology; D013315:Stress, Psychological / Q000523:psychology
D003346:Corticotropin-Releasing Hormone