title: Locus coeruleus involvement in the learning of classically conditioned bradycardia.
abstract: Opioid agonists are known to inhibit the activity of locus coeruleus (LC) neurons. In this study, microinjections of the mu-opioid agonist [D-Ala2, N-Me-Phe4, Gly5-ol]-enkephalin (DAMGO; 1.6 microM) bilaterally into the LC caused a significant impairment in the development of a heart-rate (HR) conditioned response (CR). The adverse effect of DAMGO on the HR CR could be reversed with naltrexone pretreatment. Microinjections of DAMGO into the periaqueductal gray, parabrachial nucleus, or fourth ventricle structures 1-2 mm away from the LC had no effects on the development of an HR CR. We conclude that central noradrenergic activity as mediated by the LC is critically involved in the learning and retention of conditioned cardiovascular responses.
authors.affiliation: Vollum Institute, Oregon Health Sciences University, Portland 97201.
authors.forename: G C
authors.initials: GC
authors.lastname: Harris
authors.forename: R D
authors.initials: RD
authors.lastname: Fitzgerald
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D003214:Conditioning, Classical / Q000502:physiology*; D004558:Electric Stimulation; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D004745:Enkephalins / Q000494:pharmacology; D006339:Heart Rate; D007267:Injections; D008125:Locus Coeruleus / Q000502:physiology*; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D004745:Enkephalins; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-