Effects of centrally administered anxiolytic agents on classically conditioned bradycardia.
Rats received infusions of the opioid peptide D-Ala2-Met-enkephalinamide (DALA, 10 micrograms), the alpha 2-noradrenergic agonist clonidine (CLON, 3 micrograms), UK14,304 (UK, 5 micrograms), the corticotropin-releasing factor (CRF) antagonist alpha-helical CRF (9-41) (alpha-HEL, 25 micrograms), or saline in the rostral fourth ventricle. The DALA, CLON, and UK groups showed no evidence of a heart rate (HR) conditioned response (CR) during conditioning, after antagonist administration, or on a nondrug test 48 hr after conditioning. These three groups showed the development of normal CRs when later retrained without drugs. The alpha-HEL group showed an enhanced CR. During a subsequent startle test, the presence of a conditioned stimulus resulted in a pronounced suppression of startle in the SAL and alpha-HEL groups but had no effects on startle in the DALA, CLON, and UK groups. The results indicate an important role for fourth ventricle structures containing opioid and alpha 2 receptors in the learning of an HR CR.
Harris
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GC
Vollum Institute, Oregon Health Sciences University, Portland 97201.
Fitzgerald
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D000818:Animals; D014151:Anti-Anxiety Agents / Q000494:pharmacology*; D001143:Arousal / Q000187:drug effects*; D001921:Brain / Q000187:drug effects*; D001931:Brain Mapping; D000068438:Brimonidine Tartrate; D003000:Clonidine / Q000494:pharmacology; D003214:Conditioning, Classical / Q000187:drug effects*; D003346:Corticotropin-Releasing Hormone / Q000494:pharmacology; D004744:Enkephalin, Methionine / Q000031:analogs & derivatives / Q000494:pharmacology; D006339:Heart Rate / Q000187:drug effects; D008297:Male; D010446:Peptide Fragments / Q000494:pharmacology; D011810:Quinoxalines / Q000494:pharmacology; D051381:Rats; D013216:Reflex, Startle / Q000187:drug effects
D014151:Anti-Anxiety Agents; D010446:Peptide Fragments; D011810:Quinoxalines; D000068438:Brimonidine Tartrate; D004744:Enkephalin, Methionine; C022118:enkephalinamide-Met, Ala(2)-; D003346:Corticotropin-Releasing Hormone; C045089:corticotropin releasing hormone (9-41); D003000:Clonidine