EMERGENCE OF CONDITIONED CARDIAC RESPONSES TO AN OLFACTORY CS PAIRED WITH AN ACOUSTIC STARTLE UCS DURING DEVELOPMENT - FORM AND AUTONOMIC ORIGINS

Pairing an olfactory conditioned stimulus (CS) with an acoustic startl e unconditioned stimulus (UCS) produced conditioned bradycardia in rat s ranging from 12 days of age to adulthood but failed to produce condi tioning in 10-day-olds (Experiment I). The second experiment compared! the effects of two different UCSs, acoustic startle and electric shoc k. The startle UCS produced conditioned bradycardia accompanied by imm obility. In contrast the shock UCS produced conditioned tachycardia ac companied by behavioral activation. Pharmacological analysis revealed that activation of the parasympathetic nervous system (PNS) produced t he conditioned bradycardia (Experiment 3) and that activation of the s ympathetic nervous system (SNS) produced he conditioned. tachycardia ( Hunt, Hess, & Campbell, 1994). Further comparisons revealed that the s tartle UCS established conditioning several days earlier in developmen t than the shock UCS. The ability of the PNS to respond to phasic stim ulation earlier in development than the SNS was discussed as a possibl e mechanism for the. early development of conditioned bradycardia. (C) 1997 John Wiley & Sons, Inc.