CLASSICAL-CONDITIONING IN THE FETAL-RAT - REINFORCING PROPERTIES OF DYNORPHIN-A-(1-13)

This study examined the reinforcing properties of dynorphin A (1-13) i n a single-trial classical conditioning paradigm in the E20 rat fetus. Injection of dynorphin into the cisterna magna increased fetal motor activity and reduced facial wiping in a test of perioral cutaneous res ponsiveness. Dynorphin was effective as an unconditioned stimulus (US) in a classical conditioning paradigm using an artificial nipple condi tioned stimulus (CS) and dynorphin A (1-13) US. The association betwee n CS and US was dependent on activity in the kappa opioid system. Re-e xposure to the artificial nipple CS after a single pairing of the nipp le with dynorphin resulted in conditioned activation of the kappa opio id system. Dynorphin A (1-13) functions as a reinforcer for classical conditioning in the rat fetus after intracisternal or intrahemispheric injection, with the conditioned response depending on route of admini stration and site of injection.