Disruptive influence of norepinephrine depletion on sensory preconditioning, but not first-order conditioning, in preweanling rats.
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abstract
Learning and memory processes are known to be influenced by the action of norepinephrine (NE). The present study evaluated the influence of neonatal administration of the NE neurotoxin DSP4 on sensory preconditioning (SPC) in 16- and 28-day-old rats. Rats were subcutaneously administered 50 mg/kg DSP4 or saline within 24 h after birth and tested at 16 or 28 days in two experiments. The results from Experiment 1 indicated that nondepleted 16-day-old rats exhibited strong SPC, whereas this conditioning was disrupted by neonatal administration of DSP4. No SPC was seen in either neonatal treatment group at 28 days of age, confirming previous reports of an ontogenetic decline in SPC. In Experiment 2, no effects of DSP4 were observed on first-order conditioning at either age. The brains of representative subjects were separated into forebrain, cerebellum, and brain stem samples and were analyzed to determine the extent of NE depletion. This analysis showed that DSP4 produced a marked reduction in NE concentration in the forebrain, but not in the cerebellum or brain stem. The results of this study suggest a role for forebrain NE in SPC in preweanling rats. This modulatory noradrenergic influence appears to be exerted on the formation of associations between two relatively neutral stimuli during the preexposure phase, given the absence of an effect of DSP4 on primary conditioning.
