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Depletion of peripheral sympathetic noradrenaline, induced by ip injection of 6-hydroxydopamine, led to significant decrements in escape and avoidance responding when the required response was difficult, but not when it was relatively easy to acquire. The present results are similar to those obtained with adrenal-demedullated subjects. These findings clarify the role of the sympathetic nervous system in the motivation of behavior elicited by aversive stimulation. Implications for two-process theory and the "Kamin effect" or "learned helplessness" were discussed.x This research forms part of a dissertation presented to Macquarie University by E. L. Di Giusto in partial fulfillment of the requirements for the PhD degree. The authors wish to thank Astra Chemicals Pty Ltd. for their generous supply of 6-hydroxydopamine.2 Requests for reprints should be sent to M. G.

Six experiments are reported on the effects of 2,4,5-trihydroxyphenylethylamine (6-hydroxydopamine) on two-way escape and avoidance learning. Rats were tested on either escape or avoidance learning at 80 days of age after chemical sympathectomy at birth or 40 or 80 days of age. Neonatal and chronic sympathectomy (at 40 days), but not acute sympathectomy (at 80 days), resulted in depressed escape learning. Avoidance learning was affected by neonatal sympathectomy and partially by acute sympathectomy. The results have implications for the role of the autonomic nervous system in escape-avoidance learning.

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