Noradrenaline, fear and extinction.

It has been suggested that noradrenaline in the central nervous system is involved in fear and anxiety. To test this postulate extensive depletion of ascending noradrenaline systems was accomplished by intracerebral injection of the selective neurotoxin 6-hydroxydopamine. Fear and anxiety were assessed using a Sidman avoidance task and a conditioned emotional response paradigm. No alteration in fear motivated acquisition learning of either of these tasks were detected. Resistance to extinction was seen on the conditioned emotional task, perhaps because of its continuously reinforced nature, but not on the Sidman avoidance, perhaps as a consequence of the reinforcement contingencies which render this task more similar to a partially reinforced schedule. No evidence for a role of ascending noradrenaline systems in fear or anxiety was hence obtained, but a further demonstration of a role in extinction processes was found.