Evidence for adrenergic neurons in a memory access pathway.

Injection of a beta-adrenergic blocker, propranolol, in rats within 5 min after training of a step-dowm passive avoidance response had no effect on performance either 2 or 6 hr later, however, when testing occurred 1, 3 or 7 days after training and injection a significant performance decrement was observed. If drug injection was postponed until 1 or 3 days after training and testing was conducted 2 hr later, again poor avoidance performance was obtained. No support for a state-dependency explanation [14] of the propranolol amnesia could be found. The amnesia that followed beta-adrenergic receptor block was identical to that previously reported when norepinephrine biosynthesis was reduced [9] and supports the hypothesis of a role for adrenergic neurons in memory formation and retrieval that is different from cholinergic neurons [4,10].