Aoetoxycyoloheximide (ACXH), a protein synthesis inhibitor, and/or physiological saline, was injected into the hippocampi of unrestrained rats through two cannulas. Injections were made 5 hr. before introduction to a Y maze (shock motivated, brightness discrimination). Memory was severely impaired at 6 hr., 24 hr., and 7 days, but not at 3 hr. after aquisition. The ACXH had no "state-dependent" effect. When injections were given 5 hr. before the recall tests or immediately after acquisition, memory was unimpaired. The results indicate (a) two memory systems, (b) brain protein synthesis is necessary for establishment but not for the recall of long-term memory, and (c) activity in both short-and long-term systems is initiated during acquisition. The two memory systems appear to run in parallel rather than in series.

The effects of direct brain infusions of acetoxycycloheximide (an inhibitor of protein synthesis; ACXH) on acquisition, storage and recall of memory for one-trial appetitive learning were examined in five experiments. ACXH was infused into the rats' hippocampi through implanted cannulas. Control subjects received an equal volume of physiological saline. ACXH was infused (a) 5 h before acquisition, (b) 5 hr before commencement of recall tests, and (c) immediately after acquisition. Each subject's general motor activity was recording during testing. The results indicate that (1) ACXH has similar effects on appetitive and avoidance learning. (2) ACXH administered immediately after acquisition, has no effect on memory. (3) At 4 hr after acquisition memory is affected by ACXH. (4) Short-term memory is unaffected by ACXH and can exist independently of long-term memory. (5) ACXH consistently reduces general motor activity.

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