Retrograde amnesia production by the intracisternal injection of 20 micronl of saline in rats.

The intracisternal injection of 20 micronl of saline into a rat within an hour after training it in an active avoidance response was found to induce retrograde amnesia. The results obtained by combining this procedure with the intracisternal injection of 2,6 Diaminopurine (DAP), which inhibits RNA synthesis and prevents long-term memory formation when administered at the proper time and in the correct dosage, suggest the existence of a medium term memory (MTM) mechanism. MTM was normally evident up to 75 min after training but was demonstrable up to 210 min when LTM formation was prevented by DAP.