Intra-hippocampal KN-62 hinders the memory of habituation acquired alone, but not simultaneously with a water-finding task.

Abstract

Rats were implanted bilaterally with cannulae in the CA1 region of the dorsal hippocampus. After recovery from surgery, they were submitted to a water-finding task, which required detecting a water tube in an open field, and then remembering its location under conditions of thirst. This task was acquired simultaneously with habituation to the open field. Training and test sessions lasted 2 min, in addition to the time spent at the water tube. The training-test interval was 24 h, during which the animals were deprived of water. Immediate post-training intra-hippocampal administration of the calcium/calmodulin-dependent protein kinase II (CaMKII) inhibitor KN-62 (3.6 ng/side) attenuated memory of the water-finding task, but not that of the habituation acquired concomitantly. However, when the habituation was carried out alone in the absence of the water-finding task, its retention was inhibited by KN-62. Thus, depending on circumstances, habituation can be memorized with or without hippocampal CaMKII activity. In the post-training period, CA1 neurones appear to 'choose' which task will be processed by a metabolic pathway that includes CaMKII.