A potential function of endocannabinoids in the selection of a navigation strategy by rats

One of the adaptive abilities of the brain is the generation of a strategy to optimize acquisition of information, i.e., learning. In this study, we explored the role of environmental conditions (the light-dark cycle) and of the endocannabinoid anandamide in rats to select a strategy to solve the Barnes maze (BM).

To determine the effects of manipulating the cannabinergic system on a spatial task in relation to the light-dark cycle.

Rats received an intrahippocampal or intrastriatal administration of anandamide, AM251, or their combination at two different points of the light-dark cycle (1300 and 0100 hours), and their performance in the BM was evaluated. In addition, we determined the expression of the cannabinoid 1 receptor (CB1R) in the hippocampus and striatum throughout the light-dark cycle.

Results indicate that rats solved the BM by using a spatial strategy during the light phase and a procedural (serial) strategy during the dark phase of the cycle. CB1R expression varied in the hippocampus, being higher at 1300 hours and lower at 0100 hours, whereas its expression remained unchanged in the striatum.

Changes in the brain, which include changes in the endocannabinoid system, prompt it to use different strategies (spatial and procedural, or others not evaluated in this study) to cope with the environmental demands. These cerebral changes are adaptive responses to the light-dark cycle.