BACKGROUND AND AIMS: We have previously reported that whisker-shock fear conditioning produced expansion of the cortical representation of the activated vibrissae (“trained row”), this was demonstrated by labeling with 2-deoxyglucose in layer IV of the barrel cortex. Functional reorganization of the primary somatosensory cortex was accompanied by an increase in the density of small GABAergic neurons, GAT67 boutons and GAT-1 puncta in the hollows of barrels representing the trained row. The goal of this study was to investigate how whisker-shock fear conditioning affects the expression of puncta of the cannabinoid receptor 1 (CB1), in the hollows of the trained row barrels in of the primary somatosensory cortex evaluated by immunocytochemistry 24 h after associative learning paradigm. METHODS: The present study estimates the CB1+ puncta (Abcam 1:500) mean numerical density (Nv) in hollow of all rows barrels of the barrel cortex. In a whisker-shock and control groups precise location of layer IV cells were identified using Hoechst 33258 staining of tangential sections. A confocal microscopy stereological technique, was used in the CB1+ puncta analyses. RESULTS: Our present data revealed increased CB1+ puncta density by approximately 58% in the hollows of barrels representing the trained row compared to the hollows in the barrel field of the opposite hemisphere in the same mouse. In contrast, density of CB1+ puncta was unchanged in the control groups, which received shock alone and naïve animals. We also observed very low density of CB1+ puncta concentrated in the hollows of the all rows barrels of the barrel cortex belonging to pseudoconditioned group of animals. CONCLUSION: The findings suggest that CB1 receptors plays a selective active role in fear conditioning-dependent plasticity. Funding: Scientific Research Grant 6420/B/P01/2011/40 to ES.
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