Background: Neuronal connections change during the memory formation process. The purpose of this study was to evaluate the effect of alcoholic extract of Cannabis sativa leave on the neuronal density of CA1, CA2 and CA3 regions of rat hippocampus.

Materials and Methods: In this experimental study, 24 male Wistar rats (300-350 g) were divided into two experimental and one control groups. Cannabis sativa seed was extracted using Soxhlet apparatus and then was injected in different doses (50 and 25 mg/kg, i.p, respectively) once a week for three weeks. After one month, rats were decapitated and their brain dissected, fixed in formalin (10%), sectioned (7μm thickness) and then stained with H & E. By applying dissection techniques and systematic random sampling scheme, the neuronal density of CA1, CA2, CA3 regions of hippocampus were estimated.

Results: Statistical analyses showed a significant decrease in the neuronal density of CA1 region, while there was a significant increase in the neuronal density of CA2 and CA3 regions of hippocampus in the experimental group (25 mg/kg alcoholic extract) compared to the control group (P=0).

Conclusion: It seems that the normal dose of alcoholic extract of Cannabis sativa leave induces neuronal degeneration in CA1 region of the hippocampus, while a low dose of it induces a neurogenesis in other hippocampal regions.