Δ9-Tetrahydrocannabinol Modulates Hippocampal Neurogenesis in Female Wistar Rats: Interaction with Estradiol

The endocannabinoid system (ECS) plays a key role in regulating neurogenesis and inflammatory processes in the brain. The increasing prevalence of Cannabis use among women highlights the importance of understanding sex-specific effects of cannabinoids, particularly in the context of hormonal interactions. This study aimed to investigate the effects of delta-9-tetrahydrocannabinol (THC) and estradiol benzoate (EB) on adult hippocampal neurogenesis (AHN) and inflammation in ovariectomized female Wistar rats. Sixteen rats were allocated to four experimental groups receiving THC, EB, both treatments, and vehicle. Immunohistochemical analyses were conducted to evaluate markers of proliferation (Ki-67), neurogenesis (doublecortin and PSA-NCAM), cannabinoid receptor expression (CB1), and inflammation (COX-2 and TNF-α) in the hippocampal formation. The administration of THC significantly increased Ki-67 immunoreactivity, suggesting enhanced cell proliferation. A trend toward increased doublecortin expression was observed, particularly in EB-treated animals. THC also modulated CB1 receptor expression, with significant increases in the dentate gyrus and hilus following combined THC and EB treatment. Furthermore, THC reduced inflammatory markers, with region-dependent decreases in COX-2 and TNF-α expression. These findings indicate that THC influences markers associated with hippocampal cell proliferation, neurogenesis, cannabinoid signaling and inflammation in female rats, and that some of these effects depend on estradiol status. The interaction between cannabinoids and gonadal hormones may represent an important mechanism underlying sex-specific neurobiological responses and suggests potential targets for therapeutic intervention in neuropsychiatric disorders.