Safflower seed oil, a rich source of linoleic acid, stimulates hypothalamic neurogenesis in vivo

Adult neurogenesis has been reported in the hypothalamus, subventricular zone and subgranular zone in the hippocamp. Recent studies indicated that new cells in the hypothalamus are affected by diet. We previously showed beneficial effects of safflower seed oil (SSO), a rich source of linoleic acid (LA; 74%), on proliferation and differentiation of neural stem cells (NSCs) in vitro. In this study, the effect of SSO on hypothalamic neurogenesis was investigated in vivo, in comparison to synthetic LA. Adult mice were treated with SSO (400 mg/kg) and pure synthetic LA (300 mg/kg), at similar concentrations of LA, for 8 weeks and then hypothalamic NSCs were cultured and subsequently used for Neurosphere-forming assay. In addition, serum levels of brain-derived neurotrophic factor (BNDF) were measured using enzyme-linked immunosorbent assay. Administration of SSO for 8 weeks in adult mice promoted the proliferation of NSCs isolated from SSO-treated mice. Immunofluorescence staining of the hypothalamus showed that the frequency of astrocytes (glial fibrillary acidic protein⁺ cells) are not affected by LA or SSO. However, the frequency of immature (doublecortin⁺ cells) and mature (neuronal nuclei⁺ cells) neurons significantly increased in LA- and SSO-treated mice, compared to vehicle. Furthermore, both LA and SSO caused a significant increase in the serum levels of BDNF. Importantly, SSO acted more potently than LA in all experiments. The presence of other fatty acids in SSO, such as oleic acid and palmitic acid, suggests that they could be responsible for SSO positive effect on hypothalamic proliferation and neurogenesis, compared to synthetic LA at similar concentrations.