Transgene-free magnetothermal neurostimulation and the induction of fear behaviors
Motivated by the highly efficient activation of neurons in the CeA regions of transgenic TRPV1-expressing mice by the FVIOs, we further explored the possibility of applying this nanoheater to activate endogenous TRPV1-expressing neurons in transgene-free mice. As previously reported, TRPV1 endogenously expressed on neurons in the CeA of mice[56-57], we also confirmed the endogenous expression of TRPV1 (red) on cells in the CeA regions of mice using immunohistochemical methods, as shown in Fig. 8a and 8b. Then, the FVIOs were modified with anti-TRPV1 antibodies to target endogenous TRPV1 in the CeA regions of transgene-free mice. Different doses of anti-TRPV1-FVIOs were injected into the CeA regions of these mice, and the fear behavioral response induced by FVIO-mediated magnetothermal stimulation was investigated under AMF exposure (20 mT, 275 kHz). The results verified that the anti-TRPV1-FVIOs elicited freezing behaviors in the mice at a minimum dose of 0.28 μg (Figure 8c). This transgene-free magnetothermal neurostimulation strategy avoids possible side effects arising from the overexpression of exogenous TRPV1 and gene delivery with viral vectors, which further improves the biosafety and expands the scope of magnetothermal neurostimulation applications[11, 58].