Study On Behaviors Induced By Precise Photo-Activation On Dorsal Periaqueductal Gray

The periaqueductal gray (PAG) represents the final common pathway mediating defensive reactions to fear. The dorsal part of PAG (dPAG) regulates active defensive behavior. Traditional brain stimulation methods such as electric stimulation and chemical stimulation failed to meat the feature of precision in both temporal and spacial. However, in recent years, optogenetics demonstrates its amazing application prospect. This new method has outstanding spatio-temporal controllability while limits non-specific activation/inhibition. The fast on-off switch dynamics ensures the millisecond-scale neural regulation. These advantages make it a promising method on precise study of dPAG.In this thesis, we aim to apply optogenetic technique on precise activation of rat dPAG, to illustrate ①if defensive behavior is related to optical stimulation; ② behavioral differences induced by optical stimulation and electric stimulation; ③ activation range of midbrain under different methods; ④the contribution of dPAG glutamatergic neurons on rat defensive behavior.The innovations in this thesis:① We setup steady virus packaging, concentration and purification system. High-titer infective viral particles are gained and used to infect rat dPAG in vivo.② We build the optical stimulation system and obtain parameters that applied to induce steady freezing and escaping behaviors. Plexon system is employed to record dPAG neural activity during optical stimulation. Electrophysiology shows the activation of dPAG is related to laser intensity and frequency, indicating both temporal and rate coding mechanism of dPAG.③ Behavioral differences under electric and optical methods show that optical stimulation is much steadier and gentler in inducing defensive behaviors.④ C-Fos immunohistochemistry indicates different methods lead divergent activation regions.⑤ Subtype specific activation of dPAG neurons suggests that glutamatergic neurons make great contribution to defensive behaviors.Generally, we avoid the defects of traditional brain stimulation methods. The optogenetic method has better effects on defensive behavior induction, which could be competent at basic studies on dPAG.