Characterization of DAT⁺ neurons in the dorsal raphe region projecting unto the extended amygdala.

Abstract

The dopaminergic system in the central nervous system is known to play significant roles in motor coordination and affective behaviors. The extended amygdala, which includes the oval nucleus of the bed nucleus of the stria terminalis (BNST_OV) and the lateral part of the central nucleus of the amygdala (CeL), receives dense innervations of DAT⁺ fibers from the dorsal raphe (DR) and periaquductal grey (PAG) regions. We found that DAT^DR-PAG neurons consisted of two subpopulations: DAT⁺/TH⁺/VIP^- and DAT⁺/TH^-/VIP⁺. Next, we examined the properties of synaptic transmission of DAT^DR-PAG and VIP^DR-PAG innervations in BNST_OV and CeL by whole cell patch clamp recording from acute brain slices obtained from DAT-cre::Ai32 or VIP-cre::Ai32 mice that express ChR2 in DAT⁺ or VIP⁺ fibers. Both in BNST_OV and CeL, the photo stimulation evoked excitatory synaptic currents. Finally, we measured the activity of DAT^DR-PAG and VIP^DR-PAG neurons during the head-fixed classical fear conditioning by using the GCaMP photometry technique. The unconditioned stimulus (US) was air puff, and the conditioned stimulus (CS) was tone. DAT⁺ and VIP⁺ neurons were transiently activated during US presentation, while CS presentation did not alter the activities during the habituation, training session, and test session. These results suggest that DAT⁺ neurons including VIP⁺ neurons in PAG-DR region respond to aversive stimuli and mediate aversive information to their downstream targets; BNST_OV and CeL.