Figure 2.

Defining features of the 2 most common ventrolateral periaqueductal gray (vlPAG) neuron types: Phasic and Tonic neurons. A: representative trace of a recording from a Phasic vlPAG neuron from a naive rat in response to 0-pA (bottom trace), 40-pA (middle trace), and 120-pA (top trace) current injections. Current injections were 2 s long after a 50-ms delay, followed by 250-ms return to baseline (as shown in the current protocol schematic below the traces). B: firing frequency of all Phasic neurons for current steps ranging from 0 pA to 120 pA in 20-pA increments (n_total = 112; n_female = 56, n_male = 50). The dashed line labeled P_max indicates the average firing frequency at the maximally depolarizing current step (120 pA) for Phasic neurons. The solid line labeled T_max indicates the average firing frequency at the maximally depolarizing current step (120 pA) for Tonic neurons. C: total firing duration of all Phasic neurons throughout each of the 2-s depolarizing current steps (n_total = 112; n_female = 56, n_male = 50). D: representative trace of a recording from a Tonic vlPAG neuron from a naive rat in response to 0-pA (bottom trace), 40-pA (middle trace), and 120-pA (top trace) current injections. E: firing frequency of all Tonic neurons for current steps ranging from 0 pA to 120 pA in 20-pA increments (n_total = 78; n_female = 38, n_male = 37). F: compiled data showing the total firing duration of all Tonic neurons throughout each of the 2-s depolarizing current steps (n_total = 78; n_female = 38, n_male = 37).