Figure 1.
The ventrolateral periaqueductal gray (vlPAG) contains 4 neuron types defined by distinct firing patterns. Representative traces from vlPAG neurons from naive rats showing 4 distinct neuron types based on their response to a 2-s-long 120-pA depolarizing current step. The proportion of neurons exhibiting the firing pattern out of the total neurons recorded in naive rats and the resulting percentage are shown in parentheses. Resting membrane potential is noted at the beginning of each trace, and the dotted line represents 0 mV. One hundred twelve Phasic neurons were observed from 29 female (56 neurons) and 21 male (50 neurons) naive rats; 78 Tonic neurons were observed from 22 female (38 neurons) and 19 male (37 neurons) naive rats; 23 Onset neurons were observed from 9 female (15 neurons) and 6 male (7 neurons) naive rats; 20 Random neurons were observed from 8 female (12 neurons) and 5 male (7 neurons) naive rats. A subset of cells from Sprague-Dawley (SD) rats was grouped with the Long-Evans (LE) cells after showing no differences in firing patterns observed and prevalence of neuron types (nSD = 33, nLE = 200; chi-square = 6.34, df = 3, P = 0.096).