Figure 1.

In Vivo Firing Features of MHb-Projecting Neurons in the PS

(A) The recording site of a PS cell is shown on the left. The electrode position was labeled with pontamine sky blue dye. Center: coronal section illustrating the stimulating electrode track (red arrows) within the MHb (white arrow). Right: the positions of all antidromically identified cells recorded in the PS are plotted schematically.

(B and D). The action potential waveform and pattern activity of a typical PS neuron is illustrated in (B). Plots and bar graphs reporting firing activity and coefficient of variation of the inter-spike interval (ISI) of all cells are depicted in (D).

(C) Typical traces showing the collision test allowing identification of MHb-projecting cells following antidromic stimulation. The left traces display an antidromically propagating spike (ant, top trace) following MHb stimulation (gray arrow) and its collision (^∗) when a spontaneous action potential (spont, bottom trace) preceded stimulation. On the right, the time histogram is shown for 20 stimulations of this same neuron, provided at t = 0 (1-ms bins, 0.5 Hz stimulation frequency). The gray arrow indicates stimulation onset. All antidromic spikes recorded occurred in correspondence with the red bin.

(E) Average ISI histogram of burst-displaying PS neurons. Data from all recorded cells are pooled, with the red line representing mean values and the black one depicting the SEM. A typical recording extract, showing spikes belonging to 3 distinct bursts (green dots), is shown in the inset.

(F) Graphs illustrating the main parameters of the bursting activity recorded in PS neurons.