Figure 1
From: A concurrent excitation and inhibition of dopaminergic subpopulations in response to nicotine
A subpopulation of VTA DA neurons is inhibited by nicotine.
(a) Raw in vivo single cell extracellular recordings of an excited (left) and an inhibited VTA DA neuron (right) at the time of nicotine (30 μg/kg) intravenous injection (indicated by arrowheads). Corresponding wide action potentials, typical of DA neurons, are displayed on the right. (b) Schematic showing a mouse brain in which electrodes are lowered in both hemispheres. Raw extracellular simultaneous recordings of single DA neurons located in right and left VTA, at the time of nicotine (30 μg/kg) intravenous injection (arrowheads). This pair of neurons consists of an excited cell (red, left) and an inhibited cell (blue, right), showing that the responses to nicotine are not state dependent. (c) Mean responses of excited (red, n = 102) and inhibited (blue, n = 78) VTA DA neurons. Data, expressed as variation of firing frequency from baseline, are presented as mean (thick curves) ± SEM (light curves). Arrowhead represents the time of nicotine injection. (d) Mean responses of excited (red) and inhibited (blue) VTA DA neurons to increasing doses of nicotine (excited at 5 μg/kg: n = 8, 10 μg/kg: n = 8, 15 μg/kg: n = 10, 30 μg/kg: n = 50, 60 μg/kg: n = 18, 90 μg/kg: n = 10; inhibited at 5 μg/kg: n = 2, 10 μg/kg: n = 5, 15 μg/kg: n = 5, 30 μg/kg: n = 27, 60 μg/kg: n = 15, 90 μg/kg: n = 4). Similar results are obtained whether considering a single neuron's response at different doses or when considering the mean response of the populations. (* p < 0.05, ** p < 0.01, *** p < 0.001)
