FIGURE 5.

Pharmacological stimulation of the LPO enhances the firing rate of VTA dopamine neurons and inhibits that of VTA GABA neurons. (A) Location of LPO injections: aCSF (gray), bicuculline (Bic, red for GABA neurons and blue for dopamine neurons), during recordings of GABA neurons (squares) or dopamine neurons (circles). (B) Locations of dopamine (circles) and GABA (squares) neurons within the VTA. Color indicates corresponding intra-LPO injection: aCSF (gray), bicuculline (Bic, red for GABA neurons and blue for dopamine neurons). (C) Firing in GABA neurons (delta from baseline) before and after the administration of aCSF (gray) or bicuculline (Bic, red). Time is relative to onset of 3-min microinjection; each point represents the mean ± SEM values of each group. Stimulating the LPO with bicuculline decreased firing in GABA neurons relative to aCSF control and baseline (pre-injection) activity (group × time interaction: F₍₈,₉₆₎ = 3.29, P = 0.0023, HSD, ^∗P < 0.05 compared with all pre-injection time-points). (D) Representative firing rate in a GABA neuron. There was substantial decrease in firing rate throughout injection and following. (E) Average waveform and recording traces for the neuron shown in graph (D). Symbols denote the time period from which each trace was (obtained. (F) Firing in dopamine neuron (delta from baseline) before and after the administration of aCSF (gray) or bicuculline (Bic, blue). Time is relative to onset of the 3-min microinjection; each point represents the mean ± SEM values of each group. Stimulating the LPO with bicuculline increased the firing rate of dopamine neurons, relative to aCSF control and baseline (pre-injection) activity (group × time interaction: F₍₈,₁₂₂₎ = 2.87, P = 0.0060, HSD, ^∗P < 0.05 compared with all pre-injection time-points). (G) Representative firing rate in a dopamine neuron. There was an increase in firing rate throughout the injection and following. (H) Average waveform and recording traces for the neuron shown in graph (G). Symbols denote the time period from which each trace was obtained. (I) Burst characteristics of dopamine neurons before and after the administration of aCSF or Bic (delta from baseline) for non-burst frequency (Hz) [% of spikes emitted in bursts, burst event frequency (Hz), burst duration (ms), and intra burst frequency (Hz) (HSD, ^∗P < 0.05 compared with all pre injection time-bins)]. Symbols are mean ± SEM for each group; lines are individual subjects. See main text for detailed statistics.)