Lack of light-evoked GABAB response in VTA neurons. A, Average of five consecutive traces in an NAc-connected neuron after the GABAA response was blocked with 100 μm picrotoxin and after application of the GABAB receptor antagonist CGP-55845 [(2S)-3-[(15)-1-(3,4-dichlorophenyl)ethyl]amino-2-hydroxypropyl)(phenylmethyl)phosphinic acid] shows no response to 100 Hz light stimulation. B, The amplitude of electrically evoked GABAB IPSCs depends on the stimulation frequency. C, The addition of NNC-711 (10 μm) does not reveal a light-evoked GABAB IPSC. D, NNC-711 enhanced electrically evoked GABAB IPSCs. E, Bath application of 20 μm baclofen produced a small outward current in a neuron that received input from the NAc (top) compared with the response of a control TH (+) neuron (bottom). F, Connected neurons (n = 5) showed significantly smaller baclofen responses than TH (+) control neurons (n = 9), which had larger responses to baclofen than identified TH (−) neurons (n = 5). *p < 0.05, **p < 0.01.