(A) Diagram of surgical procedures and formalin task. Retrograde Cre-dependent HSV-LS1L-hM4Di-mCherry viral vector was injected into the VTA of vglut2:cre or vgat:cre mice and a cannula implanted for intracranial injections of aCSF (control) or the hM4Di-DREADD agonist J60 (200 nL, 0.1 μg/mL) to inhibit LPO → VTA vglut2 or vgat neurons.
(B and C) hM4Di inhibition of LPO-VGluT2 inputs to the VTA reduces hindpaw licking in phase II, but not phase I, of the formalin footpad test compared with aCSF controls (phase I, t(10) = 1.69, p = 0.12; phase II, t(10) = 2.34, p = 0.04).
(D and E) hM4Di inhibition of LPO-VGaT inputs to the VTA does not affect responses in either phase of the formalin footpad test (phase I, t(16) = 0.53, p = 0.60; phase II, t(16) = 0.24, p = 0.81).
(F) hM4Di inhibition of LPO-VGaT inputs to the VTA does produce a modest reduction in the consumption of a sucrose reward compared with both aCSF controls and a within-subjects baseline test for sucrose consumption (session × treatment, F(1,11) = 10.86, p = 0.0072). *p < 0.05, **p < 0.01; all data represent mean ± SEM.