Table 1.

Overview of the experiments

Experiment	n (rats)	Surgical procedure	Experimental manipulation
1: Effect of mPFC light delivery on astrocyte and microglia markers	n = 3; continuous light n = 3; light cycles (5 s) n = 2; light cycles (5 min)	Bilateral: fiber optics implanted in dorsal mPFC	Unilateral: 30 min light delivery in vivo Contralateral hemisphere: no light delivery Rats killed 24 h after stimulation for immunohistochemical evaluation
2: Effect of mPFC light delivery on ex vivo neural activity	n = 5	Unilateral: AAV–CaMKIIα–eYFP Unilateral: AAV–CaMKIIα–eNpHR3.0–eYFP	Ex vivo (slice) electrophysiology in eNpHR3.0 and eYFP hemispheres using the following: Voltage clamp plus light delivery: measure light-evoked current Current injections plus light delivery: measure voltage change in the presence and absence of light
3: Effect of mPFC light delivery on in vivo single-unit neural activity in awake rats	n = 3	Unilateral: AAV–CaMKIIα–eNpHR3.0–eYFP Ipsilateral: drivable recording optrode	In vivo recording and light delivery in awake, freely moving rats expressing eNpHR3.0 in dorsal mPFC. Record spontaneous neuronal activity in response to the following: 5 s light cycles 2 min light cycles 30 min light cycles
4: Effect of mPFC light delivery on yohimbine-induced Fos induction	n = 8; water (i.p.) n = 9; yohimbine (i.p.)	Unilateral: AAV–CaMKIIα–eYFP Unilateral: AAV–CaMKIIα–eNpHR3.0–eYFP Bilateral: fiber optics 0.5 mm above site of viral injections	In vivo bilateral light delivery in eNpHR3.0 and eYFP hemispheres after the following: Water (i.p.) injections Yohimbine (2 mg/kg, i.p.) injections
5: Effect of mPFC light delivery on ongoing food self-administration	n = 17; eYFP n = 15; eNpHR3.0 n = 10 from each group receive light manipulation	Bilateral: AAV–CaMKIIα–eYFP Or Bilateral: AAV–CaMKIIα–eNpHR3.0–eYFP And Bilateral: fiber optics 0.5 mm above site of viral injections	Food self-administration training, followed by within-subjects food self-administration sessions with and without bilateral light delivery Food self-administration alone Food self-administration plus light delivery
6: Effect of mPFC light delivery on reinstatement of food seeking	n = 14; eYFP (from experiment 5) n = 15; eNpHR3.0 (from experiment 5)	Same as experiment 5	Food self-administration training, extinction training, followed by within-subjects reinstatement testing with and without bilateral light delivery Pellet reinstatement No pellet Pellet Pellet plus light Light alone Yohimbine reinstatement Vehicle Yohimbine Yohimbine plus light Vehicle plus light
7: Phenotypic characterization of mPFC neurons activated by yohimbine during a reinstatement test	n = 8	None	Food self-administration training, extinction training, followed by yohimbine-induced reinstatement testing Rats killed 2 h after yohimbine injection for immunohistochemical double-labeling assays