Figure 5. Temporary inactivation of the rEPN reduces LHb basal firings and preferentially diminishes LHb responses to negative motivational stimuli.

(A) Representative photomicrograph of recording electrode track in the LHb. Scalebar: 100 µm. (B) Representative photo of muscimol spread over 30 min and cannula placements in the EPN. (C) rEPN inactivation decreased basal firing, number of bursts per minute, and percentage of spikes in bursts in LHb neurons. (D–F) Responses of late- but not early-responsive LHb neurons to shock cues were eliminated by rEPN inactivation. (G–I) Responses of late- but not early-responsive LHb neurons to reward cues were eliminated by rEPN inactivation. (J, K) rEPN inactivation greatly diminished both excitotory and inhibitory LHb responses to footshocks. Black bars under time course indicate analysis windows for adjacent panels. (L) After rEPN inactivation, the population average of LHb responses only showed weak responses to cues that did not discriminate between different cue types (compared with robust responses in Figure 4F). Adjacent panel on right shows loss of monotonic responses to shock cue vs neutral cue vs reward cue (black symbols), relative to pre-infusion responses (grey symbols, adapted from Figure 4F).