Paradoxical accentuation of motivation following accumbens-pallidum disconnection

Abstract

The nucleus accumbens (NAc) and ventral pallidum (VP) are reciprocally connected, and activity within this circuit is thought to promote reward learning. Inconsistent with this notion, we find that disconnecting NAc medial shell and VP greatly enhances the attribution of value to a cue that is paired with reward. This result suggests that medial NAc shell and VP are both needed for attributing value to cues yet can also oppose one-another's functional contribution.

Keywords: Nucleus accumbens; Sign-tracking; Ventral pallidum.

Figure 1

Figure 1(a–b) AAV8-hSyn-hM4Di-mCitrine cell expression in all rats of Group Contra (a; n = 14) and Group Ipsi (b; n =12). Darker areas indicate common areas of overlap in terms of expression between rats. (c) Disconnection of NAc shell and VP dramatically enhanced the acquisition of sign-tracking. (d) Group Contra rats reached peak levels of sign-tracking 40% (4 days) faster compared to Group Ipsi rats. (e) Group Contra rats spent less time in the food cup overall compared to Group Ipsi rats. (f–g) Representative brain slice showing the area of AAV8-hSyn-hM4Di-mCitrine cell expression in the NAc shell (f) and VP (g).

Figure 2

Figure 2(a) AAV8-hSyn-hM4Di-mCitrine cell expression in all Group NAc-Gi rats (n = 7). Darker areas indicate common areas of overlap in terms of expression between rats. (b) Bilateral NAc shell inhibition had no effect on sign-tracking. (c) Bilateral NAc shell inhibition lowered food cup behavior non-discriminately.

Figure 3

Figure 3(a) Map of tetrode placements contralateral to hM4D(Gi) infusions, and recording timeline. (b–c) Populations of units that were excited, inhibited, or unaffected by CNO from recordings in the VP (t₆=2.5, p = 0.047 population size comparison) and NAc (t₆=0, p = 1). Number of units is shown below percentages (n = 3 rats; n = 26 NAc units, n = 20 VP units). (d–g) Real-time histograms (1-min bins; time zero = CNO) showing single units that were excited or inhibited in the VP and NAc. (h–k) Normalized firing rates (baseline-subtracted z-score) of pooled units with inhibition or excitation in NAc and VP.