Optogenetic Inhibition of Ventral Pallidum Neurons Impairs Context-Driven Salt Seeking

Abstract

. However, it is not known whether the VP is necessary for salt appetite in terms of seeking out salt or consuming salt following sodium depletion. Here, we used a conditioned place-preference procedure to investigate the effects of optogenetically inhibiting the VP on context-driven salt seeking and the consumption of salt following deprivation. Male rats learned to associate one context with sucrose and another context with lessdesirable salt. Following sodium depletion, and in the absence of either sucrose or salt, we found that inhibiting the VP selectively reduced the elevation in time spent in the salt-paired context. VP inhibition had minimal effects on the consumption of salt once it was made available. To our knowledge, this is the first evidence that the VP or any brain region is necessary for the ability to use contextual cues to guide salt seeking. These results highlight a dissociation between deficit-driven reward seeking and reward consumption to replenish those deficits, with the former process being particularly sensitive to on-line VP activity.

Context-driven Salt Seeking Test (Rats)

“…Neural manipulations during either the depletion and consumption tests may reveal dissociations between context-driven salt seeking and salt consumption following sodium depletion. One salient example is our prior study (Chang et al , 2017), in which we observed a specific deficit in context-driven salt seeking but not salt consumption following sodium depletion with optogenetic inhibition of the VP.…”

“…Figure 3 presents what one would expect to observe for a control group of rats in our salt appetite procedure (n = 19 male rats; group means ± SEM; adapted from Chang et al ., 2017). Rats should drink more sucrose than salt over the course of training (Figure 3A).…”

“…C. Rats should show an elevation in the consumption of salt and a decrease in the consumption of sucrose compared to the last training day with each solution following sodium depletion. Figures adapted from Chang et al ., 2017.…”

“…In other words, it is mostly unclear how the brain enables animals to seek out salt in a novel deprivation state. In a recent study, we showed that the ventral pallidum (VP) plays an important role in this phenomenon (Chang et al , 2017). The VP has previously been shown to track the changes in value of salt-paired cues before and after sodium depletion (Tindell et al ., 2009; Robinson and Berridge, 2013).…”

“…However, it was previously unknown whether the VP is necessary for mediating salt appetite in terms of cue-driven salt seeking or salt consumption. Using a novel CPP procedure, described here, we showed that optogenetic inhibition of the VP impairs context-driven salt seeking but not the consumption of salt itself following sodium depletion (Chang et al ., 2017). …”