Orexin-1 receptor signaling in ventral pallidum mediates demand for the opioid remifentanil
Signaling at the orexin-1 receptor (Ox1R) is important for motivation for various drugs of abuse. Recently, our laboratory showed that systemic blockade of Ox1Rs decreased motivation for the potent and short-acting opioid remifentanil (Porter-Stransky et al, 2017). However, the central sites through which orexin acts to mediate motivation for opioids are not known. Here, we investigated ventral pallidum (VP) as a potential site of orexin action, as VP is a known mediator of opioid reward and is densely innervated by orexin-immunoreactive fibers. We used a within-session behavioral economics (BE) paradigm in which remifentanil price (responses/{micro}g iv remifentanil) was sequentially increased throughout the session. Rats were implanted with bilateral cannulae into VP, through which microinjections of SB334867 (SB), and orexin 1 receptor (Ox1R) antagonist, were given prior to BE testing. Rats were then extinguished and subjected to cue-induced reinstatement following intra-VP SB microinjection. We found that inhibition of Ox1R signaling in VP reduced both motivation (increased demand elasticity) for remifentanil and cued reinstatement of extinguished remifentanil-seeking without affecting baseline consumption or general locomotor activity. These effects were specific to the VP, as control injections of SB immediately dorsal to VP did not affect remifentanil-seeking. Together, these findings indicate a selective role of Ox1R signaling in VP in motivation and relapse for the opioid remifentanil.