This study characterizes the PVT neuropeptide, PACAP, and its understudied protein isoform, PACAP-27, and demonstrates that it is involved in pharmacologically relevant EtOH drinking. This indicates that PACAP-27 should be further investigated for its possible role in EtOH drinking.

Methylphenidate (MPH) is used clinically to treat attention-deficit/hyperactivity disorder (ADHD) and off-label as a performance-enhancing agent in healthy individuals. MPH enhances catecholamine transmission via blockade of norepinephrine (NE) and dopamine (DA) reuptake transporters. However, it is not clear how this action affects neural circuits performing cognitive and sensorimotor functions driving performance enhancement. The dorsal lateral geniculate nucleus (dLGN) is the primary thalamic relay for visual information from the retina to the cortex and is densely innervated by NE-containing fibers from the locus coeruleus (LC), a pathway known to modulate state-dependent sensory processing. Here, MPH was evaluated for its potential to alter stimulus-driven sensory responses and behavioral outcomes during performance of a visual signal detection task. MPH enhanced activity within individual neurons, ensembles of neurons, and visually-evoked potentials (VEPs) in response to task light cues, while increasing coherence within theta and beta oscillatory frequency bands. MPH also improved reaction times to make correct responses, indicating more efficient behavioral performance. Improvements in reaction speed were highly correlated with faster VEP latencies. Finally, immunostaining revealed that catecholamine innervation of the dLGN is solely noradrenergic. This work suggests that MPH, acting via noradrenergic mechanisms, can substantially affect early-stage sensory signal processing and subsequent behavioral outcomes.

Neural circuit engagement within the nucleus accumbens (NAc) shell is implicated in the regulation of both negative and positive affect. Classically, the dynorphin/kappa opioid receptor (KOR) system in the NAc was believed to promote dysphoric behavior, while dopamine was viewed as interacting with reward behavior, and KOR activation was known to inhibit dopamine release. Recently, however, both the KOR and dopamine systems have, separately, been shown to have differential effects across the rostro-caudal axis of the NAc shell on hedonic responses. Whether or not this is due to interactions between KORs and dopamine, and if it extends to other affective behaviors, remains to be determined. In this study, we examined in rats the relationship between the KOR and dopamine systems in both the rostral and caudal NAc shell using ex vivo fast scan cyclic voltammetry and the impact of KOR activation on affective behavior using approach-avoidance assays. We report here that activation of KORs in the caudal NAc shell significantly inhibits dopamine release, stimulates novelty-induced rearing behavior, increases avoidance behavior, and reduces locomotor activity. In contrast, activation of KORs in the rostral NAc shell inhibits dopamine release to a lesser extent and instead increases approach behavior. Taken together, these results indicate that there is heterogeneity across the rostro-caudal axis of the NAc shell in the effects of KOR stimulation on affective behaviors, and they suggest that this might be due to differences in KOR control over dopamine release.

No abstract

While limited research has implicated the neuropeptide, pituitary adenylate cyclase‐activating polypeptide (PACAP), in problematic alcohol use, the brain regions and isoforms involved in this effect remain to be determined. One region that has been found both to exhibit PACAP binding and, separately, to be involved in ethanol drinking is the nucleus accumbens (NAc). Thus, this study sought to characterize the effect of the PACAP isoforms in the NAc on ethanol drinking under the intermittent‐access two‐bottle‐choice paradigm, in male and female Long–Evans rats. With microinjection into the medial NAc shell, PACAP‐27 but not PACAP‐38 was found to dose‐dependently reduce binge‐like ethanol drinking. In contrast, the PACAP receptor antagonist, PACAP (6‐27), but not PACAP (6‐38), enhanced ethanol drinking. This effect of PACAP was substance specific, as neither isoform in the NAc shell affected binge‐like sucrose drinking. It was also anatomically specific, as PACAP‐38 rather than PACAP‐27 suppressed ethanol drinking when injected into the NAc core, and PACAP‐27 instead enhanced drinking when injected into the caudal third of the medial NAc shell. Finally, while PACAP‐38 in the NAc shell affected stress‐related exploratory behavior, reducing time spent in the light chamber of a light–dark box, PACAP‐27 did not significantly affect behavior in a light–dark box or open field. Together, these results, showing that PACAP‐27 in the NAc shell attenuates binge‐like ethanol drinking without affecting select stress‐related behaviors, suggest that compounds related to this PACAP isoform should be investigated as potential novel therapeutics for the treatment of alcohol use disorder.