RZ10X Lux-I/O Processor

The ventral pallidum (VP) is necessary for reward processing and a key node in dopamine (DA) pathways. Yet the direct DA inputs have not been studied during reward learning. Here, we elucidate the role of VP DA in reward processing using circuit tracing, fibre photometry, and behavioural pharmacology in male rats. We show that VP receives both non-DA and DA inputs from the midbrain. During an instrumental reward conditioning paradigm, we characterized VP DA activity using a DA sensor (GRAB_DA1h) across learning, extinction, re-acquisition, and motivational test. Followed by pharmacological manipulation using the DA-antagonist (fluphenazine) in VP to demonstrate a causal role in reward learning and motivation. Together our findings advance the functional contributions of non-canonical mesolimbic DA pathways.

Background Animals strongly defend protein intake, but how protein status shapes moment-to-moment reward signalling in mesolimbic circuits remains unclear, particularly when the effort required to obtain food varies. Objective We tested whether dietary protein restriction altered nucleus accumbens (NAc) core dopamine signalling when mice worked for food of differing nutritional value in the home cage. Methods Under surgical anaesthesia, male C57BL/6 mice (n=12; ∼12 weeks old at diet initiation) were injected in the NAc core with a virus expressing the fluorescent dopamine sensor GRABDA and implanted with fibre-optic cannulas. In food-access tasks, nose pokes delivered either chow (protein-containing) or sucrose pellets. Across sessions, pellets required either one nose poke (FixedRatio1) or an increasing number (ProgRatio). Fibre photometry measured dopamine release for both pellet types and schedules during three dietary phases: non-restricted diet (NR1; 18% protein), protein-restricted diet (PR; 4%), and restored non-restricted diet (NR2), with 1 week of adaptation between phases. Behavioural and photometry data were analysed using repeated-measures ANOVA. Results Home-cage food intake remained stable, but bodyweight gain fell markedly during PR and partially recovered in NR2 (+10.1% NR1 vs. +1.2% PR vs. +6.0% NR2, p .05). During ProgRatio, dopamine responses at pellet delivery and retrieval did not differ between pellet types in any phase (all ps>.05). Conclusions Protein restriction did not globally amplify reward-related behaviour or dopamine signalling. Instead, it selectively biased NAc dopamine according to the animal's nutritional status, nutrient context, and task demands.

A history of use remains a key risk factor for opioid-related overdose deaths in the ongoing opioid epidemic. The locus coeruleus (LC) is the principal source of noradrenergic tone and a site for opioid neuromodulation and tolerance. How a history of opioid use affects LC activity and shapes opioid-induced respiratory depression (OIRD) remains poorly understood. Using plethysmography and fiber photometry, we assessed how fentanyl affects LC activity and OIRD before and after five days of repeat opioid use (ROU). Fentanyl increased the frequency of LC bursts independent of exposure history and was coupled to transient elevations in breathing. LC coupled ventilation (LC-Ve) persisted through ROU. After ROU, OIRD magnitude diverged across mice. Mice developing an adaptive ventilatory response (AVR) showed a smaller OIRD that coincided with improved ventilation outside LC bursts and reduced LC-Ve gain. Mice with the non-adaptive response (NVR) show no improvement in OIRD or ventilation outside LC bursts, resulting in an unchanged reliance on LC-Ve. While LC-Ve reflexively counters OIRD acutely, it may also drive oscillations to destabilize blood gas homeostasis, perpetuating pathophysiology with repeat use. Thus, LC-coupled breathing appears to be a physiological signature of divergent respiratory responses with a history of fentanyl exposure. Impact statement Noradrenergic neurons of the locus coeruleus are activated by fentanyl and coincide with brief surges in breathing during opioid-induced respiratory depression. Reliance on these surges distinguishes mice that fail to develop ventilatory tolerance.