Daniele Caprioli

Learning when to initiate or withhold actions is essential for survival, requiring the integration of past experiences with new information to adapt to changing environments. The prelimbic cortex (PL) plays a central role in this process, with a stable PL neuronal population (ensemble) recruited during operant reward learning to encode response execution. However, it is unknown how this established reward-learning ensemble adapts to changing reward contingencies, such as reward omission during extinction. Specifically, does the same ensemble adjust its activity to support behavior suppression, or is a distinct ensemble recruited for this new learning? Our data reveal that operant extinction learning recruits a distinct PL Extinction ensemble to support response inhibition, and concerted engagement of both ensembles encodes both ongoing and subsequent context-specific behavior. Using single-cell calcium imaging, we longitudinally tracked PL neurons in rats as they pressed a lever for food rewards (Training), learned to suppress responding upon reward omission (Extinction), and reinstated responding following a noncontingent “priming” pellet (Reinstatement). We trained decoders on individual rats’ PL activity patterns to predict trial-wise responses and used an in silico deletion approach to identify separate PL Training and Extinction ensembles associated with response execution and inhibition, respectively. Critically, both ensembles were reengaged and maintained their distinct roles during Reinstatement. These findings highlight ensemble-based encoding of multiple, even opposing, learned associations within the same region, demonstrating how selective ensemble recruitment enables behavioral flexibility under changing contingencies.

Background and Purpose: In some individuals, opioid use leads to decreased interest in socially relevant rewards. Recent studies showed that after extended‐access heroin self‐administration, rats strongly prefer social interaction over single unit‐dose heroin infusions. We hypothesized that this strong social preference results from access to a suboptimal heroin dose during testing, and individual differences in heroin versus social choice would emerge if rats were given access to their ‘preferred’ heroin dose. Experimental Approach: In Experiment 1, we trained male rats to lever‐press for social interaction, followed by heroin self‐administration under continuous‐access, no‐timeout schedule, which promotes burst‐patterned heroin taking. We then tested the rats for choice between single‐unit heroin dose and 1‐min full‐contact social interaction, or 5‐min heroin‐access (sufficient for burst‐patterned heroin taking) and 5‐min social interaction. In Experiment 2, we extended the 5‐min access procedure to female rats and tested heroin versus limited‐contact (screen‐based) social interaction. We also manipulated response requirements (effort) for heroin. Key Results: Rats given a single‐unit heroin dose during choice testing, strongly preferred social interaction. In rats given 5‐min heroin‐access, large individual differences in heroin preference emerged. These differences were independent of sex, social‐interaction conditions and effort manipulations. High heroin intake and burst‐patterned heroin taking during self‐administration, and high heroin seeking during abstinence predicted individual differences in heroin preference. Conclusion and Implications: Access to ‘preferred’ heroin doses during the choice tests leads to stable and effort‐independent individual differences in heroin preference. This procedure provides a platform to study mechanisms of resilience and vulnerability to opioid addiction.

Neuromelanin (NM) is a dark pigment accumulating with age in human substantia nigra pars compacta (SNpc) dopamine (DA) neurons, conferring the dark look that inspired nigral area’s name. Despite NM has long been associated with Parkinson’s disease (PD), as melanized neurons favorably degenerate during disease development, NM functions within SNpc DA neurons are still mostly elusive. Here, by exploiting an NM-producing rat model generated by viral vector-induced expression of human Tyrosinase (hTyr), we inspected NM impact on nigral DA neurons’ survival and activity, on mitochondrial functionality of SNpc, and behaviors resembling non-motor and motor PD symptoms. Our data reveal sex dimorphism in NM effects on nigrostriatal dopamine circuit, with sex-biased alterations in neuronal firing activity and underlying intrinsic currents, nigral mitochondrial functions, and non-motor PD symptoms (anxiety). In conclusion, this study discloses unrealized NM effects within nigral DA neurons, advancing our comprehension of sex-specific features shaping sex-biased vulnerability to PD.

Background and Purpose: Heroin and cocaine users tailor their dosage, frequency and administration route to maximise the drugs' effects or prevent withdrawal symptoms. Counterintuitively, preclinical self‐administration and choice experiments employ, almost invariably and regardless of the pharmacokinetic properties of the drug under examination, fixed unit‐doses and timeouts (after unit‐doses) largely resulting in uniform drug‐taking patterns. This uniformity contrasts with the large variability observed in humans, which serves as critical indicator of addiction severity and treatment success. Here, by combining behavioural and pharmacokinetics assessments, we revealed that drug self‐administration procedures without timeouts may overcome this limitation.Experimental Approach: We analysed heroin‐ and cocaine‐taking patterns and seeking and estimated drug‐brain levels in the presence or absence of timeout under different training conditions.Key Results: Removing timeouts had a profound effect on heroin‐taking patterns and seeking, promoting the emergence of burst‐like intake, yielding higher brain peak concentrations of heroin. In contrast, the removal of timeout had marginal impact on cocaine‐taking patterns and seeking.Conclusion and Implications: The removal of timeout during self‐administration revealed distinct cocaine and heroin patterns, with the latter closely resembling human heroin use patterns.

Background and Purpose. Heroin and cocaine users tailor their dosage, frequency, and method of administration, to maximize the drugs’ effects or prevent withdrawal symptoms. Counterintuitively, preclinical self-administration and choice experiments employ fixed unit-doses and timeouts (after doses) largely resulting in uniform drug-taking patterns. The application of these procedures also disregards the distinct pharmacokinetic properties of heroin and cocaine. This uniformity contrasts with the significantly different ways humans tailor their dosage and frequency of heroin and cocaine use. Here, by combining behavioral and pharmacokinetics assessments we revealed that self-administration procedures lacking the timeout may overcomes this limitation. Experimental Approach. We analyzed heroin and cocaine taking- and seeking-patterns and estimated drug-brain levels in the presence or absence of timeout. We further assessed how absence of timeout and the availability of drug or social peer (access time to the two rewards) affect drug preference in choice procedures. Key Results. Removing the timeout had a profound effect on heroin-taking patterns and seeking, promoting the emergence of burst-like intake, yielding higher brain peak concentrations of heroin. Timeout removal had marginal impact on cocaine taking patterns and seeking. Increasing the access time to the drug in the discrete choice procedure resulted in higher drug intake and increased preference for heroin, but it did not alter cocaine preference. Conclusion and Implications. Removing timeout during self-administration revealed distinct heroin and cocaine taking patterns. Self-administration without timeout and access to high heroin doses during choice more closely mimic human heroin taking patterns and related behaviors, including maladaptive choices.