Biology subjects

Holleran, K. M.

Publications and source records attributed to Holleran, K. M..

7 recordsLinked to original sources

bioRxiv2026

Kappa opioid receptors regulate cocaine effects on nucleus accumbens dopamine through phosphorylation of dopamine transporter at the threonine 53 site

Chronic cocaine exposure leads to tolerance of the dopamine transporter (DAT) to cocaine and heightened kappa opioid receptor (KOR)-induced inhibition of dopamine (DA) release in the nucleus accumbens (NAc). KORs on presynaptic DA terminals inhibit DA release and modulate DAT function, but whether KOR signaling causes DAT tolerance is unknown. We demonstrate that rats self-administering cocaine escalate their intake, and the KOR antagonist norbinaltorphimine (nBNI) blunts this escalation. We employed fast-scan cyclic voltammetry (FSCV) in acute brain slices containing the NAc core from these rats and found that the cocaine exposure paradigm resulted in tolerance of the DAT to cocaine, an effect absent in animals pre-treated with nBNI. In drug-naive mice, either superfusion of the KOR agonist U50,488 or a single in vivo injection of U69,593 inhibited DA release and reduced cocaine-induced inhibition of DA reuptake, reproducing the tolerance phenotype without any drug history. We replicated this finding in the NAc of rats, and with the uptake inhibitor nomifensine in rhesus macaques, indicating conservation across rodents and non-human primates. As KOR activation results in phosphorylation of the threonine-53 site on the DAT, we tested whether this is required for the KOR-mediated DAT tolerance to cocaine. We show that a mouse line with a phosphorylation-insensitive alanine-53 mutation of the DAT has enhanced DA release and uptake. Remarkably, KOR agonism no longer mediated DAT tolerance to cocaine in these mice, demonstrating the dependence of this effect on the threonine-53 site and highlighting a KOR-driven mechanism underlying cocaine tolerance at the DAT.

neuroscience↗

bioRxiv2025

Kappa opioid receptors delay sucrose self-administration by modulating dopamine ramps before operant responding

Chronic consumption of drugs of abuse increases sensitivity of the dynorphin/kappa opioid receptor (KOR) stress system, which reduces striatal dopamine signaling and promotes drug taking. However, there is mixed evidence on how KOR-modulation of dopamine affects operant behavior in the absence of addiction. To address this gap, we injected dLight1.2 in the nucleus accumbens of male and female C57BL/6J mice and trained them to self-administer sucrose. Mice were injected with the KOR agonist U50,488H, with or without the KOR antagonist aticaprant, prior to each session. U50,488H did not affect dopamine responses during the lever press and did not alter total presses or consumption. The primary effects of KOR activation were to delay initiation of lever pressing, and to diminish the rapid ramp-up in dopamine seen before lever presses. The first lever press of each session was preceded by the largest dopamine ramp; however, ramp size did not correlate with latency under any condition. We further tested whether KOR-modulation of dopamine ramps affects behavior throughout the session. We found that the total amount of dopamine activity 10 seconds before the lever press predicted when the next lever press would occur, specifically after U50,488H injection. When the phasic peaks were subtracted from this to quantify a slower dopamine ramp, time to the next lever press could be predicted and this effect was strongest after U50,488H injection. As U50,488H reduces basal dopamine signaling, we propose that dopamine ramps prior to behavior have a larger signal-to-noise ratio during KOR activation. This relatively greater increase in dopamine from baseline could increase the salience of the decision to perform reward-associated actions, which may play a role in habitual behaviors like drug taking.

neuroscience↗

bioRxiv2025

Fiber photometry analysis for spontaneous dopamine signals: The z-scored data are not the data

Fluorescent sensors have revolutionized the measurement of molecules in the brain, and the dLight dopamine sensor has been used extensively to examine reward- and cue-evoked dopamine release, but only recently has the field turned its attention to spontaneous release events. Analysis of spontaneous events typically requires evaluation of hundreds of events over minutes to hours, and the most common method of analysis, z-scoring, was not designed for this purpose. Here, we compare the accuracy and reliability of three different analysis methods to identify pharmacologically induced changes in dopamine release and uptake in freely moving C57BL/6J mice. The D1-like receptor antagonist SCH23390 was used to prevent dLight sensors from interacting with dopamine in the extracellular space, while cocaine was used to inhibit uptake and raclopride to increase release of dopamine in the nucleus accumbens. We examined peak-to-peak frequency, peak amplitude, and width, the time spent above an established cutoff. The three methods were 1) the widely-used "Z-Score Method", which automatically smooths baseline drift and normalizes recordings using signal-to-noise ratios, 2) a "Manual Method", in which local baselines were adjusted manually and individual cutoffs were determined for each subject, and 3) the "Prominence Method" that combines z-scoring with prominence assessment to tag individual peaks, then returns to the preprocessed data for kinetic analysis. First, SCH23390 drastically reduced the number of signals detected as expected, but only when the Manual Method was used. Z-scoring failed to identify any changes, due to its amplification of noise when signals were diminished. Cocaine increased signal width as expected using the Manual and Prominence Methods, but not the Z-Score Method. Finally, raclopride- induced increases in amplitude were correctly identified by the Manual and Prominence Methods. The Z-Score Method failed to identify any of the changes in dopamine release and uptake kinetics. Thus, analysis of spontaneous dopamine signals requires assessment of the %{Delta}F/F values, ideally using the Manual Method, and the use of z- scoring is not appropriate. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=137 SRC="FIGDIR/small/639080v1_ufig1.gif" ALT="Figure 1"> View larger version (21K): org.highwire.dtl.DTLVardef@1687207org.highwire.dtl.DTLVardef@165fa1org.highwire.dtl.DTLVardef@e06800org.highwire.dtl.DTLVardef@cbf31e_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2024

Synaptogyrin-3 Prevents Cocaine Addiction and Dopamine Deficits

Synaptogyrin-3, a functionally obscure synaptic vesicle protein, interacts with vesicular monoamine and dopamine transporters, bringing together dopamine release and reuptake sites. Synaptogyrin-3 was reduced by chronic cocaine exposure in both humans and rats, and synaptogyrin-3 levels inversely correlated with motivation to take cocaine in rats. Synaptogyrin-3 overexpression in dopamine neurons reduced cocaine self-administration, decreased anxiety-like behavior, and enhanced cognitive flexibility. Overexpression also enhanced nucleus accumbens dopamine signaling and prevented cocaine-induced deficits, suggesting a putative therapeutic role for synaptogyrin-3 in cocaine use disorder.

neuroscience↗

bioRxiv2024

Synchrony between midbrain gene transcription and dopamine terminal regulation is modulated by chronic alcohol drinking

Alcohol use disorder is marked by disrupted behavioral and emotional states which persist into abstinence. The enduring synaptic alterations that remain despite the absence of alcohol are of interest for interventions to prevent relapse. Here, 28 male rhesus macaques underwent over 20 months of alcohol drinking interspersed with three 30-day forced abstinence periods. After the last abstinence period, we paired direct sub-second dopamine monitoring via ex vivo voltammetry in nucleus accumbens slices with RNA-sequencing of the ventral tegmental area. We found persistent augmentation of dopamine transporter function, kappa opioid receptor sensitivity, and dynorphin release - all inhibitory regulators which act to decrease extracellular dopamine. Surprisingly, though transcript expression was not altered, the relationship between gene expression and functional readouts of these encoded proteins was highly dynamic and altered by drinking history. These results outline the long-lasting synaptic impact of alcohol use and suggest that assessment of transcript-function relationships is critical for the rational design of precision therapeutics.

neuroscience↗

bioRxiv2024

Kappa Opioid Receptors Negatively Regulate Real Time Spontaneous Dopamine Signals by Reducing Release and Increasing Uptake

AbstractThe role of the dynorphin/kappa opioid receptor (KOR) system in dopamine (DA) regulation has been extensively investigated. KOR activation reduces extracellular DA concentrations and increases DA transporter (DAT) activity and trafficking to the membrane. To explore KOR influences on real-time DA fluctuations, we used the photosensor dLight1.2 with fiber photometry in the nucleus accumbens (NAc) core of freely moving male and female C57BL/6 mice. First, we established that the rise and fall of spontaneous DA signals were due to DA release and reuptake, respectively. Then mice were systemically administered the KOR agonist U50,488H (U50), with or without pretreatment with the KOR antagonist aticaprant (ATIC). U50 reduced both the amplitude and width of spontaneous signals in males, but only reduced width in females. Further, the slope of the correlation between amplitude and width was increased in both sexes, suggesting that DA uptake rates were increased. U50 also reduced the frequency of signals in both males and females. All effects of KOR activation were stronger in males. Overall, KORs exerted significant inhibitory control over spontaneous DA signaling, acting through at least three mechanisms - inhibiting DA release, promoting DAT-mediated uptake, and reducing the frequency of signals.

neuroscience↗

bioRxiv2022

Nicotine Modifies Responding for Cocaine in a Concurrent Rodent Self-administration Model

Prevailing preclinical models of cocaine use have not resulted in an FDA-approved treatment for cocaine use disorder, potentially due to a focus on cocaine use in isolation, which may not translate well to polysubstance use in clinical populations. Clinically, nicotine has been shown to increase cocaines potency and reinforcing efficacy, but some preclinical studies suggest that non-contingent nicotine exposure is not sufficient to alter cocaine self-administration in rats; therefore, this experiment examined if the addition of nicotine to the cocaine solution would alter self-administration behavior. Male Sprague Dawley rats (N=7) were trained to self-administer cocaine (0.75mg/kg/inf), and tested on a long access, fixed ratio 1 schedule of reinforcement (6 hour sessions, unlimited inf, 5 days), for cocaine alone (0.75mg/kg/inf), followed by cocaine and nicotine (0.75mg/kg/inf cocaine+0.03mg/kg/inf nicotine). Finally, rats responded on a progressive ratio schedule for varied doses of cocaine with and without concurrent nicotine at a consistent dose (1.5, 0.75, 0.375, 0.19mg/kg/inf cocaine{+/-} 0.03mg/kg/inf nicotine). Unexpectedly, under long access conditions, rats self-administering cocaine and nicotine responded less than for cocaine alone, and did not escalate responding. However, under progressive ratio conditions, responding for cocaine and nicotine was greater than responding for cocaine alone across low and moderate cocaine doses, and decreased at high cocaine doses, indicating a leftward shift in the dose response curve. Together, these data highlight the importance of evaluating multiple outcome measures in nicotine + cocaine paradigms, and suggest that concurrent self-administration of cocaine and nicotine results in greater motivated responding than for cocaine alone.

neuroscience↗