Biology subjects

Beutler, M. M.

Publications and source records attributed to Beutler, M. M..

5 recordsLinked to original sources

bioRxiv2026

Negative affective states are not detected in rats following an intravenous self-administration regimen leading to incubation of oxycodone craving

In rats, cue-induced opioid craving intensifies (incubates) during abstinence from opioid self-administration and then remains high for a prolonged period. The prolonged plateau models persistent vulnerability to cue-induced craving and relapse in humans recovering from opioid use disorder. However, a very significant contributor to relapse vulnerability in these individuals is the presence of negative affective states that can persist for months to years, far beyond physical dependence. The goal of this study was to determine if the incubation of craving model recapitulates this aspect of relapse vulnerability. We began by comparing rats trained to self-administer oxycodone using a regimen leading to persistent elevation of cue-induced craving (6 h/d x 10 d) and rats trained to self-administer saline. We assessed somatic withdrawal signs in early abstinence and conducted behavioral tests modeling negative affect (open field, social preference, sucrose preference, and elevated plus maze) in late abstinence. Some somatic withdrawal signs were greater in oxycodone rats on abstinence day (AD)1, but cumulative scores did not differ between groups on AD1-3. On AD41-46, no group differences were found in behavioral tests modeling negative affect. To compare early and late abstinenceperiods, a second cohort of rats self-administered saline and oxycodoneand then received two cue-induced seeking tests (AD1 and AD40; oxycodone rats exhibited incubation of craving) and two series of negative affect tests (AD2-7 and AD41-48). While some time-dependent changes in affect were observed within each group, they were suggestive of reduced anxiety-like behavior in oxycodone rats. Finally, because rats are single-housed during our incubation studies, we compared drug-naive rats after 8-9 weeks of single vs pair housing and found no difference in behavioral tests modeling negative affect. We conclude that the persistence of elevated cue-induced craving observed after a standard opioid incubation regimen is not accompanied by negative affective states, probably due to lower drug intake during the intravenous regimen compared to non-contingent escalating dose regimens typically used to study withdrawal signs. This does not negate the utility of the incubation model for studying cue-induced opioid craving and its neurobiological basis.

neuroscience↗

bioRxiv2025

Incubation of oxycodone craving is associated with CP-AMPAR upregulation in D1 and D2 receptor-expressing medium spiny neurons in nucleus accumbens core and shell

A major problem in treating opioid use disorder is persistence of craving after protracted abstinence. This has been modeled in rodents using the incubation of craving model, in which cue-induced drug seeking increases over the first weeks of abstinence from drug self-administration and then remains high for an extended period. Incubation has been reported for several opioids, including oxycodone, but little is known about underlying synaptic plasticity. In contrast, it is well established that incubation of cocaine and methamphetamine craving depends on strengthening of glutamate synapses in the nucleus accumbens (NAc) through incorporation of calcium-permeable AMPARs (CP-AMPARs). CP-AMPARs have higher conductance than the calcium-impermeable AMPARs that mediate NAc excitatory transmission in drug-naive animals, as well as other distinct properties. Here we examined AMPAR transmission in medium spiny neurons (MSN) of NAc core and shell subregions in rats during forced abstinence from extended-access oxycodone self-administration. In early abstinence (prior to incubation), CP-AMPAR levels were low. After 17-33 days of abstinence (when incubation is stably plateaued), CP-AMPAR levels were significantly elevated in both subregions. These results explain the prior demonstration that infusion of a selective CP-AMPAR antagonist into NAc core or shell subregions prevents expression of oxycodone incubation. Then, using transgenic rats, we found CP-AMPAR upregulation on both D1 and D2 receptor-expressing MSN, which contrasts with selective upregulation on D1 MSN after cocaine and methamphetamine incubation. Overall, our results demonstrate a common role for CP-AMPAR upregulation in psychostimulant and oxycodone incubation, albeit with differences in MSN subtype-specificity.

neuroscience↗

bioRxiv2025

Dopamine and calcium dynamics in the nucleus accumbens core during food seeking

Extinction-reinstatement paradigms have been used to study reward seeking for both food and drug rewards. The nucleus accumbens is of particular interest in reinstatement due to its ability to energize motivated behavior. Indeed, previous work has demonstrated that suppression of neuronal activity or dopaminergic signaling in the nucleus accumbens reduces reinstatement to food seeking. In this study, we sought to further establish a connection between glutamatergic input, measured by proxy via a genetically encoded calcium indicator, and dopamine (DA) tone, measured simultaneously with a red-shifted DA biosensor. We performed this sensor multiplexing in the nucleus accumbens core in the classic extinction-reinstatement paradigm with food reward. We detected DA transients that changed in magnitude and/or temporally shifted over the course of self-administration training. In our calcium traces we observed a decrease from baseline time-locked to the lever press for food reward, which became more prominent with training. Both patterns were reduced in the first session of extinction with no deflections from baseline detected in either the DA or calcium traces in the last extinction session. When we recorded during reinstatement tests, bootstrapping analysis detected a calcium response when reinstatement was primed by cue or pellet+cue presentation, while a DA response was detected for pellet+cue reinstatement. These data further establish a role for nucleus accumbens core activity and DA in reinstatement of food seeking and represent the first attempt to simultaneously record the two during an extinction-reinstatement task.

neuroscience↗

bioRxiv2024

Changes in nucleus accumbens core translatome accompanying incubation of cocaine craving

In the incubation of cocaine craving model of relapse, rats exhibit progressive intensification (incubation) of cue-induced craving over several weeks of forced abstinence from cocaine self-administration. The expression of incubated craving depends on plasticity of excitatory synaptic transmission in nucleus accumbens core (NAcC) medium spiny neurons (MSN). Previously, we found that the maintenance of this plasticity and the expression of incubation depends on ongoing protein translation, and the regulation of translation is altered after incubation of cocaine craving. Here we used male and female rats that express Cre recombinase in either dopamine D1 receptor- or adenosine 2a (A2a) receptor-expressing MSN to express a GFP-tagged ribosomal protein in a cell-type specific manner, enabling us to use Translating Ribosome Affinity Purification (TRAP) to isolate actively translating mRNAs from both MSN subtypes for analysis by RNA-seq. We compared rats that self-administered saline or cocaine. Saline rats were assessed on abstinence day (AD) 1, while cocaine rats were assessed on AD1 or AD40-50. For both D1-MSN and A2a-MSN, there were few differentially translated genes between saline and cocaine AD1 groups. In contrast, pronounced differences in the translatome were observed between cocaine rats on AD1 and AD40-50, and this was far more robust in D1-MSN. Notably, all comparisons revealed sex differences in translating mRNAs. Sequencing results were validated by qRT-PCR for several genes of interest. This study, the first to combine TRAP-seq, transgenic rats, and a cocaine self-administration paradigm, identifies translating mRNAs linked to incubation of cocaine craving in D1-MSN and A2a-MSN of the NAcC.

neuroscience↗

bioRxiv2024

Dopamine transmission at D1 and D2 receptors in the nucleus accumbens contributes to the expression of incubation of cocaine craving

Relapse represents a consistent clinical problem for individuals with substance use disorder. In the incubation of craving model of persistent craving and relapse, cue-induced drug seeking progressively intensifies or incubates during the first weeks of abstinence from drug self-administration and then remains high for months. Previously, we and others have demonstrated that expression of incubated cocaine craving requires strengthening of excitatory synaptic transmission in the nucleus accumbens core (NAcc). However, despite the importance of dopaminergic signaling in the NAcc for motivated behavior, little is known about the role that dopamine (DA) plays in the incubation of cocaine craving. Here we used fiber photometry to measure DA transients in the NAcc of male and female rats during cue-induced seeking tests conducted in early abstinence from cocaine self-administration, prior to incubation, and late abstinence, after incubation of craving has plateaued. We observed DA transients time-locked to cue-induced responding but their magnitude did not differ significantly when measured during early versus late abstinence seeking tests. Next, we tested for a functional role of these DA transients by injecting DA receptor antagonists into the NAcc just before the cue-induced seeking test. Blockade of either D1 or D2 DA receptors reduced cue-induced cocaine seeking after but not before incubation. We found no main effect of sex in our experiments. These results suggest that DA contributes to incubated cocaine seeking but the emergence of this role reflects changes in postsynaptic responsiveness to DA rather than presynaptic alterations.

neuroscience↗