Ryan K. Bachtell

Dynamic BDNF activity in nucleus accumbens with cocaine use increases self-administration and relapse

A single exposure to cocaine rapidly induces the brief activation of several immediate early genes, but the role of such short-term regulation in the enduring consequences of cocaine use is poorly understood. We found that 4 h of intravenous cocaine self-administration in rats induced a transient increase in brain-derived neurotrophic factor (BDNF) and activation of TrkB-mediated signaling in the nucleus accumbens (NAc). Augmenting this dynamic regulation with five daily NAc BDNF infusions caused enduring increases in cocaine self-administration, and facilitated relapse to cocaine seeking in withdrawal. In contrast, neutralizing endogenous BDNF regulation with intra-NAc infusions of antibody to BDNF subsequently reduced cocaine self-administration and attenuated relapse. Using localized inducible BDNF knockout in mice, we found that BDNF originating from NAc neurons was necessary for maintaining increased cocaine self-administration. These findings suggest that dynamic induction and release of BDNF from NAc neurons during cocaine use promotes the development and persistence of addictive behavior.

Distinct Patterns of ΔFosB Induction in Brain by Drugs of Abuse

The transcription factor ΔFosB accumulates and persists in brain in response to chronic stimulation. This accumulation after chronic exposure to drugs of abuse has been demonstrated previously by Western blot most dramatically in striatal regions, including dorsal striatum (caudate/putamen) and nucleus accumbens. In the present study, we used immunohistochemistry to define with greater anatomical precision the induction of ΔFosB throughout the rodent brain after chronic drug treatment. We also extended previous research involving cocaine, morphine, and nicotine to two additional drugs of abuse, ethanol and Δ9‐tetrahydrocannabinol (Δ9‐THC, the active ingredient in marijuana). We show here that chronic, but not acute, administration of each of four drugs of abuse, cocaine, morphine, ethanol, and Δ9‐THC, robustly induces ΔFosB in nucleus accumbens, although different patterns in the core vs. shell subregions of this nucleus were apparent for the different drugs. The drugs also differed in their degree of ΔFosB induction in dorsal striatum. In addition, all four drugs induced ΔFosB in prefrontal cortex, with the greatest effects observed with cocaine and ethanol, and all of the drugs induced ΔFosB to a small extent in amygdala. Furthermore, all drugs induced ΔFosB in the hippocampus, and, with the exception of ethanol, most of this induction was seen in the dentate. Lower levels of ΔFosB induction were seen in other brain areas in response to a particular drug treatment. These findings provide further evidence that induction of ΔFosB in nucleus accumbens is a common action of virtually all drugs of abuse and that, beyond nucleus accumbens, each drug induces ΔFosB in a region‐specific manner in brain. Synapse 358–369, 2008.

Effects of intranucleus accumbens shell administration of dopamine agonists and antagonists on cocaine-taking and cocaine-seeking behaviors in the rat

RationaleDopamine signaling in the nucleus accumbens (NAc) plays an important role in regulating drug-taking and drug-seeking behaviors, but the role of D1- and D2-like receptors in this regulation remains unclear.ObjectivesOur objective was to study the role of NAc D1- and D2-like receptors in the reinstatement of cocaine-seeking behavior and the regulation of stabilized cocaine intake in rats.MethodsUsing a within-session reinstatement procedure, whereby animals self-administer cocaine (90xa0min) and extinguish responding (150xa0min) in a single session, we assessed the ability of NAc microinfusions of the D1 agonist SKF 81297 and the D2 agonist 7-OH-DPAT to reinstate extinguished cocaine seeking. The effects of the D1 antagonist SCH 23390 and the D2 antagonist eticlopride pretreatment on agonist- and cocaine-primed reinstatement were also measured. Similar agonist and antagonist treatments were tested for their ability to modulate stabilized cocaine and sucrose self-administration.ResultsIntra-NAc infusions of either SKF 81297 (0.3–3.0xa0μg) or 7-OH-DPAT (1.0–10.0xa0μg) dose-dependently reinstated cocaine seeking with greater efficacy in the medial core than in the shell subregion and at doses that also stimulated locomotor behavior. Intra-NAc shell infusions of SCH 23390 (1.0xa0μg) and eticlopride (3.0–10.0xa0μg) blocked cocaine-primed reinstatement (2.0xa0mg/kg, i.v.) and indiscriminately blocked reinstatement induced by either intra-NAc D1 or D2 agonists. Doses of agonists that triggered reinstatement failed to alter stabilized cocaine intake, whereas doses of antagonists that blocked reinstatement increased cocaine intake in the shell.ConclusionsBoth D1 and D2 receptors in the NAc play a prominent, and perhaps cooperative, role in regulating cocaine-taking and cocaine-seeking behaviors.

Alcohol drinking produces brain region-selective changes in expression of inducible transcription factors.

Mapping the effects of alcohol consumption on neural activity could provide valuable information on mechanisms of alcohols effects on behavior. The present study sought to identify effects of alcohol consumption on expression of inducible transcription factors (ITFs) in mouse brain. C57BL/6J mice were trained to consume 10% ethanol/10% sucrose solution during a 30-min limited access period. Control animals were given access to 10% sucrose solution or water. Following the final day of the procedure, animals were sacrificed and immunohistochemical analyses were performed for three ITFs (c-Fos, FosB, and Zif268). Alcohol-consuming animals had increased ITF expression in several brain areas. Specifically, c-Fos was significantly induced in the nucleus accumbens core (AcbC), the medial posteroventral portion of the central nucleus of the amygdala (CeMPV), and the Edinger-Westphal nucleus (EW). Expression of c-Fos was significantly lower in the dentate gyrus of alcohol-consuming animals vs. sucrose-consuming animals. However, it was not significantly different from the water controls. Induction of c-Fos in AcbC, CeMPV and EW was significantly related to blood alcohol concentrations (BAC). Furthermore, FosB expression in the CeMPV and the EW was also significantly higher in the alcohol-consuming animals vs. water controls. FosB expression in the EW was significantly related to BAC. The significance of these results is two-fold. First, our experiments demonstrate that ITF mapping is an effective strategy in identifying alcohol-induced changes following voluntary consumption. Second, they suggest a relationship between ITF expression in AcbC, CeMPV and EW and the level of alcohol intoxication.

Opioid Activation of Toll-Like Receptor 4 Contributes to Drug Reinforcement

Opioid action was thought to exert reinforcing effects solely via the initial agonism of opioid receptors. Here, we present evidence for an additional novel contributor to opioid reward: the innate immune pattern-recognition receptor, toll-like receptor 4 (TLR4), and its MyD88-dependent signaling. Blockade of TLR4/MD2 by administration of the nonopioid, unnatural isomer of naloxone, (+)-naloxone (rats), or two independent genetic knock-outs of MyD88-TLR4-dependent signaling (mice), suppressed opioid-induced conditioned place preference. (+)-Naloxone also reduced opioid (remifentanil) self-administration (rats), another commonly used behavioral measure of drug reward. Moreover, pharmacological blockade of morphine-TLR4/MD2 activity potently reduced morphine-induced elevations of extracellular dopamine in rat nucleus accumbens, a region critical for opioid reinforcement. Importantly, opioid-TLR4 actions are not a unidirectional influence on opioid pharmacodynamics, since TLR4−/− mice had reduced oxycodone-induced p38 and JNK phosphorylation, while displaying potentiated analgesia. Similar to our recent reports of morphine-TLR4/MD2 binding, here we provide a combination of in silico and biophysical data to support (+)-naloxone and remifentanil binding to TLR4/MD2. Collectively, these data indicate that the actions of opioids at classical opioid receptors, together with their newly identified TLR4/MD2 actions, affect the mesolimbic dopamine system that amplifies opioid-induced elevations in extracellular dopamine levels, therefore possibly explaining altered opioid reward behaviors. Thus, the discovery of TLR4/MD2 recognition of opioids as foreign xenobiotic substances adds to the existing hypothesized neuronal reinforcement mechanisms, identifies a new drug target in TLR4/MD2 for the treatment of addictions, and provides further evidence supporting a role for central proinflammatory immune signaling in drug reward.

ΔFosB Induction in Orbitofrontal Cortex Mediates Tolerance to Cocaine-Induced Cognitive Dysfunction

Current cocaine users show little evidence of cognitive impairment and may perform better when using cocaine, yet withdrawal from prolonged cocaine use unmasks dramatic cognitive deficits. It has been suggested that such impairments arise in part through drug-induced dysfunction within the orbitofrontal cortex (OFC), yet the neurobiological mechanisms remain unknown. We observed that chronic cocaine self-administration increased expression of the transcription factor ΔFosB within both medial and orbitofrontal regions of the rat prefrontal cortex. However, the increase in OFC ΔFosB levels was more pronounced after self-administered rather than experimenter-administered cocaine, a pattern that was not observed in other regions. We then used rodent tests of attention and decision making to determine whether ΔFosB within the OFC contributes to drug-induced alterations in cognition. Chronic cocaine treatment produced tolerance to the cognitive impairments caused by acute cocaine. Overexpression of a dominant-negative antagonist of ΔFosB, ΔJunD, in the OFC prevented this behavioral adaptation, whereas locally overexpressing ΔFosB mimicked the effects of chronic cocaine. Gene microarray analyses identified potential molecular mechanisms underlying this behavioral change, including an increase in transcription of metabotropic glutamate receptor subunit 5 and GABAA receptors as well as substance P. Identification of ΔFosB in the OFC as a mediator of tolerance to the effects of cocaine on cognition provides fundamentally new insight into the transcriptional modifications associated with addiction.

Tropomyosin-Related Kinase B in the Mesolimbic Dopamine System: Region-Specific Effects on Cocaine Reward

BACKGROUNDnPrevious studies found that brain-derived neurotrophic factor (BDNF) derived from nucleus accumbens (NAc) neurons can mediate persistent behavioral changes that contribute to cocaine addiction.nnnMETHODSnTo further investigate BDNF signaling in the mesolimbic dopamine system, we analyzed tropomyosin-related kinase B (TrkB) messenger RNA (mRNA) and protein changes in the NAc and ventral tegmental area (VTA) in rats following 3 weeks of cocaine self-administration. To study the role of BDNF-TrkB activity in the VTA and NAc in cocaine reward, we used localized viral-mediated Cre recombinase expression in floxed BDNF and floxed TrkB mice to knockdown BDNF or TrkB in the VTA and NAc in cocaine place conditioning tests and TrkB in the NAc in cocaine self-administration tests.nnnRESULTSnWe found that 3 weeks of active cocaine self-administration significantly increased TrkB protein levels in the NAc shell, while yoked (passive) cocaine exposure produced a similar increase in the VTA. Localized BDNF knockdown in either region reduced cocaine reward in place conditioning, whereas only TrkB knockdown in the NAc reduced cocaine reward. In mice self-administering cocaine, TrkB knockdown in the NAc produced a downward shift in the cocaine self-administration dose-response curve but had no effect on the acquisition of cocaine or sucrose self-administration.nnnCONCLUSIONSnTogether, these data suggest that BDNF synthesized in either VTA or NAc neurons is important for maintaining sensitivity to cocaine reward but only BDNF activation of TrkB receptors in the NAc mediates this effect. In addition, up-regulation of NAc TrkB with chronic cocaine use could promote the transition to more addicted biological states.

Increased Impulsivity during Withdrawal from Cocaine Self-Administration: Role for ΔFosB in the Orbitofrontal Cortex

Increased impulsivity caused by addictive drugs is believed to contribute to the maintenance of addiction and has been linked to hypofunction within the orbitofrontal cortex (OFC). Recent data indicate that cocaine self-administration induces the transcription factor DeltaFosB in the OFC that alters the effects of investigator-administered cocaine on impulsivity. Here, using viral-mediated gene transfer, the effects of overexpressing DeltaFosB within the OFC were assessed on the cognitive sequelae of chronic cocaine self-administration as measured by the 5-choice serial reaction time task (5CSRT). Cognitive testing occurred in the mornings, and self-administration sessions in the evenings, to enable the progressive assessment of repeated volitional drug intake on performance. Animals self-administering cocaine initially made more omissions and premature or impulsive responses on the 5CSRT but quickly developed tolerance to these disruptive effects. However, withdrawal from cocaine dramatically increased premature responding. When access to cocaine was increased, animals overexpressing DeltaFosB failed to regulate their intake as effectively and were more impulsive during withdrawal. In summary, rats develop tolerance to the cognitive disruption caused by cocaine self-administration and show a deficit in impulse control that is unmasked during withdrawal. Our findings suggest that induction of DeltaFosB within the OFC is one mediator of these effects and, thereby, increases vulnerability to addiction.

High alcohol/sucrose consumption during dark circadian phase in C57BL/6J mice: involvement of hippocampus, lateral septum and urocortin-positive cells of the Edinger-Westphal nucleus

AbstractnRationale. Identification of the neuroanatomical substrates regulating alcohol consumption is important for the understanding of alcoholism. Previous studies mapping changes in brain activity used rodent models of alcohol drinking with relatively low alcohol intakes.nObjectives. This study was aimed to identify brain regions changing activity after high voluntary intake of alcohol-containing solutions.nMethods. Adult male C57BL/6J mice were trained to drink a 10% ethanol/10% sucrose solution in daily 30-min limited-access sessions during the dark phase of the circadian cycle. Control groups of animals consumed 10% sucrose or water. Analysis of c-Fos immunohistochemistry (as a marker for neuronal activity) was performed at 90xa0min after the last alcohol drinking session.nResults. The limited access procedure led to high intakes (2.9±0.3xa0g/kg) and blood alcohol concentrations of 251±46xa0mg%. Expression of c-Fos was significantly higher in the alcohol/sucrose group than both the water and sucrose groups in the Edinger-Westphal nucleus, and significantly lower in the alcohol/sucrose group than two control groups in hippocampal subregions, posterior hypothalamus and dorsal lateral septum. Double immunohistochemistry showed that alcohol-induced c-Fos-positive cells in the Edinger-Westphal nucleus co-localized with the neuropeptide urocortin. In addition, intake and/or blood alcohol concentrations correlated with c-Fos expression in specific subregions of the hippocampus, hypothalamus, prefrontal cortex, lateral septum and midbrain.nConclusions. The dark phase voluntary limited-access procedure in mice leads to intakes of alcohol-containing solutions that are considered highly intoxicating. Brain regions showing alcohol-specific changes in c-Fos expression after this procedure can be connected into a novel neurocircuit, including lateral septum, hippocampus, hypothalamus, and the Edinger-Westphal nucleus.

Role of GluR1 expression in nucleus accumbens neurons in cocaine sensitization and cocaine-seeking behavior

Chronic cocaine use reduces glutamate levels in the nucleus accumbens (NAc), and is associated with experience‐dependent changes in (±)‐α‐amino‐3‐hydroxy‐5‐methylisoxazole‐4‐propionic acid (AMPA) glutamate receptor membrane expression in NAc neurons. These changes accompany behavioral sensitization to cocaine and increased susceptibility to cocaine relapse. The functional relationship between neuroplasticity in AMPA receptors and the behavioral manifestation of cocaine addiction remains unclear. Thus, we examined the behavioral effects of up‐ and downregulating basal AMPA receptor function in the NAc core and shell using viral‐mediated gene transfer of wild‐type glutamate receptor 1 (wt‐GluR1) or a dominant‐negative pore‐dead GluR1 (pd‐GluR1), respectively. Transient increases in wt‐GluR1 during or after cocaine treatments diminished the development of cocaine sensitization, while pd‐GluR1 expression exacerbated cocaine sensitization. Parallel changes were found in D2, but not D1, receptor‐mediated behavioral responses. As a correlate of the sensitization experiments, we overexpressed wt‐ or pd‐GluR1 in the NAc core during cocaine self‐administration, and tested the effects on subsequent drug‐seeking behavior 3u2003weeks after overexpression declined. wt‐GluR1 overexpression during self‐administration had no effect on cocaine intake, but subsequently reduced cocaine seeking in extinction and cocaine‐induced reinstatement, whereas pd‐GluR1 facilitated cocaine‐induced reinstatement. When overexpressed during reinstatement tests, wt‐GluR1 directly attenuated cocaine‐ and D2 agonist‐induced reinstatement, while pd‐GluR1 enhanced reinstatement. In both experimental procedures, neither wt‐ nor pd‐GluR1 expression affected cue‐induced reinstatement. Together, these results suggest that degrading basal AMPA receptor function in NAc neurons is sufficient to facilitate relapse via sensitization in D2 receptor responses, whereas elevating basal AMPA receptor function attenuates these behaviors.