Prior extended daily access to cocaine elevates the reward threshold in a conditioned place preference test

Activation of 5-HT1B receptors in the Lateral Habenula attenuates the anxiogenic effects of cocaine

Recent work has implicated the Lateral Habenula (LHb) in the production of anxiogenic and aversive states. It is innervated by all the major monoamine neurotransmitter systems and has projections that have been shown to modulate the activity of both dopaminergic and serotonergic brain regions. Cocaine is a stimulant drug of abuse that potentiates neurotransmission in these monoamine systems and recent research suggests that the drug's behavioral effects may be related in part to its actions within the LHb. The present research was therefore devised to test the hypothesis that alterations in serotonin (5-HT) function within the LHb can affect the behavioral response to cocaine. Male rats were fitted with intracranial guide cannula and trained to traverse a straight alleyway once a day for a 1 mg/kg i.v. injection of cocaine. Intra-LHb pretreatment with the 5-HT1B agonist CP 94,253 (0, 0.1, or 0.25 μg/side) attenuated the development of approach/avoidance "retreat" behaviors known to be a consequence of cocaine's dual rewarding (approach) and anxiogenic (avoidance) properties. This effect was reversed by co-administration of a selective 5-HT1B antagonist, NAS-181 (0.1 μg/side), demonstrating drug specificity at the 5-HT1B receptor. These data suggest that 5-HT1B signaling within the LHb contributes to the anxiogenic effects of cocaine.

Haloperidol-induced catalepsy is ameliorated by deep brain stimulation of the inferior colliculus

Deep brain stimulation (DBS) has evolved as a promising alternative treatment for Parkinson’s disease (PD), but the underlying mechanisms remain poorly understood. Moreover, conventional DBS protocols targeted at basal ganglia sites can turn out completely ineffective for some PD patients, warranting the search for alternative targets. The inferior colliculus (IC) is a midbrain auditory relay station involved in sensorimotor processes. High-frequency 2500 Hz electrical stimulation of the IC elicits escape behaviour and interferes with haloperidol-induced catalepsy in rats, a state reminiscent of Parkinsonian akinesia, but clinical implication is limited since the protocol is aversive. However, typical DBS stimulation frequencies range between 20–180 Hz. We therefore tested the effects of a low-frequency 30 Hz-DBS protocol on haloperidol-induced catalepsy and aversive behaviour in rats. We show that low-frequency 30 Hz-DBS targeted at the IC strongly ameliorates haloperidol-induced catalepsy without any evidence of stimulation-induced escape behaviour. Furthermore, 30 Hz-DBS of the IC produced no place avoidance in a place conditioning paradigm and induced no anxiety-related behaviour on the elevated plus maze, indicating that the protocol has no aversive or anxiogenic side effects. Our findings provide first evidence that the IC can serve as an alternative, non-conventional DBS target.

Drosophila: An Emergent Model for Delineating Interactions between the Circadian Clock and Drugs of Abuse

Endogenous circadian oscillators orchestrate rhythms at the cellular, physiological, and behavioral levels across species to coordinate activity, for example, sleep/wake cycles, metabolism, and learning and memory, with predictable environmental cycles. The 21st century has seen a dramatic rise in the incidence of circadian and sleep disorders with globalization, technological advances, and the use of personal electronics. The circadian clock modulates alcohol- and drug-induced behaviors with circadian misalignment contributing to increased substance use and abuse. Invertebrate models, such as Drosophila melanogaster, have proven invaluable for the identification of genetic and molecular mechanisms underlying highly conserved processes including the circadian clock, drug tolerance, and reward systems. In this review, we highlight the contributions of Drosophila as a model system for understanding the bidirectional interactions between the circadian system and the drugs of abuse, alcohol and cocaine, and illustrate the highly conserved nature of these interactions between Drosophila and mammalian systems. Research in Drosophila provides mechanistic insights into the corresponding behaviors in higher organisms and can be used as a guide for targeted inquiries in mammals.

Attenuation of the anxiogenic effects of cocaine by 5-HT1B autoreceptor stimulation in the bed nucleus of the stria terminalis of rats

RATIONALE

Cocaine produces significant aversive/anxiogenic actions whose underlying neurobiology remains unclear. A possible substrate contributing to these actions is the serotonergic (5-HT) pathway projecting from the dorsal raphé (DRN) to regions of the extended amygdala, including the bed nucleus of the stria terminalis (BNST) which have been implicated in the production of anxiogenic states.

OBJECTIVES

The present study examined the contribution of 5-HT signaling within the BNST to the anxiogenic effects of cocaine as measured in a runway model of drug self-administration.

METHODS

Male Sprague-Dawley rats were fitted with bilateral infusion cannula aimed at the BNST and then trained to traverse a straight alley once a day for a single 1 mg/kg i.v. cocaine infusion delivered upon goal-box entry on each of 16 consecutive days/trials. Intracranial infusions of CP 94,253 (0, 0.25, 0.5, or 1.0 μg/side) were administered to inhibit local 5-HT release via activation of 5-HT_1B autoreceptors. To confirm receptor specificity, the effects of this treatment were then challenged by co-administration of the selective 5-HT_1B antagonist NAS-181.

RESULTS

Intra-BNST infusions of the 5-HT_1B autoreceptor agonist attenuated the anxiogenic effects of cocaine as reflected by a decrease in runway approach-avoidance conflict behavior. This effect was reversed by the 5-HT_1B antagonist. Neither start latencies (a measure of the subject's motivation to seek cocaine) nor spontaneous locomotor activity (an index of motoric capacity) were altered by either treatment.

CONCLUSIONS

Inhibition of 5-HT_1B signaling within the BNST selectively attenuated the anxiogenic effects of cocaine, while leaving unaffected the positive incentive properties of the drug.

Binge alcohol drinking elicits persistent negative affect in mice

Cessation from chronic alcohol abuse often produces a dysphoric state that can persist into protracted withdrawal. This dysphoric state is theorized to function as a negative reinforcer that maintains excessive alcohol consumption and/or precipitates relapse in those struggling to abstain from alcohol. However, we know relatively little regarding the impact of cessation from binge drinking on behavioral measures of negative affect and related neurobiology. Male C57BL/6J mice were given access to unsweetened 20% alcohol for 6 weeks under modified Drinking-in-the-dark procedures, followed by behavioral testing beginning either 1 or 21 days into withdrawal. Mice were administered a behavioral test battery consisting of: the elevated plus maze, light/dark box, novel object test, marble burying test, Porsolt forced swim test and sucrose preference test to assess anxiogenic and depressive signs. Egr1 immunostaining was used to quantify cellular activity within the central nucleus of the amygdala (CEA), basolateral amygdala (BLA), bed nucleus of the stria terminalis (BNST), and the nucleus accumbens (Acb) shell (AcbSh) and core (AcbC). Compared to water controls, alcohol-drinking mice exhibited higher indices of emotionality in the majority of behavioral assays. The hyper-emotionality exhibited by binge drinking mice was apparent at both withdrawal time-points and correlated with higher Egr1+ cell counts in the CEA and BNST, compared to controls. These data show that affective symptoms emerge very early after cessation of binge drinking and persist into protracted withdrawal. A history of binge drinking is capable of producing enduring neuroadaptations within brain circuits mediating emotional arousal.

On the positive and negative affective responses to cocaine and their relation to drug self-administration in rats

RATIONALE

Acute cocaine administration produces an initial rewarding state followed by a dysphoric/anxiogenic "crash."

OBJECTIVE

The objective of this study was to determine whether individual differences in the relative value of cocaine's positive and negative effects would account for variations in subsequent drug self-administration.

METHODS

The dual actions of cocaine were assessed using a conditioned place test (where animals formed preferences for environments paired with the immediate rewarding effects of 1.0mg/kg i.v. cocaine or aversions of environments associated with the anxiogenic effects present 15-min postinjection) and a runway test (where animals developed approach-avoidance "retreat" behaviors about entering a goal box associated with cocaine delivery). Ranked scores from these two tests were then correlated with each other and with the escalation in the operant responding of the same subjects observed over 10 days of 1- or 6-h/day access to i.v. (0.4 mg/inj) cocaine self-administration.

RESULTS

Larger place preferences were associated with faster runway start latencies (r s = -0.64), but not with retreat frequency or run times; larger place aversions predicted slower runway start times (r s = 0.62), increased run times (r s = 0.65), and increased retreats (r s = 0.62); response escalation was observed in both the 1- and 6-h self-administration groups and was associated with increased CPPs (r s = 0.58) but not CPAs, as well as with faster run times (r s = -0.60).

CONCLUSIONS

Together, these data suggest that animals exhibiting a greater positive than negative response to acute (single daily injections of) cocaine are at the greatest risk for subsequent escalated cocaine self-administration, a presumed indicator of cocaine addiction.

The rostromedial tegmental nucleus modulates behavioral inhibition following cocaine self-administration in rats

Recent findings suggest that the mesolimbic dopamine neurons, known to promote cocaine-seeking behavior, are strongly inhibited by a newly characterized region of the midbrain known as the rostromedial tegmental nucleus (RMTg). The RMTg appears to be involved in generating reward-prediction error signals and inhibition of motivated behaviors, suggesting its potential involvement in the extinction of cocaine seeking as well. Therefore, to address this question, male Sprague-Dawley rats underwent surgeries for implantation of catheters and cannulas targeted at the RMTg. After cocaine self-administration, rats underwent modified extinction training. Pre- or post-training intra-RMTg microinjections of the allosteric AMPA receptor potentiator PEPA during the first 5 days of extinction training appeared to enhance the retention of the extinction learning. Following the extinction training, rats underwent cue-induced reinstatement or an 'inactivation-alone' extinction tests. RMTg inactivation before a cue-induced reinstatement session or inactivation alone before a standard extinction session increased overall lever pressing. To determine whether these effects generalized to other motivated behaviors, additional experiments examining food-seeking behavior were also conducted. The results from the food-seeking experiments indicate that PEPA microinjections into the RMTg did not influence the extinction of food seeking and that, at least in rats that had not been given PEPA during the extinction learning experiments, RMTg inactivation had no effect on lever pressing during the cue-induced reinstatement or inactivation-alone tests. These findings suggest that the RMTg provides general behavioral inhibition and is potentially involved in learning to extinguish cocaine-seeking behavior in rats.

Noradrenergic β-receptor antagonism within the central nucleus of the amygdala or bed nucleus of the stria terminalis attenuates the negative/anxiogenic effects of cocaine

Cocaine has been shown to produce both initial rewarding and delayed anxiogenic effects. Although the neurobiology of cocaine's rewarding effects has been well studied, the mechanisms underlying its anxiogenic effects remain unclear. We used two behavioral assays to study these opposing actions of cocaine: a runway self-administration test and a modified place conditioning test. In the runway, the positive and negative effects of cocaine are reflected in the frequency of approach-avoidance conflict that animals develop about entering a goal box associated with cocaine delivery. In the place conditioning test, animals develop preferences for environments paired with the immediate/rewarding effects of cocaine, but avoid environments paired with the drug's delayed/anxiogenic actions. In the present study, these two behavioral assays were used to examine the role of norepinephrine (NE) transmission within the central nucleus of the amygdala (CeA) and the bed nucleus of the stria terminalis (BNST), each of which has been implicated in drug-withdrawal-induced anxiety and stress-induced response reinstatement. Rats experienced 15 single daily cocaine-reinforced (1.0 mg/kg, i.v.) runway trials 10 min after intracranial injection of the β1 and β2 NE receptor antagonists betaxolol and ICI 118551 or vehicle into the CeA or BNST. NE antagonism of either region dose dependently reduced approach-avoidance conflict behavior compared with that observed in vehicle-treated controls. In addition, NE antagonism selectively interfered with the expression of conditioned place aversions while leaving intact cocaine-induced place preferences. These data suggest a role for NE signaling within the BNST and the CeA in the anxiogenic actions of cocaine.