Subanesthetic ketamine decreases the incentive-motivational value of reward-related cues

Acute MK-801 increases measures of both sign-tracking and goal-tracking in male Sprague-Dawley rats

Sign-tracking is a Pavlovian conditioned approach behavior thought to be important in understanding cue-driven relapse to drug use, and strategies for reducing sign-tracking may have some benefit in preventing relapse. A previous study successfully employed the NMDA receptor antagonist MK-801 in preventing the development of sign-tracking (but not goal-tracking) in a conditioned approach task. In this study, we focused on whether MK-801 would have similar effects on previously established sign-tracking behavior. MK-801 was administered after training in a standard sign-/goal-tracking task using a retractable lever as a conditioned stimulus and a sucrose pellet as unconditioned stimulus. It was found that MK-801 increased measures of both sign- and goal-tracking in subjects who had previously learned the task. The NMDA receptor appears to play a complex role in governing behavior related to sign-tracking.

The effects of (2R,6R)-hydroxynorketamine on oxycodone withdrawal and reinstatement

Despite the thousands of lives lost during the ongoing opioid crisis, a scarcity of new and effective clinical treatments for opioid use disorder (OUD) remains. To address this unmet need, some researchers have turned to dissociative and psychedelic drugs to treat multiple psychiatric conditions. In particular, low doses of ketamine have been shown to attenuate opioid withdrawal and drug use in clinical and preclinical studies. However, ketamine has misuse liability and dissociative side effects that may limit its widespread application as a treatment for OUD. More recently, (2R,6R)-hydroxynorketamine (HNK), a ketamine metabolite that lacks misuse potential, has gained attention for its effectiveness in depression and stress models. To uncover its role in OUD, we tested the time-dependent effects of (2R,6R)-HNK on oxycodone withdrawal and reinstatement of oxycodone conditioned place preference (CPP). In male and female oxycodone-dependent mice, we found that 24h pretreatment with (2R,6R)-HNK (10 or 30mg/kg, s.c.) reduced the frequency of withdrawal-like behaviors and global withdrawal scores during naloxone-precipitated withdrawal, whereas 1h pretreatment with (2R,6R)-HNK only reduced paw tremors and the sum of global withdrawal scores but not GWS Z-scores. In other experiments, both 1h and 24h pretreatment with (2R,6R)-HNK (30mg/kg, s.c.) blocked drug-induced reinstatement of oxycodone CPP. Finally, we found (2R,6R)-HNK (30mg/kg, sc) had no effect on locomotor activity and thigmotaxis. Together, these results indicate that acute (2R,6R)-HNK has efficacy in some preclinical models of OUD without producing locomotor or anxiety-like side effects.

Effects of bupropion on sign- and goal-tracking in male Sprague Dawley rats

Relapse into addiction is often triggered by cues that have a Pavlovian association with drugs and drug-taking. Sign-tracking involves approach of and interaction with Pavlovian conditioned signals for appetitive events (as opposed to goal-tracking, which involves approach of the site of the appetitive events themselves) and may be important in understanding cue-driven relapse. Bupropion is an atypical antidepressant and smoking cessation aid with effects on dopamine and norepinephrine that may have some utility in reducing sign-tracking. Male Sprague-Dawley rats were trained in a task where sign- and goal-tracking were possible and then administered doses of bupropion during a test phase. Bupropion decreased measures of sign-tracking and increased goal-tracking. This suggests that bupropion might be a useful adjunct medication for many kinds of behavioral disorders in which cue-driven behavior is problematic.

Appetitive 50 kHz calls in a pavlovian conditioned approach task in Cacna1c haploinsufficient rats

We have previously shown that rats emit high-frequency 50 kHz ultrasonic vocalizations (USV) during sign- and goal-tracking in a common Pavlovian conditioned approach task. Such 50 kHz calls are probably related to positive affect and are associated with meso-limbic dopamine function. In humans, the CACNA1C gene, encoding for the α_1C subunit of the L-type voltage-gated calcium channel Ca_V1.2, is implicated in several mental disorders, including mood disorders associated with altered dopamine signaling. In the present study, we investigated sign- and goal-tracking behavior and the emission of 50 kHz USV in Cacna1c haploinsufficent rats in a task where food pellet delivery is signaled by an appearance of an otherwise inoperable lever. Over the course of this Pavlovian training, these rats not only increased their approach to the reward site, but also their rates of pressing the inoperable lever. During subsequent extinction tests, where reward delivery was omitted, extinction patterns differed between reward site (i.e. magazine entries) and lever, since magazine entries quickly declined whereas behavior towards the lever transiently increased. Based on established criteria to define sign- or goal-tracking individuals, no CACNA1C rat met a sign-tracking criterion, since around 42% of rats tested where goal-trackers and the other 58% fell into an intermediate range. Regarding USV, we found that the CACNA1C rats emitted 50 kHz calls with a clear subject-dependent pattern; also, most of them were of a flat subtype and occurred mainly during initial habituation phases without cues or rewards. Compared, to previously published wildtype controls, Cacna1c haploinsufficent rats displayed reduced numbers of appetitive 50 kHz calls. Moreover, similar to wildtype littermate controls, 50 kHz call emission in Cacna1c haploinsufficent rats was intra-individually stable over training days and was negatively associated with goal-tracking. Together, these findings provide evidence in support of 50 kHz calls as trait marker. The finding that Cacna1c haploinsufficent rats show reductions of 50 kHz calls accompanied with more goal-tracking, is consistent with the assumption of altered dopamine signaling in these rats, a finding which supports their applicability in models of mental disorders.

Dextromethorphan Reduces Sign-Tracking but Not Goal-Tracking in Male Sprague-Dawley Rats

Sign-tracking is a well-known phenomenon in appetitive Pavlovian conditioning in which subjects approach the site of a conditioned stimulus (CS) associated with an appetitive unconditioned stimulus (US) even when the two are located separately. Control of sign-tracking may be important in rehabilitation from drug dependence to help ward off relapse. Recent studies have found success in using ketamine to reduce sign-tracking. In this study, we employed a similar but unscheduled drug, dextromethorphan (DXM), which affects many of the same molecular targets as ketamine, in an attempt to reduce sign-tracking in a standard paradigm. DXM was found to reduce sign-tracking at the doses examined in this study, while goal-tracking (approaching the site of the US rather than CS) was relatively unaffected. DXM offers advantages over ketamine in terms of use with patients and may have some utility in rehabilitation.

Subanesthetic ketamine with an AMPAkine attenuates motor impulsivity in rats

The concept of 'impulse control' has its roots in early psychiatry and today has progressed into a well-described, although poorly understood, multidimensional endophenotype underlying many neuropsychiatric disorders (e.g., attention deficit hyperactivity disorder, schizophrenia, substance use disorders). There is mounting evidence suggesting that the cognitive and/or behavioral dimensions underlying impulsivity are driven by dysfunctional glutamate (Glu) neurotransmission via targeted ionotropic Glu receptor (GluR) [e.g., N-methyl-D-aspartate receptor (NMDAR), α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR)] mechanisms and associated synaptic alterations within key brain nodes. Ketamine, a noncompetitive NMDAR antagonist and FDA-approved for treatment-resistant depression, induces a 'glutamate burst' that drives resculpting of the synaptic milieu, which lasts for several days to a week. Thus, we hypothesized that single and repeated treatment with a subanesthetic ketamine dose would normalize motor impulsivity. Next, we hypothesized that AMPAR positive allosteric modulation, alone or in combination with ketamine, would attenuate impulsivity and provide insight into the mechanisms underlying GluR dysfunction relevant to motor impulsivity. To measure motor impulsivity, outbred male Sprague-Dawley rats were trained on the one-choice serial reaction time task. Rats pretreated with single or repeated (3 days) administration of ketamine (10 mg/kg; i.p.; 24-h pretreatment) or with the AMPAkine HJC0122 (1 or 10 mg/kg; i.p.; 30-min pretreatment) exhibited lower levels of motor impulsivity vs. control. Combination of single or repeated ketamine plus HJC0122 also attenuated motor impulsivity vs. control. We conclude that ligands designed to promote GluR signaling represent an effective pharmacological approach to normalize impulsivity and subsequently, neuropsychiatric disorders marked by aberrant impulse control.

Evaluation of Safety and Efficacy of Prehospital Paramedic Administration of Sub-Dissociative Dose of Ketamine in the Treatment of Trauma-Related Pain in Adult Civilian Population

Opiates are addicting and have a high potential for dependency. In the past decades, opiates remained the first-line pharmaceutical option of prehospital treatment for acute traumatic pain in the civilian population. Ketamine is an N-methyl-d-aspartate (NMDA) receptor antagonist that has analgesic properties and may serve as an alternative agent for the treatment of acute traumatic pain in prehospital settings. This study aims to assess the safety and efficacy of ketamine administration by paramedics in civilian prehospital settings for the treatment of acute traumatic pain.

This was a prospective observational study in San Bernardino, Riverside and Stanislaus counties. Patients were included if they were > 15 years of age with complaints of traumatic or burn-related pain. Patients were excluded if they received opiates up to six hours prior to or concurrently with ketamine administration. The dose administered was 0.3 mg/kg intravenously over five minutes with a maximum dose of 30 mg. The option to administer a second dose was available to paramedics if the patient continued to have pain after 15 minutes following the first administration. Paired-T tests were conducted to assess the change in the primary outcome (pain score) and secondary outcomes (e.g. systolic blood pressure, pulse, and respiratory rate). P-value<0.05 was considered to be statistically significant.

A total of 368 patients were included in the final analysis. The average age was 52.9 ± 23.1 years, and the average weight was 80.4 ± 22.2 kg. There was a statistically significant reduction in the pain score (9.13 ± 1.28 vs 3.7 ± 3.4, delta=5.43 ± 3.38, p<0.0001). Additionally, there was a statistically significant change in systolic blood pressure (143.42 ± 27.01 vs 145.65 ± 26.26, delta=2.22 ± 21.1, p=0.044), pulse (88.06 ± 18 vs 84.64 ± 15.92, delta= -3.42 ± 12.12, p<0.0001), and respiratory rate (19.04 ± 3.59 vs 17.74 ± 3.06, delta=-1.3 ± 2.96, p<0.0001).

The current study suggested that paramedics are capable of safely identifying the appropriate patients for the administration of sub-dissociative doses of ketamine in the prehospital setting. Furthermore, the current study suggested that ketamine may be an effective analgesic in a select group of adult trauma patients.

Ketamine and nitrous oxide: The evolution of NMDA receptor antagonists as antidepressant agents

N-methyl-d-aspartate receptor (NMDAR) antagonists, including ketamine and nitrous oxide, are currently intensely studied as rapid-acting antidepressant agents. Interestingly, both of these compounds are also drugs of abuse. Intravenous ketamine, a dissociative anesthetic that induces complex downstream effects via NMDARs, rapidly reduces depressive and suicidal symptoms in treatment-resistant depression (TRD), as demonstrated by several trials. Recently, the United States Food and Drug Administration (FDA) approved an intranasal version of ketamine (esketamine) for TRD. The United States Drug Enforcement Agency (DEA) lists ketamine as a Class III scheduled drug (moderate-low potential for physical and psychological abuse). The FDA has established a Risk Evaluation and Management Strategy (REMS) program to ensure proper drug storage, handling, dispensing, and monitoring intranasal esketamine to minimize misuse/abuse opportunities. Nitrous Oxide is a colorless, odorless, gas that has been in medical use for over 150 years. The mechanisms of action of nitrous oxide are not fully understood; however, it is known to act as a non-competitive inhibitor of NMDA-type glutamate receptors. Currently, nitrous oxide is used for inhalational general anesthesia and analgesia for short procedures. Inhaled nitrous oxide is also used recreationally, primarily by teens and young adults, but is not believed to have strong addiction potential. In contrast to ketamine, nitrous oxide is not a controlled substance and can be legally purchased without a prescription. A recent double-blind, prospective, cross-over study demonstrated that nitrous oxide reduced depressive symptoms in a group of severely ill TRD patients. Though this is a promising initial study, further investigation is needed.

Individual variation in the attribution of incentive salience to social cues

Research on the attribution of incentive salience to drug cues has furthered our understanding of drug self-administration in animals and addiction in humans. The influence of social cues on drug-seeking behavior has garnered attention recently, but few studies have investigated how social cues gain incentive-motivational value. In the present study, a Pavlovian conditioned approach (PCA) procedure was used to identify rats that are more (sign-trackers; STs) or less (goal-trackers; GTs) prone to attribute incentive salience to food reward cues. In Experiment 1, a novel procedure employed social ‘peers’ to compare the tendency of STs and GTs to attribute incentive salience to social reward cues as well as form a social-conditioned place preference. In Experiment 2, social behavior of STs and GTs was compared using social interaction and choice tests. Finally, in Experiment 3, levels of plasma oxytocin were measured in STs and GTs seven days after the last PCA training session, because oxytocin is known to modulate the mesolimbic reward system and social behavior. Compared to GTs, STs attributed more incentive salience to social-related cues and exhibited prosocial behaviors (e.g., social-conditioned place preference, increased social interaction, and social novelty-seeking). No group differences were observed in plasma oxytocin levels. Taken together, these experiments demonstrate individual variation in the attribution of incentive salience to both food- and social-related cues, which has important implications for the pathophysiology of addiction.

Comparison of conventional and rapid-acting antidepressants in a rodent probabilistic reversal learning task

Deficits in reward processing are a central feature of major depressive disorder with patients exhibiting decreased reward learning and altered feedback sensitivity in probabilistic reversal learning tasks. Methods to quantify probabilistic learning in both rodents and humans have been developed, providing translational paradigms for depression research. We have utilised a probabilistic reversal learning task to investigate potential differences between conventional and rapid-acting antidepressants on reward learning and feedback sensitivity. We trained 12 rats in a touchscreen probabilistic reversal learning task before investigating the effect of acute administration of citalopram, venlafaxine, reboxetine, ketamine or scopolamine. Data were also analysed using a Q-learning reinforcement learning model to understand the effects of antidepressant treatment on underlying reward processing parameters. Citalopram administration decreased trials taken to learn the first rule and increased win-stay probability. Reboxetine decreased win-stay behaviour while also decreasing the number of rule changes animals performed in a session. Venlafaxine had no effect. Ketamine and scopolamine both decreased win-stay probability, number of rule changes performed and motivation in the task. Insights from the reinforcement learning model suggested that reboxetine led animals to choose a less optimal strategy, while ketamine decreased the model-free learning rate. These results suggest that reward learning and feedback sensitivity are not differentially modulated by conventional and rapid-acting antidepressant treatment in the probabilistic reversal learning task.

Effects of ketamine treatment on cocaine-induced reinstatement and disruption of functional connectivity in unanesthetized rhesus monkeys

RATIONALE

Substance use disorders are characterized by a loss of executive control over reward-based decision-making, and disruption of fronto-striatal connectivity has been implicated in this process. Sub-anesthetic ketamine has recently been shown to bolster fronto-striatal connectivity in drug-naïve subjects.

OBJECTIVES

The influence of ketamine treatment was examined on the disruptive effects of cocaine on functional connectivity (FC) and on cocaine-seeking behavior in female rhesus monkeys.

METHODS

Three female rhesus were trained for unanesthetized MRI scanning. Each received three drug-naïve/abstinent pharmacological MRI scans with acute injections of saline, cocaine (0.3 mg/kg i.v.), and cocaine (0.3 mg/kg i.v.) 48-h after a ketamine treatment (low dose = 0.345 mg/kg bolus + 0.256 mg/kg/h for 1 h; i.v.), and a fourth scan with saline injection following 2 months of daily cocaine self-administration. A separate cohort of five rhesus (4 female), all with extensive histories of cocaine exposure, underwent reinstatement testing 48 h after ketamine (or vehicle) treatment. Two sub-anesthetic doses were tested: low dose and high dose = 0.69 mg/kg + 0.512 mg/kg/h for 1 h.

RESULTS

Ketamine treatment attenuated the effects of cocaine on both global and fronto-striatal FC in drug-naïve/abstinent subjects. Two months of daily cocaine self-administration led to prolonged disruption of both global and fronto-striatal FC. Cocaine-seeking behavior during reinstatement was reduced following ketamine treatment at the low dose, but not high dose.

CONCLUSION

These findings illustrate the disruptive effects of cocaine on functional connectivity and provide evidence for the potential efficacy of ketamine as a treatment for stimulant use disorder.

The role of glutamate signaling in incentive salience: second-by-second glutamate recordings in awake Sprague-Dawley rats

The attribution of incentive salience to reward-predictive stimuli has been shown to be associated with substance abuse-like behavior such as increased drug taking. Evidence suggests that glutamate neurotransmission and sequential N-methyl-D-aspartate (NMDA) activation are involved in the attribution of incentive salience. Here, we further explore the role of second-by-second glutamate neurotransmission in the attribution of incentive salience to reward-predictive stimuli by measuring sign-tracking behavior during a Pavlovian conditioned approach procedure using ceramic-based microelectrode arrays configured for sensitive measures of extracellular glutamate in awake behaving Sprague-Dawley rats. Specifically, we show that there is an increase in extracellular glutamate levels in the prelimbic cortex (PrL) and the nucleus accumbens core (NAcC) during sign-tracking behavior to a food-predictive conditioned stimulus (CS+) compared to the presentation of a non-predictive conditioned stimulus (CS-). Furthermore, the results indicate greater increases in extracellular glutamate levels in the PrL compared to NAcC in response to the CS+, including differences in glutamate release and signal decay. Taken together, the present research suggests that there is differential glutamate signaling in the NAcC and PrL during sign-tracking behavior to a food-predictive CS+.

Disconnection of basolateral amygdala and insular cortex disrupts conditioned approach in Pavlovian lever autoshaping

Previously established individual differences in appetitive approach and devaluation sensitivity observed in goal- and sign-trackers may be attributed to differences in the acquisition, modification, or use of associative information in basolateral amygdala (BLA) pathways. Here, we sought to determine the extent to which communication of associative information between BLA and anterior portions of insular cortex (IC) supports ongoing Pavlovian conditioned approach behaviors in sign- and goal-tracking rats, in the absence of manipulations to outcome value. We hypothesized that the BLA mediates goal-, but not sign- tracking approach through interactions with the IC, a brain region involved in supporting flexible behavior. We first trained rats in Pavlovian lever autoshaping to determine their sign- or goal-tracking tendency. During alternating test sessions, we gave unilateral intracranial injections of vehicle or a cocktail of gamma-aminobutyric acid (GABA) receptor agonists, baclofen and muscimol, unilaterally into the BLA and contralaterally or ipsilaterally into the IC prior to reinforced lever autoshaping sessions. Consistent with our hypothesis we found that contralateral inactivation of BLA and IC increased the latency to approach the food cup and decreased the number of food cup contacts in goal-trackers. While contralateral inactivation of BLA and IC did not affect the total number of lever contacts in sign-trackers, this manipulation increased the latency to approach the lever. Ipsilateral inactivation of BLA and IC did not impact approach behaviors in Pavlovian lever autoshaping. These findings, contrary to our hypothesis, suggest that communication between BLA and IC maintains a representation of initially learned appetitive associations that commonly support the initiation of Pavlovian conditioned approach behavior regardless of whether it is directed at the cue or the location of reward delivery.