Steven T. Pittenger

Iptakalim attenuates self-administration and acquired goal-tracking behavior controlled by nicotine

Iptakalim is an ATP-sensitive potassium channel opener, as well as an α4β2-containing nicotinic acetylcholine receptor (nAChR) antagonist. Pretreatment with iptakalim diminishes nicotine-induced dopamine (DA) and glutamate release in the nucleus accumbens. This neuropharmacological profile suggests that iptakalim may be useful for treatment of nicotine dependence. Thus, we examined the effects of iptakalim in two preclinical models. First, the impact of iptakalim on the interoceptive stimulus effect of nicotine was evaluated by training rats in a discriminated goal-tracking task that included intermixed nicotine (0.4 mg/kg, SC) and saline sessions. Sucrose was intermittently presented in a response-independent manner only on nicotine sessions. On intervening test days, rats were pretreated with iptakalim (10, 30, 60 mg/kg, IP). Results revealed that iptakalim attenuated nicotine-evoked responding controlled by the nicotine stimulus in a dose-dependent manner. In a separate study, the impact of iptakalim on the reinforcing effects of nicotine was investigated by training rats to lever-press to self-administer nicotine (0.01 mg/kg/infusion) [Dosage error corrected]. Results revealed that pretreatment with iptakalim (1, 3, 6 mg/kg, IV) decreased nicotine intake (i.e., less active lever responding). Neither behavioral effect was due to a non-specific motor effect of iptakalim, nor to an ability of iptakalim to inhibit DA transporter (DAT) or serotonin transporter (SERT) function. Together, these finding support the notion that iptakalim may be an effective pharmacotherapy for increasing smoking cessation and a better understanding of its action could contribute to medication development.

Interoceptive conditioning with a nicotine stimulus is susceptible to reinforcer devaluation.

Pavlovian conditioning processes contribute to the etiology of nicotine dependence. Conditioning involving interoceptive stimuli is increasingly recognized as playing a role in many diseases and psychopathologies, including drug addiction. Previous animal research on diminishing the influence of interoceptive conditioning has been limited to antagonism and nonreinforced exposures to the drug stimulus. The goal of the present research was to determine whether interoceptive conditioning with a nicotine stimulus could be diminished through an unconditioned stimulus (US) devaluation procedure. In two separate experiments, male Sprague-Dawley rats received nicotine injections (0.4 mg base/kg) followed by intermittent sucrose (26%) access in a conditioning chamber. On intermixed saline sessions, sucrose was withheld. Conditioning was demonstrated by a reliable increase in head entries in the dipper receptacle on nicotine versus saline sessions. After conditioning, rats in a devaluation condition were given access to sucrose in their home cages immediately followed by a lithium chloride (LiCl) injection on 3 consecutive days. On subsequent test days, nicotine-evoked conditioned responding was significantly attenuated. Within-subject (Experiment 1) and between-subjects (Experiment 2) controls revealed that the diminished responding was not attributable to mere exposure to the sucrose US in the devaluation phase. Experiment 2 included a LiCl-alone control group. Repeated illness induced by LiCl did not reduce later nicotine-evoked responding. These findings suggest that there is a direct association between the interoceptive stimulus effects of nicotine and the appetitive sucrose US (i.e., stimulus-stimulus) rather than a stimulus-response association.

Ibudilast reverses the decrease in the synaptic signaling protein phosphatidylethanolamine-binding protein 1 (PEBP1) produced by chronic methamphetamine intake in rats

BACKGROUND Chronic methamphetamine intake has been shown to induce a neuroinflammatory state leading to significant changes in brain functioning including behavioral changes. These changes can persist for years after drug use is discontinued and likely contribute to the risk of relapse. A better understanding of inflammation responses associated with methamphetamine intake may help in designing novel and more efficacious treatment strategies. METHODS Rats were trained to self-administer methamphetamine or saline on a variable ratio 3 schedule of reinforcement (25 days). This training was followed by 12 days of extinction (i.e., methamphetamine unavailable) during which rats received daily post-session administration of ibudilast (AV411; 2.5 or 7.5mg/kg) or saline. Following extinction, synaptosomes were isolated from the prefrontal cortex (PFC) and the differential pattern of synaptic proteins was assessed using mass spectrometry based proteomics. RESULTS Treatment with ibudilast allowed for deeper extinction of active lever pressing. Quantitative mass spectrometry based proteomics on the PFC identified one potential hit; the synaptic signaling protein phosphatidylethanolamine-binding protein 1 (PEBP1). While methamphetamine intake was associated with reduced PEBP1 protein levels, treatment with ibudilast reversed this effect. Furthermore, decreased PEBP1 expression was correlated with subsequent activation of Raf-1, MEK, and ERK signaling components of the mitogen-activated protein kinase cascade (MAPK). Raf-1, MEK, and ERK expression levels were also attenuated by ibudilast treatment. CONCLUSION PEBP1, given its synaptic localization and its role as a signaling molecule acting via the ERK/MAPK pathway, could be a potential therapeutic target mediating drug-seeking behaviors associated with neuroinflammation.

The effects of varenicline on methamphetamine self-administration and drug-primed reinstatement in female rats

While research has revealed heightened vulnerability to meth addiction in women, preclinical models rarely use female subjects when investigating meth seeking and relapse. The goal of the present study was to examine the effects of varenicline (Chantix(®)), a partial α4β2 and full α7 nicotinic acetylcholine receptor agonist, on meth self-administration and reinstatement in female rats. Sprague-Dawley rats were surgically implanted with an indwelling jugular catheter. Half of the rats were then trained to self-administer meth (0.056 mg/kg/infusion) on a variable ratio 3 schedule of reinforcement; the other half earned intravenous saline during daily, 2h sessions. When responding stabilized, varenicline (0.0, 0.3, 1.0, 3.0mg/kg) was tested to determine how it altered meth taking. Varenicline was probed on 4 test days; each test separated by 2 standard self-administration sessions to assure responding remained stable. Following this testing was 15 extinction sessions. Twenty-four hours after the last extinction session were four consecutive days of meth-primed reinstatement. The same 4 doses of varenicline were examined to determine how it altered reinstatement triggered by 0.3mg/kg meth (IP). Rats readily self-administered meth. The higher doses of varenicline did not affect meth-taking in a specific fashion as active lever pressing was also slightly reduced in rats that has access to saline in the self-administration phase. Female rats displayed robust meth-primed reinstatement. Notably, the lower doses of varenicline increased meth-primed reinstatement. This amplified susceptibility to reinstatement (i.e., relapse) may be an impediment for the use of varenicline as a therapeutic to treat meth use disorder.

Interoceptive conditioning in rats: effects of using a single training dose or a set of 5 different doses of nicotine.

Interoceptive conditioning contributes to the tenacity of nicotine dependence. Previous research investigating nicotine as an interoceptive stimulus has typically employed administration of a single training dose of nicotine over an extended time. This approach has allowed for careful study of the nicotine stimulus. In humans, the nicotine stimulus is unlikely to be fixed across learning episodes. Thus, from a translational perspective, systematic variation of nicotine dose in training might better approximate interoceptive conditioning in humans. Notably, training with a class or set of discrete exteroceptive stimuli (e.g., different pictures of cars) produces interesting behavioral differences relative to training with a single stimulus. The present study sought to determine whether similar differences would occur if a set of nicotine stimuli were used in place of a single dose. To investigate this question, one group of male Sprague-Dawley rats was trained on a discriminated goal-tracking task with a set of nicotine doses (0.05, 0.125, 0.2, 0.275, and 0.35mg/kg). A second group received the standard protocol of training with a single nicotine dose (0.2mg/kg). On each nicotine session, there was intermittent access to liquid sucrose (26%) in a conditioning chamber. On intermixed saline sessions, sucrose was withheld. We examined acquisition, subsequent extinction, transfer of extinction, nicotine generalization, and mecamylamine blockade. Both groups reliably discriminated between nicotine and saline sessions, were sensitive to non-reinforcement, displayed transfer of extinction, demonstrated dose-dependent nicotine generalization, and responding was blocked by mecamylamine. There were no significant differences between the two groups. The unique nature of an interoceptive pharmacological stimulus and the challenges posed for studying the impact of training with a set of interoceptive stimuli are discussed.

Sex differences in neurotensin and substance P following nicotine self-administration in rats.

Investigator‐administered nicotine alters neurotensin and substance P levels in Sprague‐Dawley rats. This finding suggested a role of the dopamine‐related endogenous neuropeptides in nicotine addiction. We sought to extend this observation by determining the responses of neurotensin and substance P systems (assessed using radioimmunoassay) in male and female rats following nicotine self‐administration (SA). Male and female Sprague‐Dawley were trained to self‐administer nicotine, or receive saline infusions yoked to a nicotine‐administering rat during daily sessions (1‐h; 21 days). Brains were extracted 3 h after the last SA session. Nicotine SA increased tissue levels of neurotensin in the males in the anterior and posterior caudate, globus pallidus, frontal cortex, nucleus accumbens core and shell, and ventral tegmental area. Nicotine SA also increased tissue levels of neurotensin in the females in the anterior caudate, globus pallidus, nucleus accumbens core and shell, but not in the posterior caudate, frontal cortex, or ventral tegmental area. There were fewer sex differences observed in the substance P systems. Nicotine SA increased tissue levels of substance P in both the males and females in the posterior caudate, globus pallidus, frontal cortex, nucleus accumbens shell, and ventral tegmental area. A sex difference was observed in the nucleus accumbens core, where nicotine SA increased tissue levels of substance P in the males, yet decreased levels in the females. The regulation of neuropeptides following nicotine SA may play a role in the susceptibility to nicotine dependence in females and males. Synapse 70:336–346, 2016.

The effect of N-acetylcysteine or bupropion on methamphetamine self-administration and methamphetamine–triggered reinstatement of female rats

&NA; N‐acetylcysteine and bupropion are two promising candidate medications for treatment of substance use disorder. The effects of N‐acetylcysteine or bupropion on methamphetamine self‐administration of female rats are not well understood. To fill this gap, this study assessed the effects of N‐acetylcysteine (0, 30, 60, or 120 mg/kg) and bupropion (0, 10, 30, and 60 mg/kg) on methamphetamine self‐administration of female rats across the natural estrous cycle. Following a completed dose‐response curve, responding for methamphetamine self‐administration was extinguished and the effects of N‐acetylcysteine or bupropion on methamphetamine‐triggered reinstatement was evaluated in separate experiments. N‐acetylcysteine did not decrease responding maintained by methamphetamine or methamphetamine‐triggered reinstatement. Bupropion significantly decreased methamphetamine self‐administration and methamphetamine‐triggered reinstatement in female rats with highest dose (60 mg/kg) also significantly decreasing general chamber activity. In a companion experiment, testing the effect of bupropion on responding maintained by sucrose, we confirmed non‐specificity of bupropions effects as bupropion also decreased responding for sucrose. Considered together, our findings suggest that while N‐acetylcysteine has considerable promise for treatment of cocaine dependence it may not generalize to other stimulants like methamphetamine. Furthermore, although bupropion has been shown to effectively decrease methamphetamine self‐administration, and presently methamphetamine‐triggered reinstatement, its locomotor and reward suppressing effects warrant further investigation including both sexes. HighlightsFemale menstrual cycle did not affect methamphetamine self‐administration.NAC did not affect methamphetamine self‐administration or reinstatement.Bupropion attenuated methamphetamine self‐administration and reinstatement.Locomotion decreased when higher doses of bupropion were combined with methamphetamine.

Nicotine- and cocaine-triggered methamphetamine reinstatement in female and male Sprague-Dawley rats

Abstract Preclinical studies have demonstrated a return to methamphetamine (meth)‐seeking behavior (reinstatement) induced by injections of meth administered by the experimenter (drug‐prime). Notably, females tend to be more sensitive to drug‐prime; often displaying more reinstatement behavior when compared to males. While meth‐primed reinstatement of meth‐seeking behavior has been established, little is known about the ability of other drugs of abuse to substitute for meth during drug‐primed reinstatement; nicotine and cocaine were the focus of the present work. We also examined if self‐administration and/or reinstated meth‐seeking behavior was affected by repeated nicotine administration. Male and female Sprague‐Dawley rats were trained to self‐administer meth during daily sessions. During this self‐administration phase, rats were placed into 1 of 2 groups: saline or repeated nicotine exposure. Rats in the repeated nicotine group received nicotine injections 4 h after meth self‐administration sessions, whereas the remaining rats received saline. Following self‐administration was extinction in which meth was no longer available and nicotine was no longer administered. After extinction, rats were tested to determine if 0 (saline), 0.2, and 0.4 mg/kg nicotine reinstated meth‐seeking behavior. Three days of re‐extinction followed nicotine testing. Finally, rats received reinstatement tests with 0 (saline), 5, and 10 mg/kg cocaine. Nicotine and cocaine reinstated meth‐seeking behavior in male and female rats with no difference between the sexes. Repeated nicotine administration potentiated meth reinstatement following the 0.4 mg/kg nicotine‐prime. While females may be more sensitive to reinstatement triggered with the original self‐administration drug, this effect may not generalize to priming with other drugs of abuse. HighlightsRepeated nicotine treatment did not alter meth self‐administration.Repeated nicotine treatment facilitated meth extinction.Nicotine and cocaine induced meth‐seeking in male and female rats.Previous nicotine experience potentiated meth reinstatement induced by nicotine.