Oxytocin Reduces Cocaine Cued Fos Activation in a Regionally Specific Manner.

Background: Oxytocin may be a possible treatment for multiple neuropsychiatric disorders, including cocaine addiction. Little is known about the site-specific effects of oxytocin on various drug addiction-related brain regions. Furthermore, sexually dimorphic effects of oxytocin on neural function in the addiction circuit have not been established. Here, we studied Fos expression following cocaine-cued reinstatement in both male and female rats. Methods: Male and female rats underwent self-administration, extinction, and reinstatement tests. On test days, rats were given oxytocin or vehicle, and lever pressing was measured in response to conditioned cocaine cues. Rats were perfused and Fos staining measured in the central amygdala, medial prefrontal cortex, nucleus accumbens core, and subthalamic nucleus. Fos/oxytocin double labeling occurred in the paraventricular nucleus of the hypothalamus. Results: Rats reinstated to cocaine cues relative to extinction responding and oxytocin reduced cocaine seeking. Oxytocin combined with contingent cue presentations increased Fos+ oxytocin cell bodies within the paraventricular nucleus of the hypothalamus relative to vehicle. Fos expression robustly increased in the central amygdala following oxytocin administration. Oxytocin reversed cue-induced Fos expression in the medial prefrontal cortex, nucleus accumbens core, and subthalamic nucleus. Central oxytocin infusion also attenuated reinstated cocaine seeking. Conclusions: Oxytocin decreased reinstated cocaine seeking, increased Fos activation in the paraventricular nucleus of the hypothalamus and central amygdala, but normalized cue-induced Fos activation in the medial prefrontal cortex, nucleus accumbens core, and subthalamic nucleus, thereby demonstrating regionally specific activation patterns. No sex differences were seen for the effects of oxytocin on cocaine seeking and Fos activation, indicating that oxytocin acts on similar central neural circuits critical to reinstated cocaine seeking in both males and females.

Extended cocaine-seeking produces a shift from goal-directed to habitual responding in rats.

Cocaine addiction is often characterized by a rigid pattern of behavior in which cocaine users continue seeking and taking drug despite negative consequences associated with its use. As such, full acquisition and relapse of drug-seeking behavior may be attributed to a shift away from goal-directed responding and a shift towards the maladaptive formation of rigid and habit-like responses. This rigid nature of habitual responding can be developed with extended training and is typically characterized by insensitivity to changes in outcome value. The present study determined whether cocaine (primary reinforcer) and cocaine associated cues (secondary reinforcer) could be devalued in rats with different histories of cocaine self-administration. Specifically, rats were trained on two schedules of cocaine self-administration (long-access vs. short-access). Following training the cocaine reinforcer was devalued through three separate pairings of lithium chloride with cocaine infusions. Cocaine history did not have an impact on devaluation of cocaine-associated cues. However, the reinforcing properties of cocaine were devalued only in rats on a short-access cocaine schedule but not those trained on a long-access schedule. Taken together this pattern of findings suggests that, in short access rats, devaluation is specific to the primary reinforcer and not associative stimuli such as cues. Importantly, rats that received extended training during self-administration displayed insensitivity to outcome devaluation of the primary reinforcer as well as all associative stimuli, thus displaying rigid behavioral responding similar to behavioral patterns found in addiction. Alternatively, long access cocaine exposure may have altered the devaluation threshold.

Oxytocin decreases cocaine taking, cocaine seeking, and locomotor activity in female rats.

Oxytocin has been shown to decrease cocaine taking and seeking in male rats, suggesting potential treatment efficacy for drug addiction. In the present study, we extended these findings to the assessment of cocaine seeking and taking in female rats. Further, we made direct comparisons of oxytocin's impact on cocaine induced locomotor activity in both males and females. In females, systemic oxytocin (0.3, 1.0, 3.0 mg/kg) attenuated lever pressing for cocaine during self-administration and oxytocin (1.0 mg/kg) attenuated cue-induced cocaine seeking following extinction. Cocaine increased baseline locomotor activity to a greater degree in females relative to males. Oxytocin (0.1, 0.3, 1.0, and 3.0 mg/kg) reduced cocaine-induced locomotor activity in females, but not significantly in males. These data illustrate sex similarities in oxytocin's attenuation of cocaine seeking, but sex differences in cocaine-induced locomotor effects. While reductions in cocaine seeking cannot be attributed to a reduction in locomotor activity in males, attenuation of locomotor function cannot be entirely ruled out as an explanation for a decrease in cocaine seeking in females suggesting that oxytocin's effect on cocaine seeking may be mediated by different mechanisms in male and females.

Perirhinal Cortex mGlu5 Receptor Activation Reduces Relapse to Methamphetamine Seeking by Restoring Novelty Salience.

Rats that have self-administered methamphetamine (meth) under long access, but not short access, conditions do not recognize novel objects. The perirhinal cortex is critical for novelty detection, and perirhinal metabotropic glutamate 5 receptors (mGlu5) are downregulated after long-access meth. The novel positive allosteric modulator (PAM) 1-(4-(2,4-difluorophenyl) piperazin-1-yl)-2-((4-fluorobenzyl)oxy)-ethanone, or DPFE, demonstrates improved solubility compared with other mGlu5 PAMs, thus allowing brain-site-specific pharmacological studies. Infusion of DPFE into perirhinal cortex restored novel object recognition in long-access meth rats. To investigate the impact of these cognitive enhancing effects on relapse, we tested the effects of DPFE infusions into perirhinal cortex on meth-seeking under two different test conditions. In the standard cue relapse test, perirhinal DPFE infusions did not alter meth-seeking in the presence of meth cues. However, in a novel cue relapse test, wherein animals were allowed to allocate responding between a novel cue and meth-conditioned cue, perirhinal DPFE infusions shifted the pattern of responding in long-access rats toward a profile resembling short-access rats, which respond equally for novel and meth cues. Perirhinal mGlu5 are thus a promising pharmacological target for the restoration of cognitive function in meth addicts. Targeting these receptors may also reduce relapse, particularly in situations where novel stimuli compete with conditioned stimuli for control over meth seeking.

Oxytocin differentially affects sucrose taking and seeking in male and female rats.

Oxytocin has a modulatory role in natural and drug reward processes. While the role of oxytocin in pair bonding and reproduction has been extensively studied, sex differences in conditioned and unconditioned behavioral responses to oxytocin treatment have not been fully characterized. Here, we determined whether male and female rats would show similar dose response curves in response to acute oxytocin on measures of locomotor activity, sucrose seeking, and sucrose intake. Male and freely cycling female rats received vehicle or oxytocin (0.1, 0.3, 1, 3mg/kg, IP) injections before behavioral tests designed to assess general motor activity, as well as sucrose self-administration and seeking. Lower doses of oxytocin decreased motor activity in a novel environment in females relative to males. Likewise, lower doses of oxytocin in females decreased responding for sucrose during maintenance of sucrose self-administration and reinstatement to sucrose-conditioned cues. However, sucrose seeking in response to a sucrose prime was only decreased by the highest oxytocin dose in both sexes. In general, oxytocin had similar effects in both sexes. However, females were more sensitive to lower doses of oxytocin than males. These findings are consistent with the notion that oxytocin regulates many of the same behaviors in males and females, but that the effects are typically more profound in females. Therapeutic use of oxytocin should include sex as a factor in determining dose regimens.

Inactivation of the lateral habenula reduces anxiogenic behavior and cocaine seeking under conditions of heightened stress.

Recent anatomical and functional studies have renewed interest in the lateral habenula (LHb), a critical brain region that works in an opponent manner to modulate aversive and appetitive processes. In particular, increased LHb activation is believed to drive anxiogenic states during stressful conditions. Here, we reversibly inactivated the LHb with GABA receptor agonists (baclofen/muscimol) in rats prior to testing in an open field, elevated plus maze, and defensive burying task in the presence or absence of yohimbine, a noradrenergic α2-receptor antagonist that acts as an anxiogenic stressor. In a second set of experiments using a cocaine self-administration and reinstatement model, we inactivated the LHb during extinction responding and cue-induced reinstatement of cocaine seeking in the presence or absence of yohimbine pretreatment. Inactivation of the LHb after yohimbine treatment attenuated anxiogenic behavior by increasing time spent in the open arms and reducing the time spent burying. Inactivation of the LHb also reduced cocaine seeking when cue-induced reinstatement occurred in the presence of yohimbine, but did not affect extinction responding or cue-induced reinstatement by itself. These data demonstrate that the LHb critically regulates states of heightened anxiety during both unconditioned behavior and conditioned appetitive processes.

A rodent "self-report" measure of methamphetamine craving? Rat ultrasonic vocalizations during methamphetamine self-administration, extinction, and reinstatement.

Rats emit ultrasonic vocalizations (USVs) in a variety of contexts, and it is increasingly clear that USVs reflect more complex information than mere positive and negative affect states. We sought to examine USVs in a common model of addiction and relapse, the self-administration/reinstatement paradigm, in order to gain insight into subjective states experienced by rats during various types of methamphetamine seeking. We measured three subtypes of "50kHz" USVs [flats, trills, and non-trill frequency modulated (FM) USVs], as well as long and short duration "22kHz" USVs, during self-administration and extinction training, and during reinstatement elicited by cues, a methamphetamine prime, cues+prime, or the pharmacological stressor yohimbine. During self-administration and extinction, rats emitted many flats and FMs, (and short duration "22kHz" USVs on day 1 of self-administration), but few trills. In contrast, methamphetamine priming injections potently enhanced FMs and trills, and trill production was correlated with the degree of methamphetamine+cue-elicited reinstatement. Cues alone yielded increases only in flat USVs during reinstatement, though a subset of rats displaying strong cue-induced reinstatement also emitted long duration, aversion-related "22kHz" USVs. Although yohimbine administration caused reinstatement, it did not induce "22kHz" USVs in methamphetamine-experienced or methamphetamine-naïve rats (unlike footshock stress, which did induce long duration "22kHz" USVs). These findings demonstrate heterogeneity of rat USVs emitted during different types of methamphetamine seeking, and highlight their potential usefulness for gaining insight into the subjective states of rats in rodent models of drug addiction and relapse.

Sex differences in escalation of methamphetamine self-administration: cognitive and motivational consequences in rats.

RATIONALE: Male rats escalate methamphetamine (meth) intake during long-access meth self-administration, show enhanced reinstatement of meth-seeking, and exhibit meth-induced memory impairments. However, the impact of long-access daily meth self-administration on reinstatement and cognitive dysfunction has not been assessed in females, even though clinical studies on meth addiction have shown differences between men and women. OBJECTIVES: This study determined whether male and freely cycling female rats: (1) escalate meth intake in a 6-h daily-access period relative to 1-h access; (2) show different sensitivity to meth primed reinstatement after short- and long-access conditions; and (3) show deficits in novel object and object in place recognition memory. METHODS: Male and female Long-Evans rats self-administered meth in limited (1-h/day) or extended (6-h/day) daily access sessions. After 21 days, meth access was discontinued, and rats entered an abstinence period. On the seventh and 14th days of abstinence, rats were assessed for recognition memory using tests for: (a) novel object recognition memory and (b) object-in-place memory. Rats were tested for reinstatement of meth-seeking following extinction of responding. RESULTS: Female rats self-administered more meth and escalated intake faster than males during extended, but not limited, daily access. Both males and females in the extended, but not limited, access groups showed memory deficits on both tasks. Female rats showed greater reinstatement to meth-seeking with lower doses of meth priming injections than males. CONCLUSIONS: Relative to males, females were equally susceptible to meth-induced memory deficits but exhibited higher meth intake and greater relapse to meth-seeking.

Nicotine self-administration and reinstatement of nicotine-seeking in male and female rats.

BACKGROUND: Tobacco addiction is a relapsing disorder that constitutes a substantial worldwide health problem, with evidence suggesting that nicotine and nicotine-associated stimuli play divergent roles in maintaining smoking behavior in men and women. While animal models of tobacco addiction that utilize nicotine self-administration have become more widely established, systematic examination of the multiple factors that instigate relapse to nicotine-seeking have been limited. Here, we examined nicotine self-administration and subsequent nicotine-seeking in male and female Sprague-Dawley rats using an animal model of self-administration and relapse. METHODS: Rats lever pressed for nicotine (0.03 and 0.05 mg/kg/infusion, IV) during 15 daily 2-h sessions, followed by extinction of lever responding. Once responding was extinguished, we examined the ability of previously nicotine-paired cues (tone+light), the anxiogenic drug yohimbine (2.5mg/kg, IP), a priming injection of nicotine (0.3mg/kg, SC), or combinations of drug+cues to reinstate nicotine-seeking. RESULTS: Both males and females readily acquired nicotine self-administration and displayed comparable levels of responding and intake at both nicotine doses. Following extinction, exposure to the previously nicotine-paired cues or yohimbine, but not the nicotine-prime alone, reinstated nicotine-seeking in males and females. Moreover, when combined with nicotine-paired cues, both yohimbine and nicotine enhanced reinstatement. No significant sex differences or estrous cycle dependent changes were noted across reinstatement tests. CONCLUSIONS: These results demonstrate the ability to reinstate nicotine-seeking with multiple modalities and that exposure to nicotine-associated cues during periods of a stressful state or nicotine can increase nicotine-seeking.

Orexin-1 receptor mediation of cocaine seeking in male and female rats.

Previous studies have shown that female rats exhibit enhanced cocaine seeking during multiple phases of cocaine addiction compared with males. The orexin/hypocretin system recently has been implicated in drug addiction in male rats. Based on the known sex differences in cocaine addiction, in the current study we examined orexin-mediated cocaine seeking during self-administration, extinction, and reinstatement in age-matched male (initial weight 250-300 g) and female (initial weight 175-225 g) Sprague-Dawley rats by using the orexin-1 receptor (OX1R) antagonist 1-(2-methylbenzoxazol-6-yl)-3-[1,5]naphthyridin-4-yl urea (SB-334867) (10-30 mg/kg). OX1R blockade had no effect on established cocaine self-administration, but attenuated cocaine seeking during extinction in both male and female rats. It is noteworthy that OX1R blockade potently attenuated cue-induced reinstatement in males but had no effect on females. SB-334867 also reduced cocaine seeking during pharmacological stress-induced (yohimbine, 2.5 mg/kg) and yohimbine + cue-induced reinstatement in both sexes. SB-334867 failed to affect reinstatement induced by cocaine (10 mg/kg) in either male or female rats, but selectively reduced cocaine + cue-induced reinstatement only in males. In separate experiments examining basal and cocaine-induced locomotion, SB-334867 attenuated locomotion in both male and female rats. Finally, assessment of plasma and brain levels of SB-334867 showed that estrus females had slightly higher plasma levels than diestrus females, but no overall sex differences or estrous cycle differences were observed in plasma or brain SB-334867 concentrations. These results show that OX1R signaling plays a role in mediating cocaine seeking, but differs between the sexes for cue-induced reinstatement.

A BDNF infusion into the medial prefrontal cortex suppresses cocaine seeking in rats.

The medial prefrontal cortex (mPFC) is critical for reinstatement of cocaine seeking and is the main source of brain-derived neurotrophic factor (BDNF) to striatal regions of the brain relapse circuitry. To test the hypothesis that BDNF in the mPFC regulates cocaine-seeking behavior, rats were trained to press a lever for cocaine infusions (0.2 mg/inf, 2 h/day) paired with light+tone conditioned stimulus (CS) presentations on 10 consecutive days. After the last self-administration session, rats received a single infusion of BDNF (0.75 microg/0.5 microL/side) into the mPFC; this manipulation produced protracted effects on cocaine-seeking behavior (non-reinforced lever pressing). BDNF pretreatment administered after the last session attenuated cocaine seeking 22 h later and, remarkably, it also blocked cocaine-induced suppression of phospho-extracellular-regulated kinase and elevated BDNF immunoreactivity in the nucleus accumbens. The same pretreatment also suppressed cocaine-seeking behavior elicited by response-contingent CS presentations after 6 days of forced abstinence or extinction training, as well as a cocaine challenge injection (10 mg/kg, i.p.) after extinction training. However, BDNF infused into the mPFC had no effect on food-seeking behavior. Furthermore, BDNF infused on the sixth day of abstinence failed to alter responding, suggesting that the regulatory influence of BDNF is time limited. The suppressive effects of BDNF infused into the mPFC on cocaine seeking indicate that BDNF regulates cortical pathways implicated in relapse to drug seeking and that corticostriatal BDNF adaptations during early abstinence diminish compulsive drug seeking.