A circuitry model of the expression of behavioral sensitization to amphetamine-like psychostimulants

110

Social stress can engender behavioral and neural sensitization and this process appears to enhance the transition to compulsive drug abuse. Exposures to brief social defeat stress in rats have significant consequences on cocaine-reinforced behavior and on the level of functional activation within regions of the mesocorticolimbic dopamine system. The objectives of the current study were to examine the enduring consequences of brief episodes of social defeat stress on cocaine bingeing (during 24 h of continuous access) and on the emergence of neural adaptations as revealed by zif268 immediate early gene expression. Adult, male Long-Evans rats were subjected to four 25 min episodes of social defeat (once every 72 h). After 2 months, cocaine binges or zif268 mRNA gene expression were studied after confirming behavioral cross-sensitization to stimulant challenge. Sensitization to social defeat increased cocaine intake during a 24 h binge, effectively abolishing the typical circadian pattern of intake. Furthermore, 60 days after exposure to the sensitizing regimen of social defeat, levels of functional activation, measured by zif268 mRNA expression, in the central and medial amygdala were increased, while levels of activation in the medial prefrontal cortex were decreased. Persistent stress-induced levels of zif268 in the central and medial amygdala were attenuated by an injection of amphetamine (1.0 mg/kg). Divergent changes in zif268 within the amygdala and cortex 2 months after social defeat stress indicate the vulnerability of distinct cellular populations in networks that modulate the behavioral actions of psychomotor stimulants.

Section: Resultssupporting

confidence: 84%

Brief Social Defeat Stress: Long Lasting Effects on Cocaine Taking During a Binge and Zif268 mRNA Expression in the Amygdala and Prefrontal Cortex

Covington

Kikusui

Goodhue

et al. 2004

110

“…Similarly, locomotor sensitization may also reflect alterations in dopamine transmission, as an enhanced dopamine response following repeated administration of psychostimulant drugs, including nicotine, is linked with the expression of behavioral sensitization (Benwell and Balfour, 1992;Pierce and Kalivas, 1997;Vezina, 2004). Interestingly, nicotine can augment dopamine transporter function (Middleton et al, 2004) and density (Harrod et al, 2004), suggesting that enduring nicotine-induced alterations in dopamine transporter function and/or density may play a role in the enhanced effect of repeated methylphenidate following nicotine treatment.…”

Section: Discussionmentioning

confidence: 99%

Methylphenidate Enhances the Abuse-Related Behavioral Effects of Nicotine in Rats: Intravenous Self-Administration, Drug Discrimination, and Locomotor Cross-Sensitization

Wooters

Neugebauer

Rush

et al. 2007

Stimulant drugs, including D-amphetamine, cocaine, and methylphenidate, increase cigarette smoking in controlled human laboratory experiments. Although the mechanism(s) underlying this effect are unknown, it is possible that stimulants may enhance directly the abuse-related effects of nicotine. In the present study, we characterized the behavioral pharmacological interactions between methylphenidate and nicotine in the intravenous self-administration, drug discrimination, and locomotor cross-sensitization procedures. Adult male Sprague-Dawley rats were trained to respond for intravenous nicotine (0.01 or 0.03 mg/kg/infusion) or sucrose, and the acute effects of methylphenidate (1.25-10 mg/kg) were determined; in addition, separate groups of rats were treated with methylphenidate (2.5 mg/kg) or saline before 12 consecutive nicotine (0.03 mg/kg/infusion) self-administration sessions. Next, the discriminative stimulus effects of nicotine (0.03-0.3 mg/kg) and methylphenidate (1.25-10 mg/kg), alone and in combination with a low nicotine dose (0.056 mg/kg), were tested in nicotine-trained rats. Finally, the locomotor effect of repeated methylphenidate (2.5 mg/kg) was tested in rats previously treated with nicotine (0.2-0.8 mg/kg). Results indicated that acute methylphenidate increased the rate of nicotine self-administration at doses that reduced sucrose-maintained responding; furthermore, tolerance to this effect was not apparent following repeated methylphenidate. Methylphenidate, while not substituting for nicotine alone, dose-dependently enhanced the discriminative stimulus effect of a low nicotine dose. In addition, repeated nicotine exposure promoted the development of locomotor sensitization to methylphenidate. Taken together with recent clinical findings, these results suggest that methylphenidate may enhance the abuse-related behavioral effects of nicotine, perhaps increasing vulnerability to tobacco dependence.

“…However, the molecular events through which dopamine concentrations are increased in the NA markedly differ between the various drugs of abuse. Stimulants like amphetamine or cocaine increase dopamine release in the NA either directly or by blockade of the dopamine transporter (Reith et al, 1986;Pierce and Kalivas, 1997). Nicotine increases the firing rate of the dopaminergic neurons in the VTA via nicotinic acetylcholine receptors located on the cell bodies of these neurons (Mereu et al, 1987).…”

Section: Brain Metabolic Ethanol Effectsmentioning

confidence: 99%

Acute Alcohol Effects on Neuronal and Attentional Processing: Striatal Reward System and Inhibitory Sensory Interactions under Acute Ethanol Challenge

Schreckenberger

Amberg

Scheurich

et al. 2004

The acute influence of ethanol on cerebral activity induces complex psycho-physiological effects that are considerably more pronounced during acute ethanol influx than during maximal blood alcohol concentration (elimination phase). Despite the psychiatric and forensic relevance of these different ethanol effects, the underlying neuronal mechanisms are still unclear. In total, 20 male healthy volunteers were investigated each with three different experimental conditions in a randomized order using an intravenous ethanol challenge (40 g bolus infusion): during influx phase, elimination phase, and under placebo condition. During and after the ethanol (or placebo) infusion, neuropsychological testing of divided attention for visual and auditory stimuli was performed with subsequent 18-FDG PET acquisition. The PET data were analysed using SPM99. Ethanol influx and elimination phase showed focal activations in the bilateral striatum and frontal cortex and deactivations in the occipital cortex. The comparison of influx phase vs elimination phase revealed activations in the anterior cingulate and right prefrontal cortex, relevant deactivations were found in the left superior temporal cortex including Wernicke's area. Neuropsychological testing showed an attentional impairment under ethanol influx compared to ethanol elimination and placebo with an inverse correlation of the attentional performance for auditory stimuli to occipital activity and for visual stimuli to the left temporal (including auditory) cortex. Acute ethanol administration in healthy volunteers stimulates those striatal regions that are considered to have a particular relevance for alcohol craving ('reward system'). Modality specific reciprocal inhibition of sensory cortex activity seems to be relevant for attentional performance during acute alcohol impact.