Changes in dopaminergic neurotransmission do not alter somatic or motivational opiate withdrawal-induced symptoms in rats

Increased dopamine receptor activity in the nucleus accumbens shell ameliorates anxiety during drug withdrawal

A number of lines of evidence suggest that negative emotional symptoms of withdrawal involve reduced activity in the mesolimbic dopamine system. This study examined the contribution of dopaminergic signaling in structures downstream of the ventral tegmental area to withdrawal from acute morphine exposure, measured as potentiation of the acoustic startle reflex. Systemic administration of the general dopamine receptor agonist apomorphine or a cocktail of the D1-like receptor agonist SKF82958 and the D2-like receptor agonist quinpirole attenuated potentiated startle during morphine withdrawal. This effect was replicated by apomorphine infusion into the nucleus accumbens shell. Finally, apomorphine injection was shown to relieve startle potentiation during nicotine withdrawal and conditioned place aversion to morphine withdrawal. These results suggest that transient activation of the ventral tegmental area mesolimbic dopamine system triggers the expression of anxiety and aversion during withdrawal from multiple classes of abused drugs.

An anatomical basis for opponent process mechanisms of opiate withdrawal

Opponent process theory predicts that the first step in the induction of drug withdrawal is the activation of reward-related circuitry. Using the acoustic startle reflex as a model of anxiety-like behavior in rats, we show the emergence of a negative affective state during withdrawal after direct infusion of morphine into the ventral tegmental area (VTA), the origin of the mesolimbic dopamine system. Potentiation of startle during withdrawal from systemic morphine exposure requires a decrease in opiate receptor stimulation in the VTA and can be relieved by administration of the dopamine receptor agonist apomorphine. Together, our results suggest that the emergence of anxiety during withdrawal from acute opiate exposure begins with activation of VTA mesolimbic dopamine circuitry, providing a mechanism for the opponent process view of withdrawal.

Involvement of actin rearrangements within the amygdala and the dorsal hippocampus in aversive memories of drug withdrawal in acute morphine-dependent rats

Aversive memories of drug withdrawal can generate a motivational state leading to compulsive drug taking. Changes in synaptic plasticity may be involved in the formation of aversive memories. Dynamic rearrangement of the cytoskeletal actin, a major structural component of the dendritic spine, regulates synaptic plasticity. Here, the potential involvement of actin rearrangements in the induction of aversive memories of morphine withdrawal was examined. We found that lesions of the amygdala or dorsal hippocampus (DH) but not nucleus accumbens (NAc) impaired conditioned place aversion (CPA) of acute morphine-dependent rats. Accordingly, conditioned morphine withdrawal induced actin rearrangements in the amygdala and the DH but not in the NAc. In addition, we found that conditioned morphine withdrawal also increased activity-regulated cytoskeletal-associated protein (Arc) expression in the amygdala but not in the DH, although actin rearrangements were observed in both areas. We further found that inhibition of actin rearrangements by intra-amygdala or intra-DH injections of latrunculin A, an inhibitor of actin polymerization, significantly attenuated CPA. Furthermore, we found that manipulation of amygdala beta-adrenoceptor activity by its antagonist propranolol and agonist clenbuterol differentially altered actin rearrangements in the DH. Therefore, our findings reveal that actin rearrangements in the amygdala and the DH are required for the acquisition and consolidation of the aversive memories of drug withdrawal and that the beta-noradrenergic system within the amygdala modulates aversive memory consolidation by regulating actin rearrangements but not Arc protein expression in the DH, which is distinct from its role in modulation of inhibitory avoidance memory.

Development, extinction and reinstatement of morphine withdrawal-induced conditioned place aversion in rats

The motivational component of drug withdrawal may contribute to drug seeking and relapse through the negative reinforcement-based process. Here, we used conditioned place aversion (CPA) induced by naloxone-precipitated morphine withdrawal to measure the aversive effects. Using an unbiased conditioning paradigm, we treated rats with morphine hydrochloride [(10 mg/kg intraperitoneally (i.p.)] twice per day (at 08:00 and 20:00) for 6.5 days (from day 1 to day 7 morning), while gave them naloxone (0.3 mg/kg i.p.) on day 6, a precipitated withdrawal paired with a compartment that caused CPA to the side. Then, the rats exhibited CPA were received 12 extinction trials from days 7 to 13, by daily exposed to the two compartments for free exploration. On day 13, the rats with extinguished CPA were treated with a priming injection of morphine (10 mg/kg i.p.) followed by naloxone (0.3 mg/kg i.p.) that reliably reinstated CPA. These results demonstrated that repeatedly morphine-treated rats showed the formation, extinction and reinstatement of CPA. The present CPA model induced by these procedures may be useful for studying the biological mechanisms underlying the aversive motivational component of opiate withdrawal.

Measuring reward with the conditioned place preference (CPP) paradigm: update of the last decade

Conditioned place preference (CPP) continues to be one of the most popular models to study the motivational effects of drugs and non-drug treatments in experimental animals. This is obvious from a steady year-to-year increase in the number of publications reporting the use this model. Since the compilation of the preceding review in 1998, more than 1000 new studies using place conditioning have been published, and the aim of the present review is to provide an overview of these recent publications. There are a number of trends and developments that are obvious in the literature of the last decade. First, as more and more knockout and transgenic animals become available, place conditioning is increasingly used to assess the motivational effects of drugs or non-drug rewards in genetically modified animals. Second, there is a still small but growing literature on the use of place conditioning to study the motivational aspects of pain, a field of pre-clinical research that has so far received little attention, because of the lack of appropriate animal models. Third, place conditioning continues to be widely used to study tolerance and sensitization to the rewarding effects of drugs induced by pre-treatment regimens. Fourth, extinction/reinstatement procedures in place conditioning are becoming increasingly popular. This interesting approach is thought to model certain aspects of relapse to addictive behavior and has previously almost exclusively been studied in drug self-administration paradigms. It has now also become established in the place conditioning literature and provides an additional and technically easy approach to this important phenomenon. The enormous number of studies to be covered in this review prevented in-depth discussion of many methodological, pharmacological or neurobiological aspects; to a large extent, the presentation of data had to be limited to a short and condensed summary of the most relevant findings.

Active immunisation against nicotine blocks the reward facilitating effects of nicotine and partially prevents nicotine withdrawal in the rat as measured by dopamine output in the nucleus accumbens, brain reward thresholds and somatic signs

We recently showed that active immunisation with the nicotine immunoconjugate IP18-KLH reduces the nicotine-induced increase in dopamine (DA) output in the nucleus accumbens (NAC) and prevents reinstatement of nicotine-seeking behaviour in rats. These effects are mediated by altered distribution of nicotine, resulting in reduced amounts of nicotine reaching the brain, thereby interfering with the rewarding properties of the drug. The present study was designed to explore the effect of immunisation against nicotine on mecamylamine-precipitated nicotine withdrawal as assessed by the reduction in DA output in the NAC in rats. Measuring brain reward thresholds and somatic signs of nicotine withdrawal, the effects of immunisation were also tested during chronic nicotine treatment and after its withdrawal. Finally, we examined the effect of immunisation on challenge injections of nicotine on brain reward thresholds after the increases in somatic signs and reward thresholds associated with nicotine withdrawal had dissipated. The results show that immunisation with IP18-KLH prevented the decrease in DA output in the NAC associated with mecamylamine-precipitated nicotine withdrawal. Moreover, immunisation against nicotine did not precipitate a withdrawal syndrome, as measured by brain reward thresholds and somatic signs, in rats chronically exposed to nicotine. Furthermore, the withdrawal syndrome elicited after cessation of chronic nicotine administration was attenuated in immunised rats compared to that of mock-immunised rats. Finally, the lowering in reward thresholds after nicotine challenge injections was attenuated in both naïve and previously nicotine-exposed immunised rats. In conclusion, the present results show that immunisation with IP18-KLH did not precipitate nicotine withdrawal in rats. Thus, immunisation with IP18-KLH may not elicit nicotine withdrawal in smokers either. Furthermore, since the withdrawal syndrome in rats was attenuated by immunisation, the nicotine withdrawal in smokers should not be worsened but may even be ameliorated during a quit attempt.

Barium potentiates the conditioned aversion to, but not the somatic signs of, morphine withdrawal in mice

The effect of barium, a putative blocker of G-protein-activated inwardly rectifying potassium (GIRK) channels, on naltrexone-precipitated withdrawal signs in morphine-dependent mice was investigated. Mice were chronically treated with morphine (8-45 mg/kg) for 6 days. The morphine-dependent mice were then given naltrexone (1 and 3 mg/kg), after which they showed several somatic signs of withdrawal, as well as conditioned aversion, increased cortical noradrenaline turnover, and decreased dopamine turnover in the limbic forebrain. Pretreatment with barium (1.25 and 2.5 nmol) significantly potentiated the naltrexone-precipitated conditioned aversion and augmented the decrease in dopamine turnover in the limbic forebrain. However, barium pretreatment did not affect the naltrexone-precipitated somatic signs of withdrawal and increased cortical noradrenaline turnover. These findings suggest that modification of GIRK channels may be involved in the expression of aversion to morphine withdrawal mediated through the dopaminergic system but it is not involved in the somatic signs of morphine withdrawal mediated through the noradrenergic system.

Endogenous opiates and behavior: 2003

This paper is the 26th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning over a quarter-century of research. It summarizes papers published during 2003 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).