Blockade of ionotropic glutamatergic transmission in the ventral tegmental area attenuates the physical signs of morphine withdrawal in rats

Venlafaxine inhibits naloxone-precipitated morphine withdrawal symptoms: Role of inflammatory cytokines and nitric oxide

Opioid-induced neuroinflammation plays a role in the development of opioid physical dependence. Moreover, nitric oxide (NO) has been implicated in several oxidative and inflammatory pathologies. Here, we sought to determine whether treatment with venlafaxine during the development of morphine dependence could inhibit naloxone-precipitated withdrawal symptoms. The involvement of neuro-inflammation related cytokines, oxidative stress, and L-arginine (L-arg)-NO pathway in these effects were also investigated. Mice received morphine (50 mg/kg/daily; s.c.), plus venlafaxine (5 and 40 mg/kg, i.p.) once a day for 3 consecutive days. In order to evaluate the possible role of L-arg-NO on the effects caused by venlafaxine, animals received L-arg, L-NAME or aminoguanidine with venlafaxine (40 mg/kg, i.p.) 30 min before each morphine injection for 3 consecutive days. On 4^th day of experiment, behavioral signs of morphine-induced physical dependence were evaluated after i.p. naloxone injection. Then, brain levels of tissue necrosis factor-alpha (TNF-α), interleukin-1-beta (IL-1β), interleukin-6 (IL-6), interleukin-10 (IL-10), brain-derived neurotrophic factor (BDNF), NO and oxidative stress factors including; total thiol, malondialdehyde (MDA) contents and glutathione peroxidase (GPx) activity were determined. Co-administration of venlafaxine (40 mg/kg) with morphine not only inhibited the naloxone-precipitated withdrawal signs including jumping and weight loss, but also reduced the up-regulation of TNF-α, IL-1β, IL-6, NO and MDA contents in mice brain tissue. However, repeated administration of venlafaxine inhibited the decrease in the brain levels of BDNF, total thiol and GPx. Pre-administration of L-NAME and aminoguanidine improved, while L-arg antagonized the venlafaxine-induced effects. These results provide evidences that venlafaxine could be used as a candidate drug to inhibit morphine withdrawal through the involvement of inflammatory cytokines and l-arginine-NO in mice.

Electrical stimulation mPFC affects morphine addiction by changing glutamate concentration in the ventral tegmental area

Morphine addiction is known as a serious social problem. Medial prefrontal cortex (mPFC) and ventral tegmental area (VTA) are two important sites of the brain that contribute to this type of addiction, and a complicated relation exists in between. In addition, neurotransmitters like glutamate and γ--Amino Butyric Acid (GABA) play an important role in the formation of these relations. Thus, the present study was undertaken to investigate these relations by evaluating the level of associated changes in the indicated neurotransmitters in the VTA, using HPLC method. This was performed after electrical stimulation and inducing lesion of mPFC and through microinjections of N-Methyl-D-Aspartate (NMDA) and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor antagonists, respectively AP5 and CNQX, into the VTA of addicted rats. Our results showed that intra-peritoneal (i.p.) administration of morphine in 9 days in the morphine group, and also electrical stimulation (100 μA) of mPFC, receiving (i.p.) morphine, caused an increase in the glutamate release in the VTA, compared to the control group, but the increase of glutamate levels in the VTA in the morphine-stimulation group was not significant, compared to the morphine group. Moreover, GABA release into this area was decreasing in morphine and morphine- stimulation groups, compared to the control group. Our findings also showed that electrical lesion (0.4 mA) of mPFC, and also microinjection of glutamate antagonists into the VTA, receiving (i.p.) morphine in rats, caused a decrease of glutamate in the VTA. Therefore, it could be concluded that the relation between mPFC and VTA is highly effective in the formation of reward system.

Adolescent rats are resistant to adaptations in excitatory and inhibitory mechanisms that modulate mesolimbic dopamine during nicotine withdrawal

Adolescent smokers report enhanced positive responses to tobacco and fewer negative effects of withdrawal from this drug than adults, and this is believed to propel higher tobacco use during adolescence. Differential dopaminergic responses to nicotine are thought to underlie these age-related effects, as adolescent rats experience lower withdrawal-related deficits in nucleus accumbens (NAcc) dopamine versus adults. This study examined whether age differences in NAcc dopamine during withdrawal are mediated by excitatory or inhibitory transmission in the ventral tegmental area (VTA) dopamine cell body region. In vivo microdialysis was used to monitor extracellular levels of glutamate and gamma-aminobutyric acid (GABA) in the VTA of adolescent and adult rats experiencing nicotine withdrawal. In adults, nicotine withdrawal produced decreases in VTA glutamate levels (44% decrease) and increases in VTA GABA levels (38% increase). In contrast, adolescents did not exhibit changes in either of these measures. Naïve controls of both ages did not display changes in NAcc dopamine, VTA glutamate, or VTA GABA following mecamylamine. These results indicate that adolescents display resistance to withdrawal-related neurochemical processes that inhibit mesolimbic dopamine function in adults experiencing nicotine withdrawal. Our findings provide a potential mechanism involving VTA amino acid neurotransmission that modulates age differences during withdrawal.

The role of memantine in the treatment of psychiatric disorders other than the dementias: a review of current preclinical and clinical evidence

Memantine, a non-competitive NMDA receptor antagonist approved for Alzheimer's disease with a good safety profile, is increasingly being studied in a variety of non-dementia psychiatric disorders. We aimed to critically review relevant literature on the use of the drug in such disorders. We performed a PubMed search of the effects of memantine in animal models of psychiatric disorders and its effects in human studies of specific psychiatric disorders. The bulk of the data relates to the effects of memantine in major depressive disorder and schizophrenia, although more recent studies have provided data on the use of the drug in bipolar disorder as an add-on. Despite interesting preclinical data, results in major depression are not encouraging. Animal studies investigating the possible usefulness of memantine in schizophrenia are controversial; however, interesting findings were obtained in open studies of schizophrenia, but negative placebo-controlled, double-blind studies cast doubt on their validity. The effects of memantine in anxiety disorders have been poorly investigated, but data indicate that the use of the drug in obsessive-compulsive disorder and post-traumatic stress disorder holds promise, while findings relating to generalized anxiety disorder are rather disappointing. Results in eating disorders, catatonia, impulse control disorders (pathological gambling), substance and alcohol abuse/dependence, and attention-deficit hyperactivity disorder are inconclusive. In most psychiatric non-Alzheimer's disease conditions, the clinical data fail to support the usefulness of memantine as monotherapy or add-on treatment However, recent preclinical and clinical findings suggest that add-on memantine may show antimanic and mood-stabilizing effects in treatment-resistant bipolar disorder.

Effects of microinjection of angiotensin II and captopril to VTA on morphine self-administration in rats

The dopaminergic mesolimbic system is considered to be crucial in rewarding actions of opiates. Recent studies have suggested probable interaction between the renin-angiotensin and mesolimbic dopaminergic systems. The present study was undertaken to investigate the effects of Ang II and captopril injection into VTA on morphine self-administration. Male Wistar rats were initially trained to receive small pellets of food by pressing the active lever in self-administration apparatus. The animals were divided into 4 groups (saline, morphine, captopril and Ang II) and were placed in self-administration apparatus and allowed to self-administer morphine (0.5 mg per infusion all test groups) or saline (saline group) during consecutive days, for 2 h/sessions. Captopril (30 mug) and Ang II (0.25 nmol) were injected into the VTA in the corresponding groups before each session. The numbers of active and passive levers pressed in each group have been recorded. The number of active lever pressing of morphine group was significantly higher than saline group (p < 0.001). In Ang II group, the number of active lever pressing was significantly lower than morphine group (p < 0.01). This study suggests the probable interaction between Ang II and opioid system in the VTA.

Reduction of opioid withdrawal and potentiation of acute opioid analgesia by systemic AV411 (ibudilast)

Morphine-induced glial proinflammatory responses have been documented to contribute to tolerance to opioid analgesia. Here, we examined whether drugs previously shown to suppress glial proinflammatory responses can alter other clinically relevant opioid effects; namely, withdrawal or acute analgesia. AV411 (ibudilast) and minocycline, drugs with distinct mechanisms of action that result in attenuation of glial proinflammatory responses, each reduced naloxone-precipitated withdrawal. Analysis of brain nuclei associated with opioid withdrawal revealed that morphine altered expression of glial activation markers, cytokines, chemokines, and a neurotrophic factor. AV411 attenuated many of these morphine-induced effects. AV411 also protected against spontaneous withdrawal-induced hyperactivity and weight loss recorded across a 12-day timecourse. Notably, in the spontaneous withdrawal study, AV411 treatment was delayed relative to the start of the morphine regimen so to also test whether AV411 could still be effective in the face of established morphine dependence, which it was. AV411 did not simply attenuate all opioid effects, as co-administering AV411 with morphine or oxycodone caused three-to-five-fold increases in acute analgesic potency, as revealed by leftward shifts in the analgesic dose response curves. Timecourse analyses revealed that plasma morphine levels were not altered by AV411, suggestive that potentiated analgesia was not simply due to prolongation of morphine exposure or increased plasma concentrations. These data support and extend similar potentiation of acute opioid analgesia by minocycline, again providing converging lines of evidence of glial involvement. Hence, suppression of glial proinflammatory responses can significantly reduce opioid withdrawal, while improving analgesia.

A psychobiological framework of the substrates that mediate nicotine use during adolescence

Adolescents are especially likely to initiate tobacco use and are more vulnerable to long-term nicotine dependence. A unifying hypothesis is proposed based largely on animals studies that adolescents, as compared to adults, experience enhanced short-term positive and reduced aversive effects of nicotine, as well as less negative effects during nicotine withdrawal. Thus, during adolescence the strong positive effects of nicotine are inadequately balanced by negative effects that contribute to nicotine dependence in adults. This review provides a neural framework to explain developmental differences within the mesolimbic pathway based on the established role of dopamine in addiction. This pathway originates in the ventral tegmental area (VTA) and terminates in the nucleus accumbens (NAcc) where dopamine is increased by nicotine but decreased during withdrawal. During adolescence, excitatory glutamatergic systems that facilitate dopamine are overdeveloped, whereas inhibitory GABAergic systems are underdeveloped. Thus, it is hypothesized that adolescents display enhanced nicotine reward and reduced withdrawal via enhanced excitation and reduced inhibition of VTA cell bodies that release dopamine in the NAcc. Although this framework focuses on adolescents and adults, it may also apply to the understanding of enhanced vulnerability to nicotine in adults that were previously exposed to nicotine during adolescence. The hypothesis presented in this review suggests that the clinical diagnostic criteria developed for nicotine dependence in adults, based primarily on withdrawal, may be inappropriate during adolescence when nicotine withdrawal does not appear to play a major role in nicotine use. Furthermore, treatment strategies involving nicotine replacement may be harmful for adolescents because it may cause enhanced vulnerability to nicotine dependence later in adulthood.

Involvement of the midbrain tectum in the unconditioned fear promoted by morphine withdrawal

The midbrain tectum structures, dorsal periaqueductal gray (dPAG) and inferior colliculus (IC), are involved in the organization of fear and anxiety states during the exposure to dangerous stimuli. Since opiate withdrawal is associated with increased anxiety in both humans and animals, this study aimed to investigate the possible sensitization of the neural substrates of fear in the midbrain tectum and its influence on the morphine withdrawal-induced anxiety. For the production of drug withdrawal, rats received morphine injections (10 mg/kg; s.c.) twice daily during 10 days. Forty-eight hours after the interruption of the chronic treatment, independent groups were probed in the elevated plus-maze and open-field tests. Additional groups of animals were implanted with a bipolar electrode into the dPAG or the IC and submitted to the electrical stimulation of these structures for the determination of the freezing and escape thresholds after 48 h of withdrawal. Our results showed that the morphine withdrawal promoted clear-cut levels of anxiety without the somatic signs of opiate withdrawal. Moreover, morphine-withdrawn rats had an increase in the reactivity to the electrical stimulation of the dPAG and the IC. These findings suggest that the increased anxiety induced by morphine withdrawal is associated with the sensitization of the neural substrates of fear in the dPAG and the IC. So, the present results give support to the hypothesis that withdrawal from chronic treatment with morphine leads to fear states possibly engendered by activation of the dPAG and IC, regardless of the production of somatic symptoms.

Glutamatergic substrates of drug addiction and alcoholism

The past two decades have witnessed a dramatic accumulation of evidence indicating that the excitatory amino acid glutamate plays an important role in drug addiction and alcoholism. The purpose of this review is to summarize findings on glutamatergic substrates of addiction, surveying data from both human and animal studies. The effects of various drugs of abuse on glutamatergic neurotransmission are discussed, as are the effects of pharmacological or genetic manipulation of various components of glutamate transmission on drug reinforcement, conditioned reward, extinction, and relapse-like behavior. In addition, glutamatergic agents that are currently in use or are undergoing testing in clinical trials for the treatment of addiction are discussed, including acamprosate, N-acetylcysteine, modafinil, topiramate, lamotrigine, gabapentin and memantine. All drugs of abuse appear to modulate glutamatergic transmission, albeit by different mechanisms, and this modulation of glutamate transmission is believed to result in long-lasting neuroplastic changes in the brain that may contribute to the perseveration of drug-seeking behavior and drug-associated memories. In general, attenuation of glutamatergic transmission reduces drug reward, reinforcement, and relapse-like behavior. On the other hand, potentiation of glutamatergic transmission appears to facilitate the extinction of drug-seeking behavior. However, attempts at identifying genetic polymorphisms in components of glutamate transmission in humans have yielded only a limited number of candidate genes that may serve as risk factors for the development of addiction. Nonetheless, manipulation of glutamatergic neurotransmission appears to be a promising avenue of research in developing improved therapeutic agents for the treatment of drug addiction and alcoholism.

Angiotensin converting enzyme inhibitor captopril modifies conditioned place preference induced by morphine and morphine withdrawal signs in rats

Angiotensin II and angiotensin converting enzyme (ACE) inhibitors have analgesic, anticonvulsant and antidepressive effects and in some cases they can antagonize morphine. In the present study effects of angiotensin II and ACE inhibitor captopril administered intracerobroventricularily (icv) on conditioned place preference induced by morphine as well as on morphine withdrawal signs has been evaluated in rats. Icv canullas were implanted in anesthetized male rats. Rats were allowed to recover from the surgery and conditioned place preference was induced by morphine, and the time spent in morphine compartment was compared in saline, morphine, captopril and Ang II groups. Morphine withdrawal signs were compared in three other groups of rats: morphine alone, captopril+morphine and Ang II+morphine 4 days after morphine injections (three times in each day) with naloxone injection on 4th day. Results with rats conditioned place preference induced by morphine showed that icv captopril decreased significantly the time in morphine compartment (P<0.01) while Ang II had no effect. In morphine dependent rats captopril decreased some withdrawal signs after naloxone precipitation (P<0.05 and P<0.01). Ang II administration augmented some of withdrawal signs than in the morphine group (P<0.01 and P<0.001). In conclusion captopril reduced conditioned place preference induced by morphine and some withdrawal signs in morphine dependent rats.

Nalfurafine, the kappa opioid agonist, inhibits icilin-induced wet-dog shakes in rats and antagonizes glutamate release in the dorsal striatum

Icilin, a cooling compound, produces vigorous wet-dog shakes in rats. We have reported previously that icilin-induced wet-dog shakes are blocked by the kappa opioid receptor agonists, nalfurafine and U50,488H, and that icilin evokes a dose- and time-dependent increase in glutamate within the dorsal striatum. Since activation of kappa opioid receptors inhibits glutamate release intrastriatally, we targeted glutamate release within the dorsal striatum using nalfurafine and examined the role of the dorsal striatum in icilin-induced wet-dog shakes, more specifically, the effect that icilin-evoked intrastriatal glutamate release has on the overt stimulant behavior. We report that nalfurafine (0.04mg/kg) inhibits icilin (0.50mg/kg)-induced wet-dog shakes and that this inhibition is reversed by intrastriatal perfusion of the kappa opioid receptor antagonist, norbinaltorphimine (100nM). Furthermore,we antagonized icilin-evoked glutamate release with nalfurafine (0.04mg/kg), and reversed inhibition of glutamate release with intrastriatal norbinaltorphimine (100nM). These findings support a central component in the behavioral response to icilin and suggest that activation of kappa opioid receptors antagonizes icilin-induced wet-dog shakes in rats by inhibiting glutamate release within the dorsal striatum.

Attenuation of morphine tolerance and dependence by aminoguanidine in mice

The effect of aminoguanidine, an inducible nitric oxide synthase (iNOS) inhibitor, on morphine-induced tolerance and dependence in mice was investigated in this study. Acute administration of aminoguanidine (20 mg/kg, p.o.) did not affect the antinociceptive effect of morphine (10 mg/kg, s.c.) as measured by the hot plate test. Repeated administration of aminoguanidine along with morphine attenuated the development of tolerance to the antinociceptive effect of morphine. Also, the development of morphine dependence as assessed by naloxone-precipitated withdrawal manifestations was reduced by co-administration of aminoguanidine. The effect of aminoguanidine on naloxone-precipitated withdrawal was enhanced by concurrent administration of the non-competitive N-methyl-d-aspartate (NMDA) receptor antagonist, dizocilpine (0.25 mg/kg, i.p.) or the non-specific nitric oxide synthase (NOS) inhibitor, l-N(G)-nitroarginine methyl ester (l-NAME; 5 mg/kg, i.p.) and antagonized by concurrent administration of the nitric oxide (NO) precursor, l-arginine (50 mg/kg, p.o.). Concomitantly, the progressive increase in NO production, but not in brain glutamate level, induced by morphine was inhibited by repeated administration of aminoguanidine along with morphine. Similarly, co-administration of aminoguanidine inhibited naloxone-induced NO overproduction, but it did not inhibit naloxone-induced elevation of brain glutamate level in morphine-dependent mice. The effect of aminoguanidine on naloxone-induced NO overproduction was potentiated by concurrent administration of dizocilpine or l-NAME and antagonized by concurrent administration of l-arginine. These results provide evidence that blockade of NO overproduction, the consequence of NMDA receptor activation, by aminoguanidine, via inhibition of iNOS, can attenuate the development of morphine tolerance and dependence.

Ethological analysis of scopolamine treatment or pretreatment in morphine dependent rats

Although scopolamine is currently used to treat morphine addiction in humans, its extensive actions on behaviors have not been systematically analyzed yet, and the underlying mechanisms of its effects still remain ambiguous. The present study was carried out to clarify the possible mechanisms by evaluating the effects of scopolamine pretreatment and treatment on naloxone-precipitated withdrawal signs and some of other general behaviors in morphine dependent rats. Our results showed that scopolamine pretreatment and treatment attenuated naloxone-precipitated withdrawal signs including jumping, writhing posture, weight loss, genital grooming, teeth-chattering, ptosis, diarrhea and irritability, except for wet dog shakes, while general behaviors such as water intake, urine volume and morphine excretion in urine were increased. Our findings suggest that scopolamine has significant actions in the treatment of opiate addiction, which might result from increasing morphine excretion from urine.

Endogenous opiates and behavior: 2004

This paper is the 27th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning over 30 years of research. It summarizes papers published during 2004 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, and the roles of these opioid peptides and receptors in pain and analgesia; stress and social status; tolerance and dependence; learning and memory; eating and drinking; alcohol and drugs of abuse; sexual activity and hormones, pregnancy, development and endocrinology; mental illness and mood; seizures and neurologic disorders; electrical-related activity and neurophysiology; general activity and locomotion; gastrointestinal, renal and hepatic functions; cardiovascular responses; respiration and thermoregulation; and immunological responses.