吗啡对糖奖赏剥夺所致大鼠挫折反应的抑制作用

In this study,a T-maze-based frustration model in rats was established using sucrose-reward de-privation.The results revealed that rats maintained a 75% preference for the sucrose-reward arm in the reward phase.During the sucrose-deprivation frustration phase,both the preference for the sucrose-deprivation arm (62.5%) and time spent waiting in the sucrose-deprivation arm decreased.Acute injection of morphine increased the preference in a dose-dependent fashion,and prolonged the waiting duration in the sucrose-deprivation arm.These findings indicate that morphine specifically inhibited the frustration response induced by sucrose reward deprivation.To further elucidate the pharmacological mechanisms involved,the opioid receptor antagonist naloxone was given to model rats prior to the injection of morphine.The results revealed that naloxone administration markedly attenuated the anti-frustration-like effects of 3 mg/kg morphine treatment.These findings suggest that morphine attenuates the frustration-like response to reward deprivation in rats through the opioid receptor.     

Suppressive effects of morphine injected into the ventral bed nucleus of the stria terminalis on the affective,but not sensory,component of pain in rats

Pain is a complex experience with both sensory and affective components. Clinical and preclinical studies have shown that the affective component of pain can be reduced by doses of morphine lower than those necessary to reduce the sensory component. Although the neural mechanisms underlying the effects of morphine on the sensory component of pain have been investigated extensively, those influencing the affective component remain to be elucidated. The bed nucleus of the stria terminalis (BNST) has been implicated in the regulation of various negative emotional states, including aversion, anxiety and fear. Thus, this study aimed to clarify the role of the ventral part of the BNST (vBNST) in the actions of morphine on the affective and sensory components of pain. First, the effects of intra‐vBNST injections of morphine on intraplantar formalin‐induced conditioned place aversion (CPA) and nociceptive behaviors were investigated. Intra‐vBNST injections of morphine reduced CPA without affecting nociceptive behaviors, which suggests that intra‐vBNST morphine alters the affective, but not sensory, component of pain. Next, to examine the effects of morphine on neuronal excitability in type II vBNST neurons, whole‐cell patch‐clamp recordings were performed in brain slices. Bath application of morphine hyperpolarized type II vBNST neurons. Thus, the suppressive effects of intra‐vBNST morphine on pain‐induced aversion may be due to its inhibitory effects on neuronal excitability in type II vBNST neurons. These results suggest that the vBNST is a key brain region involved in the suppressive effects of morphine on the affective component of pain.     

The mGluR5 antagonist MPEP reduces the conditioned rewarding effects of cocaine but not other drugs of abuse

We examined the ability of 2-methyl-6-(phenylethynyl)-pyridine (MPEP), a selective antagonist of the type 5 metabotropic glutamate receptor (mGluR5), to reduce the rewarding effects of various drugs of abuse in the conditioned place preference (CPP) paradigm. Mice were treated with MPEP (1, 5, and 20 mg/kg i.p.) 10 min prior to cocaine (15 mg/kg i.p.), D-amphetamine (2 mg/kg i.p.), nicotine (0.5 mg/kg i.p.), morphine (5 mg/kg i.p.), or ethanol (2 g/kg i.p.) on 3 successive days of CPP conditioning trials. MPEP pretreatment dose-dependently reduced the development of CPP for cocaine only. When tested alone at the doses effective in reducing CPP, MPEP produced neither a place preference nor aversion. These data provide further support for a role of the mGluR5 receptor in the rewarding effects of cocaine.     

Nociception in mice after chronic stress and chronic narcotic antagonists during maturation

The effects of chronic, mild stress and chronic narcotic antagonism during maturation of mice on the sensitivity to pain and to the analgesic effect of morphine were examined. Analgesia was measured using the tail-flick assay. Chronic stress, produced simply by the subcutaneous injection of mice twice daily with saline starting day 5 postpartum, produced an increase in the sensitivity of these mice, when mature, to the analgesic effect of morphine. A similar schedule of saline injections for 4 weeks in adult mice did not alter the sensitivity of those mice to the analgesic effects of morphine. Chronic injections of narcotic antagonists during maturation did not produce an effect on morphine analgesia different from that after chronic injections of saline. However chronic exposure to narcotic antagonists since conception, compared to chronic injections since day 5 postpartum in the offspring, did produce differential effects on the control tail-flick latencies such that naloxone during gestation decreased, while naloxone during gestation and postpartum increased tail-flick latencies. These data suggest that exposure to chronic stress during early development is responsible for an altered sensitivity to narcotic analgesics while exposure to naloxone during maturation affects pain perception.     

Opiate mechanism in reward-related neuronal responses during operant feeding behavior of the monkey

Reward-related neuronal activity and its modulation by morphine and naloxone was investigated by extracellular single neuron recording and electrophoretic application of drugs in the lateral hypothalamus, during operant feeding of the monkey. Morphine-sensitive neurons responded more often during bar press and ingestion-reward phases. Naloxone blocked only ingestion-reward responses, especially the inhibitory ones. The results suggest that the central opiate system can be involved in reward-related neuronal responses in the lateral hypothalamic area of the monkey.     

Endogenous opioid systems: Physiological role in the self-limitation of seizures

Immediately following a seizure, the severity of subsequent seizures is significantly reduced. The involvement of endogenous opioid systems as a physiological regulator of this postseizure inhibition was studied in rats using repeated maximal electroshock (MES) seizures. Both the opiate antagonist (−)-naloxone and morphine tolerance abolished the progressive seizure protection associated with repeated MES. We propose that endogenous opioids, activated by a prior seizure, provide a central homeostatic inhibitory mechanism which may be responsible for the initiation of a postictal refractory state in the epileptic.     

The Type IV phosphodiesterase inhibitor rolipram interferes with drug-induced conditioned place preference but not immediate early gene induction in mice

Behavioural effects of psychostimulant and opiate drugs are mediated in part by cAMP pathways operating in the nucleus accumbens. Degradation of cAMP occurs through the action of phosphodiesterases, such as the Type IV phosphodiesterases (PDE4s) that are found throughout the brain. To examine the potential role of PDE4 in reward-mediated behaviour, we measured the effects of rolipram, a PDE4 selective inhibitor, on cocaine (18 mg/kg i.p.) and morphine (5 mg/kg s.c.) conditioned place preference in Swiss Webster mice. Rolipram (0, 0.2 or 1.0 mg/kg i.p.) given 30 min prior to drug administration dose-dependently reduced conditioning due to both cocaine and morphine. However, rolipram did not affect place preference induced by food, nor did it prevent the expression of a previously established place preference conditioned by cocaine or morphine. In a second experiment, rolipram administered 30 min prior to a single cocaine injection (50 mg/kg i.p.), did not alter cocaine-induced c-Fos expression in the caudate putamen or nucleus accumbens core. However, rolipram, but not cocaine, induced c-Fos in the nucleus accumbens shell. These results indicate that elevation of cAMP in neurons that express PDE4s may attenuate the rewarding properties of cocaine and morphine, but does not alter the cocaine signalling cascade that induces c-Fos expression. Thus, PDE4-mediated regulation of cAMP levels could underlie the establishment of reward valence to abused drugs.     

Naloxone can act as an analgesic agent without measurable chronic side effects in mice with a mutant mu-opioid receptor expressed in different sites of pain pathway

Midbrain periaqueductal gray (PAG) and spinal cord dorsal horn are major action sites of opioid analgesics in the pain pathway. Our previous study has shown that opioid antagonists activate MORS196A-CSTA (a mutant of mu-opioid receptor) as full agonists in vitro cell models and naloxone showed antinociceptive effects after the expression of MORS196A-CSTA in the spinal cord in mice. The purpose of this study is to investigate the site-directed antinociceptive effects of naloxone in mice injected with dsAAV-MORS196A-CSTA-EGFP at spinal cord or at periaqueductal gray. MORS196A-CSTA-EGFP was administered to ICR mice using dsAAV as vector. We measured MORS196A-CSTA-EGFP expression by detecting the EGFP visualization with a fluorescence microscope. The antinociceptive effect of naloxone was determined by tail-flick test and hot plate test. Drug rewarding effect was evaluated by the conditioned place preference test. Naloxone (10 mg/kg, s.c.) elicited both supraspinal and spinal antinociceptive responses in mice injected with the virus at PAG while only spinal antinociceptive response was observed in mice injected with virus at dorsal horn region. Chronic naloxone treatment did not induce physical dependence or rewarding effect in mice injected with MORS196A-CSTA-EGFP in spinal cord or PAG. These data suggest that the observed naloxone-induced antinociceptive response is the consequence of the local expression of MORS196A-CSTA at specific sites of pain pathway. Injection of such MOR mutant and the systemic administration of naloxone can be a new strategy in the management of chronic pain without the various side effects associated with the use of morphine.     

Role of imidazoline receptors in the anti-aversive properties of clonidine during opiate withdrawal in rats

Clonidine is used as a treatment for heroin addiction. Previous studies have reported that clonidine attenuated conditioned place aversion (CPA) to naloxone-precipitated opiate withdrawal by acting on alpha2 adrenoceptors (alpha2R). However, clonidine acts as a partial agonist both at alpha2R and at imidazoline-1 receptors (I1Rs). The current study was designed to determine the role of I1R in the induction of naloxone-induced CPA in morphine-dependent rats. Morphine dependence was induced by subcutaneous implantation of morphine pellets. Morphine-dependent rats were tested in a three-chamber place-aversion apparatus. A range of agonists were chosen on the basis of their differential selectivity for alpha2R and I1R. As expected, pretreatment with clonidine prevented naloxone-induced CPA. By contrast, pretreatment with a selective alpha2R agonist (UK14304) failed to prevent the CPA. We then tested whether the high affinity of clonidine for I1R was responsible for the difference between these two alpha2R agonists. Rilmenidine (a mixed alpha2R/I1R agonist) attenuated aversion to opiate withdrawal in a dose-dependent manner. The action of clonidine on I1R was studied by co-administering clonidine with RX821002, a specific alpha2R antagonist. Co-treatment with RX821002 and clonidine blocked naloxone-induced CPA. These results indicate that the pharmacologically protective effects of clonidine on naloxone-induced CPA are related to actions on I1RS as well as alpha2Rs.     

The acute administration of the selective dopamine D(3) receptor antagonist SB-277011A reverses conditioned place aversion produced by naloxone precipitated withdrawal from acute morphine administration in rats

We examined the effect of SB-277011A, a selective D(3) receptor antagonist, on the conditioned place aversion (CPA) response associated with naloxone-induced withdrawal from acute morphine administration in male Sprague-Dawley rats. Morphine (5.6 mg/kg i.p.) was given, followed 4 hrs later by naloxone (0.3 mg/kg i.p.) and prior to placing the animals in one specific chamber of the test apparatus. All animals were subjected to 2 of these trials. A significant CPA occurred in animals that received an i.p. injection of vehicle 30 minutes prior to the measurement of chamber preference. The pretreatment of animals (30 minutes prior to testing) with 3 mg/kg i.p. of SB-277011A did not significantly alter the CPA compared to animals treated with vehicle (1 ml/kg i.p. of deionized distilled water). In contrast, the acute pretreatment of animals with 6, 12 or 24 mg/kg i.p. of SB-277011A significantly decreased the CPA compared to vehicle-treated animals. In fact, the 12 and 24 mg/kg doses of SB-277011A significantly increased the time spent in the chamber where animals were paired with morphine and naloxone. These results suggest that the selective antagonism of D(3) receptors attenuates the CPA produced by a model of naloxone-induced withdrawal from acute morphine dependence.     

Positive reinforcement and c‐Fos expression following abuse‐like thinner inhalation in mice: Behavioural and immunohistochemical assessment

Thinners are organic solvents widely used in industrial applications, but they have also been subject to abuse by inhalation for their psychoactive and rewarding properties. In spite of the prevalence of inhalant abuse, the addictive potential and pathways mediating their reinforcing effects are not yet fully understood and thus still subject of further investigations. Here, we assessed in mice the locomotor activity and the ability of paint thinner to reinforce the conditioning in the place preference paradigm following acute (1 day), subchronic (6 weeks) and chronic (12 weeks) exposures to 300 and 600 ppm of thinner vapor. While locomotor activity was unaffected by the different thinner treatments, a positive conditioned place preference to inhaled thinner was found upon subchronic and chronic exposures. To investigate the activated brain structures underlying such behavioural changes, we analyzed the distribution of c‐Fos immunoreactivity, a marker for neuronal activation, following acute and repeated exposures to 600 ppm of thinner. Notably, thinner exposure increased the number of c‐Fos immunoreactive neurons with increasing duration of exposure in the majority of structures examined; including those typically involved in the processing of rewarding or emotionally stimuli (e.g., ventral tegmental area, core and shell of nucleus accumbens, amygdala, bed nucleus of the stria terminalis, and cingulate cortex), and olfactory stimuli (e.g., piriform cortex and olfactory tubercle). Moreover, prolonged, but not acute thinner inhalation significantly increased c‐Fos immunoreactivity in all hippocampal subregions. Taken together, the expanded distribution of thinner‐induced c‐Fos expression may underlie the observed positive reinforcement upon long‐term thinner inhalation.     

Effect of gene transfer of GLT-1, a glutamate transporter, into the locus coeruleus by recombinant adenoviruses on morphine physical dependence in rats

There is a body of evidence implying the involvement of the central glutamatergic system in morphine dependence. We previously reported changes in the mRNA expression of a glial glutamate transporter GLT-1 in some brain regions of morphine-dependent and naloxone-precipitated withdrawal rats, and inhibition of morphine physical dependence by a glutamate transporter activator in mice. These findings support the possibility that glutamate transporters such as GLT-1 are involved in morphine dependence. In this study, we examined the effects of gene transfer of GLT-1 into the locus coeruleus (LC) by recombinant adenoviruses on morphine physical dependence in rats. We constructed recombinant adenoviruses that successfully delivered the GLT-1 gene in vitro and in vivo. Local overexpression of GLT-1 within the bilateral LC by the recombinant adenoviruses before implantation of the morphine pellet significantly inhibited various somatic signs of naloxone-precipitated morphine withdrawal, compared with the control. These results suggest that GLT-1 within the LC plays an inhibitory role in morphine physical dependence.     

The caudal part of the posterior insula of rats participates in the maintenance but not the acquisition of morphine conditioned place preference

The heterogeneous insular cortex plays an interoceptive role in drug addiction by signaling the availability of drugs of abuse. Here, we tested whether the caudal part of the multisensory posterior insula (PI) stores somatosensory‐associated rewarding memories. Using Sprague Dawley rats as subjects, we first established a morphine‐induced conditioned place preference (CPP) paradigm, mainly based on somatic cues. Secondly, an electrolytic lesion of the caudal portion of the PI was carried out before and after the establishment of CPP, respectively. Our data demonstrated that the caudal PI lesions disrupted the maintenance, but not the acquisition of morphine‐induced CPP. Lesion or subtle disruption of the PI had no major impact on locomotor activity. These findings indicate that the caudal portion of the PI might be involved in either the storage or the retrieval of morphine CPP memory.     

An increase in opiate receptor-sites is associated with enhanced cardiovascular depressant, but not respiratory depressant action of morphine

Rats were treated for 4 weeks with a constant infusion of 2 mg/kg/h of the opiate antagonist naloxone. This treatment increased μ-, σ- and ξ-binding sites by 60–180% in several brain regions, suggesting effective blockade of the 3 types of opiate sites. The significance of changes in opiate binding sites for opiate receptor mediated physiological responses were examined using cardiovascular and respiratory responses to morphine (assessed after elimination of naloxone) as physiological parameters. Chronically naloxone-treated rats showed no alteration in respiratory responses to morphine, whereas there was a marked supersensitivity to depressor and bradycardic effects and a loss of pressor and tachycardic effects of morphine. These data are the first indication that cardiovascular effects of opiates vary with changes in central opiate receptor levels. Our observations, moreover, show that there are complex relationships between receptor number and receptor-mediated effects of opiates.     

The influence of opiate agonists on day-night feeding rhythms in young and old mice

Daily rhythms of feeding behavior and responses to ketocyclazocine, morphine and naloxone were measured in young (1-2 months) and old (24-30 months) male CF-1 mice. All of the mice consumed more food at night than in the day-time, though this nocturnal peak was markedly reduced in the old animals, who consumed more in the day. The young mice also displayed a significant nocturnal enhancement in ketocyclazocine- and morphine-stimulated feeding. This day-night rhythm in ingestive responses was absent in the old mice. In comparison to the young mice, the opiate-stimulated food consumptions of the old animals were reduced at all times. Additionally, the old animals failed to show any day-night variations in the suppressive effects of naloxone on deprivation-induced food intake that were displayed by the young animals.     

Morphine tolerance and dependence in the nociceptin receptor knockout mice

Summary. Here we report the involvement of nociceptin receptor in tolerance to morphine-induced antinociception and in morphine dependence. There was no different nociceptive perception and antinociceptive effects of morphine between wild-type and the nociceptin receptor knockout mice. Tolerance to morphine (10 mg/kg)-induced antinociception was developed in both wild-type and the nociceptin receptor knockout mice after administration of morphine (10 mg/kg) twice a day for 5 days. When naloxone (5 mg/kg) was administered to mice treated with morphine repeatedly on the 6th day, morphine withdrawal syndrome was observed in both wild-type and the nociceptin receptor knockout mice, which were accompanied by the elevation of cyclic AMP levels. While naloxone benzoylhydrazone (1 mg/kg), a putative antagonist for nociceptin receptor/naloxone benzoylhydrazone-sensitive sites, also induced the morphine withdrawal signs in both wild-type and the nociceptin receptor knockout mice, the jumping signs in the nociceptin receptor knockout mice were less severe than those in wild-type mice. Treatment with naloxone benzoylhydrazone in morphine-dependent wild-type mice caused a significant increase in cyclic AMP levels in the thalamus while it had no effect in the nociceptin receptor knockout mice. The analysis of opioid mu-receptor binding showed no difference between wild-type and the nociceptin receptor knockout mice. These results suggest that the nociceptin receptor/naloxone benzoylhydrazone-sensitive sites contribute to the induction of morphine withdrawal syndrome in part. Furthermore, it is demonstrated that morphine withdrawal syndrome excepting jumping can be induced by naloxone benzoylhydrazone without any changes in the cyclic AMP levels in the thalamus. Received July 17, 2000; accepted July 11, 2001     

The reinforcing effects of chronic D-amphetamine and morphine are impaired in a line of memory-deficient mice overexpressing calcineurin

It has recently emerged that there is a commonality in the molecular mechanisms underlying long-term neuronal changes in drug addiction and those mediating synaptic plasticity associated with learning and memory. In the hippocampus, the calcium-calmodulin-dependent protein phosphatase calcineurin plays a pivotal role in the molecular mechanisms that underlie learning and memory functions. Transgenic mice that express an active form of calcineurin specifically in forebrain structures have previously been shown to have a deficit in the transition from short- to long-term memory. Here, we investigated the involvement of calcineurin in the motivational effects of amphetamine and morphine using this line of transgenic mice (CN98). Our results showed that amphetamine and morphine did not induce conditioned place preference in calcineurin-mutant mice, whereas food remained an efficient reinforcer. In addition, behavioural sensitization to these two drugs, as measured by horizontal locomotion, was disturbed in the transgenic mice. In contrast, neither the horizontal locomotion in response to acute D-amphetamine or morphine nor the somatic signs of morphine withdrawal were affected in calcineurin mutant mice compared to their wild-type littermates. Our data indicate that calcineurin-mediated protein dephosphorylation in the hippocampus is involved in the long-term effects of drugs of abuse without influencing the motivational response to a natural reward or the physical component of opioid withdrawal. The present results emphasize the essential role of hippocampal-dependent learning and memory in the development of drug addiction.     

Anxiogenic treatments do not increase fear-potentiated startle in mice.

BACKGROUND: In rodents, the fear-potentiated startle paradigm (FPS; exaggerated startle as a measure of the conditioned fear response to cues associated with footshock) has demonstrated predictive validity for anxiolytic drugs. The predictive validity of the model for anxiogenic drugs, however, remains unclear. Therefore, we evaluated the bi-directionality of the FPS model for anxiety-modulating compounds in mice. METHODS: The clinical anxiogenics FG-7142 (1-20 mg/kg), yohimbine (.1-10 mg/kg), and m-Chlorophenylpiperazine (mCPP; .3-3 mg/kg), and the putative anxiogenics atipamezole (.3-3 mg/kg) and corticotropin-releasing factor (h/r-CRF; .03-1 microg) were tested in DBA/1J mice trained for FPS. RESULTS: Contrary to predictions, FG-7142 (10 and 20 mg/kg) and yohimbine (10 mg/kg) reduced FPS in mice without affecting baseline startle. Atipamezole (3 mg/kg), mCPP (3 mg/kg), and h/r-CRF (.3, 1 microg) did not affect FPS, but increased startle independently from the presence of the cue. FG-7142 and h/r-CRF had similar effects in 129SvEv mice. CONCLUSIONS: Murine FPS is not bi-directionally predictive for anxiety-modulating compounds, although murine baseline startle may have some utility as a bi-directional model of anxiety. These data corroborate the recent hypothesis that systems mediating FPS are independent from systems mediating increased startle from unconditioned and putatively anxiogenic stimuli.