The motivation for exercise over palatable food is dictated by cannabinoid type-1 receptors

The lack of intrinsic motivation to engage in, and adhere to, physical exercise has major health consequences. However, the neurobiological bases of exercise motivation are still unknown. This study aimed at examining whether the endocannabinoid system (ECS) is involved in this process. To do so, we developed an operant conditioning paradigm wherein mice unlocked a running wheel with nose pokes. Using pharmacological tools and conditional mutants for cannabinoid type-1 (CB1) receptors, we provide evidence that CB1 receptors located on GABAergic neurons are both necessary and sufficient to positively control running motivation. Conversely, this receptor population proved dispensable for the modulation of running duration per rewarded sequence. Although the ECS mediated the motivation for another reward, namely palatable food, such a regulation was independent from CB1 receptors on GABAergic neurons. In addition, we report that the lack of CB1 receptors on GABAergic neurons decreases the preference for running over palatable food when mice were proposed an exclusive choice between the two rewards. Beyond providing a paradigm that enables motivation processes for exercise to be dissected either singly or in concurrence, this study is the first to our knowledge to identify a neurobiological mechanism that might contribute to sedentary behavior.

Arc reactivity in accumbens nucleus, amygdala and hippocampus differentiates cue over context responses during reactivation of opiate withdrawal memory

Opiate withdrawal induces an early aversive state which can be associated to contexts and/or cues, and re-exposure to either these contexts or cues may participate in craving and relapse. Nucleus accumbens (NAC), hippocampus (HPC) and basolateral amygdala (BLA) are crucial substrates for acute opiate withdrawal, and for withdrawal memory retrieval. Also HPC and BLA interacting with the NAC are suggested to respectively mediate the processing of context and cue representations of drug-related memories. Here we used a paradigm of conditioned suppression of operant food seeking, allowing to differentiate context and cue related responses, to study the influence of withdrawal memories on operant behavior and the underlying neural substrates. catFISH for Arc mRNA expression was used to discriminate cellular responses during context and cue (flashing light) periods in this paradigm. We show that reactivation of the memory of the negative affective state of withdrawal suppresses active lever pressing for food, and this conditioned suppression is generalized to the context. Interestingly the behavioral responses during the context and cue light periods are associated with differential Arc mRNA activations within the NAC, BLA, and HPC. Indeed both periods led to NAC shell activation whereas the NAC core was responsive only following the cue light period. Moreover, BLA and HPC were more responsive during cue-light and context period respectively. These data further support the already reported differential role of these brain structures on cue vs context-induced reinstatement of operant behaviors, and highlight the existence of common mechanisms for the processing of positive and aversive emotional memories.

Memories of Opiate Withdrawal Emotional States Correlate with Specific Gamma Oscillations in the Nucleus Accumbens

Affective memories associated with the negative emotional state experienced during opiate withdrawal are central in maintaining drug taking, seeking, and relapse. Nucleus accumbens (NAC) is a key structure for both acute withdrawal and withdrawal memories reactivation, but the NAC neuron coding properties underpinning the expression of these memories remain largely unknown. Here we aimed at deciphering the role of NAC neurons in the encoding and retrieval of opiate withdrawal memory. Chronic single neuron and local field potentials recordings were performed in morphine-dependent rats and placebo controls. Animals were subjected to an unbiased conditioned placed aversion protocol with one compartment (CS+) paired with naloxone-precipitated withdrawal, a second compartment with saline injection (CS-), and a third being neutral (no pairing). After conditioning, animals displayed a typical place aversion for CS+ and developed a preference for CS- characteristic of safety learning. We found that distinct NAC neurons code for CS+ or CS-. Both populations also displayed highly specific oscillatory dynamics, CS+ and CS- neurons, respectively, following 80 Hz (G80) and 60 Hz (G60) local field potential gamma rhythms. Finally, we found that the balance between G60 and G80 rhythms strongly correlated both with the ongoing behavior of the animal and the strength of the conditioning. We demonstrate here that the aversive and preferred environments are underpinned by distinct groups of NAC neurons as well as specific oscillatory dynamics. This suggest that G60/G80 interplay-established through the conditioning process-serves as a robust and versatile mechanism for a fine coding of the environment emotional weight.

Specific alterations of extracellular endocannabinoid levels in the nucleus accumbens by ethanol, heroin, and cocaine self-administration

Ethanol and opiate self-administration are sensitive to manipulations of cannabinoid CB1 receptor function and, from this, a role for the endogenous cannabinoid system in the modulation of drug reward has been hypothesized. However, direct in vivo evidence of drug-induced alterations in brain endocannabinoid (eCB) formation has been lacking. To address this issue, we explored the effect of drug self-administration on interstitial eCB levels in the nucleus accumbens (NAc) shell using in vivo microdialysis. Ethanol, heroin, and cocaine were compared because the rewarding properties of ethanol and heroin are reduced by CB1 receptor inactivation, whereas cocaine reward is less sensitive to these manipulations. Ethanol self-administration significantly increased dialysate 2-arachidonoylglycerol (2-AG) levels with no concomitant change in dialysate anandamide (AEA) concentrations. Conversely, heroin self-administration significantly increased dialysate AEA levels, and induced a subtle but significant decrease in dialysate 2-AG levels. In each case, the relative change in dialysate eCB content was significantly correlated with the amount of drug consumed. In contrast, cocaine self-administration did not alter dialysate levels of either AEA or 2-AG. Local infusion of the CB1 antagonist SR 141716A into the NAc significantly reduced ethanol, but not cocaine, self-administration. Together with our previous observation that intra-NAc SR 141716A reduces heroin self-administration, these data provide novel in vivo support for an eCB involvement in the motivational properties of ethanol and heroin but not cocaine. Furthermore, the selective effects of ethanol and heroin on interstitial 2-AG and AEA provide new insight into the distinct neurochemical profiles produced by these two abused substances.

Sensory and motor interhemispheric integration after section of different portions of the anterior corpus callosum in nonepileptic patients

OBJECTIVE

We evaluated somatosensory and motor interhemispheric integration in four patients who underwent transection of different portions of the anterior corpus callosum (CC) for removal of an intraventricular cyst. The study goal was to relate their performances to the topographical organization of the CC.

METHODS

Experimental tasks included bimanual coordination, tactile cross-localization, and intermanual and interfield comparisons of somesthetic information. Response accuracy and response times were measured. In addition, interhemispheric transmission times were obtained in the somesthetic modality.

RESULTS

Section of the middle portion of the genu caused a deficit in motor coordination, which was absent in patients with more posteriorly located lesions, whereas section of more rostral portions of the genu seemed to interfere with motor planning. The most posterior section in our sample, including the anterior portion of the body of the corpus, abolished interhemispheric transfer of simple somesthetic information (perception of touch) but not tactile discrimination (intermanual comparisons of shapes). We speculate that more complex somesthetic information is transferred through the caudal region of the body of the CC, which was spared in all patients. Thus, it seems that section of different portions of the anterior CC (genu and anterior body) produces specific deficits in interhemispheric integration in the motor and somesthetic modalities. These deficits are consistent with the anteroposterior topography of anterior callosal fibers.

CONCLUSION

The specific disconnections deficits observed in this study may provide the surgeon with information regarding the consequences of anterior callosotomy and allow for remedial measures to be implemented if required.

Cannabinoid modulation of opiate reinforcement through the ventral striatopallidal pathway

Recent evidence indicates that cannabinoid-1 (CB1) receptors play a role in the mediation of opiate reward, though the neural mechanisms for this process have not been characterized. The present experiments investigated the influence of CB1 receptors in the ventral striatopallidal system on opiate-induced neurochemical events and opiate self-administration behavior in rats. Acute morphine administration (3 mg/kg) significantly reduced ventral pallidal GABA efflux in a manner similar to that produced by heroin self-administration. This neurochemical effect was reversed by doses of the selective CB1 antagonist SR 141716A (Rimonabant; 1 and 3 mg/kg) that also significantly reduce opiate reward. Morphine-induced increases in nucleus accumbens dopamine levels were unaltered by SR 141716A. Intravenous heroin self-administration (0.02 mg/infusion) was significantly reduced by intra-accumbens, but not intraventral pallidal SR 141716A infusions (1 and 3 microg/side), implicating nucleus accumbens CB1 receptors in the modulation of opiate reinforcement. In contrast, SR14716A did not alter cocaine self-administration (0.125 mg/inf), cocaine-induced (10 mg/kg) decrements in ventral pallidal GABA efflux or cocaine-induced increases in accumbens dopamine. This is consistent with evidence that selective inactivation of CB1 receptors reduces opiate-, but not psychostimulant-maintained self-administration. The CB1 receptor agonist WIN 55,212-2 (5 mg/kg) reduced pallidal GABA efflux in a manner similar to morphine, and this effect was reversed by the opiate receptor antagonist naloxone. Collectively these findings suggest that CB1 receptors modulate opiate reward through the ventral striatopallidal projection and that the modulation of this projection system may be involved in the reciprocal behavioral effects between cannabinoids, and opioids.

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.

Intravenous heroin self-administration decreases GABA efflux in the ventral pallidum: an in vivo microdialysis study in rats

Several lines of evidence suggest that opiate-induced disinhibition of the ventral pallidum participates in the mediation of opiate reward, though direct in vivo evidence to support this hypothesis has been lacking. The present experiment tested this hypothesis by investigating alterations in ventral pallidal amino acid efflux using in vivo microdialysis during ongoing intravenous heroin self-administration in rats. Concentrations of the inhibitory amino acid GABA in ventral pallidal dialysates were significantly reduced within the first 10 min of heroin self-administration (0.02 mg per infusion; FR-1), and remained approximately 65% of presession baseline levels for the remainder of the 3-h self-administration session. Dialysate glutamate levels were unaltered during the first hour of heroin intake but significantly increased to a stable level of approximately 120% presession values during the subsequent 2 h of self-administration. Thus, heroin self-administration is associated with both decreased GABA efflux and a late phase increase in glutamate efflux in the ventral pallidum. These observations are consistent with the hypothesis that heroin self-administration results in a disinhibition and/or excitation of the ventral pallidum.

SR141716A reduces the reinforcing properties of heroin but not heroin-induced increases in nucleus accumbens dopamine in rats

The present experiments tested the hypothesis that the selective CB1 receptor antagonist SR141716A alters heroin self-administration by attenuating heroin-induced increases in nucleus accumbens dopamine levels. SR141716A pretreatment dose-dependently (0.3-3 mg/kg, i.p.) reduced operant heroin self-administration by male Wistar rats under a fixed ratio schedule of reinforcement, and significantly lowered the breaking point of responding for heroin under a progressive ratio schedule of reinforcement. These observations are consistent with recent reports that CB1 receptor inactivation reduces the rewarding properties of opiates. Operant responding for water reinforcement by water-restricted rats was unaltered by these SR141716A doses. Microdialysis tests revealed that heroin self-administration significantly increases interstitial dopamine levels in the nucleus accumbens shell of vehicle-pretreated control rats. However, whereas SR141716A pretreatment dose-dependently reduced heroin self-administration, it did not alter the heroin-associated increase in nucleus accumbens dopamine. These findings suggest that the CB1 antagonist-induced attenuation of heroin reward does not involve dopaminergic mechanisms in the nucleus accumbens shell.

Inhibition of 5-HT neurotransmission increases clonidine protective effects on naloxone-induced conditioned place aversion in morphine-dependent rats

Previous pharmacological studies have implicated serotonergic brain systems in opiate-withdrawal-precipitated conditioned place aversion. To assess this hypothesis, we tested the effects of either (i). a near-total 5,7-dihydroxytryptamine-induced lesion (90% depletion) or (ii). an acute serotonin (5-HT) inhibition induced by the specific stimulation of 5-HT1A autoreceptors (8-OHDPAT 5-100 microg/kg), on naloxone-induced conditioned place aversion in morphine-dependent rats. Morphine dependence was induced by the implantation of morphine slow-release pellets. The protective properties of clonidine (an alpha-2 adrenergic agonist classically given for opiate detoxification) were also tested after inhibition of 5-HT transmission. Serotonergic lesions in morphine-dependent rats failed to alter naloxone-induced conditioned place aversion but increased the sensitivity to the protective effects of clonidine. Acute neuropharmacological blockade of serotonin transmission also potentiated the clonidine effects on naloxone-induced conditioned place aversion. When combined with the 5-HT1A agonist 8-OHDPAT, clonidine was also found to be more potent. Further understanding of this serotonin/noradrenaline interaction might help devise new therapeutic treatments for the acute opiate withdrawal syndrome.

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

Opiate withdrawal has been correlated with decreased extracellular dopamine (DA) levels in the nucleus accumbens (NAC) of morphine-dependent rats. The authors tested the hypothesis that DA transmission plays a critical role in the induction of motivational and somatic withdrawal symptoms. First, the authors used a 6-hydroxydopamine-induced lesion of the NAC to chronically disrupt mesolimbic DA transmission. Second, global DA neurotransmission was acutely stimulated by the nonselective DA agonist (apomorphine) or inhibited by nonselective DA antagonists (droperidol or flupentixol). Morphine-dependent rats bearing 6-hydroxydopamine-induced lesions displayed naloxone-precipitated motivational and somatic withdrawal symptoms similar to those of sham-lesioned rats. Administration of apomorphine did not reduce naloxone-induced opiate withdrawal. Moreover, in total absence of naloxone, DA antagonists did not precipitate either conditioned place aversion or somatic abstinence signs in dependent rats. Taken together, these findings suggested that DA transmission is not critical for the induction of opiate withdrawal syndrome.

Neural correlates of the motivational and somatic components of naloxone-precipitated morphine withdrawal

In morphine-dependent rats, low naloxone doses have been shown to induce conditioned place aversion, which reflects the negative motivational component of opiate withdrawal. In contrast, higher naloxone doses are able to induce a 'full' withdrawal syndrome, including overt somatic signs. The c-fos gene is commonly used as a marker of neuronal reactivity to map the neural substrates that are recruited by various stimuli. Using in situ hybridization, we have analysed in the brain of morphine-dependent rats the effects of acute withdrawal syndrome precipitated by increasing naloxone doses on c-fos mRNA expression. Morphine dependence was induced by subcutaneous implantation of slow-release morphine pellets for 6 days and withdrawal was precipitated by increasing naloxone doses inducing the motivational (7.5 and 15 micro g/kg) and somatic (30 and 120 micro g/kg) components of withdrawal. Our mapping study revealed a dissociation between a set of brain structures (extended amygdala, lateral septal nucleus, basolateral amygdala and field CA1 of the hippocampus) which exhibited c-fos mRNA dose-dependent variations from the lowest naloxone doses, and many other structures (dopaminergic and noradrenergic nuclei, motor striatal areas, hypothalamic nuclei and periaqueductal grey) which were less sensitive and recruited only by the higher doses. In addition, we found opposite dose-dependent variations of c-fos gene expression within the central (increase) and the basolateral (decrease) amygdala after acute morphine withdrawal. Altogether, these results emphasize that limbic structures of the extended amygdala along with the lateral septal nucleus, the basolateral amygdala and CA1 could specifically mediate the negative motivational component of opiate withdrawal.

Dorsal and median raphe serotonergic system lesion does not alter the opiate withdrawal syndrome

Previous pharmacological studies have implicated serotonergic brain systems in opiate withdrawal. To test the hypothesis that serotonin (5-HT) has a critical role in the development of opiate withdrawal, we have employed a near-total brain 5-HT system lesion technique (90% depletion) using 5,7-dihydroxytryptamine combined with induction of opiate dependence by implantation of morphine pellets or by repeated injections of increasing doses of morphine. The effects of serotonergic neuron lesion were examined on spontaneous opiate withdrawal (changes in circadian locomotor activity) and naloxone-precipitated opiate withdrawal syndrome (the somatic aspect). The antiwithdrawal properties of clonidine, an alpha(2)-adrenoceptor agonist currently used for clinical treatment for the somatic signs of opiate withdrawal, were tested also in the lesioned rats. Our findings show that serotonergic lesions in morphine-dependent rats did not alter either the spontaneous or the naloxone-induced withdrawal syndrome (with exception of jumping behavior). Moreover, clonidine alleviated the naloxone-induced withdrawal syndrome in lesioned as well as in sham-operated morphine-dependent rats. These results demonstrate that 5-HT systems are not directly responsible for the development of the somatic opiate withdrawal syndrome in morphine-dependent rats.

Behavioral expression of opiate withdrawal is altered after prefrontocortical dopamine depletion in rats: monoaminergic correlates

The objective of this study was to establish the effects of prefrontocortical dopamine depletion on opiate withdrawal and prefrontocortical neurochemical changes elicited by morphine dependence and withdrawal. The dopaminergic content was also measured in the nucleus accumbens during withdrawal, in order to detect reactive changes induced by prefrontocortical lesion. Withdrawal was induced by naloxone in morphine-dependent rats. Monoamine levels were analyzed post-mortem by high performance liquid cromatography. The results showed that chronic morphine dependence did not modify basal levels of monoamines in sham rats, revealing neuroadaptation of prefrontocortical dopamine, noradrenaline and serotonin systems to chronic morphine. The neuroadaptive phenomenon remained after prefrontocortical lesion (> 79% dopamine depletion). On the other hand, a strong increase of dopamine, noradrenaline, and serotonin contents in the medial prefrontal cortex of sham rats was detected during opiate withdrawal. However, in lesioned rats, the increase of prefrontocortical dopamine and serotonin content, but not that of noradrenaline, was much lower. In the nucleus accumbens, prefrontocortical lesion reactively enhanced the dopaminergic tone and, although opiate withdrawal reduced dopaminergic activity in both sham and lesioned rats, this reduction was less intense in the latter group. At a behavioral level, some symptoms of physical opiate withdrawal were exacerbated in lesioned rats (writhing, mastication, teeth-chattering, global score) and exploration was reduced. The findings hence indicate that: (i) prefrontocortical monoaminergic changes play a role in the behavioral expression of opiate withdrawal; (ii) the severity of some withdrawal signs are related to the dopaminergic and serotonergic tone of the medial prefrontal cortex rather than to the noradrenergic one, and (iii) an inverse relationship between mesocortical and mesolimbic dopaminergic systems exists.

A formal total synthesis of the sesterterpenoid (+/-)-dysidiolide and approaches to the syntheses of (+/-)-6-epi-, (+/-)-15-epi-, and (+/-)-6,15-bisepidysidiolide

A formal total synthesis of the sesterterpenoid (+/-)-dysidiolide (1), a structurally novel sponge metabolite that inhibits the cdc25A protein phosphatase, and approaches to the syntheses of (+/-)-15-epi- (34), (+/-)-6-epi- (36), and (+/-)-6, 15-bisepidysidiolide (39) are described.

Total neurochemical lesion of noradrenergic neurons of the locus ceruleus does not alter either naloxone-precipitated or spontaneous opiate withdrawal nor does it influence ability of clonidine to reverse opiate withdrawal

It has been suggested that an increase firing rate of noradrenergic neurons of the locus ceruleus is responsible for the opiate withdrawal syndrome. However, lesion studies have indicated that the noradrenergic neurons of the locus ceruleus are not essential for either the expression or suppression by clonidine of opiate withdrawal. The present study was designed to determine the effect of the almost complete 6-hydroxydopamine lesion of noradrenergic neurons (94%) of the locus ceruleus on various components of the opiate withdrawal syndrome and on its protection by clonidine. Morphine dependence was induced by s.c. implantation of morphine pellets (2 x 75 mg base). The following paradigms were used: 1) naloxone-induced conditioned place aversion, 2) naloxone-precipitated acute opiate withdrawal syndrome, 3) nycthemeral locomotor activity as a measure of spontaneous opiate withdrawal. The results showed that quasi-total lesion of noradrenergic neurons of the locus ceruleus did not modify opiate dependence as revealed by naloxone-induced conditioned place aversion and the expression of an acute morphine withdrawal syndrome. Moreover, clonidine prevented the opiate withdrawal syndrome in both lesioned and sham-operated rats, suggesting that the action of clonidine is certainly mediated through postsynaptic alpha(2)-adrenoceptor stimulation. Finally, the nycthemeral locomotor activity during spontaneous morphine withdrawal did not differ between the lesioned and the sham-operated rats.