Interactions between dopamine transporter and cannabinoid receptor ligands in rhesus monkeys

Rationale

??⁹-tetrahydrocannabinol (??⁹-THC) modifies dopamine efflux. However, the extent to which cannabinoid and dopamine drugs modify each other??s behavioral effects has not been fully established.

Objectives

This study examined dopamine releasers and/or transport inhibitors alone and in combination with cannabinoids in two drug discrimination assays.

Methods

Experimentally and pharmacologically experienced rhesus monkeys (n?=?5) discriminated ??⁹-THC (0.1?mg/kg i.v.) from vehicle while responding under a fixed ratio 5 schedule of stimulus-shock termination. A separate group (n?=?6) of monkeys responded under the same schedule, received daily ??⁹-THC (1?mg/kg/12?h?s.c.), and discriminated the cannabinoid antagonist rimonabant (1?mg/kg i.v.), i.e., cannabinoid withdrawal, from vehicle. A sign of withdrawal sign (head shaking) was examined in monkeys receiving ??⁹-THC daily.

Results

Rimonabant antagonized the ??⁹-THC discriminative stimulus and a dose of ??⁹-THC greater than the daily treatment attenuated the rimonabant discriminative stimulus. In monkeys discriminating ??⁹-THC, the dopamine transporter ligands cocaine, amphetamine, bupropion, RTI 113, and RTI 177 produced a maximum of 2% responding on the drug lever and blocked the discriminative stimulus effects of ??⁹-THC. In ??⁹-THC treated monkeys discriminating rimonabant, the dopamine transporter ligands partially substituted for and increased the potency of rimonabant to produce discriminative stimulus effects. The dopamine antagonist haloperidol enhanced the ??⁹-THC discriminative stimulus without significantly modifying the rimonabant discriminative stimulus. Imipramine and desipramine, which have low affinity for dopamine transporters, were less effective in modifying either the ??⁹-THC or rimonabant discriminations. The dopamine transporter ligands and haloperidol attenuated head shaking, whereas imipramine and desipramine did not.

Conclusions

Dopamine release and/or inhibition of dopamine transport blocks detection of ??⁹-THC and is potentially the mechanism by which some therapeutics (e.g., bupropion) reduce the subjective effects of marijuana and enhance the subjective effects of marijuana withdrawal.     

Cholecystokinin-A receptor ligands based on the kappa-opioid agonist tifluadom

Tifluadom, a kappa-opioid agonist and cholecystokinin-A (CCK-A) receptor antagonist, was utilized as a model to prepare a series of 2-(aminomethyl)- and 3-(aminomethyl)-1,4-benzodiazepines. These compounds were tested in vitro as inhibitors of the binding of [125I]CCK to rat pancreas and guinea pig brain receptors. All compounds with IC50's less than 100 microM proved to have greater affinity for the CCK-A receptor, with the most potent analogue, 6e, having an IC50 of 0.16 microM. The benzodiazepines described in this study are simultaneously CCK-A and opioid receptor ligands. The ramification of this dichotomy on current concepts of peptide hormone action are discussed. These results further demonstrate the versatility of the benzodiazepine core structure for designing nonpeptide ligands for peptide receptors and the ability to fine-tune the receptor interactions of these benzodiazepines by appropriate structure modifications.     

Comparison of the discriminative and neuroendocrine effects of centrally penetrating kappa-opioid agonists in rhesus monkeys

Abstract Rationale. The discriminative effects of κ-agonists may be mediated centrally, whereas their effects in a neuroendocrine biomarker assay (prolactin release) may be mediated by κ-receptors in hypothalamic areas outside the blood-brain barrier. Prolactin may thus be a useful biomarker, due to its potential to provide quantitative pharmacodynamic data for κ-opioid ligands in vivo. The potency of centrally penetrating κ-agonists could be similar in these two assays, due to their ability to occupy κ-receptor pools inside and outside the blood-brain barrier, following SC administration. Objective. To compare the potency of centrally penetrating κ-agonists in producing U69,593-like discriminative stimulus effects (U69,593 is considered a selective κ-agonist), and in producing prolactin release in rhesus monkeys. Methods. Cumulative dose-effect curves of κ-agonists (R84760, bremazocine, spiradoline and U50,488) were investigated in a food-reinforced U69,593 discrimination (n=3), and compared to those for the μ-opioids fentanyl and nalbuphine and the δ-agonist SNC80. Selected κ-opioids (R84760 and spiradoline) were compared to fentanyl, nalbuphine and SNC80 in the neuroendocrine biomarker assay, in intact female rhesus monkeys (n=4). Results. All the selective κ-agonists caused dose-dependent generalization (i.e. at least 90% drug-appropriate responding) in the U69,593 discriminating subjects, and caused robust, dose-dependent prolactin release in female rhesus monkeys. By contrast, fentanyl, nalbuphine and SNC80 did not cause generalization in these subjects. Fentanyl and nalbuphine also caused prolactin release; quantitative antagonism (apparent pK_B) experiments following nalmefene (0.01, 0.1 mg/kg) differentiated the effects of a selective κ-agonist (spiradoline) from those of a selective μ-agonist (fentanyl). A positive correlation (r=0.99) was noted between the mean log ED₅₀ of κ-agonists in the discrimination and neuroendocrine assays, from these and previous determinations. Conclusions. The potency of centrally penetrating κ-agonists in causing their neuroendocrine effects is similar to their potency in causing discriminative effects. Furthermore, apparent pK_B experiments with nalmefene differentiated the receptor mediation (i.e. κ or μ) of these compounds in the neuroendocrine biomarker assay. Electronic Publication     

Cannabinoid ligands and their effects on learning and performance in rhesus monkeys

To characterize the role of CB1 receptors in mediating the acquisition of new behavior or learning, delta 9-THC (delta 9-tetrahydrocannabinol), WIN 55,212-2 (R-(+)-(2,3-dihydro-5-methyl-3-[(4-morpho-linyl)methyl]pyrol - (1,2,3-de]-1,4-benzoxazin-6-yl)(1-naphthalenyl)methanone monomethanesulfonate), SR141716A (N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlor- phenyl)-4-methyl-1H-pyrazole-3-carboxamide hydrochloride) and cannabidiol were administered to monkeys responding under a multiple schedule of repeated acquisition and performance of conditional discriminations. SR141716A, a putative antagonist at CB1 receptors, was also administered in combination with delta 9-THC. In one component of the multiple schedule, subjects acquired a different complex discrimination each session (acquisition component), whereas in the other component the discrimination remained the same each session (performance component). Correct responding in each component was maintained by food presentation under a variable-ratio (VR) schedule, whereas incorrect responding (errors) produced a time-out. Administered prior to the start of the session, delta 9-THC and WIN 55,212-2 dose-dependently decreased overall response rate in both the acquisition and performance components. Both drugs also selectively increased the percentage errors in the acquisition component, but only at higher doses. SR141716A and cannabidiol also dose-dependently decreased overall response rate in both schedule components, but neither drug increased the percentage of errors. Decreases in response rate were also observed 24 hours after administration of SR141716A at doses greater than 1 mg/kg. When lower doses of SR141716A (0.1-1 mg/kg) were administered in combination with delta 9-THC, there was a dose-dependent antagonism of the rate-decreasing and error-increasing effects of delta 9-THC (i.e. the dose-effect curves for delta 9-THC-induced disruptions in responding were shifted rightward). In summary, CB1-receptor agonists such as delta 9-THC and WIN 55,212-2 were more disruptive to the rate and accuracy of learning in old-world monkeys than the CB1-receptor antagonist SR141716A or cannabidiol.     

Acute effects of nalmefene on LH, prolactin, and testosterone in male rhesus monkeys

The effects of the long-acting opioid antagonist, nalmefene [17-N-cyclopropylmethyl-3,14-beta-dihydroxy-4, 5-alpha-epoxy-6-methylene morphinan hydrochloride] on LH, T, and prolactin release in rhesus monkeys are unknown. The acute effects of nalmefene (0.01 and 0.10 mg/kg, IV) or placebo on LH, PRL, and T were studied, and samples were collected at 10-min intervals for 360 min to permit cluster analysis of pulsatile release patterns. LH increased significantly within 30 min after nalmefene, and remained significantly above baseline levels for 50 to 60 min (p < 0.05). Testosterone increased significantly within 70 to 80 min after nalmefene, and remained significantly above baseline for 60 min (p < 0.05). Although nalmefene antagonizes opioid agonists for 6-8 h, inhibitory feedback by testosterone appeared to limit the duration of its antagonism of endogenous opioid inhibition of LHRH and stimulation of LH. Nalmefene did not change LH or PRL pulse frequency or amplitude significantly in comparison to placebo administration.     

Biphasic effect of a kappa-opioid receptor agonist on plasma oxytocin levels in rats

The effect of the kappa-opioid receptor agonist, bremazocine, on plasma oxytocin levels in rats was measured by a sensitive radioimmunoassay. Initially, a decrease in plasma oxytocin levels was seen 30 min after injection. This was in accordance with the bremazocine inhibition of oxytocin release after submaximal electrical stimulation seen in isolated neurointermediate lobes. The initial decrease in plasma oxytocin reversed, and 4 h after injection of bremazocine a 20-fold increase in the oxytocin level was seen. The rise in plasma oxytocin was paralleled by a rise in plasma sodium. The biphasic time course of the plasma oxytocin response can be explained by a combination of an inhibition of oxytocin release from the neurohypophysis and an increased water excretion leading to an elevation in plasma sodium, which may be responsible for the late rise in plasma oxytocin. Down-regulation of the opioid receptors may also contribute to the delayed rise in plasma oxytocin.     

Model of platelet activation as experimental test system for screening kappa-opioid receptor ligands

A new model is proposed for in vitro testing the efficiency of new chemical substances with kappa-opioid receptor agonist ligand properties.     

Behavioral efficacy of diazepam against nerve agent exposure in rhesus monkeys.

The possibility that nerve agents will be used on the battlefield is real. The traditional therapy against nerve agent exposure consists of pyridostigmine pretreatment and atropine-pralidoxime chloride therapy administered after nerve agent exposure. This therapy regimen is extremely effective in preventing mortality in laboratory animals exposed to multilethal concentrations of nerve agent, yet these animals often display convulsions, brain damage, and behavioral incapacitation. We report here that the addition of diazepam to the traditional therapy for nerve agent (soman) exposure not only decreases the incidence of convulsions, but also attenuates the cognitive impairments of rhesus monkeys trained on a Serial Probe Recognition (SPR) task. Monkeys which received diazepam treatment required only 6 days before their performance on the SPR task returned to presoman exposure levels, compared to nondiazepam-treated monkeys which required 15 days. Moreover, only 1 out of the 5 monkeys which received diazepam treatment suffered tonic-clonic convulsions; in contrast all 5 monkeys which did not receive diazepam treatment experienced severe convulsive episodes. These results suggest that diazepam would be an excellent adjunct to traditional nerve agent therapy to facilitate behavioral recovery from nerve agent intoxication that might be encountered by US military personnel on the battlefield or accidental organophosphate poisoning encountered in industrial or agricultural accidents.     

The effects of kappa-opioid receptor ligands on prepulse inhibition and CRF-induced prepulse inhibition deficits in the rat

Rationale  

Kappa-opioid receptor (KOR) agonists produce dysphoria and psychotomimesis in humans. KORs are enriched in the prefrontal cortex and other brain regions that regulate mood and cognitive function. Dysregulation of the dynorphin/KOR system has been implicated in the pathogenesis of schizophrenia, depression, and bipolar disorder. Prepulse inhibition of the acoustic startle reflex (PPI), a sensorimotor gating process, is disrupted in many psychiatric disorders.     

Lack of effect of tricyclic antidepressants on serum prolactin levels

A previous report indicated that the tricyclic antidepressants imipramine and amitriptyline markedly increased plasma prolactin levels in man. We found no increases after acute or chronic treatment with either drug in usual clinical doses. The results indicate that blockade of serotonin reuptake does not affect basal prolactin levels in man.     

Effect of dietary cadmium intake on serum thyroxine and triiodothyronine concentrations in rhesus monkeys

Circulating thyroxine (T4) and triiodothyronine (T3) concentrations in rhesus monkeys were determined after various periods of cadmium administration in diet. No significant change in serum T4 and T3 levels was observed after 2 months of cadmium treatment. However, cadmium treatment for 4 months and 6 months showed a significant decrease in serum T4 and T3 levels indicating the adverse effect of long-term cadmium intake which increased gradually with duration of treatment.     

Effects of GABA agonists and GABA-A receptor modulators on cocaine discrimination in rhesus monkeys

RATIONALE: Dopaminergic systems thought to mediate the abuse-related effects of cocaine are under inhibitory control by GABAergic systems. These findings suggest that GABA agonists may attenuate some abuse-related effects of cocaine. OBJECTIVE: To assess the effects of GABA receptor agonists and GABA-A receptor modulators on cocaine discrimination in rhesus monkeys. METHODS: Rhesus monkeys were trained to discriminate 0.4 mg/kg cocaine from saline in a two-key, food-reinforced drug discrimination task. The effects of the GABA-A agonist muscimol, the GABA-B agonist baclofen, the barbiturate GABA-A receptor modulator pentobarbital, and the benzodiazepine GABA-A modulators triazolam and imidazenil were examined alone and as pretreatments to cocaine. For comparison, the effects of pentobarbital pretreatment on the cocaine-like discriminative stimulus effects of amphetamine were also examined. RESULTS: When administered alone, the GABA agonists and GABA-A receptor modulators produced primarily saline-appropriate responding. When administered as pretreatments to cocaine, pentobarbital attenuated the discriminative stimulus effects of cocaine in all monkeys tested, and the high efficacy benzodiazepine agonist triazolam attenuated cocaine's effects in three of five monkeys. Muscimol, baclofen and the low efficacy benzodiazepine agonist imidazenil did not alter cocaine's discriminative stimulus effects. Although pentobarbital blocked the effects of the monoamine reuptake blocker cocaine, it did not alter the cocaine-like effects of the monoamine releaser amphetamine. CONCLUSIONS: These results are consistent with the hypothesis that GABA-A receptor modulators attenuate the discriminative stimulus effects of cocaine in rhesus monkeys by decreasing the activity of dopaminergic systems. Direct GABA receptor agonists may be less effective in blocking the abuse-related effects of cocaine in rhesus monkeys.     

Some effects of dopamine transporter and receptor ligands on discriminative stimulus, physiologic, and directly observable indices of opioid withdrawal in rhesus monkeys

Rationale  Some monoamine uptake inhibitors (e.g., cocaine) attenuate the subjective and discriminative stimulus effects of opioid withdrawal. Objective  This study examined a role for dopamine transporters and receptors as targets for drugs to modify the discriminative stimulus effects of opioid withdrawal and further examined a subset of these drugs for their capacity to modify some directly observable and physiologic indices of withdrawal. Materials and methods  Rhesus monkeys receiving 2 mg/kg/day of l-α-acetylmethadol discriminated the opioid antagonist naltrexone (0.0178 mg/kg s.c.). Results  The naltrexone discriminative stimulus was attenuated not only by the μ agonist morphine but also by the dopamine D₂-like receptor agonists bromocryptine and quinpirole. In contrast, the naltrexone discriminative stimulus was not consistently modified by the non-selective, D₁- and D₂-like agonist apomorphine or by uptake inhibitors with high selectivity for dopamine transporters (GBR 12909, RTI 113, and RTI 177). In the same monkeys, naltrexone dose dependently decreased body temperature, increased breathing frequency, and induced directly observable signs (grimacing, salivation, and unusual posture). Hypothermia, hyperventilation, and signs of withdrawal were significantly attenuated by morphine and not by quinpirole. Conclusions  Attenuation of opioid withdrawal by D₂-like receptor agonists that have lower efficacy than dopamine, and not by uptake inhibitors with selectivity for dopamine transporters, suggests that magnitude of receptor stimulation (e.g., efficacy) and selectivity at dopamine receptors are important factors in the modulation of opioid withdrawal. Attenuation of the naltrexone discriminative stimulus by drugs that inhibit both dopamine and serotonin uptake (e.g., cocaine) could result from an inhibitory effect of serotonin on dopamine. The role of dopamine in opioid withdrawal appears to be restricted to subjective (i.e., not somatic). An erratum to this article can be found at     

Effects of medroxyprogesterone acetate on serum prolactin levels and liver prolactin binding capacity in the rat

Modifications in liver prolactin (PRL) receptor levels and serum PRL concentration induced by administration of medroxyprogesterone acetate (MPA) were investigated in rats of both sexes. MPA induced a reduction both of the levels of PRL in the serum and of liver PRL receptors in the female rat. The reduction of the number of PRL receptors caused by MPA was rapid and almost complete after 10 days of treatment and appeared earlier than that of serum PRL levels. Furthermore the MPA-induced decrease in PRL receptors was specific, since insulin binding to the same liver membranes was not affected. MPA given simultaneously with oestradiol (which increases both the number of liver PRL receptors and the serum PRL levels in the male rats) was able to counteract the increase in PRL binding induced by oestradiol. On the contrary, the oestrogen-induced increase in serum PRL was not affected by MPA treatment. Similar results were obtained using tamoxifen, a well known antioestrogenic drug. In conclusion, our results show that the reduction of PRL receptor levels induced by MPA in rat liver is specific, not correlated to serum PRL concentration, and seems to depend on the antioestrogenic activity of the drug.     

奎硫平与利培酮对女性分裂症患者的血清催乳素影响的对照研究

目的：探讨女性精神分裂症患者采用奎硫平与利培酮治疗过程中,血清催乳素（PRL）的变化。方法：选择符合诊断标准的女性精神分裂症患者64例,随机分为奎硫平组与利培酮组,治疗8周,采用阳性和阴性症状量表（PANSS）在治疗前、治疗第4周和第8周分别评定;在治疗前和治疗第4、8周测定血清PRL浓度。结果：治疗前后两组在PANSS总分上无显著差异（P〉0．05）,治疗前两组血清PRL水平无显著差异（P〉0．05）,奎硫平组治疗后PRL水平变化不明显（P均〉0．05）,利培酮组治疗后PRL水平显著升高（P均〈0．01）。结论：奎硫平不引起明显的PRL升高,而利培酮有较强的致PRL升高的作用。     

Characterization of human serum butyrylcholinesterase in rhesus monkeys: behavioral and physiological effects

The effects of a large dose of human serum butyrylcholinesterase (HuBChE) were evaluated in rhesus monkeys using a serial-probe recognition (SPR) task designed to assess attention and short-term memory. Each monkey received an intravenous injection of 150 mg (105,000 U or 30 mg/kg) of HuBChE 60 min prior to testing on the SPR task. Concurrent with the cognitive-behavioral assessment, blood was collected at various time points throughout the study and was analyzed for acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) activities, anti-BChE antibody production and gross clinical pathology (i.e., complete blood count and clinical chemistry panel). HuBChE revealed a peak blood activity of 227 U/ml at 5 min after intravenous injection and a mean residence time of approximately 72 h. No cognitive-behavioral decrements of any kind in SPR performance and no toxic signs in clinical pathology were detected in any of the blood assays during the 5 weeks of observation. Anti-HuBChE antibodies peaked at about 14 days after injection, with no concomitant behavioral changes. These results demonstrate the behavioral and physiological safety of HuBChE in rhesus monkeys and support its development as a bioscavenger for the prophylaxis of chemical warfare agent toxicity in humans.