Mario D. Aceto

Cannabinoid precipitated withdrawal by the selective cannabinoid receptor antagonist, SR 141716A

Precipitated withdrawal in rats chronically exposed to delta 9-tetrahydrocannabinol, the major psychoactive principle of the marijuana plant, was unequivocally demonstrated for the first time using a selective antagonist, SR 141716A (N-(piperidin-1-yl)-5-(4-chlorophenyl)-1(2,4- dichloro-phenyl)-4-methyl-1H-pyrazole carboxamide.HCl). This demonstration should provide a powerful stimulus for the systematic study of dependency on the psychoactive cannabinoids.

Spontaneous and precipitated withdrawal with a synthetic cannabinoid, WIN 55212-2.

Physical dependence on the synthetic cannabinoid-receptor agonist R(+)-[2,3-dihydro-5-methyl-3-[(morpholinyl)methyl]pyrrolo[1,2,3-de]-1,4-benzoxazinyl]-(1-naphthalenyl) methanone mesylate (WIN 55212-2) was demonstrated in rats by the use of a chronic continuous infusion. Spontaneous withdrawal, of moderate intensity, was shown for the first time with this class of drugs of abuse. Behavioral withdrawal signs were also elicited after challenge with (N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide.HCl (SR141716A), a specific CB(1) cannabinoid-receptor antagonist. In both instances, the high-dose regimen (4, 8, 16 and 16 mg/kg/day, i.p. on days 1-4, respectively) was sufficient to evoke a typical withdrawal syndrome quantified by the signs wet-dog shakes and facial rubs. These results are discussed relative to those obtained with Delta(9)-tetrahydrocannabinol and anandamide. With Delta(9)-tetrahydrocannabinol, precipitated but not spontaneous or abrupt withdrawal was observed, and this was ascribed to pharmacokinetic properties. Anandamide, which showed little, if any, physical dependence potential, behaved atypically. Possible implications regarding pharmacotherapeutic and human abuse issues are discussed.

Dynorphin-(1–13): Effects in nontolerant and morphine-dependent rhesus monkeys

Abstract Dynorphin-(1–13) (Dyn) substitutes for morphine in morphine-dependent monkeys. At doses which substitute for morphine, this peptide did not produce morphine-like overt effects in nontolerant monkeys. In vivo, Dyn does not behave as a typical κ-agonist. These results are consistent with the suggestion that Dyns role may be that of a regulatory peptide.

Discriminative stimulus properties of the optical isomers of nicotine

Rats were trained to discriminate 200 or 400 μg/kg (-)nicotine from saline in a two-bar operant paradigm. Dose-response relationships for optically pure (-)- and (+)nicotine as well as antagonistic effects were examined in both groups of rats. The natural isomer (-)nicotine was approximately nine-times more potent than (+)nicotine. Mecamylamine produced equal blockade of the (-)- and (+)nicotine cues. Hexamethonium and atropine were without effect. These data demonstrate the possible stereospecificity of the central nicotinic receptor that mediates the stimulus effect produced by nicotine.

Antinociceptive action of nicotine and its methiodide derivatives in mice and rats

1 Three quaternary methiodides of nicotine were prepared and tested for antinociceptive activity in the mouse tail‐flick, mouse phenylquinone and rat tail‐flick tests. 2 Following peripheral administration, all three methiodides were inactive in the mouse and rat tail‐flick procedures, whereas nicotine was active in both tests, which suggested that nicotine was acting centrally. 3 Quaternization of nicotine did not eliminate antinociceptive activity as demonstrated by the intraventricular injection of the methiodides in mice. Nicotine pyrrolidine and bis methiodides were somewhat more potent than nicotine, whereas nicotine pyridine methiodide was considerably less potent than nicotine in the tail‐flick procedure. 4 Systemically administered nicotine pyrrolidine methiodine was approximately one‐third as active as nicotine in the mouse phenylquinone test; nicotine pyridine methiodide and nicotine bis methiodide were 100 and 300 times less active, respectively. 5 Hexamethonium partially blocked nicotine and nicotine pyrrolidine methiodide, whereas mecamylamine blocked nicotine completely but nicotine pyrrolidine methiodide partially. Nicotine may have both central and peripheral actions in the mouse phenylquinone test, whereas nicotine pyrrolidine methiodide may have both nicotine and non‐nicotine like antinociceptive activity. 6 The radiolabeled methiodides were synthesized and their disposition in body tissues studied. The methiodides were found to penetrate brain poorly (plasma‐to‐brain ratios > 20). 7 The methiodides were metabolized to nicotine to a small extent. This metabolism occurred to a greater extent in mice than in rats.

Etorphines: μ-opioid receptor-selective antinociception and low physical dependence capacity

Comparative analgesic studies revealed that dihydroetorphine was more potent than etorphine in the tail-flick and hot-plate tests, respectively and nearly equipotent in the phenylquinone assay. Both compounds were short acting. Studies with selective opioid receptor antagonists beta-funaltrexamine, nor-binaltorphimine and naltrindole revealed that both etorphines were mu-selective agonists. Presumptive evidence for competitive antagonism of these compounds with naloxone was provided by Schild regressions with slopes of near unity. In a suppression test in rhesus monkeys maximally dependent on morphine, dihydroetorphine and etorphine dose-dependently replaced morphine. Drug-naive simians chronically exposed to frequent, intermittent and escalating doses of dihydroetorphine for 42 days showed few withdrawal signs when challenged with large doses of naloxone or were abruptly withdrawn from this drug. The results suggest that these atypical opioids may be useful in the clinical treatment of pain and opiate drug abuse.

Nicotine binding sites and their localization in the central nervous system.

The resolution of racemic nicotine to provide optically pure (+)-nicotine and the synthesis of radiolabeled nicotine with high specific activity have facilitated the study of nicotine binding in brain. The actions of the stereoisomers of nicotine on the central nervous system are qualitatively similar in most tests but (-)-nicotine is more potent than the unnatural (+)-isomer by 10-fold or greater. Binding of radiolabeled nicotine to brain has both saturable and nonsaturable components. Only saturable binding is affected by incubation conditions such as time, temperature, pH and ion concentration. Excess concentrations of the stereoisomers are equally effective in displacing (-)-[3H]-nicotine from brain homogenates. Nevertheless, a direct comparison of (+)-[3H]-nicotine and (-)-[3H]-nicotine binding shows that the latter has a KD three times lower than the former. (-)-[3H]-Nicotine is bound to the greatest degree in hypothalamus and hippocampus, areas that also exhibited the most stereoselectivity for nicotine. However, differences in the binding affinities of the two isomers were far less than the pharmacological stereospecificity observed.

The effects of naloxone and nalorphine during the development of morphine dependence in rhesus monkeys.

A randomized and blind experimental design was used to study the effects of naloxone and nalorphine on the development of morphine dependence in monkeys. The results suggest: (a) that significant dose-related differences existed for combined numbers of withdrawal symptoms times frequency of occurrences; (b) that naloxone and nalorphine were qualitatively similar; (c) antagonists are more effective as dependence develops; (d) naloxone is approximately 10 times more potent than nalorphine, and (e) vomiting was the only withdrawal sign with which ED50s could be calculated. Dependence on morphine still increases up to 9 months after the commonly accepted 90-day stabilization period as measured by the ED50 for vomiting for naloxone.

Effects of β-funaltrexamine (β-FNA) on morphine dependence in rats and monkeys

Abstract The opioid μ receptor antagonist β-funaltrexamine (β-FNA) blocked the development of physical dependence in rats when infused simultaneously with morphine for 6 days. In addition, β-FNA given s.c. 24 h prior to the initiation and on day 3 of a 6 day period of morphine infusion in rats reduced the development of physical dependence in a dose-dependent manner. In morphine-dependent rhesus monkeys, β-FNA precipitated a prompt and long-lasting withdrawal, which was not reversed within by 30 h by subsequent injections of morphine. In contrast, naloxone-induced withdrawal lasted approximately 90 min. These results provide further evidence that β-FNA is a long-acting antagonist of the opioid μ receptor, and that this receptor has a major role in the development of morphine-induced physical dependence.

Effects of the putative antagonist NCS382 on the behavioral pharmacological actions of gammahydroxybutyrate in mice.

Abstract.Rationale: Gammahydroxybutyrate (GHB) is an endogenous chemical found in the human brain that when administered systemically readily crosses the blood–brain barrier and produces behavioral effects. Some previously reported observations, including reports of specific antagonism by NCS382 (6,7,8,9-tetrahydro-5-[H]-benzocycloheptene-5-ol–4-ylidene acetic acid), support the hypothesis that GHB is a neurotransmitter with its own receptor system. In addition to its uncertain physiological role, the recent interest in GHB has been engendered by its illicit use and abuse. Objectives: To further characterize the behavioral effects of GHB and to evaluate NCS382 for its potential antagonistic effects. Methods: Following the administration of GHB alone and in combination with NCS382, mice were tested in a Functional Observational Battery (FOB) and for their effects on locomotor activity and on schedule-maintained behavior. Additionally, spontaneous and NCS382-precipitated withdrawal in rats chronically treated with GHB was examined. Results: In the FOB, GHB generally produced depressant-like effects that were generally not reversed by NCS382. GHB also dose dependently reduced locomotor activity and rates of operant behavior, which were generally not reversed by co-administrations with NCS382. Neither spontaneous nor NCS382-precipitated signs of physical dependence were observed following chronic GHB administration. Conclusion: GHB dose dependently produced depressant-like effects on learned and unlearned behavior. The putative GHB antagonist NCS382 failed to convincingly antagonize these effects. Physical dependence was not evident following spontaneous withdrawal or NCS382 challenge. Taken together, these results suggest that NCS382s ability to antagonize GHBs effects may be very limited.