C(21)-fluorinated thevinol scaffold for opioid ligands. 21,21,21-Trifluoro-6-O-nororvinols: Design, synthesis and analgesic activity.

Thevinols and their 3-O-demethylated relatives, orvinols, are derivatives of the Diels-Alder adduct of natural alkaloid thebaine with methyl vinyl ketone. Taken together, thevinols and orvinols constitute an important family of opioid receptor (OR) ligands playing an important role in both the OR mediated antinociception and OR antagonism. Herein, we disclose for the first time the OR activity of orvinols fluorinated within the pharmocophore associated with C(20) and its surrounding along with a dependence of the activity profile on the substituent at N(17). Starting from thevinone and 18,19-dihydrothevinone, a family of C(21)-fluorinated orvinols bearing methyl, cyclopropylmethyl (CPM), and allyl substituent at N(17) was synthesized. The fluorinated compounds were evaluated for OR activity. The orvinols bearing three fluorine atoms at C(21) were found to retain the properties of OR ligands and their activity profile depends on the substituent at N(17). Pilot in vivo experiments in a model of acute pain (tail-flick test in mice) revealed that 6-O-desmethyl-21,21,21-trifluoro-20-methylorvinol at doses 1.0-10.0 mg/kg (s.c.) exhibits analgesic activity at the level of morphine for a duration of 30-180 min. Its N(17)-CPM counterpart demonstrated the partial opioid agonist properties. The N(17)-allyl substituted derivative showed no analgesic activity. In vivo evaluation of an analgesic activity indicates that 21,21,21-trifluoro-20-methylorvinols represent a novel family of OR ligands related to buprenorphine, diprenorphine, etc. These compounds are promising for the structure-activity relationship studies among the thevinol/orvinol series as well as for a search for new OR ligands with potentially valuable pharmacological profiles.

Inhibition of PDE10A in a New Rat Model of Severe Dopamine Depletion Suggests New Approach to Non-Dopamine Parkinson's Disease Therapy.

Parkinson's disease is the second most common neurodegenerative pathology. Due to the limitations of existing therapeutic approaches, novel anti-parkinsonian medicines with non-dopamine mechanisms of action are clearly needed. One of the promising pharmacological targets for anti-Parkinson drug development is phosphodiesterase (PDE) 10A. The stimulating motor effects of PDE10A inhibition were detected only under the conditions of partial dopamine depletion. The results raise the question of whether PDE10A inhibitors are able to restore locomotor activity when dopamine levels are very low. To address this issue, we (1) developed and validated the rat model of acute severe dopamine deficiency and (2) tested the action of PDE10A inhibitor MP-10 in this model. All experiments were performed in dopamine transporter knockout (DAT-KO) rats. A tyrosine hydroxylase inhibitor, α-Methyl-DL-tyrosine (αMPT), was used as an agent to cause extreme dopamine deficiency. In vivo tests included estimation of locomotor activity and catalepsy levels in the bar test. Additionally, we evaluated the tissue content of dopamine in brain samples by HPLC analysis. The acute administration of αMPT to DAT-KO rats caused severe depletion of dopamine, immobility, and catalepsy (Dopamine-Deficient DAT-KO (DDD) rats). As expected, treatment with the L-DOPA and carbidopa combination restored the motor functions of DDD rats. Strikingly, administration of MP-10 also fully reversed immobility and catalepsy in DDD rats. According to neurochemical studies, the action of MP-10, in contrast to L-DOPA + carbidopa, seems to be dopamine-independent. These observations indicate that targeting PDE10A may represent a new promising approach in the development of non-dopamine therapies for Parkinson's disease.

Chronic Lithium Treatment Affects Anxious Behaviors and theExpression of Serotonergic Genes in Midbrain Raphe Nuclei of Defeated Male Mice.

There is experimental evidence that chronic social defeat stress is accompanied by the development of an anxiety, development of a depression-like state, and downregulation of serotonergic genes in midbrain raphe nuclei of male mice. Our study was aimed at investigating the effects of chronic lithium chloride (LiCl) administration on anxiety behavior and the expression of serotonergic genes in midbrain raphe nuclei of the affected mice. A pronounced anxiety-like state in male mice was induced by chronic social defeat stress in daily agonistic interactions. After 6 days of this stress, defeated mice were chronically treated with saline or LiCl (100 mg/kg, i.p., 2 weeks) during the continuing agonistic interactions. Anxiety was assessed by behavioral tests. RT-PCR was used to determine Tph2, Htr1a, Htr5b, and Slc6a4 mRNA expression. The results revealed anxiolytic-like effects of LiCl on social communication in the partition test and anxiogenic-like effects in both elevated plus-maze and social interaction tests. Chronic LiCl treatment upregulated serotonergic genes in midbrain raphe nuclei. Thus, LiCl effects depend on the treatment mode, psycho-emotional state of the animal, and experimental context (tests). It is assumed that increased expression of serotonergic genes is accompanied by serotonergic system activation and, as a side effect, by higher anxiety.

The Action of TAAR1 Agonist RO5263397 on Executive Functions in Rats.

Trace amine-associated receptor 1 (TAAR1) is a widely recognized new perspective target for the neuropsychiatric pharmacological treatment. Despite a growing number of studies investigating TAAR1 role in the animal models of different pathologies, information of TAAR1 agonists impact on executive cognitive functions is limited. The goal of the present study was to evaluate the activity of highly selective partial TAAR1 agonist RO5263397 on various executive cognitive functions. The results of the present study demonstrated that the pretreatment with RO5263397 was able to increase attention and decrease cognitive flexibility in rats. The analysis of the RO5263397 action on impulsivity demonstrated that the TAAR1 activation failed to affect premature responding but was able to slightly modify impulsive choice. Problem solving was resistant to the pharmacological intervention.

Morphine-induced Straub tail reaction in mice treated with serotonergic compounds.

Constitutively active 5-HT2 receptors have been suggested to contribute to motoneuronal excitability, muscle spasms and spasticity. Accordingly, 5-HT2C receptor inverse agonists have been demonstrated in pilot experiments to reduce spasticity in animal model of spasticity and patients with spinal cord injuries. Thus, 5-HT2C receptor inverse agonists may represent a novel class of anti-spasticity agents justifying a search for compounds with robust 5-HT2C receptor inverse agonist activity either among the existing medications or via a dedicated drug discovery program. Morphine-induced Straub tail response in mice is regarded as a model of transient spasticity that may be suitable for supporting such drug discovery efforts. Subcutaneous injection of morphine (10-60mg/kg) induced a dose-dependent Straub tail reaction in male Swiss mice with maximum response obtained 15-30min after the morphine administration. When given prior to morphine, 5-HT2B/2C receptor inverse agonists cyproheptadine (1-10mg/kg, i.p.) and SB206553 (0.3-3mg/kg, i.p.) diminished Straub tail reaction dose-dependently without affecting spontaneous locomotor activity. In contrast, 5-HT2B/2C receptor antagonist methysergide (1-5.6mg/kg, i.p.) and 5-HT2C receptor antagonist SB242084 (1-5.6mg/kg, i.p.) as well as 5-HT2A receptor inverse agonist pimavanserin (1-10mg/kg, i.p.) had no appreciable effects on Straub tail response. Taken together, the findings indicate that constitutive activity of 5-HT2B/2C receptor may be involved in the mechanisms of morphine-induced spasticity. Thus, morphine-induced Straub tail response may be evaluated further as a candidate higher throughput test to identify 5-HT2C receptor inverse agonists with anti-spasticity effects in vivo.

Effects of low-affinity NMDA receptor channel blockers in two rat models of chronic pain.

In contrast to conventional opioid analgesics, antagonists acting at the N-methyl-d-aspartate (NMDA) subtype of glutamate receptors are capable of suppressing pain-related phenomena in chronic pain models while having little or no effect on acute nociception. One of the few clinically used NMDA receptor antagonists, memantine, differs from prototypic antagonists with psychotomimetic activity such as phencyclidine and (+)MK-801, in showing lower receptor affinity, faster unblocking kinetics and stronger voltage-dependency. Recently, a series of novel amino-alkyl-cyclohexanes was reported to interact with NMDA receptors in a manner similar to that of memantine. The present study aimed to evaluate the effects of these compounds as well as (+)MK-801 and memantine in two rat models of chronic pain and the rotarod test. Unlike (+)MK-801 and memantine, most of the tested compounds were inactive against tactile allodynia induced by sciatic nerve ligation. On the other hand, all tested drugs were found to inhibit formalin-induced grooming behavior-a model of chronic pain induction. In agreement with previous reports on the effects of NMDA receptor antagonists in similar assays, the late phase seemed to be inhibited to a greater extent than the early phase. For all tested compounds, inhibition of formalin-induced behaviors occurred at dose levels that were also producing significant motor deficits (rotarod test). These results confirm low efficacy of acute administration of NMDA receptor antagonists in the models of established pain states. Thus, studies on the prevention and management of chronic pain should focus on preemptive or long-term administration of NMDA receptor antagonists.

Facilitation of aggressive and sexual behaviors by saccharin deprivation in rats.

The 'deprivation effect' (DE) phenomenon is expressed as an increase in the level of free choice consumption of drugs, alcohol, or saccharin following a period of forced abstinence in humans and in several species of laboratory animals. The DE may reflect relapse-like drinking and be relevant for modeling addictive behaviors. In humans, drug or alcohol abstinence is commonly associated with the increased physical and sexual abuse. The present study aimed to study whether aggressive and sexual behaviors are affected by the conditions known to result in the DE. Adult male Wistar rats had unlimited free choice access to water and saccharin-containing solution (0.1%, w/v). After the preference for saccharin was established, animals underwent repeated 7-day-long episodes of saccharin deprivation. It was found that (i) aggressive and sexual behaviors were facilitated after 7 days of saccharin deprivation, and (ii) DE was significantly reduced in animals that were allowed to interact with the nonaggressive male or receptive female conspecifics during the last day of deprivation exposure. These results suggest that the saccharin deprivation exposures may facilitate aggressive and sexual behaviors. Alternative behavioral strategy may serve as a mechanism of coping with the deprivation state.