Behavioral Characterization of the Novel GABA B Receptor- Positive Modulator GS39783 (N,NЈ-Dicyclopentyl-2- methylsulfanyl-5-nitro-pyrimidine-4,6-diamine): Anxiolytic-Like Activity without Side Effects Associated with Baclofen or Benzodiazepines

ABSTRACT The role of GABA B receptors in various behavioral processes has been largely defined using the prototypical GABA B receptor agonist baclofen. However, baclofen induces sedation, hypothermia and muscle relaxation, which may interfere with its use in behavioral paradigms. Although there is much evidence for a role of the inhibitory neurotransmitter GABA in the pathophysiology of anxiety, the role of GABA B receptors in these disorders is largely unclear. We recently identified GS39783 (N,NЈ-dicyclopentyl-2-methylsulfanyl-5-nitro-pyrimidine-4,6-diamine) as a selective allosteric positive modulator at GABA B receptors. The aim of the present study was to broadly characterize the effects of GS39783 in well-validated rodent models for motor activity, cognition, and anxiety. The following tests were included: locomotor activity in rats and mice, rotarod and traction tests (including determinations of core temperature) in mice, passive avoidance in mice and rats, elevated plus maze in rats, elevated zero maze in mice and rats, stress-induced hyperthermia in mice, and pentobarbital-and ethanol-induced sleep in mice. Unlike baclofen and/or the benzodiazepine chlordiazepoxide, GS39783 had no effect in any of the tests for locomotion, cognition, temperature, or narcosis. Most interestingly, GS39783 had anxiolytic-like effects in all the tests used. Overall, the data obtained here suggest that positive modulation of GABA B receptors may serve as a novel therapeutic strategy for the development of anxiolytics, with a superior side effect profile to both baclofen and benzodiazepines

Co-administration of memantine has no effect on the in vitro or ex vivo determined acetylcholinesterase inhibition of rivastigmine in the rat brain.

Rivastigmine, a cholinesterase inhibitor, is successfully used for the symptomatic therapy of Alzheimer's disease (AD) in the clinic. The drug has a very low potential for drug-drug interactions, as has been demonstrated within large clinical trials. Memantine, recently approved by the FDA for the treatment of moderate to severe AD, acts as a low affinity, non-competitive NMDA-antagonist, on a completely different neurotransmitter system, the glutamatergic system. Given the different sites of action, the possibility to combine a cholinergic with a glutamatergic intervention as potentially superior AD therapy has recently been proposed. In vitro studies have demonstrated that memantine, when added to reversible AChE inhibitors, such as tacrine, donepezil or galantamine, did not interfere with the inhibitory action of any of these drugs. The results from the present study provide evidence that rivastigmine as a pseudo-irreversible (or slow-reversible) AChE inhibitor shares this property described for reversible inhibitors, since memantine (1-100 microM), irrespective of whether given prior to or after rivastigmine did not influence rivastigmine's AChE inhibition in vitro. A similar observation was also made under in vivo conditions (ex vivo measurements): following a 21 day chronic, oral administration of 6 micromol/kg rivastigmine alone or of a combination of rivastigmine plus memantine (6 micromol/kg p.o. of either of the two compounds), an identical degree of AChE inhibition was observed. The concentrations of rivastigmine, its metabolite NAP 226-90 and memantine were measured in the brain of the same animals. Following an equimolar oral dose (6 micromol/kg) of both compounds, the brain level of memantine exceeded that of rivastigmine + metabolite, by a factor of around 30, when measured 2 h after the final dosing, irrespective of the duration of treatment (acute, for 3 or 21 days). This indicates that neither of the two drugs showed accumulation but also, and more importantly, that memantine does not modulate the prime therapeutic action of rivastigmine (AChE inhibition) in vitro or in vivo. Clinical trials using a combination of both drugs will provide a final proof of whether a combination therapy would lead to an increased efficacy in AD patients

Competition for sucrose pellets in tetrads of male Wistar, Fischer or Sprague-Dawley rats: is intra-group ranking reflected in the level of anxiety?

Competition for palatable food or fluids within groups of rats has been previously used to mirror intra-group ranking. The paradigm of competition for sucrose pellets in non-food-deprived male Wistar rats was here extended from triads to tetrads aiming at evaluating whether the number of poor-performing rats, those animals being likely to model aspects of human psychopathologies (anxiety/depression/social withdrawal), could be increased. To evaluate potential superiority over the previously used Wistar strain, establishment and stability of the ranking was also assessed in tetrads of male Fischer and Sprague-Dawley rats. Clear and stable rank orders were seen in around 60-70% of both triads and tetrads of Wistar rats: a high-performing, a medium-performing and one (in triads) or two (in tetrads) poor-performing rats were identifiable, indicating that the number of poor-performing rats had increased in tetrads. Comparable rank orders were also seen in tetrads of Fischer and Sprague-Dawley rats. At the end of an extended period of repeated testing, tetrads of these two strains, as well as some selected Wistar tetrads, were tested in the elevated zero-maze and plasma corticosterone levels were determined. The differentiation in competition-performance among cage mates was not paralleled by a difference in performance in the elevated zero-maze or in plasma corticosterone levels in any of the three strains. These data indicate that the level of anxiety in a non-social paradigm, the elevated zero-maze, does not reflect the competition-performance within the home cage and thus, the dominant/subordinate status in this food-competition paradigm may not reflect/being caused by different levels of anxiety

A study paradigm allowing comparison of multiple high-resolution rCBV-maps for the examination of drug effects.

Owing to the neuro-vascular coupling, measurement of changes in regional cerebral blood flow and blood volume (rCBV) can be used as surrogates reflecting the effects of central nervous system active drugs on neural transmission. As most such drugs are administered orally or intramuscularly and, in many cases, beneficial effects due to drug treatment can be observed only after chronic administration for days or weeks, the evaluation of drug efficacy requires the development of acquisition and analysis tools that allow for comparison of imaging data sets obtained in multiple sessions and for multiple subjects. In the present study, high-resolution susceptibility contrast MR perfusion imaging using a super-paramagnetic contrast agent (CA) was applied to study the effect of a single oral administration of the acetylcholine-esterase inhibitor rivastigmine (Exelon) on rCBV in rats. rCBV maps were calculated from two T2-weighted three-dimensional fast-spin-echo scans recorded before and after the injection of the CA, respectively. All MRI data sets were mapped to a reference data set obtained from a normal male Sprague-Dawley rat using an automated co-registration procedure prior to the analysis for drug effects. Rivastigmine was orally administered at doses of 2, 4 or 8 mg/kg 1 h prior to the rCBV measurement. Rivastigmine increased rCBV in several brain areas including cortex, caudate putamen and hippocampus. The observed effects were dose-dependent and the changes reached the order of 5-12% as compared with baseline levels. Vehicle-treated animals showed no significant alterations of blood volume, demonstrating the reproducibility and stability of rCBV measurements

Gamma-lactams--a novel scaffold for highly potent and selective alpha 7 nicotinic acetylcholine receptor agonists.

A novel class of alpha7 nicotinic acetylcholine receptor (nAChR) agonists has been discovered through high-throughput screening. The cis gamma-lactam scaffold has been optimized to reveal highly potent and selective alpha7 nAChR agonists with in vitro activity and selectivity and with good brain penetration in mice

Behavioral characterization of the novel GABAB receptor-positive modulator GS39783 (N,N'-dicyclopentyl-2-methylsulfanyl-5-nitro-pyrimidine-4,6-diamine) : anxiolytic-like activity without side effects associated with baclofen or benzodiazepines

The role of GABAB receptors in various behavioral processes has been largely defined using the prototypical GABAB receptor agonist baclofen. However, baclofen induces sedation, hypothermia and muscle relaxation, which may interfere with its use in behavioral paradigms. Although there is much evidence for a role of the inhibitory neurotransmitter GABA in the pathophysiology of anxiety, the role of GABAB receptors in these disorders is largely unclear. We recently identified GS39783 (N,N'-dicyclopentyl-2-methylsulfanyl-5-nitro-pyrimidine-4,6-diamine) as a selective allosteric positive modulator at GABAB receptors. The aim of the present study was to broadly characterize the effects of GS39783 in well-validated rodent models for motor activity, cognition, and anxiety. The following tests were included: locomotor activity in rats and mice, rotarod and traction tests (including determinations of core temperature) in mice, passive avoidance in mice and rats, elevated plus maze in rats, elevated zero maze in mice and rats, stress-induced hyperthermia in mice, and pentobarbital- and ethanol-induced sleep in mice. Unlike baclofen and/or the benzodiazepine chlordiazepoxide, GS39783 had no effect in any of the tests for locomotion, cognition, temperature, or narcosis. Most interestingly, GS39783 had anxiolytic-like effects in all the tests used. Overall, the data obtained here suggest that positive modulation of GABAB receptors may serve as a novel therapeutic strategy for the development of anxiolytics, with a superior side effect profile to both baclofen and benzodiazepines