dizocilpine-maleate and gacyclidine

The NMDAR glutamate receptor subtype mediates various vital physiological neuronal functions. However, its excessive activation contributes to neuronal damage in a large variety of acute and chronic neurological disorders. NMDAR antagonists thus represent promising therapeutic tools that can counteract NMDARs' overactivation. Channel blockers are of special interest since they are use-dependent, thus being more potent at continuously activated NMDARs, as may be the case in pathological conditions. Nevertheless, it has been established that NMDAR antagonists, such as MK801, also have unacceptable neurotoxic effects. Presently only Memantine is considered a safe NMDAR antagonist and is used clinically. It has recently been speculated that antagonists that preferentially target extrasynaptic NMDARs would be less toxic. We previously demonstrated that the phencyclidine derivative GK11 preferentially inhibits extrasynaptic NMDARs. We thus anticipated that this compound would be safer than other known NMDAR antagonists. In this study we used whole-genome profiling of the rat cingulate cortex, a brain area that is particularly sensitive to NMDAR antagonists, to compare the potential adverse effects of GK11 and MK801. Our results showed that in contrast to GK11, the transcriptional profile of MK801 is characterized by a significant upregulation of inflammatory and stress-response genes, consistent with its high neurotoxicity. In addition, behavioural and immunohistochemical analyses confirmed marked inflammatory reactions (including astrogliosis and microglial activation) in MK801-treated, but not GK11-treated rats. Interestingly, we also showed that GK11 elicited less inflammation and neuronal damage, even when compared to Memantine, which like GK11, preferentially inhibits extrasynaptic NMDAR. As a whole, our study suggests that GK11 may be a more attractive therapeutic alternative in the treatment of CNS disorders characterized by the overactivation of glutamate receptors.

Topics: Animals; Astrocytes; Cyclohexenes; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Female; Gyrus Cinguli; Inflammation; Injections, Intraperitoneal; Memantine; Microglia; Neurons; Piperidines; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate

Over-stimulation of NMDA receptors (NMDARs) is involved in many neurodegenerative disorders. Thus, developing safe NMDAR antagonists is of high therapeutic interest. GK11 is a high affinity uncompetitive NMDAR antagonist with low intrinsic neurotoxicity, shown to be promising for treating CNS trauma. In the present study, we investigated the molecular basis of its interaction with NMDARs and compared this with the reference molecule MK801. We show, on primary cultures of hippocampal neurons, that GK11 exhibits neuroprotection properties similar to those of MK801, but in contrast with MK801, GK11 is not toxic to neurons. Using patch-clamp techniques, we also show that on NR1a/NR2B receptors, GK11 totally blocks the NMDA-mediated currents but has a six-fold lower IC(50) than MK801. On NR1a/NR2A receptors, it displays similar affinity but fails to totally prevent the currents. As NR2A is preferentially localized at synapses and NR2B at extrasynaptic sites, we investigated, using calcium imaging and patch-clamp approaches, the effects of GK11 on either synaptic or extrasynaptic NMDA-mediated responses. Here we demonstrate that in contrast with MK801, GK11 better preserve the synaptic NMDA-mediated currents. Our study supports that the selectivity of GK11 for NR2B containing receptors accounts contributes, at least partially, for its safer pharmacological profile.

Topics: Animals; Cells, Cultured; Cyclohexenes; Dizocilpine Maleate; Dose-Response Relationship, Drug; Excitatory Amino Acid Antagonists; Hippocampus; Mice; Neuroprotective Agents; Piperidines; Rats; Receptors, N-Methyl-D-Aspartate

Gacyclidine, a channel blocker of N-methyl-D-aspartate receptors (NMDAR), exhibits potent neuroprotective properties and a low self-neurotoxicity. Preventing its interaction with NMDARs we demonstrate, through the use of its enantiomers, that gacyclidine also interacts with other ('non-NMDA') binding sites. The autoradiographic study showed that these sites displayed a uniform specific binding in the forebrain and a more discrete distribution in the molecular layer of the cerebellum. The 'non-NMDA' binding sites could exert a modulatory control on glutamatergic neurotransmission.

Topics: Animals; Autoradiography; Binding Sites; Brain Chemistry; Cerebellum; Cyclohexanes; Cyclohexenes; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Glutamic Acid; Glycine; Male; Piperidines; Rats; Rats, Wistar; Receptors, N-Methyl-D-Aspartate; Stereoisomerism; Tritium

Gacyclidine, a new neuroprotectant aimed to non-competitively antagonize N-methyl-D-aspartate (NMDA) receptors, and dizocilpine blocked the hydroxyl radical response to toxic amounts of glutamate, perfused through a microdialysis implanted in the striatum of conscious rats. Furthermore, the hydroxyl radical response resulting from the infusion of lower doses of glutamate, which could not be inhibited by the same amounts of dizocilpine nor by acute alcohol exposure, still remained sensitive to gacyclidine inhibition. Thus, oxidative stress resulting from a glutamate discharge involves the activation of both NMDA receptors, and of non-NMDA mechanism(s) which, with moderate glutamate levels, were still antagonized by gacyclidine. Enhanced blockage of toxic hydroxyl radicals might explain the different and possibly higher neuroprotective property of gacyclidine as compared with other non-competitive NMDA antagonists.

Topics: Animals; Binding, Competitive; Corpus Striatum; Cyclohexanes; Cyclohexenes; Dizocilpine Maleate; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Glutamates; Hydroxyl Radical; Male; Microdialysis; N-Methylaspartate; Neuroprotective Agents; Oxidative Stress; Piperidines; Rats; Rats, Wistar; Receptors, N-Methyl-D-Aspartate

Prevention of the immediate excitotoxic phase occurring in response to spinal cord injury (SCI) is a major issue to reduce the neuronal damage responsible for any ensuing motor deficits. The present study evaluated the neuroprotective efficacy of three noncompetitive NMDA receptor antagonists: Gacyclidine (GK-11), a new compound, Dizocilpine (MK-801), and Cerestat (CNS-1102) in a rat spinal cord contusion model. To mimic human SCI, a standardized model of rat spinal cord closed contusion in which animals spontaneously and progressively recover from the induced paraplegia was employed. Such model, characterized by a slow recovery of hindlimb locomotor function enables easy quantification of the neuroprotection at both the behavioral and cellular level. The animals were treated intravenously with the respective drugs 10 min after the spinal contusion. The dose range study suggested that 1 mg/kg of Gacyclidine was the most effective dose to promote functional recovery in reducing by half the time needed to reach full locomotor recovery. Racemate and enantiomers of Gacyclidine showed similar neuroprotective effects, but treatment with the enantiomers were not as efficacious in promoting full functional recovery. Similarly, a prolonged treatment with the racemate was not as efficious as a single dose, suggesting that a prolonged blockade of the amino-excitatory neurotransmission may be deleterious. Finally, Dizocilpine and Cerestat treatments induced only a partial and delayed neuroprotective effect compared to Gacyclidine. Neuroprotection characterized by a reduction of the cystic cavity and of the astrogliosis was observed with all treatments. As Gacyclidine is already in clinical trials, the present findings suggest the premise that it is a promising agent for limiting the initial neuronal damage induced by CNS trauma leading to better functional recovery.

Topics: Animals; Astrocytes; Cyclohexanes; Cyclohexenes; Dizocilpine Maleate; Dose-Response Relationship, Drug; Drug Administration Schedule; Excitatory Amino Acid Antagonists; Female; Gliosis; Guanidines; Neuroprotective Agents; Piperidines; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Recovery of Function; Spinal Cord; Spinal Cord Injuries; Stereoisomerism

Primary cultures of embryonic rat cerebral cortex were treated after 17 days in vitro for 10 min with a single dose of the non-competitive antagonists of N-methyl-D-aspartate (NMDA) receptor MK 801, TCP, and GK 11. They were then maintained in vitro for 31, 59, or 73 days, and then processed for the immunocytochemical detection of neuron-specific enolase (NSE). Immunoreactive cells were counted in treated and control cultures, and it was found that, except at 31 days, treated cultures contained far more NSE immunoreactive cells than controls. Moreover, this effect was dose-dependent, since with both TCP and GK 11 neuron survival was significantly higher with, respectively, 20 microM and 5 microM than with the lowest concentration of 2.5 microM. We tentatively conclude that spontaneous neuron death occurring in primary cultures in vitro is at least partly related to the NMDA-associated Ca++ channel, since the common property of the molecules we used is to block this channel. The relevance of this mechanism of cell death in vitro to neuronal death in vivo is discussed.

Topics: Animals; Cell Survival; Cells, Cultured; Cerebral Cortex; Cyclohexanes; Cyclohexenes; Dizocilpine Maleate; Embryo, Mammalian; Female; N-Methylaspartate; Neurons; Phencyclidine; Piperidines; Pregnancy; Rats; Rats, Inbred Strains