RTI-4793-14, a new ligand with high affinity and selectivity for the (+)-MK801-insensitive [3H]1-]1-(2-thienyl)cyclohexyl]piperidine binding site (PCP site 2) of guinea pig brain

Can N-Methyl-D-Aspartate Receptor Hypofunction in Schizophrenia Be Localized to an Individual Cell Type?

Hypofunction of N-methyl-D-aspartate glutamate receptors (NMDARs), whether caused by endogenous factors like auto-antibodies or mutations, or by pharmacological or genetic manipulations, produces a wide variety of deficits which overlap with-but do not precisely match-the symptom spectrum of schizophrenia. In order to understand how NMDAR hypofunction leads to different components of the syndrome, it is necessary to take into account which neuronal subtypes are particularly affected by it in terms of detrimental functional alterations. We provide a comprehensive overview detailing findings in rodent models with cell type-specific knockout of NMDARs. Regarding inhibitory cortical cells, an emerging model suggests that NMDAR hypofunction in parvalbumin (PV) positive interneurons is a potential risk factor for this disease. PV interneurons display a selective vulnerability resulting from a combination of genetic, cellular, and environmental factors that produce pathological multi-level positive feedback loops. Central to this are two antioxidant mechanisms-NMDAR activity and perineuronal nets-which are themselves impaired by oxidative stress, amplifying disinhibition. However, NMDAR hypofunction in excitatory pyramidal cells also produces a range of schizophrenia-related deficits, in particular maladaptive learning and memory recall. Furthermore, NMDAR blockade in the thalamus disturbs thalamocortical communication, and NMDAR ablation in dopaminergic neurons may provoke over-generalization in associative learning, which could relate to the positive symptom domain. Therefore, NMDAR hypofunction can produce schizophrenia-related effects through an action on various different circuits and cell types.

DARK Classics in Chemical Neuroscience: Phencyclidine (PCP)

Phencyclidine (PCP, "angel dust", an arylcyclohexylamine) was the first non-natural, man-made illicit drug of abuse, and was coined 'the most dangerous drug in America" in the late 1970s (amidst sensational horror stories of the drug's effects); however, few other illicit drugs have had such a significant and broad impact on society-both good and bad. Originally developed as a new class of anesthetic, PCP-derived psychosis gave way to the PCP hypothesis of schizophrenia (later coined the NMDA receptor hypofunction hypothesis or the glutamate hypothesis of schizophrenia), which continues to drive therapeutic discovery for schizophrenia today. PCP also led to the discovery of ketamine (and a new paradigm for the treatment of major depression), as well as other illicit, designer drugs, such as methoxetamine (MXE) and a new wave of Internet commerce for illicit drugs (sold as research chemicals, or RCs). Furthermore, PCP is a significant contaminant/additive of many illegal drugs sold today, due to its ease of preparation by clandestine chemists. Here, we will review the history, importance, synthesis (both legal and clandestine), pharmacology, drug metabolism, and folklore of PCP, a true DARK classic in chemical neuroscience.

"Atypical" neuromodulatory profile of glutapyrone, a representative of a novel 'class' of amino acid-containing dipeptide-mimicking 1,4-dihydropyridine (DHP) compounds: in vitro and in vivo studies

Glutapyrone, a disodium salt of 2-(2,6-dimethyl-3,5-diethoxycarbonyl-1,4-dihydropyridine-4-carboxamido)- glutaric acid, is a representative of a novel 'class' of amino acid-containing 1,4-dihydropyridine (DHP) compounds developed at the Latvian Institute of Organic Synthesis, Riga, Latvia. Conceptually, the glutapyrone molecule can be regarded as a dipeptide-mimicking structure formed by the "free" amino acid (glutamate) moiety and "crypto" (built into the DHP cycle) amino acid ("GABA") elements. Both of these amino acids are joined by the peptide bond. This compound unlike classical DHPs lacks calcium antagonistic or agonistic properties. Our previous studies revealed a profound and long-term anticonvulsant, stress-protective and neurodeficit-preventive activities of glutapyrone. In view of structural properties the role of glutamatergic mechanisms in the mediation of central effects of glutapyrone was considered. In the present study glutapyrone at the concentration range of 1 microM(-1) mM failed to effect both NMDA ([3H]TCP) and non-NMDA ([3H]KA and [3H]AMPA) receptor ligand binding in the rat cortical membranes in vitro. The compound markedly enhanced motor hyperactivity induced by the NMDA antagonist PCP and the dopamine releasing compound D-amphetamine in the rats. Glutapyrone displayed activity in a variety of animal models relevant for affective/depressive disorders in humans i.e. reserpine-induced ptosis and hypothermia, forced swimming test and open field test. These data indicate that the unusually "broad" pharmacological spectrum of glutapyrone might involve concomitant actions on multiple neurotransmitter systems, particularly, GABA-ergic and the catecholamines. It is discussed whether these functional properties are secondary to action on intracellular events, predominantly, G protein-related since glutapyrone appears to lack direct interactions with a number of receptors including ionotropic glutamate and GABA(A)/Bzd receptors.

Studies of the biogenic amine transporters. VII. Characterization of a novel cocaine binding site identified with [125I]RTI-55 in membranes prepared from human, monkey and guinea pig caudate

[125I]RTI-55 is a cocaine analog with high affinity for dopamine (DA) and serotonin (5-HT) transporters. Quantitative ligand binding studies revealed a novel high affinity [125I]RTI-55 binding site assayed under 5-HT transporter (SERT) conditions which has low affinity for almost all classic biogenic amine transporter ligands, including high affinity 5-HT transporter inhibitors such as paroxetine, but which retains high affinity for cocaine analogs. This site, termed SERT(site2) for its detection under 5-HT transporter conditions (not for an association with the SERT) occurs in monkey caudate, human caudate, and guinea pig caudate membranes, but not in rat caudate membranes. SERT(site2) is distinguished from the DA transporter (DAT) and SERT by several criteria, including a distinct ligand-selectivity profile, the inability to detect SERT(site2) in cells stably expressing the cloned human DAT, and insensitivity to irreversible ligands which inhibit [125I]RTI-55 binding to the DAT and SERT. Perhaps the most striking finding about SERT(site2) is that a wide range of representative antidepressant agents have very low affinity for SERT(site2). The affinity of cocaine for this site is not very different from the concentration cocaine achieves in the brain at pharmacological doses. Viewed collectively with the observation that ligands with high affinity for SERT(site2) are mostly cocaine analogs, these data lead us to speculate that actions of cocaine which differ from those of classic biogenic amine uptake inhibitors may be mediated in part via SERT(site2).