Acute pharmacological blockade of central histamine H 3 receptors (H 3 Rs) enhances arousal/attention in rodents. However, there is little information available for other behavioral domains or for repeated administration using selective compounds. ABT-239 [4-(2-{2-[(2R)-2-methylpyrrolidinyl]ethyl}-benzofuran-5-yl)benzonitrile] exemplifies such a selective, nonimidazole H 3 R antagonist with high affinity for rat (pK i ϭ 8.9) and human (pK i ϭ 9.5) H 3 Rs. Acute functional blockade of central H 3 Rs was demonstrated by blocking the dipsogenia response to the selective H 3 R agonist (R)-␣-methylhistamine in mice. In cognition studies, acquisition of a five-trial, inhibitory avoidance test in rat pups was improved with ABT-239 (0.1-1.0 mg/kg), a 10-to 150-fold gain in potency, with similar efficacy, over previous antagonists such as thioperamide, ciproxifan, A-304121 [(4-(3-(4 -furamide], and A-349821 [(4Ј-(3-((R,R)2,5-dimethyl-pyrrolidin-1-yl)-propoxy)-biphenyl-4-yl)-morpholin-4-yl-methanone]. Efficacy in this modelwas maintained for 3 to 6 h and following repeated dosing with ABT-239. Social memory was also improved in adult (0.01-0.3 mg/kg) and aged (0.3-1.0 mg/kg) rats. In schizophrenia models, ABT-239 improved gating deficits in DBA/2 mice using prepulse inhibition of startle (1.0 -3.0 mg/kg) and N40 (1.0 -10.0 mg/kg). Furthermore, ABT-239 (1.0 mg/kg) attenuated methamphetamineinduced hyperactivity in mice. In freely moving rat microdialysis studies, ABT-239 enhanced acetylcholine release (0.1-3.0 mg/kg) in adult rat frontal cortex and hippocampus and enhanced dopamine release in frontal cortex (3.0 mg/kg), but not striatum. In summary, broad efficacy was observed with ABT-239 across animal models such that potential clinical efficacy may extend beyond disorders such as ADHD to include Alzheimer's disease and schizophrenia.

Nitric oxide (NO) is a messenger molecule that is produced in the brain from the metabolism of L-arginine to L-citruline. Growing evidence suggests a physiological role for NO in long-term potentiation (LTP). Since LTP is a form of synaptic plasticity thought to be involved in learning and memory, we have tested whether inhibition of endogenous NO production affects memory capacities ofrats. We found that the NO synthase [L-arginine, NADPH:oxygen oxidoreductase (nitric oxide-forming), EC 1.14.13.39] inhibitor N01-nitro-Larginine, at doses blocking LTP in hippocampal slices, impairs spatial learning in a radial arm maze and olfactory memory in a social recognition test. In contrast, N"-nitro-L-arginine left shock-avoidance learning unaffected. These results indicate that NO is involved in some but not all forms of memory and further support the existence of a causal link between LTP and spatial learning.Nitric oxide (NO) is a diffusible molecule endowed with intercellular messenger properties in several biological systems including the brain (1, 2). NO mediates the stimulation of soluble guanylate cyclase upon activation of N-methyl-Daspartate (NMDA) receptors (3) and serves as its own negative feedback effector by blocking NMDA-evoked responses (4, 5). This messenger is produced from the enzymatic conversion of L-arginine to L-citrulline by a constitutive NO synthase [NOS; L-arginine, NADPH:oxygen oxidoreductase (nitric oxide-forming), EC 1.14.13.39] which can readily be blocked by arginine analogs, such as Nl-nitro-Larginine [Arg(NO2); also called NG-nitro-L-arginine, where G refers to the guanidino-carbon] (6, 7).Long-term potentiation (LTP) is a persistent increase, which can last for days or weeks, in the synaptic efficacy of pathways produced by brief periods of high-frequency stimulations (HFS) (8). This phenomenon, best characterized in the hippocampus, is thought to be a cellular event involved in the acquisition, storage, or retrieval of information in the brain (9-12). We and others reported recently that NOS inhibitors and NO scavengers block hippocampal LTP in rat brain slices (13)(14)(15)(16) to irreversibly block brain NOS enzymatic activity (7). Separate groups of animals were used for each experiment. Vehicle-treated animals were used as controls.Electrophysiology. Sixteen hours after the last injection, transverse hippocampal slices (0.5-mm thick) were prepared from Sprague-Dawley rats (150-200 g) pretreated with Arg(NO2) (25-100 mg/kg of body weight i.p.) or vehicle. Slices were maintained in a submersion-type recording chamber under superfusion (2.5-3 ml/min) with gassed (95% 02/5% C02) medium containing 124 mM NaCl, 5 mM KCl, 2 mM MgSO4, 2 mM CaCl2, 26 mM NaHCO3, 1.25 mM KH2PO4, and 10 mM glucose at 32°C as described (18). Stimulation and recording electrodes were positioned in the CAl-stratum radiatum, and field excitatory postsynaptic potentials (EPSPs) were evoked every 5 s. The stimulus strength (0.1-ms duration at 2-20 V) was adjusted to evoke EPSPs of at least 0.3-mV amplitude w...

Calretinin (Cr) is a Ca 2؉ binding protein present in various populations of neurons distributed in the central and peripheral nervous systems. We have generated Cr-deficient (Cr ؊/؊ ) mice by gene targeting and have investigated the associated phenotype. Cr ؊/؊ mice were viable, and a large number of morphological, biochemical, and behavioral parameters were found unaffected. In the normal mouse hippocampus, Cr is expressed in a widely distributed subset of GABAergic interneurons and in hilar mossy cells of the dentate gyrus. Because both types of cells are part of local pathways innervating dentate granule cells and͞or pyramidal neurons, we have explored in Cr ؊/؊ mice the synaptic transmission between the perforant pathway and granule cells and at the Schaffer commissural input to CA1 pyramidal neurons. Cr ؊/؊ mice showed no alteration in basal synaptic transmission, but long-term potentiation (LTP) was impaired in the dentate gyrus. Normal LTP could be restored in the presence of the GABA A receptor antagonist bicuculline, suggesting that in Cr ؊/؊ dentate gyrus an excess of ␥-aminobutyric acid (GABA) release interferes with LTP induction. Synaptic transmission and LTP were normal in CA1 area, which contains only few Cr-positive GABAergic interneurons. Cr ؊/؊ mice performed normally in spatial memory task. These results suggest that expression of Cr contributes to the control of synaptic plasticity in mouse dentate gyrus by indirectly regulating the activity of GABAergic interneurons, and that Cr ؊/؊ mice represent a useful tool to understand the role of dentate LTP in learning and memory.

The CP 55940-mediated decreases in startle amplitude confound assessment of the effects of CB(1) receptor activation on PPI. The failure of SR 141716A to reverse disruptions in PPI, hyperactivity or stereotypy induced by non-cannabinoid psychotomimetic agents suggests that blockade of the CB(1) receptor on its own is not sufficient for antipsychotic therapy.

After the discovery of the light-activation properties of the chloroplastic NADP-dependent malate dehydrogenase in 1970, the elements of the activation pathway were identified and shown to consist of the stromal proteins of the ferredoxin/thioredoxin system. It was further demonstrated that the activation was a reductive process during which disulfides were reduced into dithiols by reduced thioredoxin. Sequence alignments with the permanently active NAD-malate dehydrogenases revealed N- and C-terminal extensions specific for the light-regulated form. A regulatory disulfide was identified in the amino-terminal extension by chemical derivatisation: its reduction was correlated to the activation of the enzyme. The use of site-directed mutagenesis techniques revealed the complexity of the intramolecular activation mechanism, showing that two different disulfides were reduced per subunit of this homodimeric enzyme: one located in the N-terminal extension, the other in the C-terminal extension. A model was proposed where the C-terminal extension locks the access to the active site, whereas the N-terminal extension governs the conformation of the active site. The identification of the catalytic histidine allowed us to test the accessibility of the active site and to demonstrate the validity of the proposed model.