The behavioral and cognitive effects of nicotine suggest that nicotinic acetylcholine receptors (nAChRs) participate in central nervous system (CNS) function. Although nAChR subunit messenger RNA (mRNA) and nicotine binding sites are common in the brain, there is little evidence for synapses mediated by nAChRs in the CNS. To test whether, CNS nAChRs might modify rather than mediate transmission, the regulation of excitatory synaptic transmission by these receptors was examined. Nanomolar concentrations of nicotine enhanced both glutamatergic and cholinergic synaptic transmission by activation of presynaptic nAChRs that increased presynaptic [Ca2]i. Pharmacological and subunit deletion experiments reveal that these presynaptic nAChRs include the alpha 7 subunit. These findings reveal that CNS nAChRs enhance fast excitatory transmission, providing a likely mechanism for the complex behavioral effects of nicotine.

The immunomodulatory drug FTY720 is phosphorylated in vivo, and the resulting FTY720 phosphate as a ligand for sphingosine-1-phosphate receptors is responsible for the unique biological effects of the compound. So far, phosphorylation of FTY720 by murine sphingosine kinase (SPHK) 1a had been documented. We found that, while FTY720 is also phosphorylated by human SPHK1, the human type 2 isoform phosphorylates the drug 30-fold more efficiently, because of a lower K m of FTY720 for SPHK2. Similarly, murine SPHK2 was more efficient than SPHK1a. Among splice variants of the human SPHKs, an N-terminally extended SPHK2 isoform was even more active than SPHK2 itself. Further SPHK superfamily members, namely ceramide kinase and a "SPHK-like" protein, failed to phosphorylate sphingosine and FTY720. Thus, only SPHK1 and 2 appear to be capable of phosphorylating FTY720. Using selective assay conditions, SPHK1 and 2 activities in murine tissues were measured. While activity of SPHK2 toward sphingosine was generally lower than of SPHK1, FTY720 phosphorylation was higher under conditions favoring SPHK2. In human endothelial cells, while activity of SPHK1 toward sphingosine was 2-fold higher than of SPHK2, FTY720 phosphorylation was 7-fold faster under SPHK2 assay conditions. Finally, FTY720 was poorly phosphorylated in human blood as compared with rodent blood, in line with the low activity of SPHK1 and in particular of SPHK2 in human blood. To conclude, both SPHK1 and 2 are capable of phosphorylating FTY720, but SPHK2 is quantitatively more important than SPHK1.FTY720 is an immunomodulatory drug, which is highly efficacious in models of transplantation and of autoimmune diseases (1). It was recently found to be effective in kidney transplantation in humans (2). FTY720 elicits a lymphopenia resulting from the reversible redistribution of lymphocytes from the circulation to secondary lymphoid organs, without leading to general immunosuppression (3, 4). Conversion of FTY720 to its monophosphate appears to be essential for the effects of the drug on lymphocyte homing, since FTY720 phosphate acts as an agonist at four of the five G-protein-coupled receptors for sphingosine-1-phosphate (S1P) 1 (5, 6); it is assumed that at least one S1P receptor is critical to the lymphopenic response induced by FTY720 treatment (2). More recently, FTY720 was found to stimulate multidrug transporterdependent T-cell chemotaxis to lymph nodes (7); in this instance, FTY720 phosphate as the active metabolite is hypothesized to be responsible for stimulation of efflux activity of the lipid transporter Abcb1. FTY720 has been reported to be phosphorylated ex vivo by rodent lymphoid tissues (5) and whole blood of several species (6), and is rapidly phosphorylated in vivo (5, 6). After oral application of FTY720 to rats, the blood levels of the monophosphate exceeded those of the parent compound 2-4 fold (5). FTY720 was shown to be a substrate for recombinant murine sphingosine kinase 1a (muSPHK1a) (5). Studies with chiral analogs of FTY720 (namely the R-an...

We report here that neuregulin (NRG) isoforms with a conserved cysteine-rich domain (CRD) in their N terminus regulate expression of nicotinic acetylcholine receptors (nAChRs) at developing interneuronal synapses and report the isolation of transmembrane NRG isoforms with this CRD within the N-terminal portion. CRD-NRG mRNA and immunoreactive protein are detected early in developing presynaptic (visceral motor) neurons. The levels of expression of CRD-NRG peak prior to the formation of synapses with their postsynaptic partners, the ganglionic sympathetic neurons. Recombinant CRD-NRG mimics the effects of presynaptic input on target neurons. Functional deletion of CRD-NRG from presynaptic neurons abolishes the upregulation of nAChR expression induced by input-derived soluble material. Thus, CRD-NRG appears to be both a necessary and a sufficient signal for the control of neuronal nAChR expression during synaptogenesis.

GABAA receptor‐mediated synaptic innervation of oxytocin neurones in the supraoptic nucleus (SON) was analysed in adult female rats going through their first reproductive cycle by recording the spontaneous inhibitory postsynaptic currents (sIPSCs) at six stages of female reproduction. During pregnancy we observed a reduction in the interval between monoquantal sIPSCs. The synaptic current amplitude, current decay and neurosteroid sensitivity of postsynaptic GABAA receptors observed at this stage were not distinguishable from those measured in virgin stage SON. Upon parturition an increase in monoquantal synaptic current decay occurred, whereas potentiation by the progesterone metabolite allopregnanolone (3α‐OH‐DHP) was suppressed. Throughout a substantial part of the lactation period the decay of synaptic currents remained attenuated, whilst the potentiation by 3α‐OH‐DHP remained suppressed. Several weeks after the end of lactation sIPSC intervals, their current decay velocity as well as the potentiation by 3α‐OH‐DHP were restored to pre‐pregnancy levels, which is indicative of the cyclical nature of synaptic plasticity in the adult SON. Competitive polymerase chain reaction (PCR) analysis showed that virgin animals expressed α1 and α2 GABAA receptor subunit mRNA at a relative ratio of 2 : 1 compared with β‐actin. After pregnancy both α1 and α2 subunit mRNA levels were transiently increased, although at a relative ratio of 1 : 4, in line with the hypothesis that α2 plays a large role in postsynaptic receptor functioning. During post‐lactation both α subunits were downregulated. We propose that synaptic remodelling in the SON during pregnancy includes changes in the putative number of GABA release sites per neurone. At parturition, and during the two consecutive weeks of lactation, a subtype of postsynaptic GABAA receptors was observed, distinct from the one being expressed before and during pregnancy. Synaptic current densities, calculated in order to compare the impact of synaptic inhibition, showed that, in particular, the differences in 3α‐OH‐DHP potentiation of these two distinct GABAA receptor subtypes produce robust shifts in the impact of synaptic inhibition of oxytocin neurones at the different stages of female reproduction.

Three cyclophilin inhibitors (DEBIO-025, SCY635, and NIM811) are currently in clinical trials for hepatitis C therapy. The mechanism of action of these, however, is not completely understood. There are at least 16 cyclophilins expressed in human cells which are involved in a diverse set of cellular processes. Large-scale siRNA experiments, chemoproteomic assays with cyclophilin binding compounds, and mRNA profiling of HCV replicon containing cells were used to identify the cyclophilins that are instrumental to HCV replication. The previously reported cyclophilin A was confirmed and additional cyclophilin containing pathways were identified. Together, the experiments provide strong evidence that NIM811 reduces viral replication by inhibition of multiple cyclophilins and pathways with protein trafficking as the most strongly and persistently affected pathway.

Although multiple related genes encoding nicotinic acetylcholine receptor (AChR) subunits have been identified, how each of these subunits contributes to AChRs in neurons is not known. Sympathetic neurons express four classes of AChR channels and six AChR subunit genes (α3, α4, α5, α7, β2, and β4). The contribution of individual subunits to AChR channel subtypes in these neurons was examined by selective deletion with antisense oligonucleotides. An α3 antisense oligonucleotide decreased the number and altered the properties of the normally expressed AChactivated channels. The remaining AChR channels have distinct biophysical and pharmacological properties that indicate an important functional contribution of the α7 subunit.

No abstract

No abstract