Localization of immunoreactivity for deleted in colorectal cancer (DCC), the receptor for the guidance factor netrin-1, in ventral tier dopamine projection pathways in adult rodents

DCC (deleted in colorectal cancer)-the receptor of the netrin-1 neuronal guidance factor-is expressed and is active in the central nervous system (CNS) during development, but is down-regulated during maturation. The substantia nigra contains the highest level of netrin-1 mRNA in the adult rodent brain, and corresponding mRNA for DCC has also been detected in this region but has not been localized to any particular neuron type. In this study, an antibody raised against DCC was used to determine if the protein was expressed by adult dopamine neurons, and identify their distribution and projections. Significant DCC-immunoreactivity was detected in midbrain, where it was localized to ventrally displaced A9 dopamine neurons in the substantia nigra, and ventromedial A10 dopamine neurons predominantly situated in and around the interfascicular nucleus. Strong immunoreactivity was not detected in dopamine neurons found elsewhere, or in non-dopamine-containing neurons in the midbrain. Terminal fields selectively labeled with DCC antibody corresponded to known nigrostriatal projections to the dorsolateral striatal patches and dorsomedial shell of the accumbens, and were also detected in prefrontal cortex, septum, lateral habenular and ventral pallidum. The unique distribution of DCC-immunoreactivity in adult ventral midbrain dopamine neurons suggests that netrin-1/DCC signaling could function in plasticity and remodeling previously identified in dopamine projection pathways. In particular, a recent report that DCC is regulated through the ubiquitin-proteosome system via Siah/Sina proteins, is consistent with a potential involvement in genetic and sporadic forms of Parkinson's disease. (c) 2005 IBRO. Published by Elsevier Ltd. All rights reserved.

Dose determination of haloperidol, risperidone and olanzapine using an in vivo dopamine D-2-receptor occupancy method in the rat

The purpose of the present study was to determine antipsychotic doses that achieve 80% striatal doparnine D-2-receptor occupancy for haloperidol, risperidone and olanzapine in rats. Wistar rats were treated with normal saline vehicle (controls), haloperidol (0.25 and 0.5 mg/kg/ day), risperidone (3, 5 and 6 mg/kg/day) and olanzapine (5 and 10 mg/kg/day) for 7 days via osmotic minipumps. Striatal and cerebellar tissue were collected and in vivo dopamine D2-receptor occupancies were determined using H-3-raclopride. The doses required to achieve dopamine D-2-receptor occupancy of 80% in 11- and 24-week old rats were: haloperidol 0.25 mg/kg/day, risperidone 5 mg/kg/day and olanzapine 10 mg/kg/day. (c) 2006 Elsevier B.V All rights reserved.

Agonists and antagonists of protease activated receptors (PARs)

Protease activated receptors (PARs) are a category of G-protein coupled receptors (GPCRs) implicated in the progression of a wide range of diseases, including thrombosis, inflammatory disorders, and proliferative diseases. Signal transduction via PARs proceeds via an unusual activation mechanism. Instead of being activated through direct interaction with an extracellular signal like most GPCRs. they are self-activated following cleavage of their extracellular N-terminus by serine proteases to generate a new receptor N-terminus that acts as an intramolecular ligand by folding back onto itself and triggering receptor activation. Short synthetic peptides corresponding to this newly exposed N-terminal tethered ligand can activate three of the four known PARs in the absence of proteases. and such PAR activating peptides (PAR-APs) have served as templates for agonist/antagonist development. In fact much of the evidence for involvement of PARs in diseases has relied upon use of PAR-APs. often of low potency and uncertain selectivity. This review summarizes current structures of PAR agonists and antagonists, the need for more selective and more potent PAR ligands that activate or antagonize this intriguing class of receptors, and outlines the background relevant to PAR activation, assay methods, and physiological properties anticipated for PAR ligands.

The influence of dopamine on semantic activation in Parkinson's disease: Evidence from a multipriming task

Research has suggested that semantic processing deficits in Parkinson's disease (PD) are related to striatal dopamine deficiency. As an investigation of the influence of dopamine on semantic activation in PD, 7 participants with PD performed a lexical-decision task when on and off levodopa medication. Seven healthy controls matched to the participants with PD in terms of sex, age, and education also participated in the study. By use of a multipriming paradigm, whereby 2 prime words were presented prior to the target word, semantic priming effects were measured across stimulus onset asynchronies (SOAs) of 250 Ins and 1,200 Ins. The results revealed a similar pattern of priming across SOAs for the control group and the PD participants on medication. In contrast, within-group comparisons revealed that automatic semantic activation was compromised in PD participants when off medication. The implications of these results for the neuromodulatory influence of dopamine on semantic processing in PD are discussed.

Alpha-selenoconotoxins, a new class of potent alpha(7) neuronal nicotinic receptor antagonists

Disulfide bonds are important structural motifs that play an essential role in maintaining the conformational stability of many bioactive peptides. Of particular importance are the conotoxins, which selectively target a wide range of ion channels that are implicated in numerous disease states. Despite the enormous potential of conotoxins as therapeutics, their multiple disulfide bond frameworks are inherently unstable under reducing conditions. Reduction or scrambling by thiol-containing molecules such as glutathione or serum albumin in intracellular or extracellular environments such as blood plasma can decrease their effectiveness as drugs. To address this issue, we describe a new class of selenoconotoxins where cysteine residues are replaced by selenocysteine to form isosteric and non-reducible diselenide bonds. Three isoforms of alpha-conotoxin ImI were synthesized by t-butoxycarbonyl chemistry with systematic replacement of one([ Sec(2,8)] ImI or [Sec(3,12)] ImI), or both([Sec(2,3,8,12)] ImI) disulfide bonds with a diselenide bond. Each analogue demonstrated remarkable stability to reduction or scrambling under a range of chemical and biological reducing conditions. Three-dimensional structural characterization by NMR and CD spectroscopy indicates conformational preferences that are very similar to those of native ImI, suggesting fully isomorphic structures. Additionally, full bioactivity was retained at the alpha(7) nicotinic acetylcholine receptor, with each seleno-analogue exhibiting a dose-response curve that overlaps with wild-type ImI, thus further supporting an isomorphic structure. These results demonstrate that selenoconotoxins can be used as highly stable scaffolds for the design of new drugs.