Pesticides are widely used in agricultural and other settings, resulting in continued human exposure. Pesticide toxicity has been clearly demonstrated to alter a variety of neurological functions. Particularly, there is strong evidence suggesting that pesticide exposure predisposes to neurodegenerative diseases. Epidemiological data has suggested a relationship between pesticide exposure and brain neurodegeneration. However, an increasing debate has aroused regarding this issue. Paraquat is a highly toxic quaternary nitrogen herbicide which has been largely studied as a model for Parkinson's disease providing valuable insight into the possible mechanisms involved in the toxic effects of pesticides and their role in the progression of neurodegenerative diseases. In this work, we review the molecular mechanisms involved in the neurotoxic actions of pesticides, with a particular emphasis on the mechanisms associated with the induction neuronal cell death by paraquat as a model for Parkinsonian neurodegeneration.

The herpes simplex virus type 1 (HSV-1) latency-associated transcript (LAT) is abundantly expressed in latently infected trigeminal ganglionic sensory neurons. Expression of the first 1.5 kb of LAT coding sequences is sufficient for the wild-type reactivation phenotype in small animal models of infection. The ability of the first 1.5 kb of LAT coding sequences to inhibit apoptosis is important for the latency-reactivation cycle. Several studies have also concluded that LAT inhibits productive infection. To date, a functional LAT protein has not been identified, suggesting that LAT is a regulatory RNA. Two small RNAs (sRNAs) were previously identified within the first 1.5 kb of LAT coding sequences. In this study, we demonstrated that both LAT sRNAs were expressed in the trigeminal ganglia of mice latently infected with an HSV-1 strain that expresses LAT but not when mice were infected with a LAT null mutant. LAT sRNA1 and sRNA2 cooperated to inhibit cold shockinduced apoptosis in mouse neuroblastoma cells. LAT sRNA1, but not LAT sRNA2, inhibited apoptosis less efficiently than both sRNAs. When rabbit skin cells were cotransfected with plasmids that express LAT sRNA1 and HSV-1 genomic DNA, the amount of infectious virus released was reduced approximately 3 logs. Although LAT sRNA2 was less effective at inhibiting virus production, it inhibited expression of infected cell protein 4 (ICP4). Neither LAT sRNA had an obvious effect on ICP0 expression. These studies suggested that expression of two LAT sRNAs plays a role in the latency-reactivation cycle by inhibiting apoptosis and productive infection.Most adults in the United States harbor latent herpes simplex virus type 1 (HSV-1) (48, 71) in sensory neurons located in trigeminal ganglia (TG) or sacral dorsal root ganglia (34, 68). Acute infection is typically initiated in the mucocutaneous epithelium. Despite a vigorous immune response during acute infection, HSV-1 establishes latency in sensory neurons. Latent HSV-1 periodically reactivates from latency, resulting in the shedding of infectious virus and various recurrent clinical disorders (reviewed in references 34 and 35).Mice, rabbits, or humans latently infected with HSV-1 express abundant levels of the latency-associated transcript (LAT) in latently infected neurons (12,14,15,38,45,62,65,69,70). The primary LAT transcript is 8.3 kb, and splicing yields a stable 2-kb LAT and an unstable 6.3-kb LAT (14,62,73). The 2-kb LAT can be further spliced in infected neurons (43). The majority of the 2-kb LAT is not capped or polyadenylated and appears to be a stable intron (19,40). In general, HSV-1 LAT null mutants do not reactivate from latency as efficiently as LAT-expressing strains (reviewed in references 34, 35, and 68). Expression of the first 1.5 kb of LAT coding sequences (LAT nucleotides [nt] 1 to 1499) is crucial for wildtype (wt) levels of reactivation in small animal models (28,33,56).LAT reduces apoptosis in infected tissue culture cells (32) and promotes neuronal survival in the TG of infected rabbits (53...

The loss of dopaminergic neurons induced by the parkinsonian toxins paraquat, rotenone and 1-methyl-4-phenylpyridinium (MPP+) is associated with oxidative stress. However, controversial reports exist regarding the source/compartmentalization of reactive oxygen species (ROS) generation and its exact role in cell death. We aimed to determine in detail the role of superoxide anion (O2•−), oxidative stress and their subcellular compartmentalization in dopaminergic cell death induced by parkinsonian toxins. Oxidative stress and ROS formation was determined in the cytosol, intermembrane (IMS) and mitochondrial matrix compartments, using dihydroethidine derivatives, the redox sensor roGFP, as well as electron paramagnetic resonance spectroscopy. Paraquat induced an increase in ROS and oxidative stress in both the cytosol and mitochondrial matrix prior to cell death. MPP+ and rotenone primarily induced an increase in ROS and oxidative stress in the mitochondrial matrix. No oxidative stress was detected at the level of the IMS. In contrast to previous studies, overexpression of manganese superoxide dismutase (MnSOD) or copper/zinc SOD (CuZnSOD) had no effect on ROS steady state levels, lipid peroxidation, loss of mitochondrial membrane potential (ΔΨm) and dopaminergic cell death induced by MPP+ or rotenone. In contrast, paraquat-induced oxidative stress and cell death were selectively reduced by MnSOD overexpression, but not by CuZnSOD or manganese-porphyrins. However, MnSOD also failed to prevent ΔΨm loss. Finally, paraquat, but not MPP+ or rotenone, induced the transcriptional activation the redox-sensitive antioxidant response elements (ARE) and nuclear factor kappa-B (NF-κB). These results demonstrate a selective role of mitochondrial O2•− in dopaminergic cell death induced by paraquat, and show that toxicity induced by the complex I inhibitors rotenone and MPP+ does not depend directly on mitochondrial O2•− formation.

Previous studies demonstrated that analogs of benztropine [3␣-(diphenyl-methoxy)tropane (BZT)] bind to the dopamine (DA) transporter with high affinity, inhibit DA uptake, but do not maintain rates of responding in self-administration procedures comparable with those maintained by cocaine. Some BZT analogs have an onset of action that is slower than that for cocaine that may contribute to this decreased effectiveness. In addition, some BZT analogs have affinity for muscarinic-M1 receptors that may interfere with reinforcing effects. The present study assessed effects of BZT analogs in place-conditioning procedures designed to accommodate variations in onset of effect. Benztropine [BZT; 3␣-(diphenylmethoxy)tropane] is the parent compound in a class of dopamine (DA) transport inhibitors with structural similarity to cocaine (i.e., a tropane ring), as well as to the 1,4-dialyky(en)ylpiperazines (i.e., a diphenyl-ether moiety), exemplified by GBR 12909. A series of BZT analogs showed enhanced affinities for binding to the DA transporter relative to BZT and cocaine . Despite this increased affinity, the behavioral effects of these compounds were generally different from those of cocaine and other DA uptake inhibitors. For example, 4-chloro-3␣-(diphenylmethoxy)tropane (4-Cl-BZT) has a 30 nM affinity for the DA transporter, which is comparable with the high-affinity binding of cocaine. However, 4-Cl-BZT has reduced effectiveness as a stimulant of locomotor activity compared with cocaine and does not produce cocaine-like discriminative stimulus effects Tolliver et al., 1999). Furthermore, this compound does not maintain rates of responding as high as those maintained by cocaine in a self-administration procedure (Woolverton et al., 2000) or break points as high as those for cocaine under a progressive ratio schedule (Woolverton et al., 2001). The differences between the BZT analogs compared with cocaine may appear at odds with the DA transporter hypothesis of the behavioral effects of cocaine, which suggests that compounds that bind to the DA transporter and inhibit DA uptake will have behavioral effects like those of cocaine (Kuhar et al., 1991).Some of the BZT analogs have a time course that is different from that of cocaine. For example, Tolliver et al. (1999) and Tanda et al. (2003) showed that increases in extracellular DA produced by cocaine occurred sooner after injection than those produced by the 4-Cl analog of BZT. Those results with 4-Cl-BZT are similar to results for BZT reported previously (Church et al., 1987). A pharmacokinetic comparison of cocaine and a series of BZT analogs indicated that all of these Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.

Previous studies suggested that differences between the behavioral effects of cocaine and analogs of benztropine were related to the relatively slow onset of action of the latter compounds. Several N-substituted benztropine analogs with a relatively fast onset of effects were studied to assess whether a fast onset of effects would render the effects more similar to those of cocaine. Only one of the compounds increased locomotor activity, and the increases were modest compared with those of 10 to 20 mg/kg cocaine. In rats trained to discriminate 10 mg/kg cocaine from saline none of the compounds produced more than 40% cocaine-like responds up to 2 h after injection. None of the compounds produced place-conditioning when examined up to 90 min after injection, indicating minimal abuse liability. The compounds had 5.6 to 30 nM affinities at the dopamine transporter (DAT), with uniformly lower affinities at norepinephrine and serotonin transporters (from 490-4600 and 1420 -7350 nM, respectively). Affinities at muscarinic M 1 receptors were from 100-to 300-fold lower than DAT affinities, suggesting minimal contribution of those sites to the behavioral effects of the compounds. Affinities at histaminic H 1 sites were from 11-to 43-fold lower than those for the DAT. The compounds also had affinity for sigma, 5-hydroxytryptamine 1 (5-HT 1 ) , and 5-HT 2 receptors that may have contributed to their behavioral effects. Together, the results indicate that a slow onset of action is not a necessary condition for reduced cocaine-like effects of atypical DAT ligands and suggest several mechanisms that may contribute to the reduced cocaine-like efficacy of these compounds.