Oral tremor induced by galantamine in rats: a model of the parkinsonian side effects of cholinomimetics used to treat Alzheimer's disease

The effect of anticholinergic drugs on cognition of patients with Parkinson's disease: a cohort study from the Egyptian population

BACKGROUND

Cognitive dysfunction is a non-motor manifestation of Parkinson's disease (PD). We aimed to determine the frequency and patterns of cognitive dysfunction in treated patients with PD and their predictors.

RESEARCH DESIGN AND METHODS

This study included 80 patients (male = 48; female = 32) and 30 healthy individuals. They underwent neuropsychiatric evaluations. Measurements included Beck's depression inventory - II (BDI-II), mini-mental state examination (MMSE) and Montreal cognitive assessment (MoCA).

RESULTS

Patients had mean age of 55.56 ± 9.06 yrs, duration of PD of 4.86 ± 2.71 yrs and Hoehn and Yahr Scoring of 2.19 ± 0.89. They were on levodopa/carbidopa therapy and adjuvant therapy with benztropine mesylate, an anticholinergic drug, (n = 51) or amantadine sulfate, a dopaminergic drug, (n = 29). Sixteen (20%) had moderate depressive symptoms. Mild and moderate cognitive impairments were reported in 38.8% and 28.8% (by MMSE) and 46.3% and 31.3% (by MoCA). Patients had lower global cognitive scoring (p = 0.0001) and scorings of different cognitive functions (naming, attention, language, abstraction, memory and orientation) than controls. Patients treated with benztropine had lower cognition than with amantadine. Correlation analyses showed that lower cognition was only associated with chronic PD and its treatment (p = 0.0001).

CONCLUSIONS

Cognitive dysfunction is common with PD (77.5%) particularly with anticholinergic drugs. De-prescription of anticholinergics is recommended for patients with PD.

Therapeutic considerations of bioactive compounds in Alzheimer's disease and Parkinson's disease: Dissecting the molecular pathways

Leading neurodegenerative diseases Alzheimer's disease (AD) and Parkinson's disease (PD) are characterized by the impairment of memory and motor functions, respectively. Despite several breakthroughs, there exists a lack of disease-modifying treatment strategies for these diseases, as the available drugs provide symptomatic relief and bring along side effects. Bioactive compounds are reported to bear neuroprotective properties with minimal toxicity, however, a detailed elucidation of their modes of neuroprotection is lacking. The review elucidates the neuroprotective mechanism(s) of some of the major phyto-compounds in pre-clinical and clinical studies of AD and PD to understand their potential in combating these diseases. Curcumin, eugenol, resveratrol, baicalein, sesamol and so on have proved efficient in countering the pathological hallmarks of AD and PD. Curcumin, resveratrol, caffeine and so on have reached the clinical phases of these diseases, while aromadendrin, delphinidin, cyanidin and xanthohumol are yet to be extensively explored in pre-clinical phases. The review highlights the need for extensive investigation of these compounds in the clinical stages of these diseases so as to utilize their disease-modifying abilities in the real field of treatment. Moreover, poor pharmacokinetic properties of natural compounds are constraints to their therapeutic yields and this review suggests a plausible contribution of nanotechnology in overcoming these limitations.

Structural elucidation and anti-neuroinflammatory activity of Polygala tenuifolia polysaccharide

Polygala tenuifolia is extensively used to treat amnesia in traditional Chinese medicine, and pharmacological studies have reported the beneficial effects of P. tenuifolia on intelligence and cognition. In the present study, the crude polysaccharide alkali-extracted from P. tenuifolia roots (PTB) inhibited lipopolysaccharide-induced microglia/astrocyte activation and significantly improved the learning and memory ability of Alzheimer's disease (AD) rats. To determine its bioactive components, a heteropolysaccharide (PTBP-1-3) was isolated from PTB. Structural analysis showed that PTBP-1-3 was composed of α-L-Araf-(1 → ， → 3)-α-L-Araf-(1→, →5)-α-L-Araf-(1→, →3,5)-α-L-Araf-(1→, →2,5)-α-L-Araf-(1→, β-D-Xylp-(1→, →2,3,4)-β-D-Xylp-(1→, α-L-Rhap-(1→, β-D-Galp-(1→, →4)-α-D-Galp-(1→, →6)-α-D-Galp-(1→, →6)-α-D-Glcp-(1→, →3,6)-α-D-Glcp-(1→, →6)-α-D-Manp-(1→, and →2,4)-β-D-Manp-(1 → residues. PTBP-1-3 decreased the production of NO, TNF-α, and IL-1β in lipopolysaccharide-activated BV2 microglia cells in a manner similar to that of minocycline. In conclusion, PTBP-1-3 exhibited a potent inhibitory effect on neuroinflammation, and could be one of the bioactive ingredients in PTB for anti-neuroinflammation. PTB and PTBP-1-3 may be potential therapeutic agents for the treatment of AD.

Development and Co-design of NeuroOrb: A Novel “Serious Gaming” System Targeting Cognitive Impairment in Parkinson’s Disease

Whilst Parkinson’s disease (PD) is typically thought of as a motor disease, a significant number of individuals also experience cognitive impairment (CI), ranging from mild-CI to dementia. One technique that may prove effective in delaying the onset of CI in PD is cognitive training (CT); however, evidence to date is variable. This may be due to the implementation of CT in this population, with the motor impairments of PD potentially hampering the ability to use standard equipment, such as pen-and-paper or a computer mouse. This may, in turn, promote negative attitudes toward the CT paradigm, which may correlate with poorer outcomes. Consequently, optimizing a system for the delivery of CT in the PD population may improve the accessibility of and engagement with the CT paradigm, subsequently leading to better outcomes. To achieve this, the NeuroOrb Gaming System was designed, coupling a novel accessible controller, specifically developed for use with people with motor impairments, with a “Serious Games” software suite, custom-designed to target the cognitive domains typically affected in PD. The aim of the current study was to evaluate the usability of the NeuroOrb through a reiterative co-design process, in order to optimize the system for future use in clinical trials of CT in individuals with PD. Individuals with PD (n = 13; mean age = 68.15 years; mean disease duration = 8 years) were recruited from the community and participated in three co-design loops. After implementation of key stakeholder feedback to make significant modifications to the system, system usability was improved and participant attitudes toward the NeuroOrb were very positive. Taken together, this provides rationale for moving forward with a future clinical trial investigating the utility of the NeuroOrb as a tool to deliver CT in PD.

Optimizing Cognitive Training for the Treatment of Cognitive Dysfunction in Parkinson's Disease: Current Limitations and Future Directions

Cognitive dysfunction, primarily involving impairments in executive function, visuospatial function and memory, is one of the most common non-motor symptoms of Parkinson’s disease (PD). Currently, the only pharmacological treatments available for the treatment of cognitive dysfunction in PD provide variable benefit, making the search for potential non-pharmacological therapies to improve cognitive function of significant interest. One such therapeutic strategy may be cognitive training (CT), which involves the repetition of standardized tasks with the aim of improving specific aspects of cognition. Several studies have examined the effects of CT in individuals with PD and have shown benefits in a variety of cognitive domains, but the widespread use of CT in these individuals may be limited by motor impairments and other concerns in study design. Here, we discuss the current state of the literature on the use of CT for PD and propose recommendations for future implementation. We also explore the potential use of more recent integrative, adaptive and assistive technologies, such as virtual reality, which may optimize the delivery of CT in PD.

Neurotoxin-Induced Rodent Models of Parkinson's Disease: Benefits and Drawbacks

Parkinson's disease (PD), the second most common neurodegenerative disorder, is characterized by cardinal motor impairments, including akinesia and tremor, as well as by a host of non-motor symptoms, including both autonomic and cognitive dysfunction. PD is associated with a death of nigral dopaminergic neurons, as well as the pathological spread of Lewy bodies, consisting predominantly of the misfolded protein alpha-synuclein. To date, only symptomatic treatments, such as levodopa, are available, and trials aiming to cure the disease, or at least halt its progression, have not been successful. Wong et al. (2019) suggested that the lack of effective therapy against neurodegeneration in PD might be attributed to the fact that the molecular mechanisms standing behind the dopaminergic neuronal vulnerability are still a major scientific challenge. Understanding these molecular mechanisms is critical for developing effective therapy. Thirty-five years ago, Calne and William Langston (1983) raised the question of whether biological or environmental factors precipitate the development of PD. In spite of great advances in technology and medicine, this question still lacks a clear answer. Only 5-15% of PD cases are attributed to a genetic mutation, with the majority of cases classified as idiopathic, which could be linked to exposure to environmental contaminants. Rodent models play a crucial role in understanding the risk factors and pathogenesis of PD. Additionally, well-validated rodent models are critical for driving the preclinical development of clinically translatable treatment options. In this review, we discuss the mechanisms, similarities and differences, as well as advantages and limitations of different neurotoxin-induced rat models of PD. In the second part of this review, we will discuss the potential future of neurotoxin-induced models of PD. Finally, we will briefly demonstrate the crucial role of gene-environment interactions in PD and discuss fusion or dual PD models. We argue that these models have the potential to significantly further our understanding of PD.

Polysorbate-80 surface modified nano-stearylamine BQCA conjugate for the management of Alzheimer's disease

Acetylcholinesterase (AChE) inhibitors such as donepezil, galantamine and rivastigmine are used for the management of dementia in Alzheimer's Disease (AD). These drugs elevate endogenous acetylcholine (ACh) levels at the M1 muscarinic receptor in the brain to achieve therapeutic benefits. However, their side effects, such as nausea, vomiting, dizziness, insomnia, loss of appetite, altered heart rate, etc., are related to non-specific peripheral activation of M2-M5 muscarinic subtypes. It is logical, therefore, to develop drugs that selectively activate brain M1 receptors. Unfortunately, the orthosteric site homology among the receptor subtypes does not permit this approach. An alternative approach is to use positive allosteric modulator (PAM) of M1 receptors like benzyl quinolone carboxylic acid (BQCA). PAMs although devoid of M1 agonist activity, however, when bound, enhance the binding affinity of orthosteric ligand, Ach. The current challenge with PAMS is their low brain half-life, permeability, and higher elimination rates. This study reports active targeting of brain M1 receptors using surface modified nano lipid-drug conjugates (LDC) of M1 PAM, BQCA, to treat AD. Polysorbate-80 (P-80) surface modified stearylamine (SA)-BQCA conjugated nanoparticles (BQCA-SA-P80-NPs) were prepared by conjugating BQCA to SA, followed by the formation of nanoparticles (NPs) using P-80 by solvent injection method. The BQCA-SA-P80-NPs are near-spherical with a particle size (PS) of 166.62 ± 1.24 nm and zeta potential (ZP) of 23.59 ± 0.37 mV. In the in vitro cytotoxicity (SH-SY5Y cells) and hemolysis assays, BQCA-SA-P80-NPs, show acceptable safety and compatibility. In mice, Alzheimer's model, BQCA-SA-P80-NPs significantly prevent STZ induced changes in memory, neuronal Aβ1-42, p-Tau, APP, NF-κB, and BACE levels and neuronal cell death, when compared to untreated disease control and naïve BQCA treated group. Further, BQCA-SA-P80-NPs significantly improve the therapeutic efficacy of AChE inhibitor, donepezil (DPZ), indicating its potentiating effects. In vivo biodistribution studies in mice show selective accumulation of BQCA-SA-P80-NPs in the brain, suggesting an improved brain bioavailability and reduced peripheral side effects of BQCA. The study results demonstrate that BQCA-SA-P80-NPs can improve brain bioavailability and therapeutic efficacy of BQCA in AD.

Study of Nutraceuticals and Phytochemicals for the Management of Alzheimer's Disease: A Review

BACKGROUND

Alzheimer's disease (AD) affects several people worldwide and has devastating impacts on society with a limited number of approaches for its pharmacological treatment. The main causes of AD are not clear yet. However, the formation of senile plaques, neurofibrillary tangles, hyper-phosphorylation of tau protein, and disruption of redox homeostasis may cause AD. These causes have a positive correlation with oxidative stress, producing reactive ions, which are responsible for altering the physiological condition of the body.

CONCLUSION

Ongoing research recommended the use of phytochemicals as acetylcholinesterase inhibitors to hinder the onset and progression of AD. The natural compound structures, including lignans, flavonoids, tannins, polyphenols, triterpenes, sterols, and alkaloids have anti-inflammatory, antioxidant, and anti-amyloidogenic properties. The purpose of this article is to provide a brief introduction to AD along with the use of natural compounds as new therapeutic approaches for its management.

Postoperative Administration of the Acetylcholinesterase Inhibitor, Donepezil, Interferes with Bone Healing and Implant Osseointegration in a Rat Model

Donepezil is an acetylcholinesterase inhibitor commonly used to treat mild to moderate Alzheimer’s disease. Its use has been associated with increased bone mass in humans and animals. However, the effect of postoperative administration of donepezil on bone healing remains unknown. Therefore, this study aimed to assess the impact of postoperative injection of donepezil on bone healing, titanium-implant osseointegration, and soft tissue healing. Twenty-two Sprague-Dawley rats were randomly assigned to receive a daily dose of either donepezil (0.6 mg/kg) or saline as a control. In each rat, a uni-cortical defect was created in the right tibia metaphysis and a custom-made titanium implant was placed in the left tibiae. After two weeks, rats were euthanized, and their bones were analysed by Micro-CT and histology. The healing of bone defect and implant osseointegration in the rats treated with donepezil were significantly reduced compared to the saline-treated rats. Histomorphometric analysis showed lower immune cell infiltration in bone defects treated with donepezil compared to the saline-treated defects. On the other hand, the healing time of soft tissue wounds was significantly shorter in donepezil-treated rats compared to the controls. In conclusion, short-term administration of donepezil hinders bone healing whereas enhancing soft tissue healing.

Characterization of Polysaccharides Extracted from Pulps and Seeds of Crataegus azarolus L. var. aronia: Preliminary Structure, Antioxidant, Antibacterial, α-Amylase, and Acetylcholinesterase Inhibition Properties

Polysaccharides from the pulps (CAP) and seeds (CAS) of Crataegus azarolus L. var. aronia were extracted by hot water method. Both polysaccharides were characterized by scanning electron microscopy (SEM), Congo red test, FT-IR spectroscopy, and their antioxidant, α-amylase, antiacetylcholinesterase, and antibacterial activities were evaluated. CAP showed the highest total carbohydrate (82.35%) and uronic acid (29.39%) contents. The Congo red test revealed the lack of triple-helical conformation for both polysaccharides. The comparison of both infrared spectra indicated similar patterns with the presence of typical bands of polysaccharides. However, the microstructure of both samples indicated differences when analyzed by SEM. CAP displayed higher antioxidant, α-amylase, and acetylcholinesterase inhibitory activities. Besides, CAP showed the strongest antimicrobial effects against seven microorganisms and, notably, the Gram-positive bacteria. Overall, the results suggest that polysaccharides from C. azarolus L. var. aronia may be considered as novel sources of antioxidants and recommended as enzyme inhibitory agents in food and pharmaceutical industries.

Extraction and isolation of acetylcholinesterase inhibitors from Citrus limon peel using an in vitro method

A simple and efficient ultrafiltration-liquid chromatography-mass spectrometry-based method was developed for the rapid screening and identification of ligands from Citrus limon peel, which are suitable acetylcholinesterase inhibitors. Subsequently, the anti-Alzheimer's activity of these compounds was assessed using a PC12 cell model. Six major compounds, viz. neoeriocitrin, isonaringin, naringin, hesperidin, neohesperidin, and limonin, were identified as potent acetylcholinesterase inhibitors. A continuous and efficient online method, which involved the use of a microwave-assisted extraction device, solvent concentration tank, and centrifugal partition chromatography column, was developed for the scale-up of these compounds, and the obtained compounds presented high purity. Next, their bioactivity was evaluated using a PC12 cell model. This novel approach, which was based on ultrafiltration-liquid chromatography-mass spectrometry, microwave-assisted extraction online coupled with solvent concentration tank, and centrifugal partition chromatography along with in vitro evaluation, could represent a powerful tool for the screening and extraction of acetylcholinesterase inhibitors from complex matrices, and could be a useful platform for the large-scale production of bioactive and nutraceutical ingredients.

Panax ginseng components and the pathogenesis of Alzheimer's disease (Review)

Ginseng is one of the main representatives of traditional Chinese medicine and presents a wide range of pharmacological actions. Ginsenosides are the main class of active compounds found in ginseng. They demonstrate unique biological activity and medicinal value, namely anti-tumour, anti-inflammatory and antioxidant properties, as well as anti-apoptotic properties. Increasing levels of stress in life are responsible for the increased incidence of nervous system diseases. Neurological diseases create a huge burden on the lives and health of individuals. In recent years, studies have indicated that ginsenosides play a pronounced positive role in the prevention and treatment of neurological diseases. Nevertheless, research is still at an early stage of development, and the complex mechanisms of action involved remain largely unknown. This review aimed to shed light into what is currently known about the mechanisms of action of ginsenosides in relation to Alzheimer's disease. Scientific material and theoretical bases for the treatment of nervous system diseases with purified Panax ginseng extracts are also discussed.

Extraction and in vitro screening of potential acetylcholinesterase inhibitors from the leaves of Panax japonicus

Ultrafiltration liquid chromatography-mass spectrometry (UFLC-MS) is an efficient method that can be applied to rapidly screen and identify ligands for acetylcholinesterase (AChE) from the leaves of Panax japonicus. Using this method, we identified 5 major compounds, chikusetsusaponins V, Ib, IV, IVa, and IVa ethyl ester, as potent AChE inhibitors, which were assessed for anti-Alzheimer disease activity using the PC12 cell model. A continuous online method, which consisted of microwave-assisted extraction, a solvent concentration tank, and centrifugal partition chromatography (MAE-SCT-CPC), was newly developed for scaled up production of these compounds with high purity and efficiency. The bioactivities of the compounds separated were assessed by the PC12 cell model. This novel approach of using UFLC-MS coupled with MAE-SCT-CPC and a PC12 cell model could be applied to efficiently screen, extract, and separate AChE inhibitors from complex samples, and could serve as an important platform for the large-scale production of functional food and nutraceutical ingredients.

The MAO-B inhibitor deprenyl reduces the oral tremor and the dopamine depletion induced by the VMAT-2 inhibitor tetrabenazine

Tetrabenazine (TBZ) is prescribed for the treatment of chorea associated with Huntington's disease. Via inhibition of the vesicular monoamine transporter (VMAT-2), TBZ blocks dopamine (DA) storage and depletes striatal DA; this drug also has been shown to induce Parkinsonian motor side effects in patients. Recently, TBZ was shown to induce tremulous jaw movements (TJMs) in rats and mice. TJMs are an oral tremor that has many of the characteristics of Parkinsonian tremor in humans. The present study focused upon the ability of the well-established antiparkinsonian agent deprenyl to attenuate the behavioral and neurochemical effects of 2.0mg/kg TBZ. Deprenyl is a selective and irreversible inhibitor of monoamine oxidase-B, and administration of deprenyl produced a dose-related suppression of TBZ-induced TJMs. A second experiment employed in vivo microdialysis to examine extracellular DA levels in the ventrolateral striatum, the neostriatal region most closely associated with the production of TJMs, after administration of TBZ and deprenyl. Consistent with the behavioral data, TBZ alone produced a biphasic effect on extracellular DA, with an initial increases followed by a prolonged decrease during the period in which TJMs are displayed. Co-administration of deprenyl with TBZ increased DA levels compared to rats treated with TBZ alone. These results provide support for use of TBZ as a rodent model of Parkinsonism, and future studies should utilize this model to evaluate putative anti-Parkinsonian agents.

Fluoxetine Administration Exacerbates Oral Tremor and Striatal Dopamine Depletion in a Rodent Pharmacological Model of Parkinsonism

The cardinal motor symptoms of Parkinson's disease (PD) include resting tremor, akinesia, bradykinesia, and rigidity, and these motor abnormalities can be modeled in rodents by administration of the VMAT-2 (type-2 vesicular monoamine transporter) inhibitor tetrabenazine (9,10-dimethoxy-3-(2-methylpropyl)-1,3,4,6,7, 11b hexahydrobenzo[a]quinolizin-2-one; TBZ). Depression is also commonly associated with PD, and clinical data indicate that selective serotonin reuptake inhibitors (SSRIs) such as fluoxetine ((±)-N-methyl-γ-[4-(trifluoromethyl)phenoxy]benzenepropanamine hydrochloride; FLX) are frequently used to treat depression in PD patients. The aim of the present study was to characterize the effect of FLX on the motor dysfunctions induced by a low dose of TBZ (0.75 mg/kg), and investigate the neural mechanisms involved. This low dose of TBZ was selected based on studies with rat models of depressive symptoms. In rats, coadministration of FLX (2.5, 5.0, and 10.0 mg/kg) increased TBZ-induced oral tremor (tremulous jaw movements), and decreased locomotor activity compared with administration of TBZ alone. Coadministration of the serotonin 5-HT2A/2C antagonist mianserin (2.5 and 5.0 mg/kg) attenuated the increase in oral tremor induced by coadministration of TBZ (0.75 mg/kg) with FLX (5.0 mg/kg). Consistent with these behavioral data, coadministration of TBZ and FLX decreased DA tissue levels in the rat ventrolateral neostriatum compared with TBZ alone, and coadministration of mianserin with TBZ and FLX attenuated this effect, increasing DA tissue levels compared with the TBZ/FLX condition. These data suggest that SSRI administration in PD patients may result in worsening of motor symptoms, at least in part, by exacerbating existing DA depletions through 5-HT2A/2C-mediated modulation of DA neurotransmission.

Conditional neural knockout of the adenosine A(2A) receptor and pharmacological A(2A) antagonism reduce pilocarpine-induced tremulous jaw movements: studies with a mouse model of parkinsonian tremor

Tremulous jaw movements are rapid vertical deflections of the lower jaw that resemble chewing but are not directed at any particular stimulus. In rats, tremulous jaw movements can be induced by a number of conditions that parallel those seen in human parkinsonism, including dopamine depletion, dopamine antagonism, and cholinomimetic drugs. Moreover, tremulous jaw movements in rats can be attenuated using antiparkinsonian agents such as L-DOPA, dopamine agonists, muscarinic antagonists, and adenosine A(2A) antagonists. In the present studies, a mouse model of tremulous jaw movements was established to investigate the effects of adenosine A(2A) antagonism, and a conditional neuronal knockout of adenosine A(2A) receptors, on cholinomimetic-induced tremulous jaw movements. The muscarinic agonist pilocarpine significantly induced tremulous jaw movements in a dose-dependent manner (0.25-1.0mg/kg IP). These movements occurred largely in the 3-7.5 Hz local frequency range. Administration of the adenosine A(2A) antagonist MSX-3 (2.5-10.0 mg/kg IP) significantly attenuated pilocarpine-induced tremulous jaw movements. Furthermore, adenosine A(2A) receptor knockout mice showed a significant reduction in pilocarpine-induced tremulous jaw movements compared to littermate controls. These results demonstrate the feasibility of using the tremulous jaw movement model in mice, and indicate that adenosine A(2A) receptor antagonism and deletion are capable of reducing cholinomimetic-induced tremulous jaw movements in mice. Future studies should investigate the effects of additional genetic manipulations using the mouse tremulous jaw movement model.

The novel adenosine A(2A) antagonist prodrug MSX-4 is effective in animal models related to motivational and motor functions

Adenosine A(2A) and dopamine D2 receptors interact to regulate diverse aspects of ventral and dorsal striatal functions related to motivational and motor processes, and it has been suggested that adenosine A(2A) antagonists could be useful for the treatment of depression, parkinsonism and other disorders. The present experiments were performed to characterize the effects of MSX-4, which is an amino acid ester prodrug of the potent and selective adenosine A(2A) receptor antagonist MSX-2, by assessing its ability to reverse pharmacologically induced motivational and motor impairments. In the first group of studies, MSX-4 reversed the effects of the D2 antagonist eticlopride on a concurrent lever pressing/chow feeding task that is used as a measure of effort-related choice behavior. MSX-4 was less potent after intraperitoneal administration than the comparison compound, MSX-3, though both were equally efficacious. With this task, MSX-4 was orally active in the same dose range as MSX-3. MSX-4 also reversed the locomotor suppression induced by eticlopride in the open field, but did not induce anxiogenic effects as measured by the relative amount of interior activity. Behaviorally active doses of MSX-4 also attenuated the increase in c-Fos and pDARPP-32(Thr34) expression in nucleus accumbens core that was induced by injections of eticlopride. In addition, MSX-4 suppressed the oral tremor induced by the anticholinesterase galantamine, which is consistent with an antiparkinsonian profile. These actions of MSX-4 indicate that this compound could have potential utility as a treatment for parkinsonism, as well as some of the motivational symptoms of depression and other disorders.

Detection, quantification, and microlocalisation of targets of pesticides using microchannel plate autoradiographic imagers

Organophosphorus (OP) compounds are a diverse chemical group that includes nerve agents and pesticides. They share a common chemical signature that facilitates their binding and adduction of acetylcholinesterase (AChE) within nerve synapses to induce cholinergic toxicity. However, this group diversity results in non-uniform binding and inactivation of other secondary protein targets, some of which may be adducted and protein activity influenced, even when only a relatively minor portion of tissue AChE is inhibited. The determination of individual OP protein binding targets has been hampered by the sensitivity of methods of detection and quantification of protein-pesticide adducts. We have overcome this limitation by the employment of a microchannel plate (MCP) autoradiographic detector to monitor a radiolabelled OP tracer compound. We preincubated rat thymus tissue in vitro with the OP pesticides, azamethiphos-oxon, chlorfenvinphos-oxon, chlorpyrifos-oxon, diazinon-oxon, and malaoxon, and then subsequently radiolabelled the free OP binding sites remaining with 3H-diisopropylfluorophosphate (3H-DFP). Proteins adducted by OP pesticides were detected as a reduction in 3H-DFP radiolabelling after protein separation by one dimensional polyacrylamide gel electrophoresis and quantitative digital autoradiography using the MCP imager. Thymus tissue proteins of molecular weights -28 kDa, 59 kDa, 66 kDa, and 82 kDa displayed responsiveness to adduction by this panel of pesticides. The 59 kDa protein target (previously putatively identified as carboxylesterase I) was only significantly adducted by chlorfenvinphos-oxon (p < 0.001), chlorpyrifos-oxon (p < 0.0001), and diazinon-oxon (p < 0.01), the 66 kDa protein target (previously identified as serum albumin) similarly only adducted by the same three pesticides (p < 0.0001), (p < 0.001), and (p < 0.01), and the 82 kDa protein target (previously identified as acyl peptide hydrolase) only adducted by chlorpyrifos-oxon (p < 0.0001) and diazinon-oxon (p < 0.001), when the average values of tissue AChE inhibition were 30%, 35%, and 32% respectively. The -28 kDa protein target was shown to be heterogeneous in nature and was resolved to reveal nineteen 3H-DFP radiolabelled protein spots by two dimensional polyacrylamide gel electrophoresis and MCP autoradiography. Some of these 3H-DFP proteins spots were responsive to adduction by preincubation with chlorfenvinphos-oxon. In addition, we exploited the useful spatial resolution of the MCP imager (-70 mm) to determine pesticide micolocalisation in vivo, after animal dosing and autoradiography of brain tissue sections. Collectively, MCP autoradiographic imaging provided a means to detect targets of OP pesticides, quantify their sensitivity of adduction relative to tissue AChE inhibition, and highlighted that these common pesticides exhibit specific binding character to protein targets, and therefore their toxicity will need to be evaluated on an individual compound basis. In addition, MCP autoradiography afforded a useful method of visualisation of the localisation of a small radiolabelled tracer within brain tissue.

Pharmacological and physiological characterization of the tremulous jaw movement model of parkinsonian tremor: potential insights into the pathophysiology of tremor

Tremor is a cardinal symptom of parkinsonism, occurring early on in the disease course and affecting more than 70% of patients. Parkinsonian resting tremor occurs in a frequency range of 3-7 Hz and can be resistant to available pharmacotherapy. Despite its prevalence, and the significant decrease in quality of life associated with it, the pathophysiology of parkinsonian tremor is poorly understood. The tremulous jaw movement (TJM) model is an extensively validated rodent model of tremor. TJMs are induced by conditions that also lead to parkinsonism in humans (i.e., striatal DA depletion, DA antagonism, and cholinomimetic activity) and reversed by several antiparkinsonian drugs (i.e., DA precursors, DA agonists, anticholinergics, and adenosine A(2A) antagonists). TJMs occur in the same 3-7 Hz frequency range seen in parkinsonian resting tremor, a range distinct from that of dyskinesia (1-2 Hz), and postural tremor (8-14 Hz). Overall, these drug-induced TJMs share many characteristics with human parkinsonian tremor, but do not closely resemble tardive dyskinesia. The current review discusses recent advances in the validation of the TJM model, and illustrates how this model is being used to develop novel therapeutic strategies, both surgical and pharmacological, for the treatment of parkinsonian resting tremor.