Reduced Cholinesterase Activity Research Articles

Design, synthesis and biological evaluation of carbamate derivatives incorporating multifunctional carrier scaffolds as pseudo-irreversible cholinesterase inhibitors for the treatment of Alzheimer's disease

In this study, a series of carbamate derivatives incorporating multifunctional carrier scaffolds were designed, synthesized, and evaluated as potential therapeutic agents for Alzheimer's disease (AD). We used tacrine to modify the aliphatic substituent, and employed rivastigmine, indole and sibiriline fragments as carrier scaffolds. The majority of compounds exhibited good inhibitory activity for cholinesterase. Notably, compound C7 with sibiriline fragment exhibited potent inhibitory activities against human acetylcholinesterase (hAChE, IC50 = 30.35 ± 2.07 nM) and human butyrylcholinesterase (hBuChE, IC50 = 48.03 ± 6.41 nM) with minimal neurotoxicity. Further investigations have demonstrated that C7 exhibited a remarkable capacity to safeguard PC12 cells against H2O2-induced apoptosis and effectively suppressed the production of reactive oxygen species (ROS). Moreover, in an inflammation model of BV2 cells induced by lipopolysaccharide (LPS), C7 effectively attenuated the levels of pro-inflammatory cytokines. After 12 h of dialysis, C7 continued to exhibit an inhibitory effect on cholinesterase activity. An acute toxicity test in vivo demonstrated that C7 exhibited a superior safety profile and no hepatotoxicity compared to the parent nucleus tacrine. In the scopolamine-induced AD mouse model, C7 (20 mg/kg) significantly reduced cholinesterase activity in the brain of the mice. C7 was tested in a pharmacological AD mouse model induced by Aβ1-42 and attenuated memory deficits at doses as low as 5 mg/kg. The pseudo-irreversible cholinesterase inhibitory properties and multifunctional therapeutic attributes of C7 render it a promising candidate for further investigation in the treatment of AD.

Curcumin protects against fenvalerate-induced neurotoxicity in zebrafish (Danio rerio) larvae through inhibition of oxidative stress

Fenvalerate (FEN), a typical type II pyrethroid pesticide, is widely used in agriculture. FEN has been detected in the environment and human body. However, the neurotoxicity of FEN has not been well elucidated. This study aimed to explore the mechanisms underlying FEN-induced neurotoxicity using the zebrafish (Danio rerio) model. We also investigated whether curcumin (CUR), a polyphenol antioxidant that exhibits neuroprotective properties, can prevent FEN-induced neurotoxicity. Here, zebrafish embryos were exposed to 0, 3.5, 7 and 14 μg/L of FEN from 4 to 96 h post fertilization (hpf) and neurotoxicity was assessed. Our results showed that FEN decreased the survival rate, heart rate, body length and spontaneous movement, and increased malformation rate. FEN caused neurobehavioral alterations, including decreased swimming distance and velocity, movement time and clockwise rotation times. FEN also suppressed neurogenesis in transgenic HuC:egfp zebrafish, reduced cholinesterase activity and downregulated the expression of neurodevelopment related genes (elavl3, gfap, gap43 and mbp). In addition, FEN enhanced oxidative stress via excessive reactive oxygen species and antioxidant enzyme inhibition, then triggered apoptosis by upregulation of apoptotic genes (p53, bcl-2, bax and caspase 3). These adverse outcomes were alleviated by CUR, indicating that CUR mitigated FEN-induced neurotoxicity by inhibiting oxidative stress. Overall, this study revealed that CUR ameliorated FEN-induced neurotoxicity via its antioxidant, indicating a promising protection of CUR against environmental pollutant-induced developmental anomalies.

Tissues toxicity attenuation by vitamin E on oxidative damage induced by diazinon.

Organophosphorus insecticides such as diazinon (DZN) are used worldwide in industry, veterinary practice, and agriculture. They may induce oxidative stress in different tissues. The use of antioxidants can protect tissues against oxidative stress. The aim of this study was to investigate the prophylactic and therapeutic roles of vitamin E against DZN-induced oxidative damage and biochemical alterations in various tissues of male Wistar rats. Thirty rats were divided into five groups: Control group received only corn oil as DZN solvent, DZN group received 100 mg/kg of DZN, E group received 150 mg/kg of vitamin E, E-DZN group received vitamin E and then dosed with DZN and DZN-E group received DZN and then dosed with vitamin E. All injections were carried out intraperitoneally. Plasma and various tissues were prepared and evaluated. Results showed that acute administration of DZN caused a significant induction of oxidative damage in the tested tissues via increased malondialdehyde level and some plasma biochemical indices, depletion of glutathione (GSH), reduced cholinesterase activity and change in the activities of superoxide dismutase, catalase and glutathione-S transferase. Treatment of rats with vitamin E resulted in an elevation in the level of GSH, normalizing the antioxidant enzymes activities and decreasing lipid peroxidation, although all these tests did not return to the normal level in certain tissues. The findings of this study suggest that both prophylactic and therapeutic treatments of rats with vitamin E provide a protective role against DZN-induced oxidative stress and cholinergic hyperactivity through free radicals scavenging and membrane stabilizing.

Dual assessment of transcriptional and metabolomic responses in the American dog tick following exposure to different pesticides and repellents

The American dog tick, Dermacentor variabilis, is a major pest to humans and animals, serving as a vector to Rickettsia rickettsii, a bacterium responsible for Rocky Mountain spotted fever, and Francisella tularensis, which is responsible for tularemia. Although several tactics for management have been deployed, very little is known about the molecular response following pesticidal treatments in ticks. In this study, we used a combined approach utilizing transcriptomics and metabolomics to understand the response of the American dog tick to five common pesticides (amitraz, chlorpyrifos, fipronil, permethrin, and propoxur), and analyzed previous experimental data utilizing DEET repellent. Exposure to different chemicals led to significant differential expression of a varying number of transcripts, where 42 were downregulated and only one was upregulated across all treatments. A metabolomic analysis identified significant changes in acetate and aspartate levels following exposure to chlorpyrifos and propoxur, which was attributed to reduced cholinesterase activity. Integrating the metabolomics study with RNA-seq analysis, we found the physiological manifestations of the combined metabolic and transcriptional differences, revealing several novel biomolecular pathways. In particular, we discovered the downregulation of amino sugar metabolism and methylhistidine metabolism after permethrin exposure, as well as an upregulation of glutamate metabolism in amitraz treated samples. Understanding these altered biochemical pathways following pesticide and repellent exposure can help us formulate more effective chemical treatments to reduce the burden of ticks.

Pesticide Spraying and Reduced Cholinesterase Activity among Hill Tribe Farmers in Thailand.

Background.Farming is an important occupation in Thai hill tribe communities, which are often remote, and lack other economic opportunities along with basic educational, health care, and occupational health and safety services. Additionally, these communities have a unique culture and language.Objectives.The present study was conducted in northern Thailand to evaluate pesticide exposures and associated health impacts among hill tribe farmers, and to compare them to Thai farmers.Methods.Lahu hill tribe farmers in a mountain community were recruited by public health hospital staff, along with a reference group of lowland Thai farmers. Participants completed a survey on demographic factors and work practices, and blood and urine samples were collected by a trained nurse. Acetylcholinesterase activity (AChE) was quantified to assess pesticide exposure, whereas liver and kidney functions were evaluated using clinical biomarkers.Results.A large fraction (nearly 50%) of Lahu farmers were illiterate and could not speak Thai. Thai farmers worked fewer hours per week (39.4) than did Lahu farmers. Among Lahu farmers, AChE levels were significantly lower (worse) than those of Thai farmers. However, other health outcomes in these populations were similar. Formal education and language skills were not associated with pesticide exposures or health outcomes. Pesticide spraying was found to be a significant predictor of reduced AChE (OR=8.5, 95% CI 1.1–69.6).Conclusions.Pesticide exposures are a significant occupational health hazard among Thai hill tribe farmers. Training, potentially delivered by community health volunteers, is needed to communicate safe pesticide work practices to these farmers.Participant Consent.ObtainedEthics Approval.The study protocol was approved by the Institutional Review Board of Mae Fah Luang University (REH-61080).Competing Interests.The authors declare no competing financial interests.

Potential association of reduced cholinesterase activity with Trypanosoma evansi pathogenesis in buffaloes

The present study aimed to investigate the association of cholinesterase activity with trypanosomosis in buffaloes. Thirty-three clinical cases of trypanosomosis in water buffaloes, found positive for trypomastigotes of T. evansi on blood smear examination, were divided into two groups based on clinical manifestations. Twenty diseased buffaloes revealing only common clinical signs were allocated to Group I, while the remaining 13 buffaloes showing common clinical manifestations along with neurological disturbances were allocated to Group II. Twelve clinically healthy buffaloes, free from any haemoprotozoa infection, were kept as healthy control (Group III). Blood samples were collected from buffaloes of all three groups to determine serum cholinesterase activity. Compared to buffaloes of healthy control group, cholinesterase activity in T. evansi-infected buffaloes of Group I and II was significantly (P<0.001) lower. However, no significant difference was observed in cholinesterase activity between the T. evansi-infected buffaloes exhibiting neurological disorders and no neurological disorders. Summing up, reduced cholinesterase activity seems to be associated with the pathogenesis of natural T. evansi infection and its clinical manifestations in buffaloes possibly by evading immune response. Further studies are warranted on association of cholinesterase activity in T. evansi-infected buffaloes with neurological disorders.

Sperm exposure to carbon-based nanomaterials causes abnormalities in early development of purple sea urchin (Paracentrotus lividus)

We examined egg fertilisation in purple sea urchin (Paracentrotus lividus) after sperm exposure to carbon-based nanomaterials, carbon black (CB) and graphene oxide (GO), from 0.0001mg/L to 1.0mg/L. Gastrula stage embryos were investigated for acetylcholinesterase and propionylcholinesterase activities, and their morphological characteristics. Plutei were analysed for morphological abnormalities, with emphasis on skeletal rod formation. Egg fertilisation was significantly affected by CB, at all concentrations tested. Loss of cell adhesion at the gastrula surface was observed in eggs fertilised with sperm treated with CB. However, concentration-dependant morphological anomalies were observed in the gastrulae and plutei formed after sperm exposure to either CB or GO. The activities of both cholinesterases decreased in the gastrulae, although not in a concentration-dependent manner. These effects appear to arise from physical interactions between these carbon-based nanomaterials and the sperm, whereby nanomaterials attached to the sperm surface interfere with fertilisation, which leads to disturbances in the signalling pathways of early embryonic development. Reduced cholinesterase activity in gastrulae from eggs fertilised with nanomaterial-treated sperm confirms involvement of the cholinergic system in early sea urchin development, including skeletogenesis.

Behavioral sequelae following acute diisopropylfluorophosphate intoxication in rats: Comparative effects of atropine and cannabinomimetics

The comparative effects of atropine and the indirect cannabinomimetics URB597 (a fatty acid amide hydrolase inhibitor) and URB602 (a monoacylglycerol lipase inhibitor) on functional and neurobehavioral endpoints following acute diisopropylfluorophosphate intoxication were studied. Male Sprague–Dawley rats were treated with vehicle or DFP (2.5 mg/kg, sc), immediately post-treated with either vehicle, atropine (16 mg/kg), URB597 (3 mg/kg), URB602 (10 mg/kg) or a combination of URB597 and URB602, and functional signs of toxicity as well as nocturnal motor activity were measured daily for seven consecutive days. Performance in the elevated plus maze (for anxiety-like behavior) and the forced swimming test (for depression-like behavior) was measured at days 6–8 and 27–29 after dosing. Twenty-four hours after dosing, DFP markedly reduced cholinesterase activity in selected brain regions and peripheral tissues (diaphragm and plasma). Substantial recovery of cholinesterase activity was noted at both 8 and 29 days after dosing but significant inhibition was still noted in some brain regions at the latest time-point. DFP elicited body weight reductions and typical signs of cholinergic toxicity, and reduced nocturnal ambulation and rearing. Atropine and the cannabinomimetics (alone and in combination) partially attenuated DFP-induced functional signs of toxicity. None of the post-treatments reversed the DFP-induced reduction in ambulation or rearing, however. No significant treatment-related effects on elevated plus maze performance were noted. DFP-treated rats exhibited decreased swimming and increased immobility in the forced swimming test at both time-points. None of the post-treatments had any effect on DFP-induced changes in immobility or swimming at day 8. At day 29, atropine and the combination of URB597/URB602 significantly blocked DFP-induced changes in immobility, while URB597 and the combination reversed DFP-induced changes in swimming. The results suggest that early blockade of muscarinic receptors and enhancement of eCB signaling can attenuate both acute and delayed effects elicited by DFP.

Cholinergic Stimulation Improves Autonomic and Hemodynamic Profile During Dynamic Exercise in Patients With Heart Failure

Background Parasympathetic dysfunction is an independent risk factor for mortality in heart failure for which there is no specific pharmacologic treatment. This article aims to determine the effect of pyridostigmine, an anticholinesterase agent, on the integrated physiologic responses to dynamic exercise in heart failure. Methods and Results Patients with chronic heart failure (n = 23; 9 female; age = 48 ± 12 years) were submitted to 3 maximal cardiopulmonary exercise tests on treadmill in different days. The first test was used for adaptation and to determine exercise tolerance. The other tests were performed after oral administration of pyridostigmine (45 mg, 3 times/day, for 24 hours) or placebo, in random order. All patients were taking their usual medication. Pyridostigmine reduced cholinesterase activity by 30%, inhibited the chronotropic response throughout exercise, up to 60% of maximal effort (pyridostigmine = 108 ± 3 beats/min vs. placebo = 113 ± 3 beats/min; P = .040), and improved heart rate reserve (pyridostigmine = 73 ± 5 beats/min vs. placebo = 69 ± 5 beats/min; P = 0.035) and heart rate recovery in the first minute after exercise (pyridostigmine = 25 ± 2 beats/min vs. placebo = 22 ± 2 beats/min; P = .005), whereas peak heart rate was similar to placebo. Oxygen pulse, an indirect indicator of stroke volume, was higher under pyridostigmine during submaximal exercise. Conclusions Pyridostigmine was well tolerated by heart failure patients, leading to improved hemodynamic profile during dynamic exercise.

Homocysteine reduces cholinesterase activity in rat and human serum

In the present study we investigated the effect of homocysteine administration, the main metabolite accumulating in homocystinuria, on cholinesterase activity in rat and human serum. For the in vivo study, 8-, 15- and 60-day-old rats received one subcutaneous injection of homocysteine (0.3, 0.4 or 0.6μmol/g of body weight, respectively) or saline (control) and were sacrificed 1h later, when serum was collected in order to determine cholinesterase activity. For the in vitro studies, serum of 8-, 15- and 60-day-old untreated rats or 20–25- and 52–60-day-old human beings (healthy volunteers) were incubated with 10–500μM homocysteine. Results showed that acute hyperhomocysteinemia (in vivo study) significantly reduced cholinesterase activity in the serum of rats of all ages tested. We also observed that 500μM homocysteine added to the incubation medium (in vitro study) significantly inhibited cholinesterase activity both in serum of rats and humans. Our findings seem to reinforce the proposed associations of cholinesterase activity with hyperhomocysteinemia.

The Use of Cholinesterase Activity in Flounder ( Platichthys flesus) Muscle Tissue as a Biomarker of Neurotoxic Contamination in UK Estuaries

This study investigated the occurrence and levels of neurotoxic contamination in UK estuaries by the determination of cholinesterase (ChE) activity in the muscle of the flounder ( Platichthys flesus). Samples were obtained from 16 sites in the estuaries of the rivers Humber, Mersey, Tamar, Tees and Tyne. ChE activity levels were compared to those at a reference site- the River Alde, Suffolk. Twelve sites exhibited significantly ( p<0.05) reduced ChE activity. The Tyne estuary showed a strong gradient of effect that suggested a source of neurotoxic-contamination upstream of the sampled sites. Representative water samples from several of the estuaries were analysed for the presence of 32 organophosphate (OP) and 20 carbamate (C) pesticides from which residues of nine OPs and six Cs were detected. Correlation analysis of ChE activity with gender, size, GSI, HSI and condition factor suggested that these variables did not influence neural activity in this study. It was concluded that the reduction in ChE activity was contaminant mediated and that OP and C pesticides were probable contributors. Influences on ChE activity, higher order implications and its use as a monitoring tool, including reactivation techniques, are discussed.

Acute Effects of an Insect Repellent, N,N-Diethyl-m-toluamide, on Cholinesterase Inhibition Induced by Pyridostigmine Bromide in Rats

Acute lethal interactions have been previously described between a cholinesterase (ChE) inhibitor, pyridostigmine bromide (PB), and the insect repellent, N,N-diethyl-m-toluamide (DEET). The mechanism of toxic interaction between these agents is unknown. Alterations in membrane permeability caused by DEET could facilitate or enhance absorption, or alter the distribution of peripherally restricted PB, causing increased inhibition of ChE at a given dose. Studies were conducted to investigate PB-induced ChE inhibition in the presence of DEET. Rats received ip injections of PB (1, 2, or 3 mg/kg), DEET (200 mg/kg), or PB + DEET at doses that potentiated acute lethality. ChE activity was measured in heart, diaphragm, blood, whole brain, or specific brain areas using a modified spectrophotometric assay. DEET did not alter PB-induced inhibition of ChE activity in rat diaphragm, heart, or blood. Administration of DEET alone had no effect on ChE activity. PB alone did not inhibit ChE in whole brain, but PB (3 mg/kg) + DEET (200 mg/kg) caused significant inhibition of whole brain ChE activity to approximately 60% of controls. In specific brain areas, (cortex, cerebellum, medulla, hypothalamus, hippocampus, midbrain, and striatum) PB alone did not inhibit ChE activity. PB (3 mg/kg) + DEET (200 mg/kg) reduced ChE activity to approximately 65–75% of controls in each brain area, but those results were not statistically significant. In conclusion, DEET did not alter PB-induced inhibition of ChE activity in the periphery. While DEET may have facilitated the access of PB into the CNS at high doses, it is doubtful that the resulting minor reduction in ChE activity would have resulted in death. It is unlikely that the lethal interaction between PB and DEET is mediated through a cholinergic effect resulting from increased inhibition of ChE.

Effects of metrifonate on impairment of learning and dysfunction of cholinergic neuronal system in basal forebrain-lesioned rats

Several studies have indicated the possibility of using cholinesterase (ChE) inhibitors as therapeutic drugs for Alzheimer's disease. Metrifonate (MTF) is an organophosphorus compound that has been used in the treatment of schistosomiasis. In this study, we investigated the effects of MTF on the impairment of learning and memory, decreased ChE activity and extracellular acetylcholine (ACh) levels in basal forebrain (BF)-lesioned rats. The oral administration of MTF improved the BF-lesion-induced impairment of performance on passive avoidance task. Further, MTF reduced ChE activity in the cerebral cortex. In vivo brain microdialysis studies showed that MTF significantly increased the release of ACh, but decreased that of choline (Ch) in the cerebral cortex of BF-lesioned rats. These results indicated that MTF ameliorates the impairment of performance on passive avoidance task in BF-lesioned rats by increasing the extracellular ACh levels by inhibiting ChE. This suggested that MTF may be useful as a therapeutic drug for Alzheimer's disease.

A Case of Fatal Ingestion of Malathion

We report a case of suicide due to organophosphate poisoning in an 80-year-old woman who ingested malathion mixed with a fruit drink. She presented with signs and symptoms of cholinergic crisis and initially improved with therapy. Her plasma cholinesterase (ChE) level remained low, her course progressively deteriorated with respiratory and renal failure, and she died 12 days after hospital admission. The antemortem blood malathion level of 23.9 mg/L is the highest reported in the literature, as determined by modern methods. Postmortem toxicologic analysis revealed still greatly reduced ChE activity.

Effect of sustained drug-induced vagotonia on isolated tissue sensitivity to carbachol and histamine in guinea-pigs

The effects of sustained vagotonia induced by 7 consecutive days of pretreatment with an anticholinesterase, echothiophate iodide (ETP, 20μg/kg/day, s.c.) on carbachol-induced responses and muscarinic receptor binding characteristics in lung, heart and ileum of guinea-pigs have been investigated. The study was aimed at elucidating the mechanisms involved in the ETP-induced airway subsensitivity to carbachol observed in our previous studies.ETP-pretreatment reduced cholinesterase activity by about 40-50% in lung, heart, ileum and serum. In the lung and heart, neither the sensitivity of isolated tissues to carbachol nor the binding of [3H] quinuclidinyl benzilate ([3H]QNB) were influenced by ETP-pretreatment. In contrast, the sensitivity of isolated trachea and ileum to carbachol was reduced by ETP-pretreatment, and this sensitivity change of the ileum was associated with a fall in muscarinic receptor density without a change in receptor affinity, as determined in [3H]QNB binding experiments. ETP-pretreatment also reduced the sensitivity of trachea and ileum to histamine, although [3H] pyrilamine binding in the ileum was not affected.These results suggest that sustained vagotonia induced by chronic ETP-pretreatment reduces the sensitivity of isolated ileum and possibly trachea to carbachol and histamine through a reduction in muscarinic receptor density and also some alteration of receptor coupling to intracellular mechanisms.

Effect of induced hypomagnesaemia on the toxicity of imidocarb in calves

The hypothesis that the toxic effects of imidocarb mediated by reduced cholinesterase activity might be intensified by hypomagnesaemia was tested in calves. Hypomagnesaemia was induced in 12 males (50 kg) using an artificial milk based on a commercial nondairy coffee creamer. Although plasma magnesium levels reached 0.33 mmol litre-1 in two weeks no clinical signs were detected. In 12 control calves a daily magnesium supplement of 0.6 g was inadequate although the published requirement is 0.45 g; it was raised to 1.2 g to keep plasma magnesium normal. Lighter calves developed hypomagnesaemia more readily and fast-growing calves had lower plasma urea concentrations. Plasma calcium, but not plasma magnesium, showed significant positive correlation with plasma albumin. The only statistically significant effects of hypomagnesaemia were slight elevations of white cell count and plasma sodium. The hypomagnesaemic and normomagnesaemic calves were divided into two equal groups and treated with 3.3 mg kg-1 of imidocarb dipropionate or a placebo. The drug produced the expected clinical signs of mild toxicity and depression of cholinesterase but no other adverse effects. Transient slight depressions of plasma calcium and potassium concentration, a transient rise of plasma sodium and elevation of creatine kinase occurred. None of the effects of imidocarb treatment was intensified by hypomagnesaemia except, perhaps, constriction of the pupils; generally, hypomagnesaemic animals were affected less.

Lack of nicotinic supersensitivity in frog sympathetic neurones following denervation.

The sensitivity of bull-frog sympathetic neurones to nicotinic, cholinergic agonists has been studied in both normal (control) and surgically denervated ganglia. Using gross extracellular recording, the sensitivity to acetylcholine (ACh) increased 18-fold following denervation, while that to carbachol (CCh) was unchanged. Normal ganglia showed a similar sensitivity increase after inhibition of cholinesterase. This suggests that the rise in ACh sensitivity is due to reduced cholinesterase activity, not to true supersensitivity. There was no significant difference in resting membrane potential or input resistance between normal and denervated neurones. Neurones denervated for 7-50 days showed no significant change in sensitivity to ACh or CCh applied iontophoretically at a distance of 10 micron from the cell surface. In control ganglia, localized iontophoretic application of ACh revealed an uneven distribution of sensitivity which is attributed to the localization of receptors to synaptic areas. Fourteen days after denervation, the geometric mean sensitivity to focally applied ACh was not significantly different from that found in control ganglia. The variation in sensitivity to focally applied ACh at randomly chosen sites on denervated neurones was as great as that found in control ganglia. It is concluded that denervation does not cause frog sympathetic neurones to become supersensitive to ACh. The apparent increase in nicotinic ACh sensitivity observed using extracellular recording from whole ganglia is due not to a change in the number or distribution of ACh receptors, but to a decrease in cholinesterase activity.

Reduced cholinesterase activity and somatostatin-like immunoreactivity in the cerebrospinal fluid of patients with dementia of the Alzheimer type

Cholinesterase (ChE) activity and somatostatin-like immunoreactivity (SLI) of the cerebrospinal fluid were determined for 59 patients with dementia of the Alzheimer type (AD/SDAT) and for 19 age-matched control patients with no signs of dementia. Both ChE activities and SLI concentrations of cerebrospinal fluid were reduced significantly in dementia patients compared to the controls. In the AD/SDAT patients cholinesterase and somatostatin-like immunoreactivity levels seemed to be correlated with the severity of dementia. These findings agree with observations of reduced cortical acetylcholinesterase activities and somatostatin values in dementia of the Alzheimer type.

Cholinesterase Problems arising in a Plant Manufacturing Tri-aryl Phosphates

Eight cases with an abnormal cholinesterase, either in quantity or quality or both, are described. Case 1 falls in the subgroup U1, and Case 2 most likely also falls into this subgroup. Cases 3 and 4 fall into the intermediate group with a reduced cholinesterase activity. Cases 5,6,7 and 8 fall into the usual group with a progressive reduction in the esterase activity in Cases 5 and 6, a severe fall in the cholinesterase level in Case 7 and a markedly low initial pre-employment level in Case 8. The assessment and method of dealing with these cases are discussed.

Striatal cholinergic activity during morphine-induced catalepsy in the rat: Development of tolerance

Morphine hydrochloride (10 mg/kg, i.p.) induced marked catalepsy in rats, which was associated with significantly enhanced striatal acetylcholine levels and reduced cholinesterase activity. Rapid tolerance to morphine-induced catalepsy was noted after twice daily administrations, the tolerance being discernible after the third injection and was complete after the eleventh injection. With the development of tolerance, morphine-induced effects on striatal acetylcholine and cholinesterase were progressively reversed, confirming striatal cholinergic involvement in morphine-induced catalepsy in the rat.