Cholinesterase Activity Of Muscle Research Articles

Early Toxic Effects in a Central American Native Fish (Parachromis dovii) Exposed to Chlorpyrifos and Difenoconazole.

In Costa Rica, agriculture is one of the most important economic activities. Chlorpyrifos and difenoconazole have been identified as agrochemicals widely used in banana and pineapple crops in the Caribbean area of the country and are constantly recorded in aquatic ecosystems. The toxicity of these pesticides in Parachromis dovii was studied. Median lethal concentrations (LC50s) for each substance were obtained from 96-h acute tests. Then, fish were exposed to sublethal concentrations of both substances (10% of LC50), individually and in mixture, to evaluate biomarker responses. Ethoxyresorufin-O-deethylase (EROD), catalase, and glutathione S-transferase activities as well as lipid peroxidation were measured in liver and gill tissues as markers of biotransformation and oxidative stress processes. Cholinesterase activity in brain and muscle tissue was also quantified as a biomarker of toxicity. The LC50s were 55.34 μg/L (95% confidence interval [CI] 51.06-59.98) for chlorpyrifos and 3250 μg/L (95% CI 2770-3810) for difenoconazole. Regarding the biomarkers, a significant inhibition of brain and muscle cholinesterase activity was recorded in fish exposed to 5.50 μg/L of chlorpyrifos. This activity was not affected when fish were exposed to the mixture of chlorpyrifos with difenoconazole. Significant changes in lactate dehydrogenase activity were observed in fish exposed to 325 μg/L of difenoconazole, whereas fish exposed to the mixture showed a significant increase in EROD activity in the liver. These results suggest harmful effects of chlorpyrifos insecticide at environmentally relevant concentrations. There is also evidence for an interaction of the 2 substances that affects the biotransformation metabolism at sublethal levels of exposure. Environ Toxicol Chem 2021;40:1940-1949. © 2021 SETAC.

In vivo cholinesterase sensitivity of gilthead seabream (Sparus aurata) exposed to organophosphate compounds: Influence of biological factors

Two cholinesterases have been found in vertebrates, acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). These enzymes are present in the gilthead seabream, AChE in the brain and muscle and BChE in the muscle. Cholinesterases have been used as biomarker of effect in environmental monitoring studies. However, there are few studies about the influence of biometric parameters on ChE. This paper studies the possible influence of biological factors on brain and muscle cholinesterase (ChE) in Sparus aurata. Our results show that ChE activity in brain and muscle tissues changes depending on several biological variables. ChE activity in these tissues decreased when the age (48–152 week), body length (14.15–28.95 cm) and body weight (42.73–380.74 g) of the fishes studied increased. The relationships between brain and muscle ChE activity and several biometric factors were curvilinear.On the other hand, in vivo sensitivity of cholinesterase in the gilthead seabream exposed to organophosphorus pesticides (azinphosmethyl, dimethoate and dichlorvos) was studied in order to learn about recovery from cholinesterase present (brain and muscle) after exposure to a sublethal dose. The recovery of muscle AChE was similar to cerebral AChE, while muscular BChE showed a slower recovery.

Chronic effects of a binary insecticide Acer 35 EC on Nile tilapia Oreochromis niloticus through a multi-biomarker approach

Acer 35 EC is a widely used insecticide (a binary mixture of lambda-cyhalothrin and acetamiprid) in pest control in many West African countries, particularly in the cotton culture in north Benin. The aim of this study was to investigate the chronic effects of Acer 35 EC on Nile tilapia Oreochromis niloticus juveniles using a multi-biomarker approach under laboratory conditions. For this purpose, fish were exposed to sublethal concentrations of Acer 35 EC (0, 1 and 10% of LC50- 96 h value). After 28 and 56 days of exposure, several biomarkers were measured in males and females including enzymatic activities related to detoxification and oxidative stress, neurotoxicity and immune responses, sex steroid hormones (testosterone, 17β-estradiol and 11-keto-testosterone) and histological alterations of liver, kidney and gonads. An Integrated Biomarker Response (IBR) was then calculated. The results showed a reduction of cholinesterase activity in muscles, and intercellular superoxide anion production in both sexes. Female steroidogenesis and gametogenesis were affected, especially testosterone levels and oocyte growth. More alterations were observed in liver after exposure to Acer 35 EC. In both sexes, IBR values were higher after 56 days than after 28 days of exposure. In conclusion, based on a large set of biomarkers and IBR values, the chronic exposure to low doses of insecticide Acer 35 EC seems to impair different physiological functions in Nile tilapia juveniles on a time-dependent manner, with a stronger impact on females than on males.

Biomarker and hematological fieldwork with amphibians: is it necessary to sample all night?

In the context of the global amphibian crisis, biomonitoring constitutes a valuable assessment tool to provide critical up to date information on the status and health of amphibians worldwide. The aim of the current study was to evaluate the possible confounding effects of sex, size, and time since capture on enzymatic biomarkers and hematologic parameters of the South American frog Leptodactylus latrans. Frogs were collected by hand between 9 pm and 12 am on two consecutive nights. On the first night, captured frogs were transported for 2h by car to laboratory installations, maintained overnight in plastic containers, and blood and tissue sampled on the next morning. In contrast, frogs collected on the second night were blood and tissue sampled in the field, immediately after the capture period. Hematological parameters were analyzed, and enzymatic activities of catalase, cholinesterase (ChE), and glutathione S-transferase (GST) were determined in the plasma, liver, kidney, and muscle. A sex difference was observed only for total white blood cell counts (WBC), females exhibiting significantly greater values than males. The packed cell volume (PCV), mean corpuscular hemoglobin concentration (MCHC), WBC, and muscle ChE activity were significantly correlated with snout-vent length (SVL). The correlation was inversed in the case of MCHC, WBC, and muscle ChE, while the correlation was positive between PCV and SVL. Most examined parameters presented similar values when frogs were sampled at night following capture or the next morning. Total red blood cells (RBCs) count, and plasma enzymatic activities of ChE and GST were the only parameters that presented significantly increased values in morning samplings compared with night samplings. Overall, the current study indicates that it is best to sample the frogs as soon as possible after capture if hematologic or plasmatic biomarkers are examined. Nevertheless, it is possible to sample on the next morning if tissular biomarkers are employed.

Use of Muscular Cholinesterase of Astyanax bifasciatus (Teleostei, Characidae) as a Biomarker in Biomonitoring of Rural Streams.

Cholinesterase (ChE) activity was measured in Astyanax bifasciatus maintained in controlled conditions. Muscle ChE activity of individuals collected in field conditions in two seasons was compared among specimens collected in seven streams (forest and rural) of the lower Iguaçu river basin in association with physical, chemical, pesticides and biological factors. Significant differences in muscle ChE activity between control fish and fish collected in streams in both seasons were found, with higher activity in natural conditions. This the first time that differences in muscle ChE activity have been found among fish collected from different streams, suggesting synergism among multiple factors (e.g. temperature, pH, animal weight) and ecological attributes (richness and abundance) as influencing the variation in biomarkers. It is necessary to evaluate the quality of aquatic environments for a more accurate biomonitoring approach.

Repeated sublethal exposures to the sea lice pesticide Salmosan® (azamethiphos) on adult male lobsters (Homarus americanus) causes neuromuscular dysfunction, hypoxia, metabolic disturbances and mortality

In Atlantic Canada and other salmon-growing regions, treatment of sea lice infestations in salmon aquaculture is necessary to protect fish health. The product Salmosan®, which contains the organophosphate azamethiphos as the active ingredient, is a pesticide presently used for treatment against sea lice. It is applied as a bath treatment and then released into the surrounding seawater. The potential for lethality to non-target species following acute and chronic exposures to Salmosan® has been studied over the past decade, however, the potential for sublethal effects on lobsters remains a concern. Adult male lobsters were exposed to 0.06, 0.5, and 5µgL−1 azamethiphos for one hour, repeated five times, over 48h. Lobsters were assessed immediately after exposure and over six days of recovery. Inhibition of muscle cholinesterase activity was detected in lobsters exposed to 0.5 and 5µgL−1 azamethiphos. The 5µgL−1 dose was considered lethal (93% cumulative mortality). Significant changes in hemolymph plasma biochemistry were most apparent in the 5µgL−1 exposure group in the immediate post-exposure samples. Citrate synthase activity was significantly lower in muscles of the 0.5µgL−1 exposure group compared to control lobsters. Mean electron transport system and standard metabolic rates tended to be lower in muscle tissue of the 0.5µgL−1 exposure group than control group lobsters. These results suggest that sublethal effects on lobster energetics may occur under laboratory exposure conditions (i.e., concentrations and duration) considered environmentally relevant, which could result in impairment under natural conditions.

Effects of chlorpyrifos on cholinesterase activity and stress markers in the tropical reef fish Acanthochromis polyacanthus

Tropical coastal ecosystems, including the Great Barrier Reef (GBR) of Australia are increasingly threatened by pollution; yet few studies have investigated the sensitivity of GBR species to these pollutants. Here we exposed juveniles of the tropical reef fish Acanthochromis polyacanthus (spiny damselfish) to three concentrations of the insecticide chlorpyrifos (CPF) and measured (i) muscle cholinesterase (ChE) activity; (ii) hepatic glutathione-S-transferase (GST) activity; and (iii) coenzyme Q (CoQ) redox balance, after 6h and 96h of exposure. After 96h, muscle ChE activity was significantly inhibited by 26%, 49% and 53% when fish were exposed to 1, 10 or 100μg/L CPF, respectively. Muscle ChE characterization revealed three types of ChEs, including two atypical forms. Hepatic CoQ antioxidant form significantly increased at 10μg/L after 6h of exposure, potentially demonstrating an early response to CPF-induced oxidative stress in liver. Hepatic GST was not affected by CPF exposure.

Micro-colorimetric determination of cholinesterase activity of motor end plates in the rat diaphragm

Abstract A spectrophotometric method is described for the determination of total cholinesterase activity in groups of 3–30 end plates, after staining with copper thiocholine and dissecting from the rat diaphragm, by continuous recording of the yellow colour (412 mμ) produced by reaction between dithiobisnitrobenzoate (1mm) and thiol groups liberated enzymatically from acetylthiocholine (5mm) at pH 7·0. Cholinesterase activity of end plates after correction for muscle ranged from 3·3–22·3 times 10−11m/end plate/hr and muscle cholinesterase activity ranged from 8·8–29·4 times 10−11 μg/hr. 2·9–26·7% of measured end plate cholinesterase activity was attributable to muscle. The results for end plate cholinesterase agreed with those obtained by other workers using microgasometric techniques. It was calculated that there were approximately 3·6 times 106 cholinesterase active sites/end plate which compared closely with 6 times 106 molecules acetylcholine released/ nerve ending/impulse and 2·6 times 106 cholinergic receptors/end plate given in the literature. It is suggested that each acetylcholine molecule after liberation from a nerve ending may interact with one receptor and be destroyed by one cholinesterase active site.

Single fiber electromyographic jitter and detection of acute changes in neuromuscular function in young and adult rats

Introduction Exposure to irreversible cholinesterase (ChE)-inhibiting compounds, such as organophosphates may produce neuromuscular dysfunction. However, less is known about changes in neuromuscular transmission after treatment with reversible ChE-inhibitors. These studies adapted single fiber electromyography (SFEMG) techniques to quantify neuromuscular jitter in adult and juvenile rats after treatment with agents that alter cholinergic neurotransmission. Methods Anesthetized adult and juvenile rats were tested using stimulation SFEMG, recorded in the gastrocnemius muscle, after stimulation in the sciatic notch region. The influence of electrode placement, treatment with decamethonium (to disrupt neuromuscular transmission) or physostigmine (reversible ChE inhibitor), and the impact of varied stimulation frequency were quantified. Results No significant effects of needle placement or criterion amplitude were observed when calculating the mean consecutive difference (MCD). Treatment with decamethonium did not alter MCD values in adult or juvenile rats. However, decamethonium produced an increased blocking of muscle action potentials (MAP) in juveniles. Also, when stimulated at 9.09 Hz, both adult and juvenile animals had a greater decrease in MAP amplitude between the first and fourth responses ( T 1– T 4 decrement) after treatment with decamethonium. Prior to treatment with decamethonium, the T 1– T 4 decrement averaged about 3 fold greater in juveniles than adults, and was larger at 3.03 and 9.09 Hz than with 0.91 Hz stimulation. Treatment with physostigmine resulted in at least 50% inhibition of muscle ChE activity, but produced minimal changes in the MCD values in adults or juveniles. Combined over treatments and stimulation frequencies, the median MCD for juveniles (11.6 µs) was less than that for of adults (18.8 µs). In juveniles, the median MCD increased from 9.3 µs to 13.9 µs as the stimulation rate was increased from 0.91 to 9.09 Hz. This stimulus-dependant change was more evident in juveniles than in adults. Discussion A technique was developed to record stimulation SFEMG and neuromuscular jitter, in vivo, in adult and juvenile rats. The method was sufficiently sensitive to detect age-related differences, potentially allowing developmental processes to be examined. Based on the literature and the current data, the technique appears to be more sensitive to prolonged inhibition of ChE enzymes than the reversible inhibition produced by physostigmine.

Selective inhibition of butyrylcholinesterase in vivo in horses by the feed-through larvacide Equitrol ®

The organophosphate insecticide tetrachlorvinphos (TCVP, Rabon) is the active ingredient in “feed-through” larvacides (e.g., Equitrol ®) for fly control around horse stables. As with other organophosphates, TCVP elicits toxicity by inhibiting acetylcholinesterase, leading to accumulation of the neurotransmitter acetylcholine and cholinergic signs. Relatively little is known, however, on the effects of TCVP-containing larvacides on acetylcholinesterase or other esterases in horses. Previous in vitro studies indicated that horse plasma cholinesterase activity was substantially (>10,000-fold) more sensitive than erythrocyte cholinesterase activity to inhibition by TCVP. In the current study, we examined the relative proportion of acetylcholinesterase and butyrylcholinesterase activities in horse plasma and muscle, and evaluated the in vivo effects of Equitrol ® on target and non-target esterases following oral feeding in horses. In vitro inhibition studies suggested that essentially all cholinesterase activity in horse plasma was butyrylcholinesterase, while muscle contained >90% acetylcholinesterase activity. For in vivo studies, adult, male horses (364–590 kg; n = 3/treatment group) were given either sweet feed alone or sweet feed supplemented with Equitrol ® daily for 21 consecutive days at the recommended rate. Clinical signs (vital signs, abdominal auscultation, ophthalmic exam, body temperature) were recorded on a daily basis. Heparinized blood samples were taken at days −1, 1, 3, 7, 21, 28, and 42 while muscle (semimembranosus) biopsies were taken under aseptic conditions on days −1 and 21. No signs of overt toxicity were noted at any time during the study. Plasma cholinesterase activity was significantly inhibited (33%) in larvacide-treated horses as early as one day after treatment and peak inhibition (69–71%) was noted at days 7 and 21. Following cessation of dosing, plasma cholinesterase activity recovered (46% and 83% of control on days 28 and 42, respectively). Neither erythrocyte cholinesterase activity nor plasma carboxylesterase activity was affected by larvacide treatment in vivo. Muscle cholinesterase activity was highly variable among individual horses (pre-treatment range: 0.50–4.92 nmole/min/mg protein), but there was no suggestion of a treatment-related reduction in muscle cholinesterase activity. These in vivo results confirm our previous in vitro studies indicating marked differential sensitivity of horse plasma and erythrocyte cholinesterase to inhibition by TCVP. Furthermore, the results suggest that recommended dosing levels of the TCVP-containing larvacide in horses are unlikely to affect acetylcholinesterase activities or disrupt cholinergic neurotransmission in target tissues.

Multibiomarker assessment of three Brazilian estuaries using oysters as bioindicators

Oysters have been largely employed as bioindicators of environmental quality in biomonitoring studies. Crassostrea rhizophorae was selected to evaluate the health status of three estuarine areas impacted by anthropogenic activities along the Brazilian coast, in three estuarine complexes, ranging in latitude from 7 to 25°S. In each estuary three sites were sampled in Winter and in Summer: a site considered as reference, and two sites next to contamination sources. Condition index was similar at all sites and estuaries, with the highest values found for Itamaracá oysters in Summer. Necrosis, hyperplasia, mucocyte hypertrophy and fusion of ordinary filaments were the main histopathological lesions observed. Muscle cholinesterase activity was overall similar, but with a strong seasonal effect. Inhibition or activation of branchial total ATPase and Na,K-ATPase activities at the contaminated sites was observed. The health status of these estuarine areas is quite similar, and the combined use of biomarkers is recommended.

Inhibitory effects of donepezil hydrochloride (E2020) on cholinesterase activity in brain and peripheral tissues of young and aged rats

Donepezil hydrochloride (donepezil: E2020: (±)-2-[(1-benzylpiperidin-4-yl)methyl]-5,6-dimethoxy-indan-1-one monohydrochloride)) is a centrally acting acetylcholinesterase inhibitor developed for the treatment of Alzheimer's disease. In the present study, its inhibitory effect on the activity of cholinesterase ex vivo was evaluated in the brain, plasma, erythrocytes, heart, small intestine, liver and pectoral muscle of young adult as well as aged rats, in comparison with that of tacrine (9-amino-1,2,3,4-tetrahydroacridine hydrochloride). In aged animals, cholinesterase activity in heart, small intestine and pectoral muscle was lower, whereas that in plasma and liver was higher than in young rats. Both groups showed the highest levels in the brain. Donepezil, at doses of 1.25, 2.5 and 5 mg/kg, p.o., inhibited brain, plasma, erythrocyte, liver and pectoral muscle cholinesterase activity in young rats in a dose-dependent manner but had less effect on cholinesterase activity in heart and small intestine. In aged animals, inhibition of cholinesterase activity in the brain, erythrocytes and pectoral muscle by donepezil was more potent than that in young animals. Tacrine, at doses of 5, 10 and 20 mg/kg, p.o., dose-dependently inhibited cholinesterase activity in all tissues of both young and aged animals, but most potently in heart, small intestine and liver. The inhibition of cholinesterase activity by tacrine in the brain, plasma, erythrocytes, heart and liver was more potent in aged rats than in tissues of young rats. Brain and plasma concentrations of unchanged donepezil and tacrine were measured in the same animals as used for the cholinesterase inhibition study. Brain and plasma concentrations of donepezil and tacrine were higher in aged than in young animals. It is concluded that the inhibitory effects of donepezil and tacrine on cholinesterase activity are greater in aged than in young rats, owing to differences in the tissue concentrations of these compounds between young and aged animals. It is also suggested that the effect of donepezil on cholinesterase activity is more tissue-selective than that of tacrine.

Evidence of Necrosis in Human Intercostal Muscle following Inhalation of an Organophosphate Insecticide

Intercostal muscle samples obtained from autopsy of a 51 year old male, exposed to an organophosphate insecticide by inhalation, were analyzed for cholinesterase (ChE) activity and muscle fiber integrity. Muscle ChE activity, five days after exposure, was still reduced to 53% of control values. Histological analysis indicated the presence of muscle fibers with subsarcolemmal grouped granular basophilic inclusions and scattered necrotic fibers. Results indicate that acute organophosphate exposure through inhalation can lead to skeletal muscle fiber damage in humans, similar to results obtained by ingestion. Furthermore, the pathology is comparable to the histological alterations observed in rats following acute injection of organophosphates.

Evidence of necrosis in human intercostal muscle following inhalation of an organophosphate insecticide

Intercostal muscle samples obtained from autopsy of a 51-year-old male exposed to an organophosphate insecticide were analyzed for cholinesterase activity and muscle fiber integrity. Muscle cholinesterase activity, 5 days after exposure, was reduced to 53% of control values. Histological analysis indicated the presence of muscle fibers with subsarcolemmal grouped granular basophilic inclusions and scattered necrotic fibers. Results indicate that acute organophosphate exposure through inhalation can lead to skeletal muscle fiber damage in humans, similar to results obtained by ingestion. Furthermore, the pathology is comparable to the histological alterations observed in rats following acute injection of organophosphates.

Cholinesterase activity in developing rat skeletal muscles

The influence of testosterone on the cholinesterase (ChE) activity of a target muscle (levator ani, LA), and of a nontarget muscle (extensor digitorum longus, EDL) was studied in newborn, prepubertal, and adult male rats. From birth to puberty (45 to 60 days of age) the ChE activity was similar in both muscles, either considering the total enzyme activity per muscle or per gram of tissue. After 60 days of age the weight and the ChE activity of the LA muscle increased abruptly, but the enzyme activity per gram of tissue remained constant to 105 days of age. Development of the EDL muscle was proportional to body weight during the entire experimental period. The total ChE activity of the muscle did not increase proportionately, but the ChE activity per gram of tissue decayed with the age of the rat. The activity of the specific cholinesterase, acetylcholinesterase (AChE), which is involved in the cholinergic transmission of the neuromuscular junction, attained maximal values in both muscles at puberty. From puberty to adulthood, AChE activity constituted the major form of ChE in the LA and EDL muscles. We conclude that testosterone stimulates the growth of the LA muscle and the increase of its AChE activity, but it decreases the nonspecific cholinesterase (BuChE) activity. Except for the latter, these effects are probably related to a general increase in protein synthesis in the target muscle fibers of the LA, but not of the EDL, induced by testosterone.

Cholinesterase of skeletal muscle and its subcellular components.

The cholinesterase activity of skeletal muscle and its subcellular components, including motor endplates, was compared chemically in human, mouse and rat. The total cholinesterase activity of muscle per unit protein was in the descending order of human, mouse and rat. Cholinesterase was present in all subcellular components fractionated by differential centrifugation, and was greatest in the microsome fraction followed, in descending order, by the mitochondria, myofibril, and supernatant fractions. Each of these fractions had greater cholinesterase activity in human muscle than in mouse muscle, and in mouse muscle than in rat muscle. The ratio of the activity of the microsome fraction to the activity of muscle homogenate was 11.1 in human, 4.6 in mouse and 3.4 in rat. Because of its relatively greater proportion, the myofibril fraction seems to contribute most to the total cholinesterase activity of muscle. Muscle membrane contained high cholinesterase activity of motor endplates, and the activity was greater than the activity of the microsome fraction in rat. Cholinesterase activity per motor endplate was in the descending order of rat, human and mouse, and the variation was less than the variation in the total muscle cholinesterase activity among these species.

Muscle cholinesterase: Effect of phencyclidine and ketamine on rat and human muscle cholinesterase activity

Phencyclidine (PCP) and ketamine were found to weakly inhibit rat skeletal muscle acetylcholinesterase (AChE) activity. PCP was a slightly more effective inhibitor of AChE than ketamine in vitro. PCP inhibited AChE activity in a noncompetitive manner which suggests the interaction of PCP at the secondary anionic site(s) of AChE whereas ketamine inhibited in a competitive manner, suggesting the interaction at the active site(s) of the enzyme. Both drugs also inhibited human muscle AChE activity in vitro. In vivo, both drugs stimulated rat skeletal muscle AChE activity whereas no effect was observed on rat brain AChE activity. When combined with restraints for 30 min following PCP and ketamine, the stimulation of AChE activity was greater than that produced by drug alone or restraint alone.

Changes in cholinesterase activity of muscle after crushing the sciatic nerve of rats

The subcellular distribution of cholinesterase (ChE) was studied in the gastrocnemius muscle of rats after strong or weak nerve crushing. The ChE activities of muscle were decreased to a greater extent by strong crushing than by weak crushing. In particular, the ChE activity of the fraction containing sarcoplasmic reticulum was most greatly decreased. These results suggest that the change in the ChE activity of the microsomal fraction most finely reflects the strength of nerve crushing.

Nerve stump length and cholinesterase activity in muscle and nerve

Neural regulation of muscle cholinesterase (ChE) is well documented, although the mechanisms remain unresolved. We examined the enzyme activity changes in nerve and muscle after nerve transection, as they relate to nerve stump length and synthesis of ChE in denervated muscle. Changes in ChE activity were determined in rat skeletal muscles and sciatic nerve after nerve transection and after irreversible inhibition with paraoxon. The results showed that the decrease in enzyme activity in muscle was unrelated to the length of nerve stump. It was also shown that denervated muscle was capable of enzyme synthesis. Enzyme activity in nerve segments distal to transections decreased earlier than in denervated muscle and ChE in these samples of nerve was less sensitive to paraoxon. Although the nerve stump length and decrease in muscle enzyme activity were unrelated, the results suggest that the earlier decrease in enzyme activity in transected nerve may be related to the loss of biochemically determined muscle ChE.

Pharmacological aspects of neuromuscular transmission in the thymus deficient nude ( [formula omitted]) mouse

Contraction parameters of phrenic nerve hemidiaphragm preparations from the athymic mutant mouse ( nu nu ) were not significantly different from controls. The sensitivity of these preparations to neuromuscular blocking drugs was increased whereas their sensitivity to physostigmine was reduced. Biochemical estimates revealed greater cholinesterase activity in muscle from mutant animals, and that the activity increased with age. The significance of these observations in relation to thymic secretions is briefly discussed and it is concluded that further study on preparations from this animal will help to establish the role of the thymus in normal neuromuscular function.