Hindlimb Grip Strength Research Articles

Imatinib attenuates skeletal muscle dystrophy in mdx mice

Duchenne-Meryon muscular dystrophy (DMD) is the most common and lethal genetic muscle disease. Ameliorating muscle necrosis, inflammation, and fibrosis represents an important therapeutic approach for DMD. Imatinib, an antineoplastic agent, demonstrated antiinflammatory and antifibrotic effects in liver, kidney, lung, and skin of various animal models. This study tested antiinflammatory and antifibrotic effects of imatinib in mdx mice, a DMD mouse model. We treated mdx mice with intraperitoneal injections of imatinib at the peak of limb muscle inflammation and the onset of diaphragm fibrosis. Controls received PBS vehicle or were left untreated. Muscle necrosis, inflammation, fibrosis, and function were evaluated by measuring serum CK activity, endomysial CD45 immunoreactive inflammation area, endomysial collagen III deposition, and hind limb grip strength. Phosphorylation of the tyrosine kinase targets of imatinib was assessed by Western blot in diaphragm tissue and in primary cultures of peritoneal macrophages and skeletal muscle fibroblasts. Imatinib markedly reduced muscle necrosis, inflammation, and fibrosis, and significantly improved hind limb grip strength in mdx mice. Reduced clinical disease was accompanied by inhibition of c-abl and PDGFR phosphorylation and suppression of TNF-alpha and IL-1beta expression. Imatinib therapy for DMD may hold promise for ameliorating muscle necrosis, inflammation, and fibrosis by inhibiting c-abl and PDGFR signaling pathways and downstream inflammatory cytokine and fibrotic gene expression.

Overexpression of Galgt2 in skeletal muscle prevents injury resulting from eccentric contractions in both mdx and wild-type mice

The cytotoxic T cell (CT) GalNAc transferase, or Galgt2, is a UDP-GalNAc:beta1,4-N-acetylgalactosaminyltransferase that is localized to the neuromuscular synapse in adult skeletal muscle, where it creates the synaptic CT carbohydrate antigen {GalNAcbeta1,4[NeuAc(orGc)alpha2, 3]Galbeta1,4GlcNAcbeta-}. Overexpression of Galgt2 in the skeletal muscles of transgenic mice inhibits the development of muscular dystrophy in mdx mice, a model for Duchenne muscular dystrophy. Here, we provide physiological evidence as to how Galgt2 may inhibit the development of muscle pathology in mdx animals. Both Galgt2 transgenic wild-type and mdx skeletal muscles showed a marked improvement in normalized isometric force during repetitive eccentric contractions relative to nontransgenic littermates, even using a paradigm where nontransgenic muscles had force reductions of 95% or more. Muscles from Galgt2 transgenic mice, however, showed a significant decrement in normalized specific force and in hindlimb and forelimb grip strength at some ages. Overexpression of Galgt2 in muscles of young adult mdx mice, where Galgt2 has no effect on muscle size, also caused a significant decrease in force drop during eccentric contractions and increased normalized specific force. A comparison of Galgt2 and microdystrophin overexpression using a therapeutically relevant intravascular gene delivery protocol showed Galgt2 was as effective as microdystrophin at preventing loss of force during eccentric contractions. These experiments provide a mechanism to explain why Galgt2 overexpression inhibits muscular dystrophy in mdx muscles. That overexpression also prevents loss of force in nondystrophic muscles suggests that Galgt2 is a therapeutic target with broad potential applications.

Reductions in motor unit number estimates (MUNE) precede motor neuron loss in the plasma membrane calcium ATPase 2 (PMCA2)-heterozygous mice

The potential of MUNE as a unique electrophysiological tool to detect early motor unit abnormalities during a clinically silent period was investigated in the plasma membrane calcium ATPase 2 (PMCA2)-heterozygous mice. There was a significant reduction in MUNE in the PMCA2-heterozygous mice as compared to the wild type littermates at two months of age. In contrast, the compound motor action potential (CMAP) was not altered. The conduction velocity (CV) of the sensory nerve and sensory nerve action potentials (SNAP) were not modified indicating lack of major sensory deficits. Interestingly, despite a decline in MUNE at this age, no changes were detected in choline acetyl transferase (ChAT) positive motor neuron number in the ventral horn of the lumbar spinal cord. Hindlimb grip strength, a test that evaluates clinical dysfunction, was also similar to that of the wild type controls. However, motor neuron number significantly decreased by five months suggesting that a drop in MUNE preceded motor neuron loss. In the two-month-old PMCA2-null mice, reduced MUNE measurements coincided with lower motor neuron number and decreased hindlimb grip strength. The fall in motor neuron number was already detectable at three weeks, the earliest time studied, and became more pronounced by five months. Our results show that even partial reductions in PMCA2 levels are sufficient to cause delayed death of motor neurons and that MUNE may be a reliable and sensitive approach to detect pathology prior to cell loss and in the absence of overt clinical signs.

Time-course and characterization of orolingual motor deficits in B6SJL-Tg(SOD1-G93A)1Gur/J mice

Amyotrophic lateral sclerosis (ALS) is a progressive degenerative disease affecting upper and lower motor neurons. Symptom onset may occur in the muscles of the limbs (spinal onset) or those of the head and neck (bulbar onset). Bulbar involvement is particularly important in ALS as it is associated with increased morbidity and mortality. The purpose of this study was to characterize bulbar motor deficits in the B6SJL-Tg(SOD1-G93A)1Gur/J (SOD1-G93A) mouse model of familial ALS. We measured orolingual motor function by placing thirsty mice in a customized operant chamber that allows for measurement of tongue force and lick rhythm as animals lick water from an isometric disc. Testing spanned the pre-symptomatic, symptomatic, and end-stage segments of the disease. Rotarod performance, fore- and hindlimb grip strength, and locomotor activity were also monitored regularly during this period. We found that spinal involvement was apparent first, with both fore- and hindlimb grip strength being affected in SOD1-G93A mice from the onset of testing (64 days of age). Rotarod performance was affected by 71 days of age. Locomotor activity was not affected, even near end-stage. Bulbar involvement appeared much later, with tongue motility being affected by 100 days of age. Tongue force was affected by 115 days of age. To our knowledge, these findings are the first to describe the onset of bulbar versus spinal motor signs and characterize orolingual motor deficits in this preclinical model of ALS.

Intraparenchymal spinal cord delivery of adeno-associated virus IGF-1 is protective in the SOD1 G93A model of ALS

The potent neuroprotective activities of neurotrophic factors, including insulin-like growth factor 1 (IGF-1), make them promising candidates for treatment of amyotrophic lateral sclerosis (ALS). In an effort to maximize rate of motor neuron transduction, achieve high levels of spinal IGF-1 and thus enhance therapeutic benefit, we injected an adeno-associated virus 2 (AAV2)-based vector encoding human IGF-1 (CERE-130) into lumbar spinal cord parenchyma of SOD1 G93A mice. We observed robust and long-term intraspinal IGF-1 expression and partial rescue of lumbar spinal cord motor neurons, as well as sex-specific delayed disease onset, weight loss, decline in hindlimb grip strength and increased animal survival.

G.P.11.07 AAV mediated gene transfer of IGF-1 and VEGF to the ventricular system provides significant therapeutic benefit in a mouse model of amyotrophic lateral sclerosis

Amytrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease that is characterized by a selective loss of motor neurons in the motor cortex, brain stem and spinal cord. Currently there is no effective therapy for the treatment of ALS. Although a number of studies have demonstrated that neurotrophic factors have potent effects on motor neuron survival their delivery to the CNS remains to be a challenge. Recently it has been reported that AAV serotype 4 has an enhanced affinity for different cell types of the ventricular system including the ependymal cell layer and choroid plexus. In this study, we wished to determine if neurotrophic factor gene delivery to the ventricular system would be an effective strategy for delivering neurotrophic factors to the CNS of ALS mice in order to modify disease progression. Specifically, we evaluated the efficacy of intraventricular delivery of AAV4–IGF-1 and AAV4–VEGF in 90-day-old SOD1G93A mice. Starting at 80 days of age (and every 10 days thereafter), SOD1G93A mice underwent behavioral testing (rotarod, hindlimb and forelimb grip strength) to assess motor function. At 90 days of age (i.e., time point at which SOD1 mice exhibit overt disease symptoms of ALS) mice received intraventricular injection of AAV4–IGF-I, AAV4–VEGF, or AAV4–GFP. We found that delivery of neurotrophic expressing AAV4 vectors (regardless of transgene) significantly improved motor performance in both rotarod and grip strength behavioral tests and significantly extended lifespan (i.e., 20 days). Treatment with AAV4–GFP had no effect on any of the parameters mentioned above. Our results indicate that intraventricular injection of neurotrophic expressing AAV4 vectors is an effective approach for modifying disease progression in a mouse model of ALS.

Relationship between extracellular matrix, contractile apparatus, muscle mass and strength in case of glucocorticoid myopathy

The purpose of this study was to evaluate the effect of dexamethasone on the contractile apparatus and extracellular matrix (ECM) components of slow-twitch (ST) soleus (Sol) and fast-twitch (FT) extensor digitorum longus (EDL) muscle. The specific aim was to assess the development of glucocorticoid-induced myopathy on the level of contractile apparatus and ECM, paying attention to the expression of fibrillar forming collagen types I and III and nonfibrillar type IV collagen expression in extracellular compartment of muscle. Degradation of myofibrillar proteins increased from 2.62 ± 0.28 to 5.58 ± 0.49% per day during glucocorticoids excess. Both fibril- and network-forming collagen-specific mRNA levels decreased at the same time in both types of skeletal muscle. Specific mRNA level for MMP-2 did not change significantly during dexamethasone administration. Hindlimb grip strength simultaneously decreased. The effect of excessive glucocorticoids on the extracellular compartment did not differ significantly in skeletal muscles with different twitch characteristics.

Ageing and dexamethasone associated sarcopenia: Peculiarities of regeneration

The purpose of this study was to assess the development of ageing- and glucocorticoid-related sarcopenia on the level of myofibrillar apparatus, paying attention to the synthesis (SR) and degradation rate (DR) of contractile proteins, muscle strength, and daily motor activity. We also wanted to test the effect of ageing and dexamethasone (Dex) excess on the regeneration peculiarities of skeletal muscle autografts. Four and 30-month-old male rats of the Wistar strain were used. Ageing associated sarcopenia was calculated from gastrocnemius muscle relative mass decrease (from 5.6 ± 0.08 to 3.35 ± 0.04; p < 0.001). The SR of MyHC in old rats was ∼30% and actin ∼23% lower than in young rats. Dex treatment decreased SR of two main contractile proteins significantly in both age groups ( p < 0.001) and increased DR during ageing from 2.11 ± 0.15 to 4.09 ± 0.29%/day ( p < 0.001). Hindlimb grip strength in young rats was 5.90 ± 0.35 N/100 g bw and 2.64 ± 0.2 N/100 g bw ( p < 0.001) in old rats. Autografts of old rats have a higher content of adipose tissue 14.9 ± 1.1% in comparison with young rats 6.8 ± 0.51% ( p < 0.001) and less muscle tissue 39.8 ± 2.6% and 48.3 ± 2.8%, respectively ( p < 0.05). Both, ageing and dex-caused sarcopenic muscles have diminished capacity for regeneration.

1062. Intracerebellar Injection of AAV-IGF-1 Improves Motor Function and Extends Survival in a Mouse Model of Amyotrophic Lateral Sclerosis

Amytrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease that is characterized by a selective loss of motor neurons in the motor cortex, brain stem and spinal cord. The etiology of motor neuron degeneration remains largely unknown. Although chronic delivery of therapeutic agents to the central nervous system has proven to be difficult, recent studies have demonstrated that intramuscular delivery of adeno-associated viral vectors encoding insulin growth factor 1 (AAV-IGF-1) slowed disease progression and extended survival in SOD1G93A mice. The efficacy of viral mediated expression of IGF-1 was mediated in part by the ability of the viral vector to undergo retrograde transport from muscle to motor neurons. Previously we demonstrated that targeting the deep cerebellar nuclei (DCN) of the cerebellum with viral vectors capable of axonal transport resulted in detection of transgene protein in both the brain stem and spinal cord (Dodge et al. 2005, PNAS 102:17822-17827). In this experiment we evaluated the efficacy of bilateral delivery of AAV1|[ndash]|IGF-1 and AAV2-IGF-1 to the DCN in 90 day old SOD1G93A mice. Starting at 80 days of age (and every 10 days thereafter), SOD1G93A mice underwent behavioral testing (rotarod, hindlimb and forelimb grip strength) to assess motor function. At 90 days of age (i.e., time point at which SOD1 mice exhibit overt disease symptoms of ALS) mice received stereotaxic bilateral injections of AAV1-IGF-I (n=26), AAV2-IGF-I (n=27), AAV1-GFP (n=26) or AAV2-GFP (n=25) aimed at the deep cerebellar nuclei (DCN) of the cerebellum. We found that bilateral delivery of AAV- IGF-1 treatment (regardless of serotype) to the DCN significantly promoted motor neuron survival, improved motor performance in both rotarod and grip strength behavioral tests and significantly extended lifespan (i.e., 12 day extension for AAV1-IGF-1 and 14 day extension for AAV2-IGF-1). Treatment with AAV-GFP had no effect on any of the parameters mentioned above. Our results indicate that direct administration of AAV-IGF-1 into the DCN modifies disease progression in a mouse model of ALS and that targeting the DCN with AAV vectors is an effective approach for delivering therapeutic transgenes to both the brain and spinal cord for the treatment of ALS.

γ-Diketone Central Neuropathy: Quantitative Analyses of Cytoskeletal Components in Myelinated Axons of the Rat Rubrospinal Tract

Loss of axon caliber is a primary component of γ-diketone neuropathy [LoPachin RM, DeCaprio AP. γ-Diketone central neuropathy: axon atrophy and the role of cytoskeletal protein adduction. Toxicol Appl Pharmacol 2004;199:20–34]. It is possible that this effect is mediated by changes in the density of cytoskeletal components and corresponding spatial relationships. To examine this possibility, morphometric methods were used to quantify the effects of 2,5-hexanedione (HD) intoxication on neurofilament–microtubule densities and nearest neighbor distances in myelinated rubrospinal axons. Rats were exposed to HD at one of two daily dose-rates (175 or 400 mg/kg per day, gavage) until a moderate level of neurotoxicity was achieved (99 or 21 days of intoxication, respectively) as determined by gait analysis and measurements of hindlimb grip strength. Results indicate that, regardless of dose-rate, HD intoxication did not cause changes in axonal neurofilament (NF) density, but did significantly increase microtubule (MT) density. No consistent alterations in interneurofilament or NF–MT distances were detected by ultrastructural morphometric analyses. These data suggest that the axon atrophy induced by HD was not mediated by major disruptions of stationary cytoskeletal organization. Recent biochemical studies of spinal cord from HD intoxicated rats showed that, although the NF protein content in the stationary cytoskeleton (polymer fraction) was not affected, the mobile subunit pool was depleted substantially [LoPachin RM, He D, Reid ML, Opanashuk LA. 2,5-Hexanedione-induced changes in the monomeric neurofilament protein content of rat spinal cord fractions. Toxicol Appl Pharmacol 2004;198:61–73]. The stability of the polymer fraction during HD intoxication is consistent with the absence of significant ultrastructural modifications noted in the present study. Together, these findings implicate loss of mobile NF proteins as the primary mechanism of axon atrophy.

Effect of p75 neurotrophin receptor antagonist on disease progression in transgenic amyotrophic lateral sclerosis mice.

Neurotrophin level imbalances and altered p75 neurotrophin receptor (p75(NTR)) expression are implicated in spinal motor neuron degeneration in human and mouse models of amyotrophic lateral sclerosis (ALS). Recently, elevated reactive astrocyte-derived nerve growth factor (NGF) was linked to p75(NTR)-expressing motor neuron death in adult transgenic ALS mice. To test the role of NGF-dependent p75(NTR)-mediated signalling in ALS, we examined the effects of a cyclic decapeptide antagonist of p75(NTR) ligand binding by using neurotrophin-stimulated cell death assays and transgenic ALS mice. Murine motor neuron-like (NSC-34) cell cultures expressed full-length and truncated p75(NTR), tyrosine receptor kinase B (TrkB), and the novel neurotrophin receptor homolog-2 (NHR2) but were TrkA deficient. Accordingly, treatment of cells with NGF induced dose-dependent cell death, which was significantly blocked by the cyclic decapeptide p75(NTR) antagonist. Application of brain-derived neurotrophic factor, neurotrophin-3, or neurotrophin-4 to cultures increased cell proliferation, and such trophic effects were abolished by pretreatment with the tyrosine kinase inhibitor K-252a. Systemic administration of a modified cyclic decapeptide p75(NTR) antagonist conjugated to the TAT4 cell permeabilization sequence to presymptomatic transgenic SOD1(G93A) mice affected neither disease onset nor disease progression, as determined by hindlimb locomotor, grip strength, and survival analyses. These studies suggest that disrupting NGF-p75(NTR) interactions by using this approach is insufficient to alter the disease course in transgenic ALS mice. Thus, alternate ligand-independent pathways of p75(NTR) activation or additional NGF receptor targets may contribute to motor neuron degeneration in ALS mice.

Lack of neurotoxicity of the vascular targeting agent ZD6126 following repeated i.v. dosing in the rat

The vascular targeting agent ZD6126 is a water-soluble prodrug of N-acetylcolchinol that acts by disrupting the cytoskeleton of tumor endothelial cells. It is currently undergoing clinical evaluation in man. As peripheral neuropathy is a major dose-limiting toxicity associated with tubulin binding agents, the neurotoxic potential of ZD6126 was investigated in male and female Wistar rats. ZD6126 was administered i.v. at up to maximum tolerated doses using subacute (0 to 20 mg/kg/d for 5 days) and chronic (0 to 10 mg/kg/d for 5 days, repeated monthly for 6 months) dosing regimens. A separate study examined a combination of ZD6126 (three cycles of ZD6126 given as in the chronic dosing regimen) and paclitaxel (12 mg/kg/wk for 9 weeks) to assess whether coadministration of ZD6126 altered the time course or magnitude of a paclitaxel-induced neuropathy. Neurotoxic potential was examined using a comprehensive series of tests including a functional observation battery, measurements of muscle strength (forelimb and hind limb grip strength), nociception (tail flick test), locomotor activity, neuropathology, and whole nerve electrophysiology. There was no evidence that ZD6126 induced neurotoxicity in the rat following either subacute or chronic i.v. dosing. In a chronic electrophysiology study, ZD6126 produced a slight slowing of the maturational increase of caudal nerve amplitude, with some evidence of reversibility. However, this was not associated with any changes in caudal nerve conduction velocity, motor nerve conduction velocity or amplitude, functional observation battery behavioral and function parameters (including no effects on tail flick latency), and neuropathology. As expected, paclitaxel administration was associated with a significant decrease in caudal nerve conduction velocity (P = 0.0001). Coadministration of ZD6126 did not increase the neurotoxicity of paclitaxel. These studies suggest that ZD6126 should not induce the peripheral neuropathy associated with other antitubulin chemotherapeutic agents and that ZD6126 may not exacerbate the neurotoxicity of other agents with dose-limiting neuropathies.

Neurotoxicity of carbonyl sulfide in F344 rats following inhalation exposure for up to 12 weeks

Carbonyl sulfide (COS), a high-priority Clean Air Act chemical, was evaluated for neurotoxicity in short-term studies. F344 rats were exposed to 75–600 ppm COS 6 h per day, 5 days per week for up to 12 weeks. In rats exposed to 500 or 600 ppm for up to 4 days, malacia and microgliosis were detected in numerous neuroanatomical regions of the brain by conventional optical microscopy and magnetic resonance microscopy (MRM). After a 2-week exposure to 400 ppm, rats were evaluated using a functional observational battery. Slight gait abnormality was detected in 50% of the rats and hypotonia was present in all rats exposed to COS. Decreases in motor activity, and forelimb and hindlimb grip strength were also detected. In rats exposed to 400 ppm for 12 weeks, predominant lesions were in the parietal cortex area 1 (necrosis) and posterior colliculus (neuronal loss, microgliosis, hemorrhage), and occasional necrosis was present in the putamen, thalamus, and anterior olivary nucleus. Carbonyl sulfide specifically targeted the auditory system including the olivary nucleus, nucleus of the lateral lemniscus, and posterior colliculus. Consistent with these findings were alterations in the amplitude of the brainstem auditory evoked responses (BAER) for peaks N 3, P 4, N 4, and N 5 that represented changes in auditory transmission between the anterior olivary nucleus to the medial geniculate nucleus in animals after exposure for 2 weeks to 400 ppm COS. A concentration-related decrease in cytochrome oxidase activity was detected in the posterior colliculus and parietal cortex of exposed rats as early as 3 weeks. Cytochrome oxidase activity was significantly decreased at COS concentrations that did not cause detectable lesions, suggesting that disruption of the mitochondrial respiratory chain may precede these brain lesions. Our studies demonstrate that this environmental air contaminant has the potential to cause a wide spectrum of brain lesions that are dependent on the degree and duration of exposure.

Factors affecting grip strength testing

The rodent grip strength test was developed decades ago and is a putative measure of muscular strength. This test has been included in the functional observational battery (FOB) to screen for neurobehavioral toxicity, and changes in grip strength have been interpreted as evidence of motor neurotoxicity. Despite its widespread use, questions remain about what the grip strength test actually measures. In this study, potential confounders of the grip strength test were identified and tested, including operational parameters, disruption of peripheral sensory function and changes in body weight. Operational parameters (sampling rate, system type and trial angle but not trial speed) had dramatic effects on grip strength data. Doxorubicin (DX, 10 mg/kg iv) was used to cause sensory impairment. It decreased forelimb and hindlimb grip strength (by 27% and 32%, respectively, compared with controls), an effect that was correlated with degeneration of peripheral and central sensory components (distal tibial and sural nerves, dorsal funiculus of the spinal cord and dorsal, but not ventral, spinal roots). Feed restriction-induced loss of body weight (26% compared with controls) and muscle mass (20% compared with controls) reversibly decreased both forelimb and hindlimb grip strength (18% and 17%, respectively, compared with controls). Ignoring these confounding factors could potentially lead to increased data variability and inconsistency within single studies, across studies and in historical control data sets. To assist in data interpretation and evaluation of grip strength results, it is suggested that exact conditions of application of the test be reported in greater detail. Furthermore, given that the grip strength test can be influenced by factors other than true muscular strength, use of the term grip performance is proposed to better reflect the apical nature of this test.

Neurobehavioral effects of racemic threo-methylphenidate and its d and l enantiomers in rats

d, l-Methylphenidate (Ritalin®) is used to treat attention deficit hyperactivity disorder (ADHD) in children. The therapeutic effect is predominantly due to the d enantiomer. Dexmethylphenidate ( d-MPH; Focalin®) was therefore developed for its better therapeutic index. The present study determined and compared the acute behavioral toxicity of d, l-MPH, d-MPH and l-MPH in rats after oral dosing. Comprehensive functional observational battery (FOB) evaluations and rota-rod tests were performed 30, 60 and 120 min after dosing. Ten rats/sex/dose were administered a single dose of vehicle, 2, 20, 100 mg/kg d, l-MPH and 1, 10, 50 mg/kg d-MPH or 1, 100, 500 mg/kg l-MPH. There was no mortality. Certain FOB evaluations were statistically significant from vehicle control at any of the time points with most occurring at 60 and 120 min in the high d, l-MPH dose. These included increases in rearing, difficulty in removal from box, arousal, click, tail-pinch and decreases in hind-limb splay distance, hind-limb grip strength and handling reactivity. Behavioral responses were also present at the mid-dose d, l-MPH and high dose d- and l-MPH. Responses in female were significantly different from males in d, l- and l-MPH groups suggesting a sex difference in sensitivity. In the rota-rod test, mean latency to remain on the rod was significantly less for males compared to control given high dose d-MPH and d, l-MPH. In females, latency times were significantly less for high doses of all three compounds. In summary, fewer significant FOBs were seen with d- and l-MPH compared to equimolar doses of d, l-MPH. l-MPH was the least potent in producing FOBs. These results were supported by rota-rod studies.

Neurological Evaluation of Toxic Axonopathies in Rats: Acrylamide and 2,5-Hexanedione

This research was conducted to determine which neurological test or combination of tests can provide sufficient functional information to compliment biochemical or morphological endpoints in mechanistic studies of toxic axonopathies. Using several neurological indices, we evaluated the effects of two prototypical neurotoxicants that cause distal axonopathy: acrylamide monomer (ACR) and 2,5-hexanedione (HD). For each toxicant, rats were exposed to two daily dosing rates (ACR, 50 mg/kg per day i.p. or 21 mg/kg per day, p.o.; HD, 175 or 400 mg/kg per day, p.o.) and neurological endpoints were determined two to three times per week. Specific tests included observations of spontaneous locomotion in an open field, and measurements of hindlimb landing foot splay, forelimb and hindlimb grip strength and the hindlimb extensor thrust response. For all neurological parameters, the magnitude of defect induced by either neurotoxicant was not related to daily dose-rate, e.g. both the lower and higher ACR dose-rates produced the same degree of neurological dysfunction. Instead, dose-rate determined onset and progression of neurotoxicity, e.g. the higher ACR dose-rate produced moderate neurotoxicity after approximately 8 days of intoxication, whereas the lower dose-rate caused moderate neurotoxicity after 26 days. Regardless of dose-rate, ACR-exposed rats exhibited gait abnormalities (ataxia, splayed hindlimbs), in conjunction with increased landing hindfoot spread and decreased hindlimb grip strength and extensor thrust. HD intoxicated rats exhibited hindlimb muscle weakness as indicated by a gait abnormality (dropped hocks) and decreases in grip strength and the extensor thrust response. However, hindlimb landing foot spread was not affected by HD exposure. For both neurotoxicants, gait changes preceded or coincided with alterations in other neurologic indices. These results suggest that observations of spontaneous behavior in an open field represent a practical approach to assessing temporal development and extent of neurological dysfunction induced by axonopathic toxicants such as ACR and HD.

Long-term consequences of developmental exposure to aluminum in a suboptimal diet for growth and behavior of Swiss Webster mice

Swiss Webster mice received diets containing 7 (control), 100, 500, or 1000 μg aluminum (Al)/g throughout development (conception to 35 days of age) and were tested behaviorally as adults (>90 days of age). The basal diet contained the same percent of recommended dietary amounts of phosphate, calcium, iron, magnesium, and zinc as young women usually consume. These “realistic” dietary conditions led to 12–15% growth retardation in the Al1000 group at the time of testing. Females were evaluated in a cognitive task (Morris water maze) at 3 months of age and males were evaluated in a motor test battery at 5 months of age. Al1000 females ( n=16) were slower than controls in learning the Morris maze, as suggested by fewer mice with low latencies during the first three sessions of the four-session learning series. Influences of Al on cue utilization were also found in probe sessions eliminating salient or nonsalient cues. With motor testing, the Al1000 males ( n=20) had significantly lower hindlimb grip strength than controls, an effect that was eliminated by covariance analysis with body weight. Subtle influences of Al on rotarod and wire suspension tests were also noted. The data suggest that developmental Al exposure under normal, but less than optimal, dietary conditions can lead to subtle but long-term effects on growth and brain function in adulthood.

The Long Term Influence of Low-Level Sarin Exposure on Behavioral and Neurophysiological Functions in Rats

1. Long term effects of low doses of highly toxic organophosphorus agent sarin on behavioral and neurophysiological functions were studied in rats exposed to sarin by inhalation. The toxic effects of sarin were monitored using a functional observational battery (FOB), an automatic measurement of motor activity and a test of excitability of central nervous system at 3, 6 and 12 months following sarin exposure. 2. The results indicate that sarin at symptomatic as well as asymptomatic doses (level 2 and 3) is able to induce some neurotoxic effects (a decrease in activity and mobility, an alteration of gait, an increase in stereotyped behavior) including an increase in the excitability of central nervous system (an increase in convulsive activity following the administration of pentamethylenetetrazole) in rats at 3 months following inhalation exposure. Some sings of increased excitability were also observed in sarin-exposed rats following 6 or 12 months (an increase in exploratory activity, body temperature and a hindlimb grip strength at 6 months following exposure to sarin at asymptomatic doses, an increase in tail-pinch response at 12 months following exposure to sarin at symptomatic doses). 3. Therefore, nerve agents such as sarin seem to be harmful not only at high, clinically symptomatic doses but also at low, clinically asymptomatic doses because of long term manifestation of alteration of neurophysiological functions in sarin-exposed rats without disruption of cholinergic nervous system.

1-Bromopropane, an alternative to ozone layer depleting solvents, is dose-dependently neurotoxic to rats in long-term inhalation exposure.

1-Bromopropane has been newly introduced as an alternative to ozone layer-depleting solvents. We aimed to clarify the dose-dependent effects of 1-bromopropane on the nervous system. Forty-four Wistar male rats were randomly divided into 4 groups of 11 each. The groups were exposed to 200, 400, or 800 ppm of 1-bromopropane or only fresh air 8 h per day for 12 weeks. Grip strength of forelimbs and hind limbs, maximum motor nerve conduction velocity (MCV), and distal latency (DL) of the tail nerve were measured in 9 rats of each group every 4 weeks. The other 2 rats of each group were perfused at the end of the experiment for morphological examinations. The rats of the 800-ppm group showed poor kicking and were not able to stand still on the slope. After a 12-week exposure, forelimb grip strength decreased significantly at 800 ppm and hind limb grip strength decreased significantly at both 400 and 800 ppm or after a 12-week exposure. MCV and DL of the tail nerve deteriorated significantly at 800 ppm. Ovoid or bubble-like debris of myelin sheaths was prominent in the unraveled muscular branch of the posterior tibial nerve in the 800-ppm group. Swelling of preterminal axons in the gracile nucleus increased in a dose-dependent manner. Plasma creatine phosphokinase (CPK) decreased dose-dependently with significant changes at 400 and 800 ppm. 1-Bromopropane induced weakness in the muscle strength of rat limbs and deterioration of MCV and DL in a dose-dependent manner, with morphological changes in peripheral nerve and preterminal axon in the gracile nucleus. 1-Bromopropane may be seriously neurotoxic to humans and should thus be used carefully in the workplace.

Relationship between acrylamide reproductive and neurotoxicity in male rats

To determine whether there is a relationship between the reproductive and neurotoxic effects of acrylamide monomer (AM), the first week of the study design of Sublet et al. [14] was duplicated: Long–Evans male rats were gavaged with AM in water, 25/group, at 0, 5, 15, 30, 45, or 60 mg/kg/day for 5 days (days 1 through 5). On Day 8, males were paired overnight with untreated virgin females (1 : 1) in proestrus/estrus. On day 9, males were evaluated for forelimb and hindlimb grip strength. Five males/group were perfusion fixed, 20/group were used for andrologic assessment, and all were necropsied. Perfusion-fixed sciatic nerves were examined histologically. Sperm-positive females were examined for preimplantation and postimplantation loss at midpregnancy. At 15 to 60 mg/kg/day, males exhibited significantly reduced weight gain, reduced mating, fertility, and pregnancy indices by trend analysis (significant at 60 mg/kg/d by pairwise comparison), and increased postimplantation loss and dominant lethal factor, F L%, at 45 and 60 mg/kg/day. At 60 mg/kg/day, the sperm beat cross frequency was increased, with no significant effects on epididymal sperm motility or concentration, and hindlimb grip strength was decreased, with no pathologic lesions in sciatic nerves. Therefore, epididymal sperm, mating, and neurotoxic effects were observed at AM doses that also resulted in increased postimplantation loss, possibly by different mechanisms.