Behavioral indices of neurotoxicity

Distortion Product Otoacoustic Emission Test is Not the Test to Use in Nonclinical Safety Assessment

Ototoxicity and ocular toxicity screening are but two examples of specialty product lines that are often employed as Tier II or III nonclinical safety/hazard screening assessments. Compared to the regulatory guidelines that govern over standard toxicology or neurotoxicology programs, there is a paucity of regulatory strategies to address these specialized product lines. With respect to ototoxicity testing, we argue for the inclusion of the "least burdensome principles" adopted by the US FDA in providing the most pragmatic, efficient, and directed identification of potential harm to auditory function in the nonclinical safety arena. We argue for the exclusive use of the auditory brainstem response and the exclusion of the distortion product otoacoustic emissions (DPOAEs) in these Tiered II safety assessment programs. The inclusion of both are a burden on operational staff and, due to the extended episodes of anesthesia required to conduct both assays, this strategy poses a health and welfare concern for the selected animal species to be used. The DPOAE does not provide any sufficiently valid or reliable data above and beyond the gold standard ABR data, followed by complete oto-histopathology and cytocochleogram combination designs.

Effects of Acute Deltamethrin Exposure in Adult and Developing Sprague Dawley Rats on Acoustic Startle Response in Relation to Deltamethrin Brain and Plasma Concentrations

Deltamethrin (DLM) is a commonly used pesticide that helps to control crop destruction, disease, and nuisance insects. In rodents DLM can produce choreoathetosis, salivation, and decreased acoustic startle responses (ASR). Herein, adult Sprague Dawley rats were assessed for ASR 2 h after DLM delivered in 5 ml/kg corn oil, however no decrease was observed. Therefore, a test-retest protocol was used to reduce variability, and the effects on ASR on postnatal day 15 (P15) and adult rats were assessed 2, 4, 6, and 8 h after DLM administration (0, 1, 2, or 4 mg/kg for P15 rats and 0, 2, 8, or 25 mg/kg for adults). In a separate set of rats identically treated, DLM levels were determined in blood and brain. DLM (8 or 25 mg/kg) in adult rats decreased ASR up to 4 h, whereas in P15 rats decreases were observed between 2 and 8 h. The adult 25 mg/kg group showed consistent signs of salivation and tremor, whereas in P15 rats salivation was observed in the 2 and 4 mg/kg groups and tremor was observed at all doses over the 8-h period. Mortality was observed in all P15 dose groups but not in adults. Dose-dependent increases of DLM in blood and brain regardless of age were observed. At approximately equivalent whole brain concentrations, effects were more pronounced in P15 rats than in adult rats. Comparable brain levels of DLM do not explain differences in ASR and tremor between the P15 and adult rats. These data indicate age-dependent differences in sensitivity to DLM.

The search for translational pain outcomes to refine analgesic development: Where did we come from and where are we going?

Pain measures traditionally used in rodents record mere reflexes evoked by sensory stimuli; the results thus may not fully reflect the human pain phenotype. Alterations in physical and emotional functioning, pain-depressed behaviors and facial pain expressions were recently proposed as additional pain outcomes to provide a more accurate measure of clinical pain in rodents, and hence to potentially enhance analgesic drug development. We aimed to review how preclinical pain assessment has evolved since the development of the tail flick test in 1941, with a particular focus on a critical analysis of some nonstandard pain outcomes, and a consideration of how sex differences may affect the performance of these pain surrogates. We tracked original research articles in Medline for the following periods: 1973-1977, 1983-1987, 1993-1997, 2003-2007, and 2014-2018. We identified 606 research articles about alternative surrogate pain measures, 473 of which were published between 2014 and 2018. This indicates that preclinical pain assessment is moving toward the use of these measures, which may soon become standard procedures in preclinical pain laboratories.

MicroRNA-181a regulates endoplasmic reticulum stress in offspring of mice following prenatal microcystin-LR exposure

Microcystin-LR (MCLR) was commonly regarded as a potent hepatotoxin and has been reported to cause neurotoxicity. This study was aimed to investigate how maternal MCLR exposure during pregnancy alters behavioral responses in offspring mice and the possible molecular mechanism involved in this procedure. Three doses of MCLR solutions (0, 3 or 15 μg/kg body weight) were administered subcutaneously to pregnant C57bl/6 from gestation day (GD) 6-19. Our results showed that MCLR prenatal exposure led to the impairment of learning and memory function in offspring on postnatal days (PND) 35, accompanied by endoplasmic reticulum (ER) stress and neuronal apoptosis in hippocampal CA1 regions of mice. Sixteen miRNAs in hippocampus of pups on PND 35 were significantly affected by MCLR exposure with the markedly decreased transcription of miR-181a-5p. We then found that miR-181a-5p was down-regulated, accompanied by activation of ER stress after prenatal exposure to MCLR using qPCR analysis. Furthermore, glucose-regulated protein, 78kDa/binding immunoglobulin protein (Grp78/BIP), a major ER chaperone and signaling regulator, was identified as a target of miR-181a-5p. Our study showed that miR-181a could lead to a decrease in the mRNA expression and protein levels of Grp78 by directly binding to its 3'-untranslated region (3'-UTR) in primary hippocampal neurons. Our findings indicate that the up-regulation of Grp78 mediated by inhibition of miR-181a-5p is a possible mechanism resulting in ER stress and cognitive impairment in pups following prenatal MCLR exposure.

CNS Safety Screening Under ICH S7A Guidelines Requires Observations of Multiple Behavioral Units to Assess Motor Function

In the adoption of behavior as a critical end point in safety pharmacology and neurotoxicity screening, federal regulatory agencies have shifted the predominating scientific perspective from pharmacology back to the experimental analysis of behavior (psychology). Nowhere is this more evident than in tier I safety assessment of the central nervous system (CNS). The CNS and peripheral nervous system have multiple behavioral units of general activity. A complete picture of the motor control neural pathways cannot be measured by any one single approach. The CNS safety protocols under International Council for Harmonization of Technical Requirements for Pharmaceuticals for Human Use S7A are required to be conducted in accordance with Good Laboratory Practices by trained technical staff. The CNS safety assessments necessitate the inclusion of a thorough and detailed behavioral analysis of home cage activity, the response to handling, and transportation to and observations within an open-field apparatus with ancillary measures of basal muscle tone, muscle strength, and tremor in a functional observation battery, as well as quantitative measurements of 3-dimensional activity in an automated photobeam arena. Cost-cutting initiatives or a radical application of the "reduce use" principle of the 3 Rs only jeopardize the spirit, intent, and predictive validity of tier I safety testing assays dictated by current drug safety guidelines.

Commemorating Toxicology at the National Institute of Environmental Health Sciences on the Occasion of Its 50th Anniversary

In 1978, the National Toxicology Program (NTP) was established and headquartered at the National Institute of Environmental Health Sciences (NIEHS) in Research Triangle Park, North Carolina. On the occasion of the 50th Anniversary of the NIEHS, this article documents some of the historical and current NTP programs and scientific advances that have been made possible through this long-standing relationship.

The standardized functional observational battery: Its intrinsic value remains in the instrument of measure: The rat

The International Conference on Harmonisation's (ICH) Tripartite Guideline on Safety Pharmacology Studies for Human Pharmaceuticals has adopted the requirement that each new test substance must be tested for effects on the central nervous system prior to "first dose in man". This assessment is required to measure, at a minimum, the effects of the substance on general motor activity, behavioral changes, coordination, sensory/motor reflex responses, and body temperatures. To achieve this goal, ICH S7A recommends a neurobehavioral assessment (usually a functional observational battery (FOB) or modified Irwin test), which is generally undertaken in the rat. There seems to be a growing lack of consensus on the value of the FOB to determine CNS safety. This review highlights the importance of the time, effort and cost of training technicians to familiarize with their instrument of measure, so that each observer is better able to identify and document very subtle changes in behavior that will serve to increase the reliability and validity of these assays with respect to CNS safety assessments.

Pesticide poisoning and neurobehavioral function among farm workers in Jiangsu, People's Republic of China

Pesticides remain an integral part of agricultural activities worldwide. Although there have been a number of studies over the last two decades concerning the adverse effects of pesticide poisoning and chronic long term exposures on neurobehavioral function, the impact of recent pesticide poisoning and long term pesticide exposure on neurobehavioral function in Chinese farm workers has not been reported. China is the largest user of pesticides worldwide and figures suggest 53,300-123,000 Chinese people are poisoned every year. A case control study was conducted to examine the impact of recent pesticide poisoning on neurobehavioral function and the relationship between years worked in agriculture and lower performance on neurobehavioral tests. A total of 121 farm workers who self-reported recent pesticide poisonings within the previous 12 months (case group) and 80 farm workers who reported no pesticide poisoning in the previous 12 months (control group) were recruited from three areas of Jiangsu Province, China. The World Health Organization (WHO) recommended neurobehavioral core test battery (NCTB) was used to assess neurobehavioral functioning among cases and controls. Student's t tests and two-way covariance analysis (ANCOVA) were used to test for significant differences in the neurobehavioral test results between the groups. Scores on the Profile of Mood States (POMS) in the recently poisoned group were significantly higher for anger-hostility, depression-dejection, tension-anxiety and lower for vigor-activity compared to controls (p < .05). Digit span, digit symbol, Benton visual retention and pursuit aiming scores were all significantly lower among the recently poisoned group compared to the controls (p < .05). Two-way ANCOVA indicated significantly lower performance in correct pursuit aiming and higher error pursuit aiming amongst the recently poisoned group and those who had worked for more than 30 years in agriculture (p < .05). These findings provide important preliminary epidemiological evidence regarding the association between occupational pesticide exposure and neurobehavioral functioning in Chinese farm workers.

"Bedside-to-Bench" Behavioral Outcomes in Animal Models of Pain: Beyond the Evaluation of Reflexes

Despite the myriad promising new targets and candidate analgesics recently identified in preclinical pain studies, little translation to novel pain medications has been generated. The pain phenotype in humans involves complex behavioral alterations, including changes in daily living activities and psychological disturbances. These behavioral changes are not reflected by the outcome measures traditionally used in rodents for preclinical pain testing, which are based on reflexes evoked by sensory stimuli of different types (mechanical, thermal or chemical). These measures do not evaluate the impact of the pain experience on the global behavior or disability of the animals, and therefore only consider a limited aspect of the pain phenotype. The development of relevant new outcomes indicative of pain to increase the validity of animal models of pain has been increasingly pursued over the past few years. The aim has been to translate “bedside-to-bench” outcomes from the human pain phenotype to rodents, in order to complement traditional pain outcomes by providing a closer and more realistic measure of clinical pain in rodents. This review summarizes and discusses the most important nonstandard outcomes for pain assessment in preclinical studies. The advantages and drawbacks of these techniques are considered, and their potential impact on the validation of potential analgesics is evaluated.

The effect of occupational exposure to benzo[a]pyrene on neurobehavioral function in coke oven workers

BACKGROUND

Coke oven workers are regularly exposed to polycyclic aromatic hydrocarbons (PAHs). Benzo[a]pyrene (B[a]P), known as an indicator species for PAH contamination, is a neurobehavioral toxicant. The purpose of the study was to evaluate the relationship between B[a]P exposure, a B[a]P-related urinary metabolite and neurobehavioral function among coke oven workers.

METHODS

Coke oven workers and oxygen factory workers participated in this study. B[a]P exposure was monitored by air sampling pump, and urinary 1-hydroxypyrene (1-OHP) level was detected with high performance liquid chromatography (HPLC). A questionnaire and the neurobehavioral core test battery (NCTB) were administered to all subjects.

RESULTS

B[a]P-exposed workers were found to have higher urinary 1-OHP levels and worse NCTB performances on eight items than control workers. B[a]P concentrations were higher in the coke oven plant than that in the controls' workplace. The performances on simple reaction time, correct pursuit aiming, and error pursuit aiming decreased with increasing airborne B[a]P in coke oven workers. There were significant correlations between urinary 1-OHP level and six items of the NCTB.

CONCLUSIONS

Occupational exposure to B[a]P is associated with neurobehavioral function impairment in coke oven workers.

Functional assays for neurotoxicity testing

Neurobehavioral and pathological evaluations of the nervous system are complementary components of basic research and toxicity testing of pharmaceutical and environmental chemicals. While neuropathological assessments provide insight as to cellular changes in neurons, behavioral and physiological methods evaluate the functional consequences of disruption of neuronal communications. The underlying causes of certain behavioral alterations may be understood, but many do not have known direct associations with specific brain pathologies. In some cases, however, rapidly expanding mouse models (transgenic, knock-out) are providing considerable information on behavioral phenotypes of altered pathology. Behavior represents the integrated sum of activities mediated by the nervous system, and functional tests used for neurotoxicity testing tap different behavioral repertoires. These tests have an advantage over pathologic measures in that they permit repeated evaluation of a single animal over time to determine the onset, progression, duration, and reversibility of a neurotoxic injury. Functional assays range from a screening-level battery of tests to refined procedures to tap specific forms of learning and/or memory. This article reviews common procedures for behavioral toxicity testing and provides examples of chemical-specific neurobehavioral-pathological correlations in order to inform interpretation and integration of neuropathological and behavioral outcomes.

Effects of chronic and acute methylphenidate hydrochloride (Ritalin) administration on locomotor activity, ultrasonic vocalizations, and neuromotor development in 3- to 11-day-old CD-1 mouse pups

The present study examined the effects of chronic and acute treatment with methylphenidate hydrochloride (Ritalin) on isolation-induced ultrasonic vocalizations, spontaneous locomotor activity, and neuromotor coordination in 3- to 11-day-old CD-1 mouse pups. In Experiment 1, 3- to 11-day-old pups received daily injections of saline, 5 mg/kg or 20 mg/kg of methylphenidate hydrochloride, or no injection and were tested on postnatal Days 3, 5, 7, 9, and 11. Both doses of methylphenidate resulted in significant increases in locomotor activity at all ages, but had no significant effect on body weight, neuromotor development, or emission of ultrasonic vocalizations. In Experiment 2, pups were given a single dose of methylphenidate (5 or 20 mg/kg), saline, or no injection on one of postnatal Days 5, 7, 9, or 11. This acute methylphenidate treatment increased locomotor activity, but had no significant effects on ultrasonic vocalizations or neuromotor coordination. These results indicate that short-term, chronic methylphenidate treatment elevates locomotor responses, but has no immediate effects on anxietylike responses or on the development of neuromotor behavior of CD-1 mice in the first 11 days of life.

Toxicity of inhaled chloroprene (2-chloro-1,3-butadiene) in F344 rats and B6C3F(1) mice

Chloroprene (2-chloro-1,3-butadiene) is a high production chemical used almost exclusively in the production of polychloroprene (neoprene) elastomer. Because of its structural similarity to isoprene (2-methyl-1,3-butadiene) and to 1,3-butadiene, a potent trans-species carcinogen, inhalation studies were performed on chloroprene to characterize its toxicological potential and to provide a basis for selecting exposure concentrations for chronic toxicity and carcinogenicity studies. Thirteen-week inhalation toxicology studies were conducted in male and female F344 rats and B6C3F(1) mice at exposure concentrations of 0, 5, 12, 32 or 80 ppm (6 h/day; 5 days/week). A 200 ppm exposure group was also included for rats only, because a previous study showed that this concentration of chloroprene is lethal to mice. In mice, exposure to 80 ppm chloroprene caused a marginal decrease in body weight gain in males and epithelial hyperplasia of the forestomach in males and females. This lesion has been observed in mice exposed to isoprene or 1,3-butadiene. In rats, exposure to 80 ppm chloroprene or higher concentrations caused degeneration and metaplasia of the olfactory epithelium and exposure to 200 ppm caused anemia, hepatocellular necrosis and reduced sperm motility. These lesions have not been observed in rats exposed to isoprene or 1,3-butadiene. The profile of toxic effects of chloroprene is considerably different from that of isoprene or 1,3-butadiene; this may be due to differences in exposure concentrations that were used in toxicology studies of these compounds and /or to the influence of the chlorine substitution on the toxicokinetics of these compounds, on their biotransformation, or on the reactivity of metabolic intermediates with tissue macromolecules.

Neurodevelopmental effect of aluminum in mice: fostering studies

In order to determine sensitive periods for induction of neurodevelopmental effects of aluminum (Al), mice were fed either 25 (control) or 1000 (high Al) micrograms Al/g diet (as Al lactate) from conception through lactation and litters were fostered either within or between groups at birth. Birth parameters were not influenced by Al intake. Food intake and body weight were 10%-12% lower during lactation in dams fed the high Al diets. Both gestation and lactation high Al exposure led to growth retardation in offspring beginning on day 10 postnatal; combined gestation and lactation exposure led to the biggest weight differential at weaning (23%). For neurobehavioral measures obtained at weaning, forelimb grasp strength was influenced by gestation high Al exposure, whereas negative geotaxis was influenced by lactation exposure, and hindlimb grasp and temperature sensitivity were influenced by both gestation and lactation exposure. Pup liver and brain manganese (Mn) and liver iron (Fe) concentrations at weaning were lower after high Al lactation exposure than in controls. Pup brain and liver Al concentrations were similar among the groups. These data show that mice are susceptible to neurodevelopmental effects of high maternal dietary Al intake during both gestation and lactation, and that high maternal intake can result in altered essential trace element metabolism in the offspring.

Effects of dietary aluminum excess and manganese deficiency on neurobehavioral endpoints in adult mice

Studies in mice have suggested that both dietary Al excess and dietary Mn deficiency promote oxidative tissue damage. To determine if these factors can interact to produce functional nervous system damage, female mice (N = 10-12 per group) were fed diets with control or low Mn (35 or 3 micrograms Mn/g diet) and/or control or high Al (25 or 1000 micrograms Al/g diet, Al as Al lactate) content for a 90-day period. No overt signs of neurotoxicity were observed in any group. Excess Al produced a threefold Al accumulation in both liver and brain, a slight acceleration of growth, decreased motor activity, decreased grip strength, and decreased startle responsiveness. Manganese deprivation led to liver, brain, and femur Mn depletion and reduced liver MnSOD activity but no neurobehavioral changes. No interactive effects between Al excess and Mn deficiency were observed. Neither Al excess nor Mn deficiency altered brain or liver lipid peroxidation measures. This study suggests that (1) subchronic dietary Al at doses of 1000 micrograms Al/g diet produces elevated brain Al and altered neurobehavioral indices in adult mice; (2) brain lipid peroxidation is not altered by this treatment; (3) dietary Mn deficiency does not influence Al neurotoxicity in adult mice.