Developmental lead exposure induces tactile defensiveness in rhesus monkeys (Macaca mulatta).

BACKGROUND: Tactile defensiveness in children is associated with difficult social relations, emotional dysregulation, and inattention. However, there are no studies of lead exposure and tactile defensiveness in children or animals in spite of the fact that lead exposure is also associated with inattention and emotional dysregulation. OBJECTIVES: In this study we tested whether lead exposure induces tactile defensiveness in rhesus monkeys. METHODS: We tested 61 monkeys from a 3 (no lead, 1-year lead, 2-year lead) x 2 (succimer chelation or not) factorial experiment for tactile defensiveness at 4 years of age. Lead-treated monkeys had been orally administered lead in a daily milk solution from 8 days of life to either 1 or 2 years of age to produce blood lead levels of 35-40 mg/dL. Succimer chelation therapy or placebo was administered at 1 year of age. We measured tactile defensiveness using six repeated trials of each of three textures as a swipe to the cheek and neck. RESULTS: Lead-exposed monkeys showed higher negative responses to repeated tactile stimulation compared with controls. Blood lead during the first 3 months of life was positively correlated with the negative response on the tactile defensiveness test. There was an interaction of lead exposure x succimer chelation x trials, but it is not clear that succimer chelation was beneficial with respect to tactile defensiveness. CONCLUSIONS: This is the first report to implicate lead as a potential cause of tactile defensiveness. Research should examine whether lead exposure is associated with tactile defensiveness in children.

Sensory processing disorders in a nonhuman primate model: evidence for occupational therapy practice.

Evaluation of sensory processing function serves as a critical component of treatment planning and implementation of intervention in pediatric occupational therapy practice. We developed a Sensory Processing Scale for Monkeys (SPS-M), based on human tests, that measures behavioral responses to a series of tactile stimuli. This assessment has been used to assess sensory processing in adult rhesus monkeys exposed to prenatal alcohol, stress, or postnatal lead. Control monkeys from undisturbed pregnancies showed a habituation pattern, prenatally stressed monkeys showed sensitization, and prenatal alcohol-exposed monkeys showed relatively high responsiveness without habituation across trials. Lead-exposed monkeys showed sensitization compared to nonlead-exposed controls, and chelation reduced the sensitization in lead-exposed animals. Aversive responsiveness was associated with up-regulated striatal dopamine receptor binding measured with positron emission tomography.

Sensory processing disorder in a primate model: evidence from a longitudinal study of prenatal alcohol and prenatal stress effects.

Disrupted sensory processing, characterized by over- or underresponsiveness to environmental stimuli, has been reported in children with a variety of developmental disabilities. This study examined the effects of prenatal stress and moderate-level prenatal alcohol exposure on tactile sensitivity and its relationship to striatal dopamine system function in thirty-eight 5- to 7-year-old rhesus monkeys. The monkeys were from four experimental conditions: (a) prenatal alcohol exposed, (b) prenatal stress, (c) prenatal alcohol exposed + prenatal stress, and (d) sucrose controls. Increased D(2) receptor binding in the striatum, evaluated using positron emission tomography neuroimaging, was related to increased withdrawal (aversion) responses to repetitive tactile stimuli and reduced habituation across trials. Moreover, prenatal stress significantly increased overall withdrawal responses to repetitive tactile stimulation compared to no prenatal stress.