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Developmental exposure to perchlorate alters synaptic transmission in hippocampus of the adult rat: in vivo studies.
Citation:
GILBERT, M. E. AND L. SUI. Developmental exposure to perchlorate alters synaptic transmission in hippocampus of the adult rat: in vivo studies. ENVIRONMENTAL HEALTH PERSPECTIVES. National Institute of Environmental Health Sciences (NIEHS), Research Triangle Park, NC, 116 (6)(June):752-60, (2008).
Impact/Purpose:
To support criteria for MYP.
Description:
Perchlorate, a contaminant found in food and water supplies throughout the USA, blocks iodine uptake into the thyroid gland to reduce circulating levels of thyroid hormone. Neurological function accompanying developmental exposure to perchlorate was evaluated in the present study. Pregnant Long-Evans dams were exposed to 0, 30, 300 or 1000ppm perchlorate in the drinking water from gestational day 6 until weaning on postnatal day (PN) 30. Thyroid hormones were determined in offspring on PN4, PN14 and PN21, and adult male offspring were evaluated on a series of behavioral tasks and electrophysiological measures of synaptic function in the hippocampus. T3 and T4 were reduced in pups on PN21 at the highest dose. T4 in dams was reduced relative to controls by 12%, 24% and 56% in the 30, 300 and 1000ppm dose groups, respectively. Reductions in T4 were associated with an increase in TSH limited to the high dose group. No changes were seen in serum T3. Perchlorate did not impair motor activity, spatial learning, or fear conditioning. In field potentials recorded from the dentate gyrus, significant reductions in baseline synaptic transmission were observed at all dose levels. Reductions in inhibitory function were evident at 300 and 1000ppm dose levels, and augmentations in long-term potentiation were observed in the population spike measure at the highest dose. These findings reveal an irreversible impairment in synaptic transmission of the hippocampus in response to developmental exposure to perchlorate. Deficits were dose-dependent and detectable with relatively minor perturbations of the thyroid axis.
