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.