Lack of changes in brain muscarinic receptor and motor activity of mice after neonatal inhalation exposure to d-allethrin.

Synthetic pyrethroids are among the most common pesticides and insecticides currently in worldwide use. Eriksson and co-workers postulated that oral exposure of mice to pyrethroids during a neonatal brain growth spurt induces permanent disturbance in the cerebral muscarinic cholinergic receptor (MAChR) and behaviour. However, the scientific basis for these phenomena is now under discussion. The present study was performed to determine whether the experimental findings of Eriksson's study could be reproduced in newborn mice by inhalation. Male and female NMRI mice were exposed to d-allethrin by whole-body inhalation for 6 h per day between postnatal days 10 and 16. Actual concentrations of d-allethrin were 0.43, 1.35, 3.49 and 74.2 mg m(-3) (equivalent to 0.70, 2.2, 5.7 and 120.2 mg kg(-1) day(-1), respectively), and the mass median aerodynamic diameter and geometric log-standard deviation of mist particles ranged from 2.58 to 2.98 micro m and from 1.58 to 2.09 micro m for all groups, respectively. The highest exposure level in the present study (74.2 mg m(-3)) was ca. 13,000 times as high as the concentration used in practice. The MAChR in the three brain areas (cortex, hippocampus and striatum) and motor activity were examined at the ages of 17 days and 4 months. In addition, a water-maze test was performed at the age of 11 months. There was no systemic toxicity interfering with the interpretation of assay results. The neonatal exposure to d-allethrin by inhalation did not induce effects either on the brain MAChR density and motor activity at 17 days and 4 months or on performance in the learning/memory test at the age of 11 months. The effects of allethrins on developmental neurotoxicity that Eriksson and co-workers reported previously were not reproduced in the present study.