Repeated noise exposure affects muscarinic cholinergic receptors in the rat brain.

We examined the effect of repeated exposure to 100-dB white noise (10 daily 45-min sessions) on muscarinic cholinergic receptors in different regions of the rat brain. Twenty-four hours after the last exposure session, increase in concentration (Bmax) of [3H]quinuclidinyl benzilate ([3H]-QNB) binding sites was observed in the hippocampus, but no significant change was seen in the striatum, frontal cortex, and hypothalamus. No significant effect of noise on receptor binding affinity (Kd) was found. Pretreating the rats with naltrexone (1 mg/kg, IP) before exposure blocked the noise-induced increase in cholinergic receptors in the hippocampus.