Group 5: Stressed vehicle control—This group of rats were treated with the vehicle, i.e. PG (1 ml/kg) orally daily for 7 days. On 8th day, these rats were subjected to 30 min noise (100 dB) and sacrificed. These rats were used to rule out the effect of PG on the changes in cholinergic parameters induced by acute noise stress.
Group 6: Vehicle control—Animals of this group of rats were treated with propylene glycol (1ml/kg) orally daily for 7 days and sacrificed on 8th day without exposure to noise stress. This group was used to rule out the effect of PG alone on the base line values of cholinergic parameters.