Cat odour induced anxiety in rodents: changes in expression of neuropeptide genes in brain structures

Abstract

The effect of cat odour exposure was studied on the behaviour and neuropeptide gene expression in rodents. Exposure to the cat odour suppressed the exploratory activity of male Wistar rats in the elevated zero-maze. Treatment with morphine (1 mg/kg) increased the exploratory behaviour of rats in an unfamiliar environment. Previous exposure of animals to the cat odour completely abolished this stimulating action of morphine. Cat odour exposure induced a significant increase in the expression of Pomc1, Oprm1 and Cck genes in the brain structures related to anxiety and motivation. The similar study was also performed in female 129Sv/C57/Bl6 mice. The exposure of wild-type and homozygous CCK2 receptor deficient mice to the cat odour did not reveal substantial differences between the two genotypes. However, the following exposure of mice to the elevated plus-maze established differences as homozygous mice displayed increased exploratory activity in the plus-maze. The cat odour exposure significantly reduced exploratory activity only in homozygous mice. Together with the increased exploratory activity in homozygous mice the expression of Oprm1 gene was elevated in the frontal cortex and mesencephalon. Thus, the reduced anxiety of homozygous mice seems to be related to an increased tone of opioid system in the brain. The exposure of mice to cat odour did not change the gene expression in wild-type mice, whereas in homozygous animals a significantly increased expression of the Mc3r gene in the frontal cortex and temporal lobe, and the Pomc1 gene in the temporal lobe, mesencephalon and mesolimbic area was established. Therefore, it is likely that the increased function of melanocortin system is responsible for the anxiogenic effect of cat odour exposure in homozygous mice. In conclusion, the experiments conducted on rodents demonstrate that the cat odour exposure induced anxiety is accompanied by the compensatory changes in the activity of opioid and melanocortin systems