Effect of odorant inhalation on hypothlamic gene expression profile exposed to restraint stress in rats

As an attempt to assess physio-psychological effects elicited in odorant-inhaled rats, gene expression profiling in the central nervous system was carried out with rats housed under stressful conditions. (R)-(-)-linalool inhalation to rats during 2 h restraint significantly up-regulated the expression of genes in hypothalamus, which were found to be related to neuron differentiation and regulation of transcription as well as immediate early genes. The expressions of 104 among focused stress-regulated genes were significantly altered by the inhalation. The (R)-(-)-linalool inhalation significantly repressed the restraint-induced changes in the expression levels of 77 of the 104. It also promoted the expression of the remaining 27 genes including those related to anti-apoptotic heat shock proteins. The differences in their hypothalamic gene expressions revealed that the inhaled odorants actually influenced stress responses, based on the restraint-induced hypothalamic gene expressions related to apoptosis. These results indicate that the analysis of gene expression profiles in rats subjected to a stressful condition is useful to evaluate odorant-induced effects as shown by the particular results that (R)-(-)-linalool inhalation under only 2 h restraint- stressed condition induces neuron differentiation against apoptosis. Male Wistar rats aged 7-8 weeks were housed in a room maintained on a light / dark cycle with lights turned on at 9:00 a.m. and off at 9:00 p.m. They were allowed to get free access to food and water. After acclimatization to the environment and to investigators for 1 week, 16 rats were divided into four groups (n = 4 each); group C (control) exposed to neither stress nor odor, group S exposed to stress only, group SO exposed to both stress and odor, group O exposed to odor only.