Effect of odor inhalation of rats with restraint stress on their hypothalamic gene expression profiles

To uncover molecular mechanisms underlying reduction of responses to restraint stress by racemic (R,S)-linalool inhalation, gene expression profiling at the hypothalamus of restraint stressed rats exposed to racemic (R,S)-linalool was carried out. Inhaled (R,S)-linalool returned the expression of 560 stress-induced probe sets to a normal status. These genes were associated with synaptic transmission via neurotransmitters including anxiolytic neuropeptides such as oxytocin and neuropeptide Y, and also included a number of major histocompatibility complex (MHC) class I necessary for neural development and plasticity. These results reveal some of the molecular mechanisms for odor inhalation under stress condition at the hypothalamus. Male Wistar rats aged 7 weeks were housed in a room maintained on a light/dark cycle with lights turned on at 8:00 a.m. and off at 8:00 p.m. They were allowed to get free access to food and water. After acclimatization to the environment and to investigators for one week, 18 rats were divided into three groups (n = 6 each): group C, control; group S, exposure to stress only; and group SO, exposure to both stress and odor. Rats in groups S and SO were placed in steel-wire mesh cages for restraint treatment for 2 h (10:00 - 12:00); they were able to breathe freely but unable to turn around. Twenty microliters of (R,S)-linalool was evaporated and allowed to spread throughout a 40 L box in which the rats (group SO) with the tubes were placed. After the exposure, all the 18 rats were immediately sacrificed by decapitation and then the brains were dissected to isolate the hypothalamic blocks. To look at the brain from the ventral side, two coronal cuts were placed at the apex of the optic chiasm and at the rostral margin of the mammillary bodies using a razor blade. This slab was then placed flat, and two cuts were placed on either side of the optic chiasm. The last cut was placed just above the third ventricle. The block was then put in ice-cold RNAlater. Please note that the data was normalized in two groups; [1] the control and group S samples; [2] the group S and group SO samples, respectively.