The activity patterns shown on this website were obtained in rats between 17 and 22 days of age. At the beginning of an experiment, a litter of eight rat pups is transferred together with the dam from the home cage to a clean cage in order to reduce the carry-over of odors from soiled cages into the exposure chamber. The litter is left in this clean cage for at least one hour prior to the first exposure. Rats are weighed, injected subcutaneously at the back of the neck with [14C]2-DG (typically 1.6 microliters/g, 0.1 mCi/ml, 52 mCi/mmol, Sigma Product No. D4409, which is in 0.85% saline), and put in an odorless 2-liter glass Mason jar. Odorant then enters through a hole in the lid of the jar, which also is fitted with a vent to allow stale air to escape. The concentration of odorant therefore increases over the course of the exposure. 

Odorants are vaporized by bubbling research-grade, high purity nitrogen gas through liquid in a gas-washing bottle. Most odorants are liquids and are used undiluted. Some odorants are either solid or are available in only small quantities on our research budget. These odorants are first diluted in some solvent (usually light mineral oil, but occasionally water or ethanol) as described under the exposure condition listed with each pattern. Separate animals are exposed either to the gas vehicle only or to vapor resulting from bubbling gas vehicle through the solvent. These animals produce the "blank" activity patterns that are subtracted from the odor-evoked patterns during data transformation.  

In experiments where we compare patterns evoked by odorants of systematically different chemical structure, we usually use the odorants at equal vapor phase concentrations. In early experiments, we used the equation of Hass and Newton (1975) to estimate vapor pressures of simple aliphatic esters and acids. These values agree quite well with our newly determined values for the same compounds. Because the Hass and Newton equation is not easily adaptable to chemicals possessing multiple functional groups or complex hydrocarbon structures, we have adopted a new procedure for our recent experiments involving more complex odorants. Recently, we have used experimental and/or estimated values for vapor pressure taken from two different chemistry software packages (ChemDraw Ultra v 6.0 from CambridgeSoft and Molecular Modeling Pro v.3.14 from ChemSW) and from two Internet databases (Interactive PhysProp Database from Syracuse Research Corporation and the Chemical and Physical Properties Database from the Pennsylvania Department of Environmental Protection) to calculate saturated vapor concentrations. We then dilute the vapor in ultra zero grade air to achieve the desired concentration. Because individual values of vapor pressure for a single chemical can differ greatly, we use the median of all unique values from all four sources to represent the vapor pressure. The median vapor pressure is listed in the molecular properties pop-up box associated with each odorant on the website. It should be noted that our confidence in this value differs for different odorants because some chemicals have been far better studied than others.  

For experiments involving odorants diluted in solvents, we make no attempt to equalize vapor phase concentration. The interactions between solvents and solutes that can affect the vapor pressure of the solute have not been characterized for many combinations of odorants and odorless solvents. In some cases, the interaction between an odorant and the solvent can be stronger than that between homologous molecules of the odorant, thereby decreasing the vapor phase concentration when the odorant is diluted. In other cases, the interactions between an odorant and a solvent can be weaker than the interactions between homologous odorant molecules, resulting in greater evaporation of the odorant from the solution than from the undiluted material, which probably is responsible for the "bloom" effect experienced when perfume chemicals contact water.