Most expression data are averages based on three microarrays (U74Av2). Each individual array experiment involved a pool of brain tissue (forebrain plus the midbrain, but without the olfactory bulb) that was taken from three adult animals usually of the same age. A total of 97 arrays were used: 74 were female pools and 23 were male pools. Animals ranged in age from 56 to 441 days, usually with a balanced design (one pool at 8 weeks, one pool at ~20 weeks, one pool at approximately 1 year).