Absolute number of parvicellular and magnocellular neurons in the red nucleus of the rat midbrain: a stereological study

The absolute number of parvicellular and magnocellular neurons in the red nucleus was estimated using design-based stereological counting methods and systematic random sampling techniques. Six young adult male rats, and a complete set of serial 40-μm glycolmethacrylate sections for each rat, were used to quantify neuronal numbers. After a random start, a systematic subset (i.e. every third) of the serial sections was used to estimate the total volume of the red nucleus using Cavalieri's method. The same set of sampled sections was used to estimate the number of neurons in a known subvolume (i.e. the numerical density N_v) by the optical disector method. Multiplication of the total volume by N_v yielded the absolute number of neurons. It was found that the right red nucleus consisted, on average, of 8400 parvicellular neurons (with a coefficient of variation of 0.16) and 7000 magnocellular neurons (0.12). These total neuronal numbers provide important data for the transfer of information through these nuclei and for species comparisons.