Purkinje cell complements in mammalian cerebella and the biases incurred by counting nucleoli.

An unbiased stereological counting device (the fractionator) was used to count Purkinje neurons in mammalian cerebella of known weights in order to define the relationship between weight and number. Nucleoli were chosen as the counting unit and numbers were estimated from uniform random samples of wax-embedded tissue sections. For the cerebella of rat, rabbit, cat, dog, goat, sheep, pig, ox, horse and human, there was a significant linear relationship between log number and log weight. The allometric relationship took the form N = 748,500 x W0.627. The relative bias associated with using nucleoli as counting units was assessed separately on disector pairs of sections and amounted to roughly -5% but varied between species. When the brains of females and males were analysed separately (cat, goat, pig, ox, horse, human), there were no significant differences between the regression lines. These results are consistent with earlier findings. They imply that Purkinje neuron packing densities decrease as brain size increases. Moreover, our preliminary findings appear to indicate that, for any given cerebellar weight, females and males have similar numbers of neurons.