The impact of sexual dimorphism on neuron numbers in the superior cervical ganglion of the rat.

Other workers have reported a sexual dimorphism in the number of neurons that project from the rat superior cervical ganglion (SCG) via the internal carotid nerve (ICN). We have re-examined this situation by comparing ganglionic neuron numbers as well as the number of neurons labelled retrogradely from the iris and the pineal gland, in age-matched adult male and female rats. No significant dimorphism was seen in total cell numbers or in the cell populations supplying iris or pineal gland, although there was a trend towards more neurons in male animals. From evaluation of our results and the published data, we suggest that the variation in absolute numbers of neurons counted in the SCG is so wide, within genders, that any impact of gender differences on cell numbers is of little significance.