Gender difference in a subpopulation of rat superior cervical ganglion neurons

The number of superior cervical ganglion (SCG) neurons is equivalent in males and females on the day of birth. By 15 days, after most of the normal neuron death has occurred, males have 20-30% more neurons than females; and this difference persists in the adult. The present study was undertaken to determine whether this difference exists uniformly throughout the ganglion, or only in a subpopulation of these neurons. To study subpopulations of SCG neurons, bilateral transection of the internal carotid nerve, the external carotid nerve, or both postganglionic nerves was performed on neonatal male and female Sprague-Dawley rats on the day of birth. Littermate sham operates served as controls. Numbers of neurons were counted in SCGs of animals on either postnatal day 4 or 15, before or after normal development of the SCG sex difference. At 4 days, the number of SCG neurons in sham-operated males had females were not different, while at 15 days, sham-operated males had more SCG neurons than did sham-operated females. The number of neurons remaining in the SCG following neonatal transection of the internal carotid nerve were not different in males and females at either 4 or 15 days postnatal. The number of SCG neurons remaining following neonatal transection of the external carotid nerve was greater in males than in females at both 4 and 15 days postnatal. It was concluded that the gender difference in survival of SCG neurons lies in neurons projecting through the internal carotid nerve. The number of neurons projecting out the external carotid nerve is equivalent in males and females.