Development and regulation of dendrites in the rat superior cervical ganglion.

Intracellular injection of HRP was used to study the postnatal development of dendrites in the rat superior cervical ganglion (SCG). This study had 2 goals: to describe the growth of dendrites during normal development and to determine the influence of preganglionic innervation on dendritic growth. At birth, ganglion cell morphology is relatively simple; cells have few dendritic branches and an average total dendritic length under 300 micron. In the first postnatal month there is a 4-fold increase in dendritic length and a marked increase in the complexity of branching. Dendrites continue to grow into adulthood; at each age studied (up to 16 months old), the dendritic geometries of SCG cells became progressively more extensive and complex. The influence of innervation on the development of dendrites was assessed by cutting the cervical sympathetic trunk (CST) within a day of birth; reinnervation was prevented by ligating and displacing the proximal end of the CST. During the first postnatal month, the cells in denervated ganglia showed an increase in dendritic length indistinguishable from that seen in unoperated control ganglia. The rate of growth after 1 month was somewhat slower in experimental animals than in controls; nevertheless, the dendrites of cells in denervated ganglia showed progressively larger arbors at each time point measured. These results indicate that in the SCG the majority of dendritic growth occurs postnatally, dendrites continue to grow in adult rats, and dendritic growth is largely independent of the presence of preganglionic innervation. The significance of these findings for the regulation of innervation in this part of the nervous system is discussed.