Dendritic development in the rat superior cervical ganglion

Previous studies from our laboratory have shown that synaptogenesis in the superior cervical sympathetic ganglion (SCG) of the rat occurs predominantly during the first weeks after birth. The purpose of the present study was to examine the normal development of dendrites of the ganglion neurons, and to assess the importance of the afferent input in shaping this development. Two independent methods for examining dendritic morphology were used. One was to label neurons in the SCG by injecting a conjugate of horseradish peroxidase and wheat germ agglutinin (HRP-WGA) into a target of the SCG neurons (the submandibular gland). This procedure results in a 'Golgi-like' filling of the retrogradely labelled cell bodies and their dendrites. The second method was stereologic analysis (point-counting) of electron micrographs of sections of the SCG. At birth, the ganglion neurons give rise to an average of 2.4 primary dendrites and 1.2 secondary branches. No tertiary branches are observed at this age. The total dendritic length is 15.3 microns. Electron microscopic stereology reveals that the mean volume occupied by dendrites in the newborn SCG is 0.0093 mm3. In the adult, there is an average of 5.2 primary, 6.3 secondary, 4.8 tertiary and 1.9 quaternary dendrites. The total dendritic length is increased 23-fold to 347 microns. The mean volume occupied by dendrites is 0.0771 mm3, representing an 8-fold increase. In ganglia from adult rats which were deafferented at birth, an essentially normal dendritic form is attained. There are 4.5 primary, 6.2 secondary, 2.8 tertiary and 2.2 quaternary dendrites, and the total dendritic length is 297 microns. The mean volume of dendrites is 0.0571 micron3.(ABSTRACT TRUNCATED AT 250 WORDS)