Numbers of Axons Innervating Mystacial Vibrissa Follicles in Newborn and Adult Rats

Electron-microscopic techniques were used to determine the numbers of axons in the deep vibrissal nerves innervating the C1 and C4 follicles in newborn and adult rats. All counts were made from thin sections taken after the nerve had entered the follicle capsule (FC). In newborn animals, the nerves supplying the C1 (n = 10) and C4 (n = 10) follicles contained an average (means ± standard deviation) of 355.0 ± 40.0 and 233.9 ± 19.2 axons, respectively. In the adult animals (n = 10 for C1, and n = 9 for C4), the respective values were 314.4 ± 26.2 and 233.3 ± 34.4 axons. There were no significant differences between the values for the counts from the neonates and adults for either follicle (p > 0.01, independent t tests). In the vibrissal nerves of neonates, both degenerating axons and occasional growth cones were visible. Such profiles were not observed in the nerves taken from adults.