Number, size, conduction, and vasoconstrictor ability of unmyelinated fibers of the ovarian nerve in adult and aged rats

The effect of aging on the number, size, conduction velocity, and vasoconstrictive function of unmyelinated fibers in ovarian nerve accompanying the ovarian artery was studied in adult (4-7 mo) and aged (28-31 mo) rats. Morphological observation by electron microscopy showed that the ovarian nerve contains mainly unmyelinated fibers with only a small percentage (less than 4%) of myelinated fibers in either age group. The number of unmyelinated fibers tended to decrease in aged rats (717 ± 59) compared to adult rats (801 ± 48), especially in fibers of smaller diameter, although this difference was not statistically significant. The maximum conduction velocity of unmyelinated fibers within the ovarian nerve was similar when compared between adult (1.05 ± 0.04 m/s) and aged (1.02 ± 0.05 m/s) rats. Under anesthesia, electrical stimulation of the distal portion of a severed ovarian nerve reduced ovarian blood flow, as measured by laser Doppler flowmetry, when the stimulus intensity was above the threshold for unmyelinated C fibers. Stimulation of the ovarian nerve with supra-maximum intensity (10 V) at 2-20 Hz frequencies produced frequency-dependent reductions in ovarian blood flow in both adult and aged rats. There were no significant differences in magnitude of the reduction in ovarian blood flow with comparable frequencies of electrical stimulation of the ovarian nerve between adult and aged rats. Collectively, these data indicate that unmyelinated C fibers in ovarian nerve are maintained in number, size, conduction ability, and vasoconstrictor function in aged rats.