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 (4-7mo) and aged (28-31mo) 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±0.04m/s) and aged (1.02±0.05m/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 (10V) at 2-20Hz 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.

Vascular-dependent effects of elevated glucose on postganglionic sympathetic neurons.

Perivascular sympathetic nerves are important determinants of vascular function that are likely to contribute to vascular complications associated with hyperglycemia and diabetes. The present study tested the hypothesis that glucose modulates perivascular sympathetic nerves by studying the effects of 7 days of hyperglycemia on norepinephrine (NE) synthesis [tyrosine hydroxylase (TH)], release, and uptake. Direct and vascular-dependent effects were studied in vitro in neuronal and neurovascular cultures. Effects were also studied in vivo in rats made hyperglycemic (blood glucose >296 mg/dl) with streptozotocin (50 mg/kg). In neuronal cultures, TH and NE uptake measured in neurons grown in high glucose (HG; 25 mM) were less than that in neurons grown in low glucose (LG; 5 mM) (P < 0.05; n = 4 and 6, respectively). In neurovascular cultures, elevated glucose did not affect TH or NE uptake, but it increased NE release. Release from neurovascular cultures grown in HG (1.8 ± 0.2%; n = 5) was greater than that from cultures grown in LG (0.37 ± 0.28%; n = 5; P < 0.05; unpaired t-test). In vivo, elevated glucose did not affect TH or NE uptake, but it increased NE release. Release in hyperglycemic animals (9.4 + 1.1%; n = 6) was greater than that in control animals (5.39 + 1.1%; n = 6; P < 0.05; unpaired t-test). These data identify a novel vascular-dependent effect of elevated glucose on postganglionic sympathetic neurons that is likely to affect the function of perivascular sympathetic nerves and thereby affect vascular function.