The most common forms of diabetic neuropathies are sensory dysfunctions with hyperalgesia and reduced temperature and vibration perception thresholds, which lead to very distressing and debilitating clinical complications. The gracile nucleus and nucleus tractus solitarius (NTS) were recently shown to modulate nociceptive and somatosensory reflexes. We found that the mechanical tolerance threshold and withdrawal latencies of heat and cold stimuli to the hind foot are consistently decreased in Zucker diabetic Fatty (ZDF) rats. Hyperalgesia and hypersensitivity to temperature/ pressure in ZDF rats are improved by low-frequency electroacupuncture (EA) stimulation of acupoint ST36. We have demonstrated that neuronal nitric oxide (NO) synthase (nNOS) expression is predominantly increased in the gracile nucleus and NTS following EA ST36 in rats. Our preliminary studies show that endogenous NO is decreased in the gracile nucleus in ZDF rats, and dialysate NO release in the nucleus is enhanced by EA ST36. The analgesic responses to EA ST36 are facilitated by L-arginine NO and blocked by an inhibitor of NO synthesis in the gracile nucleus. The results support the following hypotheses: 1) EA ST36 induces endogenous NO synthesis/release in the gracile nucleus and the NTS;and 2) NO-cGMP-GABA system in the dorsal medulla inhibits somatosensory/nociceptive susceptibility resulting in improvement of sensory neuropathies. In view of the critical importance of NO on sensory/nociceptive regulation, the major aims are: 1) Examine whether NO release in the gracile nucleus/NTS is increased and is positively correlated to anti-nociceptive/hypersensitive responses to low-frequency EA ST36;2) Determine whether hyperalgesia and hypersensitivity to temperature/pressure in neuropathic rats are improved and are parallel to enhanced cFos-nNOS expressions in the gracile nucleus/NTS-thalamic pathways by 8 sessions of EA ST36;3) Investigate whether anti-nociceptive/hypersensitive responses to EA ST36 are improved by administration of NO donors and worsened by an inhibitor of NO synthesis in the gracile nucleus and/or NTS in ZDF rats;and 4) Determine whether NO-cGMP-GABA cascade in the gracile nucleus and NTS responds to NO-mediated anti-nociceptive/hypersensitive responses to acupuncture in ZDF rats. Physiological recordings of pressure, temperature, and pain thresholds will be incorporated with neuropharmacological manipulations, chemical assays and EA/acupuncture to test the hypotheses in ZDF vs. lean rats. The results will advance our understanding of the mechanisms of EA/acupuncture- induced NO with cGMP-GABA cascade in the gracile nucleus/NTS on sensory/pain modulation, and yield new insights into effects of acupuncture on nNOS-NO generation in the dorsal medulla resulting in improvement of sensory diabetic neuropathies.
These studies should advance our understanding of the biochemical mechanisms of acupuncture-induced nitric oxide on sensory/pain regulation in the dorsal medulla, and reveal a therapeutic effect of acupuncture on improving hyperalgesia and hypersensitivity by affecting nitric oxide release/synthesis in the brain sites. The results should benefit public health by exploring a novel anti-nociceptive mechanism of acupuncture and by establishing a better acupuncture therapy based on scientific evidence of inducing nitric oxide and its synthase in the dorsal medulla for treatment of sensory diabetic neuropathies and other pain syndromes.
