Nitrergic Neurodegeneration in Cerebral Arteries of Streptozotocin-Induced Diabetic Rats

Abstract

Although autonomic neuropathy is recognized as an independent risk factor for stroke in diabetes, the mechanism by which autonomic nerves are involved in this pathology is unknown. Parasympathetic (cholinergic) nerves of the autonomic nervous system are known to innervate and to cause relaxation of cerebral arteries by releasing nitric oxide (NO); hence, they are called nitrergic nerves. However, the effect of diabetes on nitrergic nerves is unknown. Here, we show that perivascular nitrergic nerves around the cerebral arteries degenerate in two phases in streptozotocin-induced diabetic rats. In the first phase, perivascular nitrergic nerve fibers remain intact while they lose their neuronal NO synthase content. This phase is reversible with insulin treatment. In the second phase, nitrergic cell bodies in the ganglia are lost via apoptosis in an irreversible manner. Throughout the two phases, irreversible thickening of the smooth muscle layer of cerebral arteries is observed. This is the first demonstration of nitrergic degeneration in diabetic cerebral arteries, which could elucidate the link between diabetic autonomic neuropathy and stroke. Diabetes 54:212-219, 2005 D iabetes is associated with an increased risk of cardiovascular disease-in particular, coronary heart disease and stroke (1-4). Mortality from stroke has been demonstrated to be increased significantly by diabetes (2). Hypertension, smoking, and dyslipidemia are major risk factors for the occurrence of strokes in diabetic patients (4). Recently, autonomic neuropathy has been described as a significant independent risk factor for diabetes-related stroke (5). However, the mechanism by which autonomic neuropathy might be involved in the pathogenesis of stroke has not been elucidated.Autonomic nerves are known to innervate cerebral arteries (6). Parasympathetic (cholinergic) nerves, which contain neuronal nitric oxide synthase (nNOS), have been shown in the walls of cerebral blood vessels in many species, including humans (7). These nerves are now called "nitrergic nerves" (8) and have been shown to originate mainly from the sphenopalatine ganglia (9 -12). Stimulation of perivascular nitrergic nerves has been demonstrated to relax the cerebral arteries by the action of nitric oxide (NO) and to increase the cortical blood flow (6,13-15). It is not known whether the nitrergic nerves in the cerebral vasculature are affected during diabetes. We therefore investigated the effect of diabetes on the morphology and nNOS content of these nerves in the cerebral arteries of streptozotocin (STZ)-induced diabetic rats. RESEARCH DESIGN AND METHODS Induction of diabetes.Male Wistar rats (225-250 g) were treated with STZ (75 mg/kg i.p.) or vehicle (saline) as described previously (16,17). Hyperglycemia was defined as a nonfasting blood glucose concentration Ͼ20 mmol/l. Insulin was administered 8 and 12 weeks after STZ injection using sustainedrelease insulin rods (7 mm, ϳ2 units/day; LinBit, LinShin Canada, Toronto, ON, Canada). Rats were killed 4, 8, 12, 16, and 20 w...

Impaired vascular responses of insulin-resistant rats after mild subarachnoid hemorrhage

“…However, this is the first study to show that the reduced dilator response of the cerebral arteries of ZO rats to acetylcholine is correlated with a lower expression of nNOS. Our results are supported by Cellek et al (12) who have previously shown that nNOSexpressing perivascular neurons around the basilar artery are progressively degenerated in streptozotocin-induced diabetic rats. While nNOS is normally localized to perivascular nerves associated with cerebral arteries and has several well-defined effects on cerebral vascular tone (11,13,29,38), nNOS has been shown to compensate for reduced NO and thereby restore normal NO-dependent dilation in eNOS knockout mice (36,37).…”

Effect of Cyclooxygenase and Nitric Oxide Synthase Inhibitors on Streptozotocin-Induced Hyperalgesia in Rats

“…Deficit in NO production may also be due to nitrergic neurodegeneration which was recently described by Cellek et al [10][11][12] . These authors showed that perivascular nerves degenerate in two phases in STZ-induced diabetes.…”

“…Increased nNOS protein and NO production coincide with accumulation of advanced glycation end-products (AGEs) in the blood and tissues. Synergistic action of AGEs and endogenous NO leads to increased oxidative stress within the cell bodies, resulting in apoptosis [10][11][12] .…”

“…Cyclooxygenases (COX, three are currently known: COX-1, COX-2 and COX-3) are among of the most important enzymes involved in the inflammatory process. Recently published reports also suggest the important role of nitric oxide (NO) and NO-related enzymes in so-called nitrergic neurodegeneration in diabetes [10][11][12] . Indomethacin (IND) is a preferential inhibitor of COX-1 and celecoxib (CEX) is a relatively selective inhibitor of COX-2.…”

Diabetes, the Metabolic Syndrome, and Ischemic Stroke

“…A recent study found a decreased response of cerebrovascular blood flow to NO synthase inhibition in diabetic patients compared with nondiabetic patients, although not enough patients were enrolled to determine significance (98). In addition, parasympathetic neurons that secrete NO into the perivascular space have been documented to degenerate and eventually die in the absence of insulin signaling (99). Numerous studies have found that HMGCoA reductase inhibitors (statins), which upregulate NO synthesis in addition to their activity in stabilizing atherosclerotic plaques (100), significantly reduce the risk of stroke (56,67,101-104).…”