Cerebral blood flow during hypoxemia and hemodilution in rabbits: different roles for nitric oxide?

Hypoxemia and anemia are associated with increased CBF, but the mechanisms that link the changes in PaO2 or arterial O2 content (CaO2) with CBF are unclear. These experiments were intended to examine the contribution of nitric oxide. CaO2 in pentobarbital-anesthetized rabbits was reduced to approximately 6.5 mL O2/dL by hypoxemia (PaO2 approximately 24 to 26 mm Hg) or hemodilution with hetastarch (hematocrit approximately 14% to 15%). Animals with normal CaO2 (approximately 17.5 to 18 mL O2/dL) served as controls. In part I, each animal was given 3, 10, and 30 mg/kg N omega-nitro-L-arginine methyl ester (L-NAME) intravenously (total 43 mg/kg) to inhibit production of nitric oxide. Forebrain CBF was measured with radioactive microspheres approximately 15 to 20 minutes after each dose. Baseline CBF was greater in hypoxemic rabbits (111 +/- 31 mL x 100 g-1 x min-1, mean +/- SD) than in hemodiluted (70 +/- 22 mL x 100 g-1 min-1) or control animals (39 +/- 12 mL x 100 g-1 min-1). L-NAME (which reduced brain tissue nitric oxide synthase activity by approximately 65%) reduced CBF in hypoxemic animals to 80 +/- 23 mL x 100 g-1 x min-1 (P < 0.0001), but had no significant effect on CBF in either anemic or control animals. In four additional rabbits, further hemodilution to a CaO2 of approximately 3.5 mL O2/dL increased baseline CBF to 126 +/- 21 mL x 100 g-1 min-1, but again there was no effect of L-NAME. In part II, animals were anesthetized as above, and a close cranial window was prepared. The cyclic GMP (cGMP) content of the artificial CSF superfusate was measured under baseline conditions, and then after the reduction of CaO2 to approximately 6.5 mL O2/dL by either hypoxemia or hemodilution. Concentrations of cGMP did not change during either control conditions or after hemodilution. However, cGMP increased significantly with the induction of hypoxemia. The cGMP increase in hypoxemic animals could be blocked with L-NAME. These results suggest that nitric oxide plays some role in hypoxemic vasodilation, but not during hemodilution.     

Gastric mucosal blood flow response to stress in streptozotocin diabetic rats: regulatory role of nitric oxide

To investigate cytoprotection against mucosal injuries of the stomach in patients with diabetes, we investigated gastric mucosal blood flow (GMBF), its response to a burn stress, and the involvement of nitric oxide (NO) in streptozotocin (STZ) diabetic rats. GMBF was measured by laser-Doppler velocimetry (LDV) and by the hydrogen gas clearance technique (HGC). The steady-state GMBF of STZ rats decreased according to the duration of diabetes, and insulin treatment blocked this decrease. Burn stress caused a rapid decrease in the GMBF. Reduction of the GMBF and gastric mucosal leakage of Evans blue (EB) after the burn stress were greater in the STZ rats than in the controls, but insulin treatment completely blocked this increase in EB leakage in the STZ rats. There was a significant negative correlation between the percent GMBF 3 h after the burn stress and EB leakage at the same time point. In the controls and the insulin-treated STZ rats, N-nitro-L-arginine (L-NNA), an NO synthase inhibitor, enhanced the decrease in postburn GMBF and EB leakage, but was without effect in the STZ rats. These results suggest that NO may be involved in the regulation of GMBF, and that persistent hyperglycemia may impair this regulation. These findings suggest that patients with diabetes have reduced cytoprotection against a variety of gastric mucosal injuries.     

Renal ischemia-reperfusion injury: contribution of nitric oxide and renal blood flow

In nocturnal rodents, the c-fos gene is directly involved in the light mechanism of resetting of the suprachiasmatic nucleus (circadian clock). Light also induces c-fos expression in the retinal ganglion cell layer (GCL), but no attempt has been made to study the retinal responses to the phase-shifting effects of light. The expression of the Fos protein in each of the two populations of the GCL (displaced amacrine cells [DACs] and ganglion cells [GCs]) was analyzed in hamsters after light stimulation delivered early (circadian time [CT13]) and in the middle (CT18) of the subjective night. To evaluate as accurately as possible the number of GCs able to phase shift the locomotor activity rhythm (LAR), neonatal hamsters treated with monosodium glutamate (MSG) were also used, an in vivo model which displays retinal degeneration and LAR normally entrained by light. In nontreated hamsters, the number of Fos-immunoreactive (Fos-ir+) nuclei in the GCL was significantly higher at CT18 than at CT13. In MSG-treated hamsters, the number of Fos-ir+ nuclei was the same at both CTs and nonsignificantly different as those of nontreated hamsters at CT13. MSG treatment destroyed as many Fos-ir+ DACs as Fos-ir- DACs or Fos-ir+ GCs. Fos-ir+ GCs were less sensitive to neurotoxic than other GCs, as only 37% of them were destroyed by treatment versus 92% for Fos-ir- GCs. At CT18, a maximum of 3,500 GCs expressed Fos protein in nontreated hamsters versus only 2,200 in MSG-treated hamsters. This minor subgroup was sufficiently potent to normally synchronize the circadian rhythms to the Light/dark cycle in treated hamsters.     

Hyperdynamic circulation of cirrhotic rats: role of substance P and its relationship to nitric oxide

BACKGROUND: It has been suggested that excessive formation of nitric oxide (NO) is responsible for the hyperdynamic circulation observed in portal hypertension. Substance P is a neuropeptide partly cleared by the liver and causes vasodilatation through the activation of the endothelial NO pathway. However, there are no previously published data concerning the plasma level of substance P in cirrhotic rats and its relationship to NO. METHODS: Plasma concentrations of substance P and nitrate/nitrite (an index of NO production) were determined in control rats and cirrhotic rats with or without ascites using an enzyme-linked immununosorbent assay and a colorimetric assay, respectively. In addition, systemic and portal hemodynamics were evaluated by a thermodilution technique and catheterization. RESULTS: Cirrhotic rats with and without ascites had a lower systemic vascular resistance (2.6 +/- 0.2 and 3.9 +/- 0.4 mmHg ml(-1) x min x 100 g body weight, respectively) and higher portal pressure (14.6 +/- 0.6 and 11.3 +/- 1.8 mmHg) than control rats (6.5 +/- 0.3 mmHg x ml(-1) x min x 100 g BW and 6.8 +/- 0.2 mmHg, respectively, P < 0.05), and cirrhotic rats with ascites had the lowest systemic vascular resistance. Plasma levels of nitrate/nitrite progressively increased in relation to the severity of liver dysfunction (control rats, 2.7 +/- 0.5 nmol/ml; cirrhotic rats without ascites, 5.6 +/- 1.3 nmol/ml; cirrhotic rats with ascites, 8.3 +/- 2.2 nmol/ml; P < 0.05). Cirrhotic rats with ascites displayed higher plasma values of substance P (57.7 +/- 5.9 pg/ml) than cirrhotic rats without ascites (37.9 +/- 3.1 pg/ml, P < 0.05) and control rats (30.1 +/- 1.0 pg/ml, P < 0.05). There was no significant difference in plasma substance P values between control rats and cirrhotic rats without ascites (P > 0.05). No correlation was found between plasma levels of substance P and nitrate/nitrite (r = 0.318, P > 0.05). CONCLUSIONS: Excessive formation of NO may be responsible, at least partly, for the hemodynamic derangements in cirrhosis. Although substance P may not participate in the initiation of a hyperdynamic circulation in cirrhosis, it may contribute to the maintenance of the hyperdynamic circulation observed in cirrhotic rats with ascites.     

Role of nitric oxide in the effect of blood flow on neointima formation

PURPOSE: Neointima formation after arterial injury is inhibited by increased blood flow. The object of this study was to determine whether nitric oxide mediates the effect of increased blood flow on neointima formation. METHOD: Balloon catheter-denuded rat carotid arteries were exposed to increased blood flow or control blood flow by ligation of the contralateral carotid artery. Beginning 2 days before balloon denudation, rats were given either saline vehicle alone or the nitric oxide synthase inhibitor N-nitro-L-arginine-methyl ester (L-NAME) at a dose of 10 mg/kg/day or 2 mg/kg/day intraperitoneally. The normalized neointima area was measured 14 days after denudation. RESULTS: Blood flow was significantly increased by ligation of the contralateral carotid artery for all drug treatments (p<0.008). In rats given saline vehicle only, normalized neointima area was significantly reduced after increased blood flow compared with control blood flow (0.33+/-0.04 compared with 0.48+/-0.03; p=0.006). Systolic blood pressure was significantly elevated by treatment with high-dose L-NAME (p=0.002 compared with vehicle), but was not altered by low-dose L-NAME (p=NS compared with vehicle). Normalized neointima area was not significantly reduced after increased carotid blood flow for rats treated with either dose of L-NAME (p=NS). CONCLUSION: The inhibition of neointima formation by increased blood flow was abolished with hypertensive and nonhypertensive doses of the nitric oxide synthase inhibitor L-NAME, which suggests that the L-NAME effects are independent of systemic hemodynamic alterations. It is concluded that flow-induced inhibition of neointima formation is mediated in part by nitric oxide.     

Postoperative motor function and mucosal blood flow of lower esophagus: comparison between terminal esophagoproximal gastrectomy and esophageal transection for esophageal varices

Reflux esophagitis and anastomotic ulcer are potential complications associated with surgery for esophagogastric lesions. This study compared 10 cases following terminal esophagoproximal gastrectomy (TEPG) for esophageal varices and 20 cases following esophageal transection (ET) for esophageal varices with respect to postoperative motor function and mucosal blood supply, to ascertain the reason for the development of anastomotic ulcer. Endoscopic findings showed that anastomotic ulcers were detected more often after TEPG than after TR. Maximum swallowing pressure, high pressure zone pressure, and length did not differ between the two groups. However, maximum swallowing pressure in the lower esophagus after both procedures was significantly lower than in the control group (20 cases; p < 0.01). The results, measured by reflectance spectrophotometry, showed that the index of esophageal mucosal blood volume following TEPG is significantly lower than that following ET and in non-operated esophageal varices (10 cases; p < 0.01). Yet the index of oxygen saturation of hemoglobin was similar in the three groups. This study has demonstrated that patients undergoing TEPG have mucosal ischemia of the lower esophagus, causing the development of anastomotic ulcers.     

Role of nitric oxide in angiotensin IV-induced increases in cerebral blood flow

Whether a rapid elevation of serum gliclazide concentration in human subjects can be achieved through an acceleration of dissolution of gliclazide from a formulation was examined. A soft gelatin capsule containing PEG 400, PEG 4000, Tween 20 and glycerin was prepared as a formulation that may accelerate dissolution of gliclazide. The in vitro dissolution of gliclazide at pH 7.2 was identical for the soft capsule and conventional tablets, Diamicron and Diberin. However, at pH 1, 2 and 4.0 the dissolution from the soft capsule was more rapid compared to the tablets. When bioavailability parameters were compared following oral administration of the soft capsule and Diamicron to 16 healthy Korean male subjects, the parameters representing the amount of adsorption (i.e. the area under the serum gliclazide concentration vs. time curve up to 24 h, AUC24, and the peak serum concentration Cmax) were not statistically different for both formulations. However, the time required to reach the peak (Tmax) was significantly shorter for the soft capsule than for the Diamicron. Our results, therefore, indicate that a rapid elevation of serum gliclazide concentration following oral administration of a formulation can be achieved by accelerating the in vitro dissolution of gliclazide from the formulation into the acidic buffers. Thus, the rate of gastrointestinal absorption of gliclazide appears to be dependent on its in vivo dissolution rate in gastric fluid. A soft capsule containing a PEG 400 suspension of gliclazide appears to be an appropriate formulation for accelerating the dissolution.     

Endothelial barrier dysfunction and oxidative stress: roles for nitric oxide?

Endothelial dysfunction has an important role to play in the pathophysiology of human vascular disease. The maintenance of barrier function is critical to the role of vascular endothelium in cardiovascular haemostasis and this function can be compromised by inflammatory mediators, cytokines or oxidants. Under conditions of oxidative stress a variety of reactive oxygen species (ROS) may be generated, which increase the permeability of the endothelial monolayer to fluid, macromolecules and inflammatory cells. The endothelium-derived nitric oxide radical (NO), whose physiological actions include effects on vascular smooth muscle, is normally inactivated by the superoxide radical anion. While large amounts of NO have cytotoxic potential, it is now becoming clear that combinations of NO with ROS can produce either cytotoxic or cytoprotective effects, depending on the relative amounts of each which are present in the target cell or its environment at a particular time. The contribution of NO to oxidant-mediated endothelial barrier dysfunction can be assessed in vitro in endothelial monolayers grown on porous membrane supports. In this model, using hydrogen peroxide (H2O2) as the oxidant, H2O2-induced losses of barrier function can be enhanced or partially offset by NO donor drugs, depending on the concentration of NO donor used. Furthermore, the injurious or cytoprotective effects of these agents appear to be determined by the quantity of NO generated. Since NO is administered clinically by inhalation in conditions such as pulmonary hypertension or the adult respiratory distress syndrome, which are themselves associated with generation of ROS, it is likely that low concentrations of NO may protect the pulmonary vascular endothelium while high concentrations might be expected to combine with ROS to yield intermediates capable of causing further endothelial injury or loss of barrier function.     

Augmentation of blood flow through cerebral collaterals by inhibition of nitric oxide synthase

We examined the influence of nitric oxide (NO) on normal and collateral cerebral blood flow after occlusion of the middle cerebral artery (MCA). Effects of NG-nitro-L-arginine (nitroarginine), an inhibitor of NO synthase, were examined during normotension and hypotension (arterial pressure, 50 mm Hg) in 49 anesthetized dogs. Following a craniotomy, a branch of the MCA was cannulated, and collateral-dependent tissue was identified using the shadow-flow technique. Regional cerebral blood flow was measured with microspheres, and pial artery pressure was measured with a micropipette. Intravenous nitroarginine reduced blood flow to normal cerebrum by approximately 40% (p < 0.05) during normotension and hypotension, with aortic pressure maintained constant after nitroarginine administration. Injection of nitroarginine during hypotension, without control of pressor effects, increased aortic and pial artery pressure approximately twofold. Concurrently, blood flow to normal cerebrum decreased (p < 0.05), while flow to collateral-dependent cerebrum increased (p < 0.05). Phenylephrine was infused during hypotension to increase arterial pressure to values similar to those achieved following nitroarginine. Blood flow to collateral-dependent cerebrum increased (p < 0.05), but flow to normal cerebrum was not altered during infusion of phenylephrine. Thus, inhibition of NO synthase during hypotension increases arterial pressure, decreases blood flow to normal cerebrum, and increases blood flow to collateral-dependent cerebrum. Phenylephrine also increases perfusion pressure and blood flow to collateral-dependent cerebrum, but in contrast to nitroarginine, it does not redistribute blood flow from normal cerebrum.     

Regulation of cytokine production by eicosanoids and nitric oxide

Cytokines are widely regarded as regulatory molecules of inflammatory and immune reactions. Nevertheless, the details of functioning of the complex cytokine network are not yet fully understood. Recent data indicate that eicosanoids, primarily the products of the inducible form of cyclooxygenase (COX-2), are involved in the regulation of cytokine production. We have shown that prostaglandins of E series are no longer only suppressor molecules but they selectively up- or down-regulate the cytokine production. Similarly, nitric oxide (NO) generated in activated immune cells by inducible isoform of nitric oxide synthase (iNOS), is considered to be an immunoregulatory molecule. In this article we present a new concept of interactions between cytokines, eicosanoids (prostaglandins and leukotrienes) and NO. Finally, the impact of these molecules on the regulation of the immune system is discussed.     

Role of nitric oxide in maintenance of basal anterior choroidal blood flow in rats

PURPOSE: The aim of this study was to use laser Doppler flowmetry to measure anterior choroidal blood flow in the anesthetized rat and to determine the role of nitric oxide (NO) in the maintenance of basal ocular blood flow in vivo. METHODS: By using laser Doppler flowmetry, blood flow from the anterior choroid in pentobarbital-anesthetized rats was measured continuously. Graded single doses (0.03-300 mg/kg) of the nonselective NO synthase inhibitor NG-nitro-L-arginine-methyl ester (L-NAME) were administered intravenously to establish dose-response relationships. Other groups of animals were tested with L-NAME after the prior administration of L-arginine, with D-NAME, or with the selective neural NO synthase inhibitor 7-nitroindazole. RESULTS: Intravenous administration of L-NAME produced a dose-related depression of anterior choroidal blood flow in the 0.3- to 30-mg/kg range. Maximal depression of approximately 60% occurred at the 30-mg/kg dose, peaked at approximately 30 minutes, and lasted throughout the 60-minute experimental period. At 10 mg/kg, L-NAME reduced ocular blood flow by approximately 50%, an effect that was abolished by pretreatment with intravenous L-arginine (300 mg/kg). Both D-NAME (10 mg/kg, intravenously) and 7-nitroindazole (50 mg/kg, intraperitoneally) were inactive with regard to ocular blood flow depression. CONCLUSIONS: Laser Doppler flowmetry appears to be a useful tool for continuous, online measurement of anterior choroidal blood flow in the rat eye. Results with L-NAME and 7-nitroindazole suggest that local tonic generation of endothelial NO plays an important role in the maintenance of basal anterior choroidal blood flow in this species.     

Anticonvulsant and proconvulsant roles of nitric oxide in experimental epilepsy models

The effect of acute (120 mg/kg) and chronic (25 mg/kg, twice a day, for 4 days) intraperitonial injection of the nitric oxide (NO) synthase (NOS) inhibitor NG-nitro-L-arginine (L-NOARG) was evaluated on seizure induction by drugs such as pilocarpine and pentylenetetrazole (PTZ) and by sound stimulation of audiogenic seizure-resistant (R) and audiogenic seizure-susceptible (S) rats. Seizures were elicited by a subconvulsant dose of pilocarpine (100 mg/kg) only after NOS inhibition. NOS inhibition also simultaneously potentiated the severity of PTZ-induced limbic seizures (60 mg/kg) and protected against PTZ-induced tonic seizures (80 mg/kg). The audiogenic seizure susceptibility of S or R rats did not change after similar treatments. In conclusion, proconvulsant effects of NOS inhibition are suggested to occur in the pilocarpine model and in the limbic components of PTZ-induced seizures, while an anticonvulsant role is suggested for the tonic seizures induced by higher doses of PTZ, revealing inhibitor-specific interactions with convulsant dose and also confirming the hypothesis that the effects of NOS inhibitors vary with the model of seizure.     

Cuffed endotracheal tubes: mucosal pressures and tracheal wall blood flow

Eighteen brands of cuffed endotracheal tubes, including those with the new low pressure cuffs, were evaluated and compared. Experiments were performed in vitro on excised dog tracheae to measure the mucosal pressure exerted by the inflated cuffs. Pressure was measured directly with a mechanical sensor. Latex cuffs exerted the highest mucosal pressures, whereas silicone cuffs exerted the lowest mucosal pressures. Polyvinyl chloride cuffs exerted intermediate levels of mucosal pressure. With each material, predistended cuffs exerted lower mucosal pressures than nonpredistended cuffs. A second set of experiments was performed in vivo to determine the effect of mucosal pressure on tracheal wall blood flow. These studies employed a thermistor technic. The data showed that, when inflated sufficiently to seal within the trachea, stiff cuffs reduced blood flow more than compliant cuffs. With all cuffs, blood flow was reduced more at the mucosa than at deeper regions of the tracheal wall.It was concluded that for clinical use, compliant cuffs are preferable to stiff cuffs because they should cause less ischemia.     

Possible role for nitric oxide releasing nerves in the regulation of ocular blood flow in the rat

AIM: To investigate the role of nitrergic nerves in the regulation of ocular blood flow. METHODS: Conscious, lightly restrained rats were treated with either the neuronal nitric oxide synthase inhibitor 7-nitroindazole (7-NI), or the nonselective inhibitor, NG-nitro-L-arginine methyl ester (L-NAME), and ocular blood flow was measured ex vivo from tissue samples, using the fully quantitative [14C]-iodoantipyrine technique. RESULTS: In the peripheral circulation, L-NAME produced an increase in arterial blood pressure (+22%) while 7-NI had no effect. In contrast, both 7-NI and L-NAME produced significant decreases in ocular blood flow (-31% and -59% respectively). The ocular vascular resistance calculated from ocular blood flow and mean arterial blood pressure increased by 29% following 7-NI, but by 130% following L-NAME. CONCLUSIONS: Nitric oxide releasing neurons may play an important contributory role in regulating ocular blood flow.     

Angiotensin II regulates choroid plexus blood flow by interacting with the sympathetic nervous system and nitric oxide

Blood flow to the rat choroid plexus has minimal variability when plasma angiotensin II (AII) concentration is changed within a broad range of levels. We tested the hypothesis that a complex interplay of the vasoconstrictor and vasodilator AII actions in choroidal tissue results in small net changes in choroidal blood flow. Blood flow was measured with 123I- or 125I-N-isopropyl-p-iodoamphetamine. AII was infused intravenously (i.v.) at 30 (moderate dose) and 300 ng kg-1 min-1 (high dose), which respectively decreased (15%) and did not change choroidal blood flow. To determine whether AII regulates choroidal blood flow by interacting with the sympathetic nervous system, rats were given phentolamine (1 mg kg-1, i.v.). This alpha-adrenoceptor antagonist by itself did not alter blood flow; however, it attenuated the blood flow-lowering effect of moderate AII dose. Phentolamine also unmasked the vasodilator AII actions at high peptide concentration. beta-Adrenoceptor blockade, with propranolol (1 mg kg-1, i.v.), reduced blood flow (18-20%) and increased vascular resistance (23-26%). During beta-adrenoceptor blockade, a further decrease in blood flow (15-21%) and increase in vascular resistance (23%) was noted when high AII dose was administered. The direct vasoconstrictor effect of AII at moderate dose on choroidal vasculature was examined in rats subjected to chronic bilateral superior cervical ganglionectomy. In these animals, AII decreased blood flow (24%) and increased vascular resistance (24%). To find out whether the hemodynamic AII actions in choroidal tissue are mediated by nitric oxide (NO), Nomega-nitro-l-arginine methyl ester (l-NAME) was used. l-NAME (0.1 mg kg-1, i.v.) by itself did not alter blood flow; however, in l-NAME-treated rats high AII dose lowered blood flow (25-32%) and increased vascular resistance (30-43%). We conclude that the vasoconstrictor AII actions involve a direct peptide effect on the choroidal vascular bed, and the AII-mediated potentiation of sympathetic activity, which results in the activation of alpha-adrenoceptors. The AII-mediated stimulation of sympathetic nerves also results in the beta-adrenoceptor-dependent relaxation of choroidal blood vessels. In addition, choroidal vasodilatory actions of AII are NO-mediated.     

Effects of nitric oxide modulation on tumour blood flow and microvascular permeability in C6 glioma

C6 glioma strongly express nitric oxide synthase. Rats bearing C6 tumours were pre-treated with i.v. Ng-nitro-L-arginine methyl ester (L-NAME), 3-morpholinosydnonimine (SIN-1) or saline before local cerebral blood flow (LCBF) or tumour capillary permeability (TCP) was measured by the [14C]iodoantipyrine autoradiographic or [14C]alpha-amino-isobutyric acid techniques. L-NAME and SIN-1 caused significant TBF alterations (-44% and +136%, respectively) with less marked (-15% and +33%) alterations in normal brain. Calculated cerebrovascular resistance changes within tumour were indeed selective. Baseline TCP was increased compared with normal brain (20-fold). L-NAME and SIN-1 administration did not alter TCP. These effects have significant implications for human malignant glioma management. Selective i.v. manipulation of LCBF, without significant changes in TCP, could increase the efficacy of chemotherapy, radiotherapy or provide better peritumoural oedema control.     

Effect of prostaglandins and nitric oxide on basal blood flow and acetylcholine-induced vasodilation in rat diaphragmatic microcirculation

We compared the ability of 4 magnetic coils to activate peripheral nerves in healthy subjects. No differences in motor threshold intensities were found between the coils, but the intensities needed to elicit maximum compound muscle action potential (CMAP) amplitudes were different. For superficial nerves maximum CMAPs in comparison with electrical stimulation were usually but not always found. CMAPs were at their maximum only when the direction of induced current flowed from proximal to distal and when a certain part of the coil was over the nerve. Distal nerve stimulation was time consuming. Due to artifacts many stimuli were necessary and sometimes no maximum CMAP could be elicited. CMAPs were much less sensitive to position changes of the coil than to changes in an electrical stimulator. Small circular coils were superior to larger coils in terms of the lower intensities necessary to elicit maximum CMAPs, better focusing of the stimulus, and less artifacts. For deep nerves amplitudes were always submaximal. Coactivation of nearby nerves and underlying muscles was another main drawback especially at proximal sites and for coils of large diameter. Despite better focusing, double coils are less useful due to their great diameter. Magnetic stimulation cannot replace electrical neurography at the moment, even if different coils are used at different sites of stimulation.