Cortical Norepinephrine Content Research Articles

1197The development and validation of a novel transcatheter microwave renal denervation system

Abstract Background Clinical studies of transcatheter radiofrequency renal denervation for treating hypertension have been hampered by the lack of consistent denervation efficacy. Microwave energy is well suited to renal denervation due to its capacity to spare vascular structures due to cooling from adjacent blood flow while enabling deep perivascular heating. Purpose We aimed to: 1) develop a transcatheter microwave system capable of safely delivering deep and circumferential perivascular renal nerve ablation, and 2) demonstrate the feasibility, short-term efficacy and safety of transcatheter microwave renal denervation. Method A novel 7F transcatheter microwave denervation system was designed, built, and iteratively prototyped in vitro and in 15 sheep. A histological grading system for microwave induced renal arterial and renal nerve injury was devised. The microwave denervation system was validated in an additional 9 sheep, which underwent unilateral renal denervation. Up to 2 microwave ablations were delivered to each artery with maximum power at 100–110W for 480s. Sheep were euthanised at 2–3 weeks post procedure. Gross microscopic histological examination as well as renal tissue norepinephrine content was analysed. Results Catheter deployment and ablation was successful in all 19 targeted vessel segments and ablation produced substantial circumferential perivascular injury; median ablation lesion area >395 (IQR 251–437) mm2, depth 17.1 (IQR 15.8–18.4) mm, length 16 (IQR 12–20) mm, without collateral visceral injury. Limiting power to 100W minimised arterial injury, while maintaining a deep circumferential perivascular ablation. At microwave ablation sites, a total of 292 nerve fascicles were identified, median distance from the renal artery of 4.2mm (IQR 2.1–8.8mm), of which 249 (85%) had sustained thermal injury with 128/249 (51%) showing grade 3–4 (moderate to severe) injury. Microwave denervation reduced median functional sympathetic nerve surface area at the renal hilum on anti-tyrosine hydroxylase staining by 100% (IQR 87%-100%), p=0.0039, and median renal cortical norepinephrine content by 83% (IQR 76%–92%), p=0.0078, compared to the paired control kidney. Conclusion Transcatheter microwave ablation can produce deep circumferential perivascular ablations over a long segment of the renal artery without significant arterial or collateral visceral injury to provide effective renal denervation. Clinical translation may enable more consistent and complete transcatheter renal denervation and antihypertensive efficacy. Acknowledgement/Funding University of Sydney; Western Sydney Local health District; National Health and Medical Research Council of Australia; National Heart Foundation (Au)

Transcatheter microwave ablation can deliver deep and circumferential perivascular nerve injury without significant arterial injury to provide effective renal denervation.

Clinical studies of transcatheter radiofrequency renal denervation for treating hypertension have been hampered by the lack of consistent denervation efficacy. We aimed to demonstrate the short-term efficacy and safety of transcatheter microwave renal denervation. A novel 7F microwave system was validated in a sheep model of unilateral renal denervation. Up to two microwave ablations were delivered to each artery with maximum power at 100-110 W for 480 s. Catheter deployment and ablation was successful in all 19 targeted vessel segments, and ablation produced substantial circumferential perivascular injury; median ablation lesion area greater than 395 [interquartile range (IQR) 251-437] mm, depth 17.1 (IQR 15.8-18.4) mm, length 16 (IQR 12-20) mm, without collateral visceral injury. Limiting power to 100 W minimized arterial injury, while maintaining a deep circumferential perivascular ablation. Microwave denervation reduced median functional sympathetic nerve surface area at the renal hilum on antityrosine hydroxylase staining by 100% (IQR 87-100%, P = 0.0039), and median renal cortical norepinephrine content by 83% (IQR 76-92%, P = 0.0078), compared to the paired control kidney at 2-3 weeks postprocedure. Transcatheter microwave ablation can produce deep circumferential perivascular ablations over a long segment of the renal artery without significant arterial or collateral visceral injury to provide effective renal denervation.

Abstract 132: Adrenergic Receptor Blockade Prevents Placental Ischemia-induced Hypertension

Hypertensive disorders of pregnancy are the number one cause of pregnancy-related deaths in the United States. Preeclampsia is a disorder of maternal hypertension and cardiovascular dysfunction typically presenting in the second half of pregnancy along with fetal growth restriction. There are no steadfast therapies besides early delivery of the fetus and ischemic placenta, which releases factors into the maternal circulation promoting hypertension. Although sympathetic nervous activity was found to be increased in preeclamptic versus normal pregnant women, it is unknown if sympathetic nervous system plays a role in placental ischemia-induced hypertension. To address this question, we tested the hypothesis that adrenergic receptor blockade prevents placental ischemia-induced hypertension. Wistar rats were randomized to receive reduced uterine perfusion pressure, (RUPP, n=6) or Sham (n=5) surgeries on gestational day 14 and examined at day 19. In RUPP vs Sham rats, respectively, mean arterial blood pressure (115 ± 4 vs 103 ±2 mmHg, P<0.05) and the number of absorbed fetuses (6 ± 1 vs 1 ± 1, P<0.05) were greater whereas average fetal weight was lower (1.7 ± 0.1 vs 2.0 ± 0.2, P<0.05) with similar placental weights (0.49 ± 0.03 vs 0.52 ± 0.03). In RUPP vs Sham rats, renal cortical norepinephrine content (HPLC) was higher (183 ± 15 vs 150 ± 8 pg/mg wet weight, P<0.05) and vasoconstriction to phenylephrine was greater in small, third order mesenteric arteries (Emax: 262 ± 19 vs 160 ± 26% of KCl response). A subset of RUPP rats (n=3) received terazosin and propranolol (3 mg/kg per day each, subcutaneous osmotic minipump) to block alpha- and beta-adrenergic receptors, respectively, beginning the day of RUPP surgery. At day 19, adrenergic blockade prevented the development of hypertension (100 ± 4 mmHg, P<0.05) and did not alter number of fetal absorptions (8 ± 1). Average fetal weight was higher (2 ± 0.1, P<0.05) and placental weight lower (0.41 ± 0.03, P<0.05) compared to the untreated RUPP rats. In conclusion, placental ischemia-induced hypertension depends on activation of the sympathetic nervous system. The mechanism for this enhanced sympathetic nerve activity is unknown but may involve factors released from the ischemic placenta.

Doses of 6-hydroxydopamine sufficient to deplete norepinephrine are not sufficient to decrease plasticity in the visual cortex

These experiments were designed to test Kasamatsu and Pettigrew's (1979, 1983, and see below) hypothesis that plasticity in the visual cortex requires cortical norepinephrine (NE). Kittens were treated with various doses of intraventricular 6-hydroxydopamine (6-OHDA) or vehicle solution. Cortical NE content was measured with high-performance liquid chromatography with electrochemical detection. We sutured the right eyes of some kittens approximately 6 weeks of age for 1 week and recorded from the left visual cortex of these kittens at the end of the week of suture. We measured the ability of the deprived eye to drive cortical cells in animals that received either 0.2 or 4.8 mg of 6-OHDA, and also in control animals that received only vehicle solution. We concluded that a particular dose of 6-OHDA decreased plasticity if it increased (relative to controls) the ability of the deprived eye to drive cortical cells. Doses of 6-OHDA as small as 0.2 mg were sufficient to produce approximately maximal depletion of NE but did not decrease cortical plasticity. Doses of 4.8 mg or more did decrease cortical plasticity, although not as much as was reported by Kasamatsu and Pettigrew. We conclude that 6-OHDA can alter cortical plasticity but the decrease in plasticity does not result from NE depletion.

Regional blood-brain barrier permeability to water and cerebral blood flow during status epilepticus: Insensitivity to norepinephrine depletion

To test whether status epilepticus alters regional blood-brain barrier (BBB) permeability to water when systemic hypertension is avoided, and whether central noradrenergic innervation contributes to the regulation of BBB in this setting, Wistar rats with unilateral 6-hydroxydopamine lesion of the nucleus locus coeruleus (LC) were subjected to 8 min of bicuculline-induced status epilepticus while ventilated with 100% oxygen; arterial normotension was preserved by withdrawal of arterial blood as required. Regional cerebral blood flow and permeability-times-surface-area product (PS) for water were measured by a double-label modification of the Kety integral strategy, with [ 14C]butanol and [ 3H]water, respectively. In normocapnic control rats, regional cerebral blood flow (rCBF) was 1.92 ± 0.57ml/g/min and water extraction fraction was 0.81 ± 0.08 (S.D.). Values in control rats breathing 100% oxygen were similar. During status epilepticus, rCBF increased two- to three-fold; water extraction fraction declined, but there were no significant side-to-side differences for either rCBF or regional PS product for water in LC-lesioned animals despite an 81% reduction of cortical norepinephrine content on the lesioned side. The PS product for water increased by 42% during status epilepticus, but the flow vs PS-product relationship did not depart from that predicted on the basis of data in control rats. Thus, when systemic hypertension is prevented, brief status epilepticus does not induce abnormal BBB permeability to water, and unilateral LC lesion fails to influence either rCBF or the cerebrovascular PS product for water.

Alterations of the cortical noradrenergic system in chronic cobalt epileptogenic foci in the rat: A histofluorescent and biochemical study

Various models of acute experimentally-induced epilepsy indicate that aminergic neurons are involved. It has been demonstrated that a decrease in the level of norepinephrine can increase the susceptibility to epileptic seizures. The present research was undertaken in order to study alterations in the cortical noradrenergic system during the evolution of a chronic epileptic model induced by application of metallic cobalt on the sensorimotor cortex in the rat. The alterations were studied by means of the glyoxylic histochemical fluorescence method combined with biochemical analysis of cortical norepinephrine content. This histochemical and biochemical approach revealed a decrease in the density of noradrenergic terminals in the perifocal area. This decrease corresponds to a significant drop in the norepinephrine level, before the onset of spiking activity. Noradrenergic fiber density was still low and the norepinephrine level was lowest when the first epileptic discharges were recorded. At the end of the epileptic syndrome, sprouting of noradrenergic fibers into the perifocal area coincided with an increase in the norepinephrine level. Thus, this study gives further support to the hypothesis that noradrenergic system is involved in epileptogenesis.

Facilitation of muricide by dorsal norepinephrine bundle lesions in olfactory bulbectomized rats

The role of the dorsal norepinephrine bundle in the occurrence of muricide was studied in olfactory bulbectomized rats. Although the incidence of muricide was 30% in the olfactory bulbectomized rat, it significantly increased up to 80% and 90% on the 5th and 10th day, respectively, after dorsal bundle lesion. Cortical norepinephrine content decreased by about 50% after dorsal bundle lesions. These results indicate that the dorsal bundle system plays an inhibitory role in the occurrence of muricide in olfactory bulbectomized rats.

Release of endogenous catecholamines from isolated rat brain tissue by fenfluramine and N-ethylamphetamine—effects of pargyline

The influence of the monoamine oxidase inhibitor, pargyline. upon the release of endogenous norepinephrine from chopped rat cerebral cortex and endogenous dopamine from chopped rat corpus striatum by fenfluramine and N-ethylamphetamine was examined. Endogenous norepinephrine and dopamine were measured using an enzymatic-isotopic assay. Both fenfluramine and N-ethylamphetamine released significant amounts of each catecholamine. Fenfluramine-induced catecholamine release was associated with the decrease in the total content (i.e. catecholamine in media + catecholamine in tissue) of both cortical norepinephrine and striatal dopamine; N-elhylamphetamine decreased only total striatal dopamine content. In brain tissue obtained from rats pretreated with pargyline HCl (100 mg/kg, 12 hr prior to sacrifice), total cortical norepinephrine content was approximately twice that in the absence of pargyline: striatal dopamine was unchanged. Pargyline pretreatment also resulted in a marked potentiation of the amounts of both catecholamines released by each drug. and in an antagonism of the above drug-induced reductions in catecholamine content. Additionally, after pargyline pretreatment. N-ethylamphetamine reduced total cortical norepinephrine content. When pargyline (2.56 × 10 −1 M) was added to the media containing chopped cortical tissue from unpretreated animals, control content was slightly increased. Only fenfluramine-induced norepinephrine release was potentiated and the degree of potentiation was less than that observed after pargyline pretreatment. As with pargyline in vivo, pargyline in vitro also resulted in an antagonism of the fenfluramine-induced decrease in total norepinephrine and was associated with an N-ethylamphetamine-induced decrease in norepinephrine content. Since the locomotor stimulant effects of both fenfluramine and N-ethylamphetamine are potentiated after pargyline. the data are consistent with the importance of catecholamines to these effects. The data also suggest that pargyline potentiates the behavioral effects of fenfluramine and N-ethylamphetamine in part by increasing the pool of norepinephrine available for release by these drugs and in part by inhibiting the deamination of the released norepinephrine and dopamine by monoamine oxidase. Decreases in total norepinephrine produced by N-ethylamphetamine may reflect alterations in the formation of O-methylated amines.