Scalable and reversible axonal neuromodulation of the sympathetic chain for cardiac control

Maladaptation of the sympathetic nervous system contributes to the progression of cardiovascular disease and risk for sudden cardiac death, the leading cause of mortality worldwide. Axonal modulation therapy (AMT) directed at the paravertebral chain blocks sympathetic efferent outflow to the heart, and may be a promising strategy to mitigate excess disease-associated sympathoexcitation. The present work evaluates AMT, directed at the sympathetic chain, in blocking sympathoexcitation using a porcine model. In anesthetized porcine (n=14), we applied AMT to the right T1-T2 paravertebral chain and performed electrical stimulation of the distal portion of the right sympathetic chain (RSS). RSS-evoked changes in heart rate, contractility, ventricular activation recovery interval (ARI), and norepinephrine release were examined with and without kilohertz frequency alternating current block (KHFAC). To evaluate efficacy of AMT in the setting of sympathectomy, evaluations were performed in the intact state and repeated after left and bilateral sympathectomy. We found strong correlations between AMT intensity and block of sympathetic stimulation-evoked changes in cardiac electrical and mechanical indices (r=0.83-0.96, effect size d=1.9-5.7), as well as evidence of sustainability and memory. AMT significantly reduced RSS-evoked left ventricular interstitial norepinephrine release, as well as coronary sinus norepinephrine levels. Moreover, AMT remained efficacious following removal of the left sympathetic chain, with similar mitigation of evoked cardiac changes and reduction of catecholamine release. With growth of neuromodulation, an on-demand or reactionary system for reversible AMT may have therapeutic potential for cardiovascular disease-associated sympathoexcitation.

Investigating the modulation of methylphenidate’s effects on impulsivity by fluoxetine

<p>The co-prescribing of methylphenidate (MPH) and a selective serotonin reuptake inhibitor for patients presenting co-morbidly with both attention deficit/hyperactivity disorder and depression or anxiety is in some cases recommended. Little research has been conducted on the specific cognitive and behavioural outcomes of this. Studies with rats have shown that SSRI’s potentiate MPH-induced dopamine release in the pre-frontal cortex, hippocampus and nucleus accumbens, as well as enhancing MPH-induced hyper-locomotion (Borycz, Zapata, Quiroz, Volkow, & Ferré, 2008; Weikop, Yoshitake, & Kehr, 2007b). Impulsivity is a behavioural construct with dissociable sub-types, of which one, ‘action restraint’, has been consistently shown to be associated with increased dopamine activity in the mesolimbic system, including the nucleus accumbens. It was hypothesised that rats would make more ‘no-go’ errors in a Go/No-Go task, indicative of an increase in ‘action restraint’ type impulsivity, when co-administered fluoxetine (FLX) and MPH compared to either drug administered alone. Although this was not shown in the current study, tentative evidence was found to suggest that the combination of these drugs may negatively impact on attention, based on a decrease in ‘go’ accuracy. A second subtype of impulsivity, “action cancellation”, was tested using a new variant of the Stop-Signal Reaction Time (SSRT) task that we have developed for rats. Studies show that this subtype of impulsivity seems to be unaffected by changes in dopamine activity, but is improved by increases in norepinephrine. In the Weikop study mentioned above, the SSRI citalopram enhanced not only MPH-induced dopamine release, but also norepinephrine release in the nucleus accumbens. Thus it was hypothesised that FLX may potentiate MPH’s impulsivity-reducing effects as measured by stopping latency in the SSRT. We were not able to show this in the current study, however the demonstration that lower doses of MPH reduced stopping latency, consistent with previous versions of the SSRT, validated the new version developed for the current study. A final experiment revealed a rapid, short-term increase in locomotor activity when rats were co-administered FLX and MPH, an effect not present when either drug was administered singly. This synergistic effect replicates previous findings, and indicates a potentiation of dopamine release in the nucleus accumbens, as was found in previous studies. Although FLX was not found to moderate MPH’s effects on impulsivity in the current study, synergistic effects of the two drugs were effects were found on motor activity and potentially on attention also. This is an indication of the value of further research into specific behavioural and cognitive process that may be affected by co-administration of MPH and an SSRI.</p>

Investigating the modulation of methylphenidate’s effects on impulsivity by fluoxetine

<p>The co-prescribing of methylphenidate (MPH) and a selective serotonin reuptake inhibitor for patients presenting co-morbidly with both attention deficit/hyperactivity disorder and depression or anxiety is in some cases recommended. Little research has been conducted on the specific cognitive and behavioural outcomes of this. Studies with rats have shown that SSRI’s potentiate MPH-induced dopamine release in the pre-frontal cortex, hippocampus and nucleus accumbens, as well as enhancing MPH-induced hyper-locomotion (Borycz, Zapata, Quiroz, Volkow, & Ferré, 2008; Weikop, Yoshitake, & Kehr, 2007b). Impulsivity is a behavioural construct with dissociable sub-types, of which one, ‘action restraint’, has been consistently shown to be associated with increased dopamine activity in the mesolimbic system, including the nucleus accumbens. It was hypothesised that rats would make more ‘no-go’ errors in a Go/No-Go task, indicative of an increase in ‘action restraint’ type impulsivity, when co-administered fluoxetine (FLX) and MPH compared to either drug administered alone. Although this was not shown in the current study, tentative evidence was found to suggest that the combination of these drugs may negatively impact on attention, based on a decrease in ‘go’ accuracy. A second subtype of impulsivity, “action cancellation”, was tested using a new variant of the Stop-Signal Reaction Time (SSRT) task that we have developed for rats. Studies show that this subtype of impulsivity seems to be unaffected by changes in dopamine activity, but is improved by increases in norepinephrine. In the Weikop study mentioned above, the SSRI citalopram enhanced not only MPH-induced dopamine release, but also norepinephrine release in the nucleus accumbens. Thus it was hypothesised that FLX may potentiate MPH’s impulsivity-reducing effects as measured by stopping latency in the SSRT. We were not able to show this in the current study, however the demonstration that lower doses of MPH reduced stopping latency, consistent with previous versions of the SSRT, validated the new version developed for the current study. A final experiment revealed a rapid, short-term increase in locomotor activity when rats were co-administered FLX and MPH, an effect not present when either drug was administered singly. This synergistic effect replicates previous findings, and indicates a potentiation of dopamine release in the nucleus accumbens, as was found in previous studies. Although FLX was not found to moderate MPH’s effects on impulsivity in the current study, synergistic effects of the two drugs were effects were found on motor activity and potentially on attention also. This is an indication of the value of further research into specific behavioural and cognitive process that may be affected by co-administration of MPH and an SSRI.</p>

Ethanol abolishes vigilance-dependent astroglia network activation in mice by inhibiting norepinephrine release

Norepinephrine adjusts sensory processing in cortical networks and gates plasticity enabling adaptive behavior. The actions of norepinephrine are profoundly altered by recreational drugs like ethanol, but the consequences of these changes on distinct targets such as astrocytes, which exhibit norepinephrine-dependent Ca2+ elevations during vigilance, are not well understood. Using in vivo two-photon imaging, we show that locomotion-induced Ca2+ elevations in mouse astroglia are profoundly inhibited by ethanol, an effect that can be reversed by enhancing norepinephrine release. Vigilance-dependent astroglial activation is abolished by deletion of α1A-adrenergic receptor from astroglia, indicating that norepinephrine acts directly on these ubiquitous glial cells. Ethanol reduces vigilance-dependent Ca2+ transients in noradrenergic terminals, but has little effect on astroglial responsiveness to norepinephrine, suggesting that ethanol suppresses their activation by inhibiting norepinephrine release. Since abolition of astroglia Ca2+ activation does not affect motor coordination, global suppression of astroglial networks may contribute to the cognitive effects of alcohol intoxication.

Regulation of GluA1 Phosphorylation by D-amphetamine and Methylphenidate in the Cerebellum

Prescription stimulants, such as d-amphetamine or methylphenidate, are potent dopamine (DA) and norepinephrine (NE) releasers used to treat children and adults diagnosed for attention-deficit/hyperactivity disorder (ADHD). Although increased phosphorylation of the AMPA receptor subunit GluA1 at Ser845 (pS845-GluA1) in the striatum has been identified as an important cellular effector for the actions of these drugs, regulation of this posttranslational modification in the cerebellum has never been recognized. Here, we demonstrate that d-amphetamine and methylphenidate increase pS845-GluA1 in the membrane fraction in both vermis and lateral hemispheres of the mouse cerebellum. This regulation occurs selectively in Bergmann Glia Cells and requires intact norepinephrine release since the effects were abolished in mice lacking the vesicular monoamine transporter-2 selectively in NE neurons. Moreover, d-amphetamine-induced pS845-GluA1 was prevented by β1-adenoreceptor antagonist, whereas the blockade of dopamine D1 receptor had no effect. Additionally, we identified transcriptional alterations of several regulators of the cAMP/PKA pathway, which might account for the absence of pS845-GluA1 desensitization in mice repeatedly exposed to d-amphetamine or methylphenidate. Together, these results point to norepinephrine transmission as a key regulator of GluA1 phosphorylation in Bergmann Glial Cells, which may represent a new target for the treatment of ADHD.

Norepinephrine released by intestinal Paneth cells exacerbates ischemic AKI

Small intestinal Paneth cells play a critical role in acute kidney injury (AKI) and remote organ dysfunction by synthesizing and releasing IL-17A. In addition, intestine-derived norepinephrine is a major mediator of hepatic injury and systemic inflammation in sepsis. We tested the hypothesis that small intestinal Paneth cells synthesize and release norepinephrine to exacerbate ischemic AKI. After ischemic AKI, we demonstrated larger increases in portal venous norepinephrine levels compared with plasma norepinephrine in mice, consistent with an intestinal source of norepinephrine release after renal ischemia and reperfusion. We demonstrated that murine small intestinal Paneth cells express tyrosine hydroxylase mRNA and protein, a critical rate-limiting enzyme for the synthesis of norepinephrine. We also demonstrated mRNA expression for tyrosine hydroxylase in human small intestinal Paneth cells. Moreover, freshly isolated small intestinal crypts expressed significantly higher norepinephrine levels after ischemic AKI compared with sham-operated mice. Suggesting a critical role of IL-17A in Paneth cell-mediated release of norepinephrine, recombinant IL-17A induced norepinephrine release in the small intestine of mice. Furthermore, mice deficient in Paneth cells (SOX9 villin Cre mice) have reduced plasma norepinephrine levels after ischemic AKI. Finally, supporting a critical role for norepinephrine in generating ischemic AKI, treatment with the selective α-adrenergic antagonists yohimbine and phentolamine protected against murine ischemic AKI with significantly reduced renal tubular necrosis, inflammation, and apoptosis and less hepatic dysfunction. Taken together, we identify Paneth cells as a critical source of norepinephrine release that may lead to intestinal and liver injury and systemic inflammation after AKI.

P1603Nicorandil suppresses ischemia-induced cardiac interstitial norepinephrine enhancement and ventricular arrhythmia in hypertrophic hearts

Background Myocardial infarction (MI) is a major cause of death in western countries and Japan, and hypertension is a major risk factor of MI. In hypertensive heart, acute myocardial infarction often leads to lethal ventricular arrhythmia. Nicorandil, an ATP sensitive potassium channel (KATP) opener, is usually used in the treatment of acute myocardial infarction. The effects of nicorandil on ischemic myocyte are fully defined. On the other hand, KATP in neuroterminals is known to regulate norepinephrine release, but the effect of nicorandil on ischemic norepinephrine release in cardiac tissue has remained unexplored. Purpose We examined whether nicorandil suppressed norepinephrine release via neuronal KATP and ventricular arrhythmia during acute ischemia in pressure overload-induced hypertrophic hearts. Methods SD Rats were divided into two groups; abdominal aortic constriction (AAC) group and sham-operated (Sham) group. Four weeks after constriction, cardiac geometry and function were examined using echocardiography. Then, myocardial ischemia was induced by the left anterior descending artery occlusion for 100 minutes in the presence or absence of intravenous infusion of nicorandil. Cardiac interstitial norepinephrine concentration in ischemic region was measured using the microdialysis method and concentration of cyclic AMP, a second messenger of norepinephrine, in cardiac tissue was measured by ELISA. Ventricular arrhythmias were monitered by ECG during whole ischemic period. Results Four weeks after constriction, remarkable left ventricular wall thickening was observed in AAC group. Before ischemia, ventricular arrhythmia was not found in both groups. Number of ventricular arrhythmia, including ventricular tachycardia and ventricular fibrillation, was increased in early ischemic period (- 40 min) in both groups, and was grater in AAC group. Before ischemia, interstitial norepinephrine concentration in cardiac tissue was higher level in AAC group than in Sham group. Ischemia obviously increased norepinephrine concentration in both groups time dependently and AAC further increased norepinephrine than Sham group. Concentration of cyclic AMP in cardiac tissue was raised in early ischemic period (- 40 min) and then gradually decreased. Nicorandil significantly suppressed the number of ventricular arrhythmias, and abolished the ventricular tachycardia and fibrillation without hemodynamic alterations. Nicorandil also attenuated norepinephrine and cAMP enhancement in acute ischemic period in both groups. Conclusion Ischemia-induced ventricular arrhythmia was more frequent and severe in hypertrophic hearts and interstitial norepinephrine enhancement may play a role in this ischemic arrhythmia. Nicorandil suppressed ischemia-induced interstitial norepinephrine release by neuronal KATP opening, which attenuated ventricular arrhythmias in normal and hypertrophic hearts.