Blockade Of Neuropeptide Research Articles

Abstract 11494: Electrophysiological Effects of Sympathoexcitation are Mitigated by Blockade of Neuropeptide Y Y2 Receptors on Cardiac Parasympathetic Nerve Terminals

Introduction: Sympathetic activation releases both norepinephrine and co-transmitter neuropeptide Y (NPY). NPY can predispose to ventricular arrhythmias via receptors on cardiomyocytes. Ex vivo studies suggest that NPY may concomitantly reduce vagal tone via activation of NPY Y2 receptors (Y2R) on parasympathetic nerves, reducing acetylcholine release and further augmenting pro-arrhythmic sympathetic effects. We evaluated if parasympathetic Y2R blockade can prevent NPY-induced vagal inhibition, restore autonomic balance and stabilize cardiac electrophysiology. Methods: Yorkshire pigs (n = 12) underwent bilateral stellate ganglia stimulation (BSGS; 10 Hz, 4 ms) for 45 secs, before and after administration of selective Y2R antagonist BIIE0246 (BIIE; 32 nmol/kg bolus + 2 nmol/kg/min infusion). Hemodynamic and electrophysiological recordings were obtained with a left ventricular pressure (LVP) catheter, surface electrogram and a 56-electrode sock placed over the ventricles to measure activation recovery intervals (ARI), a surrogate of local action potential duration, from unipolar electrograms. Heart rate variability parameters, including low to high frequency ratio (LF/HF), were analyzed pre- and post-BIIE. Results: BSGS significantly increased heart rate (HR) and LVP, and shortened ventricular ARIs. BIIE significantly reduced both the rate of change and the maximal changes in HR and ARIs during BSGS. As anticipated, BSGS significantly increased LF/HF ratio, but this effect was abolished after BIIE. BIIE did not affect BSGS related increases in LVP. Conclusions: Cardiac effects of sympathetic activation are mediated, at least in part, by suppression of vagal tone through binding of NPY to parasympathetic Y2Rs. Blockade of this receptor partially counters pro-arrhythmic electrophysiological effects of BSGS and suggests a possible novel adjuvant role for Y2R blockade as a therapy for reducing consequences of sympatho-excitation.

Blockade of Neuropeptide Y Y1 Receptors in the Dorsomedial Hypothalamus Increases Sympathetic Nerve Activity via Projections to the Hypothalamic Paraventricular Nucleus

Arcuate Neuropeptide Y (NPY) neurons tonically suppress basal sympathetic nerve activity (SNA) via binding of NPY to NPY Y1 receptors (NPY1R) in the hypothalamic paraventricular nucleus (PVN) and the dorsomedial hypothalamus (DMH). Projection targets of PVN pre‐sympathetic neurons that are inhibited by NPY include the rostral ventrolateral medulla. However, the downstream targets of DMH NPY‐receptive neurons are unknown. Because DMH neurons send a major projection to the PVN, we hypothesized that the PVN is one target. To test this hypothesis, male Npy1r‐cre mice (n=2) received unilateral DMH injections of an adeno‐associated virus, which allows for the cre‐dependent expression of a fluorescent protein (mCherry) in the cell bodies and axon fibers of NPY1R‐containing neurons. After about two weeks, the animals were sacrificed, and their brains were immunohistochemically processed to enhance the mCherry signal. In support of our hypothesis, we identified an abundance of mCherry‐labeled fibers in the PVN. A second prominent projection target was the nucleus raphe pallidus, an important medullary region involved in the regulation of brown adipose tissue thermogenesis. Next, to test the physiological significance of the DMH projection to the PVN, in α‐chloralose anesthetized WT male mice (n=5), we first bilaterally injected the selective NPY1R antagonist, BIBO3304 (30 nl of 10 mM/L), into the DMH, which increased (all P<0.05) splanchnic SNA (SSNA) by 40±12% control, mean arterial pressure (MAP) from 82±5 to 97±6 mmHg, and heart rate (HR) from 449±35 to 554±29 bpm. After 15 min, the inhibitory GABAA agonist, muscimol (30 nL of 1 mM/L), was injected bilaterally into the PVN and reversed the effects of DMH BIBO3304: SSNA decreased to 112±7 % control, MAP to 83±7 mmHg, and HR to 471±25 bpm. In conclusion, NPY tonically inhibits DMH pre‐sympathetic neurons that express NPY1R and project to the PVN.Support or Funding InformationHL128181; APS/Hearst UGSRFThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Role of the Paraventricular Nucleus of the Hypothalamus in the Sympathoexcitatory Effects of Leptin.

Leptin binds to receptors in multiple hypothalamic nuclei to increase sympathetic nerve activity; however, the neurocircuitry is unclear. Here, using anesthetized male Sprague-Dawley rats, we investigated the role of the paraventricular nucleus of the hypothalamus. Intracerebroventricular injection of leptin slowly increased lumbar sympathetic nerve activity (LSNA), heart rate, mean arterial pressure, and baroreflex control of LSNA and heart rate. Inhibition of the paraventricular nucleus with muscimol completely reversed leptin's effects. Blockade of paraventricular melanocortin 3/4 receptors with SHU9119 or ionotropic glutamate receptors with kynurenate, alone or together, each partially reversed the effects of leptin, implicating increased activation of glutamate and melanocortin 3/4 receptors. Conversely, although blockade of neuropeptide Y Y1 receptors in the paraventricular nucleus increased LSNA, mean arterial pressure, and heart rate, these responses were prevented by intracerebroventricular or arcuate nucleus injections of leptin, suggesting that, at least in part, leptin also increases sympathetic nerve activity by suppression of tonic neuropeptide Y inhibitory inputs from the arcuate nucleus. Injection of the melanocortin 3/4 receptor agonist melanotan-II into the paraventricular nucleus increased LSNA, mean arterial pressure, and heart rate only after blockade of neuropeptide Y Y1 receptors. Therefore, we conclude that leptin increases LSNA in part via increased glutamatergic and α-melanocyte-stimulating hormone drive of paraventricular sympathoexcitatory neurons, the latter of which requires simultaneous withdrawal of tonic neuropeptide Y inhibition.

Attenuation of pain-related behaviour evoked by carrageenan injection through blockade of neuropeptide Y Y1 and Y2 receptors

It is well known that neuropeptide Y (NPY) participates in the modulation of chronic pain, but its exact role has not yet been fully explained. In this study, we explored whether targeted delivery of NPY and its antagonists into dorsal root ganglion (DRG) modulates pain-related behaviour in rats with experimentally induced inflammatory nociception. Inflammatory nociception was induced by intraplantar carrageenan injection. Immediately after carrageenan injection, NPY or its antagonists were injected directly into DRG. Behavioural testing was performed on the day preceding the carrageenan injection and four times (5 h after, on the first, fifth and eighth days) following the injection. Immunohistochemical analysis was performed 8 days following the surgery. Our results showed that NPY, applied directly to DRG, induced cold allodynia in carrageenan inflammatory pain model. NPY in carrageenan-injected rats did not additionally exacerbate activation of satellite cells in DRG and astrocytes in dorsal horn caused by intraplantar carrageenan injection. However, application of NPY Y1 and Y2 antagonists directly into DRG reversed carrageenan proalgesic effects and reduced gliosis in DRG and dorsal horn. These findings indicate an important link between pain-related behaviour and neuroimmune actions of NPY Y1 and Y2 receptors.

Attenuation of pain-related behavior evoked by injury through blockade of neuropeptide Y Y2 receptor

Neuropeptide Y (NPY) has an important but still insufficiently defined role in pain modulation. We therefore examined the ability of NPY to modulate experimentally induced neuropathic pain by injecting it directly into dorsal root ganglion (DRG) immediately following spinal nerve ligation (SNL) injury. We have found that this application exacerbates pain-related behavior induced by SNL in a modality-specific fashion. When saline was injected after SNL, the expected increase in hyperalgesia responses to needle stimulation was present on the 8th postoperative day. When we injected NPY, hyperalgesic responses were increased in a manner similar to the SNL/saline group. To characterize NPY action, specific Y1 and Y2 antagonists were also delivered directly to DRG, which revealed that behavioral actions of NPY were abolished by Y2 receptor antagonist. We tested whether NPY effects were the result of its role in immunity by immunohistochemical staining for glial fibrillary acidic protein, in order to identify activation of DRG satellite cells and dorsal horn astrocytes. Exacerbation of pain-related behavior following NPY injection was accompanied by astrocyte activation in ipsilateral dorsal horn and with satellite cells activation in the DRG proximal to injury. This activation was reduced following Y2 receptor antagonist application. These findings indicate an important link between pain-related behavior and neuroimmune activation by NPY through its Y2 receptor. Prevention of early changes in dorsal root neurons by neuropeptide Y Y2 receptor can reduce behavioral consequences of spinal nerve ligation.

Blockade of neuropeptide Y(2) receptors and suppression of NPY's anti-epileptic actions in the rat hippocampal slice by BIIE0246.

Neuropeptide Y (NPY) has been shown to suppress synaptic excitation in rat hippocampus by a presynaptic action. The Y(2) (Y(2)R) and the Y(5) (Y(5)R) receptors have both been implicated in this action. We used the non-peptide, Y(2)R-selective antagonist, BIIE0246, to test the hypothesis that the Y(2)R mediates both the presynaptic inhibitory and anti-epileptic actions of NPY in rat hippocampus in vitro. NPY and the Y(2)R-selective agonist, [ahx(5-24)]NPY, both inhibited the population excitatory postsynaptic potential (pEPSP) evoked in area CA1 by stratum radiatum stimulation in a concentration-dependent manner. BIIE0246 suppressed the inhibitory effects of both agonists, suppressing the maximal inhibition without causing a change in the agonist EC(50), in a manner inconsistent with competitive antagonism. BIIE0246 washed out from hippocampal slices extremely slowly. Application of agonist at high concentrations (1 - 3 microM) for prolonged periods did not alter the rate of washout, but did partially overcome the antagonism, inconsistent with an insurmountable antagonism by BIIE0246. In the stimulus train-induced bursting (STIB) model of ictal activity in hippocampal slices, both NPY and [ahx(5-24)]NPY inhibited primary afterdischarge (1 degrees AD) activity. BIIE0246 (100 nM) completely suppressed the actions of NPY and [ahx(5-24)]NPY in this model. In contrast, the potent Y(5)R-selective agonist, Ala(31)Aib(32)NPY, affected neither 1 degrees AD activity in the presence of BIIE0246, nor, by itself, even the pEPSP in CA1. BIIE0246 potently suppresses NPY actions in rat hippocampus, suggesting a dominant role for Y(2)R there. The apparently insurmountable antagonism observed may result from the lipophilic nature of the antagonist.

Potent neuropeptide Y Y1 receptor antagonist, 1229U91: blockade of neuropeptide Y-induced and physiological food intake

Potent neuropeptide Y Y1 receptor antagonist, 1229U91: blockade of neuropeptide Y-induced and physiological food intake