Prostaglandin E2-mediated upregulation of neuroexcitation and persistent tetrodotoxin-resistant Na(+) currents in Ah-type trigeminal ganglion neurons isolated from adult female rats

Adrenomedullin-mediated depressor response with visceral afferent-specific membrane depolarization in isolated nodose ganglion neurons from adult female rat

Adrenomedullin (ADM) is an endogenous and vasoactive neuropeptide that possesses potent central/peripheral regulations on blood pressure (BP) and sex-related vasodilation under physiological conditions. However, the role of ADM on baroreflex afferent function is largely unknown. Here, BP was monitored in adult female rats while ADM was microinjected into the nodose ganglion (NG); Fluorescent intensity against ADM was analyzed in the tissue level and membrane responses elicited by ADM were tested in identified NG neurons isolated from adult female rats with gap-free protocol under current-clamp mode with or without ADM antagonist. The results showed that BP was reduced by ADM (30-300 nM) concentration-dependently; myelinated (HCN1-positive) neurons showed significantly higher fluorescent intensity against ADM antibody vs. unmyelinated (HCN1-negative) neurons. Interestingly, patch-clamp data indicated that membrane potential was not changed in 50 % (6/12) of identified A-types, only 4/12 was hyperpolarized by 30 nM ADM, while 100 nM ADM induced brief hyperpolarization followed by depolarization in 2/12 of recordings; Robustly, ADM depolarized 100 % tested myelinated Ah-type neurons with dramatic and concentration-dependent repetitive discharges; While, a majority (8/9) of unmyelinated C-types were depolarized and few with repetitive dischargers. By application of ADM (22-52), the depolarization elicited by ADM 100 nM was partially or completely abolished in Ah-types or C-types, respectively. These datasets demonstrated for the first time that baroreflex afferents especially female-distributed subpopulation of Ah-types would be a key player in ADM-mediated depressor response unveiling the dominate role of peripheral ADM in neurocontrol of hypotension via baroreflex afferent function and gender-dependent vasodilation promoted by female sex steroid.

Baroreflex afferent function is a part of insights of Leptin-mediated blood pressure reduction and Leptin-resistance hypertension

The aim of this study is to verify the impact of Leptin in blood pressure (BP) regulation and Leptin-resistance in metabolic/neurogenic hypertension through baroreflex afferents and dysregulation. Artery BP/heart rate (HR) were measured while nodose (NG) microinjection of Leptin, membrane depolarization/inward current were obtained by whole-cell patch from NG neurons isolated from adult female rats. Baroreflex sensitivity (BRS) tested with PE/SNP, distribution/expression of Leptin/receptors in the NG/nucleus tractus solitary (NTS) examined using immumostaining and qRT-PCR, and serum concentrations of Leptin/NE measured by ELISA were observed in control and high fructose-drinking induced hypertension (HTN-HFD) rats. The results showed that BP was significantly/dose-dependently reduced by Leptin NG microinjection likely through direct excitation of female-specific subpopulation of Ah-type neurons showing a potent membrane depolarization/inward currents. Sex-specific distribution/expression of OB-Ra/OB-Rb in the NG were detected with estrogen-dependent manner, similar observations were also confirmed in the NTS. As expected, BRS was dramatically decreased in the presence of PE/SNP in both male and female rats except for the female with PE at given concentrations. Additionally, serum concentration of Leptin was elevated in HFD-HTN model rats of either sex with more obvious in females. Under hypertensive condition, the mean fluorescent density of OB-R and mRNA expression for OB-Ra/OB-Rb in the NG/NTS were significantly down-regulated. These results have demonstrated that Leptin play a role in dominant parasympathetic drive via baroreflex afferent activation to buffer Leptin-mediated sympathetic activation systemically and Leptin-resistance is an innegligible mechanism for metabolic/neurogenic hypertension through baroreflex afferent dysregulation.

Prolonged PGE2 treatment increased TTX-sensitive but not TTX-resistant sodium current in trigeminal ganglionic neurons

Prostaglandin E₂ (PGE₂) is an important inflammatory mediator for the initiation and maintenance of inflammatory and neuropathic pain. The acute effect of PGE₂ on sodium currents has been widely characterized in sensory neurons; however, the prolonged effect of PGE₂ remains to be determined. Here, we performed patch clamp recordings to evaluate the acute and prolonged effects of PGE₂ on sodium currents in trigeminal ganglionic (TG) neurons from male Sprague-Dawley rats. We found that 24-h treatment with PGE₂ (10 μM) increased the peak sodium current density by approximately 31% in a voltage-dependent manner and shifted the activation curve in a hyperpolarized direction but did not affect steady-state inactivation. Furthermore, treatment with PGE₂ for 24 h increased the current density of tetrodotoxin-sensitive (TTX-S) but not TTX-resistant (TTX-R) channels significantly. Interestingly, TTX-S current was increased mostly in medium-sized, but not in small-sized, neurons after 24 h of treatment with PGE₂. Moreover, the mRNA level of TTX-S Nav1.1 but not TTX-R Nav1.8 or Nav1.9 was significantly increased after 24 h of treatment with PGE_2. In contrast, 5-min treatment with PGE₂ (10 μM) increased the peak sodium current density by approximately 29% and increased TTX-R sodium currents, but not TTX-S currents, in both small- and medium-sized TG neurons. Our results presented a differential regulation of subtypes of sodium channels by acute and prolonged treatments of PGE₂, which may help to better understand the mechanism of PGE₂-mediated orofacial pain development.