Aldosterone is synthesized in and activates bulbospinal neurons through mineralocorticoid receptors and ENaCs in the RVLM

Abstract

The effects of aldosterone and mineralocorticoid receptor (MR) blockers on presympathetic neurons in the rostral ventrolateral medulla (RVLM) are well studied. To directly investigate whether aldosterone, eplerenone (an MR blocker), FAD286 (an aldosterone synthase inhibitor) and benzamil (an epithelial sodium channel (ENaC) blocker) affect RVLM neurons, we examined changes in the membrane potentials (MPs) of bulbospinal RVLM neurons using the whole-cell patch-clamp technique during superfusion with these drugs to brainstem-spinal cord preparations. Aldosterone superfusion (0.1 lmol/l) depolarized the RVLM neurons. In contrast, eplerenone superfusion (1 lmol/l) hyperpolarized them. To evaluate the existence of aldosterone, FAD286 superfusion (10 lmol/l) was performed, and the RVLM neurons became hyperpolarized during FAD superfusion. These data suggest that MRs exist and that aldosterone is synthesized in the brainstem. Benzamil superfusion (1 lmol/l) hyperpolarized the RVLM neurons. To clarify whether aldosterone, eplerenone, FAD286 and benzamil acted directly on the RVLM neurons, a lowCa 2 þ , high-Mg 2 þ solution was used to block the synaptic input to the RVLM neurons, and the above-mentioned drugs were added during the low-Ca 2 þ superfusion. During the aldosterone superfusion, the RVLM neurons became depolarized, and they became hyperpolarized during eplerenone, FAD286 or benzamil superfusion. Importantly, when aldosterone was superfused after the benzamil solution, the MPs of the RVLM neurons did not depolarize. These results suggest that MRs are present in the RVLM neurons and that aldosterone is synthesized in the RVLM. The RVLM neurons themselves possess ENaCs, and ENaCs are the underlying mechanism by which aldosterone activates RVLM neurons. Hypertension Research (2013) 36, 504-512; doi:10.1038/hr.2012.224; published online 31 January 2013Keywords: aldosterone; benzamil; FAD286; RVLM neurons; whole-cell patch clamp INTRODUCTIONThe actions of aldosterone include vasoconstriction, vascular fibrosis, endothelial dysfunction, and sodium reabsorption and retention. These actions contribute to hypertension. However, recently, many studies have demonstrated the relationship between aldosterone and sympathetic nerve activity. In fact, aldosterone has been shown to cross the blood-brain barrier relatively easily, 1 as clarified using the model developed by Gomez-Sanchez et al. 2 showed that the intracerebroventricular infusion of antagonists of the mineralocorticoid receptor (MR), at a dose that had no effect systemically, lowered blood pressure. Intracerebroventricular infusion of aldosterone increased blood pressure, 3 and MRs were found in the brain. 4 Furthermore, aldosterone is involved in remodeling after myocardial infarction, and central blockade of aldosterone has been shown to attenuate cardiac remodeling. 5,6 Recent studies have demonstrated the existence of an aldosterone system in the brain, 4 and an increase in [Na þ ] in cerebrospinal fluid

The roles of oxidative stress, endoplasmic reticulum stress, and autophagy in aldosterone/mineralocorticoid receptor-induced podocyte injury

“…29 Aldosterone has been shown to exert its effects through genomic or non-genomic pathway. 30 Genomic effects of aldosterone are generally thought to be mediated by the MR and involve transcription, while aldosterone can also exert rapid nongenomic effects that are not blocked by inhibitors of transcription. 31 Numerous cell culture, animal, and human studies have shown aldosterone and the MR are implicated in activation of a variety of pathologic processes including inflammation, remodelling, and fibrosis in several target organs.…”

Expression and functions of β1- and β2-adrenergic receptors on the bulbospinal neurons in the rostral ventrolateral medulla

“…To avoid recording respiratory neuronal activities, we examined the phrenic nerve activity from the ventral root of C 4 and excluded neurons that displayed a strong phasic relationship with phrenic nerve discharges from the subsequent experiments. 17,18,22 …”

“…[15][16][17][18][19][20][21][22] The experimental protocols were approved by the Institutional Review Board of National Defense Medical College in accordance with the National Guidelines for the Conduct of Animal Experiments. Briefly, with the animals under deep ether anesthesia, the brainstem-spinal cord was isolated at the T helper type 2 (Th 2 ) level, and the brainstem was sectioned between the roots of cranial nerve VI and the lower border of the trapezoid body.…”

“…To determine whether each of the recorded RVLM neurons was indeed a bulbospinal neuron, the existence of antidromic action potentials (APs) in the RVLM neurons was examined by delivering electrical stimulation in the intermediolateral cell column at the Th 2 level with a tungsten electrode (30 mm tip diameter, Unique Medical, Tokyo, Japan). 17,18,22 The RVLM neurons that displayed antidromic APs with electrical stimulation in the intermediolateral cell column at the Th 2 level were considered to be bulbospinal RVLM neurons. The MPs were recorded using the current-clamp technique (20 pA increments from À100 to 20 pA, 500 ms duration).…”

“…[14][15][16][17][18][19][20][21][22] While recording the membrane potentials (MPs) of the bulbospinal RVLM neurons using the patch-clamp technique, the neurons were superfused with metoprolol (b 1 -AR antagonist), dobutamine (b 1 -AR agonist), butoxamine (b 2 -AR antagonist) or salbutamol (b 2 -AR agonist). Furthermore, to examine the direct effects of metoprolol or butoxamine on the RVLM neurons, the superfusion was conducted with each drug dissolved in a low-Ca 2 þ , high-Mg 2 þ or tetrodotoxin (TTX) solution.…”