Baro-excited neurons in the caudal ventrolateral medulla (CVLM) recorded using the whole-cell patch-clamp technique

Abstract

Caudal ventrolateral medulla (CVLM) neurons have important roles in the regulation of sympathetic nerve activity and blood pressure through their tonic inhibition of rostral ventrolateral medulla neurons. As few reports have demonstrated CVLM neuronal activity using the whole-cell patch-clamp technique, we attempted to find neurons in the CVLM that are depolarized by the stimulation of baroreceptors. To record the membrane potentials of the neurons in the CVLM, we developed a modified brainstem-spinal cord preparation that enabled us to change the pressure exerted on the aortic arch and carotid sinuses. We were able to identify neurons in the CVLM in which they were depolarized and the action potential (AP) frequency was increased upon baroreceptor stimulation. We referred to these neurons as baro-excited CVLM neurons. When these preparations were superfused with an angiotensin-II (Ang-II) solution, the frequency of the APs increased in 10 of the 14 baro-excited CVLM neurons. Superfusion with a low-Ca 2+ , high-Mg 2+ solution abolished the APs in all seven baro-excited CVLM neurons, suggesting that the baro-excited CVLM neurons did not fire spontaneously. When the preparation was superfused with a low-Ca 2+ solution, 6 of the 7 baro-excited CVLM neurons did not respond to Ang-II superfusion. We for the first time found the baro-excited CVLM neurons, which depolarized pressure dependently but may not fire spontaneously. As Ang-II did not change the activity of the CVLM neurons during superfusion with a low-Ca 2+ , high-Mg 2+ solution, the presynaptic neurons may be mandatory for the Ang-II-induced activation of postsynaptic baro-excited CVLM neurons.

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

“…[12][13][14][15][16][17][18][19][20] The experimental protocols were approved by the Institutional Review Board of National Defense Medical College and were in accordance with the National Guidelines for the Conduct of Animal Experiments. Briefly, the animals received deep ether anesthesia, and the brainstem-spinal cord was isolated at the Th 2 level (Figure 1a).…”

“…Selected neurons were traced with a camera lucida attachment at a magnification of  400. 12,19,20 Neutral-Red staining was performed to verify the position of the neurons within the RVLM, and the precise location of the marked neurons was identified.…”

“…Thus, in the present study, we investigated the effect of aldosterone, eplerenone (an MR blocker), FAD286 (an aldosterone synthase inhibitor) and benzamil (an epithelial sodium channel (ENaC) blocker) on bulbospinal RVLM neurons using brainstem-spinal cord preparations that preserved the sympathetic nervous system. [11][12][13][14][15][16][17][18][19][20] As a previous report showed that intracerebroventricular infusion of eplerenone lowered blood pressure, 2, 21 we examined the direct effect of eplerenone on RVLM neurons, using a low-Ca 2 þ , high-Mg 2 þ solution to block synaptic input into RVLM neurons. Aldosterone performs its function in the collecting ducts of the kidneys, and ENaCs are known to participate in the process through genomic action.…”

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

“…[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.…”

“…[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.…”