Effects of chemical stimulation of the rostral ventrolateral medulla on cerebral and renal microcirculation in spontaneously hypertensive rats

Downregulated Kv4.3 expression in the RVLM as a potential mechanism for sympathoexcitation in rats with chronic heart failure

Elevated central angiotensin II (ANG II) plays a critical role in the sympathoexcitation of chronic heart failure (CHF) by stimulating upregulated ANG II type 1 receptors (AT(1)R) in the rostral ventrolateral medulla (RVLM). However, the link between enhanced ANG II signaling and alterations in the electrophysiological characteristics of neurons in the RVLM remains unclear. In the present experiments, we screened for potentially altered genes in the medulla of rats with CHF that are directly related to neuronal membrane conductance using the Rat Genome 230 2.0 Array GeneChip. We found that CHF rats exhibited a 2.1-fold reduction in Kv4.3 gene expression, one of the main voltage-gated K(+) channels, in the medulla. Real-time RT-PCR and Western blot analysis confirmed the downregulation of Kv4.3 in the RVLM of CHF rats. In intact animals, we found that microinjection of the voltage-gated potassium channel blocker, 4-aminopyridine, into the RVLM evoked a sympathoexcitation and hypertension in both normal and CHF rats. CHF rats exhibited smaller responses to 4-aminopyridine than did normal rats. Finally, we used a neuronal cell line (CATH.a neurons) to explore the effect of ANG II on Kv4.3 expression and function. We found that ANG II treatment significantly downregulated mRNA and protein expression of Kv4.3 and decreased the A-type K(+) current. Employing this cell line, we also found that the ANG II-induced inhibition of Kv4.3 mRNA expression was attenuated by the superoxide scavenger Tempol and the p38 MAPK inhibitor SB-203580. The effects of ANG II were abolished by the AT(1)R antagonist losartan. We conclude that the sympathoexcitation observed in the CHF state may be due, in part, to an ANG II-induced downregulation of Kv4.3 expression and subsequent decrease in K(+) current, thereby increasing the excitability of neurons in the RVLM. The ANG II-induced inhibition of Kv4.3 mRNA expression was mediated by ANG II-AT(1)R-ROS-p38 MAPK signaling.

Long-lasting improvement of arterial hypertension after surgical treatment of a foramen magnum meningioma: case report

BACKGROUND

Neurogenic arterial hypertension has been proposed to be caused by neurovascular compression in many cases. However, there is little reference to tumors causing hypertension by local compression of the vagal nerve or the ventrolateral medulla oblongata. The following case illustrates the effects of surgery for a meningioma of the foramen magnum on arterial hypertension.

CASE DESCRIPTION

A 54-year-old woman suffered from arterial hypertension for at least 7 months, for which she required a combined medical treatment regime. She suffered for 6 months from dizziness and tinnitus, more in the left ear than in the right. Neurologic examination revealed a horizontal fixation nystagmus and a mild left-sided hearing loss. Magnetic resonance imaging and computed tomographic angiography showed a contrast-enhancing tumor on the left side of the foramen magnum compressing the medulla oblongata close to the vertebral artery and vascularized by branches of the left PICA. Complete surgical extirpation was performed using a medial craniocervical approach. The tinnitus and dizziness were gone and hearing improved. Postoperatively, the arterial hypertension showed a long-lasting improvement (observation period 8 months) with only minimal medical treatment.

CONCLUSION

Based on our case, we conclude that tumors in close proximity to the ventrolateral medulla oblongata may induce neurogenic hypertension, similar to neurovascular compression.