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Splanchnic nerve response to A5 area stimulation in rats
D Huangfu1, L J Hwang, T A Riley
1Department of Pharmacology, University of Virginia Health Sciences Center, Charlottesville 22908.
The American Journal of Physiology
|August 1, 1992
Summary
Stimulating N-methyl-D-aspartate (NMDA) in the A5 area of the pons activates sympathetic nerve discharges, particularly in the splanchnic region. This activation is mediated by noradrenergic (NE) cells and influences cardiovascular regulation.
Area of Science:
- Neuroscience
- Cardiovascular Physiology
- Autonomic Nervous System Research
Background:
- The ventrolateral pons, specifically the A5 area, plays a role in regulating sympathetic nervous system activity.
- Noradrenergic (NE) neurons within the A5 area are implicated in cardiovascular control, but their precise function in sympathetic nerve discharge (SND) remains to be fully elucidated.
- Understanding the neural pathways controlling visceral vasomotor function is crucial for addressing cardiovascular diseases.
Purpose of the Study:
- To investigate the role of N-methyl-D-aspartate (NMDA) receptor activation in the A5 area on sympathetic nerve discharges.
- To determine the involvement of noradrenergic (NE) cells and specific receptors in mediating these sympathoexcitatory effects.
- To elucidate the contribution of A5 NE cells to visceral vasomotor sympathetic control.
Main Methods:
- Microinjection of NMDA into the A5 area of halothane-anesthetized, paralyzed rats.
- Measurement of splanchnic (sSND), renal, and lumbar sympathetic nerve discharges.
- Assessment of regional vascular resistance, baroreflex gain, blood pressure, and heart rate.
- Selective destruction of NE neurons using 6-hydroxydopamine (6-OH-DA) and pharmacological blockade of adrenergic receptors (prazosin, idazoxan, propranolol).
Main Results:
- NMDA microinjection into the A5 area significantly increased splanchnic (sSND) and renal sympathetic nerve discharges, accompanied by changes in vascular resistance and baroreflex gain.
- Destruction of A5 NE neurons with 6-OH-DA markedly reduced NMDA-induced sSND activation, indicating a crucial role for these neurons.
- The sympathoexcitatory effect of NMDA in the A5 area was mediated primarily through alpha 1-NE receptors.
Conclusions:
- Noradrenergic (NE) cells in the A5 area of the ventrolateral pons possess sympathoexcitatory properties.
- These A5 NE cells contribute significantly to the control of visceral vasomotor sympathetic nerve activity.
- The findings highlight a spinal projection pathway from A5 NE cells mediating sympathoexcitation, largely via alpha 1-NE receptors.