Related Experiment Videos
Differentiation of two cardiovascular regions within caudal ventrolateral medulla
S L Cravo1, S F Morrison, D J Reis
1Department of Neurology and Neuroscience, Cornell University Medical College, New York, New York 10021.
Insights
Inactivating rostral caudal ventrolateral medulla (CVLM) neurons disrupts baroreceptor reflexes, while caudal CVLM inactivation increases sympathetic nerve activity independently. This reveals functional segregation within the CVLM for blood pressure control.
Area of Science:
- Neuroscience
- Cardiovascular Physiology
Background:
- The caudal ventrolateral medulla (CVLM) is crucial for regulating sympathetic nerve activity (SNA) and arterial pressure.
- Previous studies using lesions in the CVLM have produced conflicting results regarding its role in baroreceptor reflex control of SNA.
Purpose of the Study:
- To investigate the hypothesis that anatomically segregated neuronal populations within the CVLM subserve distinct functions in sympathetic control.
- To determine the specific roles of rostral and caudal CVLM subregions in mediating baroreceptor reflex control of SNA and arterial pressure.
Main Methods:
- Microinjections of kainic acid were used to selectively inactivate neuronal cell bodies in rostral and caudal CVLM subregions of urethane-anesthetized rats.
- Sympathetic nerve activity (SNA), arterial pressure, and baroreceptor reflex function were assessed following CVLM inactivation.
Main Results:
- Inactivation of rostral CVLM neurons significantly elevated SNA and arterial pressure, abolished baroreceptor-mediated inhibition of SNA, and eliminated the cardiac-related component of SNA.
- Inactivation of caudal CVLM neurons also increased SNA and arterial pressure but did not impair baroreceptor reflex function, instead enhancing SNA synchronization to the cardiac cycle.
Conclusions:
- The CVLM exhibits functional segregation, with rostral neurons essential for effective baroreceptor reflex control of SNA.
- Caudal CVLM neurons appear to independently regulate SNA and blood pressure, distinct from baroreceptor reflex pathways.
Abstract:
The caudal ventrolateral medulla (CVLM) plays a significant role in the regulation of sympathetic nerve activity (SNA) and arterial pressure; however, the use of lesions to examine its role in mediating baroreceptor reflex control of SNA has yielded discrepant results. We hypothesize that this may have arisen from anatomic segregation of neurons within the CVLM that subserve different functions in sympathetic control. Thus we used microinjections of the excitotoxic agent kainic acid (200 pmol in 20 nl) to determine the effects of inactivation of neuronal cell bodies in a rostral and a caudal subregion of the CVLM on SNA, arterial pressure, and baroreceptor reflex function in urethan-anesthetized rats. Interruption of neuronal activity in the rostral CVLM (sites from 0.6 mm caudal to 0.5 mm rostral to the rostral border of the lateral reticular nucleus) elevated SNA (post-kainic acid 214% of control) and arterial pressure (+34 mmHg) and eliminated the inhibition of splanchnic SNA evoked by either aortic nerve stimulation or the pressor response to intravenous norepinephrine. In addition, the cardiac-related component of spontaneous SNA was abolished as judged from post-R wave averages and from power spectral analysis. In contrast, although a similar disruption of neuronal activity in the caudal CVLM (sites 0.0-0.6 mm rostral to the caudal border of the lateral reticular nucleus) produced a comparable increase in spontaneous SNA (post-kainic acid 196% of control) and arterial pressure (+20 mmHg), it was without effect on the ability of the baroreceptor reflex to inhibit SNA, and it enhanced the synchronization of the spontaneous bursts in SNA to the cardiac cycle. Our results suggest an organization of the CVLM in which neurons in its rostral portion are required for an effective baroreceptor reflex, whereas those in the caudal CVLM serve to limit SNA and blood pressure independent of the baroreceptor reflex.