Related Experiment Videos
Baroreflex changes produced by serotonergic or catecholaminergic lesions in the rat nucleus tractus solitarius
1Department of Pharmacology, Toxicology and Therapeutics, College of Health Sciences and Hospital, University of Kansas Medical Center, Kansas City.
Abstract:
To distinguish between catecholaminergic and serotonergic mechanisms for baroreflex regulation in the medulla, we compared rats with chemical lesions produced by injecting 6-hydroxydopamine (6-OHDA) or 5,7-dihydroxytryptamine (5,7-DHT) into the nucleus tractus solitarius (NTS) bilaterally at the caudal tip of the area postrema. After 2 weeks, basal blood pressure and heart rate were unaltered, but blood pressure lability, instead of being increased, was slightly reduced. Baroreflex tests in conscious rats showed that although phenylephrine-induced reflex bradycardia was unaffected, nitroprusside-induced reflex tachycardia was enhanced by 5,7-DHT. In anesthetized rats, drug-induced reflex chronotropic responses no longer differed between groups, but attendant decreases or increases in renal nerve activity were consistently reduced by 6-OHDA. On the other hand, upon afferent aortic nerve stimulation, particularly with low current frequencies, bradycardic and sympathoinhibitory responses were enhanced by 5,7-DHT, but the sympathoinhibitory responses were reduced by 6-OHDA. Despite the absence of demonstrable necrosis or cell loss at NTS injection sites, 6-OHDA reduced norepinephrine mainly and serotonin partly, whereas 5-7-DHT reduced serotonin content alone, thereby indicating that chemical lesions had indeed been produced. Because these cardiovascular changes probably reflect differences in catecholaminergic vs. serotonergic baroreflex regulation, our results are generally compatible with the interpretation that baroreflex modulation in the NTS involves catecholaminergic facilitation and serotonergic inhibition.
Insights
This study investigated catecholaminergic and serotonergic roles in baroreflex regulation. Results suggest catecholamines facilitate and serotonin inhibits baroreflexes in the nucleus tractus solitarius.
Area of Science:
- Neuroscience
- Cardiovascular Physiology
Background:
- Baroreflex regulation is crucial for maintaining cardiovascular homeostasis.
- The roles of catecholaminergic and serotonergic systems in medullary baroreflex control remain incompletely understood.
Purpose of the Study:
- To differentiate between catecholaminergic and serotonergic mechanisms involved in baroreflex regulation within the medulla.
- To elucidate the specific contributions of these neurotransmitter systems to cardiovascular control.
Main Methods:
- Bilateral chemical lesions of the nucleus tractus solitarius (NTS) were induced using 6-hydroxydopamine (6-OHDA) or 5,7-dihydroxytryptamine (5,7-DHT) in rats.
- Cardiovascular parameters, including blood pressure, heart rate, and nerve activity, were assessed under various conditions (basal, drug-induced, and baroreceptor stimulation).
Main Results:
- 5,7-DHT enhanced nitroprusside-induced reflex tachycardia and bradycardic responses to aortic nerve stimulation.
- 6-OHDA reduced renal nerve activity changes and sympathoinhibitory responses to aortic nerve stimulation.
- Lesions selectively reduced norepinephrine (6-OHDA) or serotonin (5,7-DHT) content, confirming targeted neurochemical alterations.
Conclusions:
- The findings support a model where catecholaminergic pathways facilitate baroreflex control.
- Serotonergic pathways appear to exert an inhibitory influence on baroreflex modulation in the NTS.
- These distinct roles highlight the complex interplay of neurotransmitters in central cardiovascular regulation.