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Cardiovascular effects of neuronal activation of the extended amygdala in rats
A J Gelsema1, N E Copeland, G Drolet
1Hypertension Unit, University of Ottawa Heart Institute, Canada.
Insights
Researchers identified a depressor area in the bed nucleus of the stria terminalis (BST) and substantia innominata (SI) that influences cardiovascular control. Glutamate injections into these brain regions caused significant decreases in arterial pressure and hindquarter blood flow.
Area of Science:
- Neuroscience
- Cardiovascular Physiology
- Autonomic Nervous System
Background:
- The bed nucleus of the stria terminalis (BST) and substantia innominata (SI) are recognized as extensions of amygdaloid nuclei.
- While amygdaloid nuclei are implicated in various functions, the role of BST and SI neurons in cardiovascular regulation remains largely unexplored.
Purpose of the Study:
- To investigate the involvement of BST and SI neurons in the central control of arterial pressure (AP) and heart rate (HR).
- To identify specific sites within the BST and SI that modulate cardiovascular parameters upon stimulation.
Main Methods:
- Systematic microinjections of glutamate into the BST and SI of urethane-anesthetized Wistar rats.
- Recording of arterial pressure and heart rate changes following injections.
- In conscious rats, bilateral injections into ventral BST divisions and measurement of AP, HR, and regional blood flows using pulsed Doppler probes.
Main Results:
- Glutamate injections into 84 out of 130 verified sites in the BST and SI elicited depressor responses (mean -13.3 mmHg) with variable heart rate changes.
- In conscious rats, injections into ventral BST regions caused significant decreases in AP (-11.9 mmHg) coupled with increased hindquarter vascular conductance (+44.2%).
- Renal and mesenteric vascular conductances remained unaffected, and the drop in AP typically preceded the increase in hindquarter blood flow.
Conclusions:
- The study suggests the presence of a depressor area within the BST and SI involved in cardiovascular regulation.
- These findings highlight a potential role for BST and SI in modulating systemic blood pressure and regional blood flow.
- Further research is needed to elucidate the precise contribution of these depressor effects to the overall central control of circulation.
Abstract:
The bed nucleus of the stria terminalis (BST) and the sublenticular substantia innominata (SI) are considered rostral extensions of the medical and central amygdaloid nuclei. In contrast to amygdaloid nuclei proper, the involvement of BST and SI neurons in cardiovascular control has not been studied. These areas were systematically explored in 35 urethane-anesthetized Wistar rats for sites from which changes in arterial pressure (AP) and heart rate (HR) could be obtained by injection of 20 nl of glutamate solutions (Glu, 0.5 M). Injections into 84 of the 130 histologically verified sites were followed after an 8.0 +/- 0.7 s latency by depressor responses ranging from -4 to -33 (mean -13.3 +/- 0.8) mmHg, accompanied by variable changes in HR. Pressor responses were elicited from only 3 sites; 43 sites were not responsive. An additional group of 10 rats was instrumented for bilateral Glu injections (0.1 M, 200 nl per side) into the ventral division of the lateral BST and ventral BST and for the recording of AP, HR and regional blood flows measured with pulsed Doppler probes in the conscious state. In these rats, decreases in AP (-11.9 +/- 1.7 mmHg) were accompanied by significant increases in hindquarter conductance (44.2 +/- 11.4%), while renal and mesenteric vascular conductances remained unchanged. The fall in AP usually preceded the rise in hindquarter flow. These results suggest the existence of a depressor area in regions of the BST and SI, but the contribution of the elicited depressor effects in the overall central control of the circulation remains to be established.