Regulation of sympathetic nervous system function after cardiovascular deconditioning

Area of Science:

• Cardiovascular physiology
• Neuroscience
• Space medicine

Background:

• Prolonged bed rest and microgravity cause cardiovascular deconditioning.
• This deconditioning leads to orthostatic intolerance, characterized by reduced exercise capacity and autonomic dysfunction.
• Mechanisms include fluid balance changes, cardiac alterations, vascular dysfunction, and diminished autonomic reflexes.

Purpose of the Study:

• To investigate the role of altered arterial baroreflex control of the sympathetic nervous system in cardiovascular deconditioning.
• To evaluate the central nervous system processing of baroreceptor inputs using a hindlimb-unloaded (HU) rat model.

Main Methods:

• Utilized the hindlimb-unloaded (HU) rat model to simulate deconditioning.
• Assessed baroreflex-mediated sympathetic nerve activity (renal and lumbar) in response to hypotension.
• Examined central nervous system processing of baroreceptor afferent activity, focusing on the rostral ventrolateral medulla (RVLM).

Main Results:

• HU rats exhibited blunted baroreflex-mediated activation of sympathetic nerve activity during hypotension.
• HU rats showed impaired ability to maintain arterial pressure during hemorrhage.
• Enhanced tonic GABAA-mediated inhibition of the RVLM was observed in HU rats, suggesting altered central processing.

Conclusions:

• Blunted sympathetic nervous system activation due to altered central nervous system processing contributes to orthostatic intolerance after cardiovascular deconditioning.
• Enhanced inhibition of the RVLM is a key mechanism underlying impaired sympathoexcitation.
• These findings highlight the importance of autonomic reflex function in maintaining cardiovascular stability during deconditioning.