Decerebration does not alter hypoxic sympathoexcitatory responses in rats

Area of Science:

• Neuroscience
• Cardiovascular Physiology
• Autonomic Nervous System

Background:

• Acute hypoxia is known to elicit sympathetic nervous system activation and associated cardiovascular adjustments.
• The precise neural pathways mediating these sympathoexcitatory responses to hypoxia have been a subject of investigation.

Purpose of the Study:

• To determine the role of suprapontine neural structures in mediating the sympathetic and cardiovascular responses to acute hypoxia.
• To investigate the necessity of chemoreceptor input for these hypoxic responses.
• To confirm the critical involvement of the rostral ventrolateral medulla (RVL) in mediating sympathoexcitatory responses to acute hypoxia.

Main Methods:

• Experiments were conducted in anesthetized, paralyzed, and ventilated rats.
• Hypoxia was induced via intratracheal administration of 100% nitrogen (N2) for 20 seconds.
• Sympathetic nerve activity and cardiovascular parameters were monitored.
• Acute midcollicular decerebration was performed to eliminate suprapontine neural influences.
• Studies were performed in both chemo-innervated and chemo-denervated preparations.

Main Results:

• Acute hypoxia significantly increased sympathetic nerve activity and elicited cardiovascular responses in rats.
• Midcollicular decerebration did not alter these sympathetic and cardiovascular responses to hypoxia, irrespective of chemoreceptor innervation.
• These findings indicate that neural structures above the pons are not essential for the rapid sympathoexcitatory and cardiovascular effects of acute hypoxia.

Conclusions:

• The results strongly support the hypothesis that sympathoexcitatory responses to acute hypoxia are entirely mediated by the reticulospinal sympathoexcitatory vasomotor neurons located in the rostral ventrolateral medulla (RVL).
• Higher neural centers are not required for the immediate autonomic adjustments to severe hypoxic challenges.