Sympathetic nerve responses to hyperthermia in the anesthetized rat

Area of Science:

• Physiology
• Neuroscience
• Cardiovascular Research

Background:

• The sympathetic nervous system (SNS) plays a crucial role in regulating cardiovascular function and body temperature.
• Understanding how SNS responds to thermal stress, such as hyperthermia, is vital for comprehending physiological adaptation and potential pathologies.

Purpose of the Study:

• To investigate and characterize the sympathetic nerve responses to experimentally induced hyperthermia in an animal model.
• To determine the impact of elevated core body temperature on sympathetic nerve discharge (SND) in different nerve beds.
• To explore the influence of baroreceptor reflexes on the sympathetic response to acute heating.

Main Methods:

• Utilized chloralose-anesthetized rats for the study.
• Recorded sympathetic nerve discharges from renal, lumbar, and splanchnic nerves.
• Continuously monitored mean arterial pressure, heart rate, and sympathetic nerve discharge (SND) during progressive core body temperature (Tc) increases from 38.0 to 41.0°C.
• Employed autospectral analysis to examine the frequency distribution of SND.

Main Results:

• Observed significant increases in renal, lumbar, and splanchnic SND during hyperthermia.
• Autospectral analysis indicated alterations in the frequency distribution of renal and lumbar SND with rising Tc.
• Splanchnic SND increases in response to acute heating were comparable in both baroreceptor-innervated and -denervated rats.

Conclusions:

• Hyperthermia acts as a potent stimulus to the SNS, increasing activity across multiple sympathetic nerves innervating diverse arterial beds.
• Acute heating modifies neural circuits generating SND, evidenced by changes in the fundamental patterns of renal and lumbar SND.
• The augmentation of splanchnic SND during hyperthermia is not counteracted by arterial and cardiopulmonary baroreceptors.