Rostral ventrolateral medulla and sympathorespiratory integration in rats

Area of Science:

• Neuroscience
• Cardiovascular Physiology
• Respiratory Physiology

Background:

• Respiratory modulation of sympathetic nerve activity is essential for cardiovascular homeostasis.
• The precise neural mechanisms underlying this respiratory-sympathetic coupling remain incompletely understood.

Purpose of the Study:

• To investigate the role of the rostral ventrolateral medulla (RVLM) in respiratory modulation of lumbar sympathetic nerve discharge (LSND).
• To elucidate the involvement of specific neurotransmitter systems (GABAergic, glycinergic, glutamatergic) within the RVLM in this modulation.

Main Methods:

• Utilized phrenic nerve discharge (PND)-triggered histograms in halothane-anesthetized, paralyzed, vagotomized rats.
• Administered microinjections of receptor antagonists (bicuculline, strychnine, phaclofen, kynurenic acid) into the RVLM and medullary raphe.
• Monitored mean arterial pressure (MAP), resting LSND, PND amplitude, and respiratory rate.

Main Results:

• Bicuculline (GABA(A) antagonist) in RVLM increased MAP, LSND, and magnified respiratory modulation of LSND.
• Kynurenic acid (excitatory amino acid antagonist) in RVLM reduced PND amplitude, MAP, and greatly reduced respiratory modulation of LSND.
• Strychnine (glycine antagonist) and phaclofen (GABA(B) antagonist) had no significant effects.

Conclusions:

• The RVLM is a critical site for integrating central respiratory rhythm with vasomotor outflow.
• GABAergic and excitatory amino acid neurotransmission within the RVLM are key players in the respiratory modulation of sympathetic nerve activity.
• Respiratory modulation of sympathetic nerve discharge does not appear to involve gating of baroreceptor information pathways to RVLM.