Evidence for substance P-immunoreactive spinal afferents that mediate bronchoconstriction

Area of Science:

• Neuroscience
• Pulmonary Physiology
• Immunohistochemistry

Background:

• Substance P (SP) is a neuropeptide involved in sensory neurotransmission.
• Capsaicin is a neurotoxin that selectively activates C-fiber sensory neurons.

Purpose of the Study:

• To investigate the origin and function of capsaicin-sensitive, SP-immunoreactive (SP-IR) nerve fibers in the lower airways of guinea pigs.
• To elucidate the role of these fibers in airway reflexes and bronchoconstriction.

Main Methods:

• Surgical removal of the stellate ganglion (stellatectomy).
• Local capsaicin treatment of vagal nerves.
• Immunohistochemical analysis of SP-IR nerve fibers.
• Pharmacological assessment of capsaicin- and ether-induced bronchoconstriction.
• Chemical sympathectomy using 6-OH-dopamine.

Main Results:

• Stellatectomy significantly reduced SP-IR in the lung and pulmonary artery but did not alter fiber distribution.
• Combined stellatectomy and vagal nerve capsaicin treatment eliminated most SP-IR nerves and abolished capsaicin-induced bronchoconstriction.
• Ether inhalation-induced bronchoconstriction was reduced by combined stellatectomy and vagal capsaicin treatment.
• Stellate ganglion stimulation caused bronchoconstriction in sympathectomized animals, abolished by systemic capsaicin, indicating afferent fiber involvement.

Conclusions:

• The lower airways are innervated by SP-IR, capsaicin-sensitive C-fiber afferents of both vagal and spinal origins.
• These sensory fibers innervate bronchial smooth muscle and perivascular areas.
• The findings highlight the complex sensory innervation of the airways and its role in reflex responses.