Nitric oxide synthase and chemical coding in cat sympathetic postganglionic neurons

Area of Science:

• Neuroscience
• Autonomic Nervous System Research
• Neurotransmitter Studies

Background:

• Nitric oxide synthase (NOS) presence and function in sympathetic postganglionic neurons are not fully understood.
• Cholinergic sympathetic neurons play roles in various physiological processes, including sweating and vasodilation.

Purpose of the Study:

• To investigate the localization and co-localization of nitric oxide synthase (NOS)-like immunoreactivity in feline sympathetic ganglia.
• To determine the role of NOS in sudomotor and vasodilator neurons innervating the skin.

Main Methods:

• Immunohistochemistry using antibodies against NOS, tyrosine hydroxylase (TH), calcitonin gene-related peptide (CGRP), and vasoactive intestinal peptide (VIP).
• Reduced nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase staining was used as a marker for NOS activity.
• Triple staining experiments were performed to identify co-localization of markers in specific neuronal subpopulations.

Main Results:

• NOS-like immunoreactivity and NADPH diaphorase reactivity were found in tyrosine hydroxylase-negative (cholinergic) neurons in cat stellate and lumbar ganglia.
• 99% of presumptive sudomotor neurons (CGRP-positive) and 70% of presumptive muscle vasodilator neurons (VIP-positive, CGRP-negative) contained NOS.
• NOS-positive fibers were observed around sweat glands, skin arteries, and arteriovenous anastomoses in the paw pad.

Conclusions:

• Nitric oxide (NO) likely acts as a co-transmitter in feline sudomotor and vasodilator neurons, alongside acetylcholine, substance P, VIP, and CGRP.
• Sudomotor neurons may contribute to skin vasodilatation and sweat production through NO release.
• These findings elucidate the neurochemical coding of sympathetic neurons involved in thermoregulation and vascular control.