Immunohistochemical study of m1-m5 muscarinic receptors and nNOS in human inferior turbinate mucosa.

Conclusion: This study suggested that nitric oxide (NO) takes part in the parasympathetic nerve control functions mainly through m3 receptors and subsequently through m1 receptors.

Objectives: The regulation of glandular secretions and vasomotor tone in human nasal mucosa implicates muscarinic receptors. There are five recognized classes (m1-m5) of muscarinic receptor subtypes. NO is a free radical gas that has been found to be produced in neuronal cells by the action of enzyme neural nitric oxide synthase (nNOS). The aim of this study was to identify the colocalization of muscarinic receptor subtypes (m1-m5) and nNOS in the human inferior turbinate mucosa.

Materials and methods: Human inferior turbinate mucosa was stained by using the antibody of muscarine receptor subtypes and nNOS in an immunohistochemical double-staining method.

Results: The colocalization of m3 receptors and nNOS-immunoreactive nerve fibers was most extensively distributed on glands, vessels, and epithelium in all muscarinic receptor subtypes. These findings lead us to propose that NO also acts as a neurotransmitter in glands, vessels, and epithelium of the human nasal mucosa and can be assigned to parasympathetic nerve structures through m3 receptors mainly and m1 receptors subsequently.