Distribution of Catecholaminergic Neurotransmitters and Related Receptors in Human Bronchus-Associated Lymphoid Tissue

Abstract

Background: The functions of the bronchus-associated lymphoid tissue (BALT) are under the control of the autonomic nervous system (sympathetic and parasympathetic nerve fibers). Objectives: The relationships between the adrenergic nerve fibers and β-adrenergic receptors were studied in the human BALT with the aim to demonstrate a probable neuromodulation. Methods: Morphological observations (staining with hematoxylin-eosin and scanning electron microscopy images) were carried out on samples of human BALT harvested during autopsies. Moreover, histochemical staining for norepinephrine (adrenaline = adrenergic nerve fibers) as well as for other catecholamines was performed. Finally, β-adrenergic receptors were stained by means of a β-blocking, radiolabeled drug (pindolol ¹²⁵I). All our data were submitted to morphometric analysis (quantitative analysis of images and statistical analysis of data). Results: Our results provide direct evidence of the presence and distribution of catecholaminergic nerve fibers and related β-adrenergic receptors in BALT. β-Adrenergic receptors are present above all in the most richly innervated part of the BALT, and are, therefore, in close relationship with their related adrenergic nerve fibers. Conclusions: Studies on the distribution of adrenergicneurotransmitters and related β-adrenergic receptors in the human BALT are the first step for the demonstration of a probable neuromodulation of BALT.