Computer-assisted morphometric study of the innervation of the guinea pig heart

A computer-assisted method is introduced for the morphometric analysis of immunoreactive markers of the innervation of the heart, such as synaptophysin, neuropeptide Y (NPY), neurotensin (NT), substance P (SP), and calcitonin gene-related peptide (CGRP). Video images of stained sections were digitalized and the area density (AD) of the immunoreactive structures was measured by discrimination for grey levels within the myocardium of the right atrium, the perivascular region of epicardial arteries, and the trunk of the bundle of His. Synaptophysin immunoreactivity (IR), which served as a marker for presynaptic vesicles, indicated a dense innervation of the conductive system (AD 1.5241). Marked differences in the pattern of distribution were found between the neuropeptides. The AD of NPY-IR (0.5073) and SP-IR (0.1352) was highest in the perivascular tissue, while NT-IR (0.1628) and CGRP-IR (0.5161) exhibited maximal values in the bundle of His. The computer-assisted morphometric measurement of the AD of immunoreactive markers is suggested to be a suitable method for quantitative studies of the innervation of the heart under normal and experimental conditions.