Immunohistochemical characteristics of neurons in nodose ganglia projecting to the different chambers of the rat heart

Despite the contribution of nodose ganglia neurons to the innervation of the heart being the subject of several studies, specific neuronal subpopulations innervating the four different chambers of the heart have not been distinguished.In our study, the application of Fast Blue-loaded patch to the epicardial surface of different chambers of the rat heart (the right or left atrium or the right or left ventricle) resulted in labeling of discrete populations of immunohistochemically diverse neurons. About one half (55%) of these neurons showed immunoreactivity for the 200-kDa neurofilament protein (marker of myelinated neurons), with a higher proportion of positive staining among neurons projecting to the left than to the right ventricle. Isolectin B4 immunoreactivity (characteristic for a subset of nonmyelinated non-peptidergic neurons) was more abundant among neurons projecting to the right side of the heart (right atria and right ventricles) compared to the left side (23% vs. 16%). Calretinin immunoreactivity (possible marker of mechanosensitive neurons) was significantly higher among neurons projecting to the ventricles than among those projecting to atria (36% vs. 11%). These findings reveal that chambers of the rat heart are innervated with immunohistochemically different subpopulations of neurons from the nodose ganglia.