Jure Aljinović

Characterization of spinal afferent neurons projecting to different chambers of the rat heart

The pattern of distribution of spinal afferent neurons (among dorsal root ganglia-DRGs) that project to anatomically and functionally different chambers of the rat heart, as well as their morphological and neurochemical characteristics were investigated. Retrograde tracing using a patch loaded with Fast blue (FB) was applied to all four chambers of the rat heart and labeled cardiac spinal afferents were characterized by using three neurochemical markers. The majority of cardiac projecting neurons were found from T1 to T4 DRGs, whereas the peak was at T2 DRG. There was no difference in the total number of FB-labeled neurons located in ipsilateral and contralateral DRGs regardless of the chambers marked with the patch. However, significantly more FB-labeled neurons projected to the ventricles compared to the atria (859 vs. 715). The proportion of isolectin B(4) binding in FB-labeled neurons was equal among all neurons projecting to different heart chambers (2.4%). Neurofilament 200 positivity was found in greater proportions in DRG neurons projecting to the left side of the heart, whereas calretinin-immunoreactivity was mostly represented in neurons projecting to the left atrium. Spinal afferent neurons projecting to different chambers of the rat heart exhibit a variety of neurochemical phenotypes depending on binding capacity for isolectin B(4) and immunoreactivity for neurofilament 200 and calretinin, and thus represent important baseline data for future studies.

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.

The influence of exercise on morphological and neurochemical properties of neurons in rat nodose ganglia

Physical exercise can induce immunohistochemical changes and cell proliferation in the hippocampus. One of the main effects of prolonged exercise is resting bradycardia, most probably caused by enhanced vagal activity. To investigate whether physical exercise can cause neurochemical and morphological changes in vagal afferent neurons, we performed immunohistochemical studies of nodose neurons using isolectin B4 (IB4), 200-kDa neurofilament protein (N52) and calretinin in adult female rats. To distinguish subpopulations of neurons projecting to the left ventricle, we applied a Fast Blue patch to the epicardial surface of the left ventricle. Treadmill running for 8 weeks significantly increased the size of N52-positive cardiac projecting neurons. Furthermore, the proportion of IB4-positive neurons among all nodose ganglia neurons was significantly higher in trained animals. These data indicate that exercise leads to plastic changes in nodose ganglia neurons that may initiate changes of vagal activity caused by prolonged exercise.

Age-related changes of neurochemically different subpopulations of cardiac spinal afferent neurons in rats.

This study investigated the effect of aging on cardiac spinal afferent neurons in the rat. A patch loaded with retrograde tracer Fast Blue (FB) was applied to all chambers of the rat heart. Morphological and neurochemical characteristics of labeled cardiac spinal afferent neurons were assessed in young (2 months) and old (2 years) rats using markers for likely unmyelinated (isolectin B4; IB4) and myelinated (neurofilament 200; N52) neurons. The number of cardiac spinal afferent neurons decreased in senescence to 15% of that found in young rats (1604 vs. 248). The size of neuronal soma as well as proportion of IB4+ neurons increased significantly, whereas the proportion of N52+ neurons decreased significantly in senescence. Unlike somatic spinal afferents, neurochemically different populations of cardiac spinal afferent neurons experience morphological and neurochemical changes related to aging. A major decrease in total number of cardiac spinal afferent neurons occurs in senescence. The proportion of N52+ neurons decreased in senescence, but it seems that nociceptive innervation is preserved due to increased proportion and size of IB4+ unmyelinated neurons.