Immunohistochemical detection and gene expression of tyrosine hydroxylase and vesicular monoamine transporter type 2 in intrinsic cardiac ganglia of socially isolated rats

Social isolation induced a significant increase in resting heart rate and reduction in heart rate variability. Dysfunction of the intrinsic cardiac nervous system is implicated in the genesis of cardiovascular diseases. Previous evidence suggests that cardiac ganglia contain noradrenergic neurons. Thus, immunohistochemical expression of catecholaminesynthesizing enzyme tyrosine hydroxylase (TH) and vesicular monoamine transporter 2 (VMAT2) were analyzed, as well as the effects of social isolation stress on mRNA and protein levels of this enzyme and transporter in the intrinsic cardiac nervous system of adult rats. Our results indicate that cardiac ganglion neurons express TH and VMAT2 immunoreactivity. Chronic isolated stress of rats caused a decrease in TH mRNA and VMAT2 mRNA in the neurons of intrinsic cardiac ganglia. No significant alterations in the protein levels of TH and VMAT2 were observed in these neurons. These data indicate that the neurons of intrinsic cardiac ganglia express TH as well as VMAT2 but that social isolation stress does not change their protein levels.