Source of nitrergic inervation of the heart

Background: Nitric oxide (NO) has received a lot of attention in the last decade, because of its ability to change cardiac sympatho-vagal balance. Nitrergic neurons and their role in the heart are widely studied, but the source of external nitrergic fibers is less explored. Contradicting evidence exists, because nitrergic neurons are found in many sites related to cardiovascular regulation and little is known about their role in central parasympathic heart control. Aim of the study: To evaluate if nitrergic fibers exists in parasympathetic cardiac vagal axons and their bodies. Objectives: 1) To evaluate if nitrergic fibers exists in the root, trunk and cardiac branches of the vagus nerve 2) To examine prevalence of nitrergic neurons inside nodose ganglion, nucleus am-biguus and dorsal nucleus of the vagus nerve. Material and methods: Vagus nerve, nodose ganglion and brain sections at vagus root entry point were obtained from adult rats. Sections of vagus were taken at the heart and neck levels. Using immunofluorescent technique, sections were double labelled for neuronal nitric oxide synthase (nNOS) and choline acetyltransferase and analyzed using confocal microscopy. Results: Nitrergic fibers were found inside vagus nerve at both levels. No nNOS positive fibers were found in the root of vagus nerve. A lot of nitrergic neurons were located in nodose ganglion. Some of the neurons inside nucleus ambiguous were nNOS positive, but majority of nitrergic neu-rons were scattered around it. Single nNOS positive neurons were observed in dorsal nucleus of the vagus nerve. Conclusion: Nitrergic fibers are present in the vagus nerve at the neck and heart levels, but no ni-trergic fibers were found inside the root of the vagus nerve. Biggest population of nitrergic neurons were found in nodose ganglion, followed by small amount of nNOS positive neurons in the nucleus ambiguus and observed single nitrergic neurons in the dorsal nucleus of the vagus nerve