Thalamic dopaminergic neurons projects to the paraventricular nucleus‐rostral ventrolateral medulla/C1 neural circuit

Paraventricular nuclei (PVN) projections to the rostral ventrolateral medulla (RVLM)/C1 catecholaminergic neuron group constitute the pre-autonomic sympathetic center involved in the neural control of systemic cardiovascular function. However, the role of extra-hypothalamic and thalamic dopaminergic (DA) inputs in this circuit remains underexplored. Using retrograde neuroanatomical tracing and high contrast confocal imaging methods, we investigated the projections and morphology of the discrete thalamic DA neuron groups in the dorsal hypothalamic area and their contribution to the PVN-RVLM neural circuit. We found that DA neuron subgroups in the Zona Incerta (Zi; 60%) and Reuniens thalamic nuclei (Re; 40%) were labeled comparably to the PVN (85%) after a retrograde tracer was injected into the RVLM/C1 (P < 0.01 mean ± SEM). The Re/Zi DA neuron subgroups were characterized by angulated cell bodies, superiomedial and inferiomedial projections reaching the contralateral Re/Zi and ipsilateral PVN DA neurons respectively. Ultimately, we deduced that the DA projections of the Re/Zi to the PVN contribute to the PVN-RVLM/C1 neural circuit. As a result of these connections, the Re/Zi DA neuron groups may regulate preautonomic sympathetic events associated with the PVN-RVLM pathway. Anat Rec, 300:1307-1314, 2017.