Colocalization of Dopamine <scp>D1</scp> and <scp>D2</scp> Receptors With Neuronal Nitric Oxide Synthase in the Rat Paraventricular Nucleus: A Structural Basis for Dopaminergic–Nitrergic Interaction

The paraventricular nucleus (PVN) plays a central role in neuroendocrine and autonomic regulation, including male sexual behaviour. Dopaminergic and nitrergic signalling within the PVN are functionally linked, but their cellular relationship remains unclear. We examined the colocalization of dopamine D1 and D2 receptors with neuronal nitric oxide synthase (nNOS) in adult male rats using double-label immunohistochemistry. nNOS-immunoreactive neurons were widely distributed in PVN, with subsets co-expressing D1R or D2R. Approximately 45% of nNOS-positive neurons expressed dopaminergic receptors. These findings provide structural evidence for dopaminergic-nitrergic interaction in the PVN and support the possibility of direct dopaminergic modulation of nitrergic neurons.