The paraventricular nucleus: an important component of the central neurocircuitry regulating sympathetic nerve outflow

Aim: The sympathetic nervous system plays an important role in the regulation of physiological homeostasis under basal conditions and in response to acute and chronic stressors. It is known that multiple levels of the neuroaxis, including the paraventricular nucleus (PVN) of the hypothalamus, are involved in regulation of efferent sympathetic nerve discharge (SND). This review focuses on the role of the PVN in regulation of functional characteristics of efferent SND. Results: The available experimental evidence indicates that the level of efferent sympathetic nerve activity is altered after microinjection of numerous substances into the PVN, including excitatory amino acids, gamma -aminobutyric acid (GABA(A) ) receptor agonists and antagonists, and PVN nitric oxide synthase inhibitors. In addition, antagonism of PVN GABA(A) receptors changes the pattern of synchronized discharge bursts in efferent sympathetic nerves and enhances the frequency-domain coupling between low-frequency bursts in sympathetic nerve pairs. Finally, PVN microinjections of excitatory amino acids (L-glutamate, D,L-homocysteic acid) have been shown to produce non-uniform changes in the level of efferent sympathetic nerve activity. Conclusion: These findings support the concept that the PVN is an important component of the central neurocircuitry regulating functional characteristics (basal level of activity, bursting pattern, and relationships between discharges in nerves innervating different targets) of efferent sympathetic nerve outflow.