The Paraventricular Nucleus of the Hypothalamus in Control of Blood Pressure and Blood Pressure Variability

Abstract

The paraventricular nucleus (PVN) is a highly organized structure of the hypothalamus that has a key role in regulating cardiovascular and osmotic homeostasis. Functionally, the PVN is divided into autonomic and neuroendocrine (neurosecretory) compartments, both equally important for maintaining blood pressure (BP) and body fluids in the physiological range. Neurosecretory magnocellular neurons (MCNs) of the PVN are the main source of the hormones vasopressin (VP), responsible for water conservation and hydromineral balance, and oxytocin (OT), involved in parturition and milk ejection during lactation. Further, neurosecretory parvocellular neurons (PCNs) take part in modulation of the hypothalamic-pituitary-adrenal axis and stress responses. Additionally, the PVN takes central place in autonomic adjustment of BP to environmental challenges and contributes to its variability (BPV), underpinning the PVN as an autonomic master controller of cardiovascular function. Autonomic PCNs of the PVN modulate sympathetic outflow toward heart, blood vessels and kidneys. These pre-autonomic neurons send projections to the vasomotor nucleus of rostral ventrolateral medulla and to intermediolateral column of the spinal cord, where postganglionic fibers toward target organs arise. Also, PVN PCNs synapse with NTS neurons which are the end-point of baroreceptor primary afferents, thus, enabling the PVN to modify the function of baroreflex. Neuroendocrine and autonomic parts of the PVN are segregated morphologically but they work in concert when the organism is exposed to environmental challenges via somatodendritically released VP and OT by MCNs. The purpose of this overview is to address both neuroendocrine and autonomic PVN roles in BP and BPV regulation.

Keywords: PVN; baroreflex; blood pressure; blood pressure variability; oxytocin; vasopressin.

Figure 1

Neuroendocrine and pre-autonomic paraventricular nucleus in cardiovascular regulation. MCNs synthetize VP which is transported via their axons to neurohypophysis for systemic release. Once in the circulation, VP reaches distant targets (kidneys, resistance vessels) to exert its effects. Some portion of VP is released intranuclearly, and modulates the activity of pre-autonomic PCNs. These pre-autonomic neurons have the potential to modulate the autonomic outflow toward heart, kidneys and arterioles. Additionally, VP is co-expressed with CRH alternating the reactivity of HPA axis. VP, vasopressin; CRH, corticotropin-releasing hormone; ACTH, adrenocorticotropic hormone; MCN, Magnocellular neuron; PCNs, parvocellular neuron; SPANs, spinally projecting pre-autonimic neurons; RVLM, rostral ventrolateral medulla; IML, intermediolateral nucleus.