Brief PVH review

The PVN is anatomically composed of two types of neurons, magnocellular and parvocellular neurons. Both types of neurons are further subdivided into three magnocelluar and five parvocellular neurons. The magnocellular subdivisions are known as anterior, posterior, and medial subnuclei that project to the neurohypophysis and are responsible for the production of posterior pituitary hormones. The parvocellular neurons are subdivided into dorsal, lateral, medial, periventricular, and anterior subnuclei. These regions project to the autonomic nuclei in the brain stem as well as the spinal cord and are responsible for cardiovascular regulation through activation of sympathetic nervous system. The major regulator of the sympathetic nervous system is the RVLM which has numerous projections from the PVN that influence its regulation of arterial pressure.

Information regarding cardiovascular regulation reaches the PVH through a hindlimb brain region known as the NTS. The NTS is the main site of terminating fibers from various cardiovascular receptors such as the baroreceptors, chemoreceptors, and cardiopulmonary receptors. Axons from the caudal portion of the NTS have been found to terminate in the parvocellular and dorsal cap regions of the PVH however, the final target is not known yet.

PVH neurons are continuously active and subject to tonic inhibition arising from GABA and nitric oxide. Administration of NO causes as a decrease in sympathetic nerve activity and it has been found that the majority of the NO is the magnocellular neurons and it is hypothesized that magnocellular neurons may contribute to the autonomic regulation of SNA.  A functional experiment was performed which reported that administration of sodium nitroprusside into the PVH decreased rSNA, AP, and heart rate. Furthermore, administration of NO antagonist blocked the inhibitory effect of the NO on the SNA indicating that NO is inhibitory to sympathetic outflow.

Overall, the paper reviews several ways to examine the PVH and concludes that regulating synaptic activity of the PVH at the level of the parvocellular neurons contributes to sympathetic control and setting basal activity levels. In setting this basal tone, NO, GABA, glutamate and vasopressin are all contributors to tonic activity of the PVH. Therefore, disturbances in these pathways can lead to various cardiovascular disease states.