ANATOMICAL LOCATION

Paraventricular Nucleus is located right next to Third Ventricle (One of the four fluid filled cavities forming Ventricular System), because of its anatomical location it is named as Paraventricular (alongside a ventricle). It lies within the Periventricular Zone and must not be confused by it, which holds the more medial position underneath the Third Ventricle.

NEURONS

Paraventricular Nucleus contains Magnocellular Neurosecretory Cells (Neuroendocrine Cells) whose Axon are elongated into the Posterior Pituitary, Parvocellular Neuroendocrine Cells that project to the Median Eminence (Inferior boundary of Hypothalamus) and many populations of Peptide containing cells. These cells affect directly many different brain regions including Parvocellular Pre-autonomic Cells that goes direct to Spinal Cord and Brainstem.

MAGNOCELLULAR NEUROSECRETORY NEURONS

Magnocellular cells in PVN arrange themselves and secrete two hormones i.e Oxytocin and Vasopressin. These hormones are then packed into large vessels and then transported down the Axons of cells without Myelin Sheath (layer of Dielectric fluid) and are released into the neurosecretory nerve endings placed in Posterior Pituitary Gland.

PARVOCELLULAR NEUROSECRETORY (NEUROENDOCRINE) NEURONS

Axons of Parvocellular Neurosecretory Neurons of PVN project to Median Eminence i.e. inferior body of Hypothalamus. It is a Neurohemal organ of the brain where Neurosecretory Nerve endings secrete their hormones at the Primary Capillary Plexus of Hypophyseal System. The Median Eminence has many fiber terminals that secrete different Neurotransmitters, some of which are Vasopressin, Growth Hormone Releasing Hormone (GHRH), Dopamine (DA) and Growth Hormone Release Inhibiting Hormone (GIH) into blood vessels of Hypophyseal Portal System. These blood vessels carry the hormones to Anterior Pituitary Gland where the circulation of these hormones in body is kept in check.

CENTRALLY PROJECTING (PRE-AUTONOMIC) NEURONS

PVN also contains Inter-neurons and population of neurons projecting themselves to other brain regions. These centrally projecting neurons are as follows.

• Parvocellular Oxytocin Cells that project mainly into Brainstem and Spinal Cord are responsible for Gastric Reflexes and Penile Erection.
• Parvocellular Vasopressin Cells that are attached at many points in Hypothalamus and Limbic System as well as with Brainstem and Spinal Cord. They are responsible for Blood Pressure and Temperature Regulation.
• Parvocellular Corticotropin Releasing Hormone (CRH) Neurons that are involved in stress related behavior.

AFFERENT INPUTS TO THE PVN

PVN also receives Afferent (Central) Inputs from many brain parts i.e.

•  Inputs from neurons that lie near the anterior wall of third ventricular carry information about Electrolyte Composition of blood.
•  Inputs to Brain stem and Ventrolateral Medulla have information from heart and stomach.
•  Inputs from Hippocampus are for regulation of stress responses.