SENSORY CIRCUMVENTRICULAR ORGANS AND BRAIN HOMEOSTATIC PATHWAYS

Circumventricular organs (CVOs), small structures bordering the ventri cular spaces in the midline of the brain, have common morphological an d endocrine-like characteristics that distinguish them from the rest o f the nervous system. Among their unique features are cellular contact s with two fluid phases - blood and cerebrospinal fluid - and neural c onnections with strategic nuclei establishing circuitry for communicat ions throughout the neuraxis. A variety of additional morphological an d functional characteristics of the CVOs implicates this group of stru ctures in a wide array of homeostatic processes. For three of the circ umventricular organs - the subfornical organ (SFO), the organum vascul osum of the lamina terminalis (OVLT), and the area postrema (AP) - rec ent findings demonstrate these structures as targets for blood-borne i nformation reaching the brain. We propose that these three sensory CVO s interact with other nuclei in the maintenance of several homeostatic processes by way of neural and humoral links. We emphasize the collec tive role of brain CVOs in the maintenance of body fluid homeostasis a s a model for the functional integration of these fascinating ''window s of the brain'' within central neurohumoral systems.