VISCERAL NEURAXIS IN HOMEOSTASIS

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The visceral neuraxis of the mammalian brain is a network of neural connections that mediates homeostasis. it can be defined neuroanatomically by its connections to the autonomic nervous system, to circumventricular organs and to the pituitary gland as well as by interconnections of intervening nuclei. The circumventricular organs, which lack a blood brain barrier making them putative central receptor sites for humoral factors, and the visceral sensory afferents of the peripheral nervous system make up the sensory side of the network. The motor components are the autonomic nervous system, endocrine system and homeostatic behavior. The long term objectives of this project are to define and understand the operation of the components of the visceral neuraxis contributing to the generation of ingestive behaviors and specific behavioral states and the factors which convert them into health damaging behaviors or altered physiological states that accompany obesity, schizophrenia, hypertension, psychogenic polydipsia, stress ulcers, and essential hypernatremia. A major aim is to map from specific abdominal organs across several orders of neural connections using transsynaptic viral tracers to forebrain nuclei to determine and compare the autonomic neural organization of sites driving specific organ function and determine how this labeling is altered when rats are vagotomized to eliminate the parasympathetic route into the brain. The viral labeled neurons will be further characterized by double labeling for neuropeptides for comparison among the different abdominal organs. The second aim is to similarly map from the posterior pituitary gland using virus to forebrain nuclei to determine its second and third order neuronal afferent input and to further characterize this input by double labeling for neuropeptides. The above aims permit a more complete establishment of autonomic and endocrine areas of the forebrain with relation to specific peripheral organs (because of the powerful property of transsynaptic transfer) and their comparison to determine differences in circuit organization. in addition it will be possible to map the commonly unlabeled areas of the hypothalamus to identify potential neural substrate for homeostatic behaviors. The third aim is to characterize at the ultrastructural level the types of synapses that PRV crosses and whether there is any preference for the different cellular locations of synapses and whether this varies with different organs injected, different neuronal order or different neuropeptide content of neurons.