The Study On Signal Route From Peripheral Osmotic Receptors In Abdominal Cavity To Supraoptic Nucleus

Maintenance of osmotic pressure is a primary regulatory process essential for normal cell function. Previous study mainly focused on the hypothalamo-neurohypophysial system, which is the key integrative structure on which converges the osmosensitive information coming from the whole complex. Magnocellular neurosecretory cells (MNCs) located in the paraventricular and supraptic nuclei synthesize vasopressin and oxytocin and release them into the blood circulation. The activities of MNCs are reinforced and inhibited by hyper and hypo-osmotic stimuli respectively. However few details have been reported about the signal route from peripheral osmoreceptors to central nerve system, and about the relationship between astrocytes and neurons in this route. Our former results pointed out that hypertonicity induced Fos expression in SON astrocytes is earlier than in SON neurons. Based on the data above, we wish to find out clear evidence for the signal route from peripheral osmoreceptors to the astrocytes and neurons of supraoptic nucleus relaying in the nucleus of tractus solitarius. In addition, we initiatorily observed the changes of plasticity and relationship between astrocytes and neurons in SON after hypo-stimulation.Immunohistochemistry method was used to detect the effect of Subdiaphragmatic vagotomy (SDV) on hypertonicity activated neurons and astrocytes in SON and NTS.NTS projecting to astrocytes and neurons of SON were observed by using of BDA or WGA-HRP tracing method coupling with immunohistochemistry method or immunofluorescent.Ultrastructure between activated SON astrocytes and neurons was observed by double immune-electron-microscopic staining method.Giving hypo-osmotic stimulation through the caudal vein, we studied the time course of immunohistochemical staining of neurons and astrocytes in SON.The main results included:1. Hypertonicity induced significant increasing of Fos expression in neurons and glial fibrillary acidic protein (GFAP)-like immunoreactivity (LI) astrocytes in NTS and SON, which was inhibited by SDV.2. By using BDA anterograde tracing plus hyperosmotic stimulation, BDA labeling fibers from NTS were found in SON, some of them closely contacted with oxytocin(OT)-LI neurons and GFAP-LI astrocytes respectively. With WGA-HRP retrograde tracing plus hyperosmotic stimulation, the complexs formed of WGA-HRP / Fos / tyrosine hydroxidase (TH) triple labeled neurons and GFAP positive astrocytes were found in NTS.3. Immunoelectron microscopy established that two kinds of ultrastructures were found on junction areas between axonal end and neurons or astrocytes in SON after hyperosmotic stimuli. One was the synapse, the other was synapse-like structure formed of axonal terminal and GFAP-labeled astrocytes.