Molecular and Cellular Biology in Mechanism of Body Fluid Homeostasis (Analysis of Inter- and Intra-Cellular Signalling in the Neurosecretory Cells)

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The paraventricular nucleus (PVN) and the supraoptic nucleus (SON) in the hypothalamus are known to be one of integrative sites that regulate immune, endocrine and autonomic nervous system. The magnocellular neurosecretory cells in the PVN and the SON secrete hormones into the systemic circulation. The parvocellular neurosecretory cells in the PVN secrete hormones into the portal vessels in the median eminence and also directly influence autonomic preganglionic cells in the brainstem and spinal cord. The magnocellular neurosecretory cells in the PVN and the SON synthesize arginine vasopressin and oxytocin. Their firing rate is closely related to the amount of hormones released from the axon terminals in the neurohypophysis. we examined the effects of biological substances such as PACAP, prostaglandins (PGs), nitric oxide (NO), ATP, adenosine, glutamate, gamman aminobutyric acid (GABA), propofol (anesthetic drug) on the ion channels and neuronal activities in the rat slice preparation or acute dissociated neurosecretory cells, using extracellular, intracellular and whole cell patch-clamp recordings. Our data showed that various biological substances such as excitatory and inhibitory amino acids (glutamate, GABA), peptides, NO, PGs and purinergic substances modulate the ionic currents and neuronal activities in the neurosecretory cells. We also examined the inte- and intracellular signal transduction in the neurosecretory cells, using intracellular CaィイD12+ィエD1 imaging technique and the expression of various kinds of bioactive substance genes and receptors. These results provide new insight into understanding of the characteristics of the neurosecretory cells and the physiological implication of bioactive substances in the neuroendocrine system.