| To investigate the effect of peripheral hypertonic stimulation on the neurons of hypothalamic paraventricular nucleus (PVN) and its mechanism. Intraperitoneal injection (ip) of hyperosmotic saline (1.5 M NaCl, HS) was used as peripheral hypertonic stimulation.The unit discharge of PVN neurons was recorded extracellularly, arid immunocylochemistry was employed to observe the expression of Fos in brain includirg subfomical organ (SFO), median preoptic nucleus (MnPOX supraoptic nucleus (SON) and PVN and co-expression of arginine-vasopressin(AVP)and Fos in PVN. In addition, the changes of the response of phasic discharge PVN neurons and the Fos expression in brain induced by ip HS were examined after the angiotensin II type I receptors (AT1Rs) of the periventricular tissue were blocked by intracerebroventricular injection (icv) of losartan (an AT1R antagonist) .The experimental results indicated that: ( 1) Three types of spontaneous discharge (phasic, fast continuous and slow irregular) were observed in PVN neurons. The majority of PVN neurons could be activated by peripheral hypertonic stimulation. All of the phasic discharge units in PVN were excited and this effect could be blocked by icv losartan. (2) The expressin of Fos was significantly incresed after ip HS in many areas of brain, such as SFO, MnPO, SON and PVN. After icv losartan, the Fos expressin in these areasexcept SFO induced by ip HS reduced signf cantly. (3) Double staining showed that Fos-like immunoreactive (FLI) positive granules were observed in majority of vasopressin-immunoreactive positive neurons in PVN. The co-expression of Fos and AVP in PVN were also reduced signficantly after icv losartan.The results suggested that the neurons in PVN can be excited by peripheral hypertonic stimulation, some of them were vasopressinergic. This excitation was probably mediated by angiotensin II fibers projecting from periventricular tissue to PVN.
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