Saito T, Dayanithi G, Saito J, Onaka T, Urabe T, Watanabe T X, Hashimoto H, Yokoyama T, Fujihara H, Yokota A, Nishizawa S, Hirata Y, Ueta Y
Department of Physiology, School of Medicine, University of Occupational and Environmental Health, Kitakyushu, Japan.
J Neuroendocrinol. 2008 Feb;20(2):207-19. doi: 10.1111/j.1365-2826.2007.01632.x. Epub 2007 Nov 28.
Salusin-alpha and -beta were recently discovered as bioactive endogenous peptides. In the present study, we investigated the effects of chronic osmotic stimuli on salusin-beta-like immunoreactivity (LI) in the rat hypothalamo-neurohypophyseal system. We examined the effects of salusin-beta on synaptic inputs to the rat magnocellular neurosecretory cells (MNCs) of the supraoptic nucleus (SON) and neurohypophyseal hormone release from both freshly dissociated SONs and neurohypophyses in rats. Immunohistochemical studies revealed that salusin-beta-LI neurones and fibres were markedly increased in the SON and the magnocellular division of the paraventricular nucleus after chronic osmotic stimuli resulting from salt loading for 5 days and dehydration for 3 days. Salusin-beta-LI fibres and varicosities in the internal zone of the median eminence and the neurohypophysis were also increased after osmotic stimuli. Whole-cell patch-clamp recordings from rat SON slice preparations showed that salusin-beta did not cause significant changes in the excitatory and inhibitory postsynaptic currents of the MNCs. In vitro hormone release studies showed that salusin-beta evoked both arginine vasopressin (AVP) and oxytocin release from the neurohypophysis, but not the SON. In our hands, in the neurohypophysis, a significant release of AVP and oxytocin was observed only at concentrations from 100 nm and above of salusin-beta. Low concentrations below 100 nm were ineffective both on AVP and oxytocin release. We also measured intracellular calcium (Ca(2+)) increase induced by salusin-beta on freshly-isolated single nerve terminals from the neurohypophysis devoid of pars intermedia. Furthermore, this salusin-beta-induced Ca(2+) increase was blocked in the presence of high voltage activated Ca(2+)channel blockers. Our results suggest that salusin-beta may be involved in the regulation of body fluid balance by stimulating neurohypophyseal hormone release from nerve endings by an autocrine/paracrine mechanism.
Salusin-α和-β最近被发现是具有生物活性的内源性肽。在本研究中，我们调查了慢性渗透刺激对大鼠下丘脑-神经垂体系统中salusin-β样免疫反应性（LI）的影响。我们研究了salusin-β对大鼠视上核（SON）大细胞神经分泌细胞（MNCs）的突触输入以及大鼠新鲜分离的SON和神经垂体中神经垂体激素释放的影响。免疫组织化学研究显示，在5天高盐负荷和3天脱水导致的慢性渗透刺激后，SON和室旁核大细胞部中salusin-β-LI神经元和纤维显著增加。渗透刺激后，正中隆起内侧区和神经垂体中的salusin-β-LI纤维和曲张体也增加。大鼠SON脑片制备的全细胞膜片钳记录显示，salusin-β不会引起MNCs兴奋性和抑制性突触后电流的显著变化。体外激素释放研究表明，salusin-β可引起神经垂体释放精氨酸加压素（AVP）和催产素，但不能引起SON释放。在我们的实验中，在神经垂体中，仅在salusin-β浓度为100 nM及以上时才观察到AVP和催产素的显著释放。低于100 nM的低浓度对AVP和催产素释放均无效。我们还测量了salusin-β对不含中间部的神经垂体新鲜分离的单神经末梢诱导的细胞内钙（Ca(2+)）增加。此外，在存在高电压激活的Ca(2+)通道阻滞剂的情况下，这种salusin-β诱导的Ca(2+)增加被阻断。我们的结果表明，salusin-β可能通过自分泌/旁分泌机制刺激神经末梢释放神经垂体激素，从而参与体液平衡的调节。
