Sibbald J R, Hubbard J I, Sirett N E
Department of Physiology, University of Otago Medical School, Dunedin, New Zealand.
Brain Res. 1988 Oct 4;461(2):205-14. doi: 10.1016/0006-8993(88)90251-x.
Extracellular recordings were made in vitro from 212 single units in the rat subfornical organ (SFO) and 54 single units in the rat medial preoptic area (MPO). Units were exposed to solutions made hyper-osmotic or hypo-osmotic by 1.4-11%. A reversible 30% or greater change in frequency followed the osmotic challenge in tests of 66% of units in the SFO and 46% of units in the MPO. Responses consisted of increases in frequency (excitations) or decreases in frequency (inhibitions) and were either sustained for the whole test period or of a transitory nature. Units responded to either hyperosmotic (SFO, 19%; MPO, 43%) or to hypo-osmotic changes (SFO, 30%; MPO, 28.5%) or to both (SFO, 51%; MPO, 28.5%). The response pattern of the SFO and MPO was significantly different (chi 2 54.0, 3df, P = 0.0001). In both the SFO and MPO the stimulus to which the units responded was a change in tonicity. This was indicated by the findings that similar responses were evoked by hyperosmotic changes made with either mannitol or NaCl and there was no response to solutions containing urea, either as an additive, or as a substitute for NaCl. In the SFO, in the presence of synaptic blockade produced by raising the Mg concentration in the bathing solution to 15 mM, the frequency of 19/27 units fell significantly. Responses of 40% of units to osmotic pressure changes were blocked indicating these responses were synaptically evoked. The responses which survived synaptic blockade when compared with pre-blockade responses were more often transient (P less than 0.02) and more often inhibitions. Post blockade there were also significantly more responses in the SFO to hypo-osmotic than to hyper-osmotic changes (P = 0.01). Our results suggest that while an ability to change their firing rate in response to small changes of osmotic pressure may be a general property of neurons, the neurons of the SFO are specialised for the detection of changes in the extracellular osmotic pressure.
在体外对大鼠穹窿下器官（SFO）中的212个单神经元以及大鼠内侧视前区（MPO）中的54个单神经元进行细胞外记录。将神经元暴露于渗透压升高或降低1.4%-11%的溶液中。在SFO中，66%的神经元以及MPO中46%的神经元在渗透压刺激测试中出现频率可逆性变化30%或更大。反应包括频率增加（兴奋）或频率降低（抑制），并且在整个测试期间持续存在或呈短暂性。神经元对高渗变化（SFO为19%，MPO为43%）、低渗变化（SFO为30%，MPO为28.5%）或两者均有反应（SFO为51%，MPO为28.5%）。SFO和MPO的反应模式存在显著差异（卡方检验，54.0，3自由度，P = 0.0001）。在SFO和MPO中，神经元做出反应的刺激均为张力变化。这一点通过以下发现得以表明：用甘露醇或氯化钠引起的高渗变化会引发相似的反应，而含有尿素的溶液，无论是作为添加剂还是替代氯化钠，均无反应。在SFO中，当将浴液中的镁离子浓度提高到15 mM以产生突触阻断时，27个神经元中有19个的频率显著下降。40%的神经元对渗透压变化的反应被阻断，表明这些反应是由突触诱发的。与阻断前的反应相比，在突触阻断后仍存在的反应更常为短暂性（P < 0.02）且更常为抑制性。阻断后，SFO中对低渗变化的反应也显著多于对高渗变化的反应（P = 0.01）。我们的结果表明，虽然响应渗透压的微小变化而改变其放电频率的能力可能是神经元的普遍特性，但SFO的神经元专门用于检测细胞外渗透压的变化。
