Department of Anatomy, Queen's University, Kingston, Ontario, Canada K7L 3N6.
J Neuroendocrinol. 1990 Oct 1;2(5):737-44. doi: 10.1111/j.1365-2826.1990.tb00472.x.
Abstract Repetitive bursting (phasic firing) generated endogenously by magnocellular neuroendocrine cells (MNCs) in the rat facilitates systemic release of vasopressin from axon terminals in the neurophypophysis. However, little is known of how MNCs function in other mammals. Using coronal slices of hypothalamus we studied the firing behaviour and intrinsic membrane properties of homologous neurons in the cat supraoptic nucleus where vasopressinergic MNCs outnumber oxytocinergic cells. Less than 1% of units recorded in cat supraoptic nuclei (2 of 270) spontaneously fired in a phasic mode compared to 39% in the rat (90 of 230). A discrete level of steady current across the extracellular recording micropipette promoted phasic firing in 66 of 152 non-phasic units tested in rat supraoptic nuclei, but no phasic activity in 189 units from the cat. One or several stimuli applied dorsal to supraoptic nuclei triggered a single burst (afterdischarge) in 115 of 180 MNC units from the rat, whereas none of 173 MNC units tested in the cat fired an afterdischarge. Intracellular recordings from 56 feline MNCs revealed that unlike the rat, spike depolarizing afterpotentials were absent in all cells. This explains both the absence of phasic firing and the inability to trigger regenerative bursts in the intact cat. The possible Osmoresponsiveness of cat MNCs was examined using unit recording. These units reversibly increased their firing rate as osmolality was elevated with mannitol or NaCl (10 to 100 mOsm/kg), comparable to rat units. However, in no case did hyperosmotic conditions elicit phasic firing. We conclude that cat MNCs lack a regenerative burst capability but that unit Osmoresponsiveness is comparable to rat MNC units. We hypothesize that since the kidney of the cat normally functions at high efficiency in terms of water resorption, there may be little need for the rapid and pronounced elevation in vasopressin release evoked by phasic firing.
摘要 大鼠的大细胞神经内分泌细胞（MNCs）内源性产生的重复爆发（相发射）促进了神经垂体轴突末梢血管加压素的全身释放。然而，对于其他哺乳动物的 MNCs 功能，我们知之甚少。我们使用下丘脑冠状切片研究了猫上核中同源神经元的放电行为和内在膜特性，其中血管加压素能 MNCs 的数量超过催产素能细胞。与大鼠（230 个中的 90 个）相比，猫上核记录的单位中只有不到 1%（270 个中的 2 个）自发地以相发射模式放电。在大鼠上核中，152 个非相发射单位中有 66 个在穿过细胞外记录微电极的恒定电流中有离散水平时，促进了相发射，但在猫的 189 个单位中没有相发射活性。在上核上方施加一个或多个刺激，触发了大鼠 180 个 MNC 单位中的 115 个单位的单个爆发（后放电），而猫的 173 个 MNC 单位中没有一个单位发生后放电。对 56 个猫 MNC 的细胞内记录显示，与大鼠不同的是，在所有细胞中都不存在尖峰去极化后电位。这解释了为什么在猫中没有相发射，并且在完整的猫中无法触发再生爆发。使用单位记录检查了猫 MNC 的可能渗透压反应性。这些单位随着甘露醇或 NaCl（10 至 100 mOsm/kg）渗透压的升高，可逆地增加其放电率，与大鼠单位相当。然而，在任何情况下，高渗条件都不会引起相发射。我们得出的结论是，猫的 MNC 缺乏再生爆发能力，但单位渗透压反应性与大鼠 MNC 单位相当。我们假设，由于猫的肾脏通常在水吸收方面具有高效率，因此可能不需要相发射引起的血管加压素释放的快速和明显升高。
