Mechanism of thirst induction by sialogues

已经提出，虽然促涎剂毛果芸香碱通过直接作用于唾液腺的腺泡细胞来促进唾液分泌，但其通过作用于中枢神经系统中的毒蕈碱受体来诱导饮水行为。为了研究哪些脑区受到外周注射毛果芸香碱的影响，我们研究了c-Fos免疫反应细胞数量的变化。注射后穹窿下器、视前区正中核、终板血管器、室旁核和视上核内c-Fos免疫反应阳性细胞数增加。侧脑室注射匹罗卡品也引起c-Fos免疫反应性表达的类似变化。免疫反应性表达的增加诱导的腹腔内和脑室内注射毛果芸香碱抑制由先前脑室内注射的毒蕈碱受体拮抗剂阿托品。使用切片制备的电生理学实验。全细胞记录显示毛果芸香碱通过突触前作用使穹窿下器神经元膜去极化，抑制抑制性GABA能突触电流。结果表明，外周应用毛果芸香碱不仅作为催涎剂作用于唾液腺，而且通过作用于中枢神经系统中控制体液平衡的中枢而引起口渴感。

It has been suggested that while the sialogogue pilocarpine elicits salivary secretion by acting directly on acinar cells of the salivary glands, it induces drinking behavior by acting on muscarinic receptors in the central nervous system. To study which brain regions are affected by the peripherally injected pilocarpine, we investigated changes in the numbers of c-Fos immunoreactive cells. The injections increased the numbers of c-Fos immunoreactive cells in the subfornical organ, median nucleus of preoptic area, organum vasculosum of lamina terminalis, paraventricular nucleus and supraoptic nucleus. Intracerebroventricular injection of pilocarpine produced similar changes in the expression of c-Fos immunoreactivity. The increases in immunoreactive expression induced by both the intraperitoneally and intracerebroventricularly injected pilocarpine were suppressed by previous intracerebroventricular injection of the muscarinic receptor antagonist atropine. Electrophysiological experiments using slice preparations. and whole cell recordings showed that pilocarpine depolarized the membrane of neurons in the subfornical organ and suppressed the inhibitory GABAergic synaptic currents by a presynaptic action. The results suggest that peripherally applied pilocarpine does not act only on the salivary glands as a sialogogue, but also evokes thirst sensation by acting on the center controlling body fluid balance in the central nervous system.