Mechanism of thirst induction by sialogues

有研究表明，虽然催涎剂匹罗卡品通过直接作用于唾液腺的腺泡细胞诱导唾液分泌，但它通过作用于中枢神经系统的毒蕈碱受体诱导饮酒行为。为了研究外周注射匹罗卡品对哪些脑区有影响，我们研究了c-Fos免疫反应细胞数量的变化。不同剂量的注射增加了皮质下器官、视前正中核、终板血管器、室旁核和视上核中c-Fos免疫反应细胞的数量。脑室内注射匹罗卡品在c-Fos免疫反应性表达上产生类似的变化。腹腔注射和脑室注射匹罗卡品诱导的免疫反应性表达的增加被先前脑室注射毒蕈碱受体拮抗剂阿托品所抑制。采用切片制备的电生理实验。全细胞记录显示，匹罗卡品使皮质下器官神经元膜去极化，并通过突触前作用抑制gaba能抑制性突触电流。结果表明，外周应用的匹罗卡品不仅作为催涎剂作用于唾液腺，而且还通过作用于中枢神经系统控制体液平衡来唤起口渴感觉。

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.