Lowes V L, Sun K, Li Z, Ferguson A V
Department of Physiology, Queen's University, Kingston, Ontario, Canada.
Am J Physiol. 1995 Aug;269(2 Pt 2):R463-8. doi: 10.1152/ajpregu.1995.269.2.R463.
The area postrema (AP) is a circumventricular organ located on the dorsal surface of the medulla. Substantial evidence suggests that the AP is an important site involved in cardiovascular regulation. Arginine vasopressin (AVP) is thought to act at the AP to increase the sensitivity of the baroreceptor reflex. We have therefore examined the effects of AVP on AP neurons with the use of extracellular single unit recordings in vitro. Coronal medullary brain slices (thickness = 400 microns) were obtained from male Sprague-Dawley rats and maintained in oxygenated artificial cerebrospinal fluid (aCSF). The slices were perfused with AVP (10(-8) to 10(-6) M), and the effect on single AP neurons was recorded. A total of 79 AP neurons was tested of which 50 (63.3%) were excited by AVP and 5 (6.3%) were inhibited, whereas the remaining 24 (30.3%) cells were unaffected. The excitatory effects of AVP were dose dependent: firing rate increased 92.6 +/- 25.8% at 10(-8) M, 289.4 +/- 53.9% at 10(-7) M, and 456.8 +/- 113.1% at 10(-6) M, respectively. We also examined whether these effects of AVP resulted from direct actions of this peptide on AP cells by testing if responses were retained during blockade of synaptic transmission (achieved by perfusion with a low Ca(2+)-high Mg2+ aCSF) in 11 cells excited by AVP. Nine of these cells were excited by AVP during such synaptic blockade. Finally, we demonstrated that the excitatory responses of five AP cells to AVP were all totally abolished by perfusion of slices with aCSF containing the V1 antagonist ([1-beta-mercapto-beta,beta-cyclopentamethylene propionic acid,2-(O-methyl)tyrosine]-Arg8-vasopressin; Peninsula Laboratories, 10(-6) M).(ABSTRACT TRUNCATED AT 250 WORDS)
最后区（AP）是位于延髓背侧的一个室周器官。大量证据表明，最后区是参与心血管调节的一个重要部位。精氨酸加压素（AVP）被认为作用于最后区以增加压力感受器反射的敏感性。因此，我们利用体外细胞外单单位记录技术研究了AVP对最后区神经元的影响。从雄性Sprague-Dawley大鼠获取冠状延髓脑片（厚度 = 400微米），并置于充氧的人工脑脊液（aCSF）中。将脑片用AVP（10⁻⁸至10⁻⁶ M）灌注，并记录对单个最后区神经元的影响。共测试了79个最后区神经元，其中50个（63.3%）被AVP兴奋，5个（6.3%）被抑制，其余24个（30.3%）细胞未受影响。AVP的兴奋作用呈剂量依赖性：在10⁻⁸ M时放电频率增加92.6±25.8%，在10⁻⁷ M时增加289.4±53.9%，在10⁻⁶ M时增加456.8±113.1%。我们还通过测试在11个被AVP兴奋的细胞中突触传递被阻断（通过用低钙 - 高镁aCSF灌注实现）时反应是否保留，来研究AVP的这些作用是否由该肽对最后区细胞的直接作用所致。在这种突触阻断期间，其中有9个细胞被AVP兴奋。最后，我们证明，用含V1拮抗剂（[1 - β - 巯基 - β，β - 环戊亚甲基丙酸，2 - （O - 甲基）酪氨酸] - Arg⁸ - 加压素；半岛实验室，10⁻⁶ M）的aCSF灌注脑片后，5个最后区细胞对AVP的兴奋反应全部被消除。（摘要截断于250字）
