Slugg Robert M, Zheng Shi-Xi, Fang Yuan, Kelly Martin J, Rønnekleiv Oline K
Department of Physiology and Pharmacology, L334, Oregon Health Sciences University, 3181 Sam Jackson Park Road, Portland, OR 97201, USA.
J Physiol. 2003 Aug 15;551(Pt 1):295-308. doi: 10.1113/jphysiol.2003.041319. Epub 2003 Jun 17.
The GABAB receptors GABAB-R1 and GABAB-R2 have been cloned in several mammalian species, and the functional receptor has been shown to exist as a heterodimeric complex. We have cloned guinea pig GABAB-R1 and GABAB-R2 receptor sequences and, using in situ hybridization and immunocytochemistry for vasopressin (AVP), we found that GABAB-R1 and -R2 receptors are expressed in vasopressin neurones of the supraoptic (SON) and paraventricular nuclei (PVN). Therefore, we used both sharp electrode and whole-cell patch recording techniques to examine the effects of the selective GABAB agonist baclofen on SON and PVN magnocellular neurones and to determine the coupling of the GABAB receptor to effector pathways. Recordings were made in coronal hypothalamic slices from both female (ovariectomized) and male guinea pigs. In the presence of tetrodotoxin (TTX), baclofen hyperpolarized (DeltaVmax = 5.6 mV, EC50 = 2.3 microM) SON magnocellular neurones (n = 27) under current clamp, or induced an outward current that reversed at EK (DeltaImax = 24.2 pA) in PVN magnocellular neurones (n = 33) under voltage clamp. Seventeen of the 24 biocytin-labelled SON magnocellular neurones were identified as AVP neurones, and ten of the 33 biocytin-labelled PVN neurones were identified as AVP or neurophysin-containing neurones, although all of the cells were clustered in the vasopressin-rich core. In the absence of TTX, baclofen activated an outward K+ current that hyperpolarized SON and PVN neurones and significantly reduced their firing rate. The outward current showed inward rectification and was blocked by the K+ channel blocker barium and the GABAB receptor antagonist CGP 35348. Therefore, GABAB receptors are coupled to inwardly rectifying K+ channels in SON and PVN magnocellular neurones and may play a prominent role in modulating phasic bursting activity in guinea pig vasopressin neurones.
GABAB受体GABAB-R1和GABAB-R2已在多种哺乳动物中克隆出来，并且已证明功能性受体以异二聚体复合物形式存在。我们克隆了豚鼠GABAB-R1和GABAB-R2受体序列，并使用原位杂交和抗加压素（AVP）免疫细胞化学方法，发现GABAB-R1和-R2受体在视上核（SON）和室旁核（PVN）的加压素神经元中表达。因此，我们使用尖锐电极和全细胞膜片钳记录技术来研究选择性GABAB激动剂巴氯芬对SON和PVN大细胞神经元的影响，并确定GABAB受体与效应器途径的偶联。记录取自雌性（去卵巢）和雄性豚鼠的冠状下丘脑切片。在存在河豚毒素（TTX）的情况下进行电流钳记录时，巴氯芬使SON大细胞神经元（n = 27）超极化（ΔVmax = 5.6 mV，EC50 = 2.3 μM），在电压钳记录时，巴氯芬在PVN大细胞神经元（n = 33）中诱导出在EK处反转的外向电流（ΔImax = 24.2 pA）。在24个用生物素标记的SON大细胞神经元中，有17个被鉴定为AVP神经元，在33个用生物素标记的PVN神经元中，有10个被鉴定为含AVP或含神经垂体素的神经元，尽管所有细胞都聚集在富含加压素的核心区域。在不存在TTX的情况下，巴氯芬激活外向K+电流，使SON和PVN神经元超极化并显著降低其放电频率。外向电流表现出内向整流特性，并被K+通道阻滞剂钡和GABAB受体拮抗剂CGP 35348阻断。因此，GABAB受体与SON和PVN大细胞神经元中的内向整流K+通道偶联，可能在调节豚鼠加压素神经元的相位爆发活动中起重要作用。
