Lee Heon-Jin, Caldwell Heather K, Macbeth Abbe H, Young W Scott
Section on Neural Gene Expression, National Institute of Mental Health, National Institutes of Health, DHHS, Bethesda, MD, USA.
Prog Brain Res. 2008;170:73-7. doi: 10.1016/S0079-6123(08)00407-X.
Oxytocin (Oxt), synthesized in magnocellular neurons of the paraventricular (PVN) and supraoptic (SON) hypothalamic nuclei for transport to and release from the posterior pituitary, is released during parturition and is essential for lactation. Lesser amounts of Oxt are made by smaller cells of the PVN and a few other forebrain nuclei and released into the central nervous system (CNS) to influence various other behaviours. In both the periphery and CNS, Oxt actions are transduced by the oxytocin receptor (Oxtr). Previously, it has been reported that Oxt(-/-) (knockout, KO) mice show a failure of milk ejection and thus are incapable of rearing their offspring. Unexpectedly, these mice have largely normal reproductive and maternal behaviours, perhaps due to compensatory mechanisms through activation of the Oxtr by vasopressin or through development. To examine the specific roles of the Oxtr during development and in particular brain areas, we created conditional Oxtr(-/-) mice in which we could control the spatial and temporal inactivation of the Oxtr. We flanked the neomycin-resistance selectable marker in an Oxtr intron with FRT sites to enable its removal using FLP recombinase. Coding sequence within exons 2 and 3 was flanked by two loxP sites enabling subsequent inactivation of the gene by targeted expression of Cre recombinase. The first Oxtr KO lines we created have either total or relatively specific forebrain elimination. The latter was achieved by crossing the conditional Oxtr line with a transgenic line in which the Camk2a promoter drives expression of Cre recombinase to significant levels beginning 21-28 days after birth, thus eliminating potential compensation for a deleted Oxtr gene during early development. This Cre-expressing line also significantly spares the main olfactory bulb reducing the potential confound of an olfactory deficit. We have investigated various behaviours, most notably social recognition, in both Oxtr KO strains (Oxtr(-/-) and Oxtr(FB/FB)).
催产素（Oxt）由下丘脑室旁核（PVN）和视上核（SON）的大细胞神经元合成，运输至垂体后叶并从那里释放，在分娩时释放，对泌乳至关重要。PVN的较小细胞和其他一些前脑核产生少量Oxt，并释放到中枢神经系统（CNS）中以影响各种其他行为。在周围组织和中枢神经系统中，Oxt的作用均由催产素受体（Oxtr）介导。此前有报道称，Oxt基因敲除（KO）小鼠出现乳汁喷射失败，因此无法养育后代。出乎意料的是，这些小鼠的生殖和母性行为在很大程度上是正常的，这可能是由于血管加压素激活Oxtr或通过发育产生的补偿机制。为了研究Oxtr在发育过程中以及特定脑区的具体作用，我们创建了条件性Oxtr基因敲除小鼠，在其中可以控制Oxtr的空间和时间失活。我们在Oxtr内含子中的新霉素抗性选择标记两侧设置了FRT位点，以便使用FLP重组酶将其去除。外显子2和3内的编码序列两侧有两个loxP位点，通过Cre重组酶的靶向表达可使该基因随后失活。我们创建的第一批Oxtr基因敲除品系具有全脑或相对特异性的前脑消除。后者是通过将条件性Oxtr品系与转基因品系杂交实现的，在转基因品系中，Camk2a启动子驱动Cre重组酶在出生后21 - 28天开始表达至显著水平，从而消除早期发育过程中对缺失的Oxtr基因的潜在补偿。这个表达Cre的品系还显著保留了主要嗅球，减少了嗅觉缺陷的潜在混淆因素。我们在两种Oxtr基因敲除品系（Oxtr(-/-)和Oxtr(FB/FB)）中研究了各种行为，最显著的是社会识别行为。
