Department of Integrative Physiology, University of Colorado Boulder, CO, USA.
Front Endocrinol (Lausanne). 2011 Sep 20;2:36. doi: 10.3389/fendo.2011.00036. eCollection 2011.
In vertebrates, gonadotropin-releasing hormone (GnRH) is a crucial decapeptide that activates the hypothalamic-pituitary-gonadal axis to ensure successful reproduction. Recently, a GnRH-like molecule has been isolated from a gastropod mollusk, Aplysia californica. This GnRH (ap-GnRH) is deduced to be an undecapeptide, and its function remains to be explored. Our previous study demonstrated that ap-GnRH did not stimulate a range of reproductive parameters. Instead, it affected acute behavioral and locomotive changes unrelated to reproduction. In this study, we used electrophysiology and retrograde tracing to further explore the central role of ap-GnRH. Sharp-electrode intracellular recordings revealed that ap-GnRH had diverse effects on central neurons that ranged from excitatory, inhibitory, to the alteration of membrane potential. Unexpectedly, extracellular recordings revealed that ap-GnRH suppressed the onset of electrical afterdischarge in bag cell neurons, suggesting an inhibitory effect on female reproduction. Lastly, using immunocytochemistry coupled with nickel backfill, we demonstrated that some ap-GnRH neurons projected to efferent nerves known to innervate the foot and parapodia, suggesting ap-GnRH may directly modulate the motor output of these peripheral tissues. Overall, our results suggested that in A. californica, ap-GnRH more likely functioned as a central modulator of complex behavior and motor regulation rather than as a conventional reproductive stimulator.
在脊椎动物中，促性腺激素释放激素（GnRH）是一种至关重要的十肽，它激活下丘脑-垂体-性腺轴，以确保成功繁殖。最近，从腹足纲软体动物加利福尼亚海兔（Aplysia californica）中分离出一种类似 GnRH 的分子。这种 GnRH（ap-GnRH）被推断为十一肽，其功能仍有待探索。我们之前的研究表明，ap-GnRH 不能刺激一系列生殖参数。相反，它影响与生殖无关的急性行为和运动变化。在这项研究中，我们使用电生理学和逆行追踪进一步探讨了 ap-GnRH 的中枢作用。锐电极细胞内记录显示，ap-GnRH 对中枢神经元有多种影响，从兴奋、抑制到膜电位的改变。出乎意料的是，细胞外记录显示，ap-GnRH 抑制了袋状细胞神经元电继发放的起始，表明其对雌性生殖具有抑制作用。最后，通过免疫细胞化学结合镍回填，我们证明了一些 ap-GnRH 神经元投射到已知支配足部和副足的传出神经，这表明 ap-GnRH 可能直接调节这些外周组织的运动输出。总的来说，我们的结果表明，在加利福尼亚海兔中，ap-GnRH 更可能作为复杂行为和运动调节的中枢调节剂发挥作用，而不是作为传统的生殖刺激剂。
