Lauer Simon M, Lenschow Constanze, Brecht Michael
Bernstein Center for Computational Neuroscience Berlin, Humboldt-Universität zu Berlin, Philippstrasse 13, Haus 6, Berlin, Germany.
NeuroCure Cluster of Excellence, Humboldt-Universität zu Berlin, Berlin, Germany.
J Comp Neurol. 2017 Aug 15;525(12):2706-2718. doi: 10.1002/cne.24237. Epub 2017 May 30.
The mammalian somatosensory cortex shows marked species-specific differences. How evolution in general and sexual selection in particular shape the somatosensory cortical body representation has not been delineated, however. Here we address this issue by a comparative analysis of genital cortex. Genitals are unique body parts in that they show sexual dimorphism, major changes in puberty and typically more pronounced species differences than other body parts (Hosken & Stockley, 2004). To study the evolution of genital cortex we flattened cortical hemispheres and assembled 104 complete body maps, revealed by cytochrome-oxidase activity in layer 4 of 8 rodent and 1 lagomorph species. In two species, we also performed antibody stainings against vesicular glutamate transporter-2, which suggested that cytochrome-oxidase maps closely mirror thalamic innervation. We consistently observed a protrusion between hindlimb and forelimb representation, which in rats (Lenschow et al., 2016) corresponds to the penis representation in males and the clitoris representation in females. Consistent with the idea that this protrusion corresponds to genital cortex, we observed a size increase of this protrusion during puberty. Species differed in external genital sexual dimorphism, but we observed a sexual monomorphism of the putative genital protrusion in all species, similar to previous observations in rats. The relative size of the putative genital protrusion varied more than 3-fold between species ranging from 0.5% of somatosensory cortex area in chipmunks to 1.7% in rats. This relative size of the genital protrusion co-varied with relative testicle size, an indicator of sperm competition and sexual selection.
哺乳动物的体感皮层表现出显著的物种特异性差异。然而，一般的进化，特别是性选择如何塑造体感皮层的身体表征，尚未得到明确阐述。在这里，我们通过对生殖器皮层的比较分析来解决这个问题。生殖器是独特的身体部位，因为它们表现出两性异形，在青春期会发生重大变化，并且通常比其他身体部位表现出更明显的物种差异（霍斯肯和斯托克利，2004年）。为了研究生殖器皮层的进化，我们将皮层半球扁平化，并组装了104张完整的身体图谱，这些图谱由8种啮齿动物和1种兔形目动物第4层中的细胞色素氧化酶活性揭示。在两个物种中，我们还针对囊泡谷氨酸转运体-2进行了抗体染色，这表明细胞色素氧化酶图谱紧密反映了丘脑神经支配。我们一致观察到后肢和前肢表征之间有一个突出部分，在大鼠中（伦绍等人，2016年），该突出部分对应于雄性的阴茎表征和雌性的阴蒂表征。与该突出部分对应于生殖器皮层的观点一致，我们观察到该突出部分在青春期期间尺寸增大。不同物种的外生殖器两性异形有所不同，但我们在所有物种中都观察到假定的生殖器突出部分存在性单态性，这与之前在大鼠中的观察结果相似。假定的生殖器突出部分的相对大小在不同物种之间变化超过3倍，从花栗鼠体感皮层面积的0.5%到大鼠的1.7%不等。生殖器突出部分的这种相对大小与相对睾丸大小共同变化，相对睾丸大小是精子竞争和性选择的一个指标。
