Acetylcholinesterase-positive innervation is present at undifferentiated stages of the sea turtle Lepidochelis olivacea embryo gonads: Implications for temperature-dependent sex determination

In embryos of different reptile species, incubation temperature triggers a cascade of endocrine events that lead to gonad sex differentiation. The cel lular and molecular mechanisms by which temperature sets in motion this pro cess are still controversial. Here, we begin evaluating the possible partic ipation of the nervous system in temperature-dependent sex determination by showing the existence and origin of acetylcholinesterase (AchE)-positive n erve fibers in undifferentiated gonads of the Lepidochelys olivacea (L. oli vacea) sea turtle putative male and female embryos, along the thermosensiti ve period for sex determination (TPSD; stages 20-27). AChE-positive nerve b undles and fibers were readily visualized until developmental stage 24 and thereafter. DiI injections and confocal imaging showed that some of these g onadal nerves arise from the lower thoracic and upper lumbar spinal cord le vels, and might thus be sensory in nature. Because the vertebrate spinal co rd is capable of integrating by itself thermoregulatory responses with no i ntervention of uppermost levels of the central nervous system, we also eval uated spinal cord maturation during the TPSD. The maturation of the spinal cord was more advanced in putative female than in male embryos, when sex de termination is taking place for each sex; this process starts and ends earl ier in male than in female embryos. Together these observations open the po ssibility that the spinal cord and the innervation derived from it could pl ay a direct role in driving or modulating the process of temperature-depend ent gonad sex determination and/or differentiation, particularly in female L. olivacea embryos. (C) 1999 Wiley-Liss, Inc.