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

Abstract

In embryos of different reptile species, incubation temperature triggers a cascade of endocrine events that lead to gonad sex differentiation. The cellular and molecular mechanisms by which temperature sets in motion this process are still controversial. Here, we begin evaluating the possible participation of the nervous system in temperature-dependent sex determination by showing the existence and origin of acetylcholinesterase (AchE)-positive nerve fibers in undifferentiated gonads of the Lepidochelys olivacea (L. olivacea) sea turtle putative male and female embryos, along the thermosensitive period for sex determination (TPSD; stages 20-27). AChE-positive nerve bundles and fibers were readily visualized until developmental stage 24 and thereafter. DiI injections and confocal imaging showed that some of these gonadal nerves arise from the lower thoracic and upper lumbar spinal cord levels, and might thus be sensory in nature. Because the vertebrate spinal cord is capable of integrating by itself thermoregulatory responses with no intervention of uppermost levels of the central nervous system, we also evaluated spinal cord maturation during the TPSD. The maturation of the spinal cord was more advanced in putative female than in male embryos, when sex determination is taking place for each sex; this process starts and ends earlier in male than in female embryos. Together these observations open the possibility that the spinal cord and the innervation derived from it could play a direct role in driving or modulating the process of temperature-dependent gonad sex determination and/or differentiation, particularly in female L. olivacea embryos.

Assessment of Acetylcholinesterase Enzyme (AChE) Activity in the Developing Brain of TSD Lizard, Calotes Versicolor (Daud.)

“…Several lines of research suggest additional roles for cholinergic systems in overall brain homeostasis and plasticity [19]. Further, barring few studies on the topographical distribution of acetylcholinesterase and butyrylcholinesterase activities in the diencephalon, mesencephalon and cerebral hemisphere of the adult lizard, Calotes versicolor [10,11]; in the different parts of the adult brain and cerebral spinal cord of Agama agama [20] and in neuronal fibers of the undifferentiated gonad of Lepidochelis olivacea [21], there are nil reports on the expression/presence of AChE activity in the developing embryos. Further, in the present investigation on the developing brain of C. versicolor a slight increase in AChE activity was noticed that remained relatively more or less the same until gonadal differentiation.…”

Segment‐Specific Decrease of Both Catecholamine Concentration and Acetylcholinesterase Activity Are Accompanied by Nerve Refinement in the Rat Cauda Epididymis During Sexual Maturation

“…Furthermore, various neurotransmitters display a variety of trophic effects, when available during developmental stages, in various organs including the genital tract (Buznikov et al, 1999). Ac- cordingly, published evidence suggests that autonomic innervation might be required for cell differentiation, development, and structural integrity of various male reproductive tract organs (Hodson, 1965;Nagai et al, 1982;Gerendai et al, 1984Gerendai et al, , 1989Bergh et al, 1987;Zhu et al, 1998;Gutiérrez-Ospina et al, 1999;Chow et al, 2000).…”

“…In fact, autonomic innervation is necessary to maintain mature ovary (Burden and Lawrence, 1977;Gerendai et al, 1978;Burden et al, 1981Burden et al, , 1983 and testicular functional and structural integrity (Hodson, 1965;Nagai et al, 1982;Bergh et al, 1987;Lamano-Carvalho et al, 1996;Zhu et al, 1998;Chow et al, 2000). It has also been suggested that autonomic innervation is even required for the process of gonadal sex determination and/or differentiation in some vertebrate species (Gutiérrez-Ospina et al, 1999). Taken together, these observations suggest that the autonomic innervation might control cell differentiation and development throughout the male reproductive tract.…”