SERRANO-VELEZ, J.L.*; ROSA-MOLINAR, Eduardo; University of Puerto Rico – Rio Piedras; University of Puerto Rico – Rio Piedras: Dendritic arbors of secondary motor neurons show scaled growth during anterior transposition of the Western Mosquitofish, Gambusia affinis affinis sexually dimorphic anal fin: a study of morphometric properties.
In the present study, we examined the structural and organizational changes of the dendritic arbors of secondary motor neurons (SMN) resulting from the anterior transposition of the sexually dimorphic anal fin and its appendicular support in G. a. affinis. This anterior transposition results in a radical change in the teleost axial skeletal formulae and nervous system. 3000 MW Texas Red Amino Dextran (TDA) dye coated filter paper strips were inserted into the rhizotomized ventral nerves within the spinal cord (SP) and allowed to transport 8 hrs. Each spinal cord segment, defined by the presence of a ventral root, is roughly 100 um long and 60 um in diameter and corresponds in length to a myotomal segment. TDA was found to be an excellent dye for retrograde labeling of secondary motor neurons, including their entire soma, dendritic branching points, patterning, and elongation within the lateral motor column (LMC) of female and male G. a. affinis spinal cord. TDA whole-mount preparations of the SP combined with fractal analysis showed that the SMN dendritic arborization in this region of transposition (vertebrae 14-16) is more complex in males in terms of branching and lengthening than it is in the same region in females. Primary and secondary motor neurons within the MC and LMC anterior to the 14th nerve of the 14th vertebrae and spinal cord segments posterior to the 16th nerve of the 16th vertebrae in female and male G. a. affinis are similar. The results of this study show that SMN radically reorganize their dendritic structure and organization and this is probably related to the novel function for teleost, internal fertilization. Supported by NSF/IBN-0091120 and NIH/NS390405-06.