Excerpt(with my emphasis): “…recent studies have demonstrated that GnRH neuron dendrites… receive substantial synaptic input, and exhibit postnatal developmental and steroid-dependent plasticity (Campbell et al., 2005, 2009; Cottrell et al., 2006; Chan et al., 2011; Ybarra et al., 2011).”
My comment: However, Ybarra et al., 2011 (state with my emphasis) that. “…spatially selective remodeling of primary dendrites and consolidation of distal GnRH dendritic arbors occurs during postnatal development and is largely independent of T.”
I reiterate: “…selective remodeling… is largely independent of T.” Now, see: Dendritic spikes enhance stimulus selectivity in cortical neurons in vivo and the report that: “All the data pointed to the same conclusion,” Smith said. “The dendrites are not passive integrators of sensory-driven input; they seem to be a computational unit as well.”
Apparently, dendrites associated with visual input and dendrites associated with GnRH neurosecretory neurons act as”mini-neural computers.” Eliminating testosterone (T)-dependent selective remodeling of primary dendrites associated with visual input from further consideration enables an accurate representation of experience-dependent postnatal sexual differentiation. Simply put, the epigenetic effects of olfactory/pheromonal input on GnRH contribute to sexual differentiation sans effects of steroidogenesis.
Sexual differentiation also occurs sans dendrites in many species that adaptively evolved without a nervous system. In other species, food odors and pheromones directly effect the conserved molecular mechanisms of sexual differentiation. Beginning with a yeast model organism in 1996, it became clear that sexual differentiation is nutrient-dependent and pheromone-controlled. See: Signaling Crosstalk: Integrating Nutrient Availability and Sex.
Somewhere along the way from yeast sexual differentiation to human sexual differentiation, others changed the focus from vertebrate GnRH to correlates of GnRH-directed changes in LH/FSH ratios and steroidogenesis. Anyone who argues against the primary role of T or other steroid hormones is dismissed as someone with an unpopular opinion about sexual differentiation.
For example, a co-editor of Frontiers in Neuroendocrinology told me to not bother submitting a follow-up to an article published elsewhere: Nutrient-dependent/pheromone-controlled adaptive evolution: a model. The co-editor said that my lack of primary scientific contributions in this field made it unlikely that my submission would be deemed acceptable. Note, Elekonich and Robinson extended our 1996 model of molecular epigenetics and hormone-organized and hormone-activated mammalian behaviors to invertebrates. Thirteen years later, I had hoped to move forward with more information on nutrient-dependent pheromone-controlled protein folding and alternative splicings exemplified in invertebrates, since no evidence suggests steroid hormones such as T are primarily involved in theromodynamics of controlled sexual differentiation, which is maintained by organism-level thermoregulation.
This link to the laws of physics also brings into play the connection between nutrients and their metabolism to pheromones that epigenetically effect GnRH and immune system function, such as self vs non-self recognition, which is also associated with sexual differentiation and sexual orientation in species from microbes, such as yeasts, to man. In 1996, we (TB)wrote: “Parenthetically it is interesting to note even the yeast Saccharomyces cerevisiae has a gene-based equivalent of sexual orientation (i.e., a-factor and alpha-factor physiologies). These differences arise from different epigenetic modifications of an otherwise identical MAT locus….“
We have now seen the change from the epigenetic effects of olfactory/pheromonal input on GnRH to visual input in the context of “mini-neural computers.” The change occurs after GnRH “dendrons” were described. Therefore, it appears to exemplify how opinions about experience-dependent postnatal steroid-dependent selective remodeling of the brain trump the biological facts. The facts show that “…selective remodeling… is largely independent of T” and that selective remodeling via alternative splicings is largely epigenetically-effected by food odors and pheromones in species from insects to man.