Spatially Selective, Testosterone-Independent Remodeling of Dendrites in Gonadotropin-Releasing Hormone (GnRH) Neurons Prepubertally in Male Rats

Abstract

Adult GnRH neurons exhibit a stereotypic morphology with a small soma, single axon, and single dendrite arising from the soma with little branching. The adult morphology of GnRH neurons in mice reflects an anatomical consolidation of dendrites over postnatal development. We examined this issue in rat GnRH neurons with biocytin filling in live hypothalamic slices from infant males, as adult littermates and in gonad-intact males, castrated males, and in males with one of three levels of testosterone (T) treatment. Somatic area and total dendritic length were significantly greater in infant males than in adults. Moreover, total numbers of dendrite branches were greater in infant males as compared with adults. The number of higher order branches and the lengths of higher order branches were also greater in infant males than in adults. Most interestingly, in adults a single dendrite arose from the somata, consistently at 180° from the axon. In contrast, prepubertal animals had an average of 2.2 ± 0.2 primary dendrites arising from somata (range, one to seven primary dendrites). Angles relative to the axon at which dendrites in prepubertal males emanated from GnRH somata were highly variable. Castration at 25 d of age and castration at 25 d of age with one of three levels of T treatment did not influence morphological parameters when GnRH neurons were examined between 40 d and 48 d of age. Thus, a spatially selective remodeling of primary dendrites and consolidation of distal GnRH dendritic arbors occurs during postnatal development and is largely independent of T.

Opposite-sex housing reactivates the declining GnRH system in aged transgenic male mice with FGF signaling deficiency

“…In dnFGFR males, OS housing induces a significant shift of GnRH neuronal morphology toward a more mature distribution by PND100. This indicates that OS housing is not merely important for the rescue of number of GnRH neurons; it also participates in their anatomical remodeling, which correlates with GnRH neurons' ability to receive excitatory inputs (11,62). The differences between the genotypes disappeared by PND200, suggesting the remodeling defect in dnFGFR mice represents only a delay, not an absence, of dendritic pruning.…”

“…With regard to the former, the postnatal changes in GnRH neuronal morphology have been correlated with the functional maturation of the GnRH system (11,62). During puberty, dendritic pruning increases the proportion of unipolar neurons and decreases that of complex neurons (11,62).…”

Initiation and Propagation of Action Potentials in Gonadotropin-Releasing Hormone Neuron Dendrites

“…Remarkably, the location of the GnRH neuron axon is presently unclear. As the processes that emanate from GnRH neuron soma often become thin in diameter, some laboratories have defined the thinnest process as the axon (Ybarra et al, 2011). However, previous work from our laboratory has demonstrated that, when cells are filled with biocytin in brain slices and post hoc reconstructed, processes containing dendritic spines and a dendritic morphology can easily be identified, but not axon-like processes (Campbell et al, 2005(Campbell et al, , 2009Cottrell et al, 2006;Herde et al, 2011).…”

“…They synthesize GnRH peptide that is released from their nerve terminals in the median eminence to regulate luteinizing and folliclestimulating hormone release from the anterior pituitary and thus reproductive function (Moenter et al, 2003;Herbison, 2006). In adult mice, GnRH neurons are most commonly unipolar or bipolar with very long, unbranched dendritic processes (Campbell et al, 2005;Ybarra et al, 2011). While the long thin processes emanating from the cell body of most GnRH neurons possess spines and have a dendritic morphology (Jennes et al, 1985;Wray and Hoffman, 1986;Campbell et al, 2005Campbell et al, , 2009Cottrell et al, 2006), the origin of the GnRH neuron axon remains undetermined.…”

Multitasking in Gonadotropin-Releasing Hormone Neuron Dendrites

“…Morphological reconstructions of GnRH neurons in acute brain slices have revealed that these dendrites project for large distances in the brain [10,11,12]. Further studies have revealed that this simple dendritic morphology is acquired over the course of puberty, since the morphology of GnRH neurons reconstructed from rodents before puberty is significantly more complex, with many more dendritic branches [13,14]. …”