Tuberal hypothalamic expression of the glial intermediate filaments, glial fibrillary acidic protein and vimentin across the turkey hen (Meleagris gallopavo) reproductive cycle: Further evidence for a role of glial structural plasticity in seasonal reproduction

Abstract

Glia regulate the hypothalamic-pituitary-gonadal (HPG) axis in birds and mammals. This is accomplished mechanically by ensheathing gonadotrophin-releasing hormone I (GnRH) nerve terminals thereby blocking access to the pituitary blood supply, or chemically in a paracrine manner. Such regulation requires appropriate spatial associations between glia and nerve terminals. Female turkeys (Meleagris gallavapo) use day length as a primary breeding cue. Long days activate the HPG-axis until the hen enters a photorefractory state when previously stimulatory day lengths no longer support HPG-axis activity. Hens must then be exposed to short days before reactivation of the reproductive axis occurs. As adult hens have discrete inactive reproductive states in addition to a fertile state, they are useful for examining the glial contribution to reproductive function. We immunostained tuberal hypothalami from short and long-day photosensitive hens, plus long-day photorefractory hens to examine expression of two intermediate filaments that affect glial morphology: glial fibrillary acidic protein (GFAP) and vimentin. GFAP expression was drastically reduced in the central median eminence of long day photosensitive hens, especially within the internal zone. Vimentin expression was similar among groups. However, vimentin-immunoreactive fibers abutting the portal vasculature were significantly negatively correlated with GFAP expression in the median eminence, which is consistent with our hypothesis for a reciprocal relationship between GFAP and vimentin expression. It appears that up-regulation of GFAP expression in the central median eminence of turkey hens is associated with periods of reproductive quiescence and that photofractoriness is associated with the lack of a glial cytoskeletal response to long days.

Differences in vocal brain areas and astrocytes between the house wren and the rufous-tailed hummingbird

“…Astrocytes appear to modulate vocal learning and production circuits, a sexually selected trait in many bird species ( Gadagkar et al, 2016 ; Turk et al, 2021 ). There are few studies characterizing astrocytes in vocal areas, which have been conducted on migratory birds and non-passerine birds ( Steinman et al, 2013 ; Carvalho-Paulo et al, 2018 ; Karatu et al, 2020 ). In mammals, astrocytes participate in dopaminergic circuits and motor control, which suggests that these glial cells have an essential role in the modulation of vocal production circuits, which is a sexual characteristic in many bird species ( Gadagkar et al, 2016 ; Turk et al, 2021 ).…”