Brain-Derived Steroids, Behavior and Endocrine Conflicts Across Life History Stages in Birds: A Perspective

Abstract

Biological steroids were traditionally thought to be synthesized exclusively by the adrenal glands and gonads. Recent decades have seen the discovery of neurosteroid production that acts locally within the central nervous system to affect physiology and behavior. These actions include, for example, regulation of aggressive behavior, such as territoriality, and locomotor movement associated with migration. Important questions then arose as to how and why neurosteroid production evolved and why similar steroids of peripheral origin do not always fulfill these central roles? Investigations of free-living vertebrates suggest that synthesis and action of bioactive steroids within the brain may have evolved to regulate expression of specific behavior in different life history stages. Synthesis and secretion of these hormones from peripheral glands is broadcast throughout the organism via the blood stream. While widespread, general actions of steroids released into the blood might be relevant for regulation of morphological, physiological, and behavioral traits in one life history stage, such hormonal release may not be appropriate in other stages. Specific and localized production of bioactive steroids in the brain, but not released into the periphery, could be a way to avoid such conflicts. Two examples are highlighted. First, we compare the control of territorial aggression of songbirds in the breeding season under the influence of gonadal steroids with autumnal (non-breeding) territoriality regulated by sex steroid production in the brain either from circulating precursors such as dehydroepiandrosterone or local central production of sex steroids de novo from cholesterol. Second, we outline the production of 7α-hydroxypregnenolone within the brain that appears to affect locomotor behavior in several contexts. Local production of these steroids in the brain may provide specific regulation of behavioral traits throughout the year and independently of life history stage.

Gonadotropin inhibitory-hormone modulates neurosteroids-synthesizing enzymes expression and aggressive behavior in male sea bass, Dicentrarchus labrax

“…It is not known whether the effects of Gnih on aggressive behavior observed in the present study are mediated by peripheral E2 or, alternatively, by peripheral T converted locally to E2 by Cyp19, which could act on androgen and estrogen receptors present in the sea bass brain. However, reproductive but not aggressive behavior is affected in castrated tilapia, suggesting the involvement of independent central mechanisms in aggressive behavior (Almeida et al, 2014), which could be, at least in part, due to local production of androgens from DHEA into the fish brain (Soma et al, 2008;Wingfield et al, 2018). It is plausible to think that DHEA may also be converted to active neuroandrogens in sea bass brain through the enzymatic activities of 3b-Hsd and 17b-Hsd and exert an influence over aggressive behavior.…”

Hippocampal 7α-Hydroxylated Neurosteroids Are Raised by Training and Bolster Remote Spatial Memory with Increase of the Spine Densities

“…The brain now comes into focus as a steroidogenic organ producing neurosteroids ( Corpéchot et al., 1981 ; Akwa et al., 1992 ). Neurosteroids are implicated in a variety of brain functions such as cognition and behavior ( Baulieu, 2000 ; El Kihel, 2012 ; Tsutsui et al., 2013 ; Wingfield et al., 2018 ), although their biological roles in mammals are not fully understood. Neurosteroids are synthesized from cholesterol, which is transferred to the mitochondria by steroidogenic acute regulatory protein (StAR) as the first step of steroidogenesis ( Figure 1 A).…”

“…Then cholesterol is converted into pregnenolone, a common precursor of neurosteroids, by cholesterol monooxygenase (CYP11A1; also termed P450scc, cholesterol side chain-cleaving enzyme). Pregnenolone is subsequently converted into various bioactive steroids by hydroxylation and/or oxidation ( Akwa et al., 1992 ; Wingfield et al., 2018 ; Morfin and Courchay, 1994 ; Payne and Hales, 2004 ). Cytochrome P450-7b1 (CYP7B1) catalyzes the hydroxylation of pregnenolone at the 7α-position, and therefore CYP7B1 is essential for the biosynthesis of 7α-hydroxypregnenolone (7α-OH-Preg) ( Rose et al., 1997 ).…”

Moulting season corticosterone correlates with winter season bodyweight in an Arctic migrant bird

“…2010, Wingfield et al . 2018). CORT principally modulates homeostasis, energy balance and stress response via release by the hypothalamic–pituitary–adrenal axis in response to changing conditions (Sapolsky et al .…”