Elsevier

Psychoneuroendocrinology

Volume 91, May 2018, Pages 95-104
Psychoneuroendocrinology

Steroid 5α-reductase 2 deficiency leads to reduced dominance-related and impulse-control behaviors

https://doi.org/10.1016/j.psyneuen.2018.02.007Get rights and content

Highlights

  • 5α-reductase 2 (5αR2) catalyzes the conversion of testosterone into DHT.

  • We found that 5αR2 knockout (KO) mice have reduced dominance-related behaviors.

  • These deficits are accompanied by lower novelty-seeking and risk-taking.

  • 5αR2 KO mice exhibit reduced D2-like receptor binding in the nucleus accumbens.

Abstract

The enzyme steroid 5α-reductase 2 (5αR2) catalyzes the conversion of testosterone into the potent androgen 5α-dihydrotestosterone. Previous investigations showed that 5αR2 is expressed in key brain areas for emotional and socio-affective reactivity, yet the role of this enzyme in behavioral regulation remains mostly unknown. Here, we profiled the behavioral characteristics of 5αR2 heterozygous (HZ) and knockout (KO) mice, as compared with their wild-type (WT) littermates. While male 5αR2 KO mice displayed no overt alterations in motoric, sensory, information-processing and anxiety-related behaviors, they exhibited deficits in neurobehavioral correlates of dominance (including aggression against intruders, mating, and tube dominance) as well as novelty-seeking and risk-taking responses. Furthermore, male 5αR2 KO mice exhibited reduced D2-like dopamine receptor binding in the shell of the nucleus accumbens – a well-recognized molecular signature of social dominance. Collectively, these results suggest that 5αR2 is involved in the establishment of social dominance and its behavioral manifestations. Further studies are warranted to understand how the metabolic actions of 5αR2 on steroid profile may be implicated in social ranking, impulse control, and the modulation of dopamine receptor expression in the nucleus accumbens.

Introduction

The steroid 5α-reductase (5αR) family includes several enzymes catalyzing the saturation of the 4,5-double bond of the A ring of several 3-ketosteroids (Paba et al., 2011; Russell and Wilson, 1994); in particular, 5αRs convert testosterone and progesterone into 5α-dihydroprogesterone (DHP) and 5α-dihydrotestosterone (DHT). These products are further metabolized into neuroactive steroids that play key roles in behavioral regulation, such as 3α,5α-tetrahydroprogesterone (allopregnanolone; AP) and 5α-androstan-3α,17β-diol (3α-diol), respectively (Frye et al., 2001; Martini et al., 1996; Pinna et al., 2003). In addition, 5αRs serve the degradation of glucocorticoids, such as corticosterone and cortisol, into their 5α-reduced derivatives (Carlstedt-Duke et al., 1977).

The two best-characterized members of the 5αR family, type 1 (5αR1) and 2 (5αR2), differ by anatomical distribution and substrate specificity. While 5αR1 is abundantly expressed in the CNS throughout all developmental stages, 5αR2 is the predominant type in the prostate and male accessory sex glands (Paba et al., 2011; Thigpen et al., 1993). In addition, 5αR2 plays a primary role in the conversion of testosterone into the potent androgen DHT (Paba et al., 2011). The brain distribution of 5αR2 was initially reported to be mainly limited to perinatal periods (Poletti et al., 1998). Recent investigations, however, have shown that, in adult rats, 5αR2 is expressed in the output neurons of brain regions involved in emotional and sensorimotor regulation, including the prefrontal and somatosensory cortices, striatum, thalamus, amygdala, hippocampus and cerebellum (Castelli et al., 2013). Furthermore, unlike 5αR1, 5αR2 is not expressed in small neurons and glial cells, pointing to cell-specific patterns in the expression of this enzyme throughout the brain (Aumuller et al., 1996; Eicheler et al., 1994).

This neuroanatomical distribution raises critical questions about the role of 5αR2 in behavioral regulation. A useful experimental approach to grapple with this issue is afforded by the characterization of the neurobehavioral phenotypes associated with the congenital deficiency of this enzyme. In men, non-functional mutations of the gene encoding 5αR2 (SRD5A2) result in Imperato-McGinley syndrome, a rare disorder characterized by a dramatic reduction in DHT synthesis, which leads to ambiguous genitalia at birth (Imperato-McGinley et al., 1974). The affected individuals are often raised as girls, but experience virilization at puberty, with testicular descent, hirsutism and enlargement of the clitoris (Imperato-McGinley and Zhu, 2002). In C57BL/6 mice, the lack of 5αR2 leads to a large reduction of plasma DHT levels, as well as a reduction in prostate size and mating efficiency; however, this mutation does not affect the formation of internal and external genitalia (Mahendroo et al., 2001).

To the best of our knowledge, although 5αR2-deficient individuals do not exhibit any major psychiatric disturbance (Imperato-McGinley et al., 1974), the behavioral and brain-functional changes associated with this mutation have not been fully characterized. Thus, the present study aimed at the investigation of the behavioral repertoire of 5αR2 knockout (KO) mice – in comparison with their heterozygous (HZ) and wild-type (WT) littermates – as well as its neurochemical underpinnings. Given the role of 5αR2 in the conversion of testosterone into the more potent androgen agonist DHT, we speculated that the lack of DHT in 5αR2-deficient mice may compromise some of the behavioral paradigms affected by testosterone and DHT through the activation of androgen receptors. Our studies were particularly focused on behaviors that have been related to testosterone levels and androgen receptor activation, including aggression, dominance, sexual behavior and sensation-seeking (Batrinos, 2012; Campbell et al., 2010; Coccaro et al., 2007; Cunningham et al., 2012; Williamson et al., 2017). Furthermore, since previous work has shown that social dominance is associated with increased D2-D3 receptor binding in the nucleus accumbens (Jupp et al., 2016; Morgan et al., 2002; Nader et al., 2012), we also analyzed the levels of dopamine and dopamine receptor binding in this region.

Section snippets

Animals

The experiments included in this study were performed on adult (3–5-month old), experimentally naïve male 5αR2KO, HZ and WT mice (strain: C57BL/6), obtained from breeding colonies at the Universities of Kansas and Utah. All mice were generated from HZ x HZ crosses. Progenitors were obtained by Dr. Mala Mahendroo (Southwestern University). Unless stated otherwise for specific experimental purposes, all mice were housed in groups of 4–5/cage, with at least 1 mouse/genotype, and had ad libitum

Behavioral characterization of 5αR2 mutant mice

Neither 5αR2 KO nor HZ mice exhibited any overt abnormality in physical appearance and body weight (both across development and in adulthood), as compared with WT littermates. Similarly, the analysis of locomotor activity did not point to differences in any index, including total distance travelled (Fig. 1A), number of low-mobility bouts (Fig. 1B), maximum velocity (Fig. 1C), mean velocity of top ten runs (Fig. 1D), or average distance from the walls (Fig. 1E), an index of thigmotaxis. 5αR2 KO

Discussion

The main results of this study show that 5αR2-deficient mice exhibit a reduction in dominance-related behavioral phenotypes, including aggression against intruders, tube-dominance and mating with receptive females. These changes are not accompanied by sensorimotor deficits or abnormalities in anxiety- or reward-related responses, pointing to a specific importance of 5αR2 in dominance-related behaviors.

Confrontations between WT and 5αR2 KO mice in the tube-dominance test resulted in the

Conflict of interest

The authors declare no conflict of interest.

Contributors

LM monitored data collection, analyzed behavioral data, performed statistical analyses and wrote the first draft of the manuscript. SG and KM performed behavioral tests and performed statistical analyses. MM and SS performed biochemical testing and related statistical analyses. CG, SF and TDP designed the experiments, analyzed data and discussed the paper. MB designed the experiments, supervised the experimental execution, monitored data collection, wrote and revised the manuscript.

Acknowledgments

The present study was supported by the National Institute of Health grants R21 HD HD070611 (to M.B.), R01 MH104603-01 (to M.B.), and F31NS093939 (to L.M.), as well as the Research Grant from the Tourette Syndrome Association (to M.B.). We are grateful to Marco Orru and Hunter Strathman for their help with the execution of the studies.

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