Sex differences in testosterone reactivity and sensitivity in a non-model gerbil

Area of Science:

• Endocrinology
• Neuroscience
• Animal Behavior

Background:

• Testosterone (T) is crucial for vertebrate development, physiology, and behavior.
• Evidence suggests sex-specific regulation of testosterone, particularly along the hypothalamic-pituitary-gonadal (HPG) axis.
• Baluchistan gerbils (Gerbillus nanus) provide a non-model system to investigate these sex differences.

Purpose of the Study:

• To investigate sex differences in circulating testosterone levels and androgen receptor (AR) mRNA expression in Baluchistan gerbils.
• To explore potential sex-specific regulation points within the HPG axis.
• To understand how social housing conditions influence AR expression.

Main Methods:

• Circulating testosterone levels were measured in field and lab conditions throughout the year.
• Sex differences in testosterone response to gonadotropin-releasing hormone (GnRH) challenge and testosterone implants were assessed.
• Androgen receptor (AR) mRNA expression was quantified in various brain regions using RT-qPCR.
• Genomic sequences for AR and β-actin were identified in Gerbillinae for primer design.

Main Results:

• No significant sex differences in baseline circulating testosterone were found year-round.
• Males showed elevated testosterone after GnRH challenge, while females exhibited higher levels after T implants.
• AR mRNA levels were lower in female gerbils' striatum compared to males.
• Mixed-sex housing increased adrenal AR expression compared to solitary housing.

Conclusions:

• Testosterone regulation in gerbils appears to be sex-specific, potentially due to differential HPG axis regulation.
• Observed differences may reflect evolutionary adaptations in life-history strategies.
• Social environment influences androgen receptor expression, particularly in the adrenal glands.