Comparing Postnatal Development of Gonadal Hormones and Associated Social Behaviors in Rats, Mice, and Humans

Abstract

Postnatal development includes dramatic changes in gonadal hormones and the many social behaviors they help regulate, both in rodents and humans. Parental care-seeking is the most salient social interaction in neonates and infants, play and prosocial behaviors are commonly studied in juveniles, and the development of aggression and sexual behavior begins in peripubertal stages but continues through late adolescence into adulthood. Although parental behaviors are shown after reproductive success in adulthood, alloparenting behaviors are actually high in juveniles as well. These behaviors are sensitive to both early-life organizational effects of gonadal hormones and later-life activational regulation. However, changes in circulating gonadal hormones and the display of the previous behaviors over development differ between rats, mice, and humans. These endpoints are of interest to endocrinologist, toxicologists, and neuroscientists because of their relevance to mental health disorders and their vulnerability to effects of endocrine-disrupting chemical exposure. As such, the goal of this mini-review is to succinctly describe and relate the postnatal development of gonadal hormones and social behaviors to each other, over time, and across animal models. Ideally, this will help identify appropriate animal models and age ranges for continued study of both normative development and in contexts of environmental disruption.

Figure 1.

A summary of developmental changes in gonadal hormone concentrations in (A) rats, (B) mice, and (C) humans. Mouse records are incomplete; they may be similar to rat but require continued research. Each hormone [testosterone (T); estradiol (E); progesterone (P)] is indicated by a unique dashed line; sexes are indicated by color (blue for males, red for females). Curves are a best attempt to show overall changes over time relative to a hormone’s maximum concentration during the postnatal period in either sex. (For example, testosterone concentrations in females are shown relative to that of males, not of estradiol concentrations in females.) Not shown are fluctuations in serum estradiol or progesterone during menstrual or estrous cycles in females. Life events such as vaginal opening (VO), preputial separation (PPS), and mature sperm are shown over the developmental stages. I, infant; L. Adolescence, late adolescence; N, neonatal; Peripub., peripubertal.

Figure 2.

A summary of developmental changes in the performance of social behaviors in (A) rats, (B) mice, and (C) humans. Each behavior, including play or sociability (Soc) and aggression (Aggress), is indicated by a unique dashed line; sexes are indicated by color (blue for males, red for females, or purple for both when developmental patterns are indistinct). Curves are a best attempt to show overall changes over time relative to a behavior’s maximum display during postnatal period in either sex. (For example, levels of alloparenting in males is shown relative to that in females, not sex behavior in males.) Life events such as vaginal opening (VO), preputial separation (PPS), and mature sperm are shown over the developmental stages. I, infant; L. Adolescence, late adolescence; N, neonatal; Peripub., peripubertal.