Hypothalamic testosterone increase in the male rat at birth

Abstract

In the male rat, a dramatic increase in serum testosterone occurs during the first 2 h of postnatal life. Since the hypothalamus is known to be an important site for sexual differentiation of the brain, this early testosterone surge was a good model to use to study the transfer of serum testosterone to the hypothalamus and cerebral cortex. Endogenous testosterone was measured by radioimmunoassay in the hypothalamus and the cerebral cortex of the foetus and newborn rats during the first 6 h following birth. In the male, hypothalamic testosterone increased between 0 h in utero and 2 h; in the males gonadectomized at 0 h in utero and killed at the age of 2 h, the testosterone surge was abolished, clearly indicating the testicular origin of this hormone in the neonate. The small testosterone increase in the cerebral cortex compared with that in the hypothalamus reflects a preferential uptake of this hormone by the hypothalamus of the newborn. In the female, hypothalamic testosterone slightly decreased between 0 h in utero and 6 h. These results are in agreement with the view that hypothalamic modifications form the basis for some behavioral and physiological changes attributed to the effect of perinatal hormonal stimulation.

Effects of sex steroids on the growth of neuronal processes in neonatal rat hypothalamus‐preoptic area and cerebral cortex in primary culture

“…9"1° In contrast, aromatase activity is very low in the cerebral cortex. 9"15 Rhoda et al 26 reported that hypothalamic testosterone increased during the first 2 h of postnatal life in male rats. The increase was not detected in female rats and in males gonadectomized in utero, and the hypothalamus showed an affinity for testosterone at birth, which was not found in the cerebral cortex.…”

Organizational and activational effects of sex steroids on kisspeptin neuron development

“…This hypothesis, first proposed in the seminal 1959 paper by Phoenix et al [110], has proven to be an essential principle of sexual differentiation, though evidence now indicates that a few sex differences are governed by differences in genes on the sex chromosomes [9]. From late fetal life through early postnatal life, male rodents have significantly higher circulating T of gonadal origin than their female littermates [25; 93; 154] and this T travels to and acts in the brain [119]. It is believed that this circulating perinatal T is critical for directing most sex differences in the brain, though in most cases, it is actually E2, produced locally in the brain by aromatization from the circulating T, that is ultimately responsible for organizing neural sex differences.…”

Hypothalamic control of the male neonatal testosterone surge

“…In most species, the testosterone surge is relatively transient with levels declining within hours [6]; however, in some species such as non-human primates and humans, the elevations in testosterone may persist for many hours to weeks following birth [6,10,11]. The elevation in plasma testosterone quickly increases testosterone levels in the hypothalamus [14,15]. In rats, castration shortly after birth prevents the elevation of testosterone levels in the hypothalamus, indicating that the testes are the primary source of the rise in plasma testosterone [14].…”

“…The elevation in plasma testosterone quickly increases testosterone levels in the hypothalamus [14,15]. In rats, castration shortly after birth prevents the elevation of testosterone levels in the hypothalamus, indicating that the testes are the primary source of the rise in plasma testosterone [14]. Through the aromatization of testosterone by the enzyme P450 aromatase (CYP19A1), oestradiol levels within the hypothalamus are elevated [15].…”