Precocious Puberty: Causes, Consequences, Daily Environmental Factors, and the need for Community/Societal Support

Precocious puberty, otherwise described as a group of medical conditions that cause early puberty onset, such as a pre-adolescent boy presenting with adult pattern of penile and testicular enlargement or a pre-adolescent girl presenting with mature breast development and onset of menses. Although the sexual and physical characteristics for this condition are well-described in medical literature, the causes are very rarely known. Nevertheless, it has substantial impacts on children’s lives. This is a review on sexual development, premature sexual development, the social complications children suffer from due to early onset puberty, and the associations with daily environmental exposures as possible influences for developing precocious puberty.

Normal Reproductive function in male mice lacking pituitary kisspeptin receptor.

The anterior pituitary secretion of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) regulate gonadal development, gametogenesis and the secretion of the gonadal steroid hormones. The gonadotroph is primarily regulated by hypothalamic secretion of gonadotropin-releasing hormone (GnRH) from neurons of the rostral hypothalamus and is mediated by GnRH receptor signaling. Kisspeptin (KISS1)/kisspeptin receptor (KISS1R) signaling in GnRH neurons plays an essential role in reproductive function. As the kisspeptin receptor is present in the pituitary, kisspeptin signaling via the Kiss1r may regulate reproductive function at the level of pituitary. Using Cre/Lox technology, we deleted the Kiss1r gene in pituitary gonadotropes (PKiRKO). PKiRKO male and females have normal genital development, puberty onset, and fertility. Females have normal LH, FSH and estradiol while males had significantly increased basal serum FSH levels with no differences in basal serum LH, or testosterone levels. Overall, these findings indicate that the pituitary KISS1R does not play a role in male reproduction.

GABAB receptor antagonism from birth to weaning permanently modifies Kiss1 expression in hypothalamus and gonads in mice

Introduction: The kisspeptin gene Kiss1 is expressed in two hypothalamic areas: anteroventral periventricular nucleus/periventricular nucleus (AVPV/PeN) and arcuate nucleus (ARC), and also in gonads. Evidences suggest that gamma-amino butyric acid B receptors (GABAB) signaling can regulate Kiss1 expression. Here we inhibited GABAB signaling from PND2-PND21 and evaluated the hypothalamic-pituitary-gonadal (HPG) axis. Methods: BALB/c mice were treated on postnatal days 2-21 (PND2-PND21) with CGP55845 (GABAB antagonist), and evaluated in PND21 and adulthood: gene expression (qPCR) in hypothalamus and gonads, hormones by radioimmunoassay, gonad histochemistry (H&E), puberty onset, estrous cycles. Results: At PND21, CGP inhibited Kiss1 and Tac2 and increased Pdyn and Gabbr1 in the ARC of both sexes and decreased Th only in female AVPV/PeN. Serum follicle-stimulating hormone (FSH) and testis weight decreased in CGP-males and puberty onset was delayed. In adults, Kiss1, Tac2, Pdyn, Pgr, Cyp19a1, Gad1 were downregulated, while Gabbr1 was upregulated in the ARC of both sexes. In the AVPV/PeN, Kiss1, Th, Cyp19a1 and Pgr decreased while Gad1 increased in CGP-females, whereas Cyp19a1 increased in CGP-males. Serum FSH increased in CGP-males while prolactin increased in CGP-females. Testosterone and progesterone increased in ovaries from CGP-females, in which Kiss1, Cyp19a1 and Esr1 were downregulated while Hsd3b2 was upregulated, together with increased atretic and decreased ovulatory follicles. Testes from CGP-males showed decreased progesterone, increased Gabbr1, Kiss1, Kiss1r, Esr2 and decreased Cyp19a1 and clear signs of seminiferous tubules atrophy. Conclusion: These results demonstrate that appropriate GABAB signaling during this critical prepubertal period is necessary for the normal development of the HPG axis.

Chronic exposure to ∆9-tetrahydrocannabinol in adolescence decreases social play behaviours

Background: Cannabis use remains a major public health concern, and its use typically begins in adolescence. Chronic administration of ∆9-tetrahydrocannabinol (THC), the main psychoactive compound in cannabis, during adolescence can produce deficits in adult learning and memory, stress reactivity and anxiety. One possible mechanism behind the disruptions in adulthood from adolescent exposure to THC includes changes in social behaviours, such as social play, which has been shown to be critical to socio-cognitive development. Methods: Here, using an established animal model of adolescent THC exposure in male and female Long–Evans rats, we explored the effects of THC on play behaviour during the chronic administration period. Following puberty onset, as indicated by external changes to the genitalia, THC (5mg/kg) was administered for 14 days. Play behaviour was assessed seven days following the onset of the injection period at approximately 1 hour post treatment. The frequency of nape attacks, the likelihood and tactics of defensive behaviour, and pins were scored and analyzed. Results: THC exposure decreased playfulness in adolescent rats including the number of attacks, likelihood of defense and pins compared to control and vehicle treated rats. Conclusion: This suggests that THC suppresses both the attack and defense components of social play. This is an important finding because there is evidence that attack and defense may be mediated by different mechanisms. Furthermore, the effect of THC exposure decreasing playfulness occurred similarly in males and females.

Expression of Kisspeptin 1 in the Brain of the Adult Sea Lamprey Petromyzon marinus

Kisspeptin peptides play major roles in the regulation of reproduction and puberty onset in mammals. While most mammals only have one kisspeptin gene, other jawed vertebrates present two or three genes. Recent data also revealed the presence of two genes in lampreys (jawless vertebrates). However, apart from gene sequence data, there is almost no information on the kisspeptinergic system of lampreys. Here, we report phylogenetic and cluster-based analyses showing that the duplication of the ancestral kisspeptin gene occurred before the separation of jawless and jawed vertebrates. We also studied the expression of the kisspeptin transcripts in the brain of post-metamorphic juveniles and upstream migrating adult sea lampreys. Our in situ hybridization results revealed expression of kisspeptin 1 in hypothalamic neurons, which indicates that the hypothalamic expression of kisspeptins is an ancestral character in vertebrates. We also observed the presence of kisspeptin 1 expressing neurons in the paratubercular (posterior tubercle) nucleus of the diencephalon. This is the first description of the presence of kisspeptin 1 expressing neurons in this brain region in any vertebrate. We did not detect expression of kisspeptin 2 in the juvenile or adult sea lamprey brain with in situ hybridization. Our data provides an anatomical basis to study the role of kisspeptin 1 in the hypothalamic-pituitary system of lampreys and the contribution of diencephalic kisspeptinergic neurons to different circuits of the lamprey brain.

Evidence that pubertal status impacts KNDy neurons in the gilt

Puberty onset is a complex physiological process which enables the capacity for reproduction through increased gonadotropin-releasing hormone (GnRH), and subsequently luteinizing hormone (LH), secretion. While cells that coexpress kisspeptin, neurokinin B (NKB), and dynorphin in the hypothalamic arcuate nucleus (ARC) are believed to govern the timing of puberty, the degree to which KNDy neurons exist and are regulated by pubertal status remains to be determined in the gilt. Hypothalamic tissue from prepubertal and postpubertal, early follicular phase gilts was used to determine the expression of kisspeptin, NKB, and dynorphin within the ARC. Fluorescent in situ hybridization revealed that the majority (> 74%) of ARC neurons that express mRNA for kisspeptin coexpressed mRNA for NKB and dynorphin. There were fewer ARC cells that expressed mRNA for dynorphin in postpubertal gilts compared to prepubertal gilts (P < 0.05), but the number of ARC cells expressing mRNA for kisspeptin or NKB was not different between groups. Within KNDy neurons, mRNA abundance for kisspeptin, NKB, and dynorphin of postpubertal gilts was the same as, less than, and greater than, respectively, prepubertal gilts. Immunostaining for kisspeptin did not differ between prepubertal and postpubertal gilts, but there were fewer NKB immunoreactive fibers in postpubertal gilts compared to prepubertal gilts (P < 0.05). Together, these data reveal novel information about KNDy neurons in gilts and supports the idea that NKB and dynorphin play a role in puberty onset in the female pig.

242 Divergent Selection for Early Puberty Impacts KNDy Neuron Gene Expression in Gilts

Advancing gilt puberty onset is financially desirable for swine production. Neurons in the hypothalamic arcuate nucleus (ARC) that co-express kisspeptin, neurokinin B (NKB), and dynorphin (i.e. KNDy cells) are believed to control gonadotropin-releasing hormone (GnRH) and luteinizing hormone (LH) secretion, but their role in gilt pubertal development is unknown. We hypothesized that puberty onset in gilts would coincide with greater expression of mRNA for kisspeptin and NKB, and less expression of dynorphin. Using fluorescent in situ hybridization (RNAscope), we examined expression of kisspeptin, NKB, and dynorphin in pre- and postpubertal gilts from two genetic lines divergently selected for age at puberty. Prepubertal (n = 6/line) and postpubertal (n = 6/line) gilts were used, and postpubertal animals all received Matrix (0.22% altrenogest) orally for 14 days with tissue collection two days after the final dose. Gilts were euthanized and heads were perfused with 8 L of 4% paraformaldehyde (PFA). Hypothalamic brain tissue was removed, placed in 4% PFA for 24 hrs, and then in 20% sucrose until sectioning (50 µm). Sectioned tissue was stored in cryopreservative at -20°C until RNAscope. Data were analyzed using SAS software (Version 9.4, SAS Institute, Cary NC) with significance declared at P < 0.05. We determined mRNA expression for kisspeptin was not different between groups (P > 0.05). In addition, we found that mRNA expression for NKB was higher in prepubertal gilts compared to postpubertal gilts (P < 0.05) but was not different between lines; mRNA expression was lowest in postpubertal late puberty gilts. Furthermore, total number of dynorphin cells were higher in prepubertal gilts compared to postpubertal gilts (P < 0.05), while individual cell mRNA expression for dynorphin was greatest in postpubertal early puberty gilts (P < 0.05). Taken together, we suggest puberty onset in gilts is more dependent on NKB and dynorphin than kisspeptin.

Kisspeptin, Neurokinin B, and Dynorphin Expression during Pubertal Development in Female Sheep

The neural mechanisms underlying increases in gonadotropin-releasing hormone (GnRH) and luteinizing hormone (LH) secretion that drive puberty onset are unknown. Neurons coexpressing kisspeptin, neurokinin B (NKB), and dynorphin, i.e., KNDy neurons, are important as kisspeptin and NKB are stimulatory, and dynorphin inhibitory, to GnRH secretion. Given this, we hypothesized that kisspeptin and NKB expression would increase, but that dynorphin expression would decrease, with puberty. We collected blood and hypothalamic tissue from ovariectomized lambs implanted with estradiol at five, six, seven, eight (puberty), and ten months of age. Mean LH values and LH pulse frequency were the lowest at five to seven months, intermediate at eight months, and highest at ten months. Kisspeptin and NKB immunopositive cell numbers did not change with age. Numbers of cells expressing mRNA for kisspeptin, NKB, or dynorphin were similar at five, eight, and ten months of age. Age did not affect mRNA expression per cell for kisspeptin or NKB, but dynorphin mRNA expression per cell was elevated at ten months versus five months. Thus, neither KNDy protein nor mRNA expression changed in a predictable manner during pubertal development. These data raise the possibility that KNDy neurons, while critical, may await other inputs for the initiation of puberty.