Substance P downregulates basal and gonadotropin-releasing hormone-induced gonadotropin in vitro secretion by pituitary gland of crested newt, Triturus carnifex

Transcriptome analysis reveals pituitary lncRNA, circRNA and mRNA affecting fertility in high- and low-yielding goats

The pituitary gland serves as the central endocrine regulator of growth, reproduction, and metabolism and plays a crucial role in the reproductive process of female animals. Transcriptome analysis was conducted using pituitary gland samples from Leizhou goats with varying levels of fecundity to investigate the effects of long noncoding RNA (lncRNA), circular RNA (circRNA), and mRNA regulation on pituitary hormone secretion and its association with goat fecundity. The analysis aimed to identify lncRNAs, circRNAs, and mRNAs that influence the fertility of Leizhou goats. GO and KEGG enrichment analyses were performed on differentially expressed lncRNAs, circRNAs, and mRNAs and revealed considerable enrichment in pathways, such as regulation of hormone secretion, germ cell development, and gonadotropin-releasing hormone secretion. The pituitary lncRNAs (ENSCHIT00000010293, ENSCHIT00000010304, ENSCHIT00000010306, ENSCHIT00000010290, ENSCHIT00000010298, ENSCHIT00000006769, ENSCHIT00000006767, ENSCHIT00000006921, and ENSCHIT00000001330) and circRNAs (chicirc_029285, chicirc_026618, chicirc_129655, chicirc_018248, chicirc_122554, chicirc_087101, and chicirc_078945) identified as differentially expressed regulated hormone secretion in the pituitary through their respective host genes. Additionally, differential mRNAs (GABBR2, SYCP1, HNF4A, CBLN1, and CDKN1A) influenced goat fecundity by affecting hormone secretion in the pituitary gland. These findings contribute to the understanding of the molecular mechanisms underlying pituitary regulation of fecundity in Leizhou goats.

Sexual Dimorphic Distribution of Hypothalamic Tachykinin1 Cells and Their Innervations to GnRH Neurons in the Zebrafish

Substance P (SP) and neurokinin A (NKA), encoded by TAC1/Tac1 gene are members of the tachykinin family, which exert their neuromodulatory roles in vertebrate reproduction. In mammals, SP and NKA have been shown to regulate gonadotropin-releasing hormone (GnRH) and luteinizing hormone (LH) secretion via kisspeptin neurons. On the other hand, the role of SP/NKA in the regulation of reproduction in non-mammalian vertebrates is not well known. In the present study, we first localized expression of tac1 mRNA in the brain of male and female zebrafish, Danio rerio. Next, using an antibody against zebrafish tachykinin1 (Tac1), we examined the neural association of SP/NKA neural processes with GnRH3 neurons, and with kisspeptin (kiss2) neurons, in the brains of male and female zebrafish. In situ hybridization showed an apparent male-dominant tac1 expression in the ventral telencephalic area, the anterior and posterior parts of the parvocellular preoptic nucleus, and the suprachiasmatic nucleus. On the other hand, there was female-dominant tac1 expression in the ventral periventricular hypothalamus. Confocal images of double-labeled zebrafish Tac1 and GnRH3 showed associations between Tac1-immunoreactive processes and GnRH3 neurons in the ventral telencephalic area. In contrast, there was no apparent proximity of Tac1 processes to kiss2 mRNA-expressing neurons in the hypothalamus. Lastly, to elucidate possible direct action of SP/NKA on GnRH3 or Kiss2 neurons, expression of SP/NKA receptor, tacr1a mRNA was examined in regions containing GnRH3 or Kiss2 neurons by in situ hybridization. Expression of tacr1a mRNA was seen in several brain regions including the olfactory bulb, preoptic area and hypothalamus, where GnRH3 and Kiss2 cells are present. These results suggest that unlike in mammals, Tac1 may be involved in male reproductive functions via direct action on GnRH3 neurons but independent of kisspeptin in the zebrafish.

TAC1 Gene Products Regulate Pituitary Hormone Secretion and Gene Expression in Prepubertal Grass Carp Pituitary Cells

Tachykinin-1 (TAC1) is known to have diverse functions in mammals, but similar information is scarce in fish species. Using grass carp as a model, the pituitary actions, receptor specificity and postreceptor signaling of TAC1 gene products, namely substance P (SP) and neurokinin A (NKA), were examined. TAC1 encoding SP and NKA as well as tachykinin receptors NK1R and NK2R were cloned in the carp pituitary. The newly cloned receptors were shown to be functional with properties similar to mammalian counterparts. In carp pituitary cells, SP and NKA could trigger luteinizing hormone (LH), prolactin (PRL), and somatolactin α (SLα) secretion, with parallel rises in PRL and SLα transcripts. Short-term SP treatment (3 hours) induced LH release, whereas prolonged induction (24 hours) could attenuate LHβ messenger RNA (mRNA) expression. At pituitary cell level, LH, PRL, and SLα regulation by TAC1 gene products were mediated by NK1R, NK2R, and NK3R, respectively. Apparently, SP- and NKA-induced LH and SLα secretion and transcript expression were mediated by adenylyl cyclase/cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA), phospholiphase C (PLC)/inositol 1,4,5-triphosphate/protein kinase C (PKC), and Ca2+/calmodulin (CaM)/CaM-dependent protein kinase-II pathways. The signal transduction for PRL responses was similar, except for the absence of a PKC component. Regarding SP inhibition of LHβ mRNA expression, the cAMP/PKA- and PLC/PKC-dependent (but not Ca2+/CaM-dependent) cascades were involved. These results, as a whole, suggest that TAC1 gene products play a role in LH, PRL, and SLα regulation via overlapping postreceptor signaling coupled to different subtypes of tachykinin receptor expressed in the carp pituitary.

Tachykinins and the hypothalamo-pituitary-gonadal axis: An update

Tachykinins play a critical role in neuroendocrine regulation of reproduction. The best known members of the family are substance P (SP), neurokinin A and neurokinin B. Tachykinins mediate their biological actions through three G protein-coupled receptors, named NK1, NK2, and NK3. SP was suggested to play an important role in the ovulatory process in mammals and humans. Recent findings suggest a role of tachykinins in the aging of the hypothalamo-pituitary-gonadal axis. A high presence of SP was found in the sheep pars tuberalis and evidence indicates that it may have some role in the control of prolactin secretion. The presence of SP was confirmed in Leydig cells of the rat testes of animals submitted to constant light or treated with estrogens. Tachykinins were found to increase the motility of human spermatozoa. Tachykinins were also found to be present in the mouse ovary and more specifically, in the granulose cells. It is possible that tachykinins may play an important role in the ovarian function. NKB has been implicated in the steroid feedback control of GnRH release. Human mutations in the gene encoding this peptide or its receptor (TACR3) lead to a defect in the control of GnRH. A specific subset of neurons in the arcuate nucleus of the hypothalamus, colocalized three neuropeptides, kisspeptin, NKB and dynorphin. This subpopulation of neurons mediates the gonadal hormone feedback control of GnRH secretion. NKB/NK3 signaling plays a role in puberty onset and fertility in humans. This minireview summarizes the recent data about the action of tachykinins on the hypothalamo-pituitary-gonadal axis.

Three-dimensional representation of the neurotransmitter systems of the human hypothalamus: inputs of the gonadotrophin hormone-releasing hormone neuronal system

The gonadotrophin-releasing hormone (GnRH) represents the final common pathway of a neuronal network that integrates multiple external and internal factors to control fertility. Among the many inputs GnRH neurones receive, oestrogens play the most important role. In females, oestrogen, in addition to the negative feedback, also exhibits a positive feedback influence upon the activity and output of GnRH neurones to generate the preovulatory luteinising hormone surge and ovulation. Until recently, the belief has been that the GnRH neurones do not contain oestrogen receptors and that the action of oestrogen upon GnRH neurones is indirect, involving several, oestrogen-sensitive neurotransmitter and neuromodulator systems that trans-synaptically regulate the activity of the GnRH neurones. Although this concept still holds for humans, recent studies indicate that oestrogen receptor-beta is expressed in GnRH neurones of the rat. This review provides three dimensional stereoscopic images of GnRH-immunoreactive (IR) and some peptidergic (neuropeptide Y-, substance P-, beta-endorphin-, leu-enkaphalin-, corticotrophin hormone-releasing- and galanin-IR) and catecholaminergic neurones and the communication of these potential oestrogen-sensitive neuronal systems with GnRH neurones in the human hypothalamus. Because the post-mortem human tissue does not allow the electron microscopic identification of synapses on GnRH neurones, the data presented here are based on light microscopic immunocytochemical experiments using high magnification with oil immersion, semithin sections or confocal microscopy.