The gonadotropin-releasing hormone cell-specific element is required for normal puberty and estrous cyclicity

The Impact of Methylphenidate on Pubertal Maturation and Bone Age in ADHD Children and Adolescents: Results from the ADHD Drugs Use Chronic Effects (ADDUCE) Project

OBJECTIVE

The short-term safety of methylphenidate (MPH) has been widely demonstrated; however the long-term safety is less clear. The aim of this study was to investigate the safety of MPH in relation to pubertal maturation and to explore the monitoring of bone age.

METHOD

Participants from ADDUCE, a two-year observational longitudinal study with three parallel cohorts (MPH group, no-MPH group, and a non-ADHD control group), were compared with respect to Tanner staging. An Italian subsample of medicated-ADHD was further assessed by the monitoring of bone age.

RESULTS

The medicated and unmedicated ADHD groups did not differ in Tanner stages indicating no higher risk of sexual maturational delay in the MPH-treated patients. The medicated subsample monitored for bone age showed a slight acceleration of the bone maturation after 24 months, however their predicted adult height remained stable.

CONCLUSION

Our results do not suggest safety concerns on long-term treatment with MPH in relation to pubertal maturation and growth.

Daily GnRH agonist treatment effectively delayed puberty in female rats without long-term effects on sexual behavior or estrous cyclicity

The present study examined the long-term effects of suppressing puberty with a GnRH agonist on reproductive physiology and behavior in female rats. We have recently reported that administration of the GnRH agonist leuprolide acetate (25 µg/kg) daily between postnatal day (PD) 25-50 delayed puberty and disrupted the development of copulatory behavior and sexual motivation in male rats. However, pilot data from our lab suggest that this low dose of leuprolide acetate (25 µg/kg) was not high enough to significantly delay puberty in female rats. Therefore, we injected female Long-Evans rats with leuprolide acetate at a higher dose (50 µg/kg) or 0.9% sterile saline, daily , starting on PD 25 and ending on PD 50. Vaginal opening was monitored daily starting on PD 30 for signs of pubertal onset and first estrous cycle. In addition, we measured estrous cyclicity starting approximately 2 weeks after the last injection of leuprolide (∼PD 64). Immediately after monitoring estrous cyclicity, the female rats were mated on their first day in behavioral estrus using the partner-preference paradigm, with and without physical contact (PD 95-110). We found that this dose of leuprolide (50 µg/kg) significantly delayed puberty; however, neither estrous cyclicity nor sexual motivation was significantly affected by periadolescent exposure to leuprolide. Together with our findings in male rats, these results add to our understanding of the developmental effects of chemically suppressing puberty in rats.

The Requirement of Ubiquitin C-Terminal Hydrolase L1 (UCHL1) in Mouse Ovarian Development and Fertility †

Ubiquitin C-Terminal Hydrolase L1 (UCHL1) is a de-ubiquitinating enzyme enriched in neuronal and gonadal tissues known to regulate the cellular stores of mono-ubiquitin and protein turnover. While its function in maintaining proper motor neuron function is well-established, investigation into its role in the health and function of reproductive processes is only just beginning to be studied. Single-cell-sequencing analysis of all ovarian cells from the murine perinatal period revealed that Uchl1 is very highly expressed in the developing oocyte population, an observation which was corroborated by high levels of oocyte-enriched UCHL1 protein expression in oocytes of all stages throughout the mouse reproductive lifespan. To better understand the role UCHL1 may be playing in oocytes, we utilized a UCHL1-deficient mouse line, finding reduced number of litters, reduced litter sizes, altered folliculogenesis, morphologically abnormal oocytes, disrupted estrous cyclicity and apparent endocrine dysfunction in these animals compared to their wild-type and heterozygous littermates. These data reveal a novel role of UCHL1 in female fertility as well as overall ovarian function, and suggest a potentially essential role for the ubiquitin proteasome pathway in mediating reproductive health. Summary sentence: Ubiquitin C-Terminal Hydrolase L1 (UCHL1) is required for proper ovarian folliculogenesis, estrous cyclicity, and fertility in the female mouse.

Development of the gonadotropin-releasing hormone system

This review summarizes the current understanding of the development of the neuroendocrine gonadotropin-releasing hormone (GnRH) system, including discussion on open questions regarding (1) transcriptional regulation of the Gnrh1 gene; (2) prenatal development of the GnRH1 system in rodents and humans; and (3) paracrine and synaptic communication during migration of the GnRH cells.

Thimet Oligopeptidase (EC 3.4.24.15) Key Functions Suggested by Knockout Mice Phenotype Characterization

Thimet oligopeptidase (THOP1) is thought to be involved in neuropeptide metabolism, antigen presentation, neurodegeneration, and cancer. Herein, the generation of THOP1 C57BL/6 knockout mice (THOP1^−/−) is described showing that they are viable, have estrus cycle, fertility, and a number of puppies per litter similar to C57BL/6 wild type mice (WT). In specific brain regions, THOP1^-/- exhibit altered mRNA expression of proteasome beta5, serotonin 5HT2a receptor and dopamine D2 receptor, but not of neurolysin (NLN). Peptidomic analysis identifies differences in intracellular peptide ratios between THOP1^-/- and WT mice, which may affect normal cellular functioning. In an experimental model of multiple sclerosis THOP1^-/- mice present worse clinical behavior scores compared to WT mice, corroborating its possible involvement in neurodegenerative diseases. THOP1^-/- mice also exhibit better survival and improved behavior in a sepsis model, but also a greater peripheral pain sensitivity measured in the hot plate test after bradykinin administration in the paw. THOP1^-/- mice show depressive-like behavior, as well as attention and memory retention deficits. Altogether, these results reveal a role of THOP1 on specific behaviors, immune-stimulated neurodegeneration, and infection-induced inflammation.

Impairments in the reproductive axis of female mice lacking estrogen receptor β in GnRH neurons

The effect of estrogen on the differentiation and maintenance of reproductive tissues is mediated by two nuclear estrogen receptors (ERs), ERα, and ERβ. Lack of functional ERα and ERβ genes in vivo significantly affects reproductive function; however, the target tissues and signaling pathways in the hypothalamus are not clearly defined. Here, we describe the generation and reproductive characterization of a complete-ERβ KO (CERβKO) and a GnRH neuron-specific ERβKO (GERβKO) mouse models. Both ERβKO mouse models displayed a delay in vaginal opening and first estrus. Hypothalamic gonadotropin-releasing hormone (GnRH) mRNA expression levels in both ERβKO mice were similar to control mice; however female CERβKO and GERβKO mice had lower basal and surge serum gonadotropin levels. Although a GnRH stimulation test in both female ERβKO models showed preserved gonadotropic function in the same animals, a kisspeptin stimulation test revealed an attenuated response by GnRH neurons, suggesting a role for ERβ in normal GnRH neuron function. No alteration in estrogen-negative feedback was observed in either ERβKO mouse models after ovariectomy and estrogen replacement. Further, abnormal development of ovarian follicles with low serum estradiol levels and impairment of fertility were observed in both ERβKO mouse models. In male ERβKO mice, no differences in the timing of pubertal onset or serum luteinizing hormone and follicle-stimulating hormone levels were observed as compared with controls. Taken together, these data provide in vivo evidence for a role of ERβ in GnRH neurons in modulating puberty and reproduction, specifically through kisspeptin responsiveness in the female hypothalamic-pituitary-gonadal axis.

Circadian disruption of food availability significantly reduces reproductive success in mice

Circadian disruptions impair reproductive health in human populations and in animal models. We tested the hypothesis that mistimed food, a common disruptive feature of shift work, impairs reproductive success in mice. Male and female mPer2^Luc mice on a C57BL/6 background were fed during the light or dark phase in two experiments. Food-induced internal misalignment of the liver clock was verified by in vivo bioluminescence in anesthetized mice in both experiments. In Experiment 1, food-restricted pairs were monitored for litters for 18 weeks. In the light-fed group, birth of the first litter was significantly delayed, and total reproductive output was significantly reduced by 38%. In Experiment 2, estrous cycling was monitored for 3 weeks, and then after pairing, copulatory plugs, pregnancy, litter sizes, and uterine implantation sites were measured. Fewer light-fed females birthed litters (25% versus 73%). This was attributable to a difference in behavior as mating success was significantly reduced in light-fed mice: 42% were observed with a copulatory plug compared to 82% for dark-fed mice. The proportion of mice displaying uterine implantation sites was the same as the proportion observed with copulatory plugs, suggesting no deficit in initiating pregnancy after mating. Estrous cycling and pregnancy maintenance did not differ between the groups. We conclude that mistimed feeding inhibits reproduction in mice by reducing successful mating behavior.

Multiple exposures of sevoflurane during pregnancy induces memory impairment in young female offspring mice

Background

Earlier studies have reported conflicting results regarding long-term behavioral consequences after anesthesia during the fetal period. Previous studies also suggest several factors that may explain such conflicting data. Thus, we examined the influence of age and sex on long-term behavioral consequences after multiple sevoflurane exposures during the fetal period.

Methods

C57BL/6J pregnant mice received oxygen with or without sevoflurane for 2 hours at gestational day (GD) 14-16. Offspring mice were subjected to behavioral assays for general activity (open field test), learning, and memory (fear chamber test) at postnatal day 30–35.

Results

Multiple sevoflurane exposures at GD 14–16 caused significant changes during the fear chamber test in young female offspring mice. Such changes did not occur in young male offspring mice. However, general activity was not affected in both male and female mice.

Conclusions

Multiple sevoflurane exposures in the second trimester of pregnancy affects learning and memory only in young female mice. Further studies focusing on diverse cognitive functions in an age-, sex-dependent manner may provide valuable insights regarding anesthesia-induced neurotoxicity.

The Methylcytosine Dioxygenase Ten-Eleven Translocase-2 (tet2) Enables Elevated GnRH Gene Expression and Maintenance of Male Reproductive Function

Reproduction depends on the establishment and maintenance of elevated GnRH neurosecretion. The elevation of primate GnRH release is accompanied by epigenetic changes. Specifically, cytosine residues within the GnRH gene promoter are actively demethylated, whereas GnRH mRNA levels and peptide release rise. Whether active DNA demethylation has an impact on GnRH neuron development and consequently reproductive function remains unknown. In this study, we investigated whether ten-eleven translocation (tet) enzymes, which initiate the process of active DNA demethylation, influence neuronal function and reproduction. We found that tet2 expression increases with age in the developing mouse preoptic area-hypothalamus and is substantially higher in a mature (GT1-7) than an immature (GN11) GnRH cell line. GnRH mRNA levels and mean GnRH peptide release elevated after overexpression of tet2 in GN11 cells, whereas CRISPR/cas9-mediated knockdown of tet2 in GT1-7 cells led to a significant decline in GnRH expression. Manipulations of tet2 expression altered tet2 genome binding and histone 3 lysine 4 trimethylation abundance at the GnRH promoter. Mice with selective disruption of tet2 in GnRH neurons (GnRH-specific tet2 knockout mice) exhibited no sign of altered pubertal timing in either sex, although plasma LH levels were significantly lower, and fecundity was altered specifically in adult male GnRH-specific tet2 knockout animals, indicating that tet2 may participate in the maintenance GnRH neuronal function. Exposure to bisphenol A, an environmental contaminant that alters GnRH neuron activity, caused a shift in tet2 subcellular localization and a decrease in histone 3 lysine 4 trimethylation abundance at the GnRH promoter. Finally, evaluation of tet2 protein interactions in GT1-7 cells suggests that the influence of tet2 on neuronal function are not limited to nuclear mechanisms but could depend on mitochondrial function, and RNA metabolism. Together, these studies implicate tet2 in the maintenance of GnRH neuronal function and neuroendocrine control of male reproduction.

A Novel Gonadotropin-Releasing Hormone 1 (Gnrh1) Enhancer-Derived Noncoding RNA Regulates Gnrh1 Gene Expression in GnRH Neuronal Cell Models

Gonadotropin-releasing hormone (GnRH), a neuropeptide released from a small population of neurons in the hypothalamus, is the central mediator of the hypothalamic-pituitary-gonadal axis, and is required for normal reproductive development and function. Evolutionarily conserved regulatory elements in the mouse, rat, and human Gnrh1 gene include three enhancers and the proximal promoter, which confer Gnrh1 gene expression specifically in GnRH neurons. In immortalized mouse hypothalamic GnRH (GT1-7) neurons, which show pulsatile GnRH release in culture, RNA sequencing and RT-qPCR revealed that expression of a novel long noncoding RNA at Gnrh1 enhancer 1 correlates with high levels of GnRH mRNA expression. In GT1-7 neurons, which contain a transgene carrying 3 kb of the rat Gnrh1 regulatory region, both the mouse and rat Gnrh1 enhancer-derived noncoding RNAs (GnRH-E1 RNAs) are expressed. We investigated the characteristics and function of the endogenous mouse GnRH-E1 RNA. Strand-specific RT-PCR analysis of GnRH-E1 RNA in GT1-7 cells revealed GnRH-E1 RNAs that are transcribed in the sense and antisense directions from distinct 5’ start sites, are 3’ polyadenylated, and are over 2 kb in length. These RNAs are localized in the nucleus and have a half-life of over 8 hours. In GT1-7 neurons, siRNA knockdown of mouse GnRH-E1 RNA resulted in a significant decrease in the expression of the Gnrh1 primary transcript and Gnrh1 mRNA. Over-expression of either the sense or antisense mouse GnRH-E1 RNA in immature, migratory GnRH (GN11) neurons, which do not express either GnRH-E1 RNA or GnRH mRNA, induced the transcriptional activity of co-transfected rat Gnrh1 gene regulatory elements, where the induction requires the presence of the rat Gnrh1 promoter. Together, these data indicate that GnRH-E1 RNA is an inducer of Gnrh1 gene expression. GnRH-E1 RNA may play an important role in the development and maturation of GnRH neurons.

FBXW12, a novel F box protein-encoding gene, is deleted or methylated in some cases of epithelial ovarian cancer

Epithelial ovarian cancer is one of the most lethal of gynecological malignancies. Due to its lack of early symptoms, detection usually occurs when the tumor is no longer confined to the ovary. We previously identified Fbxw15, a gene encoding an F-box protein in the mouse ovary, and showed that its expression is developmentally regulated. Here we report the molecular analysis of its human homologue, FBXW12 in epithelial ovarian tumors. To search for FBXW12 gene mutations, we PCR-amplified and sequenced the coding region of FBXW12, the gene's 5-untranslated region and the proximal promoter in each of 30 EOC tumors. Promoter methylation was determined by DNA bisulfite conversion, followed by methylation specific PCR. FBXW12 intracellular localization was identified by means of immunohistochemistry. A complete deletion of the gene's coding region, the 5'-UTR and the proximal promoter, was observed in 3 EOC samples. Eight of the remaining 27, had a deletion of the 5'-UTR, and the proximal promoter. FBXW12 mRNA was detected in 2 of the 19 samples without deletions. The methylation specific PCR results demonstrated CpGs methylation in the FBXW12 proximal promoter. Immunohistochemistry assay revealed that within the normal ovary, FBXW12 has an oocyte specific expression, whereas in EOC samples it is present in the ovarian surface epithelium. Our results indicate that the FBXW12 gene is deleted in approximately ten percent of the EOC cases studied; such deletions comprised either the FBXW12 promoter or the mRNA-encoding region. Moreover, FBXW12 could be epigenetically silenced by CpGs methylation in some of these EOC cases.

Insulin receptor signaling in the GnRH neuron plays a role in the abnormal GnRH pulsatility of obese female mice

Infertility associated with obesity is characterized by abnormal hormone release from reproductive tissues in the hypothalamus, pituitary, and ovary. These tissues maintain insulin sensitivity upon peripheral insulin resistance. Insulin receptor signaling may play a role in the dysregulation of gonadotropin-releasing hormone (GnRH) secretion in obesity, but the interdependence of hormone secretion in the reproductive axis and the multi-hormone and tissue dysfunction in obesity hinders investigations of putative contributing factors to the disrupted GnRH secretion. To determine the role of GnRH insulin receptor signaling in the dysregulation of GnRH secretion in obesity, we created murine models of diet-induced obesity (DIO) with and without intact insulin signaling in the GnRH neuron. Obese control female mice were infertile with higher luteinizing hormone levels and higher GnRH pulse amplitude and total pulsatile secretion compared to lean control mice. In contrast, DIO mice with a GnRH specific knockout of insulin receptor had improved fertility, luteinizing hormone levels approaching lean mice, and GnRH pulse amplitude and total secretion similar to lean mice. Pituitary responsiveness was similar between genotypes. These results suggest that in the obese state, insulin receptor signaling in GnRH neurons increases GnRH pulsatile secretion and consequent LH secretion, contributing to reproductive dysfunction.

Kisspeptin cell-specific PI3K signaling regulates hypothalamic kisspeptin expression and participates in the regulation of female fertility

Hypothalamic kisspeptin neurons integrate and translate cues from the internal and external environments that regulate gonadotropin-releasing hormone (GnRH) secretion and maintain fertility in mammals. However, the intracellular signaling pathways utilized to translate such information into changes in kisspeptin expression, release, and ultimately activation of the kisspeptin-receptive GnRH network have not yet been identified. PI3K is an important signaling node common to many peripheral factors known to regulate kisspeptin expression and GnRH release. We investigated whether PI3K signaling regulates hypothalamic kisspeptin expression, pubertal development, and adult fertility in mice. We generated mice with a kisspeptin cell-specific deletion of the PI3K catalytic subunits p110α and p110β (kiss-p110α/β-KO). Using in situ hybridization, we examined Kiss1 mRNA expression in gonad-intact, gonadectomized (Gdx), and Gdx + steroid-replaced mice. Kiss1 cell number in the anteroventral periventricular hypothalamus (AVPV) was significantly reduced in intact females but not in males. In contrast, compared with WT and regardless of steroid hormone status, Kiss1 cell number was lower in the arcuate (ARC) of kiss-p110α/β-KO males, but it was unaffected in females. Both intact Kiss-p110α/β-KO males and females had reduced ARC kisspeptin-immunoreactive (IR) fibers compared with WT animals. Adult kiss-p110α/β-KO males had significantly lower circulating luteinizing hormone (LH) levels, whereas pubertal development and fertility were unaffected in males. Kiss-p110α/β-KO females exhibited a reduction in fertility despite normal pubertal development, LH levels, and estrous cyclicity. Our data show that PI3K signaling is important for the regulation of hypothalamic kisspeptin expression and contributes to normal fertility in females.

The regulation of reproductive neuroendocrine function by insulin and insulin-like growth factor-1 (IGF-1)

The mammalian reproductive hormone axis regulates gonadal steroid hormone levels and gonadal function essential for reproduction. The neuroendocrine control of the axis integrates signals from a wide array of inputs. The regulatory pathways important for mediating these inputs have been the subject of numerous studies. One class of proteins that have been shown to mediate metabolic and growth signals to the CNS includes Insulin and IGF-1. These proteins are structurally related and can exert endocrine and growth factor like action via related receptor tyrosine kinases. The role that insulin and IGF-1 play in controlling the hypothalamus and pituitary and their role in regulating puberty and nutritional control of reproduction has been studied extensively. This review summarizes the in vitro and in vivo models that have been used to study these neuroendocrine structures and the influence of these growth factors on neuroendocrine control of reproduction.

Agouti-related peptide plays a critical role in leptin's effects on female puberty and reproduction

Deficient leptin signaling causes infertility via reduced activity of GnRH neurons, causing a hypogonadal state in both rodents and humans. Because GnRH neurons do not express leptin receptors, leptin's effect on GnRH neurons must be indirect. Neurons within the hypothalamic arcuate nucleus that coexpress AGRP and NPY are considered to be important intermediate neurons involved in leptin regulation of GnRH neurons. Previously, we reported that the absence of AGRP and haploinsufficiency of MC4R in leptin receptor mutant (Lepr(db/db)) females result in restoration of fertility and lactation despite the persistence of obesity and insulin resistance. The overarching hypothesis in the present study is that the absence or reduction of leptin's inhibition of AGRP/NPY neurons leads to suppression of GnRH release in cases of leptin signaling deficiency. Since TAC2 (NKB)-TAC3R signaling plays a role in puberty maturation and is modulated by metabolic status, the other aim of this study is to test whether TAC2/NKB neurons in ARC regulated by melanocortinergic signals herein affect leptin's action on puberty and reproduction. Our data showed that AGRP deficiency in Lepr(db/db) females restores normal timing of vaginal opening and estrous cycling, although uterine weight gain and mammary gland development are morphologically delayed. Nonetheless, Agrp(-/-) Lepr(db/db) females are fertile and sustain adequate nutrition of pups with lactation to weaning age. AGRP deficiency results in advanced vaginal opening in wild-type female mice. The postpubertal increase in hypothalamic TAC2 mRNA was not observed in Lepr(db/db) females, whereas AGRP deficiency restored it in Lepr(db/db) females. Additionally, MC4R activation with MTII induced FOS expression in TAC2 neurons, supporting the concept of melanocortinergic regulation of TAC2 neurons. These studies suggest that AGRP imposes an inhibitory effect on puberty and that TAC2 neurons may transmit melanocortinergic inhibition of GnRH neurons.

Genetic mechanisms mediating kisspeptin regulation of GnRH gene expression

Kisspeptins (Kiss) have been shown to be key components in the regulation of gonadotropin-releasing hormone (GnRH) secretion. In vitro studies have demonstrated an increase in GnRH gene expression by Kiss suggesting regulation of GnRH at both the secretory and pretranslational levels. Here, we define genetic mechanisms that mediate Kiss action on target gene expression. In vitro, sequential deletions of the mouse GnRH (mGnRH) gene promoter fused to the luciferase (LUC) reporter gene localized at kisspeptin-response element (KsRE) between -3446 and -2806 bp of the mGnRH gene. In vivo, transgenic mice bearing sequential deletions of the mGnRH gene promoter linked to the LUC reporter localized an identical KsRE. To define the mechanism of regulation, Kiss was first shown to induce nucleosome-depleted DNA within the KsRE, and a potential binding site for the transcription factor, Otx-2, was revealed. Furthermore, increased Otx-2 mRNA, protein, and binding to the KsRE after Kiss treatment were demonstrated. In conclusion, this work identified elements in GnRH-neuronal cell lines and in transgenic mice that mediate positive regulation of GnRH by Kiss. In addition, we show for the first time that Otx-2 is regulated by Kiss, and plays a role in mediating the transcriptional response of mGnRH gene.

Neurokinin B causes acute GnRH secretion and repression of GnRH transcription in GT1-7 GnRH neurons

Genetic studies in human patients with idiopathic hypogonadotropic hypogonadism (IHH) identified mutations in the genes that encode neurokinin B (NKB) and the neurokinin 3 receptor (NK3R). However, determining the mechanism whereby NKB regulates gonadotropin secretion has been difficult because of conflicting results from in vivo studies investigating the luteinizing hormone (LH) response to senktide, a NK3R agonist. NK3R is expressed in a subset of GnRH neurons and in kisspeptin neurons that are known to regulate GnRH secretion. Thus, one potential source of inconsistency is that NKB could produce opposing direct and indirect effects on GnRH secretion. Here, we employ the GT1-7 cell model to elucidate the direct effects of NKB on GnRH neuron function. We find that GT1-7 cells express NK3R and respond to acute senktide treatment with c-Fos induction and increased GnRH secretion. In contrast, long-term senktide treatment decreased GnRH secretion. Next, we focus on the examination of the mechanism underlying the long-term decrease in secretion and determine that senktide treatment represses transcription of GnRH. We further show that this repression of GnRH transcription may involve enhanced c-Fos protein binding at novel activator protein-1 (AP-1) half-sites identified in enhancer 1 and the promoter, as well as chromatin remodeling at the promoter of the GnRH gene. These data indicate that NKB could directly regulate secretion from NK3R-expressing GnRH neurons. Furthermore, whether the response is inhibitory or stimulatory toward GnRH secretion could depend on the history or length of exposure to NKB because of a repressive effect on GnRH transcription.

Cell-type specific expression of oxytocin and vasopressin genes: an experimental odyssey

The supraoptic nucleus (SON) is a particularly good model for the study of cell-type specific gene expression because it contains two distinct neuronal phenotypes, the oxytocin (OT) and vasopressin (AVP) synthesising magnocellular neurones (MCNs). The MCNs are found in approximately equal numbers and selectively express either the OT or the AVP gene in approximately 97% of the MCN population in the SON. An unresolved issue has been to determine what mechanisms are responsible for the highly selective regulation of the cell-type specific expression of OT and AVP genes in the MCNs. Previous attempts to address this question have used various bioinformatic and molecular approaches, which included using heterologous cell lines to study the putative cis-elements in the OT and AVP genes, and the use of OT and/or AVP transgenes in transgenic rodents. The data from all of the above studies identified a region < 0.6 kbp upstream of OT exon I and approximately 3 kb upstream of AVP exon I as being sufficient to produce cell-specific expression of the OT and AVP genes, respectively, although they failed to identify the specific cis-domains responsible for the MCN-specific gene expression. An alternative experimental approach to perform promoter deletion analysis in vivo (i.e. to use stereotaxic viral vector gene transfer into the SON to further dissect the cis-elements in the OT and AVP genes) will be described here. This in vivo method uses adeno-associated viral (AAV) vectors expressing OT-promoter deletion constructs and utilises the enhanced green fluorescent protein (EGFP) as the reporter. The AAV constructs are stereotaxically injected into the rat brain above the SON and, 2 weeks post injection, the rats are sacrificed and assayed for EGFP expression. Using this method, it has been possible to identify specific regions upstream of the transcription start site in the OT and AVP gene promoters that are responsible for conferring the cell-type specificity of the OT and AVP gene expression in the SON.