GnRH is essential for the regulation of mammalian reproductive processes. It regulates the production and release of pituitary gonadotropins, thereby influencing steroidogenesis and gametogenesis. While primarily produced in the hypothalamus, GnRH is also produced in peripheral organs, such as the gonads and placenta. GnRH analogs, including agonists and antagonists, have been synthesized for the reproductive management of animals and humans. This review focuses on the functions of hypothalamic GnRH in the reproductive processes of cattle. In addition to inducing the surge release of LH, the pulsatile secretion of GnRH stimulates the pituitary gland to release FSH and LH, thereby regulating gonadal function. Various GnRH-based products have been synthesized to increase their potency and efficacy in regulating reproductive functions. This review article describes the chemical structures of GnRH and its agonists. This discussion extends to the gene expression of GnRH in the hypothalamus, highlighting its pivotal role in regulating the reproductive process. Furthermore, GnRH is involved in regulating ovarian follicular development and luteal phase support, and estrus synchronization is involved. A comprehensive understanding of the role of GnRH and its analogs in the modulation of reproductive processes is essential for optimizing animal reproduction.

During oncogenesis, cancer not only escapes the body\'s regulatory mechanisms, but also gains the ability to affect local and systemic homeostasis. Specifically, tumors produce cytokines, immune mediators, classical neurotransmitters, hypothalamic and pituitary hormones, biogenic amines, melatonin, and glucocorticoids, as demonstrated in human and animal models of cancer. The tumor, through the release of these neurohormonal and immune mediators, can control the main neuroendocrine centers such as the hypothalamus, pituitary, adrenals, and thyroid to modulate body homeostasis through central regulatory axes. We hypothesize that the tumor-derived catecholamines, serotonin, melatonin, neuropeptides, and other neurotransmitters can affect body and brain functions. Bidirectional communication between local autonomic and sensory nerves and the tumor, with putative effects on the brain, is also envisioned. Overall, we propose that cancers can take control of the central neuroendocrine and immune systems to reset the body homeostasis in a mode favoring its expansion at the expense of the host.

Brain tumours make up nearly one-third of paediatric malignancies. Over time, advancements in oncological treatments like radiotherapy have helped reduce normal-tissue toxicity when treating cancers in the brain. However, clinicians are still facing a trade-off between treatment efficacy and potential side effects. The aim of this review is to address the late effects of cranial irradiation on the neuroendocrine system and to identify factors that make patients more vulnerable to radiation-induced endocrine sequelae. Radiation damage to the hypothalamic-pituitary axis, which orchestrates hormone release, can lead to endocrinopathy; up to 48.8% of children who have undergone cranial irradiation develop a hormone deficiency. This may lead to further health complications that can appear up to decades after the last treatment, lowering the patients\' quality of life and increasing long-term costs as lifelong hormone replacement therapy may be required. Growth hormone deficiency is the most common sequelae, followed by either thyroid or gonadotropic hormone deficiency. Adrenocorticotropic hormone deficiency tends to be the least common. Identified factors that increase the risk of late endocrine deficiency include total radiation dose, age at treatment, and time since last treatment. However, as there are various other factors that may potentiate the damage, a universal solution proven to be most effective in sparing the endocrine tissues is yet to be identified. Until then, accounting for the identified risk factors during treatment planning may in some cases help reduce the development of endocrine sequelae in childhood cancer survivors.

Central diabetes insipidus (CDI) occurs secondary to deficient synthesis or secretion of arginine vasopressin peptide from the hypothalamo-neurohypophyseal system (HNS). It is characterized by polydipsia and polyuria (urine output >30mL/kg/day in adults and >2l/m2/24h in children) of dilute urine (<250mOsm/L). It can result from any pathology affecting one or more components of the HNS including the hypothalamic osmoreceptors, supraoptic or paraventricular nuclei, and median eminence of the hypothalamus, infundibulum, stalk or the posterior pituitary gland. MRI is the imaging modality of choice for evaluation of the hypothalamic-pituitary axis (HPA), and a dedicated pituitary or sella protocol is essential. CT can provide complimentary diagnostic information and is also of value when MRI is contraindicated. The most common causes are benign or malignant neoplasia of the HPA (25%), surgery (20%), and head trauma (16%). No cause is identified in up to 30% of cases, classified as idiopathic CDI. Knowledge of the anatomy and physiology of the HNS is crucial when evaluating a patient with CDI. Establishing the etiology of CDI with MRI in combination with clinical and biochemical assessment facilitates appropriate targeted treatment. This chapter illustrates the wide variety of causes and imaging correlates of CDI on neuroimaging, discusses the optimal imaging protocols, and revises the detailed neuroanatomy required to interpret these studies.

OBJECTIVE: Primary central nervous system lymphoma (PCNSL) involving the hypothalamic-pituitary axis (H-P axis) is a rare intracranial neoplasm. We aimed to determine the unique characteristics and treatment outcomes of patients with PCNSL at the H-P axis and review the literature.
METHODS: We retrospectively reviewed the electronic medical records of patients with PCNSL in our institute from 2000 to 2017. We analyzed patient characteristics, clinicopathologic features, imaging results, and treatment outcomes. Furthermore, we searched the PubMed database and gathered more cases from published studies to analyze patient treatment outcomes.
RESULTS: A total of 488 patients were diagnosed with central nervous system lymphoma at our institute. Seven (1.4%) patients had H-P axis involvement, five had diffuse large B-cell lymphoma, and two had mucosa-associated lymphoid tissue lymphoma. All patients had anterior pituitary lobe dysfunction, and two had posterior lobe dysfunction. The median progression-free survival (PFS) for seven patients was 29.0 (range: 0.9-48.1) months, and the 3-year survival rate was 42.9%. Pooled analysis included 45 patients. The median PFS for these patients was 7.0 months (0.9-52.0), and the 2-year survival rate was 20%. Univariate and multivariate analyses revealed that the patients with visual field defects had better prognosis (p = 0.0153 and 0.043, respectively).
CONCLUSIONS: PCNSL at the H-P axis is associated with a higher rate of pituitary dysfunction than other parasellar pathologies. PCNSL at the H-P axis has a worse treatment outcome than PCNSL at other sites. However, visual field defect is related to a favorable prognosis in these patients.

Cranial irradiation is used in the management of a diverse group of intracranial pathologies. However, if any part of the hypothalamic-pituitary axis is included in the radiation field, there is a risk of developing neuroendocrine dysfunction. Growth hormone is the most radiosensitive of the anterior pituitary hormones, followed by the gonadotropins, adrenocorticotropic hormone and thyroid-stimulating hormone. A number of factors determine both the occurrence and severity of hypothalamic-pituitary dysfunction, including: the dose of radiation received by the hypothalamic-pituitary axis (determined by a number of factors including total dose and fractionation schedule and ultimately expressed as the biological effective dose); length of time since cranial irradiation; age of the patient at the time of cranial irradiation; type of radiotherapy administered; and the different inherent radiosensitivities of the anterior pituitary hormones. These neuroendocrine abnormalities usually develop a number of years after the initial insult and, therefore, patients who have received cranial irradiation should receive annual endocrine assessments. The establishment of endocrine late-effect clinics for the survivors of childhood cancers have gone some way to addressing this problem; however, other groups of patients, particularly those receiving cranial irradiation in adult life, may not have systematic endocrine assessment.

Parkinson\'s disease (PD) is a progressive and multifactorial neurodegenerative disease. It has been suggested that a dysregulation of the hypothalamic-pituitary-adrenal axis (HPA) occurs in PD. Furthermore, this dysregulation may be involved in triggering, exacerbation or progression of disease. The objective of this study was to systematically review the literature regarding cortisol levels and their relation with motor, cognitive and behavioral symptoms in patients with PD. A systematic search was performed in PubMed and Embase databases, according to PRISMA norms. Twenty-one studies were included, which evaluated baseline levels of cortisol and motor, cognitive, behavioral symptoms, drugs administration or deep brain stimulation to PD treatment. Sample size ranged from 7 to 249 individuals. In 14 studies that assessed cortisol levels in PD patients, seven showed elevation of cortisol levels. In relation to symptomatology, high levels of cortisol were associated with worst functional scores evaluated by UPDRS, depression and behavior in risk preference. Medication interactions showed an influence on the regulation of cortisol release, mainly, conventional drugs used in the PD\'s treatment, such as levodopa. The results found in this review point to a possible relationship between cortisol levels and symptoms in PD, indicating that an HPA axis dysfunction related to cortisol level occurs in PD.

The environment which living organisms inhabit is not constant and many factors, such as light, temperature, and food availability, display cyclic and predictable variations. To adapt to these cyclic changes, animals present biological rhythms in many of their physiological variables, timing their functions to occur when the possibility of success is greatest. Among these variables, many endocrine factors have been described as displaying rhythms in vertebrates. The aim of the present review is to provide a thorough review of the existing knowledge on the rhythms of the endocrine system of fish by examining the hormones that show rhythmicity, how environmental factors control these rhythms and the variation in the responses of the endocrine system depending on the time of the day. We mainly focused on the hypothalamic-pituitary axis, which can be considered as the master axis of the endocrine system of vertebrates and regulates a great variety of functions, including reproduction, growth, metabolism, energy homeostasis, stress response, and osmoregulation. In addition, the rhythms of other hormones, such as melatonin and the factors, produced in the gastrointestinal system of fish are reviewed.

Although decades of research has examined the association between cortisol regulation and premenstrual syndrome/premenstrual dysphoric disorder (PMS/PMDD), no review exists to provide a general set of conclusions from the extant research. In the present review we summarize and interpret research that has tested for associations between PMS/PMDD and cortisol levels and reactivity (n=38 original research articles). Three types of studies are examined: correlational studies, environmental-challenge studies, and pharmacological-challenge studies. Overall, there was very little evidence that women with and without PMS/PMDD demonstrate systematic and predictable mean-level differences in cortisol, or differences in cortisol response/reactivity to challenges. Methodological differences in sample size, the types of symptoms used for diagnosis (physical and psychological vs. only affective), or the type of cortisol measure used (serum vs. salivary), did not account for differences between studies that did and did not find significant effects. Caution is recommended before accepting the conclusion of null effects, and recommendations are made that more rigorous research be conducted, considering symptom-specificity, within-person analyses, and multiple parameters of cortisol regulation, before final conclusions are drawn.

To determine whether it is the hypothalamic-pituitary axis or the ovary that plays the predominant role in abnormal estrous cycling induction by postnatal exposure to estrogenic compounds, female rats were subcutaneously injected with 100mg/kg p-tert-octylphenol or vehicle for 5 or 15 days after birth (OP-PND5, OP-PND15 or control). Ovaries were exchanged between control and treated groups on PND28. Controls receiving control or OP-PND5 ovaries showed normal cycles within 4 weeks after the exchange, and corpora lutea were detected in transplanted ovaries. Controls receiving OP-PND15 ovaries consistently increased persistent estrus (PE). OP-PND15 rats receiving control or OP-PND15 ovaries immediately descended into PE, and transplanted ovaries were atrophic with cystic follicles, indicating anovulation. OP-PND5 rats receiving control or OP-PND5 ovaries showed early onset of PE after normal cycling. The hypothalamic-pituitary axis is predominant in abnormal cycling induction by postnatal exposure to OP. OP-PND15 ovaries were impaired compared to other groups.