Hypothalamo-hypophysial Research Articles

Epilepsy onset in puberty

Objective: To research age of epilepsy onset in puberty in girls. Methods: Research was a part of prospective observational uncontrolled comparative study of the antiepileptic drugs reproductive side effects. The age of epilepsy onset were studied in 155 female patients in reproductive age. 3 groups of puberty age and 4 subgroups of puberty period were allocated. STATISTICA for Windows system (version 5.5) was used. Results: Patients were divided into three groups according WHO classification of puberty age (1997): 1gr. – before puberty- 1–9y.o., 2gr. – puberty- 10–18, 3g. – after puberty- older 18. There were 23 patients (15%) in 1 gr., 92 (59%) – in 2gr, 40 (26%) – in 3 gr. Differences in the epilepsy onset in the comparison groups were statistically significant above in puberty (p<0,001). Epilepsy began in childhood (until 18 y.o) in 75%. Frequency of epilepsy onset was studied in 4 subgroups of puberty period according phases of maturing of hypothalamo-hypophysial system: 10–11y.o- beginning of hypothalamo- hypophysial hormones secretion , 12-13 – beginning menses, 14-15- becoming of ovulatory peak, 17-18- establishment of a constant rhythm of hormones secretion. There were 18 patients (20%) into 1subgr., 35 (38%) – 2nd, 24 (26%)- 3d, 15 (16%) into 4 subgroup. Prevalence of epilepsy onset in the integrated age range of 12-16 years was statistically reliable (p<0,001). Conclusion: Thus, hormonal changes during the puberty period often provoked epilepsy onset. The epilepsy onset prevailed during the periods of the beginning oestradiolum production and its ovulatory peaks. It has confirmed estrogens proconvulsive effect. The reported study was funded by Russian humanitarian scientific fund according to the research project № 15-06-10816.

Hypothalamo‑hypophysial system in rats with autotransplantation of the adrenal cortex.

Patients with bilateral pheochromocytoma often require an adrenalectomy. Autotransplantation of the adrenal cortex is an alternative therapy that could potentially be performed instead of receiving glucocorticoid replacement following adrenalectomy. Adrenal cortex autotransplantation aims to avoid the side effects of long‑term steroid treatment and adrenal insufficiency. Although the function of the hypothalamo‑hypophysial system is critical for patients who have undergone adrenal cortex autotransplantation, the details of that system, with the exception of adrenocorticotropic hormone in the subjects with adrenal autotransplantation, have been overlooked for a long time. To clarify the precise effect of adrenal autotransplantation on the pituitary gland and hypothalamus, the current study examined the gene expression of hormones produced from the hypothalamus and pituitary gland. Bilateral adrenalectomy and adrenal autotransplantation were performed in 8 to 9‑week‑old male rats. The hypothalamus and pituitary tissues were collected at 4weeks after surgery. Transcriptional regulation of hypothalamic and pituitary hormones was subsequently examined by reverse transcription‑quantitative polymerase chain reaction. Proopiomelanocortin, glycoprotein hormone α polypeptide, and thyroid stimulating hormone β were significantly elevated in the pituitary gland of autotransplanted rats when compared with sham‑operated rats. In addition, there were significant differences in the levels of corticotropin releasing hormone receptor1 (Crhr1), Crhr2, nuclear receptor subfamily3 groupC member 1 and thyrotropin releasing hormone receptor between the sham‑operated rats and autotransplanted rats in the pituitary gland. In the hypothalamus, corticotropin releasing hormone and urocortin 2mRNA was significantly upregulated in autotransplanted rats compared with sham‑operated rats. The authors identified significant alterations in the function of not only the hypothalamus‑pituitary‑adrenal axis, but also the adenohypophysis thyrotropes in autotransplanted rats. In the future, it will be important to examine other tissues affected by glucocorticoids following adrenal cortex autotransplantation.

Role of the Kiss1/Kiss1r system in the regulation of pituitary cell function

Kisspeptin (Kiss1) is an amidated neurohormone that belongs to the RF-amide peptide family, which has a key role in the control of reproduction. Specifically, kisspeptin regulates reproductive events, including puberty and ovulation, primarily by activating the surface receptor Kiss1r (aka GPR54), at hypothalamic gonadotropin-releasing hormone (GnRH) neurons. More recently, it has been found that kisspeptin peptide is present in the hypophyseal portal circulation and that the Kiss1/Kiss1r system is expressed in pituitary cells, which suggest that kisspeptin could exert an endocrine, paracrine or even autocrine role at the pituitary gland level. Indeed, mounting evidence is pointing towards a direct role of kisspeptin in the control of not only gonadotropins but also other pituitary secretions such as growth hormone or prolactin. In this review, we summarize the most recent advances in the study of the role that the Kiss/Kiss1r system plays in the control of pituitary gland function, paying special attention to the direct role of this neuropeptide on pituitary cells and its interactions with other relevant regulators.

Arginine vasopressin (AVP): a review of its historical perspectives, current research and multifunctional role in the hypothalamo-hypophysial system.

This publication reviews the function of arginine vasopressin and focuses on the morphologic and functional correlation between the hormone and its effect on stress, the hypophysial-adrenocortical axis, neuroimmune responses, renal function and corticotroph pituitary tumors. A literature review was performed using various search engines for information regarding the morphology and the multifunctional role of arginine vasopressin. Although a large number of studies were published discussing these interactions, there are several important areas that are still obscure. The questions of how does arginine vasopressin affect the morphology and function of these various areas, and how does the secretion of ACTH and adrenocortical hormones influence the morphology of arginine vasopressin-producing cells and their hormone secretion requires further investigation.

Architecture of GnRH-Gonadotrope-Vasculature Reveals a Dual Mode of Gonadotropin Regulation in Fish.

The function and components of the hypothalamic-pituitary axis are conserved among vertebrates; however, in fish, a neuroglandular mode of delivery (direct contact between axons and endocrine cells) was considered dominant, whereas in tetrapods hypothalamic signals are relayed to their targets via the hypophysial portal blood system (neurovascular delivery mode). By using a transgenic zebrafish model we studied the functional and anatomical aspects of gonadotrope regulation thus revisiting the existing model. FSH cells were found to be situated close to the vasculature whereas the compact organization of LH cells prevented direct contact of all cells with the circulation. GnRH3 fibers formed multiple boutons upon reaching the pituitary, but most of these structures were located in the neurohypophysis rather than adjacent to gonadotropes. A close association was observed between FSH cells and GnRH3 boutons, but only a fifth of the LH cells were in direct contact with GnRH3 axons, suggesting that FSH cells are more directly regulated than LH cells. GnRH3 fibers closely followed the vasculature in the neurohypophysis and formed numerous boutons along these tracts. These vessels were found to be permeable to relatively large molecules, suggesting the uptake of GnRH3 peptides. Our findings have important implications regarding the differential regulation of LH and FSH and contradict the accepted notion that fish pituitary cells are mostly regulated directly by hypothalamic fibers. Instead, we provide evidence that zebrafish apply a dual mode of gonadotrope regulation by GnRH3 that combines both neuroglandular and neurovascular components.

“Brain sex differentiation” in teleosts: Emerging concepts with potential biomarkers

“Brain sex differentiation” in teleosts is a contentious topic of research as most of the earlier reports tend to suggest that gonadal sex differentiation drives brain sex differentiation. However, identification of sex-specific marker genes in the developing brain of teleosts signifies brain–gonadal interaction during early sexual development in lower vertebrates. In this context, the influence of gonadotropin-releasing hormone (GnRH)–gonadotropin (GTH) axis on gonadal sex differentiation, if any requires in depth analysis. Presence of seabream (sb) GnRH immunoreactivity (ir−) in the brain of XY Nile tilapia was found as early as 5days post hatch (dph) followed by qualitative reduction in the preoptic area-hypothalamus region. In contrast, in the XX female brain a steady ir− of sbGnRH was evident from 15dph. Earlier studies using sea bass already implied the importance of hypothalamic gonadotropic axis completion during sex differentiation period. Such biphasic pattern of localization was also seen in pituitary GTHs using heterologous antisera in tilapia. However, more recent analysis in the same species could not detect any sexually dimorphic pattern using homologous antisera for pituitary GTHs. Detailed studies on the development of hypothalamo–hypophyseal–gonadal axis in teleosts focusing on hypothalamic monoamines (MA) and MA-related enzymes demonstrated sex-specific differential expression of tryptophan hydroxylase (Tph) in the early stages of developing male and female brains of tilapia and catfish. The changes in Tph expression was in agreement with the levels of serotonin (5-HT) and 5-hydroxytryptophan in the preoptic area-hypothalamus. Considering the stimulatory influence of 5-HT on GnRH and GTH release, it is possible to propose a network association between these correlates during early development, which may bring about brain sex dimorphism in males. A recent study from our laboratory during female brain sex development demonstrated high expression of tyrosine hydroxylase in correlation with catecholamine levels, brain aromatase and its related transcription factors such as fushi tarazu factor 1, Ftz-f1 and fork head box protein L2, foxl2. Taken together, gender differences in the levels of various transcripts provide new perspectives on brain sex differentiation in lower vertebrates. Sexually dimorphic or differentially expressing genes may play an essential role at the level of brain in response to gonadal differentiation, which might consequentially or causatively respond to gonadal sex.

Effect of p53 Inhibition by Pifithrin-Alpha on Functional Activity of Vasopressin Neurons in Rat Hypothalamus

In the present work we investigated the effects of p53 inhibition by pifithrin-alpha (PFT) in vitro and in vivo on functioning vasopressinergic magnocellular neurones of rat hypothalamus. In vivo treatments with PFT were done by intra-hypothalamic microinjections or by intra peritoneal injections. In in vitro experiments hypothalamic slices containing supraoptic nuclei and intact pituitary were incubated with or without PFT. In all experiments we observed accumulation of vasopressin (VP) in the cell perikarya after PFT injections, however expression of VP mRNA was not changed. Analysis of VP content in the posterior pituitary demonstrated that amount of VP was significantly decreased after PFT treatments. Additionally, long-term inhibition of p53 in experiments with intra-hypothalamic injections of PFT resulted in an increased diuresis rate. The obtained results demonstrated that in all experiments PFT treatments inhibited VP anterograde transport from the cells of supraoptic nuclei. Moreover, analysis of MEK/ERK activities revealed that phosphorylation levels of MEK1/2 and ERK1/2 were decreased after PFT treatments. Our findings provide new evidences that p53 could be involved in the control of VP secretion from hypothalamo-hypophyseal system and that this action probably can be mediated by ERK signalling pathway.

Juxtapositions between the somatostatinergic and growth hormone-releasing hormone (GHRH) neurons in the human hypothalamus

Somatostatin is a 14–28 amino acid peptide that is located not only in the gastrointestinal system but also in multiple sites of the human brain. The inhibitory effect of somatostatin on the growth hormone (GH) secretion of the pituitary gland is a well-established phenomenon. There is a general consensus that somatostatin is released into the hypophysial portal blood and modulates GH secretion by hormonal action. In the present study, we explored the possibility that in addition to the hormonal route, somatostatin may also influence GH secretion via influencing the growth hormone-releasing hormone (GHRH) secretion by direct contacts that may be functional synapses.Since the verification of these putative synapses by electron microscopy is virtually impossible in humans due to the long post mortem time, in order to reveal the putative somatostatinergic-GHRH juxtapositions, light microscopic double-label immunohistochemistry was utilized.By examining the slides with high magnification, we observed that the vast majority of the GHRH perikarya received contacting somatostatinergic axonal varicosities in the arcuate nucleus. In contrast, GHRH axonal varicosities rarely contacted somatostatinergic perikarya.The morphology and the abundance of somatostatin to GHRH juxtapositions indicate that these associations are functional synapses, and they represent, at least partially, the morphological substrate of the somatostatin-influenced GHRH secretion. Thus, in addition to influencing the GH secretion directly via the hypophysial portal system, somatostatin may also modulate GH release from the anterior pituitary by regulating the hypothalamic GHRH secretion via direct contacts. The rare GHRH to somatostatin juxtapositions indicate that the negative feedback effect of GH targets the somatostatinergic system directly and not via the GHRH system.

Pesticide- and sex steroid analogue-induced endocrine disruption differentially targets hypothalamo–hypophyseal–gonadal system during gametogenesis in teleosts – A review

Pesticide-induced endocrine disruption often mimics sex steroidal action resulting in physiological functional disarray of hypothalamo–hypophyseal–gonadal (HHG) system at multiple levels. Among various group of pesticides, organochlorine and organophosphate family of pesticides are known to impart sex steroidal mimicking activity with slightly higher resemblance to estrogens when compared to androgenic action. This review will highlight the effects of organochlorine (for e.g. endosulfan) and organophosphate (for e.g. malathion) pesticides in comparison with sex-steroid analogue-induced changes on HHG axis during gametogenesis in few teleost fish models. Interestingly, the effects of these compounds have produced differential effects in juveniles and adults which also vary based on exposure dosage and duration. Further, the treatments had caused at times sexually dimorphic effects indicating that the action of these compounds bring out serious implications in sexual development. A comprehensive overview has been provided by considering all these aspects to recognize the adverse impacts of pesticide-induced endocrine disruption with special reference to endosulfan and malathion as those had been applied even today or used before for controlling agricultural pests in several Asian countries including India. This review also compares the effects of sex-steroid analogues where in sex reversal to reproductive dysfunction is evident, which may imply the extent of sexual plasticity in teleosts compared to other vertebrates.

PO-0863a Puberty Period And Epilepsy Onset

Purpose Study connection between epilepsy onset and puberty period at female patients. Methods work was the part of the antiepileptic drugs reproductive side effects study. Epilepsy onset were studied at 155 female patients older 16 y. Patients were divided into 3 groups according WHO classification of puberty age: 1gr. - before puberty- 1–9 y.o., 2 gr. – puberty- 10–18, 3 g. – after puberty – older 18. Frequency of epilepsy onset was studied in 4 subgroups of puberty period according phases of maturing of hypothalamo-hypophysial system: 10–11 y.- beginning of hypothalamo-hypophysial hormones secretion, 12–13- beginning menses, 14–15- becoming of ovulatory peak, 17–18- establishment of a constant rhythm of hormones secretion. Ages of epilepsy onset and menarche were compared. STATISTICA for Windows system (version 5.5) was used. Results There were 23 patients (15%) in 1 gr., 92 (59%) – 2 gr, 40 (26%) – 3 gr. Differences in the comparison groups were statistically significant above in puberty (p Conclusion Thus, hormonal changes in pubertyoften provoked epilepsy onset. It confirms proconvulsive effect of estrogens. Information is very important for patients with burdened neurologic anamnesis.

Advent and Recent Advances in Research on the Role of Pituitary Adenylate Cyclase-activating Polypeptide (PACAP) in the Regulation of Gonadotropic Hormone Secretion of Female Rats

PACAP (ADCYAP1) was isolated from ovine hypothalami. PACAP activates three distinct receptor types: G-protein coupled PAC1, VPAC1, and VPAC2 with seven transmembrane domains. Eight splice variants of PAC1 receptor are described. A part of the hypothalamic PACAP is released into the hypophyseal portal circulation. Both hypothalamic and pituitary PACAP are involved in the dynamic control of gonadotropic hormone secretion. In female rats, PACAP in the paraventricular nucleus is upregulated in the morning and pituitary PACAP is upregulated in the late evening of the proestrus stage of the reproductive cycle. PACAP mRNA peak in the hypothalamic PVN precedes the LHRH release into the portal circulation. It is supposed that PACAP peak is evoked by the elevated estrogen on proestrous morning. At the beginning of the so-called critical period of the same day, PACAP level starts to decline allowing LHRH release into the portal circulation, resulting in the LH surge that evokes ovulation. Just before the critical period, icv-administered exogenous PACAP blocks the LH surge and ovulation. The blocking effect of PACAP is mediated through CRF and endogenous opioids. The effect of the pituitary-born PACAP depends on the intracellular cross-talk between PACAP and LHRH.

Brain Endothelial Cells Control Fertility through Ovarian-Steroid–Dependent Release of Semaphorin 3A

Author SummaryIn the developing embryo, endothelial cells release chemotropic signals such as Semaphorin 3A (Sema3A) that, upon activation of its receptor Neuropilin-1 (Nrp1), regulate neuronal migration and axon guidance. However, whether endothelial cells in the adult brain retain the ability to secrete molecules that influence neuronal function is unknown. Here we show in the adult brain of rodents that vascular endothelial cells release Sema3A and that the amount released is regulated by the ovulatory cycle. Sema3A, in turn, promotes the outgrowth of axons of hypothalamic neurons that express Neuropilin-1 towards the endothelial wall of portal blood vessels. These neurons release there the neuropeptide that controls reproduction: gonadotropin-releasing hormone (GnRH). Notably, this endothelial-cell-mediated sprouting of GnRH axons regulates neuropeptide release at a key stage of the estrous cycle, the proestrus, when the surge of GnRH triggers ovulation. Thus, by promoting GnRH axonal growth in the adult brain, Sema3A/Neuropilin-1 plays a pivotal role in orchestrating the central control of reproduction. Our results suggest a model in which vascular endothelial cells are dynamic signaling components that relay peripheral information to the brain to control key physiological functions, including species survival.

How Much Kissing Is Required for Fertility?

The mammalian reproductive axis is regulated by neuroendocrine signaling pathways within the hypothalamus that control pulsatile secretion of GnRH into the hypophyseal portal system. GnRH stimulates gonadotropic hormone secretion from the anterior pituitary to activate pubertal maturation of the gonads and regulate fertility. Thus, substancesandphysiological inputs thataffectGnRHrelease provide important control mechanisms for regulation of the reproductive axis. Within the past decade, kisspeptins have beenidentifiedasakeyregulatorofGnRHrelease(forreview see Ref. 1). Kisspeptins are a family of overlapping amidated neuropeptides encoded by the Kiss1 gene that act as potent agonists of GnRH release by binding to their membrane receptor (kisspeptin receptor, KISS1R, also known as G-protein coupled receptor 54, GPR54) expressed by GnRH neurons (2). Kiss1 neurons reside within 2 regions of the hypothalamus; the arcuate (ARC) and the anteroventral periventricular (AVPV) nuclei. The Kiss1 neurons in the ARC are thought to regulate GnRH pulse frequency, whereas the AVPV neurons, which are sexually dimorphic with greater numbers in females, are required for inducing the preovulatory LH surge. Thecriticalrolethatkisspeptinsplayinmaintainingmammalian fertility was highlighted by the effect of loss of expression of these neuropeptides in transgenic mice (for review see Ref. 3). Disruption of the Kiss1 gene in mice results in failure of sexual maturation at puberty and infertility. The mutantmicehavehypogonadotropichypogonadism,similar to that found in patients with inactivating mutations of the kisspeptin receptor (4, 5). Mutant female mice do not show normal estrous cycling but have times of persistent estrus, probably reflecting their failure to ovulate. Consistent with this phenotype, the mutant female mice were incapable of eliciting an estradiol-induced LH surge required for ovulation (6). In contrast, however, female mice in which Kiss1 neurons were chronically ablated during development by cell-restricted expression of a diphtheria toxin entered puberty at the normal time and were fertile (7). This was a completely unexpected finding given that loss of Kiss1 neurons produced a less severe phenotype than loss of the kisspeptin protein and led to the controversial suggestion that kisspeptin signaling is not essential for female fertility. To account for these differences, it was suggested that compensatory changes occur during brain development that overcome the loss of the Kiss1 neurons. In support of this, it was shown that temporal ablation of Kiss1 neurons in 20-weekold adult females caused infertility, possibly because neuronalcompensationcouldnotoccur.Female infertilitywasalso found when Kiss1 neurons were ablated at postnatal day 20, suggesting that compensation occurs before this time point. The paper published in this issue of Endocrinology by Popa and colleagues (8) is an important contribution to this field because it provides data regarding the minimum amount of kisspeptin protein that is required to maintain fertility in mice. The authors report the reproductive phenotype of a transgenic mouse line that carries a hypomorphic mutation in the Kiss1 gene. These mice contain a CRE-GFP transgene inserted between the transcriptional start site and the coding region of the Kiss1 gene (9), which reduces expression of Kiss1 transcripts and greatly diminishes kisspeptin protein levels. Male mice with only a 5% level of Kiss1 transcripts are fertile and give rise to normal-sized litters. Female mice are also fertile but show a more severe effect than in males with reduced fertility rates and smaller litter sizescomparedwithwild-typemice.This sexuallydimorphic difference in the severity of the reproductive defect may indicate that male mice can cope with lower kisspeptin levels than females. It is likely that the mutant males will have a reduced sperm count because they have smaller testes and lowerFSHlevels thannormalbut that the spermnumbersdo

GnRH Neurons Elaborate a Long-Range Projection with Shared Axonal and Dendritic Functions

Information processing by neurons has been traditionally envisioned to occur in discrete neuronal compartments. Specifically, dendrites receive and integrate synaptic inputs while axons initiate and conduct spikes to distal neuronal targets. We report here in mice, using morphological reconstructions and electrophysiology, that the gonadotropin-releasing hormone (GnRH) neurons that control mammalian fertility do not conform to this stereotype and instead possess a single projection structure that functions simultaneously as an axon and dendrite. Specifically, we show that the GnRH neuron projection to the median eminence to control pituitary hormone secretion possesses a spike initiation site and conducts action potentials while also exhibiting spines and synaptic appositions along its entire length. Classical axonal or dendritic markers are not detectable in the projection process. Activation of ionotropic glutamate and/or GABA receptors along the GnRH neuron projection is capable of depolarizing the membrane potential and initiating action potentials. In addition, focal glutamate application to the projection is able to regulate the width of propagating spikes. These data demonstrate that GnRH neurons elaborate a previously uncharacterized neuronal projection that functions simultaneously as an axon and dendrite. This structure, termed a "dendron," greatly expands the dynamic control of GnRH secretion into the pituitary portal system to regulate fertility.

EFFECTS OF PROLACTIN ON THYROIDECTOMIZED BUFO BUFO LARVAE

SUMMARY Young Bufa bufo larvae (Rossi's stage V to VII), were thyroidectomized by means of a single dose of I131 (20 μC). Starting on the 37th day after radioactive iodine treatment, these larvae were given a daily injection of 0.3 I.U. of pure ovine prolactin (Richter) for 14 days. As compared to untreated larvae, prolactin-treated ones underwent a statistically significant (P < 0.001) higher loss in body weight during their last week of life; they exhibited a less marked degranulation of both the acidophilic cells that are regarded as producing a prolactin-like hormone, and of the thyrotropic cells. The possibility of some direct inhibitory effect being exerted by prolactin on the pituitary cells in correlation with the incomplete development of the hypothalamo-hypophysial axis, due to thyroidectomy, is discussed. In the integument, exogenous prolactin seems to have enhanced the differences brought about by thyroidectomy with respect to normal larvae (i.e. further gland rudiment reduction and more unifo...

Cyclic Changes In The Hypothalamo Neurohypophysial System of Xenentodon Cancila (HAM.)

The presence of functional hypothalamo-hypophysial neurosecretory system in vertebrates has led to revise earlier views regarding the hypothalamus-pituitary relationship. The hypothalamo-neurohypophysial system which consists of hypothalamic nuclei, their axonal fibres forming tractus preoptico-hypophyses and the neurohypophysis) works as a morphological as well as a physiological connection between the hypothalamus and the pituitary gland. In fishes, fibres from the neurosecretory hypothalamic nuclei terminate in the neurohypophysis, which remains inter digitized with the adenohypophysis and provides a very close association between the neurosecretory fibres and pars intermedia of the pituitary gland forming a neuro-intermediate lobe. Hypothalamo-Neurosecretory complex of Xenentodon cancila consists of Nucleus Pre-opticus (NPO), Nucleus Lateralis Tuberis (NLT) and their axonal tracts. NPO is a paired structure situated on either side of the third ventricle anterodorsal to the optic chiasma. NPO is divisible into a dorsal Pars Magnocellularis (PMC) consisting of large neurosecretory cells and Pars Parvocellularis (PPC) formed of smaller neurons. Neurons of PMC and PPC contribute beaded axons to form neurohypophysial tract. Herring bodies are seen in the anterior as well as posterior neurohypophysis.

Luteinizing hormone-releasing hormone distribution in the anterior hypothalamus of the female rats.

Luteinizing hormone-releasing hormone (LHRH) neurons and fibers are located in the anteroventral hypothalamus, specifically in the preoptic medial area and the organum vasculosum of the lamina terminalis. Most luteinizing hormone-releasing hormone neurons project to the median eminence where they are secreted in the pituitary portal system in order to control the release of gonadotropin. The aim of this study is to provide, using immunohistochemistry and female brain rats, a new description of the luteinizing hormone-releasing hormone fibers and neuron localization in the anterior hypothalamus. The greatest amount of the LHRH immunoreactive material was found in the organum vasculosum of the lamina terminalis that is located around the anterior region of the third ventricle. The intensity of the reaction of LHRH immunoreactive material decreases from cephalic to caudal localization; therefore, the greatest immunoreaction is in the organum vasculosum of the lamina terminalis, followed by the dorsomedial preoptic area, the ventromedial preoptic area, and finally the ventrolateral medial preoptic area, and in fibers surrounding the suprachiasmatic nucleus and subependymal layer on the floor of the third ventricle where the least amount immunoreactive material is found.

Melatonin-induced changes in the expression of thyroid hormone-converting enzymes in hypothalamus depend on the timing of melatonin injections and genetic background in mice

Recent studies have identified TSHB, Dio2, and Dio3 as key genes for the photoperiodic regulation of gonads. In mammals, the expression of these genes is controlled by melatonin. Surprisingly, this effect of melatonin was shown to be conserved in several reproductively non-photoperiodic laboratory mouse strains that have thus become a valuable model to decipher the mechanisms through which melatonin controls the expression of TSHB, Dio2, and Dio3. In this study, we assessed the effects of intraperitoneal melatonin injections and of their timing on the expression of TSHB, TSHR, Dio2, and Dio3 in the hypothalamo-hypophysial systems of melatonin-proficient CBA/N and melatonin-deficient C57BL/6J mice kept under long-day conditions. In CBA/N mice, Dio3 expression was induced by a daily melatonin injection at ZT14 only, whereas in C57BL/6J mice, a daily melatonin injection induced Dio3 expression at all time points investigated (ZT8, 14, and 20) without changes in TSHB expression in both strains. Dio2 expression was suppressed by a daily melatonin injection only in C57BL/6J mice and only at ZT8. Effect of a daily melatonin injection on TSHR expression was strain- and region- specific. Melatonin levels elevated in plasma and hypothalamus after intraperitoneal injections of melatonin at ZT8 for 7days in C57BL/6J returned to basal levels within 1h after the final injection, while in CBA/N mice melatonin levels in hypothalamus remained high for at least 1h. These data suggest that Dio2 and Dio3 expression in the hypothalamus is differentially regulated by the timing of melatonin injections through strain-specific mechanisms.

Catecholaminergic system innervates galanin-immunoreactive neurons in the human diencephalon

Galanin released into the hypophysial portal circulation in the hypothalamus may function as a hypophysiotropic factor regulating the anterior pituitary function or it may function as a neurotransmitter/neuromodulator acting at synaptic sites regulating neuronal activity of many neurons in the brain. Catecholamines (adrenaline, noradrenaline, and dopamine) primarily regulate anterior pituitary functions indirectly via innervating hypophysiotropic neurons. The aim of the present studies was to explore with double-label immunocytochemistry if, as in rodents, catecholamines interact with galanin in the human diencephalon. Due to the long post-mortem period and subsequent lack of optimal preservation of the cell membranes in the brain, electron microscopy could not be employed to show the presence of catecholaminergic-immunoreactive synapses on galanin-immunoreactive neurons. Therefore, we used light microscopic immunocytochemistry and high-magnification microscopy with oil immersion to identify putative juxtapositions between catecholamines and galanin-utilizing antisera against key enzymes of catecholamine synthesis (tyrosine hydroxylase (TH), representing all three catecholamines; dopamine-beta-hydroxylase (DBH), representing noradrenaline; and phenylethanolamine-N-methyltransferase (PNMT), representing adrenaline) and galanin. Our studies show that among the three catecholamines, dopamine is the most abundant and the vast majority of catecholaminergic contacts on galanin-immunoreactive neurons is dopaminergic. The number of DBH-immunoreactive contacts is less and the number of PNMT-immunopositive contacts is negligible. Among the hypothalamic regions, the periventricular region above the infundibulum (infundibular or arcuate nucleus) contained the largest number of contacts. These en passant-type intimate associations between catecholamine- and galanin-immunoreactive neuronal elements may be functional synapses and may provide the morphological basis for the catecholamine-mediated galanin release.

GnRH-Induced Ca2+ Signaling Patterns and Gonadotropin Secretion in Pituitary Gonadotrophs. Functional Adaptations to Both Ordinary and Extraordinary Physiological Demands

Pituitary gonadotrophs are a small fraction of the anterior pituitary population, yet they synthesize gonadotropins: luteinizing (LH) and follicle-stimulating (FSH), essential for gametogenesis and steroidogenesis. LH is secreted via a regulated pathway while FSH release is mostly constitutive and controlled by synthesis. Although gonadotrophs fire action potentials spontaneously, the intracellular Ca2+ rises produced do not influence secretion, which is mainly driven by Gonadotropin-Releasing Hormone (GnRH), a decapeptide synthesized in the hypothalamus and released in a pulsatile manner into the hypophyseal portal circulation. GnRH binding to G-protein-coupled receptors triggers Ca2+ mobilization from InsP3-sensitive intracellular pools, generating the global Ca2+ elevations necessary for secretion. Ca2+ signaling responses to increasing (GnRH) vary in stereotyped fashion from subthreshold to baseline spiking (oscillatory), to biphasic (spike-oscillatory or spike-plateau). This progression varies somewhat in gonadotrophs from different species and biological preparations. Both baseline spiking and biphasic GnRH-induced Ca2+ signals control LH/FSH synthesis and exocytosis. Estradiol and testosterone regulate gonadotropin secretion through feedback mechanisms, while FSH synthesis and release are influenced by activin, inhibin, and follistatin. Adaptation to physiological events like the estrous cycle, involves changes in GnRH sensitivity and LH/FSH synthesis: in proestrus, estradiol feedback regulation abruptly changes from negative to positive, causing the pre-ovulatory LH surge. Similarly, when testosterone levels drop after orquiectomy the lack of negative feedback on pituitary and hypothalamus boosts both GnRH and LH secretion, gonadotrophs GnRH sensitivity increases, and Ca2+ signaling patterns change. In addition, gonadotrophs proliferate and grow. These plastic changes denote a more vigorous functional adaptation in response to an extraordinary functional demand.