Anterior Hypothalamic Area Research Articles

Effects of Arginine-vasopressin in the Brain on Social Behavior and Communication in a Psychosocial Stress Animal Model

Psychosocial stressors (e.g., anxiety, personality traits, social isolation) are risk factors for negative health outcomes, including cardiovascular disease and neuropsychiatric disorders. However, there is a knowledge gap regarding the biological mechanisms that underlie these risk-outcome relationships. To address this gap, our team uses the Syrian hamster ( Mesocricetus auratus) as an animal model for investigating psychosocial behaviors and stress responses. Our previous findings and work reported by others indicate that the neuropeptide arginine-vasopressin (AVP) acts in the brain to regulate the expression of social behavior and communication. In the present study, stereotaxic surgeries were used to cannulate six adult hamsters (1 female, 5 males) with cannulae aimed at different forebrain regions, mostly focusing on hypothalamic areas. Cannulated animals were microinjected with 200 nl of a 9 μM AVP solution and saline in counterbalanced order with a 4-day inter-test interval. Three of the six animals displayed a type of social communication behavior called flank marking in response to AVP, whereas none of the animals flank marked in response to saline; these group differences were statistically significant (χ2 (1, N=6)= 4.0, p< 0.05). Previous research groups confirmed the anterior hypothalamic area (AHA) as a site of action for the effects of AVP on social behaviors. Our results suggest that, in addition to the AHA, the dorsomedial hypothalamic nucleus (DM) and posterior hypothalamic area (PH) may also be sites of action for AVP. We are currently testing the behavioral effects of AVP when microinjected into the midbrain. The preliminary findings reported here will help us identify areas of the brain that are part of a larger neural network that is involved in the regulation of social behavior and stress responses by AVP. Our long-term goal is to develop a psychosocial stress model to test the hypothesis that AVP may have therapeutic potential for psychosocial stress-associated conditions, including cardiovascular disease and neuropsychiatric disorders. This research is supported by NIH grant #5K01HL145339-03 (PI: M. Gil). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Anterior hypothalamic parvalbumin neurons are glutamatergic and promote escape behavior

The anterior hypothalamic area (AHA) is a critical structure for defensive responding. Here, we identified a cluster of parvalbumin-expressing neurons in the AHA (AHAPV) that are glutamatergic with fast-spiking properties and send axonal projections to the dorsal premammillary nucleus (PMD). Using invivo functional imaging, optogenetics, and behavioral assays, we determined the role of these AHAPV neurons in regulating behaviors essential for survival. We observed that AHAPV neuronal activity significantly increases when mice are exposed to a predator, and in a real-time place preference assay, we found that AHAPV neuron photoactivation is aversive. Moreover, activation of both AHAPV neurons and the AHAPV → PMD pathway triggers escape responding during a predator-looming test. Furthermore, escape responding is impaired after AHAPV neuron ablation, and anxiety-like behavior as measured by the open field and elevated plus maze assays does not seem to be affected by AHAPV neuron ablation. Finally, whole-brain metabolic mapping using positron emission tomography combined with AHAPV neuron photoactivation revealed discrete activation of downstream areas involved in arousal, affective, and defensive behaviors including the amygdala and the substantia nigra. Our results indicate that AHAPV neurons are a functional glutamatergic circuit element mediating defensive behaviors, thus expanding the identity of genetically defined neurons orchestrating fight-or-flight responses. Together, our work will serve as a foundation for understanding neuropsychiatric disorders triggered by escape such as post-traumatic stress disorder (PTSD).

NMDA Receptors in the Lateral Preoptic Hypothalamus Are Essential for Sustaining NREM and REM Sleep.

The lateral preoptic (LPO) hypothalamus is a center for NREM and REM sleep induction and NREM sleep homeostasis. Although LPO is needed for NREM sleep, we found that calcium signals were, surprisingly, highest in REM sleep. Furthermore, and equally surprising, NMDA receptors in LPO were the main drivers of excitation. Deleting the NMDA receptor GluN1 subunit from LPO abolished calcium signals in all cells and produced insomnia. Mice of both sexes had highly fragmented NREM sleep-wake patterns and could not generate conventionally classified REM sleep. The sleep phenotype produced by deleting NMDA receptors depended on where in the hypothalamus the receptors were deleted. Deleting receptors from the anterior hypothalamic area did not influence sleep-wake states. The sleep fragmentation originated from NMDA receptors on GABA neurons in LPO. Sleep fragmentation could be transiently overcome with sleeping medication (zolpidem) or sedatives (dexmedetomidine). By contrast, fragmentation persisted under high sleep pressure produced by sleep deprivation - mice had a high propensity to sleep but woke up. By analyzing changes in delta power, sleep homeostasis (also referred to as “sleep drive”) remained intact after NMDA receptor ablation. We suggest NMDA glutamate receptor activation stabilizes firing of sleep-on neurons, and that mechanisms of sleep maintenance differ from that of the sleep drive itself.

Surface models and true-color sectioned images of hypothalamic nuclei and its neighboring structures.

BACKGROUND: Knowledge regarding the hypothalamic nuclei is essential for understanding neuroanatomy and has substantial clinical relevance.OBJECTIVE: The aim was to contribute to elucidate the complex hypothalamic architecture for research and provide an anatomical basis for clinical brain operation.METHODS: In this research, high-resolution and true-color sectioned images from Visible Korean were employed for hypothalamic nuclei and neighboring structures surface modeling, and a high-resolution three-dimensional atlas of the hypothalamus was created.RESULTS: Surface models of 26 structures including the hypothalamic nuclei and its neighboring structures were produced, which contained 5 anterior hypothalamic areas’ nuclei, 4 intermediate hypothalamic areas’ nuclei, 3 lateral hypothalamic areas’ nuclei, and 2 posterior hypothalamic areas’ nuclei, as well as 12 hypothalamic neighboring structures.CONCLUSIONS: The study evaluated the topographical anatomy of the hypothalamic nuclei and its neighboring structures based on true-color and highresolution sectioned images of Visible Korean.

Functional Connectivity Differences Between Two Culturally Distinct Prairie Vole Populations: Insights Into the Prosocial Network

BackgroundThe goal of this study was to elucidate the fundamental connectivity—resting-state connectivity—within and between nodes in the olfactory and prosocial (PS) cores, which permits the expression of social monogamy in males; and how differential connectivity accounts for differential expression of prosociality and aggression. MethodsUsing resting-state functional magnetic resonance imaging, we integrated graph theory analysis to compare functional connectivity between two culturally/behaviorally distinct male prairie voles (Microtusochrogaster). ResultsIllinois males display significantly higher levels of prosocial behavior and lower levels of aggression than KI (Kansas dam and Illinois sire) males, which are associated with differences in underlying neural mechanisms and brain microarchitecture. Shared connectivity 1) between the anterior hypothalamic area and the paraventricular nucleus and 2) between the medial preoptic area and bed nucleus of the stria terminalis and the nucleus accumbens core suggests essential relationships required for male prosocial behavior. In contrast, Illinois males displayed higher levels of global connectivity and PS intracore connectivity, a greater role for the bed nucleus of the stria terminalis and anterior hypothalamic area, which were degree connectivity hubs, and greater PS and olfactory intercore connectivity. ConclusionsThese findings suggest that behavioral differences are associated with PS core degree of connectivity and postsignal induction. This transgenerational system may serve as powerful mental health and drug abuse translational model in future studies.

Prenatal Androgen Exposure Alters KNDy Neurons and Their Afferent Network in a Model of Polycystic Ovarian Syndrome.

Polycystic ovarian syndrome (PCOS), the most common endocrinopathy affecting women worldwide, is characterized by elevated luteinizing hormone (LH) pulse frequency due to the impaired suppression of gonadotrophin-releasing hormone (GnRH) release by steroid hormone negative feedback. Although neurons that co-express kisspeptin, neurokinin B, and dynorphin (KNDy cells) were recently defined as the GnRH/LH pulse generator, little is understood about their role in the pathogenesis of PCOS. We used a prenatal androgen-treated (PNA) mouse model of PCOS to determine whether changes in KNDy neurons or their afferent network underlie altered negative feedback. First, we identified elevated androgen receptor gene expression in KNDy cells of PNA mice, whereas progesterone receptor and dynorphin gene expression was significantly reduced, suggesting elevated androgens in PCOS disrupt progesterone negative feedback via direct actions upon KNDy cells. Second, we discovered GABAergic and glutamatergic synaptic input to KNDy neurons was reduced in PNA mice. Retrograde monosynaptic tract-tracing revealed a dramatic reduction in input originates from sexually dimorphic afferents in the preoptic area, anteroventral periventricular nucleus, anterior hypothalamic area and lateral hypothalamus. These results reveal 2 sites of neuronal alterations potentially responsible for defects in negative feedback in PCOS: changes in gene expression within KNDy neurons, and changes in synaptic inputs from steroid hormone-responsive hypothalamic regions. How each of these changes contribute to the neuroendocrine phenotype seen in in PCOS, and the role of specific sets of upstream KNDy afferents in the process, remains to be determined.

Adipsic diabetes insipidus patient in postoperative pituitary macroadenoma.

Adipsic diabetes insipidus is a rare condition secondary to injury to osmoreceptors in the anterior hypothalamic area. Only two cases have been published secondary to pituitary tumor surgery. A 43-year-old man, postoperative of a non-functioning pituitary macroadenoma invading the third ventricle and compressing the hypothalamus. Reoperated for headache and rhinorrhachia, developing diabetes insipidus in the postoperative period was discharged with 20 μg/day nasal desmopressin. He came again due to sensorial disorder and hypernatremia, managing to control with intravenous hydration and desmopressin. It presents with recurrence of hypernatremia every time intravenous hydration is suspended and taken orally. With high sodium levels, there is an absence of thirst. A diagnosis of adipsic diabetes insipidus is made, indicating supervised administration of water orally with favorable evolution. Adipsic diabetes insipidus is a rare variant of central diabetes insipidus caused by damage to osmoreceptors in the hypothalamus. It manifests with absence of perception of thirst, hypernatremia and polyuria. Its management is complex and requires strict control of the water balance and adherence to treatment.

Regions of the basal ganglia and primary olfactory system are most sensitive to neurodegeneration after extended sevoflurane anesthesia in the perinatal rat

Extended general anesthesia early in life is neurotoxic in multiple species. However, little is known about the temporal progression of neurodegeneration after general anesthesia. It is also unknown if a reduction in natural cell death, or an increase in cell creation, occurs as a form of compensation after perinatal anesthesia exposure. The goal of this study was to evaluate markers of neurodegeneration and cellular division at 2, 24, or 72 h after sevoflurane (Sevo) exposure (6 h) in fully oxygenated postnatal day (PND) 7 rats. Neurodegeneration was observed in areas throughout the forebrain, while the largest changes (fold increase above vehicle) were observed in areas associated with either the primary olfactory learning pathways or the basal ganglia. These regions included the indusium griseum (IG, 25-fold), the posterior dorso medial hippocampal CA1 (17-fold), bed nucleus of the stria terminalis (Bed Nuclei STM, 5-fold), the shell of the nucleus accumbens (Acb, 5-fold), caudate/putamen (CPu, 5-fold), globus pallidus (GP, 9-fold) and associated thalamic (11-fold) and cortical regions (5-fold). Sevo neurodegeneration was minimal or undetectable in the ventral tegmentum, substantia nigra, and most of the hypothalamus and frontal cortex. In most brain regions where neurodegeneration was increased 2 h post Sevo exposure, the levels returned to <4-fold above control levels by 24 h. However, in the IG, CA1, GP, anterior thalamus, medial preoptic nucleus of the hypothalamus (MPO), anterior hypothalamic area (AHP), and the amygdaloid nuclei, neurodegeneration at 24 h was double or more than that at 2 h post exposure. Anesthesia exposure causes either a prolonged period of neurodegeneration in certain brain regions, or a distinct secondary degenerative event occurs after the initial insult. Moreover, regions most sensitive to Sevo neurodegeneration did not necessarily coincide with areas of new cell birth, and new cell birth was not consistently affected by Sevo. The profile of anesthesia related neurotoxicity changes with time, and multiple mechanisms of toxicity may exist in a time-dependent fashion.

Neurochemical characterization of the hypothalamus of the early fetal and newborn alpaca Vicugna pacos.

In this study we performed a neurochemical characterization of the hypothalamus in the developing alpaca (Vicugna pacos) with the aim of revealing the distributions of immunoreactive (-ir) cells containing parvalbumin (PV), calbindin (CB), calretinin (CR), the somatostatin (SOM), the enzyme aromatase P450 (P450Arom), the estrogen receptor α (ER-α), and estrogen receptor β (ER-β) in embryonal stages, early fetal age, and in the newborn. This analysis has been carried out on embryos at 20, 30, 45 days, fetuses at 90 days, and newborn alpaca. Our immunohistochemical results revealed no cells-ir throughout the embryonic hypothalami of 20, 30, and 45 days. On the fetal stage of 90 days, SOM-ir cells were observed in the lateral hypothalamus and the ventromedial nuclei of the tuberal region. We checked for the presence of P450Arom-ir cells in the periventricular area and dorsomedial hypothalamic nucleus of the tuberal region. In these fetal stages, no PV-ir, CB-ir, CR-ir or ERs-ir cells were identified. In the newborn, the PV-ir, CB-ir, CR-ir, and SOM-ir cells were detected in both the anterior and tuberal hypothalamic area. The P450Arom-ir cells the ER-α-ir and ER-β-ir cells were found in the anterior hypothalamus. Our results offer a contribution in the future purpose to obtain a time-expression pattern of the considered markers in alpaca during gestation and represents a foundation for future investigations on the alpaca brain to define the cross talk between PV, CB, CR, P450Arom, SOM, and ERs in the hypothalamus, the strategic region for the control of the reproductive behavior.

Fiber dissection and 3-tesla diffusion tensor tractography of the superior cerebellar peduncle in the human brain: emphasize on the cerebello-hypthalamic fibers.

Experimental studies in various species using tract-tracing techniques showed clear evidence of the presence of cerebello-hypothalamic projections. However, these connections were not clearly described in humans. In the present study we aimed to describe the direct cerebello-hypothalamic connections within the superior cerebellar peduncle (SCP) using fiberdissectiontechniques on cadaveric brains and diffusion tensor tractography (DTI) in healthy adults. Fiber dissection was performed in a stepwise manner from lateral to medial on 6 cerebral hemispheres. The gray matter was decorticate and fiber tracts were revealed. The SCP was exposed and the fibers were traced distally using wooden spatulas. The MRI examinations were performed in seven cases using 3-tesla 3T unit. The direct cerebello-hyothalamic pathways were exposed using high-spatial-resolution DTI. The present study using both fiber dissection and DTI in adult human showed direct cerebello-hypothalamic fibers within the SCP. The SCP fibers course anterolateral to the cerebral aqueduct reaching the level of the red nucleus of the midbrain. The majority of the fibers crosses over and reached the contralateral diencephalic structures and some of these fibers terminated at the contralateral anterior hypothalamic area. Some of the uncrossed SCP fibers reached the ipsilateral diencephalic structures and terminated at the ipsilateral posterior hypothalamic area. We further reported the close relationship of the SCP with the MCP, lateral lemniscus, red nucleus and substantia nigra. In the DTI evaluations of the SCP we exposed unilateral left cerebello-hypothalamic fibers in five cases and bilateral cerebello-hypothalamic fibers in two cases. The present study demonstrates the direct cerebello-hypothalamic connections within the SCP for the first time using fiber dissection and DTI technique in the human brain. The detailed knowledge of the cerebello-hypothalamic fibers can outlinethe unexplained deficit that may occur during regional surgery.

Perineuronal net expression in the brain of a hibernating mammal.

During hibernation, mammals like the 13-lined ground squirrel cycle between physiological extremes. Most of the hibernation season is spent in bouts of torpor, where body temperature, heart rate, and cerebral blood flow are all very low. However, the ground squirrels periodically enter into interbout arousals (IBAs), where physiological parameters return to non-hibernating levels. During torpor, neurons in many brain regions shrink and become electrically quiescent, but reconnect and regain activity during IBA. Previous work showed evidence of extracellular matrix (ECM) changes occurring in the hypothalamus during hibernation that could be associated with this plasticity. Here, we examined expression of a specialized ECM structure, the perineuronal net (PNN), in the forebrain of ground squirrels in torpor, IBA, and summer (non-hibernating). PNNs are known to restrict plasticity, and could be important for retaining essential connections in the brain during hibernation. We found PNNs in three regions of the hypothalamus: ventrolateral hypothalamus, paraventricular nucleus (PVN), and anterior hypothalamic area. We also found PNNs throughout the cerebral cortex, amygdala, and lateral septum. The total area covered by PNNs within the PVN was significantly higher during IBA compared to non-hibernating and torpor (P < 0.01). Additionally, the amount of PNN coverage area per Nissl-stained neuron in the PVN was significantly higher in hibernation compared to non-hibernating (P < 0.05). No other significant differences were found across seasons. The PVN is involved in food intake and homeostasis, and PNNs found here could be essential for retaining vital life functions during hibernation.

Abstract 041: Hypoxic Peripheral Chemoreceptor Activation Engages Sympathetic Brainstem and Hypothalamic Nuclei in Human Subjects

Peripheral carotid chemoreceptors, which raise sympathetic activation at the brainstem level, may serve as targets for antihypertensive therapy. However, human peripheral chemoreflex regulation in the brainstem is poorly understood due to lack of suitable methodologies. Therefore, we combined measurements of beat-by-beat blood pressure and SpO 2 , and high-resolution functional magnetic resonance imaging (fMRI) to elucidate human brainstem circuits engaged through hypoxic peripheral chemoreceptor activation. We submitted 12 healthy men (29.7 ±6.6 years; 24.0 ±1.86 kg/m 2 ) to five hypoxic episodes by breathing 10% oxygen for 180 seconds followed by 90 seconds normoxia during multiband fMRI brain acquisitions. We monitored continuous finger arterial blood pressure using customized hardware, ECG, and SpO 2 . Brainstem and hypothalamus fMRI images were analyzed to identify nuclei involved in peripheral chemoreflex processing. Systolic blood pressure (SBP) and SpO 2 time courses were correlated with the blood-oxygen-level dependent signals with a general linear model. With hypoxia, SpO 2 decreased by 12.32 ±3.68% (p &lt; 0.01), heart rate increased 13.86 ±3.47 bpm (p &lt; 0.01), and SBP decreased with hypoxia 5.45 ±5.5 mmHg (p &lt; 0.01). In the brainstem, the nucleus tractus solitarii (t-values: SpO 2 : 5.9; SBP: 4.79), the caudal ventrolateral medulla (SpO 2 : 5.61; SBP: 5.59), intermediate reticular nucleus (SpO 2 : 4.7, SBP: 5.98), nucleus ambiguus (SpO 2 : 5.03, SBP: 5.59), dorsal motor nucleus of the vagal nerve (SBP: 4.79), and inferior olive (SpO 2 : 4.7, SBP: 6.16) were identified with high sensitivity and corrected for multiple comparisons (p &lt; 0.01). Furthermore, we observed activation of the following hypothalamic nuclei: paraventricular nucleus (SpO 2 : 7.67), anterior and lateral hypothalamic area (SpO 2 : 7.67, SBP: 4.79), supraoptic nucleus, and tuberomammillary nucleus (SpO 2 : 7.07). High-resolution brainstem fMRI during repeated hypoxia traces brainstem circuits engaged by peripheral chemoreceptors. The methodology can be applied to study peripheral chemoreceptor contributions to human cardiovascular disease and may have utility in identifying patients likely to respond to peripheral chemoreceptor modulation.

Hypothalamic concentrations of kisspeptin and gonadotropin‐releasing hormone during the breeding season and non‐breeding season in ewes

Current methods to quantify kisspeptin (KP) are limited. To this end, a radioimmunoassay (RIA) specific for KP was developed and validated. We hypothesized that use of a RIA would reveal multiple hypothalamic regions as targets of negative seasonal feedback of estradiol on KP production in sheep. Ovariectomized (OVX) ewes bearing a subcutaneous implant of estradiol were euthanized during the breeding season (BS) (n=4) and non-breeding season (NBS) (n=3). Coronal sections of preoptic area (POA), anterior hypothalamic area (AHA), and mediobasal hypothalamus (MBH) were collected, as well as the median eminence (ME), cortex, brain stem, and cerebellum. Amounts of KP and gonadotropin-releasing hormone (GnRH) in individual hypothalamic nuclei were quantified by radioimmunoassay. Concentration and content of KP were lower during the NBS than the BS in the MBH (P<0.01) and POA (P<0.01). Levels of KP in tissue adjacent to the POA and MBH were much lower, and neither concentration nor content of KP differed between the BS and NBS. Kisspeptin was also detected in the cortex, brain stem, and cerebellum, but concentrations were not affected by season. In addition, concentration and content of GnRH in the POA, AHA, MBH, and ME were similar between seasons. Our RIA results indicate that in addition to the MBH, the POA and AHA appear to be involved in the seasonal negative feedback of estradiol on KP expression.

Mice keep their cool.

Ptgds-expressing neurons in the preoptic area of anterior hypothalamus detect increases in brain temperature and reduce core body temperature via increased production of prostaglandin D2.

Thermoregulation via Temperature-Dependent PGD2 Production in Mouse Preoptic Area

Body temperature control is essential for survival. In mammals, thermoregulation is mediated by the preoptic area of anterior hypothalamus (POA), with ∼30% of its neurons sensitive to brain temperature change. It is still unknown whether and how these temperature-sensitive neurons are involved in thermoregulation, because for eight decades they have only been identified via electrophysiological recording. By combining single-cell RNA-seq with whole-cell patch-clamp recordings, we identified Ptgds as a genetic marker for temperature-sensitive POA neurons. Then, we demonstrated these neurons' role in thermoregulation via chemogenetics. Given that Ptgds encodes the enzyme that synthesizes prostaglandin D2 (PGD2), we further explored its role in thermoregulation. Our study revealed that rising temperature of POA alters the activity of Ptgds-expressing neurons so as to increase PGD2 production. PGD2 activates its receptor DP1 and excites downstream neurons in the ventral medial preoptic area (vMPO) that mediates body temperature decrease, a negative feedback loop for thermoregulation.

Cerebral oxidative metabolism mapping in four genetic mouse models of anxiety and mood disorders

The psychopathology of depression is highly complex and the outcome of studies on animal models is divergent. In order to find brain regions that could be metabolically distinctively active across a variety of mouse depression models and to compare the interconnectivity of brain regions of wild-type and such genetically modified mice, histochemical mapping of oxidative metabolism was performed by the measurement of cytochrome oxidase activity. We included mice with the heterozygous knockout of the vesicular glutamate transporter (VGLUT1−/+), full knockout of the cannabinoid 1 receptor (CB1−/−), an anti-sense knockdown of the glucocorticoid receptor (GRi) and overexpression of the human 5-hydroxytryptamine transporter (h5-HTT). Altogether 76 mouse brains were studied to measure oxidative metabolism in one hundred brain regions, and the obtained dataset was submitted to a variety of machine learning algorithms and multidimensional scaling. Overall, the top brain regions having the largest contribution to classification into depression model were the lateroanterior hypothalamic nucleus, the anterior part of the basomedial amygdaloid nucleus, claustrum, the suprachiasmatic nucleus, the ventromedial hypothalamic nucleus, and the anterior hypothalamic area. In terms of the patterns of inter-regional relationship between wild-type and genetically modified mice there was little overall difference, while the most deviating brain regions were cortical amygdala and ventrolateral and ventral posteromedial thalamic nuclei. The GRi mice that most clearly differed from their controls exhibited deviation of connectivity for a number of brain regions, such as ventrolateral thalamic nucleus, the intermediate part of the lateral septal nucleus, the anteriodorsal part of the medial amygdaloid nucleus, the medial division of the central amygdaloid nucleus, ventral pallidum, nucleus of the vertical limb of the diagonal band, anteroventral parts of the thalamic nucleus and parts of the bed nucleus of the stria terminalis. Conclusively, the GRi mouse model was characterized by changes in the functional connectivity of the extended amygdala and stress response circuits.

A small population of hypothalamic neurons govern fertility: the critical role of VAX1 in GnRH neuron development and fertility maintenance

Fertility depends on the correct maturation and function of approximately 800 gonadotropin-releasing hormone (GnRH) neurons in the brain. GnRH neurons are at the apex of the hypothalamic-pituitary-gonadal axis that regulates fertility. In adulthood, GnRH neurons are scattered throughout the anterior hypothalamic area and project to the median eminence, where GnRH is released into the portal vasculature to stimulate release of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) from the pituitary. LH and FSH then regulate gonadal steroidogenesis and gametogenesis. Absence of GnRH neurons or inappropriate GnRH release leads to infertility. Despite the critical role of GnRH neurons in fertility, we still have a limited understanding of the genes responsible for proper GnRH neuron development and function in adulthood. GnRH neurons originate in the olfactory placode then migrate into the brain. Homeodomain transcription factors expressed within GnRH neurons or along their migratory path are candidate genes for inherited infertility. Using a combined in vitro and in vivo approach, we have identified Ventral Anterior Homeobox 1 (Vax1) as a novel homeodomain transcription factor responsible for GnRH neuron maturation and fertility. GnRH neuron counts in Vax1 knock-out embryos revealed Vax1 to be required for the presence of GnRH-expressing cells at embryonic day 17.5 (E17.5), but not at E13.5. To localize the effects of Vax1 on fertility, we generated Vax1flox mice and crossed them with Gnrhcre mice to specifically delete Vax1 within GnRH neurons. GnRH staining in Vax1flox/flox:GnRHcre mice show a total absence of GnRH expression in the adult. We performed lineage tracing in Vax1flox/flox:GnRHcre:RosaLacZ mice which proved GnRH neurons to be alive, but incapable of expressing GnRH. The absence of GnRH leads to delayed puberty, hypogonadism and complete infertility in both sexes. Finally, using the immortalized model GnRH neuron cell lines, GN11 and GT1-7, we show that VAX1 is a direct regulator of Gnrh1 transcription by binding key ATTA sites within the Gnrh1 promoter. This study identifies VAX1 as a key transcription factor regulating GnRH expression and establishes VAX1 as a novel candidate gene implicated in heritable infertility.

Maternal thyroid hormone is required for parvalbumin neurone development in the anterior hypothalamic area.

Thyroid hormone (TH) is crucial for brain development and function. This becomes most evident in untreated congenital hypothyroidism, leading to irreversible mental retardation. Likewise, maternal hypothyroxinaemia, a lack of TH during pregnancy, is associated with neurological dysfunction in the offspring, such as autism and reduced intellectual capacity. In the brain, TH acts mainly through TH receptor α1 (TRα1). Consequently, mice heterozygous for a dominant-negative mutation in TRα1 display profound neuroanatomical abnormalities including deranged development of parvalbumin neurones. However, the exact timing and orchestration of TH signalling during parvalbumin neurone development remains elusive. In the present study, we dissect the development of parvalbumin neurones in the anterior hypothalamic area (AHA) in male mice using different mouse models with impaired pre- and postnatal TH signalling in combination with bromodeoxyuridine birth dating and immunohistochemistry. Our data reveal that hypothalamic parvalbumin neurones are born at embryonic day 12 and are first detected in the AHA at postnatal day 8, reaching their full population number at P13. Interestingly, they do not require TH postnatally because their development is not impaired in mice with impaired TH signalling after birth. By contrast, however, these neurones crucially depend on TH through TRα1 signalling in the second half of pregnancy, when the hormone is almost exclusively provided by the mother. For the first time, our findings directly link a maternal hormone to a neuroanatomical substrate in the foetal brain, and underline the importance of proper TH signalling during pregnancy for offspring mental health. Given the role of hypothalamic parvalbumin neurones in the central control of blood pressure, the present study advocates the inclusion of cardiovascular parameters in the current discussion on possible TH substitution in maternal hypothyroxinaemia.

A Newly Defined Area of the Mouse Anterior Hypothalamus Involved in Septohypothalamic Circuit: Perifornical Area of the Anterior Hypothalamus, PeFAH.

Although the hypothalamus is classified into more than 10 compartments, it still contains uncharacterized areas. In this study, we identified a new triangular-shaped area between the paraventricular hypothalamic nucleus (PVN) and the fornix area in the mouse anterior hypothalamus, which is enriched in chondroitin sulfate proteoglycans (CSPGs). We designated this region as the perifornical area of the anterior hypothalamus (PeFAH) based on its anatomical location. As evidenced by Nissl staining, the PeFAH was distinguishable as an area of relatively low density. Immunohistochemical and DNA microarray analyses indicated that PeFAH contains sparsely distributed calretinin-positive neurons and densely clustered enkephalin-positive neurons. Furthermore, the PeFAH was shown to have bidirectional neural connections with the lateral septum. Indeed, we confirmed enkephalinergic projections from PeFAH neurons to the lateral septum, and inversely, calbindin-positive lateral septum neurons as afferents to the PeFAH. Finally, c-Fos expression analysis revealed that the activity of certain PeFAH neuronal populations tended to be increased by psychological stressors, but not that of enkephalinergic neurons. We proposed PeFAH as a new region in the AH.

Obestatin stimulates the somatotrophic axis activity in sheep

The effects of obestatin (an anorexigenic peripheral peptide) on somatotrophic axis activity in ruminants have not yet been determined. The aim of this study was to investigate the consequence of intracerebroventricular infusions of obestatin on the activity of the somatotrophic axis in peripubertal female sheep. Animals were randomly divided into two groups: control group received intracerebroventricular infusions of the vehicle, and the obestatin group was infused with obestatin (25 µg/120 µL h−1). The series of four hourly infusions on three consecutive days were performed. The blood samples were collected on day 0 and on day 3. Immediately after the end of experiment sheep were slaughtered. Parts of the brains were fixed in situ for further immunohistochemical analysis, while the remaining brains were frozen for Real Time RT-qPCR analysis.Substantial changes in the activity of the somatotrophic axis were observed in obestatin-infused sheep. In those animals obestatin evoked an increase in growth hormone-releasing hormone (GHRH) mRNA expression and a decrease in somatostatin mRNA expression in the anterior hypothalamic area. Moreover, a decrease in somatostatin immunoreactivity in the periventricular nucleus and an increase in somatostatin immunopositive fibers in the median eminence were noted. Changes in the GHRH and somatostatin activity are associated with an increase in growth hormone (GH) gene expression and in the amount of GH immunoreactive material stored in the somatotrophic pituitary cells. Consequently, an increase in GH concentration in the peripheral blood, due to an increase in the number of pulses was observed.It was revealed that obestatin affects the somatostatin/GHRH/GH system at the level of protein synthesis, accumulation and release. It is suggested that obestatin participates in the mechanism modulating somatotrophic axis activity at the central level by stimulating GH release through suppression of somatostatin output. Thereby, it can be concluded that obestatin may be involved in the modulation of growth processes in sheep.