Postoperative Hyponatremia after Endoscopic Endonasal Resection of Pituitary Adenomas: Historical Complication Rates and Risk Factors.

BACKGROUND: Hyponatremia is a common complication following endoscopic endonasal resection (EER) of pituitary adenomas. We report a single center, multi-surgeon study detailing baseline clinical data, outcomes, and factors associated with postoperative hyponatremia. METHODS: A retrospective cohort study of patients undergoing EER for pituitary adenoma at Tufts Medical Center was conducted. Most procedures were performed by the senior author (CBH). Cases were included if at least one postoperative sodium value was available and pathology confirmed pituitary adenoma. Hyponatremia was considered postoperative sodium <135 mEq/L. RESULTS: 272 patients underwent 310 EER procedures that met study criteria. Mean age was 53.3 years and mean tumor size was 18.8 mm. Postoperative hyponatremia occurred in 12.6% of cases, with 3.6% developing hyponatremia prior to discharge. Lower pre-operative sodium was associated with increased risk of developing any postoperative hyponatremia. Older age, prolactinoma pathology, and SSRI use were associated with moderate-severe hyponatremia (≤129 mEq/L), while lower preoperative sodium was associated with mild hyponatremia (130-134 mEq/L). Hyponatremia-related readmissions within 30 days occurred in 3.9% of patients. African-American race and postoperative hyponatremia were both associated with an increased risk of 30-day readmission. Mean nadir sodium for hyponatremic patients was 129.9 mEq/L. Growth hormone secreting pathology was associated with lower postoperative nadir sodium, while higher preoperative sodium was associated with higher postoperative nadir sodium. CONCLUSIONS: Hyponatremia is a common postoperative complication of EER for pituitary lesions that can cause significant morbidity, increase readmissions, and lead to increased healthcare costs.

TRH and NPY Interact to Regulate Dynamic Changes in Energy Balance in the Male Zebra Finch.

In contrast to mammals, birds have a higher basal metabolic rate and undertake wide range of energy-demanding activities. As a consequence, food deprivation for birds, even for a short period, poses major energy challenge. The energy-regulating hypothalamic homeostatic mechanisms, although extensively studied in mammals, are far from clear in the case of birds. We focus on the interplay between neuropeptide Y (NPY) and thyrotropin-releasing hormone (TRH), 2 of the most important hypothalamic signaling agents, in modulating the energy balance in a bird model, the zebra finch, Taeniopygia guttata. TRH neurons were confined to a few nuclei in the preoptic area and hypothalamus, and fibers widely distributed. The majority of TRH neurons in the hypothalamic paraventricular nucleus (PVN) whose axons terminate in median eminence were contacted by NPY-containing axons. Compared to fed animals, fasting significantly reduced body weight, PVN pro-TRH messenger RNA (mRNA) and TRH immunoreactivity, but increased NPY mRNA and NPY immunoreactivity in the infundibular nucleus (IN, avian homologue of mammalian arcuate nucleus) and PVN. Refeeding for a short duration restored PVN pro-TRH and IN NPY mRNA, and PVN NPY innervation to fed levels. Compared to control tissues, treatment of the hypothalamic superfused slices with NPY or an NPY-Y1 receptor agonist significantly reduced TRH immunoreactivity, a response blocked by treatment with a Y1-receptor antagonist. We describe a detailed neuroanatomical map of TRH-equipped elements, identify new TRH-producing neuronal groups in the avian brain, and demonstrate rapid restoration of the fasting-induced suppression of PVN TRH following refeeding. We further show that NPY via Y1 receptors may regulate PVN TRH neurons to control energy balance in T. guttata.

Origin of thyrotropin-releasing hormone neurons that innervate the tuberomammillary nuclei.

Hypophysiotropic thyrotropin-releasing hormone (TRH) neurons function as metabolic sensors that regulate the thyroid axis and energy homeostasis. Less is known about the role of other hypothalamic TRH neurons. As central administration of TRH decreases food intake and increases histamine in the tuberomammillary nuclei (TMN), and TMN histamine neurons are densely innervated by TRH fibers from an unknown origin, we mapped the location of TRH neurons that project to the TMN. The retrograde tracer, cholera toxin B subunit (CTB), was injected into the TMN E1-E2, E4-E5 subdivisions of adult Sprague-Dawley male rats. TMN projecting neurons were observed in the septum, preoptic area, bed nucleus of the stria terminalis (BNST), perifornical area, anterior paraventricular nucleus, peduncular and tuberal lateral hypothalamus (TuLH), suprachiasmatic nucleus and medial amygdala. However, CTB/pro-TRH178-199 double-labeled cells were only found in the TuLH. The specificity of the retrograde tract-tracing result was confirmed by administering the anterograde tracer, Phaseolus vulgaris leuco-agglutinin (PHAL) into the TuLH. Double-labeled PHAL-pro-TRH boutons were identified in all subdivisions of the TMN. TMN neurons double-labeled for histidine decarboxylase (Hdc)/PHAL, Hdc/Trh receptor (Trhr), and Hdc/Trh. Further confirmation of a TuLH-TRH neuronal projection to the TMN was established in a transgenic mouse that expresses Cre recombinase in TRH-producing cells following microinjection of a Cre recombinase-dependent AAV that expresses mCherry into the TuLH. We conclude that, in rodents, the TRH innervation of TMN originates in part from TRH neurons in the TuLH, and that this TRH population may contribute to regulate energy homeostasis through histamine Trhr-positive neurons of the TMN.

Cocaine- and amphetamine-regulated transcript peptide- and dopamine-containing systems interact in the ventral tegmental area of the zebra finch, Taeniopygia guttata, during dynamic changes in energy status.

The mesolimbic dopamine (DA)-pathway regulates food-reward, feeding-related behaviour and energy balance. Evidence underscores the importance of feeding-related neuropeptides in modulating activity of these DA neurons. The neuropeptide, CART, a crucial regulator of energy balance, modulates DA-release, and influences the activity of ventral tegmental area (VTA) DAergic neurons in the mammalian brain. Whether CART- and DA-containing systems interact at the level of VTA to regulate energy balance, however, is poorly understood. We explored the interaction between CART- and DA-containing systems in midbrain of the zebra finch, Taeniopygia guttata, an interesting model to study dynamic changes in energy balance due to higher BMR/daytime body temperature, and rapid responsiveness of the feeding-related neuropeptides to changes in energy state. Further, its midbrain DA-neurons share similarities with those in mammals. In the midbrain, tyrosine hydroxylase-immunoreactive (TH-i) neurons were seen in the substantia nigra (SN) and VTA [anterior (VTAa), mid (VTAm) and caudal (VTAc)]; those in VTA were smaller. In the VTA, CART-immunoreactive (CART-i)-fibers densely innervated TH-i neurons, and both CART-immunoreactivity (CART-ir) and TH-immunoreactivity (TH-ir) responded to energy status-dependent changes. Compared to fed and fasted birds, refeeding dramatically enhanced TH-ir and the percentage of TH-i neurons co-expressing FOS in the VTA. Increased prepro-CART-mRNA, CART-ir and a transient appearance of CART-i neurons was observed in VTAa of fasted, but not fed birds. To test the functional interaction between CART- and DA-containing systems, ex-vivo superfused midbrain-slices were treated with CART-peptide and changes in TH-ir analysed. Compared to control tissues, CART-treatment increased TH-ir in VTA but not SN. We propose that CART is a potential regulator of VTA DA-neurons and energy balance in T. guttata.

Adult-born proopiomelanocortin neurons derived from Rax-expressing precursors mitigate the metabolic effects of congenital hypothalamic proopiomelanocortin deficiency.

OBJECTIVE: Proopiomelanocortin (POMC) neurons of the hypothalamic arcuate nucleus are essential regulators of energy balance. Selective loss of POMC production in these cells results in extreme obesity and metabolic comorbidities. Neurogenesis occurs in the adult hypothalamus, but it remains uncertain whether functional POMC neurons emerge in physiologically significant numbers during adulthood. Here, we tested whether Rax-expressing precursors generate POMC neurons in adult mice and rescue the metabolic phenotype caused by congenital hypothalamic POMC deficiency. METHODS: Initially, we identified hypothalamic Rax-expressing cell types using wild-type and Rax-CreERT2:Ai34D mice. Then we generated compound Rax-CreERT2:ArcPomcloxTB/loxTB mice in which endogenous hypothalamic Pomc expression is silenced, but can be restored by tamoxifen administration selectively in neurons derived from Rax+ progenitors. The number of POMC neurons generated by Rax+ progenitors in adult mice and their axonal projections was determined. The metabolic effects of these neurons were assessed by measuring food intake, bodyweight, and body composition, along with glucose and insulin levels. RESULTS: We found that Rax is expressed by tanycytes and a previously unrecognized cell type in the hypothalamic parenchyma of adult mice. Rax+ progenitors generated ~10% of the normal adult hypothalamic POMC neuron population within two weeks of tamoxifen treatment. The same rate and steady state of POMC neurogenesis persisted from young adult to aged mice. These new POMC neurons established terminal projections to brain regions that were involved in energy homeostasis. Mice with Rax+ progenitor-derived POMC neurons had reduced body fat mass, improved glucose tolerance, increased insulin sensitivity, and decreased bodyweight in proportion to the number of new POMC neurons. CONCLUSIONS: These data demonstrate that Rax+ progenitors generate POMC neurons in sufficient numbers during adulthood to mitigate the metabolic abnormalities of hypothalamic POMC-deficient mice. The findings suggest that adult hypothalamic neurogenesis is a robust phenomenon in mice that can significantly impact energy homeostasis.

HEREDITARY ENDOCRINE TUMOURS: CURRENT STATE-OF-THE-ART AND RESEARCH OPPORTUNITIES: Early thyroidectomy in multiple endocrine neoplasia: a four decade experience.

Forty years ago, physicians caring for the J-kindred, a 100+ member family with multiple endocrine neoplasia type 2A (MEN2A), hypothesized that early thyroidectomy based on measurement of the biomarker calcitonin could cure patients at risk for development of medullary thyroid carcinoma (MTC). We re-evaluated 22 family members with proven RET proto-oncogene mutations (C634G) who underwent thyroidectomy and central lymphadenectomy between 1972 and 1994 based on stimulated calcitonin abnormalities. Current disease status was evaluated by serum calcitonin measurement and neck ultrasound in 18 of the 22 prospectively screened patients. The median age of the cohort at thyroidectomy was 16.5 years (range 9-24). The median duration of follow-up at the time of examination was 40 years (range 21-43) with a median current age of 52 years (range 34-65). Fifteen of the 18 patients had no detectable serum calcitonin (<2 pg/mL). Three had detectable serum calcitonin measurements, inappropriately elevated following total thyroidectomy. None of the 16 patients imaged had an abnormal ultrasound. Survival analysis shows no MTC-related deaths in the prospectively screened patients, whereas there were many in prior generations. Early thyroidectomy based on biomarker testing has rendered 15 of 18 MEN2A patients (83%) calcitonin-free with a median follow-up period of 40 years. There have been no deaths in the prospectively screened and thyroidectomized group. We conclude that early thyroidectomy and central lymph node dissection is an effective prophylactic treatment for hereditary MTC.

A Glial-Neuronal Circuit in the Median Eminence Regulates Thyrotropin-Releasing Hormone-Release via the Endocannabinoid System.

Based on the type-I cannabinoid receptor (CB1) content of hypophysiotropic axons and the involvement of tanycytes in the regulation of the hypothalamic-pituitary-thyroid (HPT) axis, we hypothesized that endocannabinoids are involved in the tanycyte-induced regulation of TRH release in the median eminence (ME). We demonstrated that CB1-immunoreactive TRH axons were associated to DAGLα-immunoreactive tanycyte processes in the external zone of ME and showed that endocannabinoids tonically inhibit the TRH release in this tissue. We showed that glutamate depolarizes the tanycytes, increases their intracellular Ca2+ level and the 2-AG level of the ME via AMPA and kainite receptors and glutamate transport. Using optogenetics, we demonstrated that glutamate released from TRH neurons influences the tanycytes in the ME. In summary, tanycytes regulate TRH secretion in the ME via endocannabinoid release, whereas TRH axons regulate tanycytes by glutamate, suggesting the existence of a reciprocal microcircuit between tanycytes and TRH terminals that controls TRH release.

Distributions of hypothalamic neuron populations coexpressing tyrosine hydroxylase and the vesicular GABA transporter in the mouse.

The hypothalamus contains catecholaminergic neurons marked by the expression of tyrosine hydroxylase (TH). As multiple chemical messengers coexist in each neuron, we determined if hypothalamic TH-immunoreactive (ir) neurons express vesicular glutamate or GABA transporters. We used Cre/loxP recombination to express enhanced GFP (EGFP) in neurons expressing the vesicular glutamate (vGLUT2) or GABA transporter (vGAT), then determined whether TH-ir neurons colocalized with native EGFPVglut2 - or EGFPVgat -fluorescence, respectively. EGFPVglut2 neurons were not TH-ir. However, discrete TH-ir signals colocalized with EGFPVgat neurons, which we validated by in situ hybridization for Vgat mRNA. To contextualize the observed pattern of colocalization between TH-ir and EGFPVgat , we first performed Nissl-based parcellation and plane-of-section analysis, and then mapped the distribution of TH-ir EGFPVgat neurons onto atlas templates from the Allen Reference Atlas (ARA) for the mouse brain. TH-ir EGFPVgat neurons were distributed throughout the rostrocaudal extent of the hypothalamus. Within the ARA ontology of gray matter regions, TH-ir neurons localized primarily to the periventricular hypothalamic zone, periventricular hypothalamic region, and lateral hypothalamic zone. There was a strong presence of EGFPVgat fluorescence in TH-ir neurons across all brain regions, but the most striking colocalization was found in a circumscribed portion of the zona incerta (ZI)-a region assigned to the hypothalamus in the ARA-where every TH-ir neuron expressed EGFPVgat . Neurochemical characterization of these ZI neurons revealed that they display immunoreactivity for dopamine but not dopamine ß-hydroxylase. Collectively, these findings indicate the existence of a novel mouse hypothalamic population that may signal through the release of GABA and/or dopamine.

Thyrotropin-Releasing-Hormone-Synthesizing Neurons of the Hypothalamic Paraventricular Nucleus Are Inhibited by Glycinergic Inputs.

Background: Glycine is a classical neurotransmitter that has role in both inhibitory and excitatory synapses. To understand whether glycinergic inputs are involved in the regulation of the hypophysiotropic thyrotropin-releasing hormone (TRH) neurons, the central controllers of the hypothalamic-pituitary-thyroid axis, the glycinergic innervation of the TRH neurons was studied in the hypothalamic paraventricular nucleus (PVN). Methods: Double-labeling immunocytochemistry and patch-clamp electrophysiology were used to determine the role of glycinergic neurons in the regulation of TRH neurons in the PVN. Anterograde and retrograde tracing methods were used to determine the sources of the glycinergic input of TRH neurons. Results: Glycine transporter-2 (GLYT2), a marker of glycinergic neurons, containing axons were found to establish symmetric type of synapses on TRH neurons in the PVN. Furthermore, glycine receptor immunoreactivity was observed in these TRH neurons. The raphe magnus (RMg) and the ventrolateral periaqueductal gray (VLPAG) were found to be the exclusive sources of the glycinergic innervation of the TRH neurons within the PVN. Patch-clamp electrophysiology using sections of TRH-IRES-tdTomato mice showed that glycine hyperpolarized the TRH neurons and completely blocked the firing of these neurons. Glycine also markedly hyperpolarized the TRH neurons in the presence of tetrodotoxin demonstrating the direct effect of glycine. In more than 60% of the TRH neurons, spontaneous inhibitory postsynaptic currents (sIPSCs) were observed, even after the pharmacological inhibition of glutamatergic and GABAergic neuronal transmission. The glycine antagonist, strychnine, almost completely abolished these sIPSCs, demonstrating the inhibitory nature of the glycinergic input of TRH neurons. Conclusions: These data demonstrate that TRH neurons in the PVN receive glycinergic inputs from the RMg and the VLPAG. The symmetric type of synaptic connection and the results of the electrophysiological experiments demonstrate the inhibitory nature of these inputs.

Comparison of Pheochromocytoma-Specific Morbidity and Mortality Among Adults With Bilateral Pheochromocytomas Undergoing Total Adrenalectomy vs Cortical-Sparing Adrenalectomy.

Importance: Large studies investigating long-term outcomes of patients with bilateral pheochromocytomas treated with either total or cortical-sparing adrenalectomies are needed to inform clinical management. Objective: To determine the association of total vs cortical-sparing adrenalectomy with pheochromocytoma-specific mortality, the burden of primary adrenal insufficiency after bilateral adrenalectomy, and the risk of pheochromocytoma recurrence. Design, Setting, and Participants: This cohort study used data from a multicenter consortium-based registry for 625 patients treated for bilateral pheochromocytomas between 1950 and 2018. Data were analyzed from September 1, 2018, to June 1, 2019. Exposures: Total or cortical-sparing adrenalectomy. Main Outcomes and Measures: Primary adrenal insufficiency, recurrent pheochromocytoma, and mortality. Results: Of 625 patients (300 [48%] female) with a median (interquartile range [IQR]) age of 30 (22-40) years at diagnosis, 401 (64%) were diagnosed with synchronous bilateral pheochromocytomas and 224 (36%) were diagnosed with metachronous pheochromocytomas (median [IQR] interval to second adrenalectomy, 6 [1-13] years). In 505 of 526 tested patients (96%), germline mutations were detected in the genes RET (282 patients [54%]), VHL (184 patients [35%]), and other genes (39 patients [7%]). Of 849 adrenalectomies performed in 625 patients, 324 (52%) were planned as cortical sparing and were successful in 248 of 324 patients (76.5%). Primary adrenal insufficiency occurred in all patients treated with total adrenalectomy but only in 23.5% of patients treated with attempted cortical-sparing adrenalectomy. A third of patients with adrenal insufficiency developed complications, such as adrenal crisis or iatrogenic Cushing syndrome. Of 377 patients who became steroid dependent, 67 (18%) developed at least 1 adrenal crisis and 50 (13%) developed iatrogenic Cushing syndrome during median (IQR) follow-up of 8 (3-25) years. Two patients developed recurrent pheochromocytoma in the adrenal bed despite total adrenalectomy. In contrast, 33 patients (13%) treated with successful cortical-sparing adrenalectomy developed another pheochromocytoma within the remnant adrenal after a median (IQR) of 8 (4-13) years, all of which were successfully treated with another surgery. Cortical-sparing surgery was not associated with survival. Overall survival was associated with comorbidities unrelated to pheochromocytoma: of 63 patients who died, only 3 (5%) died of metastatic pheochromocytoma. Conclusions and Relevance: Patients undergoing cortical-sparing adrenalectomy did not demonstrate decreased survival, despite development of recurrent pheochromocytoma in 13%. Cortical-sparing adrenalectomy should be considered in all patients with hereditary pheochromocytoma.

Chiari Malformation Type 1 in EPAS1-Associated Syndrome.

A syndrome of multiple paragangliomas/pheochromocytomas, somatostatinoma, and polycythemia due to somatic mosaic gain-of-function mutation of EPAS1, encoding HIF-2α, was previously described. HIF-2α has been implicated in endochondral and intramembranous ossification. Abnormal bone growth of the skull base may lead to Chiari malformation type I. We report two cases of EPAS1 gain-of-function mutation syndrome with Chiari malformation and developmental skull base anomalies. Patients were referred to the Section on Medical Endocrinology, Eunice Kennedy Shriver NICHD, NIH for evaluation of recurrent and metastatic paragangliomas or pheochromocytoma. The syndrome was confirmed genetically by identification of the functional EPAS1 gain-of-function mutation in the resected tumors and circulating leukocytes. Both patients were confirmed for characteristics of EPAS1 gain-of-function mutation syndrome by complete blood count (CBC), plasma biochemistry, and computed tomography (CT) of the abdomen and pelvis. Chiari malformation type I and abnormal bony development of the posterior fossa was found on MRI and CT of the head. The present study implicates EPAS1 mutations in abnormal posterior fossa development resulting in Chiari malformation type I.

Selective Restoration of Pomc Expression in Glutamatergic POMC Neurons: Evidence for a Dynamic Hypothalamic Neurotransmitter Network.

Hypothalamic POMC deficiency leads to obesity and metabolic deficiencies, largely due to the loss of melanocortin peptides. However, POMC neurons in the arcuate nucleus (ARC) are comprised of glutamatergic and GABAergic subpopulations. The developmental program, relative proportion and function of these two subpopulations are unresolved. To test whether glutamatergic POMC neurons serve a distinct role in maintaining energy homeostasis, we activated Pomc expression Cre- dependently in Vglut2-expressing neurons of mice with conditionally silenced Pomc alleles. The Vglut2-Pomc restored mice had normal ARC Pomc mRNA levels, POMC immunoreactivity, as well as body weight and body composition at age 12 weeks. Unexpectedly, the cumulative total of Vglut2+ glutamatergic- and Gad67+ GABAergic-Pomc neurons detected by in situ hybridization (ISH) exceeded 100% in both Vglut2- Pomc restored and control mice, indicating that a subpopulation of Pomc neurons must express both neuronal markers. Consistent with this hypothesis, triple ISH of C57BL/6J hypothalami revealed that 35% of ARC Pomc neurons were selectively Gad67+, 21% were selectively Vglut2+, and 38% expressed both Gad67 and Vglut2. The single Gad67+ and Vglut2+Pomc neurons were most prevalent in the rostral ARC, while the Vglut2/Gad67+ dual-phenotype cells predominated in the caudal ARC. A lineage trace using Ai9-tdTomato reporter mice to label fluorescently all Vglut2-expressing neurons showed equal numbers of tdTomato+ and tdTomato- POMC immunoreactive neurons. Together, these data suggest that POMC neurons exhibit developmental plasticity in their expression of glutamatergic and GABAergic markers, enabling re-establishment of normal energy homeostasis in the Vglut2-Pomc restored mice.

Thyrotropin-releasing hormone (TRH) in the brain and pituitary of the teleost, Clarias batrachus and its role in regulation of hypophysiotropic dopamine neurons.

Thyrotropin-releasing hormone (TRH) regulates the hypothalamic-pituitary-thyroid axis in mammals and also regulates prolactin secretion, directly or indirectly via tuberoinfundibular dopamine neurons. Although TRH is abundantly expressed in teleost brain and believed to mediate neuronal communication, empirical evidence is lacking. We analyzed pro-TRH-mRNA expression, mapped TRH-immunoreactive elements in the brain and pituitary, and explored its role in regulation of hypophysiotropic dopamine (DA) neurons in the catfish, Clarias batrachus. Partial pro-TRH transcript from C. batrachus transcriptome showed six TRH progenitors repeats. Quantitative real-time polymerase chain reaction (qRT-PCR) identified pro-TRH transcript in a number of different brain regions and immunofluorescence showed TRH-immunoreactive cells/fibers in the olfactory bulb, telencephalon, preoptic area (POA), hypothalamus, midbrain, hindbrain, and spinal cord. In the pituitary, TRH-immunoreactive fibers were seen in the neurohypophysis, proximal pars distalis, and pars intermedia but not rostral pars distalis. In POA, distinct TRH-immunoreactive cells/fibers were seen in nucleus preopticus periventricularis anterior (NPPa) that demonstrated a significant increase in TRH-immunoreactivity when collected during preparatory and prespawning phases, reaching a peak in the spawning phase. Although tyrosine hydroxylase (TH)-immunoreactive neurons in NPPa are hypophysiotropic, none of the TRH-immunoreactive neurons in NPPa accumulated neuronal tracer DiI following implants into the pituitary. However, 87 ± 1.6% NPPa TH-immunoreactive neurons were surrounded by TRH-immunoreactive axons that were seen in close proximity to the somata. Superfused POA slices treated with TRH (0.5-2 µM) significantly reduced TH concentration in tissue homogenates and the percent TH-immunoreactive area in the NPPa. We suggest that TRH in the brain of C. batrachus regulates a range of physiological functions but in particular, serves as a potential regulator of hypophysiotropic DA neurons and reproduction.

Endocannabinoid and nitric oxide systems of the hypothalamic paraventricular nucleus mediate effects of NPY on energy expenditure.

OBJECTIVE: Neuropeptide Y (NPY) is one of the most potent orexigenic peptides. The hypothalamic paraventricular nucleus (PVN) is a major locus where NPY exerts its effects on energy homeostasis. We investigated how NPY exerts its effect within the PVN. METHODS: Patch clamp electrophysiology and Ca2+ imaging were used to understand the involvement of Ca2+ signaling and retrograde transmitter systems in the mediation of NPY induced effects in the PVN. Immuno-electron microscopy were performed to elucidate the subcellular localization of the elements of nitric oxide (NO) system in the parvocellular PVN. In vivo metabolic profiling was performed to understand the role of the endocannabinoid and NO systems of the PVN in the mediation of NPY induced changes of energy homeostasis. RESULTS: We demonstrated that NPY inhibits synaptic inputs of parvocellular neurons in the PVN by activating endocannabinoid and NO retrograde transmitter systems via mobilization of Ca2+ from the endoplasmic reticulum, suggesting that NPY gates the synaptic inputs of parvocellular neurons in the PVN to prevent the influence of non-feeding-related inputs. While intraPVN administered NPY regulates food intake and locomotor activity via NO signaling, the endocannabinoid system of the PVN selectively mediates NPY-induced decrease in energy expenditure. CONCLUSION: Thus, within the PVN, NPY stimulates the release of endocannabinoids and NO via Ca2+-influx from the endoplasmic reticulum. Both transmitter systems appear to have unique roles in the mediation of the NPY-induced regulation of energy homeostasis, suggesting that NPY regulates food intake, energy expenditure, and locomotor activity through different neuronal networks of this nucleus.

Prss56 expression in the rodent hypothalamus: Inverse correlation with pro-opiomelanocortin suggests oscillatory gene expression in adult rat tanycytes.

We recently reported that the number of hypothalamic tanycytes expressing pro-opiomelanocortin (Pomc) is highly variable among brains of adult rats. While its cause and significance remain unknown, identifying other variably expressed genes in tanycytes may help understand this curious phenomenon. In this in situ hybridization study, we report that the Prss56 gene, which encodes a trypsin-like serine protease and is expressed in neural stem/progenitor cells, shows a similarly variable mRNA expression in tanycytes of adult rats and correlates inversely with tanycyte Pomc mRNA. Prss56 was expressed in α1, ß1, subsets of α2, and some median eminence γ tanycytes, but virtually absent from ß2 tanycytes. Prss56 was also expressed in vimentin positive tanycyte-like cells in the parenchyma of the ventromedial and arcuate nuclei, and in thyrotropin beta subunit-expressing cells of the pars tuberalis of the pituitary. In contrast to adults, Prss56 expression was uniformly high in tanycytes in adolescent rats. In mice, Prss56-expressing tanycytes and parenchymal cells were also observed but fewer in number and without significant variations. The results identify Prss56 as a second gene that is expressed variably in tanycytes of adult rats. We propose that the variable, inversely correlating expression of Prss56 and Pomc reflect periodically oscillating gene expression in tanycytes rather than stable expression levels that vary between individual rats. A possible functional link between Prss56 and POMC, and Prss56 as a potential marker for migrating tanycytes are discussed.

Regression of a nonfunctioning pituitary macroadenoma on the CDK4/6 inhibitor palbociclib: case report.

A 71-year-old female patient was referred in 2013 for evaluation of an asymptomatic nonsecreting pituitary adenoma. The adenoma, measuring 13 mm in height by 10 mm in width, was discovered incidentally on imaging in 2012. Biochemical testing demonstrated a nonfunctioning adenoma. Given the relatively small lesion size and the lack of symptoms, observation was preferred over surgical intervention. The patient was monitored with routine MRI, which until 2016 demonstrated minimal growth. In early 2016, the patient developed recurrence of metastatic breast cancer and was treated with palbociclib, a cyclin-dependent kinase (CDK) 4/6 inhibitor. This inhibitor acts on a pathway believed to be involved in pituitary adenoma tumorigenesis. One year after starting palbociclib, routine imaging demonstrated significant regression of her pituitary adenoma. The authors hypothesize that inhibition of the CDK4/6 pathway by palbociclib contributed to adenoma regression in this patient, and that palbociclib may represent a possible adjuvant therapy for the treatment of nonfunctioning pituitary adenomas.

Neuronal connections of the central amygdalar nucleus with refeeding-activated brain areas in rats.

Following fasting, satiety is accompanied by neuronal activation in brain areas including the central amygdalar nucleus (CEA). Since CEA is known to inhibit food intake, we hypothesized that CEA contributes to the termination of meal during refeeding. To better understand the organization of this satiety-related circuit, the interconnections of the CEA with refeeding-activated neuronal groups were elucidated using retrograde (cholera toxin-ß subunit, CTB) and anterograde (phaseolus vulgaris leucoagglutinin, PHA-L) tracers in male rats. C-Fos-immunoreactivity was used as marker of neuronal activation. The refeeding-activated input of the CEA primarily originated from the paraventricular thalamic, parasubthalamic and parabrachial nuclei. Few CTB-c-Fos double-labeled neurons were detected in the prefrontal cortex, lateral hypothalamic area, nucleus of the solitary tract (NTS) and the bed nuclei of the stria terminalis (BNST). Only few refeeding-activated proopiomelanocortin-producing neurons of the arcuate nucleus projected to the CEA. Anterograde tract tracing revealed a high density of PHAL-labeled axons contacted with refeeding-activated neurons in the BNST, lateral hypothalamic area, parasubthalamic, paraventricular thalamic and parabrachial nuclei and NTS; a low density of labeled axons was found in the paraventricular hypothalamic nucleus. Chemogenetic activation of the medial CEA (CEAm) inhibited food intake during the first hour of refeeding, while activation of lateral CEA had no effect. These data demonstrate the existence of reciprocal connections between the CEA and distinct refeeding-activated hypothalamic, thalamic and brainstem nuclei, suggesting the importance of short feedback loops in the regulation of satiety and importance of the CEAm in the regulation of food intake during refeeding.

Role of TRH/UCN3 neurons of the perifornical area/bed nucleus of stria terminalis region in the regulation of the anorexigenic POMC neurons of the arcuate nucleus in male mice and rats.

Two anorexigenic peptides, thyrotropin-releasing hormone (TRH) and urocortin 3 (UCN3), are co-expressed in a continuous neuronal group that extends from the perifornical area to the bed nucleus of stria terminalis, raising the possibility that this cell group may be involved in the regulation of energy homeostasis. In this study, therefore, we tested the hypothesis that the TRH/UCN3 neurons regulate food intake by influencing feeding-related neuropeptide Y (NPY) and/or proopiomelanocortin (POMC) neurons in the arcuate nucleus (ARC). Triple-labeled immunofluorescent preparations demonstrated that only very few NPY neurons (4.3 ± 1.3%) were contacted by double-labeled TRH/UCN3 axons in the ARC. In contrast, more than half of the POMC neurons (52.4 ± 8.5%) were contacted by double-labeled axons. Immuno-electron microscopy demonstrated that the UCN3 axons established asymmetric synapses with POMC neurons, indicating the excitatory nature of these synaptic specializations. Patch clamp electrophysiology revealed that TRH and UCN3 have antagonistic effects on the POMC neurons. While UCN3 depolarizes and increases the firing rate of POMC neurons, TRH prevents these effects of UCN3. These data demonstrate that TRH/UCN3 neurons in the perifornical/BNST region establish abundant synaptic associations with the POMC neurons in the ARC and suggest a potentially important role for these neurons in the regulation of food intake through an antagonistic interaction between TRH and UCN3 on the electrophysiological properties of POMC neurons.

A Transgenic Mouse Model for Detection of Tissue-Specific Thyroid Hormone Action.

Thyroid hormone (TH) is present in the systemic circulation and thus should affect all cells similarly in the body. However, tissues have a complex machinery that allows tissue-specific optimization of local TH action that calls for the assessment of TH action in a tissue-specific manner. Here, we report the creation of a TH action indicator (THAI) mouse model to study tissue-specific TH action. The model uses a firefly luciferase reporter readout in the context of an intact transcriptional apparatus and all elements of TH metabolism and transport and signaling. The THAI mouse allows the assessment of the changes of TH signaling in tissue samples or in live animals using bioluminescence, both in hypothyroidism and hyperthyroidism. Beyond pharmacologically manipulated TH levels, the THAI mouse is sufficiently sensitive to detect deiodinase-mediated changes of TH action in the interscapular brown adipose tissue (BAT) that preserves thermal homeostasis during cold stress. The model revealed that in contrast to the cold-induced changes of TH action in the BAT, the TH action in this tissue, at room temperature, is independent of noradrenergic signaling. Our data demonstrate that the THAI mouse can also be used to test TH receptor isoform-specific TH action. Thus, THAI mouse constitutes a unique model to study tissue-specific TH action within a physiological/pathophysiological context and test the performance of thyromimetics. In conclusion, THAI mouse provides an in vivo model to assess a high degree of tissue specificity of TH signaling, allowing alteration of tissue function in health and disease, independently of changes in circulating levels of TH.