Portal Capillaries Research Articles

Doublecortin-like knockdown in mice attenuates obesity by stimulating energy expenditure in adipose tissue

Crosstalk between peripheral metabolic organs and the central nervous system is essential for body weight control. At the base of the hypothalamus, β-tanycytes surround the portal capillaries and function as gatekeepers to facilitate transfer of substances from the circulation into the cerebrospinal fluid and vice versa. Here, we investigated the role of the neuroplasticity gene doublecortin-like (DCL), highly expressed by β-tanycytes, in body weight control and whole-body energy metabolism. We demonstrated that DCL-knockdown through a doxycycline-inducible shRNA expression system prevents body weight gain by reducing adiposity in mice. DCL-knockdown slightly increased whole-body energy expenditure possibly as a result of elevated circulating thyroid hormones. In white adipose tissue (WAT) triglyceride uptake was increased while the average adipocyte cell size was reduced. At histological level we observed clear signs of browning, and thus increased thermogenesis in WAT. We found no indications for stimulated thermogenesis in brown adipose tissue (BAT). Altogether, we demonstrate an important, though subtle, role of tanycytic DCL in body weight control through regulation of energy expenditure, and specifically WAT browning. Elucidating mechanisms underlying the role of DCL in regulating brain-peripheral crosstalk further might identify new treatment targets for obesity.

Evaluation and management of abnormal liver enzymes in the liver transplant recipient: When, why, and what now?

Evaluation and management of abnormal liver enzymes in the liver transplant recipient: When, why, and what now?

Vasopressin gene products are colocalised with corticotrophin-releasing factor within neurosecretory vesicles in the external zone of the median eminence of the Japanese macaque monkey (Macaca fuscata).

Arginine vasopressin (AVP), when released into portal capillaries with corticotrophin-releasing factor (CRF) from terminals of parvocellular neurones of the hypothalamic paraventricular nucleus (PVH), facilitates the secretion of adrenocorticotrophic hormone (ACTH) in stressed rodents. The AVP gene encodes a propeptide precursor containing AVP, AVP-associated neurophysin II (NPII), and a glycopeptide copeptin, although it is currently unclear whether copeptin is always cleaved from the neurophysin and whether the NPII and/or copeptin have any functional role in the pituitary. Furthermore, for primates, it is unknown whether CRF, AVP, NPII and copeptin are all colocalised in neurosecretory vesicles in the terminal region of the paraventricular CRF neurone axons. Therefore, we investigated, by fluorescence and immunogold immunocytochemistry, the cellular and subcellular relationships of these peptides in the CRF- and AVP-producing cells in unstressed Japanese macaque monkeys (Macaca fuscata). Reverse transcription-polymerase chain reaction analysis showed the expression of both CRF and AVP mRNAs in the monkey PVH. As expected, in the magnocellular neurones of the PVH and supraoptic nucleus, essentially no CRF immunoreactivity could be detected in NPII-immunoreactive (AVP-producing) neurones. Immunofluorescence showed that, in the parvocellular part of the PVH, NPII was detectable in a subpopulation (approximately 39%) of the numerous CRF-immunoreactive neuronal perikarya, whereas, in the outer median eminence, NPII was more prominent (approximately 52%) in the CRF varicosities. Triple immunoelectron microscopy in the median eminence demonstrated the presence of both NPII and copeptin immunoreactivity in dense-cored vesicles of CRF-containing axons. The results are consistent with an idea that the AVP propeptide is processed and NPII and copeptin are colocalised in hypothalamic-pituitary CRF axons in the median eminence of a primate. The CRF, AVP and copeptin are all co-packaged in neurosecretory vesicles in monkeys and are thus likely to be co-released into the portal capillary blood to amplify ACTH release from the primate anterior pituitary.

Tanycytes and the Control of Thyrotropin-Releasing Hormone Flux Into Portal Capillaries.

Central and peripheral mechanisms that modulate energy intake, partition and expenditure determine energy homeostasis. Thyroid hormones (TH) regulate energy expenditure through the control of basal metabolic rate and thermogenesis; they also modulate food intake. TH concentrations are regulated by the hypothalamus-pituitary-thyroid (HPT) axis, and by transport and metabolism in blood and target tissues. In mammals, hypophysiotropic thyrotropin-releasing hormone (TRH) neurons of the paraventricular nucleus of the hypothalamus integrate energy-related information. They project to the external zone of the median eminence (ME), a brain circumventricular organ rich in neuron terminal varicosities and buttons, tanycytes, other glial cells and capillaries. These capillary vessels form a portal system that links the base of the hypothalamus with the anterior pituitary. Tanycytes of the medio-basal hypothalamus express a repertoire of proteins involved in transport, sensing, and metabolism of TH; among them is type 2 deiodinase, a source of 3,3′,5-triiodo-L-thyronine necessary for negative feedback on TRH neurons. Tanycytes subtypes are distinguished by position and phenotype. The end-feet of β2-tanycytes intermingle with TRH varicosities and terminals in the external layer of the ME and terminate close to the ME capillaries. Besides type 2 deiodinase, β2-tanycytes express the TRH-degrading ectoenzyme (TRH-DE); this enzyme likely controls the amount of TRH entering portal vessels. TRH-DE is rapidly upregulated by TH, contributing to TH negative feedback on HPT axis. Alterations in energy balance also regulate the expression and activity of TRH-DE in the ME, making β2-tanycytes a hub for energy-related regulation of HPT axis activity. β2-tanycytes also express TRH-R1, which mediates positive effects of TRH on TRH-DE activity and the size of β2-tanycyte end-feet contacts with the basal lamina adjacent to ME capillaries. These end-feet associations with ME capillaries, and TRH-DE activity, appear to coordinately control HPT axis activity. Thus, down-stream of neuronal control of TRH release by action potentials arrival in the external layer of the median eminence, imbricated intercellular processes may coordinate the flux of TRH into the portal capillaries. In conclusion, β2-tanycytes appear as a critical cellular element for the somatic and post-secretory control of TRH flux into portal vessels, and HPT axis regulation in mammals.

SUN-403 Drinking Water from a Dirty Prison Sink: A Rare Case of Acute Myeloid Leukemia with Diabetes Insipidus and Panhypopituitarism

Panhypopituitarism is an extremely rare disorder in acute myeloid leukemia (AML) with only 6 cases previously reported to date. The mechanism of AML causing panhypopituitarism is unclear, but some of the leading hypotheses support leukemic infiltration or leukostasis. A 30-year-old incarcerated woman with a history of intravenous drug use and hepatitis C presented with 5 days of fevers, vomiting, and progressive abdominal pain. She reported an unintentional 30 lb weight loss and a month of polyuria and polydipsia severe enough to cause her to drink water from the dirty sink in her prison cell. Patient denied headache, visual disturbance, or galactorrhea. Initial laboratory studies showed a white blood cell count of 350K with 90% myeloblasts, consistent with AML. She received emergent leukocytapheresis and was started on cytarabine and daunorubicin chemotherapy. Upon admission, she was also noted to have hypernatremia (Na 152 mmol/L), persistent hypotension (BP 80s/40s) unresponsive to fluid resuscitation, and high urine output of 5-14 L/day. Desmopressin (DDAVP) 4 mcg IV was administered and resulted in increased urine osmolality from 116 to 451 mOsm/L with significant decrease in urine output, consistent with central diabetes insipidus (cDI). Brain MRI showed heterogeneous thickening of the infundibulum and an absence of the posterior pituitary T1 bright spot, which can be seen in cDI. Hormonal evaluation revealed low free T4 0.77 ng/dL (ref. 0.93-1.70) and normal TSH 4.03 mIU/mL (ref. 0.27-4.20), consistent with central hypothyroidism. Prolactin was mildly elevated at 39 ng/mL (ref. 4.8-23.3). She was also noted to have low AM cortisol 3 µg/dL (ref. 5-20) prompting a cosyntropin stimulation test which showed baseline cortisol of 5.9 rising to 13.2 µg/dL, which is an inadequate response. She was treated for panhypopituitarism with hydrocortisone 50 mg IV Q8H tapered gradually to a replacement dose, DDAVP 50 mcg PO QHS, and levothyroxine 50 mcg PO daily. Her remaining hospital course was complicated by neutropenic fever. She was ultimately transferred to Massachusetts General Hospital on hospital day 19 (Day 16 of chemotherapy) to be closer to her family. This is a rare case report of a young patient with new diagnosis of AML presenting with both cDI and panhypopituitarism. The mechanism remains unclear. One possible rationale is pituitary stalk involvement by leukemic infiltration which is evidenced by a thickening appearance on MRI. Another explanation is an ischemic or thrombotic effect related to hyperleukocytosis. The resulting hyperviscosity and subsequent disruption of hypophyseal portal capillary flow can impede release of hypothalamic hormones destined for the pituitary. Our patient had MRI findings of an abnormally thickened stalk and lack of “bright spot” which supports the hypothesis of leukemic infiltration and significant disruption of the hypothalamic-pituitary axes.

Dopamine Release Dynamics in the Tuberoinfundibular Dopamine System.

The relationship between neuronal impulse activity and neurotransmitter release remains elusive. This issue is especially poorly understood in the neuroendocrine system, with its particular demands on periodically voluminous release of neurohormones at the interface of axon terminals and vasculature. A shortage of techniques with sufficient temporal resolution has hindered real-time monitoring of the secretion of the peptides that dominate among the neurohormones. The lactotropic axis provides an important exception in neurochemical identity, however, as pituitary prolactin secretion is primarily under monoaminergic control, via tuberoinfundibular dopamine (TIDA) neurons projecting to the median eminence (ME). Here, we combined electrical or optogenetic stimulation and fast-scan cyclic voltammetry to address dopamine release dynamics in the male mouse TIDA system. Imposing different discharge frequencies during brief (3 s) stimulation of TIDA terminals in the ME revealed that dopamine output is maximal at 10 Hz, which was found to parallel the TIDA neuron action potential frequency distribution during phasic discharge. Over more sustained stimulation periods (150 s), maximal output occurred at 5 Hz, similar to the average action potential firing frequency of tonically active TIDA neurons. Application of the dopamine transporter blocker, methylphenidate, significantly increased dopamine levels in the ME, supporting a functional role of the transporter at the neurons' terminals. Lastly, TIDA neuron stimulation at the cell body yielded perisomatic release of dopamine, which may contribute to an ultrafast negative feedback mechanism to constrain TIDA electrical activity. Together, these data shed light on how spiking patterns in the neuroendocrine system translate to vesicular release toward the pituitary and identify how dopamine dynamics are controlled in the TIDA system at different cellular compartments.SIGNIFICANCE STATEMENT A central question in neuroscience is the complex relationship between neuronal discharge activity and transmitter release. By combining optogenetic stimulation and voltammetry, we address this issue in dopamine neurons of the neuroendocrine system, which faces particular spatiotemporal demands on exocytotic release; large amounts of neurohormone need to be secreted into the portal capillaries with precise timing to adapt to physiological requirements. Our data show that release is maximal around the neurons' default firing frequency. We further provide support for functional dopamine transport at the neurovascular terminals, shedding light on a long-standing controversy about the existence of neuroendocrine transmitter reuptake. Finally, we show that dopamine release occurs also at the somatodendritic level, providing a substrate for an ultrashort autoregulatory feedback loop.

Acute antibody- mediated rejection in ABO-incompatible pediatric liver transplantation: a single center experience in Japan

Introduction: It was reported that patients younger than two years of age were able to accept ABO-incompatible liver transplantation (ABO-I LTx) without any preoperative desensitization treatment. However, evidences of acute antibody-mediated rejection (aAMR) following ABO-I LTx remain limited in pediatric LTx. The aim of this study was to clarify clinical details of aAMR following pediatric ABO-I LTx. Method: We retrospectively analyzed our database of patients who underwent ABO-I LTx in our institute between November 2005 and June 2019. Diagnosis of aAMR was proven by histological findings of dilatation of portal capillaries and positive staining for C4d. Result: There were 103 (18.4%) cases of ABO-I LTx among 560 LTx in our institute. The number of patients under two years of age was 80 (77.7%), who did not receive prophylactic Rituximab as our protocol. The incidence of acute AMR was 6.8% (7 cases) including four patients under two years of age. The youngest was 8-month-old. Two patients over two years of age suffering from aAMR did not receive prophylactic Rituximab due to urgent LTx (acute liver failure). Postoperative anti-donor blood type IgM titers (AdB-IgM) were significantly higher in the cases of aAMR: median titers of aAMR cases was 1:32; that of non aAMR cases was 1:2 (p<0.01). The cutoff values were estimated by a ROC curve as 1:16. On the other hands, preoperative AdB IgM did not show significant difference. As the treatments of aAMR, steroid bolus injection therapy and IVIG were immediately introduced for all patients and additional plasma exchange was performed for three patients, followed by administration of MMF. Although all patients recovered from aAMR, biliary stricture was occurred in a case. Conclusion: It was considered that Rituximab prophylaxis should be extended to the patients under two years of age and we have not to overlook mild elevation of AdB-IgM after pediatric ABO-I LTx.

Age and Long-Term Hormone Treatment Effects on the Ultrastructural Morphology of the Median Eminence of Female Rhesus Macaques

The median eminence (ME) of the hypothalamus comprises the hypothalamic nerve terminals, glia (especially tanycytes) and the portal capillary vasculature that transports hypothalamic neurohormones to the anterior pituitary gland. The ultrastructure of the ME is dynamically regulated by hormones and undergoes organizational changes during development and reproductive cycles in adult females, but relatively little is known about the ME during aging, especially in nonhuman primates. Therefore, we used a novel transmission scanning electron microscopy technique to examine the cytoarchitecture of the ME of young and aged female rhesus macaques in a preclinical monkey model of menopausal hormone treatments. Rhesus macaques were ovariectomized and treated for 2 years with vehicle, estradiol (E₂), or estradiol + progesterone (E₂ + P₄). While the overall cytoarchitecture of the ME underwent relatively few changes with age and hormones, changes to some features of neural and glial components near the portal capillaries were observed. Specifically, large neuroterminal size was greater in aged compared to young adult animals, an effect that was mitigated or reversed by E₂ alone but not by E₂ + P₄ treatment. Overall glial size and the density and tissue fraction of the largest subset of glia were greater in aged monkeys, and in some cases reversed by E₂ treatment. Mitochondrial size was decreased by E₂, but not E₂ + P₄, only in aged macaques. These results contrast substantially with work in rodents, suggesting that the ME of aging macaques is less vulnerable to age-related disorganization, and that the effects of E₂ on monkeys' ME are age specific.

Substance P Immunoreactivity Exhibits Frequent Colocalization with Kisspeptin and Neurokinin B in the Human Infundibular Region

Neurons synthesizing neurokinin B (NKB) and kisspeptin (KP) in the hypothalamic arcuate nucleus represent important upstream regulators of pulsatile gonadotropin-releasing hormone (GnRH) neurosecretion. In search of neuropeptides co-expressed in analogous neurons of the human infundibular nucleus (Inf), we have carried out immunohistochemical studies of the tachykinin peptide Substance P (SP) in autopsy samples from men (21-78 years) and postmenopausal (53-83 years) women. Significantly higher numbers of SP-immunoreactive (IR) neurons and darker labeling were observed in the Inf of postmenopausal women than in age-matched men. Triple-immunofluorescent studies localized SP immunoreactivity to considerable subsets of KP-IR and NKB-IR axons and perikarya in the infundibular region. In postmenopausal women, 25.1% of NKB-IR and 30.6% of KP-IR perikarya contained SP and 16.5% of all immunolabeled cell bodies were triple-labeled. Triple-, double- and single-labeled SP-IR axons innervated densely the portal capillaries of the infundibular stalk. In quadruple-labeled sections, these axons formed occasional contacts with GnRH-IR axons. Presence of SP in NKB and KP neurons increases the functional complexity of the putative pulse generator network. First, it is possible that SP modulates the effects of KP and NKB in axo-somatic and axo-dendritic afferents to GnRH neurons. Intrinsic SP may also affect the activity and/or neuropeptide release of NKB and KP neurons via autocrine/paracrine actions. In the infundibular stalk, SP may influence the KP and NKB secretory output via additional autocrine/paracrine mechanisms or regulate GnRH neurosecretion directly. Finally, possible co-release of SP with KP and NKB into the portal circulation could underlie further actions on adenohypophysial gonadotrophs.

Glutamatergic and GABAergic innervation of GnRH neurons in the human hypothalamus

Event Abstract Back to Event Glutamatergic and GABAergic innervation of GnRH neurons in the human hypothalamus E. Hrabovszky1*, C. S. Molnár1, I. Kallo2, B. Borsay3, L. Sarkadi3, L. Herczeg3, M. Watanabe4 and Z. Liposits1, 2 1 Hungarian Academy of Sciences, Institute of Experimental Medicine, Hungary 2 Pázmány Péter Catholic University, Department of Neuroscience, Hungary 3 University of Debrecen, Department of Forensic Medicine, Hungary 4 Hokkaido University School of Medicine, Department of Anatomy, Japan Neurosecretory projections of gonadotropin-releasing hormone (GnRH) neurons to the hypophysial portal capillaries represent the final common output way of the hypothalamus in the neuroendocrine control of reproduction. GnRH neurons receive afferent input from a variety of neurotransmitter systems which are only partly characterized in the human. In the present study we used immunohistochemical approaches to address the contribution of the amino acid neurotransmitters GABA and glutamate to the afferent regulation of human GnRH neurons. According to previous findings in rodents where GABA represents the main neurotransmitter in the afferent control of GnRH neurons, we found that vesicular GABA transporter-immunoreactive GABAergic axons abundantly innervated the cell bodies and the dendrites of human GnRH neurons. While in rats, only glutamatergic axons of the VGLUT2 phenotype innervate GnRH neurons, in human samples we observed both VGLUT1- and VGLUT2 immunoreactive afferent contacts on GnRH neurons, with a preferential accumulation on GnRH dendrites. These morphological observations implicate the classic amino acid neurotransmitters GABA and glutamate in the afferent regulation of human GnRH neurons. As in rodents, GABA-ergic and glutamatergic afferents may have important contributions to metabolic-, sex steroid-, circadian- and stress signaling to the reproductive axis. Acknowledgements Supported by: OTKA K69127, T73002 and K83710; ETT 122/2009; FP7/2007-2013 (n° 245009) Keywords: Neuroendocrinology, Neuroscience Conference: 13th Conference of the Hungarian Neuroscience Society (MITT), Budapest, Hungary, 20 Jan - 22 Jan, 2011. Presentation Type: Abstract Topic: Neuroendocrinology Citation: Hrabovszky E, Molnár CS, Kallo I, Borsay B, Sarkadi L, Herczeg L, Watanabe M and Liposits Z (2011). Glutamatergic and GABAergic innervation of GnRH neurons in the human hypothalamus. Front. Neurosci. Conference Abstract: 13th Conference of the Hungarian Neuroscience Society (MITT). doi: 10.3389/conf.fnins.2011.84.00141 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 03 Mar 2011; Published Online: 23 Mar 2011. * Correspondence: Dr. E. Hrabovszky, Hungarian Academy of Sciences, Institute of Experimental Medicine, Budapest, Hungary, hrabovszky.erik@koki.mta.hu Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers E. Hrabovszky C. S Molnár I. Kallo B. Borsay L. Sarkadi L. Herczeg M. Watanabe Z. Liposits Google E. Hrabovszky C. S Molnár I. Kallo B. Borsay L. Sarkadi L. Herczeg M. Watanabe Z. Liposits Google Scholar E. Hrabovszky C. S Molnár I. Kallo B. Borsay L. Sarkadi L. Herczeg M. Watanabe Z. Liposits PubMed E. Hrabovszky C. S Molnár I. Kallo B. Borsay L. Sarkadi L. Herczeg M. Watanabe Z. Liposits Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

QOF

The relationship between neuronal impulse activity and neurotransmitter release remains elusive. This issue is especially poorly understood in the neuroendocrine system, with its particular demands on periodically voluminous release of neurohormones at the interface of axon terminals and vasculature. A shortage of techniques with sufficient temporal resolution has hindered real-time monitoring of the secretion of the peptides that dominate among the neurohormones. The lactotropic axis provides an important exception in neurochemical identity, however, as pituitary prolactin secretion is primarily under monoaminergic control, via tuberoinfundibular dopamine (TIDA) neurons projecting to the median eminence (ME). Here, we combined electrical or optogenetic stimulation and fast-scan cyclic voltammetry to address dopamine release dynamics in the male mouse TIDA system. Imposing different discharge frequencies during brief (3 s) stimulation of TIDA terminals in the ME revealed that dopamine output is maximal at 10 Hz, which was found to parallel the TIDA neuron action potential frequency distribution during phasic discharge. Over more sustained stimulation periods (150 s), maximal output occurred at 5 Hz, similar to the average action potential firing frequency of tonically active TIDA neurons. Application of the dopamine transporter blocker, methylphenidate, significantly increased dopamine levels in the ME, supporting a functional role of the transporter at the neurons9 terminals. Lastly, TIDA neuron stimulation at the cell body yielded perisomatic release of dopamine, which may contribute to an ultrafast negative feedback mechanism to constrain TIDA electrical activity. Together, these data shed light on how spiking patterns in the neuroendocrine system translate to vesicular release toward the pituitary and identify how dopamine dynamics are controlled in the TIDA system at different cellular compartments. <b>SIGNIFICANCE STATEMENT</b> A central question in neuroscience is the complex relationship between neuronal discharge activity and transmitter release. By combining optogenetic stimulation and voltammetry, we address this issue in dopamine neurons of the neuroendocrine system, which faces particular spatiotemporal demands on exocytotic release; large amounts of neurohormone need to be secreted into the portal capillaries with precise timing to adapt to physiological requirements. Our data show that release is maximal around the neurons9 default firing frequency. We further provide support for functional dopamine transport at the neurovascular terminals, shedding light on a long-standing controversy about the existence of neuroendocrine transmitter reuptake. Finally, we show that dopamine release occurs also at the somatodendritic level, providing a substrate for an ultrashort autoregulatory feedback loop.

The hypothalamic median eminence and its role in reproductive aging

The median eminence at the base of the hypothalamus serves as an interface between the neural and peripheral endocrine systems. It releases hypothalamic-releasing hormones into the portal capillary bed for transport to the anterior pituitary, which provides further signals to target endocrine systems. Of specific relevance to reproduction, a group of about 1000 neurons in mammals release the gonadotropin-releasing hormone (GnRH) peptide from neuroterminals in the median eminence. During the life cycle, there are dramatic changes in reproductive demands, and we focus this review on how GnRH terminals in the median eminence change during reproductive senescence. We discuss morphological and functional properties of the median eminence, and how relationships among GnRH terminals and their microenvironment of nerve terminals, glial cells, and the portal capillary vasculature determine the ability of GnRH peptide to be secreted and to reach its target in the anterior pituitary gland.

Dual Somatic Recordings from Gonadotropin-Releasing Hormone (GnRH) Neurons Identified by Green Fluorescent Protein (GFP) in Hypothalamic Slices

Gonadotropin-Releasing Hormone (GnRH) is a small neuropeptide that regulates pituitary release of luteinizing hormone (LH) and follicle-stimulating hormone (FSH). These gonadotropins are essential for the regulation of reproductive function. The GnRH-containing neurons are distributed diffusely throughout the hypothalamus and project to the median eminence where they release GnRH from their axon terminals into the hypophysiotropic portal system (1). In the portal capillaries, GnRH travels to the anterior pituitary gland to stimulate release of gonadotropins into systemic circulation. GnRH release is not continuous but rather occurs in episodic pulses. It is well established that the intermittent manner of GnRH release is essential for reproduction (2, 3).Coordination of activity of multiple GnRH neurons probably underlies GnRH pulses. Total peptide content in GnRH neurons is approximately 1.0 pg/cell (4), of which 30% likely comprises the releasable pool. Levels of GnRH during a pulse (5, 6), suggest multiple GnRH neurons are probably involved in neurosecretion. Likewise, single unit activity extracted from hypothalamic multi-unit recordings during LH release indicates changes in activity of multiple neurons (7). The electrodes with recorded activity during LH pulses are associated with either GnRH somata or fibers (8). Therefore, at least some of this activity arises from GnRH neurons.The mechanisms that result in synchronized firing in hypothalamic GnRH neurons are unknown. Elucidating the mechanisms that coordinate firing in GnRH neurons is a complex problem. First, the GnRH neurons are relatively few in number. In rodents, there are 800-2500 GnRH neurons. It is not clear that all GnRH neurons are involved in episodic GnRH release. Moreover, GnRH neurons are diffusely distributed (1). This has complicated our understanding of coordination of firing and has made many technical approaches intractable. We have optimized loose cell-attached recordings in current-clamp mode for the direct detection of action potentials and developed a recording approach that allows for simultaneous recordings from pairs of GnRH neurons.

Dual Somatic Recordings from Gonadotropin-Releasing Hormone (GnRH) Neurons Identified by Green Fluorescent Protein (GFP) in Hypothalamic Slices

Gonadotropin-Releasing Hormone (GnRH) is a small neuropeptide that regulates pituitary release of luteinizing hormone (LH) and follicle-stimulating hormone (FSH). These gonadotropins are essential for the regulation of reproductive function. The GnRH-containing neurons are distributed diffusely throughout the hypothalamus and project to the median eminence where they release GnRH from their axon terminals into the hypophysiotropic portal system (1). In the portal capillaries, GnRH travels to the anterior pituitary gland to stimulate release of gonadotropins into systemic circulation. GnRH release is not continuous but rather occurs in episodic pulses. It is well established that the intermittent manner of GnRH release is essential for reproduction (2, 3). Coordination of activity of multiple GnRH neurons probably underlies GnRH pulses. Total peptide content in GnRH neurons is approximately 1.0 pg/cell (4), of which 30% likely comprises the releasable pool. Levels of GnRH during a pulse (5, 6), suggest multiple GnRH neurons are probably involved in neurosecretion. Likewise, single unit activity extracted from hypothalamic multi-unit recordings during LH release indicates changes in activity of multiple neurons (7). The electrodes with recorded activity during LH pulses are associated with either GnRH somata or fibers (8). Therefore, at least some of this activity arises from GnRH neurons. The mechanisms that result in synchronized firing in hypothalamic GnRH neurons are unknown. Elucidating the mechanisms that coordinate firing in GnRH neurons is a complex problem. First, the GnRH neurons are relatively few in number. In rodents, there are 800-2500 GnRH neurons. It is not clear that all GnRH neurons are involved in episodic GnRH release. Moreover, GnRH neurons are diffusely distributed (1). This has complicated our understanding of coordination of firing and has made many technical approaches intractable. We have optimized loose cell-attached recordings in current-clamp mode for the direct detection of action potentials and developed a recording approach that allows for simultaneous recordings from pairs of GnRH neurons.

Synchronized Network Oscillations in Rat Tuberoinfundibular Dopamine Neurons: Switch to Tonic Discharge by Thyrotropin-Releasing Hormone

The pituitary hormone, prolactin, triggers lactation in nursing mothers. Under nonlactating conditions, prolactin secretion is suppressed by powerful inhibition from hypothalamic tuberoinfundibular dopamine (TIDA) neurons. Although firing pattern has been suggested as integral to neuroendocrine control, the electrical behavior of TIDA cells remains unknown. We demonstrate that rat TIDA neurons discharge rhythmically in a robust 0.05 Hz oscillation. The oscillation is phase locked between neurons, and while it persists during chemical synaptic transmission blockade, it is abolished by gap junction antagonists. Thyrotropin-releasing hormone (TRH) potently stimulates prolactin release, an effect assumed to take place in the pituitary. In TIDA cells, TRH caused a transition from phasic to tonic firing through combined pre- and postsynaptic effects. These findings suggest a model for prolactin regulation where a TIDA network switch from oscillations to sustained discharge converts dopamine from an antagonist at high concentrations to a functional agonist as dopamine output from the network decreases.

Cell organization of the rat pars tuberalis. Evidence for open communication between pars tuberalis cells, cerebrospinal fluid and tanycytes

The pars tuberalis (PT) is the only pituitary region in close contact with the medial-basal hypothalamus and bathed by cerebrospinal fluid (CSF). Although PT has long been recognized as an endocrine gland, certain aspects of its structure remain obscure. The present investigation has been designed to gain information concerning (1) the cellular organization of PT, (2) the PT/median eminence spatial relationship and (3) the exposure of various cell compartments of PT to CSF. Non-endocrine cells (S100-reactive) appear as the organizer of the PT architecture. The apical poles of these cells line large cistern-like cavities and the processes of these cells establish a close spatial relationship with PT-specific secretory cells, portal capillaries and tanycytes. The cisterns are also endowed with clusters of ciliated cells and with a highly electron-dense and PAS-reactive content. The unique spatial organization of endocrine and non-endocrine cells of the PT supports a functional relationship between both cell populations. PT endocrine cells display a hallmark of PT-specific cells, namely, the paranuclear spot, which is a complex structure involving the Golgi apparatus, a large pool of immature secretory granules and a centriole from which originates a single 9+0 cilium projecting to the intercellular channels. Horseradish peroxidase (HRP) injected into the CSF readily reaches the intercellular channels of PT and the inner channel of the single cilium and is incorporated by the endocytic machinery of the secretory cells. The PT endocrine cells, through their single 9+0 cilium, may act as sensors of the CSF. HRP also reaches the lumen of the cisterns, indicating that this PT compartment is also exposed to CSF. PT endocrine cells establish direct cell-to-cell contacts with hypothalamic beta(1) tanycytes, suggesting a second means of brain-PT communication.

Oxytocin in health and disease

Oxytocin is a nonapeptide of the neurohypophyseal protein family that binds specifically to the oxytocin receptor to produce a multitude of central and peripheral physiological responses. Within the central nervous system oxytocin is expressed by the neurons of the hypothalamus that project into higher brain centres and the posterior pituitary gland, from where it enters the circulation by release into the portal capillaries. Centrally, it modulates, maternal, sexual, social and stress related behaviour. Peripheral actions of oxytocin are commonly associated with smooth muscle contraction, particularly within the female and male reproductive tracts. Local synthesis of oxytocin along with its receptor in these regions indicates the presence of local oxytocinergic systems. More sinister implications for oxytocin in autism, depression and several cancers have recently been identified. A greater understanding of the role of oxytocinergic mechanisms will determine the potential for targeting this regulatory peptide in the pharmacological management of these disorders.

Identification of hypophysiotropic luteinizing hormone-releasing hormone (LHRH) neurons by combined retrograde labeling and immunocytochemistry.

The decapeptide luteinizing hormone-releasing hormone (LHRH) is produced by telencephalic and diencephalic neurons and transported to the median eminence (ME). After having been released from nerve terminals, it is carried by the hypophysial portal vessels to the anterior pituitary, where it stimulates the production and release of luteinizing hormone (LH) and follicle stimulating hormone (FSH). Those LHRH neurons which project to the ME represent the final common pathway for the regulation of the pituitary/gonadal axis. We identified these neurons by injecting a retrograde tracer, the lectin wheat germ agglutinin (WGA), into the external zone of the ME. Eight to 24 hours later colchicine was given into the lateral ventricle and 24-48 hours after the WGA injection the animals were sacrificed. Vibratome sections of the brains were stained simultaneously for WGA and LHRH with a dual immunocytochemical technique. Approximately 70% of the LHRH neurons in the septum and the anterior hypothalamus were double-labeled, indicating that they projected to the ME. Double labeled LHRH cells were either smooth, fusiform or "spiny". WGA-accumulating LHRH perikarya were intermixed with single-labeled LHRH cells. The remaining 30% of the LHRH neurons which were not labeled with WGA appeared to project to different hypothalamic and extrahypothalamic areas of the brain. Our results suggest that there are at least two populations of LHRH neurons, one with access to the portal capillaries of the ME and functionally related to the regulation of the pituitary, and one without access to capillaries of the ME, functionally probably related to intracerebral neurotransmission or modulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Current status of liver transplantation across ABO blood-type barrier

Outcomes of ABO-blood type incompatible liver transplantation have recently improved owing to various treatments. The typical clinical manifestations of antibody mediated rejection (AMR) are hepatic necrosis and intrahepatic biliary complication (IHBC). The prognosis of AMR is poor. AMR is the result of circulatory disturbance which is caused by injury to the endothelium due to an antibody-antigen-complement reaction. Diffuse C4d staining in the portal capillaries and periportal areas in severe AMR. Since natural antibodies against A/B carbohydrate determinants are likely to develop as a result of exposure to environmental bacteria that express similar determinants, the B-1 lineage has been speculated to be the major population of B-cell types responding to A/B determinants. Calcineurin inhibitors block B-1 cell differentiation. Rituximab can be used to deplete both cells that are producing IgM antibodies and those that have already differentiated into B-1 cells. Mycophenolate mofetil is required to inhibit the production of IgG subclass of antibodies. The outcome is now similar to that of blood-type-matched transplantation. However, there are still issues to be solved in order to further improve the outcome via a decrease of infection.

Prolactin and Antipsychotic Medication

Prolactin is a hormone secreted by the lactotroph cells of the anterior pituitary gland. Although it is present in both males and females of all ages, its main function in humans is to stimulate the production of breast milk in the postpartum period. Like other pituitary hormones, prolactin is regulated by the hypothalamus, which produces factors which stimulate and inhibit its synthesis and secretion. In the case of prolactin, the primary hypothalamic regulation is a tonic inhibition of its secretion which is mediated by dopamine, a neurotransmitter produced in the hypothalamus and secreted into the hypothalamic–pituitary portal capillaries which then carry it to the anterior pituitary gland. Dopamine acts on D2–dopamine receptors on the pituitary lactotroph cells to inhibit both synthesis and secretion of prolactin. Although the hypothalamus also produces prolactin–stimulating factors such as thyrotropin–releasing hormone (TRH) and vasoactive intestinal polypeptide (VIP), these appear to play minor roles in regulating prolactin secretion in humans. All conventional (first generation) antipsychotic agents act as antagonists on the D2–dopamine receptor. Atypical (second generation) antipsychotics are more variable in their affinity for the D2 receptor and thus vary in their effects on prolactin secretion. The relative potency of antipsychotic agents in elevating serum prolactin is: