nih public access hypothalamus following hyponatremia j...

Vacuolar Pathology in the Median Eminence of theHypothalamus Following Hyponatremia

Seymour Levine, MD1,*, Arthur Saltzman, MS1, and Stephen D. Ginsberg, PhD1,2,#1Center for Dementia Research, Nathan Kline Institute, Orangeburg, New York2Departments of Psychiatry and Physiology & Neuroscience, New York University LangoneMedical Center, New York, New York

AbstractThe median eminence of the hypothalamus is an important conduit by which neurosecretoryhormones from hypothalamic nuclei are delivered to the pars nervosa (neural lobe) of the pituitaryen route to the bloodstream. Dilutional hyponatremia was produced in adult rats to determine theeffect on the morphology of the median eminence of the hypothalamus. Hyponatremia was causedby reducing electrolyte and organic osmolyte reserves in order to block the excretion of waterthrough delivery of the nephrotoxin mercuric chloride (HgCl2). Histological examination of thebrain 1 day following a hyponatremic insult revealed vacuolation within the median eminence ofthe hypothalamus. No other lesions were found in other parts of the brain following hyponatremia.The hyponatremic lesion consisted of a band of closely packed vacuoles that crossed the floor ofthe third ventricle. Vacuoles associated with hyponatremia were predominantly in thesubependymal, fiber, reticular, and palisade layers of the median eminence. Vacuolation was notobserved in the tanycyte layer of the median eminence. This study indicates that the medianeminence is a potentially vulnerable site in human hyponatremic conditions that should beevaluated further in relevant animal models.

KeywordsAdenohypophysis; Cisterns; Hyponatremia; Pituitary; Tanycyte; Vacuoles

INTRODUCTIONHyponatremia, also referred to as ‘water intoxication,’ is the result of the progressivehypotonicity of body fluids (1,2). Severe hyponatremic insults can result in brain edema anddeath. Hyponatremia is a common complication of disorders in which there is rapid sodiumloss (e.g. profuse diarrhea or vomiting), or when excess water accumulates at a higher ratethan can be excreted (3). Hyponatremia is also observed following the aberrant secretion ofthe antidiuretic hormone vasopressin; antagonists of vasopressin are effective for the

#Correspondence and reprint requests to: Stephen D. Ginsberg, PhD, Center for Dementia Research, Nathan Kline Institute, NYULangone Medical Center, 140 Old Orangeburg Road, Orangeburg, NY 10962. Telephone: 845-398-2170; Fax: 845-398-5422;[email protected].*Dr. Seymour Levine passed away in the spring of 2010. Mr. Saltzman and Dr. Ginsberg dedicate this manuscript to the memory ofSeymour Levine and to acknowledge his prolific scientific career in neuropathology.This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providingthis early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before itis published in its final citable form. Please note that during the production process errors may be discovered which could affect thecontent, and all legal disclaimers that apply to the journal pertain.

NIH Public AccessAuthor ManuscriptJ Neuropathol Exp Neurol. Author manuscript; available in PMC 2012 February 1.

Published in final edited form as:J Neuropathol Exp Neurol. 2011 February ; 70(2): 151–156. doi:10.1097/NEN.0b013e318208fc5d.

NIH

-PA Author Manuscript

NIH


NIH


treatment of hyponatremia under certain conditions (4-6). Vasopressin is a secretory productof the magnocellular supraoptic and paraventricular nuclei in the hypothalamus and passesthrough the median eminence en route to the pars nervosa (neural lobe) of the pituitary glandwhere it is discharged into the bloodstream (7,8). Hyponatremia is also observed whenserum sodium is rapidly diluted (e.g. hypertriglyceridemic and hyperglycemic conditionsand in patients with various illnesses when excessive quantities of hypotonic fluids areadministered for therapy [9]), and it is associated with a fatal syndrome of central diabetesmellitus and diabetes insipidus (10). Importantly, hyponatremia is the most commonelectrolyte balance disorder found in hospitalized patients (11,12). Hyponatremia can beassociated with neuropsychiatric disorders, including schizophrenia, whereby affectedindividuals voluntarily consume excessive quantities of water (polydipsia) (5,13).

In rats, acute hyponatremia has also been demonstrated to be a secondary insult followingtraumatic brain injury in which it may involve the swelling of astrocytic end feet nearperivascular spaces and the upregulation of the glial water channel aquaporin-4 (14,15).Renal tubular necrosis with subsequent pituitary damage can be produced in relevant animalmodels by delivery of a nephrotoxin such as intravenous injection of HgCl2 orintraperitoneal injection of D-serine (16). Our group has reported hydropic degeneration ofthe pituitary pars distalis (adenohypophysis) in both of these experimental rat models ofuremia, which are associated with hyponatremia (16,17). Specifically, we demonstrated thatdelivery of HgCl2 (as well as injection of nephrotoxic levels of the amino acid D-serine)caused hyponatremic insults within the adenohypophysis that were indistinguishablemorphologically from one another (17). Despite the clinical importance of understandingbrain and pituitary changes during hyponatremic insults, little morphologic or mechanisticinformation is currently available in relevant animal models. The present study aimed todetermine whether an acute hyponatremic insult in rats could produce brain as well aspituitary pathology.

MATERIALS AND METHODSAll procedures were approved by the Institutional Animal Care and Use Committee of theNathan Kline Institute. Lewis rats of either sex (n = 19) were kept in hanging shoebox typeplastic cages with corncob bedding. Laboratory Rodent Diet 5001 chow (Purina, Scott’sDistribution, Hudson, NH) was available ad libitum. Rats were used when 7 to 10 weeks old(180-260 g). At the time of experimentation, rat chow was replaced by pure sucrose cubes(Domino Dots, West Palm Beach, FL). Metal grids were placed at the bottom of each cageto reduce coprophagy. Rats were given an i.v. injection of HgCl2 (Sigma, St. Louis, MO) in1 mg/ml distilled water while anesthetized with isoflurane, as previously described (17).There were 2 dosing regimens, i.e. 0.25 ml/100 g body weight (n = 9) and 0.5 ml/100 g bodyweight (n = 5). Distilled water (10 mg/100 g body weight) was injected s.c. 10 minutes afterthe HgCl2 injection on the left side of the body; this was repeated 5 hours later on the rightside of the body. To prevent leakage, the 20-gauge needle was advanced alternately throughthe subcutis and then the dermis 3 or 4 times before the water was injected into the subcutis(valve technique). Control rats (n = 5), were treated identically except they received distilledwater instead of HgCl2.

Rats were killed by exsanguination while under CO2 anesthesia. Serum sodium levels wereassessed by preparing blood taken from the inferior vena cava at the time of death. Sodiumwas assayed by atomic absorption spectrophotometry, as described (18,19). The brains wereremoved quickly, placed into Bouin’s fluid and the base of the skull was immersed inBouin’s fluid to fix the pituitary in situ for 24 hours at 22°C. The brain and pituitary wereembedded in paraffin, serially sectioned at 5 μm, and selected sections stained withhematoxylin and eosin (Sigma) and with periodic acid-Schiff-hematoxylin (PAS) (18,19).

Levine et al.

J Neuropathol Exp Neurol. Author manuscript; available in PMC 2012 February 1.

NIH


NIH


NIH


Particular emphasis was placed on evaluating the median eminence based upon previousresults (16,17). The median eminence measures approximately 1.6 to 1.8 mm in the anterior-posterior plane in fixed rat brain (20). Tissue sections were evaluated at 4 levels throughoutthe extent of the median eminence to assess the ependymal (tanycyte) layer, subependymallayer, fiber layer, reticular layer, and palisade layer, as well as the pars tuberalis of theinfundibulum (19). Tissue sections were examined at 400x magnification and vacuolesthroughout the median eminence were quantified as previously described (16,17). Vacuolarpathology was assessed on a semiquantitative scale as follows: 0, no vacuolar pathology; 1+,scattered vacuoles in any one of the layers; 2+, numerous vacuoles in 1-2 layers, sometimesgrouped together; 3+, profuse vacuolation, organized in short bands across part of the widthof the median eminence and spanning at least 2 laminae; 4+, severe vacuolar pathologyorganized in long bands, spanning the median eminence. This approach obviated concernsregarding tissue selection bias (17-19). Vacuoles in the median eminence had no detectablecontent and were interpreted as a hydropic change (16,17).

RESULTSSodium levels were significantly decreased in hyponatremic rats (110.43 ± 7.59 mEq/L) vs.control rats (145.4 ± 1.67 mEq/L) (t-test; p < 0.001). No differences in serum sodium levelswere observed between the 2 dosing conditions of HgCl2 (low, 111.78 ± 9.07 mEq/L; high,108.0 ± 3.39 mEq/L). Vacuolar pathology was present in the median eminence of 14/15(93.3%) of rats with acute dilutional hyponatremia (Table). Control rats withouthyponatremia did not display vacuoles in the median eminence. No pathological alterationswere observed in the arcuate, supraoptic, or paraventricular nuclei of the hypothalamus orother cortical or subcortical areas. Rats with hyponatremic insults also had hydropicdegeneration of the anterior pituitary, as described (17). The 2 doses of HgCl2 caused nearlysimilar semiquantitative scores of vacuolar pathology (Table), although the lower dose had 2rats with milder (1+) pathology. In rats with hyponatremia, a band of closely packedvacuoles extended across most or all of the median eminence, encompassing the fiber andreticular layers (Figs. 1-3). The ependymal layer (containing the tanycytes) did not displaysignificant vacuolar pathology, although vacuoles filled the adjacent subependymal layer aswell as the fiber layer and reticular layer (Fig. 1). Vacuolated bands were also observedconsistently within the palisade layer (Figs. 1, 2). Thus, nearly the full anterior-posteriorextent of the median eminence was subject to vacuolar pathology, and laterally the vacuolesreached the level of the tuberoinfundibular sulcus, which effectively demarcated the lateraledge of the median eminence. Vacuoles were usually elliptical in shape with the long axisoriented in the dorsoventral plane, similar to the tanycyte processes and the fibers of thepalisade layer. Glial nuclei were visualized in and around the band of vacuoles, but the vastmajority of the vacuoles were optically empty. Vacuolar pathology also appeared opticallyempty in the PAS stain, indicating that these vacuoles did not contain glycogen.

Immediately lateral to the median eminence and the floor of the third ventricle, the adjoininghypothalamic tissue often contained clusters of a few cisternal-like structures of a differentmorphological appearance than the aforementioned vacuoles. Unlike the vacuoles caused byhyponatremia, the cisternal-like structures were readily observed in both control andexperimental rats. These round elements, termed “hypothalamic cisternae” (19,21-23), werepresent in the lateral margins of the median eminence and the tuberohypophysial sulci andwere markedly different in location and shape from the vacuoles of the median eminenceassociated with the hyponatremic insult (Fig. 1-3). Importantly, they were seen in rats withor without vacuolar degeneration of the median eminence (Fig. 1).

Levine et al.


NIH


NIH


NIH


DISCUSSIONVacuolar pathology within the median eminence appeared to be specific to the hyponatremicinsult; no similar vacuoles have been reported in the median eminence (or other brainregions) of rodents using a variety of experimental paradigms including excitotoxicity,hyperlipemia, inflammation, lithium treatment, gonadal steroid delivery, and vitamin Dtreatment, among others (18,19,24-29). Dilutional hyponatremia was generated in thepresent study through injection of the nephrotoxic agent HgCl2 similar to our previousstudies (16,17). The nephrotoxicity of HgCl2 delivery is well established (30,31), notablywithin the dosing range used in this report (16,17). Mercury, particularly in the vapor form,is also neurotoxic (32). Mercuric salts including HgCl2, although neurotoxic to varyingdegrees, appear to be less neurotoxic than the vapor form and are less blood-brain barrierpenetrant (32). Glial cells, including astrocytes, may be potential mediators of HgCl2toxicity within the brain, although their contribution to hypothalamic and/or pituitarychanges remain unknown (33,34). To our knowledge, the potential of direct neurotoxicity ofintravenous HgCl2 delivery on the mediobasal hypothalamus and pituitary has not beendetermined. Accordingly, we cannot formally exclude the possibility that HgCl2 has somedirect effects upon the median eminence. However, this is unlikely within the currentparadigm, as the 2 doses of HgCl2 produced equivalent levels of serum sodium depletion aswell as vacuolar pathology within the median eminence, consistent with our previousanalysis (17).

The present objective was to determine whether acute dilutional hyponatremia couldproduce lesions in brain and pituitary as observed in humans with a fatal syndrome ofdiabetes mellitus and diabetes insipidus (10). The vacuolar, fluid-filled character of thelesions could have been expected inasmuch as hyponatremia and water intoxication arealmost synonymous. However, the location of these vacuoles within the median eminence ofthe hypothalamus was not anticipated. There is experimental evidence that cerebrospinalfluid can pass directly from the third ventricle through the median eminence (35-37).Moreover, orientation of the elliptical vacuoles in hyponatremic rats is in register with theorientation of the tanycytes and their processes. Therefore, the content of the vacuolesobserved in the median eminence following hyponatremia may be cerebrospinal fluid. Toour knowledge, vacuolar pathology of this type following a hyponatremic insult has notbeen reported in the brain. It has been reported that hyponatremic rats exhibit degenerationof the adenohypophysis (17) as well as the vacuolar pathology within the median eminence.Moreover, the present findings within the median eminence are similar to peripheralvacuolar changes in renal glomeruli following nephrotoxic insults (38,39).

The layers of the median eminence from dorsal (upper) to ventral (lower) are the ependymallayer (tanycyte layer), subependymal layer, fiber layer, reticular layer, and palisade layer(19,20). The palisade layer is readily identified by the closely compacted parallel fibersperpendicular to the pars tuberalis of the pituitary and by the highly vascularized (portalcirculation) lowest portion of the layer (19,20). The delicate arachnoid membrane is attachedto the pars tuberalis. The observation that vacuolar pathology following an acutehyponatremic insult was selective for the laminae of the median eminence is intriguing fromseveral perspectives. A goal is to determine the intrinsic morphological, molecular, and orcellular underpinnings that cause this selective vulnerability within the median eminence.The relative sparing of vacuolar pathology within the tanycyte layer is also of interest, asthis layer displays more mitotic figures (likely originating from specialized astrocytes calledpituicytes) following osmotic stress than the other median eminence laminae (19). Further,we suspect that the cisterns that are normally present within the median eminence predisposethis region to vacuolation. Tangential evidence for this hypothesis is supported by a studywhereby adrenalectomy in adult rats increased the abundance of hypothalamic cisterns (40).

Levine et al.


NIH


NIH


NIH


Since adrenalectomy causes low serum sodium, this observation is consistent with ourfindings in the present hyponatremic model. Additional ultrastructural assessment within thelaminae of the median eminence is warranted following hyponatremia to determine theprecise morphological characteristics of these vacuolar lesions. Furthermore, assessment ofvasopressin levels within the hypothalamus and the median eminence in hyponatremicmodels may prove useful to determine the potential mechanism of action in humanhyponatremic syndromes. Although numerous models and systems exist to study the effectsof hyponatremia peripherally, relatively little is available for the brain and pituitary. Ourmorphological results in a rat model of acute hyponatremia suggest that the medianeminence is a crucial structure to monitor and assess for understanding mechanismsunderlying the hyponatremic process as well as providing a substrate (vacuolar pathology)to test interventions aimed at reducing the negative sequela associated with hyponatremia.

AcknowledgmentsWe thank Corrinne M. Peterhoff for assistance with the photomicrography.

Supported by NIH grants MH083571 (SDG), MH086385 (SDG), and an anonymous private donation (SL).

REFERENCES1. Sterns RH, Hix JK, Silver S. Treatment of hyponatremia. Curr Opin Nephrol Hypertens. 2010;

19:493–8. [PubMed: 20539224]2. Oh MS. Pathogenesis and diagnosis of hyponatremia. Nephron. 2002; 92(Suppl 1):2–8. [PubMed:

12401931]3. Mount DB. The brain in hyponatremia: both culprit and victim. Semin Nephrol. 2009; 29:196–215.

[PubMed: 19523569]4. Arai Y, Fujimori A, Sasamata M, et al. New topics in vasopressin receptors and approach to novel

drugs: research and development of conivaptan hydrochloride (YM087), a drug for the treatment ofhyponatremia. J Pharmacol Sci. 2009; 109:53–9. [PubMed: 19151543]

5. Josiassen RC, Goldman M, Jessani M, et al. Double-blind, placebo-controlled, multicenter trial of avasopressin V2-receptor antagonist in patients with schizophrenia and hyponatremia. BiolPsychiatry. 2008; 64:1097–2100. [PubMed: 18692175]

6. Rozen-Zvi B, Yahav D, Gheorghiade M, et al. Vasopressin receptor antagonists for the treatment ofhyponatremia: systematic review and meta-analysis. Am J Kidney Dis. 2010; 56:325–37. [PubMed:20538391]

7. Armstrong WE, Warach S, Hatton GI, et al. Subnuclei in the rat hypothalamic paraventricularnucleus: a cytoarchitectural, horseradish peroxidase and immunocytochemical analysis.Neuroscience. 1980; 5:1931–58. [PubMed: 7432630]

8. Swanson LW, Sawchenko PE. Hypothalamic integration: organization of the paraventricular andsupraoptic nuclei. Annu Rev Neurosci. 1983; 6:269–324. [PubMed: 6132586]

9. Baylis PH. The syndrome of inappropriate antidiuretic hormone secretion. Int J Biochem Cell Biol.2003; 35:1495–9. [PubMed: 12824060]

10. Fraser CL, Arieff AI. Fatal central diabetes mellitus and insipidus resulting from untreatedhyponatremia: a new syndrome. Ann Intern Med. 1990; 112:113–9. [PubMed: 2294815]

11. Bagshaw SM, Townsend DR, McDermid RC. Disorders of sodium and water balance inhospitalized patients. Can J Anaesth. 2009; 56:151–67. [PubMed: 19247764]

12. Upadhyay A, Jaber BL, Madias NE. Epidemiology of hyponatremia. Semin Nephrol. 2009;29:227–38. [PubMed: 19523571]

13. Goldman MB. The assessment and treatment of water imbalance in patients with psychosis. ClinSchizophr Relat Psychoses. 2010; 4:115–23. [PubMed: 20643634]

14. Ke C, Poon WS, Ng HK, et al. Impact of experimental acute hyponatremia on severe traumaticbrain injury in rats: influences on injuries, permeability of blood-brain barrier, ultrastructuralfeatures, and aquaporin-4 expression. Exp Neurol. 2002; 178:194–206. [PubMed: 12504879]

Levine et al.


NIH


NIH


NIH


15. Vajda Z, Promeneur D, Doczi T, et al. Increased aquaporin-4 immunoreactivity in rat brain inresponse to systemic hyponatremia. Biochem Biophys Res Commun. 2000; 270:495–503.[PubMed: 10753653]

16. Levine S, Saltzman A. Acute uremia produced in rats by nephrotoxic chemicals is alleviated byprotein deficient diet. Ren Fail. 2003; 25:517–23. [PubMed: 12911155]

17. Levine S, Saltzman A. Hydropic degeneration of the anterior pituitary gland (adenohypophysis) inuremic rats. Toxicol Lett. 2004; 147:121–6. [PubMed: 14757315]

18. Levine S, Saltzman A, Katof B, et al. Proliferation of glial cells induced by lithium in the neurallobe of the rat pituitary is enhanced by dehydration. Cell Prolif. 2002; 35:167–72. [PubMed:12027952]

19. Levine S, Saltzman A, Ginsberg SD. Mitotic figures in the median eminence of the hypothalamus.Neurochem Res. 2010; 35:1743–6. [PubMed: 20680457]

20. Monroe BG, Paull WK. Ultrastructural changes in the hypothalamus during development andhypothalamic activity: the median eminence. Prog Brain Res. 1974; 41:185–208. [PubMed:4614312]

21. Bodoky M, Koritsanszky S, Rethelyi M. A system of intraependymal cisternae along the marginsof the median eminence in the rat: structure, three-dimensional arrangement and ontogeny. CellTissue Res. 1979; 196:163–73. [PubMed: 421248]

22. Scott V, Brown CH. State-dependent plasticity in vasopressin neurones: dehydration-inducedchanges inactivity patterning. J Neuroendocrinol. 2010; 22:343–54. [PubMed: 20088912]

23. Srebro Z. Electron microscopic observations on giant vacuoles present in the median eminence ofrats. Folia Biol (Krakow). 1986; 34:421–4. [PubMed: 3817225]

24. Hatton GI, Perlmutter LS, Salm AK, et al. Dynamic neuronal-glial interactions in hypothalamusand pituitary: implications for control of hormone synthesis and release. Peptides. 1984; 5(Suppl1):121–38. [PubMed: 6384946]

25. Holzwarth-McBride MA, Hurst EM, Knigge KM. Monosodium glutamate induced lesions of thearcuate nucleus. I. Endocrine deficiency and ultrastructure of the median eminence. Anat Rec.1976; 186:185–205. [PubMed: 984473]

26. Lawson LJ, Perry VH, Gordon S. Microglial responses to physiological change: osmotic stresselevates DNA synthesis of neurohypophyseal microglia. Neuroscience. 1993; 56:929–38.[PubMed: 8284045]

27. Levine S, Saltzman A. A procedure for inducing sustained hyperlipemia in rats by administrationof a surfactant. J Pharmacol Toxicol Methods. 2007; 55:224–6. [PubMed: 16839786]

28. Levine S, Saltzman A, Ginsberg SD. Different inflammatory reactions to vitamin D(3) among thelateral, third and fourth ventricular choroid plexuses of the rat. Exp Mol Pathol. 2008; 85:117–21.[PubMed: 18675267]

29. Olney JW. Brain lesions, obesity, and other disturbances in mice treated with monosodiumglutamate. Science. 1969; 164:719–21. [PubMed: 5778021]

30. Kim KB, Um SY, Chung MW, et al. Toxicometabolomics approach to urinary biomarkers formercuric chloride (HgCl)-induced nephrotoxicity using proton nuclear magnetic resonance ((1)HNMR) in rats. Toxicol Appl Pharmacol. 2010; 249:114–26. [PubMed: 20804780]

31. Durante P, Romero F, Perez M, et al. Effect of uric acid on nephrotoxicity induced by mercuricchloride in rats. Toxicol Ind Health. 2010; 26:163–74. [PubMed: 20176775]

32. Aschner M, Aschner JL. Mercury neurotoxicity: mechanisms of blood-brain barrier transport.Neurosci Biobehav Rev. 1990; 14:169–76. [PubMed: 2190116]

33. Aschner M, Mullaney KJ, Fehm MN, et al. Astrocytes as potential modulators of mercuric chlorideneurotoxicity. Cell Mol Neurobiol. 1994; 14:637–52. [PubMed: 7641225]

34. Cookson MR, Pentreath VW. Alterations in the glial fibrillary acidic protein content of primaryastrocyte cultures for evaluation of glial cell toxicity. Toxicol In Vitro. 1994; 8:351–9. [PubMed:20692926]

35. Amat P, Pastor FE, Blazquez JL, et al. Lateral evaginations from the third ventricle into the ratmediobasal hypothalamus: an amplification of the ventricular route. Neuroscience. 1999; 88:673–7. [PubMed: 10363808]

Levine et al.


NIH


NIH


NIH


36. Guerra M, Blazquez JL, Peruzzo B, et al. Cell organization of the rat pars tuberalis. Evidence foropen communication between pars tuberalis cells, cerebrospinal fluid and tanycytes. Cell TissueRes. 2010; 339:359–81. [PubMed: 19937347]

37. Knigge KM, Joseph SA, Sladek JR, et al. Uptake and transport activity of the median eminence ofthe hypothalamus. Int Rev Cytol. 1976; 45:283–408. [PubMed: 182653]

38. Perez-Perez AJ, Pazos B, Sobrado J, et al. Acute renal failure following massive mannitol infusion.Am J Nephrol. 2002; 22:573–5. [PubMed: 12381962]

39. Riemenschneider T, Bohle A. Morphologic aspects of low-potassium and low-sodiumnephropathy. Clin Nephrol. 1983; 19:271–9. [PubMed: 6872364]

40. Brion JP, Depierreux M, Couck AM, et al. Transmission and scanning electron-microscopicobservations on tanycytes in the mediobasal hypothalamus and the median eminence ofadrenalectomized rats. Cell Tissue Res. 1982; 221:643–55. [PubMed: 7055840]

Levine et al.


NIH


NIH


NIH


Figure 1.Low- and high-magnification images of the mediobasal hypothalamus in coronal sectionsfrom a control (A) and hyponatremic (B-D) rats. The median eminence extends below thethird ventricle (III v.), across the bottom of the photomicrographs. Cisterns (arrows) locatedjust lateral to the median eminence often appeared to be attached to the pars tuberalis at thelevel where it separates the median eminence from the rest of the hypothalamus. (A) Controlrat. (B) Vacuolation is symmetrically distributed in the subependymal layer of the medianeminence of a hyponatremic rat (scored at 1+). Tanycytes, which form the floor of the thirdventricle, are not vacuolated. (C) Vacuolation is distributed symmetrically in thesubependymal, fiber, and reticular layers (scored at 3+). (D) Vacuoles are prominent in thefiber, reticular and palisade layers of the median eminence (scored at 4+). Vacuoles on theleft side palisade layer adjacent to the pars tuberalis are confluent with an asymmetric groupof larger cisterns. Hematoxylin and eosin. Scale bars: A-D = 20 μm.

Levine et al.


NIH


NIH


NIH


Figure 2.Low (left panels) and higher (right panels) photomicrographs showing vacuolation in thefiber, reticular, and palisade layers following a hyponatremic insult. (A) Clusters of vacuolesare concentrated in the palisade layer adjacent to pars tuberalis of pituitary (scored at 3+).Numerous cisterns are also seen at higher magnification. (B) Widespread, symmetricalvacuolar pathology throughout the median eminence (scored at 4+). In this rat, hypothalamiccisterns were scarce and separated laterally from vacuoles within the median eminence.Scale bar = 20 μm.

Levine et al.


NIH


NIH


NIH


Figure 3.Prominent vacuolation within the median eminence following hyponatremia. Low (leftpanel) and higher (right panel) photomicrographs illustrating profuse vacuoles throughoutthe median eminence but not the adjacent mediobasal hypothalamus. (A) Severe vacuolarlesions within the median eminence of a hyponatremic rat (scored at 4+). The shallowtuberoinfundibular sulcus (arrow) is seen near cisterns within the lateral margins of themedian eminence. (B) Vacuolation throughout the subependymal, fiber, reticular, andpalisade layers of the median eminence. Hypothalamic cisterns are large and numerous inthe lateral margins of the median eminence. Scale bars: A, B = 20 μm.

Levine et al.


NIH


NIH


NIH


NIH


NIH


NIH


Levine et al.

Table 1

Semiquantitative Scoring of Vacuolar Pathology within the Median Eminence and Serum Sodium Levels inIndividual Rats following Treatment with HgCl2

HgCl2mg/100 g

Serum NamEq/L

Median EminenceVacuolar Pathology

Score

0 144 0

0 144 0

0 145 0

0 146 0

0 148 0

0.25 121 0

0.25 109 1+

0.25 115 1+

0.25 110 2+

0.25 127 3+

0.25 97 4+

0.25 102 4+

0.25 111 4+

0.25 114 4+

0.50 109 3+

0.50 110 3+

0.50 104 4+

0.50 105 4+

0.50 112 4+


nih public access hypothalamus following hyponatremia j...

Documents