Regional changes of brain Na+,K+-transporting adenosine triphosphatase related to ovarian function

Preoptic and hypothalamic regulation of multi-tiered, chronologically arranged female rat sexual behavior

As in many mammalian behaviors, sexual behavior exhibits structure. Each modular components of the structure, that are linked together over time, occur in probabilistic manner. Endocrine milieu, in particular sex hormones, define the probability to synchronize the behavior with the production of gametes. Developmental experience and environmental cues affect the hormonal milieu of the brain. This is especially true in female mammals, in which ova mature with certain intervals along with ovarian secretion of sex hormones. Estrogens secreted by mature ovarian follicles support both affiliative and executive components of female sexual behavior. In the absence of the ovarian steroids, females avoid males when possible, or antagonize and reject males when put together. Female sexual behavior is intimately linked with the estrous cycle in many species such that females are only receptive for a brief period at the estrus stage surrounding ovulation. Thus, in the rat, females strongly influence the outcome of mating encounter with a male. Affiliative or solicitatory behavior shown by females in estrus leads to the female adapting the lordosis posture, which is characterized by hindleg postural rigidity and lordotic dorsiflexion of the spine, in response to touch-pressure somatosensory stimuli on the skin of the flanks, rump-tail base, perineum region given by male partner. The posture facilitates intromission and consequently fertilization. Although dependence on estrogens is the most important feature of female rat sexual behavior, cervical probing combined with palpation of the hindquarter skin acts as a supranormal stimulus to elicit lordosis. Thus, lordosis behavior is a hub of multi-tiered, chronologically arranged set of behaviors and estrogen appear to alter excitability of neural network for lordosis.

Postoperative hyponatremia following calvarial vault remodeling in craniosynostosis

BACKGROUND

  The incidence, severity, and risk factors for the development of hyponatremia in patients undergoing craniosynostosis surgery are not well known.

OBJECTIVE

  To determine the incidence and severity of hyponatremia as a complication in surgical correction of craniosynostosis and to identify risk factors for postoperative hyponatremia.

METHODS

  A retrospective medical record review for 2003-2008 of the Cleft and Craniofacial Database was made. Specific data collected included sodium values, age, weight, type of surgery, duration of surgery, administration of DDAVP, composition and volume of pre-operative, intra-operative, postoperative parenteral fluids, volume of blood, colloid, and crystalloid transfused, estimated blood loss (EBL), medications, comorbidities, pre-operative signs of elevated intracranial pressure (ICP), syndromic vs nonsyndromic craniosynostosis, and the complications associated with hyponatremia.

RESULTS

  A total of 72 records were reviewed. The incidence of postoperative hyponatremia was 30.6%. There was no intra-operative hyponatremia. While hospital stay was not prolonged, ICU stay was significantly longer (1.9 vs 2.9 days, P = 0.001). Elevated ICP was significantly associated with hyponatremia (P < 0.002). A greater volume of blood loss (EBL) was associated with postoperative hyponatremia (P = 0.019). Patients with normal pre-operative ICP were more likely to become hyponatremic if they were female (relative risk = 2.43; P < 0.05). The average decrease in sodium was greater in patients receiving hyponatremic (hypotonic) vs normonatremic (isotonic) postoperative IVF's (5.5 vs 3.2 mEq·l(-1), P = 0.039). There were no postoperative complications related to hyponatremia.

CONCLUSIONS

  The incidence of postoperative hyponatremia after calvarial vault remodeling was determined to be 30.6%. Hyponatremia was significantly associated with increased pre-operative ICP, blood loss, and female gender (normal pre-operative ICP). The average decrease in sodium was greater in patients receiving hyponatremic postoperative IVF's.

Ovariectomy alters energy metabolism in rat striatum: effect of supplementation with soy diet rich in isoflavones

In the present study we investigated the effect of ovariectomy on some parameters of energy metabolism, namely Na(+),K(+)-ATPase and pyruvate kinase activities, as well as the mitochondrial respiratory chain enzymes activities succinate dehydrogenase, complex II and cytochrome c oxidase in rat striatum. The influence of soy diet rich in isoflavones on the effects elicited by ovariectomy on enzyme activities was also evaluated. Female adult Wistar rats were assigned to one of the following groups: sham (submitted to surgery without removal of the ovaries) and ovariectomized. Seven days after surgery animals were fed for 30 days on a special diet with soy protein or a standard diet with casein (control). Rats were sacrificed after treatment and the striatum was dissected. Results showed that rats subjected to ovariectomy presented a significant increase in Na(+),K(+)-ATPase, succinate dehydrogenase and complex II activities. Treatment with isoflavones-rich soy diet was able to reverse the increase of Na(+),K(+)-ATPase activity, but was not effective in reversing the changes caused by ovariectomy on succinate dehydrogenase and complex II activities. Since ovariectomy mimics postmenopausal changes, our findings suggest that dysfunction of brain energy metabolism may be related to neurological symptoms observed in some postmenopausal women.

Enhanced pressor response to increased CSF sodium concentration and to central ANG I in heterozygous alpha2 Na+ -K+ -ATPase knockout mice

Intracerebroventricular (ICV) infusion of NaCl mimics the effects of a high-salt diet in salt-sensitive hypertension, raising the sodium concentration in the cerebrospinal fluid (CSF [Na]) and subsequently increasing the concentration of an endogenous ouabain-like substance (OLS) in the brain. The OLS, in turn, inhibits the brain Na(+)-K(+)-ATPase, causing increases in the activity of the brain renin-angiotensin system (RAS) and blood pressure. The Na(+)-K(+)-ATPase alpha (catalytic)-isoform(s) that mediates the pressor response to increased CSF [Na] is unknown, but it is likely that one or more isoforms that bind ouabain with high affinity are involved (e.g., the Na(+)-K(+)-ATPase alpha(2)- and/or alpha(3)-subunits). We hypothesize that OLS-induced inhibition of the alpha(2)-subunit mediates this response. Therefore, a chronic reduction in alpha(2) expression via a heterozygous gene knockout (alpha(2) +/-) should enhance the pressor response to increased CSF [Na]. Intracerebroventricular (ICV) infusion of artificial CSF containing 0.225 M NaCl increased mean arterial pressure (MAP) in both wild-type (+/+) and alpha(2) +/- mice, but to a greater extent in alpha(2) +/-. Likewise, the pressor response to ICV ouabain was enhanced in alpha(2) +/- mice, demonstrating enhanced sensitivity to brain Na(+)-K(+)-ATPase inhibition per se. The pressor response to ICV ANG I but not ANG II was also enhanced in alpha(2) +/- vs. alpha(2)+/+ mice, suggesting an enhanced brain RAS activity that may be mediated by increased brain angiotensin converting enzyme (ACE). The latter hypothesis is supported by enhanced ACE ligand binding in the organum vasculosum laminae terminalis. These studies demonstrate that chronic downregulation of Na(+)-K(+)-ATPase alpha(2)-isoform expression by heterozygous knockout increases the pressor response to increased CSF [Na] and activates the brain RAS. Since these changes mimic those produced by the endogenous brain OLS, the brain alpha(2)-isoform may be a target for the brain OLS during increases in CSF [Na], such as in salt-dependent hypertension.

Brain cell volume regulation in hyponatremia: role of sex, age, vasopressin, and hypoxia

Hyponatremia is the most common electrolyte abnormality in hospitalized patients. When symptomatic (hyponatremic encephalopathy), the overall morbidity is 34%. Individuals most susceptible to death or permanent brain damage are prepubescent children and menstruant women. Failure of the brain to adapt to the hyponatremia leads to brain damage. Major factors that can impair brain adaptation include hypoxia and peptide hormones. In children, physical factors--discrepancy between skull size and brain size--are important in the genesis of brain damage. In adults, certain hormones--estrogen and vasopressin (usually elevated in cases of hyponatremia)--have been shown to impair brain adaptation, decreasing both cerebral blood flow and oxygen utilization. Initially, hyponatremia leads to an influx of water into the brain, primarily through glial cells and largely via the water channel aquaporin (AQP)4. Water is thus shunted into astrocytes, which swell, largely preserving neuronal cell volume. The initial brain response to swelling is adaptation, utilizing the Na(+)-K(+)-ATPase system to extrude cellular Na(+). In menstruant women, estrogen + vasopressin inhibits the Na(+)-K(+)-ATPase system and decreases cerebral oxygen utilization, impairing brain adaptation. Cerebral edema compresses the respiratory centers and also forces blood out of the brain, both lowering arterial Po(2) and decreasing oxygen utilization. The hypoxemia further impairs brain adaptation. Hyponatremic encephalopathy leads to brain damage when brain adaptation is impaired and is a consequence of both cerebral hypoxia and peptide hormones.

Supplementation with vitamins E plus C or soy isoflavones in ovariectomized rats: effect on the activities of Na(+), K (+)-ATPase and cholinesterases

Since a previous study demonstrated that ovariectomized rats present an activation of Na(+), K(+)-ATPase and acetylcholinesterase (AChE) activities, in the present study we investigated the influence of vitamins E plus C or soy isoflavones on the effects elicited by ovariectomy on the activities of these enzyme in hippocampus of ovariectomized rats. We also determined the effect of the same compounds on the reduction of serum butyrylcholinesterase (BuChE) activity caused by ovariectomy. Female adult Wistar rats were assigned to one of the following groups: sham (submitted to surgery without removal of the ovaries) and ovariectomized. Seven days after surgery, animals were treated for 30 days with a single daily intraperitoneous injection of vitamins E (40 mg/kg) plus C (100 mg/kg) or saline (control). In another set of experiments, the rats were fed for 30 days on a special diet with soy protein or a standard diet with casein (control). Rats were sacrificed after treatments and the hippocampus was dissected and serum was separated. Data demonstrate that vitamins E plus C reversed the activation of Na(+), K(+)-ATPase and AChE in hippocampus of ovariectomized rats. Conversely, soy protein supplementation reversed the increase of AChE activity, but not of Na(+), K(+)-ATPase activity, caused by ovariectomized group. Neither treatment was able to reverse the reduction of serum BuChE activity. Furthermore, treatments with vitamins E plus C or soy were unable to reverse the decrease in estradiol levels caused by ovariectomy. Our findings show that the treatment with vitamins E plus C significantly reversed the effect of ovariectomy on hippocampal Na(+), K(+)-ATPase and AChE activities. However, a soy diet that was rich in isoflavones was able to reverse just the increase of AChE. Neither treatment altered the reduction in serum BuChE activity. Taken together, these vitamins and soy may have a protective role against the possible brain dysfunction observed in some menopause women. Vitamins E plus C and soy isoflavones may be a good alternative as a novel therapeutic strategy.

Visualizing forebrain-specific usage of an estrogen receptor α promoter for receptor downregulation in the rat

Transgenic rats expressing enhanced green fluorescent protein (EGFP) under the control of an estrogen receptor (ER) alpha promoter were generated to tag ERalpha-positive neurons in the brain. Two transgenes, one containing sequences for promoter A and DsRed and the other containing sequences for promoter 0/B and EGFP, were injected simultaneously into Wistar rat zygotes. Twenty-two founders with both transgenes were identified. Ten lines of these founders expressed the EGFP tag in the brains of their first filial generation, whereas none similarly expressed the DsRed tag. In two lines selected for the brightness of the EGFP fluorescence in their brains, tagged cells showed essentially the same patterns. Tagged cells were in the preoptic area (POA), bed nucleus of the stria terminalis (BNST), hypothalamic arcuate nucleus and medial amygdala. ERalpha-immunoreactive neurons were identified in all of these structures by immunohistochemistry. In ovariectomized females, approximately 75% of the EGFP-fluorescent cells in the POA-BNST were immunoreactive for ERalpha. In the POA-BNST, ovariectomy increased the number of EGFP-immunopositive cells and estrogen supplementation reversed this effect, indicating that the promoter 0/B is involved in estrogen-induced downregulation of ERalpha. EGFP was also present in cells in the cerebral cortex and hippocampus, which have not previously been associated with endocrine regulation. Conversely, only a few cells were tagged in the hypothalamic ventromedial nucleus, which contained many ERalpha-immunoreactive neurons. This discrepancy could have arisen as a result of differential promoter usage.

Inhibition of ATPases enzyme activities on brain disturbing normal oestrous cycle

Wistar rats treated with alpha-methyl-DL-p-tyrosine methylester showed significant level of inhibition in the activity of Na+, K+ -ATPase, Mg2+ -ATPase and Ca2+ -ATPase enzymes in different regions of the brain. The enzyme activity was assayed in cerebral hemispheres, hypothalamus, thalamus, hippocampus, amygdala and septum at proestrous (12 h), estrous (25 h), metestrous (38 h) and diestrous periods (92 h) of the rat. The Na+, K+ -ATPase activity was significantly inhibited in most of the brain regions after treated with alpha-methyl-DL-p-tyrosine methylester (MPT) and this indicated that MPT affected the active transport system and nerve impulse transmission. Mg2+ -ATPase and Ca2+ -ATPase was also significantly (P < 0.001) reduced in different regions of the brain. The results revealed that MPT affected active transport system and nerve impulse transmission by inhibiting Na+, K+ -ATPase and Ca2+ -ATPase. It has induced energy crisis by inhibiting Mg2+ -ATPase and all these cumulative effects of MPT have adversely affected the female Wistar rats. These effects have been manifested in the form of aberrations in the behavior of MPT treated female rats, which have shown their inability to perform their normal sexual activity.

Ovariectomy increases Na+, K+-ATPase, acetylcholinesterase and catalase in rat hippocampus

In the present work we investigated the effect of ovariectomy on Na+, K+-ATPase and acetylcholinesterase (AChE) activities in rat hippocampus. We also studied some parameters of oxidative stress, namely total radical-trapping antioxidant potential (TRAP), thiobarbituric acid-reactive substances (TBA-RS), as well as the antioxidant enzyme activities superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSH-Px) activities. Our hypothesis is that ovariectomy might cause alterations in essential enzyme activities necessary to brain normal functioning and that these chances could be caused by oxidative stress. Female adult Wistar rats were divided into three groups: (1) naive (control); (2) sham-operated; and (3) ovariectomized. Thirty days after ovariectomy rats were sacrificed. Results showed that rats subjected to ovariectomy presented a significant increase in Na+, K+-ATPase, AChE and CAT activities, but did not change the oxidative stress parameters studied when compared to sham or naive rats. Since ovariectomy mimics postmenopausal changes, our findings showing alteration in the activities of brain Na+, K+-ATPase, AChE and CAT may be related to problems in postmenopausal women.

Influence of hypoosmolality on the blood-brain barrier permeability during epileptic seizures

Changes in the blood-brain barrier permeability to macromolecules were investigated during pentylenetetrazol-induced seizures, using Evans-blue as an indicator, in water-intoxicated and nonintoxicated Wistar albino (210-250 g) adult rats of both sexes. Evans-blue albumin extravasation was judged visually and estimated quantitatively with a spectrophotometer using homogenized brain to release the dye. Hypoosmolar treatment (water intoxication) was performed by the intraperitoneal administration of distilled water to a volume of 10% of the body weight; Six groups of rats were studied. Group I: female control (n=10), Group II: male control (n=10), Group III: nonwater-intoxicated female+seizure (n=15), Group IV: nonwater-intoxicated male+seizure (n=15), Group V: water-intoxicated female+seizure (n=15), Group VI: water-intoxicated male+seizure (n=15). Approximately 2 h after the injection of water, the plasma osmolarity had decreased by 25-30 mosm. Our results revealed that in female rats, the extravasation of Evans-blue albumin was greater in the brains of water-intoxicated rats compared to nonwater-intoxicated rats after pentylenetetrazol-induced seizures. In addition, hypoosmotic female rats were shown to have a larger increase in blood-brain barrier permeability than hypoosmotic male rats after pentylenetetrazol-induced seizures. This difference between male and female rats was found to be significant (P=.005).

Na-K-ATPase activity decreases with aging in female rat brain synaptosomes

To understand why elderly females are better able to tolerate hyponatremia, we measured brain Na-K-ATPase activity to determine whether this adaptive mechanism was affected by age. Using synaptosomes from 2-, 12-, and 19-mo-old female rats, we show in our results that Na-K-ATPase activity changes with age in female rats. Enzyme activity was significantly (P = 0.0026) reduced (17%) from 0.416 +/- 0.01 at 2 mo to 0.345 +/- 0.01 at 12 mo and reduced (P = 0.0001) (34%) to 0.274 +/- 0.02 micromol. min(-1). mg protein(-1) at 19 mo. To determine whether this decrease was due to reduced transport function of the Na-K-ATPase pump, we performed potassium transport using rubidium ((86)Rb+) as tracer. Ouabain-sensitive potassium uptake at 2 mo was 16.18 +/- 1.31 nmol/mg protein, was significantly (P = 0.0063) reduced (39%) to 9.79 +/- 1.44 nmol/mg at 12 mo, and was significantly (P = 0.0003) reduced (62%) to 6.12 +/- 1.05 nmol/mg protein at 19 mo. On the contrary, Na-K-ATPase activity remained elevated in males during aging. These data suggest that the Na-K-ATPase pump in female rat brain synaptosomes is decreased with increased age, and that this decrease is probably due in part to decreased potassium transport by the Na-K-ATPase pump.

Endometrial Na+, K+-ATPase pump function and vasopressin levels during hysteroscopic surgery in patients pretreated with GnRH agonist

STUDY OBJECTIVE

To investigate the effects of gonadotropin-releasing hormone (GnRH) analog pretreatment on endometrial Na+, K+-adenosine triphosphatase (ATPase) pump function and peripheral blood vasopressin levels, and their role in fluid absorption and mechanisms of hyponatremia in patients undergoing hysteroscopic endometrial ablation.

DESIGN

Prospective, randomized, placebo-controlled study (Canadian Task Force classification I).

SETTING

University-affiliated hospital.

PATIENTS

Seventeen women with dysfunctional uterine bleeding.

INTERVENTION

Nine women received a GnRH analog and eight received saline approximately 6 to 8 weeks before hysteroscopic ablation by electrosurgery.

MEASUREMENTS AND MAIN RESULTS

Both before randomization and immediately before surgery, endometrial biopsy samples were obtained and numbered consecutively without patient identification. Operative hysteroscopy was performed with glycine 1.5% mixed with 2% alcohol. The amount of irrigant and irrigant deficit; blood levels of albumin and ethanol; hematocrit and hemoglobin; changes in sodium levels; and central venous pressure were compared. The Na+, K+-ATPase pump activity was significantly increased in the GnRH analog group compared with the saline group and correlated with decreased estradiol levels (0.4 +/- 0.08 vs 0.26 +/- 0.06 micro mol/min/ml). Vasopressin levels were significantly lower in the GnRH group (3.2 +/- 0.9 vs 7.6 +/- 1.7 micro mol/L). Mean volume of irrigant used and operating time were similar in both groups. Volume deficit, decrease in protein, and hematocrit were less in GnRH than in the saline group. Blood ethanol levels, decrease in sodium, and irrigant deficit were significantly lower in GnRH group.

CONCLUSION

Pretreatment with GnRH analogs may prevent the adverse effects of estradiol on endometrial Na+, K+-ATPase and creates a protective mechanism against iatrogenic hyponatremia, which is more critical in women than men in case of absorption of irrigating fluid. Moreover, created hypoestrogenism may enhance Na+, K+-ATPase activity in brain as well as endometrium, thus decreasing women's susceptibility to hyponatremic complications and brain damage. Suppressed vasopressin levels may be protective against fluid absorption in GnRH analog-treated patients.

Salmon calcitonin plus intravaginal estriol: an effective treatment for the menopause

OBJECTIVE

Intravaginal estriol (E3) effectively improves postmenopausal genito-urinary disturbances, without stimulating endometrial proliferation. The aim of the present study was to evaluate the effect of intravaginal estriol (E3) plus nasal spray salmon calcitonin (sCT), to improve neurovegetative symptoms and to prevent the decline of bone mineral density (BMD) of postmenopausal women.

METHODS

Two hundred and fourteen (214) healthy postmenopausal women were treated for 12 months with: (1) E3 (0.5 mg every other day) + Ca (0.5 g/day); (2) E3 + Ca + sCT (50 IU x 2/day); (3) sCT + Ca; (4) Ca. Climacteric complaints, such as hot flushes and sweating, BMD at the distal 1/10 of the radius, analyzed by dual photon absorptiometry, urinary excretion of hydroxyproline and serum alkaline phosphatase were evaluated at baseline and every 6 months. At the same time, patient compliance and drug tolerability were evaluated.

RESULTS

E3 but not sCT, improved hot flushes and sweating. E3 blunted but not completely counteracted the BMD decline observed in women treated with only Ca, and reduced urinary hydroxyproline excretion. sCT markedly increased BMD values and reduced both urinary hydroxyproline excretion and serum alkaline phosphatase. These effects were not potentiated by E3 coadministration. All treatments were well tolerated.

CONCLUSIONS

Present data indicate that the combined administration of intravaginal E3 and sCT may represent an alternative therapeutic regimen for those postmenopausal women who do not accept or have contraindications to classical hormone replacement therapy.

Neurobiological correlates of masculine sexual behavior

The experimental analysis of the neuroendocrine interactions regulating sexual behavior has traditionally relied on studying the effects of CNS lesions and pharmacological treatments with hormones or drugs purportedly acting through specific neurotransmitter systems. New methodological developments have allowed the assessment of several indices of neural function in experimental animals, particularly the rat, as they relate to behavioral changes. In the field of sexual behavior, ex vivo analyses have been used to measure markers of energy metabolism, such as 2-deoxyglucose uptake and Na,K-ATPase activity, the tissue content of neurotransmitters and metabolites, the levels of steroid receptors and neurosteroids, and immediate-early gene expression products in different areas of the CNS. In vivo studies have monitored brain electrical activity and temperature, as well as the extracellular levels of neurotransmitters and metabolites by cerebrospinal fluid sampling, push-pull perfusion and, especially, electrochemical recordings and microdialysis, in the course of mating and exposure to various relevant stimuli. The findings with the different methodologies are generally consistent and agree with those of previous surgical and pharmacological manipulations. They provide data on temporal relationships between neurobiological and behavioral events and suggest new interpretations for different aspects of the male copulatory pattern.

Transdermal estradiol and medroxyprogesterone acetate in hormone replacement therapy are both antioxidants

We have evaluated the effects of the different components of hormone replacement therapy (HRT) on the production of free radicals in platelet membranes from menopausal women. The study included 12 women in menopause for at least 6 months to a maximum of 4 years. First, the effect was determined of progestin only during the administration of 20 mg/day medroxyprogesterone acetate for 5 days. The peroxide production level was measured on day 0 and day 5. The second set of experiments was carried out in the first month of cyclic HRT with transdermal estradiol 50 micrograms/day from day 1 to day 25 and medroxy-progesterone acetate from day 13 to day 25. In this experiment, the peroxide level was evaluated on days 0, 12 and 25. A significant reduction of peroxide level was observed after oral medroxyprogesterone acetate administration. During HRT, we observed a similar reduction in lipid oxidation at the peak of the estrogen effect, and a further decrease with the administration of medroxyprogesterone acetate. It is concluded that reduction of lipid peroxidation during HRT is not only due to estrogens, but also depends upon the combined action of sex steroids. This observation justifies not only the combined regimen (estrogens plus progestin) in HRT, but also the positive effects of progestins alone on patients who cannot use estrogens.

Hormonal dependence of the effects of metabolic encephalopathy on cerebral perfusion and oxygen utilization in the rat

Previous studies have demonstrated that in adult rats with chronic hyponatremia, both symptoms of encephalopathy and mortality largely depend upon the gender of the animal and the presence of elevated plasma levels of vasopressin (AVP). Since effects of AVP on blood vessels may be gender dependent, the present study was designed to compare the effects of chronic (4 days) hyponatremia on cerebral blood flow (CBF), cerebral oxygen consumption (CMRO2), and cerebral perfusion index (CPI) in adult male and female rats. CBF (intra-arterial 133Xe injection method) and CMRO2 (arteriovenous difference of cerebral oxygen contentxCBF) were measured in normonatremic and hyponatremic (hyponatremia induced with 140 mmol/L glucose and either AVP or desmopressin [dDAVP], plasma sodium = 100 to 110 mmol/L) adult rats of both genders. The CPI was assessed from magnetic resonance imaging of the transit of magnetic susceptibility contrast agent through the brain. Female rats with AVP-induced chronic hyponatremia had a 36% decrease in CBF and a 60% decrease in CMRO2. In male animals, both parameters were not different from control values. AVP-induced hyponatremia resulted in a 45% decrease in CPI in female rats, but hyponatremia induced with dDAVP did not affect CPI in either male or female rats. Chronic (4 days) administration of AVP did not affect CPI in either male or female normonatremic rats. When rats with AVP-induced chronic hyponatremia were pretreated with estrogen, the CPI in males was not different from that in females. Our results demonstrate that during AVP-induced chronic hyponatremia in female rats, there is significant depression of both oxygen utilization and blood flow in the brain.

Diametrically opposite effects of estrogen on the excitability of female rat medial and lateral preoptic neurons with axons to the midbrain locomotor region

Electrical stimulation of the midbrain locomotor region (MLR) in 76 ovariectomized, urethan-anesthetized female rats elicited antidromic action potentials in 252 preoptic neurons. Thresholds and refractory periods for the activation ranged from 60 to 1550 microA and 1.3 to 5.0 ms, respectively. The probability distribution for the peak-to-peak amplitude (2-14 mV) or the overall duration (0.7-4.4 ms) was bell-shaped, whereas that for the latency (1.8-33.5 ms) was distinctively bimodal with a division at 12.0 ms. Two groups of preoptic neurons of a similar soma size therefore project to the MLR presumably via different routes. In 121 neurons with latencies < or = 12.0 ms, estrogen lowered the antidromic activation thresholds (nested analysis of variance, P < 0.02), but 131 neurons with latencies > 12.0 ms had their thresholds increased (P < 0.005) and refractory periods prolonged (P < 0.02) by estrogen. Even though both overlapped in part, many potentials with the shorter latencies were recorded from the medial part of the lateral preoptic area (mLPO), lateral to the recording sites of the longer-latency potentials in the medial preoptic area (MPO). The observed antagonistic effects of estrogen on the two groups of preoptic neurons with axons to the MLR may contribute to increased locomotor activity in female rats in estrus.

Female sex hormones inhibit volume regulation in rat brain astrocyte culture

To determine whether sex steroids play any role in the increased morbidity associated with acute symptomatic hyponatremia in menstruant females, we studied the actions of estradiol, progesterone, and testosterone on regulatory volume decrease (RVD) of brain astrocytes in culture. To determine intracellular space with the use of 3-O-[methyl-D-3H] glucose, cells were cultured in media containing either estradiol or progesterone. Those treated with ouabain were unable to regulate volume normally, whereas testosterone-treated cells displayed normal RVD. After 15 s of hypotonic exposure, control cell volume and 100 nM testosterone-treated cell volume increased by 26 and 31%, respectively. Cell volume in control cells changed from 1.74 +/- 0.24 to 2.41 +/- 0.28 microliters/mg protein. At the same time, cells treated with either 10 nM estradiol or 10 nM progesterone significantly (P < 0.01) increased their volume by 129 and 90%, respectively. Both the antiestrogen agent tamoxifen and the antiprogesterone agent mifepristone (RU-486) blocked the effects of estradiol and progesterone. The Na-K-ATPase pump, which plays an important role in cell RVD, was significantly (P < 0.03) inhibited by 32 and 21% in estradiol- and progesterone-treated cells, but significantly (P < 0.001) stimulated (49%) by testosterone treatment. Taken together, these results provide a possible explanation for the increased morbidity associated with acute symptomatic hyponatremia in menstruant females.

Glucocorticoid regulation of mRNA encoding (Na+K) ATPase alpha 3 and beta 1 subunits in rat brain measured by in situ hybridization

The effect of glucocorticoids on (Na+K)ATPase mRNA synthesis was studied in 19 brain areas of adrenalectomized (ADX) rats untreated or receiving dexamethasone (DEX). For in situ hybridization, we employed a [35S]oligonucleotide probe for the alpha 3-subunit isoform, and a [3H]cDNA coding for the beta 1-subunit of the enzyme. Mean levels of grain density for the alpha 3 subunit mRNA of DEX-treated rats were significantly higher by a 't' test in medial septum, amygdala lateralis (AL) and medialis (AME), gyrus dentatus, CA4 hippocampal area, substantia nigra and periventricular gray, compared to untreated rats. For the beta 1-subunit, mean levels after DEX were significantly higher in AL and lateral preoptic area. In addition, the Kolmogorov-Smirnov test applied to frequency histograms of neuronal densities indicated a coordinate increase in alpha 3 and beta 1-subunit mRNA expression for the CA2 subfield and preoptic area medialis (POA MED). We conclude that (1) glucocorticoids are positive modulators of (Na+K)ATPase mRNA; (2) analysis of frequency histograms suggests that glucocorticoids promote in a few regions (AL, POA MED, CA2 subfield) a coordinate increase in the biosynthesis of the alpha 3 and beta 1-subunit mRNA. In 11 other areas stimulation occurs for one subunit mRNA only, whereas 5 areas were insensitive to glucocorticoid effects on this enzyme.

Osmotic regulation of sodium pump in rat brain synaptosomes: the role of cytoplasmic sodium

The effect of hypoosmolality of incubation medium on the rat of ouabain-sensitive 86Rb+ transport in rat brain synaptosomes was studied. A decreased osmolality from 310 to 250 mOsm increased the rate of 86Rb+ uptake from 3.72 to 6.23 nmol/mg of protein min. To evaluate the involvement of cytoplasmic sodium in sodium pump stimulation inhibitors of ion channels and transport pathways able to increase [Na+]in were used. Tetrodotoxin (1 microM), amiloride (0.5 mM) and verapamil (0.1 mM) had no influence on the osmotic response of the sodium pump. The decrease of sodium concentration in incubation medium to 15 mM, leading to a practical loss of its transmembrane gradient, did not abolish stimulation of pump. No increase in 22Na+ influx or intrasynaptosomal sodium content was registered at hypotonic conditions. It is suggested that osmotic regulation of Na+,K(+)-ATPase is not connected with an increase of internal sodium through opening of sodium channels, or with activation of other membrane sodium-transporting systems.

Developmental effect of testosterone on estrogen sensitivity of the rat preoptic neurons with axons to the ventral tegmental area

The neonatal effect of testosterone on neuronal sensitivity to estrogen was examined in the medial preoptic area of the rat when adult. Electrical stimulation of the ventral tegmental area induced antidromic action potentials in 683 neurons in 106 urethane-anesthetized animals which consisted of 38 males castrated on the day of birth (day 1), 30 females androgenized by testosterone injection on day 5, and 38 normal females. All females were used after ovariectomy when adult. Histological localization of the antidromically activated neurons was similar in all the animal groups. The latency jump in 40% of the potentials indicated that activated preoptic axons terminate in the stimulation site. The latency for activation was in the range 1.6-43.7 ms and the threshold was as low as 60 microA. The absolute refractory period did not exceed 1700 microseconds. Estrogen increased the threshold among 278 cells in the normal females and 181 cells in the neonatally castrated males. Preoptic neurons in the androgenized females (n = 224) differ from those in others in that their threshold, regardless of estrogen treatment, was at the ceiling values seen in the other groups in the presence of estrogen. Estrogen also prolonged the absolute refractory period in the females but not in the androgenized females. The reduced excitability and the lack of estrogen sensitivity may be responsible for the insensitivity of the androgenized females to feminine actions of estrogen, that may presumably underlie a sex difference in certain behavioral functions.

Hyponatraemia and death or permanent brain damage in healthy children

OBJECTIVE

To determine if hyponatraemia causes permanent brain damage in healthy children and, if so, if the disorder is primarily limited to females, as occurs in adults.

DESIGN

Prospective clinical case study of 16 affected children and a review of 24,412 consecutive surgical admissions at one medical centre.

PATIENTS

16 children (nine male, seven female; age 7 (SD 5) years) with generally minor illness were electively hospitalised for primary care. Consultation was obtained for the combination of respiratory arrest with symptomatic hyponatraemia (serum sodium concentration less than or equal to 128 mmol/l).

MAIN OUTCOME MEASURES

Presence, gender distribution, and classification of permanent brain damage in children with symptomatic hyponatraemia in both prospective and retrospective studies.

RESULTS

By retrospective evaluation the incidence of postoperative hyponatraemia among 24,412 patients was 0.34% (83 cases) and mortality of those afflicted was 8.4% (seven deaths). In the prospective population the serum sodium concentration on admission was 138 (SD 2) mmol/l. From three to 120 inpatient hours after hypotonic fluid administration patients developed progressive lethargy, headache, nausea, and emesis with an explosive onset of respiratory arrest. At the time serum sodium concentration was 115 (7) mmol/l and arterial oxygen tension 6 (1.5) kPa. The hyponatraemia was primarily caused by extrarenal loss of electrolytes with replacement by hypotonic fluids. All 16 patients had cerebral oedema detected at either radiological or postmortem examination. All 15 patients not treated for their hyponatraemia in a timely manner either died or were permanently incapacitated by brain damage. The only patient treated in a timely manner was alive but mentally retarded.

CONCLUSIONS

Symptomatic hyponatraemia can result in high morbidity in children of both genders, which is due in large part to inadequate brain adaptation and lack of timely treatment.

Effects of deoxycorticosterone treatment on beta-subunit mRNA for (Na + K)ATPase in brain regions determined by in situ hybridization

1. We have used in situ hybridization techniques to determine the mRNA for (Na + K)ATPase in 20 brain regions from control rats and rats treated with high doses of deoxycorticosterone (DOC). 2. DOC-treated rats developed a salt appetite following the second hormone administration on alternate days and were used after the fourth DOC administration. 3. DOC treatment did not change the number of silver grains/cell deposited in cells from Ca1, CA2, CA3, and CA4 hippocampal subfields, dentate gyrus, cerebral cortex, medial preoptic area (POA), substantia nigra, and periventricular gray matter. 4. Nonsignificant reductions were detected in lateral POA, medial and lateral septum, caudate-putamen, and three amygdaloid nuclei (cortical, basolateral, and central) from DOC-treated rats. 5. Significant reductions were obtained, after DOC administration, in arcuate and ventromedial hypothalamic nuclei and medial and lateral amygdala. 6. The results suggested that regulation of the beta-subunit mRNA of (Na + K)-ATPase may be related to the central actions of mineralocorticoids in the control of salt intake.

Differential regulation of estrogen-dependent sexual development of rat brain by growth factors

Intraventricular infusion of antiserum to nerve growth factor (ANGF), but not that to insulin, epidermal growth factor nor normal rabbit serum, resisted estrogen-induced behavioral defeminization in the female rat neonates. A significant number of the ANGF-treated rats showed lordosis as adults despite neonatal estrogen, but positive feedback of estrogen on serum luteinizing hormone was absent. Sexual phenotype in behavioral and gonadotropic functions may be under differential development regulation.

Estrogen-induced suppression of female rat forebrain neurons with axons to ventral midbrain

In estrogen-treated and non-treated ovariectomized female rats under urethan anesthesia, 278 neurons were antidromically identified in the medial preoptic and other basal forebrain areas by electrical stimulation of their terminals in the ventral tegmental area. Responses from the estrogen-treated rats had a significantly higher threshold, longer latency and absolute refractory period than those from the non-treated rats. Estrogen may decrease excitability of the preoptic axons along its length.

Changes of salt intake and of (Na+K)-ATPase activity in brain after high dose treatment with deoxycorticosterone

Mineralocorticoids (MC) have a dual effect on salt intake: in adrenalectomized rats, they reduce previously elevated salt intake; and in intact rats a high MC dose increases salt intake. We have studied the activity of (Na+K)-ATPase and [3H]ouabain binding in rats treated with deoxycorticosterone (DOC) in doses that elicited a salt appetite. Brains were removed from control and treated animals, and 20 different areas were punched out from brain slices cut every 300 microns. DOC treatment significantly reduced (Na+K)-ATPase activity in the lateral hypothalamic area, anterior amygdaloid and lateral amygdaloid nuclei, while increasing it in the periventricular gray matter; changes in other regions were not significant. Binding of [3H]ouabain was not modified by DOC treatment. In parallel experiments, we determined MC receptors in adrenalectomized rats. Binding of [3H]aldosterone was preferentially found in hippocampus, followed by lateral septum, anterior, posterior and lateral amygdaloid areas, with lower levels in other regions. However, there was no correlation between [3H]aldosterone binding and (Na+K)-ATPase activity in brain punches from either control or DOC-treated rats. Further experiments are needed to ascertain if (Na+K)-ATPase changes in discrete areas of the brain containing moderate levels of mineralocorticoid receptors, are related to the behavioral effects of DOC.

Na+-K+-ATPase pump function in rat brain synaptosomes is different in males and females

To understand the increased morbidity and mortality associated with acute hyponatremia in young women, we characterized the Na+-K+-adenosinetriphosphtase (ATPase) pump in rat brain synaptosomes to determine if this adaptive mechanism was different between the sexes. Veratridine-stimulated sodium (Na+) uptake was significantly greater (P less than 0.001) in females than in males (8.08 +/- 0.3 vs. 5.56 +/- 0.4 nmol/mg protein), suggesting either an increased rate of Na+ uptake and/or decreased extrusion of Na+ by the Na+-K+-ATPase pump in females. Uptake rate was determined by measuring Na+ transport at 5 s, and it was found to be twice as large in females as in males (1.01 +/- 0.2 vs. 0.46 +/- 0.1 nmol/mg protein). However, in the presence of 2.5 mM ouabain, uptake in both groups were similar, suggesting that the difference was probably due to decreased function of the Na+-K+-ATPase pump in females. Transport evaluation of the Na+-K+-ATPase pump showed ouabain-sensitive K+ uptake in males to be significantly greater (P less than 0.001) than in females (10.53 vs. 4.97 nmol/mg protein), and ouabain-sensitive Na+ uptake in inverted synaptosomes was 70% greater in males (4.00 vs. 2.37 nmol/mg protein). [3H]ouabain binding studies showed maximum binding capacity in males and females to be similar (103 +/- 12 vs. 110 +/- 15 pmol/mg protein), whereas the dissociation constant was significantly (P less than 0.005) greater in males (109 +/- 8 vs. 82 +/- 6 nM).(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in forebrain Na,K-ATPase activity and serum hormone levels during sexual behavior in male rats

We have previously shown that Na,K-ATPase activity (the enzymatic machinery for the sodium pump) in brain areas such as the medial basal hypothalamus (MBH) and the preoptic-suprachiasmatic region (POSC) can be changed by experimental manipulations of gonadal function. We now report enzyme levels in brain regions as related to hormonal changes occurring during sexual behavior. Male rats were exposed to receptive females and decapitated immediately after displaying one of the following behavioral events: the start of copulatory activity, first ejaculation, and the beginning of a second copulatory series. A group of noncopulating animals were used as control. The variables measured included serum levels of LH, PRL and testosterone and Na,K-ATPase activity in MBH, POSC and parietal cerebral cortex (CC). A steady increase in enzyme activity in the POSC, but not the MBH or CC, was found in copulating animals. Serum LH levels changed in a similar fashion. A sharp increase in serum PRL levels, seemingly related to ejaculation, was also observed. These data are consistent with our previous findings on monoaminergic neurotransmission in brain regions related to male sexual behavior.

Gonadal influences on spinal cord and brain monoamines in male rats

Concentrations of norepinephrine (NE), dopamine (DA), 3,4-dihydroxy phenylacetic acid (DOPAC), serotonin (HT) and 5-hydroxyindoleacetic acid (HIAA) were measured by high-performance liquid chromatography-electrical detection (HPLC-ED) in homogenates of lumbosacral spinal cord, mediobasal hypothalamus and cerebral cortex of male rats. The effects of castration and testosterone propionate (TP) (20 micrograms/day X 2 days) were compared. Castrated animals had the highest levels of DA and DOPAC in the cerebral cortex and NE, HT and HIAA in the spinal cord, as well as decreased hypothalamic DOPAC. Testosterone treatment returned spinal cord monoamine concentrations to intact control levels. These findings point to the spinopetal monoaminergic pathways as sensitive targets for androgen action.

Neurochemical correlates of male sexual behavior

This report presents evidence of changes in the concentration of monoamine neurotransmitters and their metabolites in homogenates of spinal cord and brain areas of male rats related to specific events of their mating behavior. Intact male rats were allowed to copulate with receptive females and decapitated immediately after either the first intromission or the first ejaculation. Non-mating control animals were exposed to other males, instead of females. The concentration of monoamines (norepinephrine, dopamine and serotonin) and some of their major metabolites (DOPAC and HIAA) in homogenates of discrete brain areas (parietal cortex, preoptic region, mediobasal hypothalamus) and lumbosacral spinal cord were measured by HPLC-ED. Results suggest that sexual arousal is associated with both increased dopaminergic activity in the preoptic region and inhibition of descending monoaminergic signals to the lumbosacral cord, whereas ejaculation is accompanied by increased activity of the serotonergic, as well as dopaminergic, innervation of the preoptic region. These findings give neurochemical support to notions of central monoamines involvement in sexual behavior suggested by previous pharmacological studies.