Validity of intraoperative pathological diagnosis of paratracheal lymph node as a strategy for selection of patients for cervical lymph node dissection during esophagectomy.

The aim of this paper is to examine whether intraoperative examination of paratracheal nodes can indicate cervical node dissection and whether this approach is valid. From 1988 to 1997, 76 patients with thoracic esophageal squamous cell carcinoma received esophagectomies with and without cervical lymph node (LN) dissection based on the results of intraoperative pathological diagnosis from selective checking of paratracheal LN. We retrospectively examined the outcomes for the patients and the micro metastasis in the dissected lymph node using cytokeratin staining. Three of the seven patients with cervical LN dissection were detected as having cervical LN metastasis by postoperative hematoxylin-eosin or cytokeratin staining. Five (7%) of the 69 patients without cervical LN dissection had cervical LN recurrence after the operation. Four of the seven patients who were diagnosed as having metastasis or micro metastasis in paratracheal LN by postoperative examination had cervical LN recurrence after the operation. In conclusion, the esophagectomy with and without cervical LN dissection for thoracic esophageal squamous cell carcinoma based on the results of intraoperative pathological diagnosis from selective checking of paratracheal LN was not fully acceptable. The reliability of intraoperative pathological diagnosis of selective checking may improve by increasing the number of checked LN and the detection of micro metastasis.

Prevention of glucoprivic stimulation of corticosterone secretion by leptin does not restore high frequency luteinizing hormone pulses in rats.

We have previously determined that exogenous leptin prevents the inhibition of pulsatile luteinizing hormone (LH) release in the fasting rodent. The present study tested the hypothesis that the mechanism by which leptin facilitates high LH secretion is through an attenuation of the stress response produced by a deficit in energy. Because hypogonadotropism is associated with activation of the hypothalamic-pituitary-adrenal (HPA) axis during both metabolic stress and nonmetabolic stress, our approach included a comparison of whether exogenous leptin could prevent the rise in corticosterone produced by a nonmetabolic stress (immobilization for 2 h), as well as by a widely used metabolic stress (transient glucoprivation by 2-deoxyglucose, 2DG; 400 mg/kg, b.w., i.v.). Each stressor was applied to well-fed ovariectomized rats (n = 4-6 per group), 2 h after leptin (3 microg/g, b.w., i.p.) or vehicle administration. Blood samples were collected through an indwelling atrial cannula every 6 min for 1 h before and for 2 h after the stress treatment to measure LH, leptin and corticosterone. During metabolic stress (acute glucoprivation), circulating leptin decreased, corticosterone increased and LH decreased; leptin administration abolished the increase in corticosterone, but pulsatile LH secretion remained inhibited. In contrast, during nonmetabolic stress (immobilization), leptin secretion was unaffected, but circulating corticosterone increased and LH decreased; leptin treatment did not prevent either the increase in corticosterone or the decrease in LH secretion. An important overall finding is that leptin can differentially alter the HPA axis depending upon the type of stress. In addition, whether the pattern of leptin is altered depends upon the type of stress. Although a glucoprivic-induced decrease in endogenous leptin can be a stressor responsible for the increase in corticosterone secretion, a nonmetabolic stress-induced increase in corticosterone is not mediated by leptin. Moreover, our results reveal that the depression of LH secretion when leptin is low during reduced energy availability is not due to activation of the HPA axis. During an energy deficit, exogenous leptin could not restore high frequency LH secretion when HPA function was restored to normal. Finally, the inability of leptin to increase LH secretion in the face of 2DG supports the notion that the action of leptin is dependent upon the degree of glucose availability.

Central, but not peripheral, glucose-sensing mechanisms mediate glucoprivic suppression of pulsatile luteinizing hormone secretion in the sheep.

Changes in glucose availability are proposed to modulate pulsatile GnRH secretion, and at least two anatomical sites, the liver and hindbrain, may serve as glucose sensors. The present study determined the relative importance of these putative glucose-sensing areas in regulating pulsatile LH secretion in the sheep. Our approach was to administer the antimetabolic glucose analog, 2-deoxy-D-glucose (2DG) into either the hepatic portal vein or the fourth ventricle in gonadectomized females in which LH pulse frequency was high. In the first study, a catheter was placed in the ileocolic vein to determine the effects of local injection of 2DG into the hepatic portal system on the release of LH. After monitoring the pattern of LH secretion for 4 h, 2DG (250 mg/kg) was infused (500 microl/min) into the liver for 2 h. For comparison, animals were also given the same dose of 2DG into a jugular vein for 2 h. Administration of 2DG into either the hepatic portal or jugular vein reduced LH pulse frequency to the same extent. Infusion of the lower dose (50 mg/kg) locally into the hepatic portal vein did not affect plasma LH profiles. Collectively, these results are interpreted to indicate that the liver does not contain special glucose-sensing mechanisms for the glucoprivic suppression of LH pulses. In the second study, 2DG (5 mg/kg) was infused (50 l/min) for 30 min into the fourth ventricle or lateral ventricle. During the subsequent 4-h sampling period, pulsatile LH secretion was significantly suppressed, but there was no significant difference in LH pulse frequency between sites of infusion. Peripheral 2DG concentrations were not detectable after either fourth or lateral ventricle infusions, indicating that the 2DG had acted centrally to suppress LH pulses. Plasma cortisol concentrations increased more in animals infused with 2DG into the fourth ventricle than in those infused into the lateral ventricle, suggesting that 2DG infused into lateral ventricle is transported caudally into the fourth ventricle and acts within the area surrounding the fourth ventricle. Overall, these findings suggest that an important glucose-sensing mechanism is located circumventricularly in the fourth ventricle. Moreover, the liver does not appear to play an important role in detecting glucoprivic action of 2DG to suppress pulsatile LH secretion.

Leptin regulates pulsatile luteinizing hormone and growth hormone secretion in the sheep.

Administration of leptin during reduced nutrition improves reproductive activity in several monogastric species and reverses GH suppression in rodents. Whether leptin is a nutritional signal regulating neuroendocrine control of pituitary function in ruminant species is unclear. The present study examined the control of pulsatile LH and GH secretion in sheep. We determined whether exogenous leptin could prevent either the suppression of pulsatile LH secretion or the enhancement of GH secretion that occur during fasting. Recombinant human met-leptin (rhmet-leptin; 50 microg/kg BW; n = 8) or vehicle (n = 7) was administered s.c. every 8 h during a 78-h fast to estrogen-treated, castrated yearling males. LH and GH were measured in blood samples collected every 15 min for 6 h before fasting and during the last 6 h of fasting. Leptin was measured both by a universal leptin assay and by an assay specific for ovine leptin. During the fast, endogenous plasma leptin fell from 1.49 +/- 0.16 to 1.03 +/- 0.13 ng/ml. The average concentration of rhmet-leptin 8 h after leptin administration was 18.0 ng/ml. During fasting, plasma insulin, glucose, and insulin-like growth factor I levels declined, and nonesterified fatty acid concentrations increased similarly in vehicle-treated and leptin-treated animals. In vehicle-treated animals, LH pulse frequency declined markedly during fasting (5.6 +/- 0.5 vs. 1.1 +/- 0.5 pulses/6 h; fed vs. fasting; P < 0.0001). Leptin treatment prevented the fall in LH pulse frequency (5.0 +/- 0.4 vs. 4.9 +/- 0.4 pulses/6 h; P = 0.6). Neither fasting nor leptin administration altered GH pulse frequency. Fasting produced a modest increase in mean concentrations of circulating GH in control animals (2.4 +/- 0.5 vs. 3.4 +/- 0.6 ng/ml; P = 0.04), whereas there was a much greater increase in GH during leptin treatment (2.7 +/- 0.6 vs. 8.6 +/- 1.6 ng/ml; P = 0.0001). GH pulse amplitudes were also increased by fasting in control (P = 0.04) and leptin-treated sheep (P = 0.007). The finding that exogenous rhmet-leptin regulates LH and GH secretion in sheep indicates that this fat-derived hormone conveys information about nutrition to mechanisms controlling neuroendocrine function in ruminants.

Appearance of a nocturnal peak of leptin secretion in the pubertal rat.

Whether leptin is involved in the timing of puberty remains highly controversial in the rat. Daytime leptin secretion shows little change during the transition into adulthood. Because leptin exhibits a diurnal variation in the adult, it is possible that the ontogeny of such a rhythm provides important information for the timing of puberty. To begin to evaluate this hypothesis, we determined the development of the diurnal leptin secretion in the rat. The young females were raised in a light-controlled environment (12L, 0700 h light on). A cannula was placed in the right atrium on the previous day, and blood samples were collected every 4 h on Days 21, 24, 28, 32, 36 (1 day after vaginal opening), and 48 (adult, diestrus of estrous cycle). In addition to vaginal opening, plasma prolactin levels were determined as an endocrine index of puberty. Changes in food intake were monitored because nocturnal food intake has been considered to be a synchronizer for the leptin rhythm. This pattern of food intake was clearly evident throughout the ages studied. By contrast, there was no leptin rhythm at 21 and 24 days of age. Beginning at 28 days, leptin secretion exhibited a significant nocturnal peak (2300 h); this nocturnal peak increased in amplitude at 32 and 36 days and was still apparent in the cycling adult at Day 48. Plasma prolactin did not exhibit a diurnal rhythm but it increased from Days 32 to 48. The present findings indicate that in the rat, both the appearance of the nocturnal leptin rhythm and the nocturnal increase in circulating leptin levels during development carry information for timing the onset of puberty.

Regulation of pulsatile luteinizing hormone secretion by insulin in the diabetic male lamb.

This study tested the hypothesis that LH secretion is modulated by insulin and that the responsiveness to hypoinsulinemia is enhanced by sex steroids. The model was the developing male lamb (12-26 wk of age) rendered diabetic by chemically induced necrosis of insulin-secreting tissue (streptozotocin). Our approach was to monitor LH secretion under diabetic conditions, with or without insulin supplementation, either in the presence or in the absence of gonadal steroids. The first experiment determined if chronic insulin supplementation could sustain LH secretion in diabetic lambs. After documentation of the induced diabetic condition, twice-daily treatment with a long-acting insulin preparation (Lente) minimized diabetes-induced hyperglycemia, sustained growth, and maintained LH pulse frequency at levels comparable to pre-diabetic conditions. A second experiment evaluated the acute regulation of LH secretion by insulin. Twenty-four hours of insulin withdrawal decreased LH pulse frequency, increased circulating glucose levels, increased the concentration of plasma non-esterified fatty acids (NEFAs), and increased urinary output of ketones. LH pulse frequency continued to decline after 96 h of insulin withdrawal. By contrast, 24 h of insulin re-supplementation increased LH pulse frequency, reduced circulating glucose and NEFA concentrations, decreased plasma cortisol, and reduced urinary output of ketones. After 96 h of insulin re-supplementation, LH pulse frequency increased further, to levels comparable with those before insulin withdrawal. A third experiment determined if the effects of insulin withdrawal on LH secretion are influenced by the presence of gonadal steroids. The same individuals were treated with a physiologic dose of estradiol (Silastic capsule, s.c.) and subsequently monitored for changes in LH secretion in the presence and in the absence of exogenous insulin. Prior to insulin withdrawal, estradiol decreased both LH pulse frequency and pulse amplitude. Moreover, after 96 h of insulin withdrawal, estradiol potentiated the decline in LH pulse frequency (47% reduction in LH pulse frequency in the presence of estradiol versus 26% reduction in LH pulse frequency in the absence of estradiol). These findings support the contention that insulin and/or insulin-dependent changes in glucose availability modulate LH(GnRH) pulse frequency, and that such effects are potentiated by, but not dependent upon, gonadal steroids.

Central action of insulin regulates pulsatile luteinizing hormone secretion in the diabetic sheep model.

This study tested the hypothesis that central mechanisms regulating luteinizing hormone (LH) secretion are responsive to insulin. Our approach was to infuse insulin into the lateral ventricle of six streptozotocin-induced diabetic sheep in an amount that is normally present in the CSF when LH secretion is maintained by peripheral insulin administration. In the first experiment, we monitored cerebrospinal fluid (CSF) insulin concentrations every 3-5 h in four diabetic sheep given insulin by peripheral injection (30 IU). The insulin concentration in the CSF was increased after insulin injection, and there was a positive relationship between CSF and plasma concentrations of insulin (r = 0.80, P < 0.01). In the second experiment, peripheral insulin administration was discontinued, and the sheep received either an intracerebroventricular (i.c.v.) infusion of insulin (12 mU/day in 2.4 ml saline) or saline (2.4 ml/day) for 5 days (n = 6) in a crossover design. The dose of insulin (i.c.v.) was calculated to approximate the increase in CSF insulin concentration found after peripheral insulin treatment. To monitor LH secretory patterns, blood samples were collected by jugular venipuncture at 10-min intervals for 4 h on the day before and 5 days after the start of i.c.v. insulin infusion. To monitor the increase in CSF insulin concentrations, a single CSF sample was collected one and four days after the start of the central infusion. The i.c.v. insulin infusion increased CSF insulin concentrations above those in saline-treated animals (P < 0.05) and maintained them at or above the peak levels achieved after peripheral insulin treatment. Central insulin infusion did not affect peripheral (plasma) insulin or glucose concentrations. LH pulse frequency in insulin-treated animals was greater than that in saline-treated animals (3.5 +/- 0.2 vs. 2.3 +/- 0.3 pulses/4 h, P < 0.01), but it was less than that during peripheral insulin treatment (4.8 +/- 0.2 pulses/4 h, P < 0.01). Our findings suggest that physiologic levels of central insulin supplementation are able to increase pulsatile LH secretion in diabetic sheep with low peripheral insulin. These results are consistent with the notion that central insulin plays a role in regulating pulsatile GnRH secretion.

Physiological perspectives on leptin as a regulator of reproduction: role in timing puberty.

How nutrition regulates reproductive activity remains a major unsolved question of reproductive biology. Reducing the level of nutrition during adulthood can lead to infertility, primarily through reduction of GnRH secretion. Inquiry about such a mechanism has its roots in the search for cues timing the onset of fertility, because the tempo of sexual maturation is much more closely associated with body growth than with chronological age. Growth depends on the quantity and quality of food intake. When food availability is low, small, short-lived species with high metabolism and reduced growth may not even attain puberty before they die. In longer-lived species, puberty is delayed for months or even years until more food becomes available. To appreciate fully how the pubertal progression is timed will require understanding how peripheral signals relating information about energy metabolism are sensed by the brain and how such information is routed through pathways controlling GnRH secretion. Here, we provide some background and physiologic perspective on the question of whether the fat-derived hormone leptin is the unique peripheral signal, is an important signal, is but one of a constellation of signals, or is not a signal timing puberty.

Glucose availability modulates the timing of the luteinizing hormone surge in the ewe.

To determine if glucose availability modulates the timing of the positive feedback action of oestrogen on gonadotropin secretion, we monitored the estradiol-induced luteinizing hormone (LH) surge in sheep (n = 5/group) made transiently hypoglycemic by insulin. Experiment 1 determined an effective insulin treatment, one which would depress tonic LH secretion. Two injections of insulin (5 IU/kg iv) 4 h apart were found to induce extended hypoglycemia (10-13 h) and to decrease the LH pulse frequency for 8 h (5.0 +/-0.32 pulses/4 h before versus 2.5+/-0.34 pulses/4 h after insulin; P<0.05; mean +/- SEM). Using this same paradigm, experiment 2 determined the influence of the transient hypoglycemia on the LH surge mechanism. In control sheep, estradiol (subcutaneous implants at hour 0) evoked an LH surge with a latency period of 12.4+/-0.5 h. When insulin was administered either before (hours -4 and 0) or after the estradiol stimulus (hours 4 and 8, or 12 and 16), the onset of the LH surge was delayed to 29.0+/-2.4 h (average of all three time groups, P <0.05). Infusion of glucose from hours 12-30, along with insulin, prevented hypoglycemia and restored the normal timing of the oestrogen-induced LH surge to that of controls (15.4+/-0.93 h, P>0.05). These findings suggest that not only is the tonic mode of LH secretion sensitive to metabolic fuel availability, but the surge mode of LH secretion is as well.

Evidence for GnRH regulation by leptin: leptin administration prevents reduced pulsatile LH secretion during fasting.

Administration of leptin during undernutrition improves reproductive function, but whether this occurs at the level of the brain, pituitary, or gonads is not yet clear. The present study tested the hypothesis that one important mechanism is the control of pulsatile gonadotropin-releasing hormone (GnRH) secretion. Our approach was to determine if leptin could prevent the marked suppression of pulsatile luteinizing hormone (LH) secretion which occurs during fasting. Leptin (3 micrograms/g i.p.; three times/48 h) or vehicle was administered during a 48-hour fast in adult ovariectomized and estrogen-treated ovariectomized rats (n = 5-7/group). LH was measured in blood samples collected every 6 min for 2 h before and after fasting. In vehicle-treated animals, plasma insulin and leptin levels decreased after fasting. As expected, the LH pulse frequency also decreased markedly. When circulating leptin remained artificially elevated during fasting, the suppression of LH pulse frequency did not occur. Leptin treatment maintained a high LH pulse frequency in the presence or absence of estrogen. The finding that leptin modulates LH pulse frequency indicates that this fat-derived hormone conveys information about nutrition to mechanisms which regulate pulsatile gonadotropin-releasing hormone secretion. Because this occurs in the absence of estrogen, the mechanism does not necessarily involve modulation of negative feedback.

Effect of heat treatment on stainless steel lingual arch appliances.

This study evaluated the effect of heat treatment on 0.036" diameter stainless steel wire. Forty wires were bent into arch forms (20 experimental and 20 control). The arch width changes were measured and the forces generated were determined over an eight week period. Heat treatment resulted in immediate and significant expansion (p < 0.001) followed by stabilization of arch width. The control wires continued to expand throughout the study. The force generated by the control group and experimental group expansion was capable of producing tooth movement.

Paraventricular norepinephrine release mediates glucoprivic suppression of pulsatile luteinizing hormone secretion.

Restriction of glucose availability by 2-deoxyglucose (2DG) suppresses pulsatile LH release. The aim of the present study was to determine whether norepinephrine (NE) release in the paraventricular nucleus (PVN) is involved in the glucoprivic suppression of LH secretion in ovariectomized rats. Twelve days after ovariectomy, animals were stereotaxically implanted with a guide cannula for microdialysis in the PVN. Two days later, the PVN was perfused continuously with Ringer's solution or Ringer's solution containing a catecholamine synthesis inhibitor, alpha-methyl-p-tyrosine (100 microM), through a microdialysis probe inserted in the guide cannula 2 h before the beginning of sampling, which lasted 3 h. Blood samples were collected every 6 min through an atrial cannula, and dialysates were collected every 20 min. One hour after the beginning of sampling, 2DG (400 mg/kg BW) was administered iv through the atrial cannula. Paraventricular NE levels significantly increased immediately after 2DG injection (P < 0.05), and both mean LH concentrations and the frequency of LH pulses decreased. By contrast, when alpha-methyl-p-tyrosine was administered into the PVN, 2DG did not produce an increase in paraventricular NE, and no depression of LH secretion occurred. These results suggest that the PVN mediates the glucoprivic suppression of LH pulses via the release of NE.

Novel estrogen feedback sites associated with stress-induced suppression of luteinizing hormone secretion in female rats.

1. The fasting-induced suppression of LH secretion is totally dependent on steroidal milieu because the suppression is observed only in intact or ovariectomized estrogen-primed rats but not in ovariectomized animals. The following neural pathway mediating fasting-induced suppression of LH secretion has been suggested by a series of experiment: A neural signal emanating from the stomach during fasting reaches the medulla oblongata via afferent vagal nerve so as to activate the noradrenergic system projecting to the PVN: this results in an increased CRH release, and in turn the suppression of the LHRH release and then LH release. Estrogen seems to activate the neural pathway by acting on somewhere in the pathway. 2. We found that the paraventricular nucleus of the hypothalamus (PVN) and A2 region of the medulla oblongata is the estrogen feedback sites associated the dependence of the fasting-induced suppression of LH secretion on estrogen. The estrogen feedback action on the PVN does not involve an increase in norepinephrine release in the PVN. In addition, we also found that estrogen receptors are increased in the PVN and A2 region by acute fasting. Therefore, the following hypothesis is proposed: fasting first induces an transient increase in the activity of noradrenergic system at the beginning of the first dark phase after the food deprivation; this activation results in an increase in estrogen receptors in the PVN and A2 region; the increase in estrogen receptors leads to an increase in the sensitivity of noradrenergic systems to the neural inputs associated with fasting to these nuclei. 3. The response of the reproductive activity to various external stimuli including stress is modulated by ovarian steroids. The estrogen feedback action on the PVN and A2 is totally different from the so-called "negative feedback action" of estrogen that is for monitoring the ovarian condition. The novel estrogen feedback action may alter the response of neurons regulating gonadal axis to the signal associated with environmental cues such as stress.

Reduction of glucose availability suppresses pulsatile luteinizing hormone release in female and male rats.

Glucose availability controls reproductive activity through modulation of LH secretion. The aim of the present study was to determine whether the glucoprivic suppression is potentiated by gonadal steroids and if glucoprivic suppression of pulsatile LH release is sexually differentiated. Pulsatile LH secretion was examined in rats after peripheral (jugular) administration of the competitive inhibitor of glycolysis, 2-deoxyglucose (2DG). Fourteen days after gonadectomy, blood samples were collected every 6 min for 3 h. One hour after the onset of sampling, 2DG was administered peripherally (200, 400, or 800 mg/kg BW, iv), and food intake was determined after 2DG injection in gonadectomized males and females in the presence or absence of sex steroids (testosterone or estradiol). To test the ability of the pituitary to produce LH under glucoprivic conditions, LHRH was injected every 30 min for 2.5 h in ovariectomized (OVX) rats 30 min after treatment with 400 mg/kg 2DG. At all peripheral doses of 2DG in females and at the middle and high doses of 2DG in males, mean plasma LH and LH pulse frequency decreased (P < 0.05) in the presence of steroids. However, in the absence of sex steroids, the lowest dose in females and the middle dose in males were not effective. Pituitary function appeared normal, because increases in mean plasma LH in response to the exogenous LHRH occurred in OVX rats treated with the middle dose of 2DG. Food intake significantly (P < 0.05) increased after 2DG injection in all groups except estrogen-treated OVX females at the low and high doses of 2DG. These findings suggest that glucoprivic suppression of LH pulses is potentiated by gonadal steroids in both sexes. Moreover, the hypothalamo-hypophyseal axis of the female rat seems to be more sensitive to the decreased glucose availability induced by 2DG than that of the male.

Suppression of luteinizing hormone pulses by restriction of glucose availability is mediated by sensors in the brain stem.

The availability of metabolic fuels such as glucose is known to influence reproductive function. Peripheral administration of 2-deoxyglucose (2DG), a competitive inhibitor of glycolysis, inhibits pulsatile LH secretion in the rat and growth-retarded lamb. We hypothesized that such glucoprivic suppression of LH secretion is mediated by the lower brain stem, because studies of both ingestive and reproductive behavior implicate lower brain stem structures, such as the area postrema, as a site that is sensitive to glucose availability. In the present study, the effect of a 2DG infusion, targeted to the fourth ventricle, on pulsatile LH secretion was examined in male rats. The males were castrated or castrated and immediately implanted with testosterone. Blood samples were collected through an indwelling atrial cannula every 6 min for 4 h for LH determination. After the first hour of blood sampling, 2DG (4 or 40 mg/kg) was infused into the fourth ventricle at a flow rate of 0.2 microliter/min through a cannula that had been stereotaxically implanted 1 week before sampling. The high dose of 2DG (40 mg/kg), but not the low dose (4 mg/kg), suppressed pulsatile LH secretion and increased food intake in both castrated and testosterone-treated castrated rats. LH secretion and food intake were not affected by the infusion of xylose (40 mg/kg) as an isoosmotic control. The site specificity of the 2DG treatment was confirmed by histological examination after an isovolumetric infusion of dye (0.2 microliter/min). These results suggest that glucose availability could influence LH secretion as well as feeding through a central sensor in the lower brain stem and are consistent with the idea that the area postrema might be an important glucosensor involved in the modulation of LH secretion.

A rapid suppressive effect of estrogen in the paraventricular nucleus on pulsatile LH release in fasting-ovariectomized rats.

The paraventricular nucleus (PVN) and A2 are novel estrogen feedback sites where estrogen may modulate the neural response to adrenergic inputs during fasting. In the present study, the effects of local estradiol (E(2)) perfusion through a microdialysis probe placed in the PVN or A2 on pulsatile luteinizing hormone (LH) secretion and on norepinephrine (NE) release in the PVN were examined in 48-h fasting ovariectomized (OVX) rats to determine whether local estrogen administered in the PVN or A2 rapidly inhibits LH secretion during fasting and whether this inhibition is mediated by an increase of NE release in the PVN. Five days after ovariectomy, animals (n=5 per group) stereotaxically implanted with a guide cannula for microdialysis in the PVN (experiment 1) or both PVN and A2 (experiment 2) were deprived of food for 48 h. Blood samples and dialysates were then collected every 6 min for 3 h and every 12 min (experiment 1) or 20 min (experiment 2) for 3 h, respectively. The PVN or A2 was perfused with E(2) (5 ng/ml in artificial cerebrospinal fluid) through a microdialysis probe after the first hour of sampling. E(2) perfusion in the PVN caused a rapid and significant suppression of mean plasma LH levels and LH pulse frequency in fasting rats but no changes in unfasting animals. NE release in the PVN was not affected by the local E(2) perfusion of the PVN in either fasting or unfasting groups. This perfusion in A2, however, did not cause any apparent changes in plasma LH and perfusate NE levels in the PVN and A2. The present results indicate that estrogen feedback action at the PVN suppresses LH secretion rapidly during fasting and does not involve an increase of NE release in the PVN.

Estrogen feedback needed at the paraventricular nucleus or A2 to suppress pulsatile luteinizing hormone release in fasting female rats.

The feedback sites of estrogen within the hypothalamus and lower brain stem involved in the suppression of pulsatile LH secretion during 48-h fasting were examined in ovariectomized rats with local estradiol (E2) implants. The animals were ovariectomized and immediately implanted stereotaxically with stainless steel cannula containing crystal E2 diluted 10 times with crystal cholesterol into the medial preoptic area, paraventricular nucleus (PVN), arcuate nucleus (ARC), locus ceruleus, or A1 or A2 region of the brain. Five days later, animals were deprived of food for 48 h, and blood samples were collected every 6 min for 3 h. Animals were immediately refed for 45 h and bled again as described above. Changes in the mean LH concentrations over the 3-h sampling period and the frequency and amplitude of LH pulses were determined by calculating the differences in these parameters between the first and second blood samplings in each animal. Fasting significantly lowered mean LH concentrations in animals implanted with E2 in the A2. The more potent suppression of pulsatile LH release during fasting was found in rats with E2 implants in the PVN: the mean LH concentrations and LH pulse frequency were significantly reduced by fasting in this group. In the animals with E2 implants in the medial preoptic area, ARC, locus ceruleus, or A1, 48-h fasting did not induce any significant changes in LH pulse parameters compared to those in cholesterol-implanted controls. A decrease in LH pulse amplitude was apparent in refed rats as well as fasted animals only when E2 was implanted in the ARC. These results suggest that the feedback action of estrogen at the PVN and/or A2 is required for fasting-induced suppression of pulsatile LH release, as opposed to the so-called negative feedback action of estrogen, which tonically suppresses LH release in nonfasting rats.

Corticotropin-releasing hormone mediates suppression of pulsatile luteinizing hormone secretion induced by activation of alpha-adrenergic receptors in the paraventricular nucleus in female rats.

The present study examined which subtype of adrenergic receptor in the paraventricular nucleus (PVN) has a role in regulating pulsatile LH secretion and whether CRH mediates the effect of norepinephrine (NE) injection into the PVN on pulsatile LH secretion in ovariectomized (OVX) and ovariectomized estradiol (E2)-treated (OVX + E2) rats. All animals were OVX, and some were sc implanted with Silastic capsules containing E2 dissolved in peanut oil. One week after ovariectomy and E2 implantation, guide cannulae for injection of agent and alpha-helical CRF-(9-41) (alpha-hel CRF), an antagonist of CRH, were stereotaxically implanted into the PVN and third ventricle, respectively. Animals were bled for 3 h at 6-min intervals through an atrial cannula immediately after PVN injection of NE or various adrenergic receptor agonists (phenylephrine, an alpha 1-adrenergic receptor agonist; clonidine, an alpha 2-agonist; and isoproterenol, a beta-agonist). Some of the animals were injected with alpha-hel CRF 5 min before NE injection. NE and both alpha-receptor agonists inhibited pulsatile LH secretion throughout the 3-h sampling period in OVX + E2 rats and significantly reduced the mean plasma LH levels and the LH pulse frequency. On the other hand, LH secretion was inhibited transiently for the first 1-2 h by an injection of NE or an alpha 2-receptor agonist into the PVN in OVX rats, resulting in a significant decrease only in mean plasma LH levels in the NE-injected group. Injection of a beta-agonist did not affect pulsatile LH secretion in either OVX or OVX + E2 animals. Intracerebroventricular injection of alpha-hel CRF before PVN injection of NE completely blocked the NE-induced suppression of pulsatile LH secretion in OVX+E2 rats. These results suggest that 1) the noradrenergic system projecting to the PVN suppresses pulsatile LH secretion via the activation of alpha-adrenergic receptors; 2) this inhibition is mediated by CRH release; and 3) estrogen enhances this suppression.

Partially arrested root formation in a permanent maxillary central incisor subsequent to trauma to the primary dentition.

When the primary dentition sustains a traumatic insult, the development of the succedaneous teeth can be disturbed leading to a number of malformations. In this case report, the patient presented with a history of prior trauma to his primary maxillary incisors which resulted in partially arrested root formation for a permanent incisor. The considerations in formulating a treatment plan which included orthodontics are discussed.