Current variations and practice patterns in tympanic membrane perforation repair.

OBJECTIVE: Management of tympanic membrane perforations is varied. This study aimed to better understand current practice patterns in myringoplasty and type 1 tympanoplasty. METHODS: An electronic questionnaire was distributed to American Academy of Otolaryngology - Head and Neck Surgery members. Practice patterns were compared in terms of fellowship training, practice length, practice setting, paediatric case frequency and total cases per year. RESULTS: Of the 321 respondents, most were comprehensive otolaryngologists (60.4 per cent), in private practice (60.8 per cent), with a primarily adult practice (59.8 per cent). Fellowship training was the factor most associated with significant variations in management, including pre-operative antibiotic usage (p = 0.019), contraindications (p < 0.001), approach to traumatic perforations (p < 0.001), use of local anaesthesia (p < 0.001), graft material (p < 0.001), tympanoplasty technique (p = 0.003), endoscopic assistance (p < 0.001) and timing of post-operative audiology evaluation (p = 0.003). CONCLUSION: Subspecialty training appears to be the main variable associated with significant differences in peri-operative decision-making for surgical repair of tympanic membrane perforations.

Sudden sensorineural hearing loss and coronavirus disease 2019.

OBJECTIVE: To determine if otolaryngologists and audiologists of the American Academy of Otolaryngology - Head and Neck Surgery have noticed an increase in the incidence of sudden sensorineural hearing loss during the coronavirus disease 2019 pandemic. METHODS: A questionnaire was developed for the purpose of providing a cross-sectional descriptive analysis of perceived association between the coronavirus disease 2019 pandemic and an increase in the incidence of sudden sensorineural hearing loss. RESULTS: Of respondents, 63.0 per cent did not notice an increase in sudden sensorineural hearing loss during the coronavirus disease 2019 pandemic. There was a weak positive correlation between patients identified with sudden sensorineural hearing loss and the percentage of coronavirus disease 2019 positive patients reported by each medical care provider (Spearman correlation = 0.20, 95 per cent confidence interval = 0.05-0.33). There was no association between geographical location and perceived increase in sudden sensorineural hearing loss (p = 0.38). CONCLUSION: The majority of respondents did not perceive an increase in the incidence of sudden sensorineural hearing loss during the coronavirus pandemic, regardless of geographical region.

Local-scale fluxes of carbon dioxide in urban environments: methodological challenges and results from Chicago.

Much attention is being directed to the measurement and modeling of surface-atmosphere exchanges of CO2 for different surface types. However, as yet, few measurements have been conducted in cities, even though these environments are widely acknowledged to be major sources of anthropogenic CO2. This paper highlights some of the challenges facing micrometeorologists attempting to use eddy covariance techniques to directly monitor CO2 fluxes in urban environments, focusing on the inherent variability within and between urban areas, and the importance of scale and the appropriate height of measurements. Results from a very short-term study of CO2 fluxes, undertaken in Chicago, Illinois in the summer of 1995, are presented. Mid-afternoon minimum CO2 concentrations and negative fluxes are attributed to the strength of biospheric photosynthesis and strong mixing of local anthropogenic sources in a deep mixed layer. Poor night-time atmospheric mixing, lower mixed layer depths, biospheric respiration, and continued missions from mobile and fixed anthropogenic sources, account for the night-time maxima in CO2 concentrations. The need for more, longer-term, continuous eddy covariance measurements is stressed.

Effects of cocaine on basal and pulsatile prolactin levels in rhesus monkeys.

OBJECTIVES: Cocaine abuse is often associated with reproductive cycle dysfunction including altered menstrual cyclicity and decreased ovulation rates. Cocaine might also alter prolactin (PRL) secretion, presumably through the effects of this drug on hypothalamic dopamine, the primary factor regulating pituitary PRL secretion. We assessed basal and pulsatile PRL levels to determine whether hyperprolactinemia is associated with cocaine-induced disruption of menstrual cyclicity in rhesus monkeys. METHODS: Normally cycling, drug-naïve monkeys were studied. Cocaine-treated animals were pair-fed with controls to minimize cocaine-related differences in caloric intake. Twenty-eight monkeys were randomized to receive daily intravenous (iv) infusion of saline or cocaine (1, 2, or 4 mg/kg) on cycle days 2-14. Daily blood samples were obtained through indwelling catheters for measurement of ovarian steroids, gonadotropins, and PRL. Laparoscopy was performed 2 days after the midcycle estradiol surge to document ovulation. Sixteen other monkeys were randomized to receive daily iv infusion of saline or cocaine (4 mg/kg). Blood samples were obtained every 15 minutes for 8 hours in the early (cycle day 1-5), mid- (cycle day 6-10), and late (cycle day 11-15) follicular phase. Plasma was assayed for PRL, and pulses were identified by cluster analysis. RESULTS: All seven control monkeys had laparoscopically confirmed ovulation compared to two of seven monkeys receiving 1 mg/kg, three of seven monkeys receiving 2 mg/kg, and one of seven receiving 4 mg/kg of cocaine hydrochloride. Cycle length was normal in six of seven controls, and in one of seven, two of seven, and two of seven monkeys receiving the 1, 2, and 4 mg/kg of cocaine, respectively. Estradiol levels were significantly higher in controls versus cocaine-treated monkeys, but there was no difference in basal gonadotropin levels during treatment. Mean PRL levels during treatment were significantly lower (P <.05) in controls (4.6 +/- 0.2 ng/mL) as compared to monkeys receiving 1 (6.5 +/- 0.6 ng/mL), 2 (6.1 +/- 0.4 ng/mL), and 4 mg/kg (7.2 +/- 0.6 ng/mL) of cocaine. There was no significant difference in PRL pulse amplitude or frequency between controls and cocaine-treated monkeys during each cycle phase. CONCLUSIONS: Circulating PRL levels were slightly higher in monkeys receiving cocaine during the follicular phase. Although this increase was statistically significant, PRL levels remained well within the euprolactinemic range in cocaine-treated monkeys.

Cocaine impairs ovarian response to exogenous gonadotropins in nonhuman primates.

OBJECTIVE: Determine whether cocaine directly impairs ovarian steroid production and ovulation. METHODS: Normally cycling adult female rhesus monkeys received daily intravenous normal saline (control; n = 8) or cocaine (4 mg/kg; n = 8) through the follicular phase. Monkeys were injected daily with human menopausal gonadotropin (hMG; Pergonal) at a dose of 6 IU/kg intramuscularly beginning on cycle day 2. Daily blood samples were obtained, and serum estradiol (E(2)) and progesterone (P(4)) were measured by radioimmunoassay. When serum levels of E(2) declined, plateaued, or exceeded 600 pg/mL, laparoscopy was performed to count the number of follicles. If no new corpus luteum was present, monkeys were injected intramuscularly with 1000 IU of hCG. Laparoscopy was repeated 2 days later to document the number of ovulatory stigma. RESULTS: During ovarian stimulation, cocaine-treated monkeys required an average additional 1.5 days of hMG injections (P =.01), and this resulted in a greater total dose of hMG compared with control monkeys (351 +/- 16 IU versus 297 +/- 15 IU [mean +/- standard error of the mean], P =.03). For spontaneous and hCG-triggered ovulation, the number of ovulatory stigma was significantly lower (P <.003) in the cocaine-treated versus control monkeys (16 versus 31). Peak E(2) levels were significantly (P =.05) lower in cocaine-treated monkeys compared with controls. Luteal phase P(4) levels were lower in the cocaine-treated monkeys, but the difference was not statistically significant when compared with controls. CONCLUSION: Cocaine impaired ovarian responsiveness to exogenous gonadotropins and decreased ovulatory stigma in nonhuman primates. These findings suggest that cocaine has direct ovarian effects.

Clinicopathologic analysis of HER-2/neu immunoexpression among various histologic subtypes and grades of osteosarcoma.

Overexpression of the HER-2/neu oncogene appears to have prognostic significance in breast cancer. Recently, some have reported a relationship between increased immunohistochemical expression in osteosarcoma and poor clinical outcome. Despite limited data, a pilot trial of Herceptin, which targets the oncogene product, has been initiated for the therapy of some metastatic osteosarcomas (CCG-P9852). Archival formalin-fixed, paraffin-embedded tissue obtained from 41 patients diagnosed with osteosarcoma was examined immunohistochemically by 2 antibodies against the HER-2/neu oncogene product: CB-11 (monoclonal, 1/100) and Oncor (polyclonal, 1/200). All but one tumor (case of recurrent dedifferentiated parosteal osteosarcoma) represented primary tumor samples; when applicable, only prechemotherapy biopsies were analyzed. The study sample included the full spectrum of histologic subtypes and grades of osteosarcoma (25 conventional high grade; 3 telangiectatic; 1 small cell; 6 parosteal; 1 periosteal; and 5 low-grade intramedullary). A case of metastatic breast cancer with known overexpression of the HER-2/neu oncogene served as the positive control. Complete membranous positivity, considered prognostically significant in breast cancer, was not seen in any of our osteosarcoma cases. At least focal cytoplasmic positivity was documented in 40 (98%) tumors using the CB11 antibody and in 34 (83%) using the Oncor antibody. The intensity of the cytoplasmic staining (0, 1-3+) did not correlate with histologic subtype/grade, response to chemotherapy (<90% versus > or = 90% necrosis), metastasis, or survival. Immunohistochemical overexpression of the HER-2/neu oncogene, defined as complete membranous positivity, is not present in our series of osteosarcomas. Cytoplasmic positivity is observed in most osteosarcomas, irrespective of histologic subtype/grade, and is not associated with response to preoperative chemotherapy or disease progression.

Robust estimators of the concordance correlation coefficient.

This paper proposes a generalized version of Lin' s concordance correlation coefficient for the agreement assessment of continuous data. Lin's coefficient evaluates the accuracy and precision between two measures, and is based on the expected value of the squared distance function. We generalize Lin's coefficient, apply alternative distance functions, and produce more robust versions of the concordance correlation coefficient. In this paper, we develop the asymptotic theory for this class of estimators, investigate small-sample properties via computer simulation, and demonstrate their use with two real data examples.

Effect of acute administration of cocaine on pituitary gonadotrophin secretion in female rats.

The aim of this study was to characterize the acute effects of cocaine administration on pituitary gonadotrophin secretion in adult female rats. Ovariectomized, oestradiol-treated rats were infused i.v. with 0.1 ml normal saline or 2 mg cocaine hydrochloride kg(-1). Blood samples were collected immediately before cocaine infusion and at 3, 10, 30 and 60 min after cocaine infusion. Circulating LH concentrations were increased by 10 min after cocaine administration (P < 0.05 versus saline-treated controls) and decreased thereafter. Serum FSH concentrations were not significantly different from those of saline-infused controls at any time. In a second experiment, oestradiol-treated, ovariectomized rats were infused i.v. with: saline only, 2 mg cocaine hydrochloride kg(-1) in saline, 200 ng synthetic GnRH in 100 microl PBS or 200 ng synthetic GnRH plus 2 mg cocaine hydrochloride kg(-1) in PBS. Blood samples were collected immediately before drug infusions and 20 min later. Cocaine had no effect on either GnRH-stimulated LH or FSH secretion. In a third experiment, pituitary cells were obtained from oestradiol-treated, ovariectomized rats. The cell cultures were exposed to 25 ng cocaine hydrochloride ml(-1), 10(-10)-10(-7) mol GnRH (-1) with and without 25 ng cocaine hydrochloride ml(-1), or vehicle only. Medium was collected before and after exposure to GnRH to determine concentrations of secreted LH and FSH. Similar to the results of the second study, cocaine had no effect on GnRH-stimulated LH or FSH secretion from pituitary cells in vitro. On the basis of these results it is suggested that acutely administered cocaine stimulates release of hypothalamic GnRH, which, in turn, stimulates pituitary gonadotrophin secretion. Acute administration of cocaine does not appear to affect pituitary gonadotrophin secretion directly.

Mediation in a family-directed program for prevention of adolescent tobacco and alcohol use.

BACKGROUND: Family Matters is a universal intervention designed to prevent adolescent tobacco and alcohol use through involvement of family members and by targeting family risk factors for tobacco and alcohol use. Previously reported findings suggest that the program reduced the prevalence of both adolescent smoking and drinking in the 12 months after program completion. This paper reports analyses conducted to identify the mediators through which the program influenced adolescent smoking and drinking. METHODS: One thousand fourteen adolescents ages 12 to 14 years and their families, identified by random-digit dialing, were entered into a randomized trial. Adolescents and their parents provided data by telephone for measuring mediator and behavioral variables at baseline, 3 months, and 12 months after program completion. Repeated-measures logistic regression with generalized estimating equations was used to assess mediation processes. RESULTS: The program resulted in statistically significant changes in several substance-specific aspects of the family, such as rule setting about tobacco and alcohol use. However, the intermediate family effects did not account for the program effects on adolescent behavior. CONCLUSIONS: The variables hypothesized to explain program effects were not identified by direct empirical examination.

A generalized concordance correlation coefficient for continuous and categorical data.

This paper discusses a generalized version of the concordance correlation coefficient for agreement data. The concordance correlation coefficient evaluates the accuracy and precision between two measures, and is based on the expected value of the squared function of distance. We have generalized this coefficient by applying alternative functions of distance to produce more robust versions of the concordance correlation coefficient. In this paper we extend the application of this class of estimators to categorical data as well, and demonstrate similarities to the kappa and weighted kappa statistics. We also introduce a stratified concordance correlation coefficient which adjusts for explanatory factors, and an extended concordance correlation coefficient which measures agreement among more than two responses. With these extensions, the generalized concordance correlation coefficient provides a unifying approach to assessing agreement among two or more measures that are either continuous or categorical in scale.

Extraction and quantification of epibatidine in plasma.

Epibatidine was extracted from human and mouse plasma into a hexane-isopropanol mixture and back-extracted into a phosphate buffer, pH 2.5, then identified by HPLC isocratically using a CN column and quantified with ultraviolet detection at a fixed wavelength of 214 nm. The percent recovery of epibatidine from spiked plasma samples was 83.6% and the percent extraction was linear between 10 and 1,000 ng/ml. Desipramine was used as the internal standard. For spiked control samples containing 50 and 750 ng/ml, between-day precisions were 20.8 and 7.2% (RSD%), respectively; accuracy was 87.0 and 99.1%, respectively. The limit of detection was 2 ng/ml. Using this method, an intraperitoneal dose of 0.1 mg/kg of epibatidine produced mean levels of 7.3 and 37.1 ng/ml in pooled male and female plasma samples from C57BL/10 J mice, respectively. This is a simple and straightforward procedure by which plasma samples may be analyzed for epibatidine.

The influence of a family program on adolescent tobacco and alcohol use.

OBJECTIVES: This study examined a family-directed program's effectiveness in preventing adolescent tobacco and alcohol use in a general population. METHODS: Adolescents aged 12 to 14 years and their families were identified by random-digit dialing throughout the contiguous United States. After providing baseline data by telephone interviews, they were randomly allocated to receive or not receive a family-directed program featuring mailed booklets and telephone contacts by health educators. Follow-up telephone interviews were conducted 3 and 12 months after program completion. RESULTS: The findings suggested that smoking onset was reduced by 16.4% at 1 year, with a 25.0% reduction for non-Hispanic Whites but no statistically significant program effect for other races/ethnicities. There were no statistically significant program effects for smokeless tobacco or alcohol use onset. CONCLUSIONS: The family-directed program was associated with reduced smoking onset for non-Hispanic Whites, suggesting that it is worthy of further application, development, and evaluation.

Postoperative sleep disturbance: influences of opioids and pain in humans.

STUDY OBJECTIVES: To test the hypothesis that opioids and pain contribute independently to postoperative sleep disturbance, 10 women undergoing surgery requiring a low abdominal incision for treatment of benign gynecologic conditions were randomized to receive either epidural opioid (fentanyl) (n=6) or epidural local anesthetic (bupivacaine) (n=4) for intraoperative and postoperative analgesia. DESIGN: N/A. SETTING: N/A. PATIENTS OR PARTICIPANTS: N/A. INTERVENTIONS: N/A. MEASUREMENTS: Polysomnography was performed in a standard patient room on the preoperative and first three postoperative nights. Pain at rest and with coughing was evaluated using a visual-analogue pain scale each evening and morning. RESULTS: On the first postoperative night, rapid eye movement (REM) sleep was abolished in all patients. On the third postoperative night, the mean +/- SE REM sleep time increased significantly (p=.003) to 9.8% +/- 3.1% in the fentanyl group, and 12.9% +/- 3.8% in the bupivacaine group. Conversely, light non-REM (NREM) sleep (%stage 1 + %stage 2) was higher on the first postoperative night and significantly lower on the third postoperative night (p=0.011). Between group comparison revealed only that the mean % slow-wave sleep (SWS) in the fentanyl group (6.0%, 2.0%, and 14.7%) was different from the bupivacaine group (7.8%, 9.1%, and 10.6%) in the postoperative period after adjusting for the preoperative night % SWS (p=0.021). Pain was well controlled in all patients, but was slightly better controlled in the fentanyl group than in the bupivacaine group on postoperative night 2 (p=0.024). There was no statistically significant association between pain score and any polysomnographically defined stage. CONCLUSION: Postoperative patients suffer a profound sleep disturbance even when opioids are avoided and pain is well controlled.

Medical training debt and service commitments: the rural consequences.

This study assesses how student loan debt and scholarships, loan repayment and related programs with service requirements influence the incomes young physicians seek and attain, influence whether they choose to work in rural practice settings and affect the number of Medicaid-covered and uninsured patients they see. Data are from a 1999 mail survey of a national probability sample of 468 practicing family physicians, general internists and pediatricians who graduated from U.S. medical schools in 1988 and 1992. A majority of these generalist physicians recalled "moderate" or "great" concern for their financial situations before, during and after their training. Eighty percent financed all or part of their training with loans, and one-quarter received support from federal, state or community-sponsored scholarship, loan repayment and similar programs with service obligations. In their first job after residency, family physicians and pediatricians with greater debt reported caring for more patients insured under Medicaid and uninsured than did those with less debt. For no specialty was debt associated with physicians' income or likelihood of working in a rural area. Physicians serving commitments in exchange for training cost support, compared to those without obligations, were more likely to work in rural areas (33 vs. 7 percent, respectively, p < 0.001) and provided care to more Medicaid-covered and uninsured patients (53 vs. 29 percent, p < 0.001), but did not differ in their incomes ($99,600 vs. $93,800, p = 0.11). Thus, among physicians who train as generalists, the high costs of medical education appear to promote, not harm, national physician work force goals by prompting participation in service-requiring financial support programs and perhaps through increasing student borrowing. These positive outcomes for generalists should be weighed against other known and suspected negative consequences of the high costs of training, such as discouraging some poor students from medical careers altogether and perhaps influencing some medical students with high debt not to pursue primary care careers.

Melatonin secretion after surgery.

Sleep disturbance is common postoperatively. We examined whether melatonin concentrations were related to this disturbance in seven postoperative patients. Nocturnal concentrations of melatonin were significantly (p=0.005) lower on the first than on the second or third nights after surgery. This finding raises the possibility that melatonin suppression and associated sleep disturbance might be prevented by melatonin replacement.

State scholarship, loan forgiveness, and related programs: the unheralded safety net.

CONTEXT: In the mid-1980s, states expanded their initiatives of scholarships, loan repayment programs, and similar incentives to recruit primary care practitioners into underserved areas. With no national coordination or mandate to publicize these efforts, little is known about these state programs and their recent growth. OBJECTIVES: To identify and describe state programs that provide financial support to physicians and midlevel practitioners in exchange for a period of service in underserved areas, and to begin to assess the magnitude of the contributions of these programs to the US health care safety net. DESIGN: Cross-sectional, descriptive study of data collected by telephone, mail questionnaires, and through other available documents, (eg, program brochures, Web sites). SETTING AND PARTICIPANTS: All state programs operating in 1996 that provided financial support in exchange for service in defined underserved areas to student, resident, and practicing physicians; nurse practitioners; physician assistants; and nurse midwives. We excluded local community initiatives and programs that received federal support, including that from the National Health Service Corps. MAIN OUTCOME MEASURES: Number and types of state support-for-service programs in 1996; trends in program types and numbers since 1990; distribution of programs across states; numbers of participating physicians and other practitioners in 1996; numbers in state programs relative to federal programs; and basic features of state programs. RESULTS: In 1996, there were 82 eligible programs operating in 41 states, including 29 loan repayment programs, 29 scholarship programs, 11 loan programs, 8 direct financial incentive programs, and 5 resident support programs. Programs more than doubled in number between 1990 (n = 39) and 1996 (n = 82). In 1996, an estimated 1306 physicians and 370 midlevel practitioners were serving obligations to these state programs, a number comparable with those in federal programs. Common features of state programs were a mission to influence the distribution of the health care workforce within their states' borders, an emphasis on primary care, and reliance on annual state appropriations and other public funding mechanisms. CONCLUSIONS: In 1996, states fielded an obligated primary care workforce comparable in size to the better-known federal programs. These state programs constitute a major portion of the US health care safety net, and their activities should be monitored, coordinated, and evaluated. State programs should not be omitted from listings of safety-net initiatives or overlooked in future plans to further improve health care access. JAMA. 2000;284:2084-2092.

Influence of a family-directed program on adolescent cigarette and alcohol cessation.

Programs to reduce adolescent cigarette or alcohol use by users in general populations have only recently been evaluated. Moreover, in spite of the substantial influence families have on their children, few family-directed programs designed to reduce the prevalence of adolescent smoking and drinking have been rigorously evaluated. This paper reports the findings of research designed to determine whether a family program reduced use of cigarettes or alcohol by users. The program consisted of a series of booklets mailed to families and follow-up telephone calls by health educators. A randomized experimental design involved families with children ages 12-14 throughout the United States. Data were collected by telephone at baseline and 3 and 12 months after the program was completed. No statistically significant program effects were observed for cessation or decrease in smoking and drinking by users.

Thrombin-stimulated increases in cytosolic Ca2+ level and gonadotropin-releasing hormone release in GT1-7 neurons.

The effects of thrombin on cytosolic calcium levels ([Ca2+]cyt), and on gonadotropin-releasing hormone (GnRH) release, were characterized in cultured GT1-7 neurons. GnRH release from GT1-7 neurons was pulsatile with an average pulse amplitude of 14.3+/-5.8 pg x min x ml(-1) and an average pulse duration of 21.3+/-4.2 min. The [Ca2+]cyt response to 0.005 to 0.2 U/ml thrombin was saturable and concentration dependent (EC50 = 0.0268 U/ml). Ethyleneglycotetraacetic acid (EGTA) chelation of extracellular Ca2+ resulted in an approximately 70% attenuation of thrombin-stimulated increase in [Ca2+]cyt. By use of a special superfusion system, a 5-min exposure to 0.1 U/ml thrombin significantly increased the amplitude (193.2+/-67.8 pg x min x ml(-1); P = 0.001) but not the duration (22.5+/-2.4 min; P = 0.8) of GnRH release. These results suggest that thrombin increases [Ca2+]cyt and GnRH release from GT1-7 neurons via specific membrane-bound receptors.

Low-dose follicular-phase cocaine administration disrupts menstrual and ovarian cyclicity in rhesus monkeys.

OBJECTIVE: To evaluate the effects of daily low-dose follicular-phase cocaine administration on menstrual cyclicity, ovulation rates, corpus luteum function, and hormone levels in rhesus monkeys. METHOD: Normally cycling, drug-naive, adult rhesus monkeys were randomized to receive either 1 mg/kg of cocaine (n = 7), 2 mg/kg of cocaine (n = 7), or normal saline (n = 7) daily on cycle days 2 to 14. Daily blood samples were obtained through indwelling catheters for measurement of serum gonadotropins and ovarian steroids. Daily vaginal swabs were obtained to determine onset of menses. Laparoscopy was performed 2 days after the midcycle estrogen peak to document ovulation. Daily caloric intakes as well as pretreatment and posttreatment weights were recorded. RESULTS: Two of seven monkeys receiving 1 mg/kg per day and two of seven monkeys receiving 2 mg/kg per day of cocaine had timely ovulation and normal menstrual cycle lengths. One monkey receiving the 2-mg/kg dose ovulated on cycle day 24 and had a short luteal phase (7 days) with a mean progesterone level of 2.4 ng/mL. All seven saline-treated control monkeys ovulated normally; the mean cycle length was 29 days and all had adequate luteal phases. The difference in ovulation rates between cocaine-treated and control monkeys was statistically significant (P = .003). There were no differences in basal levels of LH or FSH between treatment groups. There were no significant differences in weight change or caloric intake among groups. One third of the subsequent menstrual cycles in cocaine-treated monkeys were of abnormal duration. CONCLUSION: Daily low-dose follicular-phase cocaine administration disrupts menstrual cyclicity and folliculogenesis. This effect is independent of weight loss, caloric intake, and basal gonadotropin levels. Cocaine exposure may have a persistent effect on menstrual and ovarian cyclicity in some monkeys.

Concentration-dependent effects of muscimol to enhance pulsatile GnRH release from GT1-7 neurons in vitro.

Immortalized GT1-7 neurons were used to characterize the effect of muscimol, a GABAA receptor agonist, to enhance pulsatile gonadotropin-releasing hormone (GnRH) release. GT1-7 neurons were grown on Cytodex-3 beads and placed in special superfusion microchambers. The cells were superfused at a rate of 6.2 ml x h-1 with Media 199 (pH 7.35) using a commercially available perfusion system. After a pre-muscimol period of 120 min, the cells were exposed for 5 min to 0.35, 1, 5 or 10 microM muscimol or 5 microM muscimol+20 microM of the GABAA receptor antagonist, bicuculline. Following removal of the muscimol (and bicuculline, in the case of the latter experiment), the superfusion was continued for another 115 min. Sample fractions were collected at 5 min intervals throughout the perfusion. Basal GnRH release from the GT1-7 neurons was pulsatile with an average interpulse interval of 45.4+/-0.5 min and an average pulse amplitude of 191.5+/-22.6 pg x min x ml-1. Our results also demonstrated that the GABAA receptor agonist, muscimol, enhances pulsatile GnRH release from GT1-7 neurons in culture. The response to muscimol was saturable and concentration-dependent with an EC50 of 0.47 microM. The effects of 5 microM muscimol to increase GnRH pulsatility were blocked by co-exposure to the GABAA receptor antagonist, bicuculline. The average GnRH interpulse intervals were 41.7+/-1.8 min, 32.5+/-2.9 min, 30.6+/-0.7 min and 25.5+/-0.4 min in the period following exposure to 0.35, 1, 5 and 10 microM of muscimol, respectively (post-muscimol period). GnRH pulse amplitude (mean-area for each pulse) was increased during exposure to muscimol but not during the pre- or post-muscimol periods. The GABAA receptor antagonist, bicuculline, itself had no effect on pulsatile GnRH release. These results are consistent with previously published reports suggesting that activation of the GABAA receptor stimulates hypothalamic GnRH release in embryonic and neonatal animals.