Standard Stimulation Protocol Research Articles

Recombinant human chorionic gonadotropin (R-HCG) and urinary HCG (U-HCG) are equally effective with controlled ovarian stimulation in egg donors

Objective: Human chorionic gonadotropin (u-hCG), derived from urine in pregnancy, has been successfully employed for many years for final follicular maturation and early luteinization in women after controlled ovarian stimulation (COS) in Assisted Reproductive Technology (ART) programs. A recombinant hCG (r-hCG) for subcutaneous injection was introduced in September of 2000. Since improved patient tolerability and ease of administration are observed with r-hCG, this study was conducted to compare the clinical efficacy of r-hCG (Ovidrel) to that of u-hCG (Novarel, Profasi, Pregnyl) in a standard egg donor stimulation protocol.

Evaluation of methods for eliciting somatosensory-evoked potentials in the awake, freely moving rat

To standardise the method of eliciting somatosensory-evoked potentials (SEPs), SEPs were generated by electrical stimulation of different stimulus sites and recorded bilaterally from the primary somatosensory cortex (S1) and from midline in awake, freely moving rats. Increasing stimulus intensity enhanced amplitudes of all SEPs. At supramaximal stimulation, SEPs following vibrissae and tail stimulation (V-SEP and Ta-SEP, respectively) but not following trunk stimulation (Tr-SEP), fulfilled our criterion of signal-to-noise ratio ≥4. The first V-SEP component coincided with a stimulus artefact, disqualifying these recordings for a standard stimulation protocol. The Ta-SEP generated stable and reproducible recordings and was considered to be the preferred technique. Early components of the contralateral S1 recorded V-SEP and Tr-SEP occurred at latencies different from the other recordings. Increasing stimulus repetition rate (SRR) decreased amplitudes of all SEPs. At the highest obtainable SRR, the amplitude between the V-SEP second positive and second negative components in all recordings was 70–80% of the amplitude at 0.1 Hz, whereas peak amplitudes of subsequent components and those of the Tr-SEP and Ta-SEP were 20–50%. These results indicate that the different SEP components might be generated by different ascending neural pathways.

Clinical management of low ovarian response to stimulation for IVF: a systematic review.

Poor response is not a rare occurrence in ovarian stimulation. Although not fully accepted, the most dominant criteria for poor ovarian response are small numbers of follicles developed or oocytes retrieved, and low estradiol (E2) levels after the use of a standard stimulation protocol. There is no ideal predictive test as the poor responder is revealed only during ovulation induction; however, increased levels of day 3 FSH and E2 as well as decreased levels of inhibin B can be used to assess ovarian reserve. Several protocols have been proposed for clinical management of low ovarian response in IVF. Although high doses of gonadotrophins have been used by the vast majority of authors, results have been controversial and prospective randomized studies have shown little or no benefit. The few available relevant studies do not indicate that recombinant FSH improves outcome. Flare-up GnRH agonist protocols (including all dosage varieties) produce better results than standard long luteal protocols. Luteal initiation GnRH agonist 'stop' protocols were shown to improve ovarian response according to prospective studies with historical controls, but this was not confirmed by well-designed prospective, randomized, controlled studies. The few available data obtained with GnRH antagonists have not shown any benefits. Adjuvant therapy with growth hormone (GH) or GH-releasing factors results in no significant improvement. The use of corticosteroids reduces the incidence of poor ovarian response in women undergoing IVF treatment. The limited data obtained with nitric oxide donors are encouraging. Pretreatment with combined oral contraceptives prior to stimulation may help ovarian response. No benefit was observed with standard use of ICSI or assisted hatching of zona pellucida. Finally, natural cycle IVF has produced results which are comparable with those obtained with stimulated cycles in true poor responders. Well-designed, large-scale, randomized, controlled trials are needed to assess the efficacy of these different management strategies.

Metabotropic glutamate receptors mediate expression of LTP in slices of rat visual cortex.

Long-term-potentiation (LTP) can be induced by application of a standard theta-burst stimulation protocol in slice preparations of the neocortex. This type of LTP is known to be dependent on the activation of NMDA receptors. The present study used specific experimental conditions to evoke a non-NMDA receptor mediated type of LTP. By use of weak theta-burst stimulation (wTBS) we describe a non-NMDA receptor dependent LTP in rat visual cortex in vitro, which is sensitive to an antagonist of metabotropic glutamate receptors (mGluR). In slices of the visual cortex we stimulated ascending inputs in cortical layer IV and recorded extracellular field potentials (FPs) from cortical layers II/III. In disinhibited slices (with 1 microm picrotoxin), a wTBS induced LTP to 138% of control. The expression of this potentiation was insensitive to the NMDA-receptor antagonist, D-AP5, but could be abolished by application of the mGluR antagonist MCPG. These data suggest an NMDA-independent mechanism for LTP induction in the visual cortex which can be observed in layer II/III neurons.

Predicting the number of oocytes at collection and the fertilization rate for assisted reproductive technologies.

Objective: Evaluating the failed IVF cycle often provides useful prognostic information. Before undergoing another attempt, patients experiencing an unsuccessful IVF cycle frequently request information about the probability of future success. To predict the number of oocytes at collection and their fertilization rate, we have introduced the concept of a repeatability coefficient and formulae to predict the next IVF cycle outcome. Design: Retrospective review of IVF cycle data and statistical analysis. Materials/Methods: Patient data with more than two IVF cycles between January 1998 and December 2000 were collected in our IVF center. During this period, all patients were treated by our standard stimulation protocol (LA/HMG, HCG 10,000 IU/ml) before oocyte retrieval. A repeatability coefficient (the intraclass correlation coefficient of repeated measurements on the same individual), (r) was estimated by the formula: r = (MSb − MSw)/(MSb + MSw (k − 1)). Where, MSb is the mean variance among patients, MSw is the mean variance of the different cycle times within a patient, and k indicates the weighted IVF cycle times. Based on this repeatability coefficient, a prediction may be calculated by formula: Px = kr/(1 + (k − 1) r × (Pk − Â) + Â. Px indicates the patient’s predicted value (for example, number of oocytes at collection or fertilization rate for the next cycle), Pk is the patient average of different cycle times, Â indicates the average level of all patients. k and r indicate the weighted IVF cycle times and repeatability coefficient, respectively. Results: A total of 66 patients undergoing 174 IVF retrieval cycles were analyzed. Each patient had an average of 2.63 retrieval cycles (range 2 to 7 cycles), an average retrieval of 11.3 ± 7.29 oocytes, and a repeatability coefficient of r = 0.52 (P < 0.01). In the fertilization rate group, a total of 65 patients with 168 IVF cycles were analyzed. Each patient had an average of 2.58 cycles (range 2 to 7), an average fertilization rate of 57.1% ± 23.5%, and repeatability coefficient of r = 0.58 (P < 0.01). These results indicate that the number of oocytes at collection and the fertilization rate are highly repeatable and allow the use of the formula: Px = 0.52k/(0.48 + 0.52k) × (Pk − 11.3) + 11.3 to predict the future number of oocytes per retrieval and the formula: Px = 0.58K/(0.42+0.58k) × (Pk − 57.1) + 57.1 to estimate the fertilization rate for a patient’s future IVF cycle. Conclusions: The introduction of a repeatability coefficient, commonly used to predict outcomes in animal genetics, to our human IVF program allows us to reliably predict future IVF cycle outcomes. The variables of oocyte number retrieved and fertilization rate demonstrate high repeatability, which provides a basis for the accurate prediction of these outcomes in future cycles. Accurate prediction of a subsequent IVF cycle attempt can provide prognostic information on which patients can make informed decisions and may allow for modification of the stimulation protocol to optimize cycle success.

A low-dose stimulation protocol using highly purified follicle-stimulating hormone can lead to high pregnancy rates in in vitro fertilization patients with polycystic ovaries who are at risk of a high ovarian response to gonadotropins

Objective: To study the benefits of a low-dose stimulation (LDS) protocol with purified urinary follicle-stimulating hormone in patients with polycystic ovaries who have presented previously with a very high ovarian response to a standard hMG stimulation. Design: Cohort study. Setting: Fertility center in a university hospital. Patient(s): Sixty-one patients involved in an IVF/ICSI program from January 1995 to December 1996. Intervention(s): The patients were first stimulated with a standard protocol using hMG and presented with a very high ovarian response. These patients were then stimulated a second time using a low-dose protocol. Cryopreserved embryos were transferred in later artificial or natural cycles until to December 1999. Main Outcome Measure(s): Number of gonadotropin ampules; estradiol level on the day of ovulation induction; follicles, oocytes, and cryopreserved zygotes; fertilization, implantation, and pregnancy rates; and number of ovarian hyperstimulation syndromes (OHSS). Result(s): The number of ampules used, the estradiol level reached, and the number of oocytes obtained were significantly lower under the LDS than the standard protocol. High implantation (21.8%) and clinical pregnancy (38.4%) rates were obtained after LDS. The cumulated deliveries per cycle started and per patient were, respectively, 41.6% and 52.5%. Five patients suffered OHSS with the standard protocol, and none with the LDS. Conclusion(s): The LDS protocol offers a safe and efficient treatment for patients who present with echographic polycystic ovaries and are at risk of an excessive ovarian response to standard IVF stimulation protocols.

Dissociation between synaptic depression and block of long-term depression induced by raising the temperature in rat hippocampal slices.

The influence of raising the bath temperature (39 degrees C) on synaptic transmission and neuronal plasticity was studied in the CA1 region of the rat hippocampus using an extracellular recording technique. Increasing the bath temperature from 32 to 39 degrees C resulted in a depression of field excitatory postsynaptic potential (fEPSP). Application of the selective A(1) receptor agonist, 2-chloro-adenosine (2-CADO, 1 microM) reduced the fEPSP and subsequently occluded the raised temperature-induced synaptic depression. On the other hand, the selective adenosine A(1) receptor antagonist 8-cyclopentyl-1, 3-dipropylxanthine (DPCPX) blocked depression of fEPSP produced by raising the temperature. These results suggest that raising temperature-induced synaptic depression is due to an alteration of extracellular adenosine concentration. Long-term depression (LTD) could be reliably induced by the standard low-frequency stimulation (LFS, 1 Hz for 15 min) protocol at 32 degrees C but not at 39 degrees C. The raised temperature-induced block of LTD was mimicked by 2-CADO. Unexpectedly, despite the presence of DPCPX, LFS still could not elicit LTD. NMDA receptor-mediated synaptic component (fEPSP(NMDA)) was decreased when increasing the temperature to 39 degrees C and DPCPX failed to reverse such a depression. The increase in the NMDA response in 0.1 mM Mg(++) compared with 1 mM Mg(++) was significantly greater at 32 degrees C than at 39 degrees C. These results suggest that, by increasing the sensitivity of Mg(++) block, an increase in temperature modulates NMDA responses and thereby inhibits the induction of LTD.

Use of a Microdose Gonadotropin Releasing Hormone Agonist (GnRH-a) Stimulation Protocol in Assisted Reproductive Technology (ART) Patients with Poor Ovarian Response

Objectives: One of the most difficult problems facing ART programs is the effective management of the “low responder” patient. Previous reports have suggested that the use of microdoses of GnRH agonist in conjunction with controlled ovarian hyperstimulation might be useful for these difficult patients. Our objectives in this study were to assess the effectiveness of the microdose GnRH-a protocol and to compare it to our standard stimulation protocol.

Minimal Controlled Ovarian Hyperstimulation (COH) Using Clomiphene Citrate/Gonadotropin for IVF/ET: Equivalent Results Compared to the Standard Long Stimulation Protocol with a Significant Reduction in Cost

Objectives: Minimal COH using clomiphene citrate followed by gonadotropin during IVF/ET cycles has been offered to patients at this institution since 1995 in an effort to lower the cost of assisted reproduction. The objective of this study was to compare IVF outcomes between the minimal stimulation protocol and a standard long protocol.

Increased risk of early pregnancy loss by profound suppression of luteinizing hormone during ovarian stimulation in normogonadotrophic women undergoing assisted reproduction.

The impact of suppressed concentrations of circulating luteinizing hormone (LH) during ovarian stimulation on the outcome of in-vitro fertilization or intracytoplasmic sperm injection treatment in 200 consecutive, normogonadotrophic women (couples) was analysed retrospectively. A standard stimulation protocol with mid-luteal gonadotrophin-releasing hormone (GnRH) agonist down-regulation and ovarian stimulation with recombinant follicle stimulating hormone (FSH) was used in all cases. Blood was sampled from each woman on stimulation days 1 and 8 for analysis of oestradiol and LH in serum. A threshold value of serum LH of 0.5 IU/l on stimulation day 8 (S8) was chosen to discriminate between women with low or 'normal' LH concentrations. Low concentrations of LH on S8 (<0.5 IU/l) were found in 49% (98/200) of the women. This group of women was comparable with the normal LH group with regard to pre-treatment clinical parameters, and to the parameters characterizing the stimulation protocol with the exception of serum oestradiol concentration, which on S8 was significantly lower than in the normal LH group (P < 0.001). The proportion of positive pregnancy tests was similar in the two groups (30% versus 34% per started cycle), but the final clinical treatment outcome was significantly different, with a five-fold higher risk of early pregnancy loss (45% versus 9%; P < 0.005) in the low LH group and consequently a significantly poorer chance of delivery than in the normal LH group. It is concluded that a substantial proportion of normogonadotrophic women treated with GnRH agonist down-regulation in combination with FSH, devoid of LH activity, experience LH suppression, which compromises the treatment outcome. Whether these women would benefit from supplementation with recombinant LH or human menopausal gonadotrophin during ovarian stimulation, remains to be proven in the future by prospective randomized trials.

Blastocyst-ET and monozygotic twinning.

To examine the rate of monozygotic twinning associated with blastocyst transfer using commercially available, cell-free culture systems with unmanipulated blastocysts. A retrospective analysis was conducted in multiple private and academic infertility centers throughout the United States, of 199 pregnant patients following in vitro fertilization (IVF) blastocyst embryo transfer (ET). Human embryos obtained through standard IVF stimulation protocols were cultured in commercially available, cell-free media systems and transferred as blastocysts. The main outcome measure was the rate of monozygotic twinning. A total of 199 blastocyst-ET pregnancies were achieved during the study period at the fertility centers examined. Monozygotic twinning was noted in 10/199 (5%) of these pregnancies. All were monochorionic diamnionic. Monozygotic twinning previously has been reported following IVF, especially in relation to assisted hatching. While blastocyst transfer has been available for many years using coculture, there have been no published multicenter reports of monozygotic twinning associated with unmanipulated blastocysts. In a multicenter analysis, a definite increase in monozygotic twinning was seen following blastocyst-ET. We believe this phenomenon is real and that this information should be considered when counseling patients for treatment.

Evaluation of a low-dose synthetic adrenocorticotropic hormone stimulation test in clinically normal dogs and dogs with naturally developing hyperadrenocorticism

Objective To determine whether low doses of synthetic ACTH could induce a maximal cortisol response in clinically normal dogs and to compare a low-dose ACTH stimulation protocol to a standard high-dose ACTH stimulation protocol in dogs with hyperadreno-corticism. Design Cohort study. Animats 6 clinically normal dogs and 7 dogs with hyperadrenocorticism. Procedure Each clinically normal dog was given 1 of 3 doses of cosyntropin (1, 5, or 10 μg/kg [0.45, 2.3, or 4.5 μg/lb] of body weight, IV) in random order at 2-week intervals. Samples for determination of plasma cortisol and ACTH concentrations were obtained before and 30, 60, 90, and 120 minutes after ACTH administration. Each dog with hyperadrenocorticism was given 2 doses of cosyntropin (5 μg/kg or 250 μg/dog) in random order at 2-week intervals. In these dogs, samples for determination of plasma cortisol concentrations were obtained before and 60 minutes after ACTH administration. Results In the clinically normal dogs, peak cortisol concentration and area under the plasma cortisol response curve did not differ significantly among the 3 doses. However, mean plasma cortisol concentration in dogs given 1 μg/kg peaked at 60 minutes, whereas dogs given doses of 5 or 10 μg/kg had peak cortisol values at 90 minutes. In dogs with hyperadrenocorticism, significant differences were not detected between cortisol concentrations after administration of the low or high dose of cosyntropin. Ctinical Implications Administration of cosyntropin at a rate of 5 μg/kg resulted in maximal stimulation of the adrenal cortex in clinically normal dogs and dogs with hyperadrenocorticism. (J Am Vet Med Assoc 1999;214:1497-1501)

Effect of smoking on ovarian reserve and ovarian stimulation in in-vitro fertilization and embryo transfer.

The effect of cigarette smoking on ovarian reserve as measured by basal serum follicle stimulating hormone (FSH) concentrations, and by the response to a standard ovarian stimulation protocol, was examined retrospectively in 173 consecutive women (108 non-smokers and 65 smokers) undergoing in-vitro fertilization (IVF) and embryo transfer treatment. Women who smoked had a higher mean basal serum FSH concentration (P < or = 0.0001), in particular younger (<36 years) women, and required a statistically significantly higher mean dosage of gonadotrophins for ovarian stimulation than the non-smokers (48.1 +/- 15.6 versus 38.9 +/- 13.6 ampoules, 75 IU/ampoule; P < 0.0001). A lower mean number of oocytes was obtained in smokers than non-smokers (6.2 +/- 3.4 versus 11.1 +/- 6.3, oocytes P < or = 0.0001) and the rate of abandoned cycles (18.5 versus 8.5%) and total fertilization failure (18.5 versus 8.5%) was higher. The clinical pregnancy rate per cycle in smokers was 16.9% versus 21.3% in non-smokers but this was not statistically significant. In conclusion, cigarette smoking in women appears to significantly reduce their ovarian reserve and lead to poor response to ovarian stimulation at an earlier age.

Mutual interactions of the presynaptic histamine H 3 and prostaglandin EP 3 receptors on the noradrenergic terminals in the mouse brain

We studied whether interactions between the presynaptic histamine H 3 and prostaglandin EP 3 receptors on the noradrenergic neurons of the mouse brain cortex occur. Cerebral cortex slices from the mouse (and, in few experiments, from the rat) were preincubated with [ 3H]noradrenaline and then superfused with a physiological salt solution. Tritium overflow was evoked electrically, either at 0.3 or 3 Hz (2 min) (standard stimulation protocol) or at 100 Hz (eight pulses) (stimulation protocol under which almost no activation of the presynaptic α 2-adrenoceptors by endogenous noradrenaline occurs). In another set of experiments, Ca 2+ ions were introduced into Ca 2+-free K +-rich medium containing tetrodotoxin to evoke tritium overflow. The electrically-evoked tritium overflow (0.3 Hz) was inhibited by histamine or the H 3 receptor agonist imetit, acting via H 3 receptors, and by prostaglandin E 2 or the EP 3 receptor agonist sulprostone, acting via EP 3 receptors. When histamine or imetit was given first (at concentrations causing the maximum effect at H 3 receptors), the effect of prostaglandin E 2 on the evoked tritium overflow was attenuated by 5–10%. When prostaglandin E 2 or sulprostone was given first (at concentrations causing the maximum effect at EP 3 receptors), the effect of histamine or imetit on the evoked overflow was attenuated by almost 50%. The previous administration of prostaglandin E 2 also blunted the effect of histamine on the evoked tritium overflow evoked at 3 Hz; the degree of attenuation was identical when the current strength was 25 mA or was increased to 100 or 200 mA in order to partially compensate for the inhibitory effect of prostaglandin E 2 on the evoked overflow. In addition, prostaglandin E 2 attenuated the effect of histamine when tritium overflow was evoked (i) by 100 Hz, eight pulses or (ii) by Ca 2+ ions or (iii) when rat (instead of mouse) brain cortex slices were used. An interaction of prostaglandin E 2 or sulprostone with the H 3 receptor recognition site could be excluded since both prostanoids did not affect the specific binding of the H 3 agonist radioligand [ 3H]N α -methylhistamine to rat brain cortex membranes. In conclusion, mutual interactions occur between the presynaptic H 3 and EP 3 receptors involved in the inhibition of noradrenaline release in the mouse brain cortex. Pre-activation of the H 3 receptor slightly attenuates the EP 3 receptor-mediated effect whereas pre-activation of the EP 3 receptor more markedly attenuates the H 3 receptor-mediated effect. The interactions may occur between the receptors themselves or at a step behind the receptors (e.g., at the level of G proteins). The physiological significance of these interactions may be to limit the total extent of inhibition of noradrenaline release in a scenario under which both receptors are activated simultaneously.

Programmed stimulation of the ventricles--back to the future.

In the inaugural issue of this journal appeared two articles describing programmed electrical stimulation of the ventricles. Fisher et al. evaluated a new method for induction of ventricular tachycardia, in “Ultrarapid Train Stimulation versus Conventional Programmed Electrical Stimulation for Induction of Ventricular Arrhythmias in Patients with Coronary Artery Disease”[1]. Wyse et al. describe the effects of a conventional programmed stimulation protocol on QT dispersion, in “Divergence of Endocardial QT Interval Components during Programmed Electrical Stimulation Including Observations during Induction of Sustained Ventricular Tachyarrhythmias”[2]. The publication of these articles, 25 years after Wellens ~rst described programmed stimulation of the ventricles in humans [3], offers an opportunity to re_ect on the status of programmed electrical stimulation in clinical electrophysiology, its utility and limitations. In order to interpret appropriately the signi~cance of these two studies, it may be useful to consider how we use programmed ventricular stimulation in practice. While programmed stimulation was initially applied to elucidate the mechanisms responsible for monomorphic sustained ventricular tachycardia, and to aid in its diagnosis [3], later investigators applied the technique to patients who had experienced syncope or survived cardiac arrest (without documentation of the initiating arrhythmia), for similar reasons that it had been utilized in patients with spontaneous sustained ventricular tachycardia [4,5]. It has been used more recently in patients who have never experienced any symptomatic arrhythmia, in order to assess their risk for sudden cardiac death [6]. Further complicating these matters, is the fact that the technique has been applied to patients with the above arrhythmias occurring in association with a variety of anatomic substrates, including coronary artery disease, cardiomyopathies, etc. Why are these factors important? It is very likely that not only are the mechanisms responsible for ventricular tachyarrhythmias dependent on the type of associated heart disease, but even within the subset of patients with coronary artery disease for example, the characteristics of tachycardias are dependent in many respects on the clinical presentation [7]. There is also evidence that within the group of patients with coronary artery disease, the site of previous myocardial infarction can in_uence the arrhythmia substrate [8,9]. In this light, I would like to review brie_y the highlights of the studies by Fisher and Wyse. Fisher and his colleagues extended their earlier studies of the termination of ventricular tachycardia by ultrarapid stimulation trains, to the potential of this technique for initiation of ventricular tachycardia [10]. By coupling ultrarapid trains (at cycle lengths of 10, 20, or 30 msec) of progressively increasing duration to a standard “drive” of seven or eight beats, they were able to deliver 1, 2, or 3 extrastimuli with the greatest possible degree of prematurity relatively quickly. Their results show a high degree of concordance for inducible ventricular tachyarrhythmias between their standard stimulation protocol, and the ultrarapid train protocol, but the train protocol reached one of the predetermined endpoints in signi~cantly less time (5.25 versus 16.1 minutes). Unfortunately, the reproducibility of tachycardia induction was evaluated in only 3 patients. Wyse and his colleagues examined the effect of programmed ventricular stimulation on the difference between the endocardial QT intervals of the last extrastimulus, recorded at the right ventricular apex and out_ow tract. By using unique and original recording technology, the investigators were able to achieve very high ~delity measures of local QT intervals. The duration of the initial portion of the QT interval bore a linear relationship to the prematurity of the extrastimulus in the control group of patients without structural heart disease. As expected, this interval shortened as the extrastimulus prematurity increased. Of interest, the terminal portions of the QT interval did not exhibit the expected rate adaptation, but rather remained constant or increased with increasing extrastimulus prematurity. In contrast, the experimental patient group, consisting of patients with prior myocardial infarction undergoing electrophysiologic studies for evaluation of spontaneous ventricular tachyarrhythmias, showed a blunting of the adaptation of the initial and total QT interval to extrastimulus prematurity. The terminal component of the QT interval in the study patients behaved in a manner similar to that of the control group. The control patients showed minimal “dispersion” of the QT intervals that displayed a _at relationship to extrastimulus prematurity. The QT “dispersion” of patients with ventricular arrhythmias Journal of Interventional Cardiac Electrophysiology 1997;1:281–285 © Kluwer Academic Publishers. Boston. Printed in U.S.A.

Spontaneous Parthenogenesis in Human Oocytes.

A total of 1,923 follicular human ova were collected for use in intracytoplasmic sperm injection (ICSI). Timed ovulation was induced by means of a standard ovarian stimulation protocol involving set dosages of follicle stimulating hormone (FSH), human menopausal gonadotrophin (HMG) and human chorionic gonadotrophin (hCG). Prior to performing ICSI, all of the ova were subjected to thorough examination which led to the discovery of only two parthenogenetic oocytes, also referred to as parthenogens, out of the total 1,923. These oocytes were retrieved from different patients. Although genetic analysis revealed that one of the parthenogens had a haploid number of chromosomes, it was impossible to analyze the second because it had not yet reached the metaphase stage. The 0.1 percent incidence of spontaneous parthenogenesis in this study clearly indicates that this phenomenon is extremely rare.

LTP saturation and spatial learning disruption: effects of task variables and saturation levels

The prediction that "saturation" of LTP/LTE at hippocampal synapses should impair spatial learning was reinvestigated in the light of a more specific consideration of the theory of Hebbian associative networks, which predicts a nonlinear relationship between LTP "saturation" and memory impairment. This nonlinearity may explain the variable results of studies that have addressed the effects of LTP "saturation" on behavior. The extent of LTP "saturation" in fascia dentata produced by the standard chronic LTP stimulation protocol was assessed both electrophysiologically and through the use of an anatomical marker (activation of the immediate-early gene zif268). Both methods point to the conclusion that the standard protocols used to induce LTP do not "saturate" the process at any dorsoventral level, and leave the ventral half of the hippocampus virtually unaffected. LTP-inducing, bilateral perforant path stimulation led to a significant deficit in the reversal of a well-learned spatial response on the Barnes circular platform task as reported previously, yet in the same animals produced no deficit in learning the Morris water task (for which previous results have been conflicting). The behavioral deficit was not a consequence of any after-discharge in the hippocampal EEG. In contrast, administration of maximal electroconvulsive shock led to robust zif268 activation throughout the hippocampus, enhancement of synaptic responses, occlusion of LTP produced by discrete high-frequency stimulation, and spatial learning deficits in the water task. These data provide further support for the involvement of LTP-like synaptic enhancement in spatial learning.

Comparison of number of extrastimuli versus change in basic cycle length for induction of ventricular tachycardia by programmed ventricular stimulation

Objectives. The purpose of this study was to examine the effects of varying basic cycle lengths in a programmed stimulation protocol if up to seven extrastimuli were available at each basic cycle length.Background. There is no uniformly accepted protocol for induction of ventricular tachycardia. Most protocols limit the number of extrastimuli to two or three but use several basic cycle lengths.Methods. Twenty-eight patients with coronary artery disease and documented spontaneous sustained ventricular tachycardia or ventricular fibrillation were studied. In the absence of antiarrhythmic drugs, each patient underwent three inductions of ventricular tachycardia/ventricular fibrillation using sinus rhythm or right ventricular pacing at 600 or 400 ms as the basic cycle length. Up to seven extrastimuli were allowed at each basic cycle length.Results. The maximal yield of clinical tachycardia (96%) was identical for each basic cycle length and was achieved using a maximum of seven, five and four extrastimuli for sinus rhythm and 600 and 400 ms, respectively. A basic cycle length of 400 ms required fewer extrastimuli (2.4 ± 0.7) to induce ventricular tachycardia/ventricular fibrillation than did 600 ms (2.7 ± 1.1, p = 0.014) or sinus rhythm (3.4 ± 1.2, p < 0.001). There was no significant difference in the cycle lengths of the induced ventricular tachycardia, incidence of induced ventricular fibrillation or requirement for direct current countershock.Conclusions. The use of an adequate number of extrastimuli obviates the need for multiple basic cycle lengths for induction of ventricular tachycardia and does not increase induction of unwanted ventricular fibrillation. If only one basic cycle length is used, the ease of inducibility can be quantified in terms of the number of extrastimuli required. Fewer extrastimuli were required for induction of ventricular tachycardia if a basic cycle length of 400 ms was used. These data favor the use of ventricular pacing at a basic cycle length of 400 ms with up to at least four extrastimuli as the standard stimulation protocol for induction of ventricular tachycardia.

On the interpretation of voltage-clamp data using the Hodgkin-Huxley Model

This paper describes a method to extract membrane model parameters from experimental voltage-clamp records. The underlying theory is based on two premises: (1) the membrane dynamics can be described by a Hodgkin-Huxley (HH) model, and (2) the most reliable data provided by voltage clamp experiments are peak current ( I p) measurements. First, the steady-state characteristics of activation ( x ∞) and inactivation ( z ∞) must be estimated, and it is shown that I p data provided by standard voltage-clamp stimulation protocols are sufficient for this purpose for the case of well-separated activation (τ x) and inactivation (τ z) time constants, τ x ⪡ τ z. Next, we propose a test ( R test) to establish the suitability of the HH model to represent the data. When the HH model is applicable (successful R test), the procedure yields the degree of the gating variables, a range of maximum membrane conductance ( ḡ) values, and a τ x τ z ratio that relates x ∞ and z ∞ to the I p data. When additional information is available, such as the time of occurence of I p or an estimate of τ z> from the late portion of the ionic current response, one can narrow down the value of ḡ and estimate all the HH parameters and functions. Otherwise, when the R test is not successful, one can conclude that x ∞ and z ∞ have been incorrectly estimated because τ x and τ z are not sufficiently separated or that the HH model is not applicable to the data.

Reproducibility of successful drug trials in patients with inducible sustained ventricular tachycardia.

Patients whose inducible sustained ventricular tachycardia is suppressed during serial electrophysiological testing have a small but gradually increasing actuarial incidence of recurrent arrhythmias despite therapy with the "successful" drug. In an effort to improve the predictive value of a drug response, in 1990 we began to require that our full stimulation protocol be repeated successfully several times before considering a drug to be effective. In 23 consecutive patients who had inducible sustained ventricular tachycardia which was suppressed by at least one drug during invasive serial drug testing using a standard stimulation protocol, the identical stimulation protocol was performed six times during therapy with the initially successful drug (three trials on Day 1 and three trials on Day 2). Repeat trials were completed (i.e., either all six trials were successfully finished or sustained tachycardia was induced) for 29 initially successful drugs in these 23 patients. With 18 of these 29 initially successful drugs (62%), sustained ventricular tachycardia was eventually induced during repeat trials. The eventual drug failures could not be correlated with specific drugs tested, subtherapeutic or falling serum drug levels, marked fluctuations in autonomic tone, or changes in anatomic substrate. The proportion of patients failing each repeat trial was relatively constant: 4/29 (14%) failed Trial 2, 2/25 (8%) failed Trial 3, 7/23 (30%) failed Trial 4, 2/16 (13%) failed Trial 5, and 3/14 (21%) failed Trial 6. The increase in the cumulative incidence of drug failure during repeat trials was nearly linear. Inducibility of ventricular tachycardia appears to be a probability function; a successful drug study should not be regarded as an absolute phenomenon.