Biomedical subjects

K A Martin

Publications and source records attributed to K A Martin.

At least 55 records · Page 3Linked to original sources

PubMed1997

HIV-1 entry and macrophage inflammatory protein-1beta-mediated signaling are independent functions of the chemokine receptor CCR5.

The human immunodeficiency virus type 1 (HIV-1) requires the presence of specific chemokine receptors in addition to CD4 to enter its target cell. The chemokine receptor CCR5 is used by macrophage-tropic strains of HIV-1, which predominate during the asymptomatic stages of infection. Here we investigate whether the ability of CCR5 to signal in response to its beta-chemokine ligands is necessary or sufficient for viral entry. Three CCR5 mutants with little or no ability to mobilize calcium in response to macrophage inflammatory protein-1beta could nonetheless support HIV-1 entry and the early steps in the virus life cycle with efficiencies comparable with those of wild-type CCR5. Conversely, a chimeric receptor with the N terminus of CCR2 replacing that of CCR5 responded to macrophage inflammatory protein-1beta and MCP-1 but did not efficiently support viral entry. These results demonstrate that chemokine signaling and HIV-1 entry are separable functions of CCR5 and that only viral entry requires the N-terminal domain of CCR5.

Animals↗

PubMed1997

Conserved gene clusters in bacterial genomes provide further support for the primacy of RNA.

Five complete bacterial genome sequences have been released to the scientific community. These include four (eu)Bacteria, Haemophilus influenzae, Mycoplasma genitalium, M. pneumoniae, and Synechocystis PCC 6803, as well as one Archaeon, Methanococcus jannaschii. Features of organization shared by these genomes are likely to have arisen very early in the history of the bacteria and thus can be expected to provide further insight into the nature of early ancestors. Results of a genome comparison of these five organisms confirm earlier observations that gene order is remarkably unpreserved. There are, nevertheless, at least 16 clusters of two or more genes whose order remains the same among the four (eu)Bacteria and these are presumed to reflect conserved elements of coordinated gene expression that require gene proximity. Eight of these gene orders are essentially conserved in the Archaea as well. Many of these clusters are known to be regulated by RNA-level mechanisms in Escherichia coli, which supports the earlier suggestion that this type of regulation of gene expression may have arisen very early. We conclude that although the last common ancestor may have had a DNA genome, it likely was preceded by progenotes with an RNA genome.

Archaea↗

PubMed1997

Exogenous gonadotropin stimulation is associated with increases in serum androgen levels in in-vitro fertilization-embryo transfer cycles.

OBJECTIVE: To examine serum androgen profiles in women undergoing ovarian stimulation with exogenous gonadotropins in the setting of IVF-ET. DESIGN: Prospective study. SETTING: University hospital IVF-ET program. PATIENT(S): Seventeen ovulatory women undergoing IVF-ET for endometriosis, male factor infertility, or tubal disease. INTERVENTION(S): A standard long protocol of GnRH agonist (GnRH-a) pretreatment (1 mg of leuprolide acetate SC for 10 days) was administered before ovulation induction with a urinary gonadotropin preparation. MAIN OUTCOME MEASURE(S): After 10 days of GnRH-a treatment and on the day of hCG administration, serum concentrations of LH, T, androstenedione (A), sex hormone-binding globulin (SHBG), and DHEAS; the free androgen index (T/SHBG); and the number of follicles, oocytes, and embryos were assessed. RESULT(S): Serum samples after 10 days of GnRH-a treatment showed incomplete LH suppression. While continuing the agonist during ovarian stimulation, LH values were suppressed further. However, serum T and A concentrations and the free androgen index showed a significant increase (samples drawn just before hCG administration). Serum T levels after 10 days of GnRH-a (before the administration of exogenous gonadotropins) were correlated negatively with the subsequent number of embryos. CONCLUSION(S): Serum LH suppression with a conventional regimen of GnRH-a is incomplete in this heterogeneous group of ovulatory women. Exogenous gonadotropin stimulation results in a marked increase in ovarian androgen secretion.

Adult↗

PubMed1997

Complications of long-term drainage of fetal pleural effusion: case report and review of the literature.

Severe fetal pleural effusion and ascites in the second trimester are associated with poor prognosis. We present a case where long-term drainage of several pleural effusion by a double reverse pig tail stent was achieved. Although the ultimate outcome was successful, complications seen in this case include accidental placement of the proximal opening of the catheter, first into the myometrium, then between amnion and chorion; development of oligohydramnios; intrathoracic migration of the catheter. Review of the literature reveals a multitude of other complications associated with this procedure, specifically difficulties at the time of placement and failure of function due to obstruction, migration of the catheter, or removal by the fetus. It is important to consider these complications in the counseling and management of the patients. Ongoing research is required to further improve the design of the catheters.

Adult↗

PubMed1997

A competitive mechanism of CArG element regulation by YY1 and SRF: implications for assessment of Phox1/MHox transcription factor interactions at CArG elements.

In the promoters of many immediate early genes, including c-fos, CArG DNA regulatory elements mediate basal constituitive expression and rapid and transient serum induction. CArG boxes also occur in the promoters of muscle-specific genes, including skeletal alpha-actin, where it confers muscle-specific expression. These elements are regulated, at least in part, by the ubiquitous transcription factors serum response factor (SRF) and YY1. The homeobox transcription factor Phox1/MHox has also been implicated in regulation of the c-fos CArG element and is thought to function by facilitating SRF binding to DNA. Here, we provide in vitro and in vivo evidence that the mechanism of YY1 repression of CArG elements results from competition with SRF for overlapping binding sites. We describe in detail the binding sites of YY1 and SRF through serial point mutations of the skeletal alpha-actin proximal CArG element and identify a mutation that dramatically reduces YY1 binding but retains normal SRF binding. YY1 competes with SRF for binding to wild-type CArG elements, but not to this point mutant in vitro. This mutant is sufficient for muscle-specific expression in vivo but is much less sensitive to repression by YY1 overexpression. We utilized the YY1/SRF competition to address the role of Phox1 at these elements. Phox1 overexpression did not diminish YY1-mediated repression, suggesting that transcriptional activation by Phox1 does not result from enhanced SRF binding to these elements. These methods may prove to be useful for assessing interactions between other CArG element regulatory factors.

Actins↗

PubMed1997

An intracellular study of the contrast-dependence of neuronal activity in cat visual cortex.

Extracellular recordings indicate that mechanisms that control contrast gain of neuronal discharge are found in the retina, thalamus and cortex. In addition, the cortex is able to adapt its contrast response function to match the average local contrast. Here we examine the neuronal mechanism of contrast adaptation by direct intracellular recordings in vivo. Both simple (n = 3) and complex cells (n = 4) show contrast adaptation during intracellular recording. For simple cells, that the amplitude of fluctuations in membrane potential induced by a drifting grating stimulus follows a contrast response relation similar to lateral geniculate relay cells, and does not reflect the high gain and adaptive properties seen in the action potential discharge of the neurons. We found no evidence of significant shunting inhibition that could explain these results. In complex cells there was no change in the mean membrane potential for different contrast stimuli or different states of adaptation, despite marked changes in discharge rate. We use a simplified electronic model to discuss the central features of our results and to explain the disparity between the contrast response functions of the membrane potential and action potential discharge in simple cells.

Action Potentials↗

PubMed1997

Down-regulation of P2U-purinergic nucleotide receptor messenger RNA expression during in vitro differentiation of human myeloid leukocytes by phorbol esters or inflammatory activators.

HL-60 human promyelocytic leukocytes express G protein-coupled P2U-purinergic nucleotide receptors (P2UR or P2Y2R) that activate inositol phospholipid hydrolysis and Ca24 mobilization in response to ATP or UTP. We examined the expression of functional P2UR and P2UR mRNA levels during in vitro differentiation of HL-60 cells by dibutyryl-cAMP (Bt2cAMP), which induces a granulocyte/neutrophil phenotype, or by phorbol-12-myristate-13-acetate (PMA), which induces a monocyte/macrophage phenotype. Both P2UR function and P2UR mRNA levels were only modestly attenuated during granulocytic differentiation by Bt2cAMP. In contrast, P2UR function, as assayed by either Ca2+ mobilization or inositol trisphosphate generation, was greatly reduced in PMA-differentiated cells. This inhibition of P2UR function was strongly correlated with PMA-induced decreases in P2UR mRNA levels, as assayed by Northern blot analysis or reverse transcription-polymerase chain reaction-based quantification. Although PMA induced an early, transient up-regulation of P2UR mRNA, this was rapidly followed by a sustained decrease in P2UR mRNA to a level 5-10-fold lower than that in undifferentiated HL-60 cells. The half-life of the P2UR transcript in HL-60 cells was approximately 60 min, and this was not affected by acute exposure (< or = 4 hr) to Bt2cAMP or PMA. PMA down-regulated P2UR mRNA in THP-1 monocytes and HL-60 granulocytes but not in A431 human epithelial cells or human keratinocytes. P2UR mRNA was also down-regulated in THP-1 monocytes differentiated into inflammatory macrophages by gamma-interferon and endotoxin. These data indicate that myeloid leukocytes possess tissue-specific mechanisms for the rapid modulation of P2UR expression and function during differentiation and inflammatory activation.

Bucladesine↗

PubMed1997

Utilization of C-C chemokine receptor 5 by the envelope glycoproteins of a pathogenic simian immunodeficiency virus, SIVmac239.

We examined chemokine receptors for the ability to facilitate the infection of CD4-expressing cells by viruses containing the envelope glycoproteins of a pathogenic simian immunodeficiency virus, SIVmac239. Expression of either human or simian C-C chemokine receptor CCR5 allowed the SIVmac239 envelope glycoproteins to mediate virus entry and cell-to-cell fusion. Thus, distantly related immunodeficiency viruses such as SIV and the primary human immunodeficiency virus type 1 isolates can utilize CCR5 as an entry cofactor.

Animals↗

PubMed1997

Angiotensin II activates the beta 1 isoform of phospholipase C in vascular smooth muscle cells.

Vascular smooth muscle cells (VSMC) contribute to the pathophysiology of hypertension through cell growth and contraction, and phospholipase C (PLC) is a critical effector enzyme in growth factor and vasoconstrictor signaling. There is indirect evidence that angiotensin II (ANG II) receptors are linked to the PLC-beta isoform signaling pathways. However, recent studies suggest that PLC-beta isoforms may not be expressed in VSMC. Our data demonstrate that in human aortic VSMC, PLC-beta 1 and PLC-gamma 1 proteins were detected by immunoblot analysis, and PLC-beta 1 mRNA was identified by reverse transcriptase-polymerase chain reaction in rat aortic VSMC. Incubation of permeabilized VSMC with anti-PLC-beta 1 or anti-Gq alpha antibodies inhibited ANG II-dependent inositol polyphosphate (IP) formation, while anti-PLC-gamma 1 antibodies did not inhibit ANG II-regulated IP formation. Conversely, anti-PLC-gamma 1 antibodies completely abolished platelet-derived growth factor (PDGF)-dependent IP generation, whereas anti-PLC-beta 1 antibodies had no effect on PDGF-induced PLC activation. Inhibition of tyrosine phosphorylation with genistein or herbimycin A did not diminish ANG II-stimulated IP formation or cytosolic free Ca2+ concentration transients, thereby confirming that ANG II signals via a PLC-gamma 1-independent mechanism. In summary, PLC-beta 1 and PLC-gamma 1 are expressed in human aortic VSMC, and PLC-beta 1 is the isoform that is critical for ANG II-regulated PLC signaling in these cells.

Angiotensin II↗

PubMed1997

Stage-specific expression of P2Y receptors, ecto-apyrase, and ecto-5'-nucleotidase in myeloid leukocytes.

The expression of P2 purinergic receptor subtypes in leukocytes varies with both lineage and developmental stage. Given the recent identification and cloning of at least seven distinct G protein-coupled ATP receptor subtypes (P2Y family), we investigated P2Y receptor subtype expression during myeloid cell differentiation. We observed that KG-1 myeloblasts express P2Y1 but not P2Y2 receptors (previously termed P2U receptors), whereas later myeloid progenitors, including HL-60 promyelocytes and THP-1 monocytes, expressed P2Y2 but not P2Y1 receptors. In KG-1 cells, significant activation of Ca2+ mobilization by P2Y1 receptors was only observed after preincubation with potato apyrase, an exogenous ATPase. This indicated that P2Y1 receptors are desensitized in KG-1 cells by autocrine mechanisms that may involve enhanced release of endogenous nucleotides and/or decreased expression of cell-surface ecto-nucleotidases. We compared the levels of ecto-apyrase activity and expression in KG-1 myeloblasts and HL-60 promyelocytes. Extracellular ATP was rapidly metabolized by HL-60 but not by KG-1 cells. Reverse transcription-polymerase chain reaction analysis indicated that mRNA for CD39 (cluster of differentiation), an identified ecto-apyrase, was present in HL-60 but not KG-1 cells. Ecto-apyrase activity was modestly increased with differentiation of myeloid progenitors with either phorbol 12-myristate 13-acetate (PMA) or dibutyryl adenosine 3',5'-cyclic monophosphate (DBcAMP). Differentiation of HL-60 cells with PMA, but not DBcAMP, strongly induced ecto-5'-nucleotidase activity and CD73 mRNA expression. These observations indicate that signal transduction by extracellular ATP in myeloid leukocytes can be regulated by developmentally programmed changes in the expression of P2Y receptor subtypes and multiple ecto-nucleotidases.

5'-Nucleotidase↗

PubMed1997

Determinants of abnormal gonadotropin secretion in clinically defined women with polycystic ovary syndrome.

UNLABELLED: Polycystic ovary syndrome (PCOS) is a heterogeneous disorder of reproductive age women characterized in its broadest definition by the presence of oligoamenorrhea and hyperandrogenism and the absence of other disorders. Defects of gonadotropin secretion, including an elevated LH level, elevated LH to FSH ratio, and an increased frequency and amplitude of LH pulsations have been described, but the prevalence of these defects in a large, unbiased population of PCOS patients has not been determined. Sixty-one women with PCOS defined by oligomenorrhea and hyperandrogenism and 24 normal women in the early follicular phase had LH samples obtained every 10 min for 8-12 h. Pool LH levels from the frequent sampling studies were within the normal range in the 9 PCOS patients (14.8%) who were studied within 21 days after a documented spontaneous ovulation. Excluding these post-ovulatory patients, 75.0% of the PCOS patients had an elevated pool LH level (above the 95th percentile of the normal controls), and 94% had an elevated LH to FSH ratio. In the anovulatory PCOS patients, pool LH correlated positively with 17-OH progesterone (R = 0.30, P = 0.03), but not with estradiol, estrone, testosterone, androstenedione, or DHEA-S. Pool LH and LH to FSH ratio correlated positively with LH pulse frequency (R = 0.40, P = 0.004 for pool LH, and R = 0.39; P = 0.005 for LH/FSH). There was also a strong negative correlation between pool LH and body mass index (BMI) (R = -0.59, P < 10(-5)). The relationship between BMI and LH secretion in the PCOS patients appeared to be strongest with body fatness, as pool LH was correlated inversely with percent body fat, whether measured by skinfolds (R = -0.61, P < 10(-5)), bioimpedance (R = -0.55, P < 10(-4)), or dual energy x-ray absorptiometry (DEXA) (R = -0.70, P = 0.001; n = 18 for DEXA only). By DEXA, the only body region that was highly correlated with pool LH was the trunk (R = -0.71, P = 0.001). The relationship between body fatness and LH secretion occurred via a decrease in LH pulse amplitude (R = -0.63, P < 10(-5) for BMI; R = -0.58, P < 10(-4) for bioimpedance; and R = -0.64, P = 0.004 for whole body DEXA), with no significant change in pulse frequency with increasing obesity (R = -0.17, P = 0.23 for BMI). IN CONCLUSION: 1) the prevalence of gonadotropin abnormalities is very high in women with PCOS selected on purely clinical grounds, but is modified by recent spontaneous ovulation; 2) the positive relationship between LH pulse frequency and both pool LH and LH to FSH ratio supports the hypothesis that a rapid frequency of GnRH secretion may play a key etiologic role in the gonadotropin defect in PCOS patients; 3) pool LH and LH pulse amplitude are inversely related to body mass index and percent body fat in a continuous fashion; and 4) the occurrence of a continuous spectrum of gonadotropin abnormalities varying with body fat suggests that nonobese and obese patients with PCOS do not represent distinct pathophysiologic subsets of this disorder.

Adolescent↗

PubMed1997

Frequency modulation of follicle-stimulating hormone (FSH) during the luteal-follicular transition: evidence for FSH control of inhibin B in normal women.

To isolate the impact of GnRH pulse frequency on FSH secretion and to examine the effect of differing levels of FSH on inhibin B secretion during the luteal-follicular transition, exogenous GnRH was administered to GnRH-deficient women using one of two regimens, and the results were compared to those in normal women. In the GnRH-deficient women, the GnRH pulse frequency was increased from every 4 h in the late luteal phase to every 90 min on the day of menses to mimic normal cycling women (physiological frequency transition; n = 8 studies) or the GnRH pulse frequency was kept constant at a late luteal phase frequency of every 4 h through the first 6 days of the subsequent early follicular phase of cycle 2 (slow frequency transition; n = 6 studies). The differential rise in FSH secretion induced in these studies allowed us to examine the subsequent contribution of varying levels of FSH to inhibin B secretion. A physiological regimen of GnRH during the luteal-follicular transition resulted in a rise in FSH and inhibin B levels that did not differ from that in normal cycling women and a normal follicular phase length. On the other hand, maintaining a luteal frequency of GnRH for 6 days into the subsequent early follicular phase produced FSH levels significantly lower than those in the physiological transition (P < 0.05), with the greatest difference seen on the day after menses (9.1 +/- 1.0 vs. 16.4 +/- 1.4 IU/L for the slow and physiological transition groups, respectively; P < 0.005), but no difference in LH. This slower rise of FSH secretion in the slow frequency group was associated with significantly lower inhibin B levels (43.3 +/- 21.5 vs. 140.0 +/- 24.4 pg/mL, mean days 1, 3, and 5; P < 0.02), a later doubling of estradiol from baseline (day 9.6 +/- 0.9 vs. day 5.6 +/- 0.1; P < 0.02), and a longer follicular phase length (16.0 +/- 1.4 vs. 11.6 +/- 0.9 days; P < 0.05) compared with those in the physiological transition group. In conclusion, during the luteal-follicular transition, the GnRH pulse frequency contributes to but is not solely responsible for the FSH rise that initiates folliculogenesis. Alteration of FSH dynamics induced by changes in GnRH pulse frequency in GnRH-deficient women provides evidence that FSH stimulates inhibin B production in the human. Timely follicular development indicated by both estradiol and inhibin B secretion appears to be dependent on the pattern of increase in FSH during the luteal-follicular transition.

Adolescent↗

PubMed1996

Excitatory synaptic inputs to spiny stellate cells in cat visual cortex.

In layer 4 of cat visual cortex, the monocular, concentric receptive fields of thalamic neurons, which relay retinal input to the cortex, are transformed into 'simple' cortical receptive fields that are binocular and selective for the precise orientation, direction of motion, and size of the visual stimulus. These properties are thought to arise from the pattern of connections from thalamic neurons, although anatomical studies show that most excitatory inputs to layer 4 simple cells are from recurrently connected circuits of cortical neurons. We examined single fibre inputs to spiny stellate neurons. We examined single fibre inputs to spiny stellate neurons in slices of cat visual cortex, and conclude that thalamocortical synapses are powerful and the responses they evoke are unusually invariant for central synapses. However, the responses to intracortical inputs, although less invariant, are strong enough to provide most of the excitation to simple cells in vivo. Our results suggest that the recurrent excitatory circuits of cortex may amplify the initial feedforward thalamic signal, subserving dynamic modifications of the functional properties of cortical neurons.

Animals↗

PubMed1996

The role of synapses in cortical computation.

The synapse, first introduced as physiological hypothesis by C.S. Sherrington at the close of the nineteenth century, has, 100 years on, become the nexus for anatomical and functional investigations of interneuronal communication. A number of hypotheses have been proposed that give local synaptic interactions specific roles in generating an algebra or logic for computations in the neocortex. Experimental work, however, has provided little support for such schemes. Instead, both structural and functional studies indicate that characteristically cortical functions, e.g., the identification of the motion or orientation of objects, involve computations that must be achieved with high accuracy through the collective action of hundreds or thousands of neurons connected in recurrent microcircuits. Some important principles that emerge from this collective action can effectively be captured by simple electronic models. More detailed models explain the nature of the complex computations performed by the cortical circuits and how the computations remain so remarkably robust in the face of a number of sources of noise, including variability in the anatomical connections, large variance in the synaptic responses and in the trial-to-trial output of single neurons, and weak or degraded input signals.

Animals↗

PubMed1996

The P1 ParA protein and its ATPase activity play a direct role in the segregation of plasmid copies to daughter cells.

The P1 ParA protein is an ATPase that recognizes the parA promoter region where it acts to autoregulate the P1 parA-parB operon. The ParB protein is essential for plasmid partition and recognizes the cis-acting partition site parS. The regulatory role of ParA is also essential because a controlled level of ParB protein is critical for partition. However, we show that this regulatory activity is not the only role for ParA in partition. Efficient partition can be achieved without autoregulation as long as Par protein levels are kept within a range of low values. The properties of ParA mutants in these conditions showed that ParA is essential for some critical step in the partition process that is independent of par operon regulation. The putative nucleotide-binding site for the ParA ATPase was identified and disrupted by mutation. The resulting mutant was substantially defective for autoregulation and completely inactive for partition in a system in which the need for autoregulation is abolished. Thus, the ParA nucleotide-binding site appears to be necessary both for the repressor activity of ParA and for some essential step in the partition process itself. We propose that the nucleotide-bound form of the enzyme adopts a configuration that favours binding to the operator, but that the ATPase activity of ParA is required for some energetic step in partition of the plasmid copies to daughter cells.

Adenosine Triphosphatases↗

PubMed1996

A randomized, controlled trial of estradiol replacement therapy in women with hypergonadotropic amenorrhea.

Premature ovarian failure is classically defined as menopause occurring before age 40 and is associated with elevated serum FSH levels. If elevated FSH levels indicate lack of ovarian feedback and depletion of primordial follicles, women with prematurely elevated FSH levels should have infertility. However, there are many reports of pregnancies in affected women occurring during estrogen therapy leading to the hypothesis that estrogen may have a salutary effect on folliculogenesis and conception. This randomized, controlled trial was designed to investigate whether estrogen replacement therapy offered a significant therapeutic benefit in hypergonadotropic amenorrhea and to evaluate the potential pathophysiologic mechanisms that would explain the reported pregnancies. Thirty seven women, aged 16 to 40, with menstrual dysfunction and documented FSH levels elevated above the 95% confidence limits of the mid-cycle gonadotropin peak of the normal menstrual cycle (> 40 IU/L 2nd IRP hMG in our RIA) on at least two occasions, entered the study. The average duration of their amenorrhea was 15.9 months (range 2-96 months). Subjects were randomized to begin estradiol replacement (micronized estradiol [Estrace TM], 2 mg orally each day) or no therapy for 6 weeks in a 12-week, cross-over design with weekly monitoring by both pelvic ultrasonography and serum hormone levels. Thirty-one women completed the entire randomized study. As expected, estradiol therapy increased mean serum estradiol levels by 98 pg/mL and was associated with a significant decrease in mean LH and FSH levels (LH: 45.4 IU/L 2nd IRP hMG vs. 37.1 IU/L, FSH: 63.4 IU/L vs. 40.6 IU/L, geometric means). However, there was no effect of estradiol replacement on mean ovarian volume, the number or size of new follicles, or the ovulation rate in all subjects or in the subset with no identified cause for their hypergonadotropic hypogonadism (n = 20). Two pregnancies occurred during the randomized trial, one on and one off estradiol. In both arms of the study, the majority of subjects developed cystic ovarian structures by ultrasound that were temporally associated with increasing serum estradiol levels, indicating functional ovarian follicles. Seventy-eight percent of all subjects grew at least one new follicle over 10 mm in diameter and 46% ovulated at least once, as determined by a serum progesterone level more than 4 ng/mL. Although ovulations were significantly more common in the 10 women subjects who had less than 3 months of amenorrhea (all of whom ovulated) than in the 27 with greater than 3 months of amenorrhea (only 7 of whom ovulated (26%), P < 0.001), there was no significant difference in eventual pregnancies (2 of the 10 women with less than 3 months of amenorrhea vs. 3 of the 27 with greater than 3 months of amenorrhea, P = 0.47). We conclude that in hypergonadotropic women with amenorrhea: 1) folliculogenesis occurs often but is less frequently followed by ovulation and rarely by pregnancy, suggesting that elevated FSH is a marker of oocyte dysfunction occurring distinct from and earlier than granulosa cell or follicular dysfunction; and 2) estrogen therapy does not improve the rate of folliculogenesis or ovulation.

Adolescent↗

PubMed1996

Homologous in vitro bioassay for follicle-stimulating hormone (FSH) reveals increased FSH biological signal during the mid- to late luteal phase of the human menstrual cycle.

Monitoring of the secretory dynamics of FSH during the human menstrual cycle has demonstrated conflicting results between the amounts of FSH measured by dimer-specific immunoassays and previous heterologous in vitro bioassays. These differences suggest somewhat different models of the steroidal and nonsteroidal regulation of FSH secretion and its control of folliculogenesis in the human. We have developed a homologous in vitro bioassay, using the recombinant human FSH receptor cotransfected into Chinese hamster ovary cells with a cAMP-responsive luciferase reporter gene, that overcomes many of the theoretic shortfalls of previous assays and allows reevaluation of the changes in bioactive FSH across the menstrual cycle. Bioactive FSH levels measured across 12 menstrual cycles in 11 normal women ranged from 4-40 IU/L. FSH bioactivity was constant during the menstrual cycle, with elevations noted only during the mid- to late luteal phase. Bioactive FSH levels were similar to immunoactive FSH levels across the cycle as indicated by a ratio of bioactive to immunoreactive FSH (FSH B/I) of 1.10 +/- 0.04 across the follicular and early luteal phases. However, during the mid- to late luteal phase, the mean FSH B/I rose to 1.65 +/- 0.07, which significantly exceeded that during the rest of the cycle (P < 0.001). This change in FSH B/I occurs at a critical time during folliculogenesis when the next cohort of follicles is being recruited and appears to be secondary to a decrease in immunoreactive FSH unaccompanied by a similar decrease in in vitro bioactivity. There was good agreement between immunoassay and bioassay results on the day of the midcycle gonadotropin surge (FSH B/I = 1.07 +/- 0.14), which was not different from that in the follicular phase (days -17 to -2; FSH B/I = 1.06 +/- 0.05) or the FSH B/I measured in postmenopausal women (0.93 +/- 0.2). These observations using a novel homologous human FSH in vitro bioassay indicate that bioactive FSH levels are not declining during the time of active corpus luteum formation and secretory activity. Thus, there is a previously undetected increased biologic signal during the mid- to late luteal phase, suggesting that the influence of elevated FSH on the cohort of developing follicles (including the subsequent dominant follicle) begins earlier during the luteal-follicular transition than previously predicted by FSH immunoreactivity.

Adult↗

PubMed1995

Recurrent excitation in neocortical circuits.

The majority of synapses in the mammalian cortex originate from cortical neurons. Indeed, the largest input to cortical cells comes from neighboring excitatory cells. However, most models of cortical development and processing do not reflect the anatomy and physiology of feedback excitation and are restricted to serial feedforward excitation. This report describes how populations of neurons in cat visual cortex can use excitatory feedback, characterized as an effective "network conductance", to amplify their feedforward input signals and demonstrates how neuronal discharge can be kept proportional to stimulus strength despite strong, recurrent connections that threaten to cause runaway excitation. These principles are incorporated into models of cortical direction and orientation selectivity that emphasize the basic design principles of cortical architectures.

Animals↗