1,721,229 research outputs found
Signal transduction mechanism for LH in the cumulus-oocyte complex
No full textThe paper reviews recently described signalling mechanisms by which cumulus cells exposed to peak levels of gonadotropins, activate oocyte maturation. Cumulus cells react to LH with a prompt Ca raise which diffuses through gap junctions in a few minutes also into the oocyte where a local amplification system spreads the signal all over the cell. Few h later, still as a consequence of LH stimulation, cumulus cells undergo aprogressive depolarisation of their plasma membrane potential. Due to the electric coupling with these cells the oocyte depolarises too and this open specific voltage gated Ca channels responsible for a second wider and more sustained intracellular Ca rise. As a result of changes throughout maturation with a consequent modification of the size and charge of the molecules that can diffuse from one cell compartment to the other. This cell to cell interaction is further modified with cumulus expansion that leads to a progressive uncoupling of outer cumulus cells while the inner cell layer, corona radiata, remains in oocyte maturation by addressing to the oocyte nutrients and instructions in a well-orchestrated sequence. The identification of these mechanisms are a fundamental prerequisite for the development of in vitro systems suitable to produce oocytes matured in vitro with normal developmental competence[...
Oocyte maturation involves important changes required for activation competence
No full textThe Authors studied the influence of the culture conditions on the ability of oocytes matured in vitro to activate in response to parthenogenetic activation (7% ethanol, etOH, for 5 min). Sheep oocytes were matured as cumulus enclosed oocytes (COCs) or as COCs cocultured with suspended granulosa cells in the presence or absence of gonadotropins. The reactivity of the eggs was evaluated at three different levels. First, intracellular calcium (Ca) was evaluated with the fluorescent dye Indol at the time of exposure of the eggs to the activating stimulus, parthenogenetic development was then ascertained 5h after etOH by recording the formation of pronuclei (PN), and 4 days later by recording early embryo development. Intracellular Ca levels after etOH were significantly higher in oocytes matured in the presence of granulosa cells than in COCs cultured alone. The presence of gonadotropins throughout maturation further increased the amount of Ca released after etOH and FSH was significantly more effective than LH. Culture conditions similarly influenced the formation of IN (Fig 4) and the subsequent development of parthenogenetic embryos (Table 2) These results demonstrate that: a) culture conditions throughout maturation affect the ability of the egg to activate, b) follicle somatic cells in coculture are required for the acquisition of activation competence, c) gonadotropins and FSH in particular improves the reactivity of the oocytes, d) the different reactivity of the eggs are due to the different ability to release Ca following parthenogenetic stimulation.[...
Estimates on degenerate jump-diffusion processes and regularity of the related valuation equation
Full text linkMany risk-neutral pricing problems proposed in the finance literature require
to be dealt with by solving the corresponding Partial Integro-Differential Equation. Unfortunately, neither the standard Sobolev spaces theory, or the present literature on viscosity
solution theory is able to deal with some problems of interest in finance. A recent result presented by Costantini, Papi and D’Ippoliti accepted for pubblication on Finance and
Stochastics [17], shows that, under general conditions on the coefficients of the stochastic
integro-differential equation, whenever a Lyapunov-type condition is satisfied, the stochastic process does not reach the boundary of the domain where is defined. Furthermore, in
the same work it has been proved that there exists a unique viscosity solution to the pricing
problem when we deal with the corresponding pricing problem for European-type derivatives. The viscosity solution theory ensures just the continuity of the solution, when data
are continuous, but does not guarantees that such a solution has some additional regularity.
The aim of this work is to improve, for the pure differential case, the results existing in
literature dealing with the regularity of both the solutions X of the underlying stochastic
differential equations, and the solutions of the corresponding PDE. In particular we will
provide some estimates related to dependence with respect to the initial data for the process
X. Furthermore, dealing with the pricing problem, we improve our understanding on the
assumptions that ensure the viscosity solution to have additional regularity properties beside
the mere continuity.
A Lipschitz-type dependence result with respect to initial data, until a stopping time τ ,
is shown whenever the coefficients are locally Lipschitz continuous, and a Lyapunov-type
condition is satisfied. Such a result can be improved if a suitable weight function is put in
place.
A standard result in PDE theory ensures that, if the assumptions we assume in our work are
satisfied, then in each compact subset where the diffusion matrix is positive defined, there
exists a unique classical solution to the localized problem if initial data are continuous (see
e.g. [35] or [9]). We make use of such a result in order to prove that this classical solution
coincides, in the same subset, with the unique viscosity solution found in [17].
We give an application of such results, applying our evidences to the stochastic volatility
model proposed by Ekstrom and Tysk in [29]. In such a case all the hypotheses we are ¨
currently assuming are satisfied, and the expression of the Lyapunov function can be explicitely provided for different final payoff. As a consequence, we are able to get the results
of the existence and uniqueness of a classical solution to the pricing problem presented in[29] in an independent way. Furthermore it is possible to consider weakened assumptions
on the final payoff. On the other hand we try to consider a generalization of the model,
allowing the process exhibits sudden jumps provided that the jump measure satisfies some
suitable properties. In such a case, the expression for the Lyapunov function is provided as
well, hence we are able to state that the considered valuation problem admits one and only
one viscosity solution.Many risk-neutral pricing problems proposed in the finance literature require
to be dealt with by solving the corresponding Partial Integro-Differential Equation. Unfortunately, neither the standard Sobolev spaces theory, or the present literature on viscosity
solution theory is able to deal with some problems of interest in finance. A recent result presented by Costantini, Papi and D’Ippoliti accepted for pubblication on Finance and
Stochastics [17], shows that, under general conditions on the coefficients of the stochastic
integro-differential equation, whenever a Lyapunov-type condition is satisfied, the stochastic process does not reach the boundary of the domain where is defined. Furthermore, in
the same work it has been proved that there exists a unique viscosity solution to the pricing
problem when we deal with the corresponding pricing problem for European-type derivatives. The viscosity solution theory ensures just the continuity of the solution, when data
are continuous, but does not guarantees that such a solution has some additional regularity.
The aim of this work is to improve, for the pure differential case, the results existing in
literature dealing with the regularity of both the solutions X of the underlying stochastic
differential equations, and the solutions of the corresponding PDE. In particular we will
provide some estimates related to dependence with respect to the initial data for the process
X. Furthermore, dealing with the pricing problem, we improve our understanding on the
assumptions that ensure the viscosity solution to have additional regularity properties beside
the mere continuity.
A Lipschitz-type dependence result with respect to initial data, until a stopping time τ ,
is shown whenever the coefficients are locally Lipschitz continuous, and a Lyapunov-type
condition is satisfied. Such a result can be improved if a suitable weight function is put in
place.
A standard result in PDE theory ensures that, if the assumptions we assume in our work are
satisfied, then in each compact subset where the diffusion matrix is positive defined, there
exists a unique classical solution to the localized problem if initial data are continuous (see
e.g. [35] or [9]). We make use of such a result in order to prove that this classical solution
coincides, in the same subset, with the unique viscosity solution found in [17].
We give an application of such results, applying our evidences to the stochastic volatility
model proposed by Ekstrom and Tysk in [29]. In such a case all the hypotheses we are ¨
currently assuming are satisfied, and the expression of the Lyapunov function can be explicitely provided for different final payoff. As a consequence, we are able to get the results
of the existence and uniqueness of a classical solution to the pricing problem presented in[29] in an independent way. Furthermore it is possible to consider weakened assumptions
on the final payoff. On the other hand we try to consider a generalization of the model,
allowing the process exhibits sudden jumps provided that the jump measure satisfies some
suitable properties. In such a case, the expression for the Lyapunov function is provided as
well, hence we are able to state that the considered valuation problem admits one and only
one viscosity solution.LUISS PhD Thesi
Ram-induced ovulation to improve artificial insemination efficiency with frozen semen in the sheep
No full textRam effect, defined as shortening of seasonal anestrus in ewes by exposure to the ram, is now well recognized but the underlying mechanisms are still unclear. Little information also exists whether the ram is able to influence the estrus cycle and ovulation. Three experiments were conducted to investigate endocrine response, time of ovulation and pregnancy rate of ewes in proestrus, exposed to the ram (treated) or an adult ewe (control). In the first experiment, ewes (n = 20) were treated with fluorgestone acetate pessaries for 12 days and were given eCG and cloprostenol one day before withdrawal of pessaries. On the day after removal of the pessaries ewes in the treated group (n = 10) were exposed to the sam and those in the control group (n = 10) were exposed to an adult ewe. Blood samples were taken for LH assay every 20 min from 2 h before to 24 h after ram exposure. In the second experiment, ewes (n = 120) were induced into proestrus and on the day after removal of the pessaries were exposed to either a ram (n = 60) or a ewe (n = 60) as described above and were laparoscoped 50, 60 or 70 h after pessary withdrawal (n = 20 at each time interval). In the third experiment ewes (n = 90) were induced and exposed to the ram (n = 45) or an adult ewe (n = 45) and inseminated via a laparoscope whit frozen-thawed semen at 50 or 60 h after pessary removal, respectively. Exposure to the ram was followed in 2 h by a marked rise in LH, equivalent to a preovulatory surge in duration and amplitude. It was also followed by concentrated ovulation within 25 to 30 h and by an increased pregnancy rate in exposed ewes (73.3 vs. 53.3%). [...
Characteristics of receptors for prostaglandin F-2 alpha in bovine and equine corpora lutea.
No full textMembrane depolarisation triggers maturation in meiotically arrested pig oocyte by activating P type Ca channels on the oolemma
No full textCALCIUM AND POTASSIUM CURRENTS IN PORCINE GRANULOSA CELLS MAINTAINED IN FOLLICULAR OR MONOLAYER TISSUE CULTURE.
No full textWe studied membrane currents in granulosa cells (GC), immediately after collection or after variable culture time in the everted-follicle wall or in the monolayer. GC in both systems express an inward calcium current (I(Ca)) with T-type kinetics and voltage dependence. GC in the everted-follicle culture express an outward potassium current (I(K)) kinetics, which remains unchanged during three days in culture. I(K) has delayed-rectifier kinetics, but is insensitive to TEA, 4-AP and apamine. GC in monolayer culture develop a new, inactivating delayed-rectifier potassium current (I(nK)), which progressively dominates as cells advance from day one to day three in culture. A similar I(nK) was recorded in large luteal cells. A possible link between luteinization and the appearance of I(nK) is hypothesized.[...
Influence of progesterone on boar sperm capacitation
No full textThis research investigates the effect of progesterone (P-4) on boar sperm capacitation. Ejaculated spermatozoa were washed and incubated under capacitating conditions with or without P-4. At different times of incubation samples of sperm were exposed to solubilized zonae pellucidae (ZP) and the degree of capacitation was evaluated by the incidence of zona-induced acrosome reaction (AR). The status of the acrosome was studied by using an FITC-conjugated lectin (Pisum sativum agglutinin; FITC-PSA). The effect of P-4 on the fertilizing ability of semen was then evaluated in an in vitro fertilization system by exposing in vitro matured oocytes to sperm preincubated for 2 or 4 h with or without P-4, under capacitating conditions. PSA staining showed that P-4 does not affect the incidence of spontaneous AR. By contrast, spermatozoa incubated with P-4 showed a higher percentage of AR than controls after the exposure to solubilized ZP. This enhanced reactivity to ZP suggests a direct effect of P-4 on sperm capacitation. The in vitro fertilization assay was consistent with these results demonstrating a higher fertilizing ability in sperm preincubated with P-4 than in controls while the steroid was without effect when added only during the fertilization step. These results demonstrate that P-4 improves the fertilizing ability of boar semen essentially by facilitating the process of capacitation.[...
Luteinizing hormone inhibits potassium outward currents in swine granulosa cells by intracellular calcium mobilization
No full textPotassium currents of swine granulosa cells were studied using the patch clamp technique in the whole cell configuration. Granulosa cells stepped to positive potentials (+60 mV) from -40 mV holding potential exhibit a slowly activating, noninactivating outward potassium current. Tail current reverse potential (between -90 and -100 mV) and the current inhibition brought about by the replacement of KCl with CsCl in the pipette solution indicate that this current is carried by K ions. LH was found to significantly reduce the amplitude of this current. The effect was dose and time dependent. Similar inhibition (20-30% of the initial current) was reached with doses of 1-50-mu-g/ml, but in times proportionally shorter as the dose increased (50% inhibition was reached in 170-180 and 30-40 sec with 1 and 50-mu-g LH/ml, respectively). Much longer and variable times (3-10 min) were required with lower doses (0.2-mu-g/ml). The effect of LH was independent of extracellular Ca, while preexposure of cells to TMB-8, an inhibitor of intracellular Ca mobilization, completely prevented the effect of LH. Outward currents after LH treatment could be completely restored by perfusing the cells with ionomycin in Ca-free medium to facilitate calcium efflux from the cells. The present studies indicate that LH modifies the bioelectrical properties of swine granulosa cells. This effect is mediated by an elevation of intracellular calcium, probably mobilized from intracellular stores. The induced changes in K conductance may play a specific role in the transduction mechanisms for LH.[...
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