Biomedical subjects

M Mirolli

Publications and source records attributed to M Mirolli.

At least 19 recordsLinked to original sources

PubMed1997

Submicroscopic mathematical evaluation of spermatozoa in assisted reproduction. 4. The bovine fertilization (Notulae seminologicae 10).

In this paper we apply a modification of the formula of Baccetti et al. (1995) in the evaluation of submicroscopical characteristics of bull spermatozoa used in assisted reproduction. In the present experiment sperm quality is proposed as a useful parameter in predicting the success of fertilization. Our results demonstrate that the percentage of spermatozoa devoid of submicroscopic defects, according to the particular Bayesan formula proposed by us, is clearly correlated with the result of artificial insemination. In fact, the parameter concerning sperm quality obtained in variously successful donors shows a large correlation with fertility power. The synthetic parameters observed are therefore a good tool in the prediction of sperm power in artificial fertilization. The evaluation is mainly concerned with the quality of the acrosomal characters, the status of the chromatin, the shape of mitochondria, the position of the postacrosomal sheath, the perinuclear space and the axonemal pattern. All these characters are expressed with different means in ejaculates. All these data confirm that submicroscopic-mathematical evaluation offers a convincing and reliable diagnosis based upon sperm structure and functions such as acrosomal reaction and cell motility. It has been also demonstrated that sperm quality is a major factor in the success of artificial insemination and it is clearly revealed in the integrity of most of sperm organelles.

Animals↗

PubMed1992

Histochemical study of the heart of the axolotl (Ambystoma mexicanum).

We have investigated the presence of cells containing monoamines, substance P, and neuron-specific enolase (NSE) in the heart and in the pericardial wall of a urodele amphibian, the axolotl. Fibers containing substance P-like immunoreactivity were present in the heart but not in the pericardial wall. Also present in the heart were small branched cells, which stained metachromatically with toluidine blue. Similar cells were found in the peritoneum and were tentatively identified as mast cells. NSE-immunoreactive fibers were found both in the heart and in the pericardial wall. Small intensely fluorescent (SIF) cells of the pericardial wall contained a high concentration of norepinephrine but no other monoamines, substance P, or NSE. Comparison with data available for the mudpuppy, Necturus maculosus, a closely related amphibian species, suggests that the innervation of the heart in the axolotl is substantially different.

Ambystoma mexicanum↗

PubMed1988

The organization of the cardiac ganglion of the axolotl (Ambystoma mexicanum).

The heart of the axolotl Ambystoma mexicanum was studied with histochemical methods to determine the distribution of neurons containing acetylcholine esterase, catecholamines and 5-hydroxytryptamine. The cardiac ganglion is made up of cholinergic nerve fibers and somata, and of catecholaminergic fibers. Small intensely fluorescent cells were found along blood vessels in the pericardial wall at the base of the heart, but not in the heart itself, except, in a few instances, in the region bordering the pericardial wall. Both the cholinergic and the catecholaminergic innervation of the heart were poorly developed at hatching and reached their mature state after a few months. Cholinesterase staining fibers appeared several weeks before catecholaminergic fibers. The number of postganglionic cholinergic neurons in the heart increased several-fold during the first month after hatching. Histofluorescence studies of organ cultures suggested that all the catecholamine present in the heart are of extrinsic origin. Liquid chromatography with electrochemical detection demonstrated that the dominant catecholamine in the heart is norepinephrine. No neurons containing 5-hydroxytryptamine were found.

Acetylcholinesterase↗

PubMed1987

Structure and localization of synaptic complexes in the cardiac ganglion of a portunid crab.

The cardiac ganglion of Portunus sanguinolentus exhibits spontaneous rhythmic activity when isolated. The ganglion contains five large and four small intrinsic neurons and is innervated by three pairs of fibres originating in the thoracic ganglia. We have identified the processes of the large neurons in electron micrographs by injecting these cells with two electron-dense markers, horseradish peroxidase (HRP) and Procion Rubine (PR). In addition we have studied the processes of the four smaller neurons by light microscopy serial reconstructions and by electron microscopy of selected regions. Both markers were found only in neuronal processes and not in glial cells nor in the extracellular space, except close to the soma of the injected cell. We found contacts between the small secondary (collateral) processes of the large cells but not between their somata or their primary processes (axons and dendrites). Two specialized structures present at the contacts between the collateral processes were small membrane close appositions, possibly the site of electrotonic junctions, and chemical synapses. Contacts between processes marked by HRP and those marked by PR were common, as were contacts between processes marked by either HRP or PR and those of the other intrinsic neurons. Adjacent processes stained by PR could contain PR deposits of different densities, but it is unclear whether this finding was due to intercellular diffusion of the dye or to its diffusing at different rates into branches of the same process. Identified processes of all the intrinsic neurons contained the same type of vesicles, which were different from those found in processes of the extrinsic fibres. Chemical synapses were present at contacts between processes of the extrinsic and intrinsic neurons, as well as at contacts between processes of the intrinsic neurons. The axons of three small cells made a series of contacts at which extensive arrays of membrane close appositions, but not chemical synapses, were found. These three axons also formed contacts, either directly or through their collateral branches, with processes of the large cells, at which both membrane close appositions and chemical synapses were present. The axon of the fourth small cell could not be followed in our series.

Animals↗

PubMed1983

Inward and outward currents in isolated dendrites of Crustacea coxal receptors.

Segments from the nonspiking peripheral dendrites of a crustacean coxal receptor (T fiber) were studied using the voltage clamp technique. The peripheral endings of the T fiber are sensitive to stretch applied to a specialized receptor muscle by rotation of the coxa. The intraganglionary portion of the T fiber is presynaptic to the motor neurons innervating the coxal muscle. Depolarizing commands activated three separate fast channels: (i) a transient inward sodium current, INa, which is blocked by tetrodotoxin (TTX); (ii) a transient outward current, Io1 , having the same voltage-dependent characteristics as INa; and (iii) a second, longer-lasting, outward current, Io2 . Both INa and Io1 were inactivated when segments were clamped at voltages more positive than -50 mV, whereas Io2 could be activated at voltages more positive than -50 mV. Io1 and Io2 were blocked by 4-aminopyridine (4-AP) and by tetraethylammonium (TEA), although Io2 shows a greater sensitivity to TEA than Io1 . It is suggested that Io1 may be a factor in determining the nonspiking behavior of the dendrites and that Io2 may limit the stretch-induced depolarization in the dendrite to a value more negative than that at which the maximum rate of transmitter release occurs. In addition to the three fast currents, the presence of a slow inward and slow outward current could also be demonstrated. The effects of the slow currents were longer in segments cut from the proximal part of the dendrites.

Animals↗

PubMed1981

Fast inward and outward current channels in a non-spiking neurone.

Although the crustacean coxal receptors and no-spiking, indirect pharmacological and electrophysiological evidence suggests that fast sodium channels may be present in their membrane. The properties of these channels are not known, but it has been suggested that they might be "incompletely differentiated", perhaps lacking "appropriate gating mechanisms", and/or "too sparsely distributed". The former hypothesis is not supported by the results of voltage-clamping experiments done on dendritic segments isolated from these mechanoreceptors. Instead, the results reported here provide direct evidence for a voltage-dependent fast inward current, sensitive to tetrodotoxin (TTX) and requiring external sodium (but not calcium). This current is shunted by a transient fast outward current, also voltage dependent, and it is suggested that this shunting may account, at least in part, for the non-spiking behaviour of the coxal receptors.

Animals↗

PubMed1979

The electrical properties of a crustacean sensory dendrite.

1. The input properties and the response to stretch of a coxal receptor, the S fibre of the crab Scylla serrata, were studied using two and three intracellular microelectrodes. 2. In the relaxed receptor the transmembrane potential ranged from about -60 to -70 mV, and the input resistance, RT, from 1 to 3 M omega. The input IV relationship, studied by injecting slow-rising current ramps, was not linear either in the hyperpolarizing or in the depolarizing quadrants. 3. Low values of RT and linear IV relationship were associated with a large leakage of the microelectrodes. 4. The response to step stretches was complex, consisting of an initial depolarizing transient, Va, and a steady-state depolarizing plateau, Vs. Both Va and Vs propagated with decrement in the fibre which was about 9 mm long. The spatial decrement of Va and Vs was equal to that of the response to distally injected current pulses of comparable duration and amplitude. 5. On the basis of the spatial decrement of both Va and Vs the dendrite can be considered equivalent, for current flowing from its distal to its proximal end, to a semi-infinite cable having a length constant of between 4 and 6 cm. 6. The voltage transients recorded in response to long current pulses reached 84% of their final value in a time (t84%) ranging from 150 to 180 ms in fibres in which RT was 2 M omega or larger. t84% was smaller in fibres having a lower RT. 7. The time course of the transients recorded in response to injected current pulses deviated from the semi-infinite cable model in a manner suggesting the presence of a partial short-circuit. For this reason the membrane time constant of the fibre is considered larger (by an undetermined amount/ than t84%. 8. The fibre presented less resistance to current flowing from its proximal to its distal end than to current flowing in the opposite direction. For this reason, and also because of the time course of the voltage transient, it is concluded that the distal sensory endings of the fibre have the properties of a leaky end termination, even in the non-stimulated receptors.

Animals↗

PubMed1979

Electrogenic Na+ transport in a crustacean coxal receptor.

1. The response of the coxal receptors of the crab Scylla serrata to step stretches consisted of a partial action potential, Va, followed by a steady-state depolarization, Vs. The input resistance of the fibre was reduced during Vs. 2. In the absence of stimulation, the dendrites of the receptors depolarized when external Na+ was substituted with choline or Li+, and when the external K+ concentration was increased or decreased. The dendrites also depolarized when ouabain was added to the saline. 3. The amplitude of both Va and Vs was dependent on external Na+. In cells which were depolarized by ouabain, the amplitude of Vs increased when the K+ concentration of the saline was reduced. 4. Vs was followed by a small, but long-lasting, after-potential which was depolarizing when the membrane potential was between -70 and -60 mV. In cells depolarized by ouabain or by low K+ saline, the after-potential became hyperpolarizing. 5. When trains of brief stretches (each 5 ms in duration) were used as stimuli, the cells responded with trains of Va responses. During this tetanic stimulation the cells hyperpolarized; cessation of the stimulus train was followed by a long-lasting hyperpolarization (PTH). 6. PTH was abolished in Li+ saline, in low K+ saline, and in the presence of ouabain. In control or in low K+ saline, PTH was not accompanied by a decrease in the input resistance of the fibres. 7. It is concluded that an electrogenic Na+ pump (or equivalent process) contributes a substantial fraction of the membrane potential of the unstimulated coxal receptors. Pump activity could be increased by Na+-loading the distal part of the cells with trains of Va responses. By contrast, during the steady-state response to stretch, the pump was not activated.

Animals↗

PubMed1975

Morphological changes associated with stretch in a mechano-receptor.

The S neurons of decapod crustacean coxal receptors respond to a constant stimulus with a steady-state response lasting for at least 20 min. This property makes it possible to fix neurons in the stretched or relaxed condition by rotating and pinning the coxa up or down respectively. In specimens perfused with 5 mM lanthanum chloride before fixation, it was found that the extracellular space around the nerve terminals, particularly the naked tubular endings, is open to ions. The cross-sections of the tubular processes (dendritic fingers) are about 25% smaller in stretched specimens, and the secondary dendritic branches connecting the fingers with the remainder of the dendrite appear shorter and thicker. The presence of mitochondria at the periphery of the main part of the dendrite and in the secondary branches, but not in the fingers, is interpreted as evidence for an electrical model similar to that proposed for vertebrate photoreceptors. The observed morphological effects of stretch are discussed in terms of this model.

Animals↗

PubMed1972

The geometrical factors determining the electrotonic properties of a molluscan neurone.

1. Light and electron micrographs of sections of the gastro-oesophageal giant neurone (G cell) of the nudibranch mollusc, Anisodoris nobilis, show that its somatic and axonal membranes are deeply infolded. The surface and volume of its soma and axon have been calculated from measurements taken at the light and electron microscope on sections of the G cell.2. The surface of the soma is approximately 7.5 times as large as that of a sphere having the same volume. For a typical cell the soma has a volume of 1.5 x 10(-5) cm(3) and a surface of 2 x 10(-2) cm(2); the axon has a volume of 5 x 10(-5) cm(3) and a surface of 5 x 10(-1) cm(2).3. Because the axon is star shaped in cross-section, its geometry cannot be described by a single parameter (diameter or radius). Furthermore, the axon is beaded, and both the area (A) and the perimeter (P) of its cross-section change from point to point.4. However, in spite of the apparent irregularity of their cross-sections, all axons examined could be characterized by a constant A/P ratio. This ratio also remains constant when the axons are stretched.5. According to the equations derived in the Appendix, the geometrical factor for the length constant in a folded fibre is H = radical(A/P); therefore, in the G cell the length constant (and hence the conduction velocity) should be independent of the stretch applied to the axon.6. The geometrical factor required to calculate the axonal input conductance is M = radical(A.P). M changes in adjacent segments of the same axon; in each segment its value depends on how much the axon is stretched.7. The input conductance of the whole axon can be calculated by applying a modified form of Rall's equations for dendritic trees. The results suggest that the input conductance of the G cell axon should vary with stretch and should be large in comparison to that of the soma.

Action Potentials↗

PubMed1972

The passive electrical properties of the membrane of a molluscan neurone.

1. The passive electrical properties of the membrane of the gastrooesophageal giant neurone (G cell) of the marine mollusc, Anisodoris nobilis were studied with small current steps.2. The membrane transient response can be fitted with a theoretical curve assuming as a model for the cell a sphere (soma) connected to a cable (axon). The axo-somatic conductance ratio (rho), determined by applying this model, is large (approximately 5) and the membrane time constant (tau) is long (approximately 1 sec).3. When the actual surface area of the cell, corrected for surface infoldings, and the spread of current along its axon is taken into account, the electrical measurements imply a specific resistance of the membrane of approximately 1.0 MOmega.cm(2).4. Estimates of specific membrane capacity, either from measurements of the initial portion of the membrane transient or from the ratio of the time constant to the specific membrane resistance are close to the value of 1 muF/cm(2) expected for biological membranes.5. Thus, our measurements of specific capacitance, time constant, length constant and axo-somatic conductance ratio all indicate that the value found for the specific membrane resistance of the G cell, while unexpectedly large, is valid.6. The magnitude of this value suggests that the conductance (permeability) of its membrane to ions is much smaller than that previously assumed for nerve membranes; this small conductance may be related to the larger surface-to-volume ratio of the G cell.

Animals↗

PubMed1970