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P Valli

Publications and source records attributed to P Valli.

At least 37 records · Page 2Linked to original sources
PubMed1995

Mechanisms for sensory adaptation in frog vestibular organs.

The effects of external low-Ca, high-Mg solutions were tested both on frog isolated semicircular canals and on single cells isolated from these sensory organs. Our results showed that these media were able to cancel slow adaptation of the ampullar microphonic current in the whole organ and to abolish a Ca-dependent K current (IK(Ca)) in single hair cells, suggesting that IK(Ca) is involved in vestibular sensory adaptation.

Adaptation, Physiological↗
PubMed1995

Osmolar changes and neural activity in frog vestibular organs.

The effects of hypotonic and hypertonic solutions (the normal value was 240 mOsm) on posterior canal resting and evoked discharge were studied in isolated labyrinth preparations. Hypotonic solutions (60-180 mOsm) were obtained by reducing the perilymphatic NaCl content. Hypertonic solutions (300-420 mOsm) were obtained by adding to normal perilymphatic solutions suitable amounts of NaCl, glucose, sucrose, glycerol, mannitol and urea. The results demonstrated that any kind of receptor activity was inhibited by hypotonic solutions. On the contrary, hypertonic solutions produced different effects on resting and evoked activity. The resting discharge was, with the exception of urea, constantly increased whereas the evoked responses were constantly decreased by all the hypertonic solutions tested. The possible effects of media with changed osmolarity in Meniere's patients is also discussed.

Animals↗
PubMed1994

Glutamate and carnosine in the vestibular system of the frog.

We demonstrate that both glutamate-like and carnosine-like immunoreactivities are present in hair cells and in fibers of the vestibular organ of the frog inner ear. Comparison of the two immunoreactivity patterns indicates that glutamate and carnosine might be colocalized in some hair cells. The presence of glutamate-like immunoreactivity in hair cells is consistent with biochemical and pharmacological data indicating glutamate as the excitatory neurotransmitter in these sensory receptors. There is also evidence that carnosine might have a neuromodulatory function.

Amino Acid Sequence↗
PubMed1993

Sensory adaptation in frog vestibular organs.

Adaptation, i.e., the decrease with time in sensory units' afferent discharge to a constant stimulus, appears to be a common feature of the receptors belonging to acoustico-lateralis system: However, the mechanisms underlying this process are still a matter of debate. The present experiments demonstrate that sensory adaptation to both mechanical and electrical stimuli can be nearly suppressed after perilymphatic ouabain administration. This clearly indicates that the K+ homeostatic mechanisms [Valli et al., (1990) J. Physiol. (London) 430, 585-594] which control the K+ concentration gradient at both ends of vestibular hair cells play a predominant role in this process. The possible importance of different K+-dependent mechanisms in hair cell adaptation is discussed.

Adaptation, Physiological↗
PubMed1993

NMDA receptors in frog semicircular canals.

The effects of competitive (2-amino-5-phosphonovaleric acid) and noncompetitive (Mg2+, ketamine and kynurenic acid) NMDA receptor antagonists were tested in isolated semicircular canals of the frog. All these antagonists reduced the resting firing rate recorded from the whole ampullar nerve of the posterior canal. This suggests that NMDA receptors are present at the cytoneural junctions between hair cells and afferent nerve terminals in frog vestibular organs.

Afferent Pathways↗
PubMed1992

Evidence for L-glutamate release in frog vestibular organs.

The present study was devised in order to ascertain whether L-glutamate (Glu) is the neurotransmitter at the primary afferent synapse in frog vestibular organs. To this end different groups of frog isolated semicircular canals were stimulated by means of solutions slightly enriched in K+ (5 mM K(+)-rich solutions are sufficient to produce a strong, long-lasting, transmitter release from the basal pole of sensory cells) both in normal conditions and after low-Ca(2+)-high-Mg2+ impairment of the synaptic transmission. The concentration of Glu in the surrounding medium, determined by means of a bioluminescence-enzymatic method, was evaluated in two different experimental conditions: a) when the canals (5 canals placed inside little net bags) were immersed in a 5 mM K(+)-stimulating solution; b) during the superfusion of the canals (25 canals placed into a little perfusion chamber) with a 5 mM K(+)-stimulating solution. The net bag experiments demonstrated that K(+)-rich solutions can provoke an outflow of Glu from canal organs only if the crista ampullaris is present and functioning. Glu fluctuations were in fact suppressed by employing canals deprived of the ampulla or after low-Ca2(+)-high-Mg2+ synaptic blockade. The superfusion experiments demonstrated that the time course of 5 mM K(+)-induced release of Glu from the sensory organ strictly parallels the time course of 5 mM K(+)-induced EPSPs and spike discharge in afferent axons. These results strongly support the hypothesis that Glu is, or is released with, the afferent transmitter in frog inner ear sensory organs.

Animals↗
PubMed1992

Streptomycin blocks the afferent synapse of the isolated semicircular canals of the frog.

This study aimed to define the acute electrophysiological effects of the perilymphatic perfusion of streptomycin in the sensory apparatus of the semicircular canals of the frog. The ampullary DC potential, the vestibular nerve multiunit discharge, the nerve DC potential and the unitary EPSP activity were recorded in isolated semicircular canals of the frog (Rana esculenta L). The results demonstrated that perilymphatic microperfusion of streptomycin (0.1, 0.3, 1 and 3 mM) reduced both resting and mechanically evoked afferent discharge, while the response of the hair cells remains unchanged. Intracellular recordings from single afferent axons showed that the reduction of the afferent discharge was mainly due to a reduction of the amplitude, but not the frequency, of the EPSPs. These results indicate that streptomycin, when applied in the fluid bathing the synaptic pole of the sensory cells, can act as an antagonist of the vestibular afferent transmitter at the postsynaptic level.

Afferent Pathways↗
PubMed1992

Tracheostomy in pediatric patients.

From 1978 to 1987, tracheostomy was performed on 33 children, 13 boys and 20 girls, with a male to female ratio of 0.65:1. The mean age at the time of tracheostomy was 726 days, 76% of the children being under the age of two years. The incidence of pediatric tracheostomy per hospital admissions was 0.05%. Subglottic stenosis (13 children) and respiratory distress syndrome with prolonged endotracheal ventilation (11 children) were the most common indications for tracheostomy. The mean duration of prolonged endotracheal intubation before tracheostomy was 64 days, and that of tracheostomy treatment 117 days. During the tracheostomy period, five children died, but only one death was related to tracheostomy. The total rate of complications was 30%. We emphasize the importance of strict indications for pediatric tracheostomy.

Adolescent↗
PubMed1992

Effects of cromakalim (BRL 34915) on resting and evoked activity in frog semicircular canals.

The effects of endolymphatic administration of cromakalim and glibenclamide were tested in isolated semicircular canals of the frog. The actions of the drugs were evaluated by recording: (1) the transepithelial potential between the endolymphatic and the perilymphatic sides of the crista ampullaris; (2) the slow nerve potential from the ampullar nerve; (3) the action potential discharge in afferent ampullar nerve fibres; and (4) the perilympathatic potassium concentration in the fluid bathing the outer surface of the crista ampullaris. The above mentioned parameters were recorded both at rest and during mechanical stimulation of the sensory organ. The results demonstrated that the endolymphatic administration of cromakalim (10(-4) M) produced an increase in both ampullar receptor resting activity and in perilymphatic K+ resting levels. By contrast all the parameters related to the mechanically evoked responses were practically unaffected. Glibenclamide (10(-4) M) proved able to cancel or to prevent cromakalim effects. These data suggest that the membrane of the hair cells is endowed with K+ channels regulated by internal ATP whose activation is mainly involved in the processes sustaining ampullar receptors' resting firing rate.

Adenosine Triphosphate↗
PubMed1992

Experimental approaches to the study of degenerative and regenerative processes in the nervous tissue. I). Morphological changes in the frog cerebellum after unilateral transection of the VIII statoacustic nerve.

The cell density was evaluated in Purkinje neuron and internal granule cell layers of the frog (Rana esculenta L.) cerebellum at 3, 8, 14, or 30 days after unilateral transection of the VIII statoacustic nerve. After 3 days, the cell density of the Purkinje cell layer was markedly reduced, the cellular loss amounting to 30% at 30 days. In the internal granule cell layer (IGL), after an abrupt decrease in the cell density at 3 and 8 days, the number of cells increased at 14 days and reached the values of control animals at 30 days. In the dorsal part of the ependymal lining of the IV ventricle, there was morphological indication of resumption of the proliferative activity. This can be in relationship with the restored cytoarchitecture of the IGL after the initial cell degeneration. All the above changes were evident in both the ipsi and contralateral parts to the neurotomy though at different extent. This is in agreement with the anatomical data about the nervous circuit connection between the two cerebellar sides and may be also expression of vestibular compensation, induced by unilateral nerve transection in the contralateral side.

Animals↗
PubMed1991

Effects of hydrostatic pressure on sensory discharge in frog semicircular canals.

The effects of endolymphatic and perilymphatic pressure changes on resting and mechanically evoked responses were studied in isolated posterior semicircular canals of the frog. The results demonstrated that ampullar receptors are extremely sensitive to hydrostatic pressure changes (0.25 mm H2O were sufficient to produce distinct changes), being inhibited by endolymphatic pressure increases and facilitated by perilymphatic ones. Intracellular recordings from single afferent axons showed that the effects of hydrostatic pressure result from a modified transmitter release from the synaptic pole of the hair cells. Unlike resting activity, mechanically evoked activity was always depressed in the presence of a hydrostatic pressure. This indicates that the sensitivity of ampullar receptors to mechanical stimuli, i.e. the gain of the conversion process, is maximal when no pressure is present between the inner and the outer fluid. The possible action of hydrostatic pressure on vestibular receptors is discussed.

Afferent Pathways↗
PubMed1990

Pre- and postsynaptic excitatory action of glutamate agonists on frog vestibular receptors.

In order to investigate the localization and the type(s) of excitatory amino acid receptors in the frog vestibular system, the exogenous amino acid agonists Quisqualic acid, Kainic acid and N-methyl-D-aspartic acid were tested on the sensory organ of semicircular canals. Intracellular recordings of the resting discharge from single afferents showed that these agonists exerted a complex excitatory action consisting in a rapid and brief increase in frequency of both EPSPs and spikes, followed by a slower and longer lasting membrane depolarization. The progressive impairment of natural transmitter release achieved by adding Mg2+ or Co2+ in the bath caused a dose-dependent decrease of the agonist-induced afferent discharge, without substantially affecting axonal depolarization. These results suggest that the exogenous amino acid agonists act both pre- and postsynaptically on the vestibular organs. Quisqualic acid and kainic acid were much more potent than N-methyl-D-aspartic acid in inducing excitatory effects, suggesting that the amino acid receptors located on both hair cells and afferent endings are mainly of the non-NMDA type. The present findings, while not excluding that an excitatory amino acid may be the afferent transmitter, highlight its possible function as a presynaptic modulator of the afferent transmission in the frog vestibular system.

Afferent Pathways↗
PubMed1990

Subglottic stenosis in neonates and children. Clinical findings and therapy.

From 1978 through 1987, acquired subglottic stenosis was confirmed endoscopically in 31 children. The mean gestational age of the children was 32 weeks and mean birthweight 2,180 g. Of the children 84% were below 12 months of age at the time of diagnosis. Respiratory distress syndrome was confirmed in 17 children. Before diagnosis, 97% of the children had been treated by endotracheal intubation for ventilatory support, the mean duration of intubation being 37 days. In 10 children, subglottic stenosis was mild and mature and these children were followed up only. Endolaryngeal prosthesis was employed in 2 children and laryngotomy with autogenous bone graft in 5 children. Mean follow-up time was 5 years 4 months. At follow-up, 18 of the children showed good or excellent results.

Child↗
PubMed1990

Perilymphatic potassium changes and potassium homeostasis in isolated semicircular canals of the frog.

1. Endolymphatic and perilymphatic potassium concentrations were measured with K(+)-sensitive microelectrodes in isolated semicircular canals of the frog. K+ levels were evaluated both at rest and during sinusoidal stimulation (0.05 Hz) of the sensory organ. 2. Mechanical stimulation of hair cells was associated with sinusoidal changes (about 0.2 mM) in the perilymphatic K+ concentration. 3. Perilymphatic K(+)-fluctuations were modified neither by impairment of the synaptic transmission at cyto-neural junctions nor by chronic denervation of the crista ampullaris, thus indicating that K+ ions were actually released by hair cells. 4. Voltage-clamp experiments of the whole sensory organ showed that K+ flows across the crista ampullaris can vary from 3 X 10(11) molecules of K+ s-1 at rest up to about 15 X 10(11) molecules of K+ s-1 during mechanical stimuli. 5. Measurement of intra-ampullar K+ concentration demonstrated that the amount of K+ transported from the perilymph towards the endolymph can be rapidly altered by modifying its perilymphatic levels. This suggests that vestibular organs are endowed with K+ homeostatic mechanisms able to buffer in a very efficient way the concentration of K+ in both the fluids bathing the crista ampullaris. 6. The possible role of K+ homeostatic mechanisms in hair cell adaptation is discussed.

Action Potentials↗
PubMed1989

Lumbar sympathetic ganglia in man: an electrophysiological study in vitro.

A method has been developed for the removal, preservation and electrophysiological study 'in vitro' of sympathetic lumbar chains (L1-L3) from subjects undergoing lumbar ganglionectomy in the treatment of peripheral vascular diseases. Extracellular recordings from interganglionic trunks, and intracellular recordings from single sympathetic neurons, were performed. The extracellular experiments substantiated the concept, hitherto deduced from animal experiments, that the preganglionic fibres in the sympathetic lumbar chain are mainly of a descending nature. In fact, stimulation of the interganglionic trunk cranial to ganglia is always much more effective in driving ganglion neurons to fire than stimulation of the interganglionic trunk caudal to ganglia. The intracellular experiments produced a good definition of the main electrical characteristics of human sympathetic neurons. The results can be summarized as follows: the resting membrane potential ranged from 50 to 75 mV (63.4 +/- 9.2 mV; 21 neurons); action potential amplitude from 62 to 93 mV (74.3 +/- 8.1 mV; 27 neurons); membrane input resistance was 42.3 +/- 12.6 m omega (8 neurons) and total membrane capacitance 83.7 +/- 15.3 pF (8 neurons).

Action Potentials↗
PubMed1989

Pediatric bronchoscopy. A report of methodology and results.

Data for this article were obtained from a retrospective analysis of 386 pediatric bronchoscopies from 1979 through 1986. Endoscopic procedures were carried out under general anesthesia using a rigid open bronchoscope. There were 235 boys (61%) and 151 girls (39%). The mean age was 2 years, 3 months. Eight percent of the girls were under 1 month of age, compared with only 4 percent of the boys. The lightest patient weighed 650 g. In children under 1 year of age, the most common indications were dyspnea (32%) and anomaly or suspicion of anomaly (20%). In children over 1 year of age suspected foreign body (32%) and recurrent respiratory infections (30%) were the most common indications. In 15 percent of patients, laryngomalacia and/or an abnormal epiglottis was confirmed. Subglottic stenosis, congenital or acquired, was confirmed in 9 percent and tracheal compression in 12 percent of cases. Seventeen percent of the children showed totally normal findings. There were only eight complications in the whole series and no death or cardiac arrest. The authors confirm the safety of bronchoscopy when careful attention is paid to preoperative investigations, selection of the instruments used, and postoperative care.

Adolescent↗
PubMed1989

Chromatin changes in frog neurons after eighth nerve transection.

Fourteen days after unilateral eighth nerve transection in the frog, Purkinje neurons of the lobus vestibulolateralis and corpus of the cerebellum and medium-sized neurons of the vestibular nuclear complex showed changes in metabolic activity. In the ipsilateral parts, and to a lesser extent in the contralateral parts, of operated frogs, the Feulgen-DNA values were higher and the nuclear areas larger, associated with decondensation of chromatin. The cytoplasmic basophilia was also less. These changes could be due to anabolic responses of the neuronal populations during regeneration. The anabolic reaction of the corpus cerebelli and contralateral vestibular nuclear complex is only partially non-specific and ascribable to the surgical trauma (comparison between sham-operated and unoperated frogs). The results indicate clear patterns of connection between the ipsilateral and contralateral parts and between the cerebellar and vestibular nuclear complex neurons.

Animals↗