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G Zucca

Publications and source records attributed to G Zucca.

At least 55 records · Page 3Linked to original sources
PubMed1983

[Temperature dependence of electrical potentials in the frog semicircular canal].

The temperature dependence of conversion processes in the sensory organ of frog semicircular canals has been tested in the range 0-28 degrees C by recording the ampullar (Adc) and nerve (Ndc) slow potentials as well as the afferent discharge of impulses (Nfr) in the VIII nerve fibres. The results have shown that Adc is scarcely affected by temperature changes (Q10 less than 2) thus suggesting that stimulus conversion in labyrinthine cells does not imply chemical processes but mainly potassium conductance changes at their apical membrane. By converse, postsynaptic potentials and propagated spikes are markedly reduced at low temperatures (Q10 2.8 and 7 respectively) and only slightly increased between 20 and 28 degrees C. These observations are interpreted by considering the chemical nature of the processes which are involved. The temperature dependence in labyrinthine receptor activation is discussed in the view of its physiological meaning.

Animals↗
PubMed1982

[Effects of increased temperature on the sensory transduction process induced by frog ampullar receptors].

The function of the sensory organ in semicircular canals of the frog has been tested, at increasing temperatures from 20 to 34 degrees C, by recording the ampullar (Adc) and nerve (Ndc) potentials together with the afferent discharge of impulses in the VIII nerve fibres. The amplitude of the receptor potential increases by increasing the temperature up to 30 degrees C. Postsynaptic potentials and propragated spikes, by converse, are only slightly modified between 20-28 degrees C and are drastically depressed over 28 degrees C. The results are discussed also in connection with the possible use of the enzimatic pretreatment of the preparations to facilitate the insertion of microelectrodes in labyrinthine cells.

Animals↗
PubMed1981

[Experimental research on the toxicity of PVC administered orally].

The AA. report the results of two experiments carried out on 24 rats Wistar treated with PVC dust ingestion. A group received 1 g of PVC dust in distilled water for only 15 days; the second group received PVC dust mixed with standard food almost 5 months till to 15 months. Pathological findings consist in marked hyperplasia of gastro-enteric mucosa, with polipoidfigures, and in a marked activation of pulmonary linforeticular tissue with cellular atipias. In one case a subcutaneous histiocytic lymphoma was observed.

Administration, Oral↗
PubMed1980

[Effects of some bivalent and trivalent ions and of EGTA on the process of activation of the ampullar receptors].

In order to define the role of Ca++ in labyrinthine receptors the endolymph in isolated canal preparations was replaced with modified solutions containing Ca-substitutes(Sr++, Ba++), Ca-antagonists(La+++, Cd++, Mg++) and Ca-chelating agents(EGTA). The response of the receptors was evaluated by recording the slow and propagated potentials from the ampullar nerve. All the tested solutions proved able to depress or cancel the mechanically evoked responses of ampullar receptors. The presence of Ca++ in the endolymph is therefore essential to grant the mechanosensitivity of the hair cells. The receptor blockade produced by Ca-withdrawal develops much earlier under continuous mechanical stimulation. This suggests that Ca++ might be bound in some structures and released during cupula deflections.

Animals↗
PubMed1976

Effects of Ba ions on frog's isolated muscle spindle.

Dilute solutions of Barium Chloride have been tested on frog's isolated muscle spindles with the aim of clarifying the processes leading to the afferent discharge. In the presence of Ba++ the spindle properties are modified as follows: 1. The discharge of slack spindles increases and becomes extremely regular. 2. The phasic response to stretching is enhanced, the tonic responses being on the contrary virtually suppressed. Under Ba-treatment therefore the spindle changes from a phasic-tonic receptor to a merely phasic receptor. 3. The "silent period" following every propagated spike is prolonged while the safety margin of the "abortive" into propagated spike conversion becomes maximal under Ba-treatment. Additionally, this analysis showed that, when a "true" action potential arises in the spindle, it propagates not only to the stem fibre, but also to all the sensory endings in the spindle intracapsular network. Comparison between the effects of Ba++ and those produced by TEA and ouabain indicates that the action of Ba++ on muscle spindles results from conjunction of two factors : a) reduction of K permeability, and b) enhanced efficiency of an electrogenic Na/K-pump in spindle nerve membranes.

Action Potentials↗
PubMedDate not supplied

The origin of slow potentials in semicircular canals of the frog.

Slow potentials generated in the sensory organ of the ampulla were recorded in isolated semicircular canals of the frog by means of fluid electrodes. These potentials, which may be picked up from the intrampullar fluid and those from the ampullar nerve appear to be generated at different stages of the process taking place in crista ampullaris. Slow intra-ampullar potentials apparently reflect receptor potentials of hair cells. They are preserved after degeneration of the nerve fibre endings and are relatively insensitive to DNP poisoning; their amplitude is maximum at high K+ concentrations. Slow nerve potentials appear to be due to electronic spreading of post-synaptic excitatory potentials generated at cytoneural junctions. They disappear after degeneration of the nerve fibres, in low Ca++ and high Mg++ solutions and are extremely sensitive to DNP poisoning. An analysis of the time-course of the slow ampullar and nerve potentials referred to the discharge of impulses in afferent fibres was performed with a view to interpreting the transduction mechanism of semicircular canals.

Animals↗
PubMedDate not supplied

The importance of potassium in the function of frog semicircular canals.

The slow potentials and afferent discharge of impulses in frog semicircular canals have been studied at different endolymphatic and perilymphatic K+ concentrations. Results indicate that the presence of K ions in the bathing fluids is essential for maintaining the receptor function in crista ampullaris, although very low concentrations of this ion in the perilymph are sufficient to preserve the receptor responsiveness to mechanical stimuli. The hypothesis is put forward that K+ may be pumped from the exterior of the canal towards the intracupular structures, where it accumulates. A K-rich endolymphatic environment does, however, appear to be necessary to ensure the resting activity of ampullar receptors and their ability to be "disfacilitated" during inhibitory cupula deflections.

Action Potentials↗