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Preganglionic discharge induced by acetylcholine in the superior cervical ganglia of the rat
No full textACh (5.10(-4) M), when applied to isolated ganglion preparations elicited an apparently antidromic discharge in the cervical sympathetic trunk. The intensity of this back-firing was found to be about 10 times lower than that of the postganglionic discharge evoked by ACh in the internal carotid nerve. Both responses however displayed a similar time course consisting mainly of an early and a late component. In the back-firing the early component died out in few seconds, while the late one lasted 20-30 seconds. The two components were cancelled by d-tubocurarine (5.10(-6) M) and atropine (10(-6) M) respectively, suggesting that both nicotinic and muscarinic cholinoceptive sites are involved. In chronically decentralized preparations ACh evoked a clear back-firing response not substantially different from that elicited in normal ganglia. Therefore it is likely that the back-firing phenomenon is not due to antidromic activation of preganglionic fibers. The back-firing observed in the rat superior cervical ganglion was interpreted as being due to activation of sympathetic neurons, known to give rise to recurrent axons in the cervical sympathetic cord
Acetylcholine-induced back-firing in the preganglionic trunk of the rat superior cervical ganglion
No full textACh (5 X 10(-4) M), when applied to isolated ganglion preparations elicited an apparently antidromic discharge in the cervical sympathetic trunk. The intensity of this back-firing was found to be about 10 times lower than that of the postganglionic discharge evoked by ACh in the internal carotid nerve. Both responses, however, displayed a similar time course and consisted of an early and a late component. In the back-firing the early component died out in a few seconds, while the late one lasted for 20-30 s. The two components were cancelled by d-tubocurarine (5 X 10(-6) M) and atropine (10(-6) M), respectively, suggesting that both nicotinic and muscarinic cholinoceptive sites are involved. In chronically decentralized preparations ACh evoked a clear back-firing response not substantially different from that elicited in normal ganglia. Therefore it is likely that the back-firing phenomenon is not due to antidromic activation of preganglionic fibers. The back-firing observed in the rat superior cervical ganglion was interpreted as being due to activation of sympathetic neurons known to give rise to recurrent axons in the cervical sympathetic trunk
Ionic mechanisms sustaining activity in ampullar receptors of the frog
No full textIonic mechanisms sustaining sensory transduction in crista ampullaris sensory cells have been investigated chiefly by replacing the endolymph with solutions with K+ and Ca++ chelators added. The effects of the modified solutions were evaluated by extracellular and intracellular recordings of both and the presynaptic and postsynaptic activity of ampullar receptors. The results strongly suggest that the receptor current in labyrinthine cells is carried exclusively by K+. Moreover evidence are reported indicating that the transducer membrane in ampullar receptors is provided with Ca++ sensitive potassium channels whose opening is depending on free Ca++ released from cupular structures during excitatory deflections
Corrente di recettore nelle cellule ciliate del sacculo di rana
No full textThe present study aims to provide further contribution towards identifying the ions which actually sustain the receptor current in labyrinthine sensory cells. The experiments were carried out on isolated sacculi of the frog. The macular epithelium of the sacculus was positioned in a two compartment chamber which allows the fluid bathing the inside and the outside of the sacculus to be replaced separately with solutions having different ionic composition. The potential across the epithelium was clamped to zero and both the receptor current and the postsynaptic potentials in response to mechanical stimuli were first recorded when the endolymphatic fluid had a normal ionic composition and then, at different time intervals, after replacing the endolymph with solutions deprived of K+ (replaced with Na+, Rb+, Cs+ and Ca++) and Na+ (replaced with choline and saccharose). The results have shown that both the receptor current and the postsynaptic potentials are abolished after replacing the endolymphatic K+ with Na+, Cs+ or Ca++, whereas are partially preserved when K+ is replaced with Rb+. These findings strongly suggest that the receptor current in labyrinthine sensory cells is carried almost exclusively by K+ and that this current flows across specific K-channels
Effetti dell'incremento di temperatura sul processo di trasduzione operato dai recettori ampollari di rana
No full textThe 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
Recurrent neurons of the superior cervical ganglion of the rat: an electrophysiological study
No full textPeripheral organization of the vestibular efferent system in the frog: an electrophysiological study
No full textThe distribution and the properties of efferent fibers in vestibular nerve were studied in the isolated frog labyrinth. Electrical stimulation of the central stump of any vestibular nerve branchlet elicited compound action potentials in all the other eighth nerve branchlets, indicating the existence of neural links between the various vestibular organs. The same experimental paradigm, when repeated in frogs with chronic section of the eighth nerve roots, demonstrated that these pathways are efferent collaterals extending to all vestibular organs. There are more collaterals linking the 3 semicircular canals than the otolith organs and the otoliths with the canal organs. Efferent connections in the eighth nerve were preserved in full after ablation of the ipsilateral hemi-cerebellum, suggesting that the efferent pathways probably originate in the brainstem. Intracellular recordings from single afferent fibers of both canal and otolith organs revealed that efferent fiber activation could elicit either inhibition or facilitation of the receptor discharge. It was concluded that the frog efferent vestibular system is endowed with non-selective control channels which allow single neurons to influence the receptor activity of different labyrinthine organs
Axonal organization of the peripheral efferent system in the frog labyrinth
No full textThe purpose of the present work is to investigate the distribution of the nerve fibres subserving efferent control in frog labyrinth. Following electrical stimulation of a twig of the isolated VIII nerve compound action potentials could be picked up from the others nervous twigs. Denervation experiments suggest that these compound potentials are sustained by efferent fibres which branch in the VIII nerve providing collaterals to otolith and canal organs. This axonal organization, therefore, enables single efferent neurones to control the activity arising from different types of labyrinthine receptors
Effetti della temperatura sui potenziali postsinaptici nelle giunzioni cito-neurali dei canali semicircolari della rana
No full textAn analysis of the EPSPs recorded intracellularly from single fibres of the VIII nerve revealed that the resting release of chemical transmitter at the cyto-neural junctions in the sensory organ of frog semicircular canals displays a rather low temperature dependence. This provides evidence that, in labyrinthine receptors, the resting activity is actually "evoked" in nature. A comparison between the discharge of EPSPs and propagated spikes in the VIII nerve fibres has shown that the "encoders" of primary vestibular neurones are highly sensitive to temperature changes and irreversibly damaged at temperatures exceeding 28 degrees C
Effetti delle variazioni di K+ nel liquido perilinfatico sulla attività dei recettori vestibolari della rana
No full textThe effect of rapid changes in K+ concentration (from 0 up to 5 mM) in the perilymphatic fluid was tested on ampullar receptor activity in isolated semicircular canals of the frog. The effects of the different K-concentrations were evaluated by recording both the transepithelium potentials (Adc) and the postsynaptic potentials (EPSPs and spikes discharge) led off from the ampullar nerve. The results have clearly demonstrated that crista ampullaris sensory cells are extremely sensitive to K-changes (+/- 0.25 mM). In fact both transepithelial potentials and discharge activity (EPSPs and propagated spikes) of first order vestibular neurones may be decreased or increased by decreasing or increasing the K-concentration in the outer fluid. The possible mechanism of action of K+ on ampullar receptors is discussed
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