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.

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.

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).

Evidence for the presence of substance P-like immunoreactivity in the human cerebellum

Preliminary results on the localization of substance P-like immunoreactivity in the human cerebellum are presented. Cerebella from newborn and adult subjects were examined. While only sporadic positive fibres were detected in the adult tissue, the immunoreactive material appeared more abundant in the cerebella from newborn subjects. Varicose and non-varicose fibres and dot-like nerve terminals were present with different density in various regions. The paucity of immunoreactive perikarya suggests that most of the cerebellar substance P-like immunoreactive material has an extrinsic origin.

The human hippocampal formation and parahippocampal gyrus: localization of substance P-like immunoreactivity in newborn and adult post-mortem tissue

The localization of substance P-like immunoreactive nervous structures in the human post-mortem hippocampal formation and parahippocampal gyrus was studied by the indirect immunofluorescence technique of Coons and Kaplan (1950), J. exp. Med. 91, 1-9. Specimens were obtained from brains of both newborn and adult subjects. Substance P-positive perikarya were easily detectable in these regions, being particularly abundant in the stratum oriens of the hippocampus and in the hilus of the fascia dentata. The nerve fibres and terminals were also widely and unevenly distributed. Comparison of the newborn and adult tissue revealed differences in the distribution of substance P-like immunoreactivity in ontogenetic stages. Our results, together with data available in the literature, further suggest that substance P is differently distributed in the various cortical areas of the human brain, and that the distribution of substance P may vary among species.

Functional organization of the peripheral efferent vestibular system in the frog

The functional organization of the efferent vestibular system (EVS) was studied in the isolated frog labyrinth. To ascertain whether, besides the efferent branching fibres that innervate several end-organs, the EVS is also endowed with efferent non-branching axons which might control a given population of sensory units in each end-organ, the 8th nerve and one of its branchlets were electrically stimulated while recordings of the spontaneous activity arising from the different sensors were made by impaling single afferent axons in all the 8th nerve branchlets. The results demonstrated that the vast majority of the sensory units whose activity was modified by stimulating the whole 8th nerve was also affected by stimulating an 8th nerve branchlet. These findings therefore rule out the possibility that the EVS is endowed with projective fibres and strengthen the view that the EVS is a highly divergent system with collaterals arising from single parent axons that innervate several end-organs. These experiments have also shown that the percentage of sensory units which are actually controlled by the EVS varies amongst the different labyrinthine organs. It is maximal in the sacculus (ca. 90%), somewhat lower in canal organs (ca. 80%) and the utriculus (ca. 70%) and considerably lower in the lagena (ca. 50%). This EVS arrangement therefore might allow information arising from some organs to be modified more extensively than that from others.

[Receptor current in ciliate cells of the frog sacculus]

The 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.

[Effects of changes in K+ in the perilymphatic fluid on the activity of vestibular receptors in the frog]

The 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.

The effect of glutamate on the frog semicircular canal

L-glutamate (Glu) has at least two sites of action in the frog semicircular canal: the hair cell (presynaptic) and the primary afferent nerve fibres (postsynaptic). Glu's action on the hair cell results in an increased release of the natural transmitter which is responsible for a substantial increase in the frequency of firing in primary afferents. The presynaptic action of Glu is antagonized by D-alpha-aminoadipate (D alpha AA). Glu produces a long-lasting depolarization on the afferent nerve fibres which does not by itself elicit any afferent discharge of impulses when the release of the natural transmitter is prevented. Glu-induced nerve depolarization is only partially antagonized by D alpha AA. The difficulty of reconciling some of the observations made of the effects of Glu in semicircular canals with its presumed role as an afferent transmitter in this organ is discussed, but this role is not definitely rejected.

[Effect of various vasoactive drugs on synaptic transmission in the orthosympathetic ganglia in man]

The effects of the following vasoactive drugs: Bencyclan fumarate, Cetiedil citrate, Cinepazide maleate, Dihydroergocristine methane sulphonate, Nafthydrofuril acid oxalate, Papaverine hydrochloride, Piribedil monomethane sulphonate, Raubasine, Thymoxamine hydrochloride and Xanthinol nicotinate, in concentrations ranging between 0.001 - 2 mM, were tested on the compound action potentials led off from human isolated sympathetic ganglions. The experiments, carried out on 50 isolated lumbar ganglion preparations removed from 23 subjects with arteriopathy of the limbs, indicated that all the drugs are able to impair the synaptic transmission, although at different concentrations. These findings are in favour of the hypothesis that the vasodilatatory effects observed after therapeutic treatment of patients with vasoactive drugs are partially produced by the vasodilatation following the depression of the sympathetic nervous transmission.

Local mechanisms in vestibular receptor control. Effects of curare on the EPSPs and spike discharge recorded from single afferent fibres of the posterior canal nerve of the frog

In the frog, the afferent discharge of EPSPs and spikes has been recorded intracellularly from single fibres of the posterior ampullar nerve before and after administration of D-tubocurarine (5 X 10(-6) M) in the following experimental conditions: (a) in animals in which the labyrinth was merely exposed (intact frogs), (b) in isolated acute labyrinth preparations, (c) in isolated chronic labyrinth preparations after degeneration of the efferent fibres. In both (a) and (c), curare induced either facilitation or inhibition of the resting discharge in a large number of units. By contrast, after degeneration of the efferent fibres, the effects of the drug were almost completely suppressed. These results indicate the existence of peripheral mechanisms involving the efferent nerve terminals which can control the release of afferent transmitter even in the absence of any central influence.

[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.

[Effects of temperature on postsynaptic potentials at the cyto-neural junctions of the frog semicircular canal]

An 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.

Ionic mechanisms sustaining activity in ampullar receptors of the frog

Ionic 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.

[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.

Experimental skeletal muscle revascularization by jejunal loop implant

The possible onset of a vascular connection between the parietal network of a jejunal loop transposed into the crural region and the quadriceps muscle in hypoperfused condition has been experimentally studied. Ten dogs were included in this study. Sixty days after the operation the angiograms obtained by cannulating the artery of the implanted loop showed a rich neovascularity in the muscular area near the implant and the direct visualization of the venous outflow of the thigh. Histology of the specimens showed no substantial abnormalities of the muscular tissue. From these data the possible effective role of the skeletal muscle revascularization in the management of some severe ischemic conditions, after the failure of all the conventional reconstructive procedures, is suggested.

Sipple's Syndrome: Description of One Case

The case reported involves a young woman with a medullary thyroid carcinoma. Only during autopsy was it possible to show a pheochromocytoma of the left adrenal gland; multiple foci of atypical proliferation were observed, only microscopically, also in the adrenal gland. The authors emphasize the difficulty of a correct diagnosis during life and outline the necessity of an accurate screening of family members of a patient with Sipple's syndrome.

[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.