G. Della Torre

The role of capsaicin‐sensitive muscle afferents in fatigue‐induced modulation of the monosynaptic reflex in the rat

1 The role of group III and IV afferent fibres of the lateral gastrocnemious muscle (LG) in modulating the homonymous monosynaptic reflex was investigated during muscle fatigue in spinalized rats. 2 Muscle fatigue was induced by a series of increasing tetanic electrical stimuli (85 Hz, 600 ms) delivered to the LG muscle nerve. Series consisted of increasing train numbers from 1 to 60. 3 Potentials from the spinal cord LG motor pool and from the ventral root were recorded in response to proprioceptive afferent stimulation and analysed before and during tetanic muscle activations. Both the pre‐ and postsynaptic waves showed an initial enhancement and, after a ‘12‐train’ series, an increasing inhibition. 4 The enhancement of the responses to muscle fatiguing stimulation disappeared after L3‐L6 dorsal root section, while a partial reflex inhibition was still present. Conversely, after section of the corresponding ventral root, there was only a reduction in the inhibitory effect. 5 The monosynaptic reflex was also studied in animals in which a large number of group III and IV muscle afferents were eliminated by injecting capsaicin (10 mM) into the LG muscle. As a result of capsaicin treatment, the fatigue‐induced inhibition of the pre‐ and postsynaptic waves disappeared, while the response enhancement remained. 6 We concluded that the monosynaptic reflex inhibition, but not the enhancement, was mediated by those group III and IV muscle afferents that are sensitive to the toxic action of capsaicin. The afferents that are responsible for the response enhancement enter the spinal cord through the dorsal root, while those responsible for the inhibition enter the spinal cord through both the ventral and dorsal roots.

NMDA receptor-mediated long term modulation of electrically evoked field potentials in the rat medial vestibular nuclei.

SummaryThe effect of high frequency stimulation (HFS) of the primary vestibular afferents on field potentials recorded in the ipsilateral Medial Vestibular Nuclei (MVN) was studied. Our results show that potentiation and depression can be induced in different portions of MVN, which are distinguishable by their anatomical organization. HFS induces potentiation of the monosynaptic component in the ventral portion of the MVN, whereas it provokes depression of the polysynaptic component in the dorsal portion of the same nucleus. The induction of both potentiation and depression was blocked under AP5 perfusion, thus demonstrating that NMDA receptor activation mediates both phenomena. Furthermore, the finding that the field potentials were not modified during perfusion with DL-AP5, as previously reported, supports the hypothesis that NMDA receptors are not involved in the normal synaptic transmission from the primary vestibular afferent fibres, but are only activated following hyperstimulation of this afferent system. Our results suggest that the mechanisms of long term modification of synaptic efficacy observed in MVN may underlie the plasticity phenomena occurring in vestibular nuclei.

S-100b protein regulates the activity of skeletal muscle adenylate cyclase in vitro.

We have investigated the effect of the b isoform of S‐100 proteins on adenylate cyclase activity of rat skeletal muscle. S‐100b inhibits the adenylate cyclase activity in the presence of Mg2+ (5.0–50 mM), while it activates the same enzyme in the presence of Ca2+ (0.1–1.0 mM) dose‐dependently in both cases. S‐100b counteracts the stimulatory effect of NaF on adenylate cyclase in the presence of Mg2+ and the inhibitory effect of RMI 12330 A in the presence of Ca2+.

Differential distribution of vagal afferent neurons from the rat liver

Selective injection of horseradish peroxidase (HRP) into the left and median lobes (LM) and into the right and caudate (RC) lobes of the liver is followed by labeling of neuronal somata in the right and left nodose ganglia. The size distribution of the labeled neuronal population shows that the afferent neurons from the two parts of the liver can be grouped in two corresponding classes; a third class is apparent following injection into the LM lobes. Small neurons are more numerous after injection into the LM lobes, whereas large ones are labeled in the left nodose ganglion after injection into the RC lobes. It is suggested that the two parts of the liver may have a different functional role in conveying afferent signals.

Allopurinol Metabolites and Xanthine Accumulation in Allopurinol-Treated Tobacco

Summary The metabolic conversion products of allopurinol were analyzed in tobacco plants allopurinol-treated by root absorption. The data presented indicate that two transformation proceses occur within the plant: i) oxidation to oxipurinol and xanthine accumulation, and ii) ribosyl transfer reactions with synthesis of ribonucleoside derivatives. While oxipurinol was detectable at 2 days after allopurinol application, 6 days were needed to detect ribonucleosides. Both proceses also took place when allopurinol and oxipurinol were applied by leaf infiltration. This is the first report of in vivo metabolic ribsosidation of allopurinol and oxipurinol in plants, well-known in human organisms and bacterial cells. in vivo treatment of tobacco tisues by allopurinol and the above mentioned allopurinol derivatives indicates that oxipurinol is the active compound in inhibiting tobacco xanthine oxidase. In contrast, in vitro experiments on xanthine oxidase immobilized on polyacrylamide gel rods after electrophoresis of leaf extract showed that only allopurinol was an effective tobacco xanthine oxidase inhibitor.

Allopurinol metabolic conversion products and xanthine accumulation in allopurinol-treated plants

Abstract Allopurinol metabolic products and xanthine accumulation were determined in allopurinol-treated bean, broad bean and wheat plants. The results obtained demonstrate that allopurinol applied through roots undergoes two main transformations in the plants: (i) xanthine oxidase-mediated oxidation to oxipurinol and (ii) ribosyl transfer reactions with consequent synthesis of ribonucleoside derivatives of both allopurinol and oxipurinol. In bean and broad bean leaves ribosidation prevailed over oxidation, whereas in wheat leaves ribosidation conversion was negligible while xanthine oxidase-mediated oxidation was greatly in excess. Therefore, the allopurinol absorbed by wheat was almost totally available for xanthine oxidase inhibition in the plant, while in bean and broad bean, due to the high conversion to ribonucleoside which does not inhibit the enzyme, only part was available for this purpose. Consequently, in wheat leaves the same rate of xanthine accumulation, a consequence of in vivo xanthine oxidase inhibition, was achieved with concentrations about 5 times lower than in bean and broad bean applied through roots. These and previous results in tobacco plants are the first report on in vivo metabolic ribosidation of allopurinol and oxipurinol in plants. The present results are discussed in relation to the already reported allopurinol-mediated biotrophical rust fungi growth inhibition and support the proposition that this phenomenon is connected mainly with in vivo allopurinol-mediated host xanthine oxidase inhibition.

Effect of rust infection on galactolipids and galactolipid fatty acids of Vicia faba chloroplasts

Abstract Galactolipid content and galactolipid fatty acid composition of chloroplasts isolated from healthy and rust-affected Vicia faba leaves were determined. Rust infection induced a general decrease in monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG) from 2 to 14 days after inoculation. The drop in both galactolipids was particularly marked at 8, 10 and 14 days after inoculation. The level of unsaturation and the 18:3 to 18:2 ratio of MGDG fatty acids were slightly reduced at advanced stages of the disease, while in DGDG the decrease of both parameters was observed only at 2 days after inoculation.