Functional differentiation of splanchnic A delta fibres in relation to viscerosomatic reflexes.

The splanchnic afferent signal in the myelinated fibre spectrum was analysed in cats and its relationship to viscerosomatic reflex activity was studied. In addition to Abeta and Adelta components, a further elevation was observed in the sympathetic chain neurogram. According to the conduction rate (15 plus or minus 4 m/sec), it was caused by myelinated fibres 2-3 mu in diameter. The presence of this component at thoracic dorsal root level, or in the sympathetic chain in stimulation of the postganglionic part of the nerve trunk, confirmed the afferent nature of the observed activity. The threshold stimulus for these fibres, which were termed group Adelta2, was four times higher than for Abeta fibres. Correlation of the neurogram with evoked activity in the intercostal nerves confirmed the different functional role of group Adelta2 fibres. Adelta2 fibre activity evokes the early component of the two-component viscerosomatic discharge and Adelta2 fibre activity its later component. The authors discuss the functional significance of Adelta2 fibres, which probably mediate nociceptive information from the viscera.     

Monitoring of potassium-stimulated catecholamine changes in striatal synaptosomal preparations and in corpus striatum of rats: a comparative voltammetric study.

Voltammetric techniques were used to compare the effects of K(+)-induced depolarization on catecholamine levels in in vitro synaptosomal preparations of the corpus striatum with those in the in vivo corpus striatum of anaesthetized animals. In vitro, the catechol-oxidation currents could be recorded only in dopamine-preloaded synaptosomes. In isolated synaptosomes prepared in the presence of elevated concentrations of Ca2+ (1 mmol.l-1) and Na+ (135 mmol.l-1), K(+)-induced depolarization had variable effects on catechol-oxidation current. The stimulatory effect of K(+)-induced depolarization (a short transient increase of catechol-oxidation current lasting for 30 s) could be observed after the addition of dopamine loaded synaptosomes in EGTA into the medium with elevated K+ concentration (90 mmol.l-1) and decreased concentrations of Na+ (75 mmol.l-1) and Ca2+ (0.75 mmol.l-1). These results suggest that experimental procedures and parameters of ionic composition of incubation media have to be carefully controlled, owing to an enhanced in vitro permeability of membranes of isolated synaptosomes for Ca2+ and Na+. In in vivo experiments, microinjection of KCl (3 microliters of 0.5 mol.l-1 KCl in 10 mmol.l-1 HEPES, pH 7.4) resulted in the appearance of several phases of catechol-oxidation current: the current increased (to severalfold of the control values) followed by a decrease or even total disappearance, with a gradual return to control values. Under conditions of depletion of extracellular calcium by EGTA (5 microliters of 0.5 mol.l-1 KCl + 0.25 mol.l-1 EGTA in 10 mmol.l-1 HEPES, pH 7.4) K(+)-induced depolarization confirmed the key role of calcium in the release of catecholamine transmitters as well as that in processes regulating the uptake and metabolism of these transmitters. The voltammetric techniques used in the present study may be a useful tool in extending of our knowledge about the cellular mechanisms of stimulus-response coupling in nerve cells.     

Performance and Mortality of Rumex obtusifolius and R. crispus in Managed Grasslands are Affected by Nutrient Availability

The reasons for the greater incidence of Rumex obtusifolius in grasslands compared with R. crispus have never been investigated. In a small-plot field experiment in which seedlings of R. obtusifolius and R. crispus were transplanted into a sward dominated by Dactylis glomerata, the growth and survival of seedlings were monitored over three years under control and P, N, NP and NPK fertilizer treatments. The highest plants of R. obtusifolius and R. crispus were generally recorded in the N, NP and NPK treatments and the lowest in the control and P treatment. The maximum recorded heights of R. obtusifolius were 100?cm and of R. crispus 80?cm. The number of leaves per plant, weight of individual plants, cover and fertility were generally higher for R. obtusifolius than for R. crispus. 30% to 80% of transplanted R. obtusifolius plants flowered in the first (seeding) year and this contrasted with no flowering of transplanted R. crispus plants. After cutting, substantially better regrowth of R. obtusifolius was recorded compared to that of R. crispus and surviving R. crispus plants tended to show a gradual reduction in leaf number. The mortality of R. obtusifolius over three years ranged from 0% in the NPK treatment to 13% in the control, with an average of 8% over all treatments. The mortality of R. crispus ranged from 19% in the control to 94% in the NPK treatment with an average of 64% over all treatments. We concluded that R. obtusifolius is better adapted to growing in highly productive temperate grasslands than R. crispus because of its perennial character, larger plant size and higher fertility.     

Sex-linked,androgen-dependent differences in renal retention of trimethylselenonium ions

The metabolism of trimethylselenonium ions (TMSe) was studied in male and female rats during maturation. Selenium (Se) retention in the whole body as well as in organs was found to be significantly higher in male rats than in female a few hours after parenteral administration of TMSe. The pronounced Se accumulation was observed in male kidneys. This sex-linked difference was dependent on the presence of gonades and started to be manifested with sexual maturation during the third decade of postnatal life. The effects of steroid hormones on the retention of Se from TMSe were examined in female and castrated male rats. The results indicate that TMSe metabolism in rat kidneys may be influenced by androgen steroids.