This paper reviews some of our findings which have shown the usefulness of in vitro methods in the study of hypothalamic neurones. (1) Membrane current analyses of dispersed neurones of the rat preoptic and anterior hypothalamus (POA) during thermal stimulation have revealed that warm-sensitive neurones are endowed with a non-inactivating Na+ channel having a high Qjo in the hyperthermic range (35-41 °C). (2) A brain slice study has shown that neurones in the organum vasculosum lamina terminalis (OVLT) region have much higher sensitivity to PGE2 than POA neurones. This provides further evidence of a critical role of the OVLT in translation of blood-borne cytokine signals into brain signals for fever induction. (3) Local application of IL -1/9 and IFNa altered the activity of thermosensitive (TS) neurones and glucose responsive (GR) neurones in vitro in an appropriate way to produce fever and anorexia. While the responses to IL -1/9 required the local release of prostaglandins, the responses to IFNa were found to be mediated by opioid receptor mechanisms. (4) The responses of POA TS neurones and VMH GR neurones to IL -1/9 but not those to IFNa, were reversibly blocked by aMSII, an endogenous antipyretic peptide. Thus, immune cytokines and their related neuroactive substances may affect hypothalamic TS and GR neurones thereby producing elaborately regulated changes in homeostatic functions such as thermoregulation (fever) and feeding (anorexia), which are considered as host defence responses.
We have studied the mechanism of Na+ deprivation-induced catecholamine secretion from freshly isolated bovine adrenal chromaffin cells. Na+ deprivation-induced catecholamine secretion depended on free extracellular Ca2+ concentrations and was almost parallel to 45Ca2+ influx into the cells under various experimental conditions. Furthermore, Na+ deprivation-induced 45Ca2+ influx and catecholamine secretion were actually induced by a relative Na+ concentration gradient across the plasma membrane, but not by simple omission of Na+ from the medium. These results indicate that the deprivation of Na+ from the medium changes the relative Na+ gradient across the plasma membrane and results in Ca2+ influx via a reverse mode of Na+-Ca2+ exchange rather than by inducing Ca2+ entry through Ca2+ channels by eliminating the competition between extracellular Na+ and Ca2+., M. Isosaki, T. Nakashima., and Obsahuje bibliografii
The photoprotective function of leaf betacyanin in water-stressed Amaranthus cruentus plants was examined by comparing leaves of two strains which differ significantly in the amount of betacyanin. At 0, 1, and 2 days after the imposed water stress, leaves were subjected to high-light (HL) treatment to assess their photosynthetic capacity and photoinhibition susceptibility. The water stress equally reduced leaf relative water content (RWC),
gas-exchange rate and chlorophyll (Chl) contents in both leaves, indicating that the severity of water stress was comparable between the strains. Consequently, the extent of photoinhibition after the HL treatment increased in both strains as water stress developed; however, it was significantly greater in acyanic leaves than in betacyanic leaves, suggesting lower photoinhibition susceptibility in the betacyanic strain. The betacyanic leaves also exhibited approximately 30% higher values for photochemical quenching coefficient (qP) during the period of water stress despite the nonphotochemical quenching coefficient (qN) did not differ significantly between the strains. These results may be partially explained by the increased amount of leaf betacyanin under water stress. Moreover, a decrease in Chl content in betacyanic leaves might have enhanced light screening effect of betacyanin by increasing relative abundance of betacyanin to Chl molecule. In addition, reduced Chl content increased light penetrability of leaves. As a result, the extent of photoinhibition at the deeper tissue was exacerbated and the Chl fluorescence emitted from these tissues was more readily detected, facilitating assessment of photoinhibition at deeper tissues where the effect of betacyanic light screening is considered to be most apparent. Our results demonstrated that leaf betacyanin contributes to total photoprotective capacity of A. cruentus leaves by lowering excitation pressure on photosystem II (PSII) via attenuation of potentially harmful excess incident light under water stress. and T. Nakashima, T. Araki, O. Ueno