The strength of all chemical synapses can be rapidly up- or down-regulated by their recent activities to reshape the postsynaptic signal through a mechanism of short-term facilitation or depression. It is also true that sensory experience is essential for maturation of cortical circuits and function. We studied the effect of sensory experience on the short-term plasticity in brain slices of rat visual cortex. Repetitive stimulation was applied in layer II/III and the response of pyramidal neuron in layer V was examined by whole-cell recording. We deprived the visual experience of rats by rearing the animals in dark environment.We found that dark rearing (DR) had no effects on paired-pulse interactions of either excitatory postsynaptic currents (EPSCs) or inhibitory postsynaptic currents (IPSCs). However, DR increased the level of IPSCs steady-state depression at stimulation frequency of 20 Hz or more. This result, together with the finding that DR reduced the excitability of neural circuit in visual cortex, suggested a compensatory mechanism, which may be important in enhancing the network excitability at a time when synapses are immature.

To elucidate the temperature dependence and underlying thermodynamic determinants of the elementary Ca21 release from the sarcoplasmic reticulum, we characterized Ca21 sparks originating from ryanodine receptors (RyRs) in rat cardiomyocytes over a wide range of temperature. From 35 C to 10 C, the normalized fluo-3 fluorescence of Ca21 sparks decreased monotonically, but the D[Ca21]i were relatively unchanged due to increased resting [Ca21]i. The time-to-peak of Ca21 sparks, which represents the RyR Ca21 release duration, was prolonged by 37% from 35 C to 10 C. An Arrhenius plot of the data identified a jump of apparent activation energy from 5.2 to 14.6 kJ/mol at 24.8 C, which presumably reflects a transition of sarcoplasmic reticulum lipids. Thermodynamic analysis of the decay kinetics showed that active transport plays little role in early recovery but a significant role in late recovery of local Ca21 concentration. These results provided a basis for quantitative interpretation of intracellular Ca21 signaling under various thermal conditions. The relative temperature insensitivity above the transitional 25 C led to the notion that Ca21 sparks measured at a "warm room" temperature are basically acceptable in elucidating mammalian heart function.

The interleukin-1 (IL-l) system possesses two distinct receptors (type I and type II) which, together with the accessory protein, mediate a multitude of responses to IL-la and IL-l@, including fever. So far, no receptor subtype-specific ligands have been described. Since both types of IL-l receptors occur in the thermoregulatory areas it was unclear which IL-l receptor type mediates fever. We report here that for a series of deletion mutants of human recombinant IL-lb (hrIL-l/I), the affinity of these ligands for the type I IL-1 receptor correlates with their efficacy to evoke the fever response (hrIL-l/I>des-SND 52-54>des-QGE48-50>des-156). Thus, the results suggest that agonist occupancy of the type I IL-l receptor is essential for IL-l/I-mediated fever.