Acta biochimica et biophysica Hungarica最新文献

In random graph theory it has been proved that with the increasing size of a graph, the proportion of the non-symmetric graphs increases and this class becomes the dominant one while the number of symmetric cases turns to be 'negligible'. Thus the asymmetry (AS) is the generic property. Since nervous systems are representable by graphs or better with special digraphs, the networks, it follows that the brains are asymmetric in a strong sense according to which all cells are distinguishable from each other alone by their internal connections. Such a consequence holds perfectly only if a random evolution or generation of neural networks is supposed. Thus apparent symmetries have to come from heavily controlled (i.e. non random) ontogenetic processes. At the present time the possible total cellular heterogeneity of the various nervous systems has still unclear functional implications. In small nervous systems the odd number of neurons alone is neither a sufficient nor a necessary condition of the asymmetry in the outlined sense.

Sciatic nerves were implanted into the cervical spinal cord as bypass autografts. Nerve fibers growing into the bypass were shown to be authentic dorsal column axons. Ingrowth of axons is dependent of intact basal laminae in the autograft.

We compare the power spectra of activities of neural cultures from the cortex and spinal cord of embryonic rat. The measurements were made in a microelectrode culture chamber by non-invasive methods. The data suggest that the fundamental frequencies of cortical and spinal cultures significantly differ, while the general patterns of the spectra are rather similar.

Patch-clamp technique was used in order to study properties of the steady-state Na-channel in snail neurons. Experiments revealed that Pb-ions, applied extracellularly, close these channels, which are preferably in open state at the resting membrane potential. Elementary currents have a linear current-voltage (I-V) relationship with single channel conductance of 14 pS between -100 and -40 mV both in control saline and in the presence of 50 microM Pb in the pipette. Pb-ions decreased the mean open and increased the mean closed time. It was found that both open and closed times showed little voltage-dependence, however the probabilities of the open and closed times proved to be voltage-dependent. Open and closed time histograms were fitted by one exponential, therefore first order kinetics were assumed for the blocking effect of Pb2+ at the single channel level.

The effects of chronic administration of the calcium channel antagonist verapamil on the anesthetic effects of a novel specific alpha 2-receptor agonist (dexmedetomidine) were studied in rats. It is presumed that this agonist acts on both pre- and postsynaptic alpha 2-adrenoceptors. To determine whether the central postsynaptic receptors are involved in the anesthetic interactions between these drugs, rats were treated with DSP-4 to deplete endogenous norepinephrine. Loss of the righting reflex was used to determine the presence of anesthesia and the duration of hypnosis. Chronic treatment with verapamil (1 or 5 mg/kg) significantly increased the duration of the hypnotic-anesthetic effect of dexmedetomidine. Neither acute treatment with verapamil nor the calcium channel agonist BAY K 8644 (0.5 or 1 mg/kg) influenced the dexmedetomidine-induced hypnosis after DSP-4 treatment. The results seem to support the idea that the hypnotic action of dexmedetomidine can be affected via modulation of the transmembraneous calcium movement in the central nervous system. Further, the data on catecholamine-depleted rats with DSP-4 suggest that the interactions between verapamil and dexmedetomidine may be mediated through presynaptic or homoreceptors on noradrenergic neurons.