Biomedical subjects
Publications and source records attributed to E Cherubini.
The action of glycine (Gly) on rat cortical neurons was studied. Gly, iontophoretically applied, hyperpolarized the membrane potential, blocked the firing rate and decreased the amplitude of EPSP-IPSP sequences. Generally the membrane resistance during the aminoacid ejection decreased. The role of Gly in the rat cortical inhibition is discussed.
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Intracellular recordings from CA1 pyramidal neurones of the rat hippocampal slice preparation were used to study changes in neuronal excitability induced by the excitatory amino acid analogues kainate (KA) and N-methyl-D-aspartate (NMDA). Low concentrations of bath-applied KA (50-200 nM) or NMDA (1-3 microM) elicited a relatively small membrane depolarization and increased the number of spikes fired by a constant current pulse. The spike after-hyperpolarization (AHP) was depressed by KA but enhanced by NMDA. After blockade of the voltage-sensitive Na+ conductances with tetrodotoxin, intracellularly applied current pulses elicited Ca2+ spikes. Whereas NMDA always increased the duration (and number) of Ca2+ spikes and of their AHP, KA conversely reduced these spikes and (in almost half of the cells tested) the late phase of their AHP. When Ba2+ was used to replace extracellular Ca2+, prolonged plateau potentials developed and were also blocked by KA. NMDA had no effect on Ba2(+)-dependent responses. These results suggest that low concentrations of KA profoundly modified the electroresponsiveness of CA1 neurones perhaps by depressing a Ca2(+)-dependent K+ conductance mechanism responsible for dampening the excitability of these cells.
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Several neurotoxins have been isolated from bee venom. One of these, the mast cell degranulating peptide (MCD), releases histamine from mast cells and on central administration produces arousal at low concentrations and convulsions at higher doses. These effects are mediated through specific high-affinity binding sites which are concentrated in cortical structures, notably the hippocampus. This structure appears to be the source of changes in the electrocorticogram that follow injections of MCD into the cerebral ventricle, and which induce a quasi-permanent hippocampal theta rhythm in the motionless rat alternating with epileptiform spike waves. We report here that brief application of MCD to the CA1 region of hippocampal slices induces long-term potentiation, that is, a long-lasting increase in the efficacy of synaptic transmission. This potentiation seems to be indistinguishable from the classical LTP produced by trains of high-frequency electrical stimulation and considered to be related in some way to memory. Using binding to synaptosomal membranes and radioimmunoassay techniques, we have also found an endogenous peptide equivalent of MCD in brain extracts. This raises the possibility that a MCD-like peptide may be important in long-term potentiation.
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Changes of the H reflex during sleep were studied in 13 children with cerebral palsy (8 with spastic tetraplegia, 2 with a mixed form of cerebral palsy without spasticity, 3 with hypotonic diplegia or tetraplegia). These modifications were compared with those of 5 normal children of the same age. During repeated night recordings, responses in the calf muscle elicited by electrical stimuli to the posterior tibial nerve were studied at the same time as the EEG, EOG and EMG of the mental muscles. The results show that:--in normal children the max H reflex progressively decreases in amplitude from wakefulness to REM sleep; -- in spastic patients there is only a slight decrease in the H reflex in NREM sleep and no significant change in REM sleep; the amplitude of the H reflex is always greater than that in the control group; -- in the dystonic and hypotonic group the results obtained are similar to those of the control group. From these results one may draw the conclusion that in spastic patients as opposed to the control, dystonic and hypotonic groups, normal balance between the function of supraspinal systems regulating the amplitude of the spinal reflexes is alterated probably through the scarce functionality of the supraspinal inhibitory structures.
Starting from biochemical hypotheses on hepatic encephalopathy, which presuppose at the basis of this disease first of all some modifications of the plasmatic values of octopamine, ammonia, serotonin and of particular aromatic aminoacids, the Authors compared the levels of ammoniemia and of octopaminemia with eegraphic data, in two groups of cirrhotic patients, operated of porto-cava anastomosis (16 patients) ad of mesenterico-cava by-pass (24 patients). All this in order to value if there are significant correlations between these values and the cerebral damage and also if there are differences between the two types of operation. Attained data show a good correlation between neuropsychiatric symptomatology and importance of the cerebral damage noticeable at the E.E.G. As to the possible correlations existing between biochemical data and E.E.G., while as to plasmatic octopamine no significant modifications were found, as to ammoniemia, highest values correspond to findings of greater cerebral compromission. Moreover, it seems that between the two types of operations, the mesenterico-cava by-pass is the one that allows a better clinical and eegraphic evolution.
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