Structural Lability Research Articles

The relationship between certain forms of potentials and the variations in brain excitability (based on EEG, recorded during photic stimuli triggered by rhythmic brain potentials)

1. 1. It is known that timing of stimuli with reference to the phase of the brain waves affects the pattern of activity. Investigation into the exact nature of these relationships, however, raises considerable difficulties. Pertinent experimental data recorded in the literature reveal the contradictory results obtained by different investigators. 2. 2. The problem has been studied by the authors by using stimuli triggered by brain potential rhythms, with varying stimulus to phase relations. 3. 3. It has been shown that, within one single complete alpha cycle, there may be one, two, or even three, time zones during which the application of a stimulus evokes a synchronization of the activity. There may also be one, two, or three, time zones during which stimuli evoke enhanced desynchronization of potentials. 4. 4. There may be various degrees of dependence of the EEG pattern on the relationship between the stimulus and the phase of the brain wave, and there may be different degrees of the stability of this relationship. These may change under the effects of drugs and with alteration of the patient's condition. The results of this investigation are analyzed in terms of the current views on the relations between brain waves and variations in brain excitability, due consideration being given to Wedenski's concepts of the lability of neurodynamic structure.

Organization of mitochondrial DPN-linked systems: II. Regulation of alternative electron transfer pathways

Structural labilization of mitochondria, as induced by pretreatment in the presence of Ca ++ or in the absence of Mg ++, in both cases with hexo-kinase-glucose in the preincubating medium, results in a decreased sensitivity of respiration to amytal and antimycin A, as tested in the presence of DPN and cytochrome c, and with glutamate as a substrate. The amytal and antimycin A-sensitivity of respiration is restored by ATP and Mn ++. If mitochondria, brought to a DPN deficient state by preincubation in the absence of Mg ++, are treated for five minutes with ATP and Mn ++, they become partially inaccessible to added DPN. Upon treatment of mitochondria with increasing concentrations of Ca ++, or for increasing periods of time in the absence of Mg ++, there is an initial disparity between the rates at which external DPN and DPNH gain access to the intramitochondrial enzymic sites. Upon relatively mild treatment, the mitochondrial complement of DPN is lost and external DPN acquires free access to the mitochondrial dehydrogenases; at the same time, external DPNH has significantly lower access to the amytal sensitive DPNH-cytochrome c reductase than has internal DPNH. More drastic treatment results in a gradual decrease of the level of the DPN-dependent, amytal-sensitive respiration, but this can be restored by ATP and Mn ++. These results have been interpreted to indicate that DPN and DPNH are reversibly associated with the mitochondrial structure, but the association of DPNH is firmer than that of DPN. The experimental data presented in Parts I and II of the present work are discussed in relation to the role played by ATP in maintaining the mitochondrial structure in a reversible state of organization, and to the implications of this mechanism to the functional pattern of the mitochondrial energy transfer system. It is postulated that a reversible labilization of the mitochondrial structure may constitute a physiological principle of metabolic control.