PubMed · 14250989
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P W GAGE, J I HUBBARD. 1964-08-08. IONIC CHANGES RESPONSIBLE FOR POST-TETANIC HYPERPOLARIZATION.. https://doi.org/10.1038/203653a0
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Cortical activity depends on the balance between excitatory and inhibitory influences. Several different excitatory and inhibitory systems in the human motor cortex can be tested by transcranial magnetic stimulation (TMS). While considerable information is known about these different inhibitory and excitatory phenomena individually, how they are related to each other and how they interact is not well understood. Several recent studies have investigated the interactions between some of these circuits by applying them together. It has been found that short-interval intracortical inhibition (SICI) and long-interval intracortical inhibition (LICI) are mediated by different circuits. LICI appears to inhibit SICI, which may occur through presynaptic GABA(B) receptors. Interhemispheric inhibition elicited by stimulation of the contralateral motor cortex also inhibits SICI and may share inhibitory mechanisms with LICI. Long-interval afferent inhibition induced by median nerve stimulation inhibits LICI but does not interact with SICI. Based on these results, a model of interactions between different inhibitory systems that can be tested and refined in the future is proposed. Further studies of the interaction between different cortical inhibitory and excitatory circuits should improve our understanding of the functional organization of the motor cortex and allow better interpretation of abnormal findings in disease states. It may also be developed into a new way of studying the pathophysiology of diseases and the effects of intervention.
Reciprocal inhibition between ankle flexors and extensors has been the subject of numerous studies in Man. They have demonstrated that this reciprocal inhibition is in all likelihood caused by a disynaptic pathway at least partly fed by Ia afferents. It is thus generally agreed that this reciprocally organized inhibition between ankle flexors and extensors in Man is similar to the reciprocal Ia inhibition described in the cat. This conclusion has, however, been challenged, when Jankowska and McCrea described in the cat a non-reciprocal group I inhibition involving interneurones co-excited by Ia and Ib afferents and mediating inhibition to both antagonistic and non-antagonistic motoneurones. The only way to distinguish between reciprocal Ia inhibition and non-reciprocal group I inhibition is to test if the inhibition is blocked by recurrent inhibition, since only Ia interneurones are inhibited by recurrent inhibition. In the present study, reciprocal inhibition from soleus to tibialis anterior was thus investigated following activation of soleus-coupled Renshaw cells in normal human subjects. It was found that reciprocal inhibition induced in tibialis anterior motoneurones by the activation of soleus group I afferents is deeply depressed by activation of soleus-coupled Renshaw cells. This finding provides the missing data to identify disynaptic inhibition between antagonistic ankle muscles as a reciprocal Ia inhibition.
The kinetics of Lactobacillus plantarum inactivation by pulsed electric fields (PEF) was studied in two different growth stages (exponential and stationary), but in the same reference medium (0.6% peptone water). Electric field intensity and treatment time varied from 20 to 28 kV/cm and 30 to 240 micros, respectively. The experimental data showed that cells in the exponential growth stage were more sensitive to PEF treatment than those in the stationary stage. The inactivation data were adjusted to the Bigelow and Hülsheger models and the Weibull frequency distribution function, and constants were calculated for both growth stages in each model. The models were tested and their accuracy was assessed by using the Accuracy Factor. According to this parameter, the Weibull frequency distribution function gave better fittings for the inactivation by PEF than Bigelow or Hülsheger models. On the other hand, the Bigelow model gave a good accuracy factor and is simpler.