Disinhibition-induced bursting activity in cultures of fetal rat spinal cord is mainly controlled by intrinsic spiking with subsequent recurrent excitation of the network through glutamate synaptic transmission, and by autoregulation of neuronal excitability. Here we investigated the contribution of the electrogenic Na/K pump to the autoregulation of excitability using extracellular recordings by multielectrode arrays (MEAs) and intracellular whole cell recordings from spinal interneurons. The blockade of the electrogenic Na/K pump by strophanthidin led to an immediate and transient increase in the burst rate together with an increase in the asynchronous background activity. Later, the burst rate decreased to initial values and the bursts became shorter and smaller. In single neurons, we observed an immediate depolarization of the membrane during the interburst intervals concomitant with the rise in burst rate. This depolarization was more pronounced during disinhibition than during control, suggesting that the pump was more active. Later a decrease in burst rate was observed and, in some neurons, a complete cessation of firing. Most of the effects of strophanthidin could be reproduced by high K+-induced depolarization. During prolonged current injections, spinal interneurons exhibited spike frequency adaptation, which remained unaffected by strophanthidin. These results suggest that the electrogenic Na/K pump is responsible for the hyperpolarization and thus for the changes in excitability during the interburst intervals, although not for the spike frequency adaptation during the bursts.
"Several proposals have been made concerning other potential burst-terminating mechanisms, including mechanisms based on (a) slowly activating voltage-dependent potassium current (e.g., Butera et al., 1999a, Model 2) or Ca 2þ -activated potassium current (suggesting [Ca 2þ ] in accumulation during bursts via high voltage-activated calcium currents, e.g., Bevan and Wilson, 1999; El Manira et al., 1994; Ryczko et al., 2010), (b) Na þ -activated potassium currents (e.g., Krey et al., 2010; Wallen et al., 2007; Yuan et al., 2003), and (c) activation of the Na þ /K þ electrogenic pump (e.g., Ballerini et al., 1997; Darbon et al., 2003; Del Negro et al., 2009; Krey et al., 2010). The two latter mechanisms suggest an important role of [Na þ ] in accumulation during bursts. "
[Show abstract][Hide abstract] ABSTRACT: The pre-Bötzinger complex (pre-BötC), a neural structure involved in respiratory rhythm generation, can generate rhythmic bursting activity in vitro that persists after blockade of synaptic inhibition. Experimental studies have identified two mechanisms potentially involved in this activity: one based on the persistent sodium current (INaP) and the other involving calcium (ICa) and/or calcium-activated nonspecific cation (ICAN) currents. In this modeling study, we investigated bursting generated in single neurons and excitatory neural populations with randomly distributed conductances of INaP and ICa. We analyzed the possible roles of these currents, the Na(+)/K(+) pump, synaptic mechanisms, and network interactions in rhythmic bursting generated under different conditions. We show that a population of synaptically coupled excitatory neurons with randomly distributed INaP- and/or ICAN-mediated burst generating mechanisms can operate in different oscillatory regimes with bursting dependent on either current or independent of both. The existence of multiple oscillatory regimes and their state dependence may explain rhythmic activities observed in the pre-BötC under different conditions.
Progress in brain research 04/2014; 209:1-23. DOI:10.1016/B978-0-444-63274-6.00001-1 · 2.83 Impact Factor
"can entail a membrane depolarization, thus a disinhibition, even in the spinal cord neurons (Darbon et al., 2003); this would explain the finding of a cervical N13 recovery cycle suppressed in a lesser degree in migraine patients compared to healthy subjects (Valeriani et al., 2005). Some years later, the same authors showed that in pediatric migraine the abnormal SEP recovery cycle can be partially restored by an effective prophylactic treatment with topiramate (Vollono et al., 2010). "
[Show abstract][Hide abstract] ABSTRACT: Although primary headaches are very prevalent also in pediatric age, most neurophysiologic studies in these diseases concerned only the adulthood. The neurophysiologic investigation of the pathophysiological mechanisms subtending migraine and tension-type headache in children and adolescents could be particularly interesting, since during the developmental age the migrainous phenotype is scarcely influenced by many environmental factors that can typically act on adult headache patients. The neurophysiologic abnormality most frequently found in adult migraineurs, that is the reduced habituation of evoked potentials, was confirmed also in migraine children, although it was shown to involve also children with tension-type headache. Some studies showed abnormalities in the maturation of brain functions in migraine children and adolescents. While the visual system maturation seems slowed in young migraineurs, the psychophysiological mechanisms subtending somatosensory spatial attention in migraine children are more similar to those of healthy adults than to those of age-matched controls. There are some still unexplored fields that will have to be subjects of future studies. The nociceptive modality, which has been investigated in adult patients with primary headaches, should be studied also in pediatric migraine. Moreover, the technique of transcranial magnetic stimulation, not yet used in young migraineurs, will possibly provide further elements about brain excitability in migraine children.
Clinical neurophysiology: official journal of the International Federation of Clinical Neurophysiology 06/2013; 125(1). DOI:10.1016/j.clinph.2013.04.335 · 3.10 Impact Factor
"Yuan et al., 2003; Wallen et al., 2007; Krey et al., 2010); and (iii) activation of the Na + /K + electrogenic pump (e.g. Ballerini et al., 1997; Darbon et al., 2003; Del Negro et al., 2009; Krey et al., 2010). The two latter mechanisms suggest an important role of intracellular Na + accumulation during bursts. "
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