Extracellular translational motion in the brain is generally considered to be governed by diffusion and tortuosity. However, the brain as a whole has a significant ζ-potential, thus translational motion is also governed by electrokinetic effects under a naturally occurring or applied electric field. We have previously measured ζ-potential and tortuosity in intact brain tissue; however, the method was tedious. In this work, we use a four-electrode potentiostat to control the potential difference between two microreference electrodes in the tissue, creating a constant electric field. Additionally, some alterations have been made to simplify our previous procedure. The method entails simultaneously injecting two 70 kDa dextran conjugated fluorophores into rat organotypic hippocampal cultures and observing their mobility using fluorescence microscopy. We further present two methods of data analysis: regression and two-probe analysis. Statistical comparisons are made between the previous and current methods as well as between the two data analysis methods. In comparison to the previous method, the current, simpler method with data analysis by regression gives statistically indistinguishable mean values of ζ-potential and tortuosity, with a similar variability for ζ-potential, −21.3 ± 2.8 mV, and a larger variability for the tortuosity, 1.98 ± 0.12. On the other hand, we find that the current method combined with the two-probe analysis produces accurate and more precise results, with a ζ-potential of −22.8 ± 0.8 mV and a tortuosity of 2.24 ± 0.10.
Abstract: This study addresses the possible involvement of an agonist‐induced postischemic hyperactivity in the delayed neuronal death of the CA1 hippocampus in the rat. In two sets of experiments, dialytrodes were implanted into the CA1 either acutely or chronically (24 h of recovery). During 20 min of cerebral ischemia (four‐vessel occlusion model) and 8 h of reflow, we followed extracellular amino acids and multiple‐unit activity. Multiple‐unit activity ceased within 20 sec of ischemia and remained zero during the ischemic insult and for the following 1 h of reflow. During ischemia, extracellular aspartate, glutamate, taurine, and ‐γ‐aminobutyric acid increased in both acute and chronic experiments (seven‐to 26‐fold). Multiple‐unit activity recovered to preischemic levels following 4–6 h of reflow. In the group with dialytrodes implanted acutely, the continuous increase in multiple‐unit activity reached 110% of basal at 8 h of reflow. In the group with dialytrodes implanted chronically, multiple‐unit activity recovered faster and reached 140% of control at 8h, paralleled by an increase in extracellular aspartate (5.5‐fold) and glutamate (twofold). In conclusion, the postischemic increase of excitatory amino acids and the recovery of the neuronal activity may stress the CA1 pyramidal cells, which could be detrimental in combination with, e.g., postsynaptic impairments.
Abstract: The effect of severe insulin‐induced hypoglycemia on the extracellular levels of endogenous amino acids in the rat striatum was examined using the brain microdialysis technique. A characteristic pattern of alterations consisting of a 9–12‐fold increase in aspartate (Asp), and more moderate increases in glutamate (Glu), taurine (Tau), and γ‐aminobutyric acid (GABA), was noted following cessation of electroencephalographic activity (isoelectricity). Glutamine (Gln) levels were reduced both during and after the isoelectric period and there was a delayed increase in extracellular phosphoethanolamine (PEA) content. The effects of decortication and excitotoxin lesions on the severe hypoglycemia‐evoked efflux of endogenous amino acids in the striatum were also examined. Decortication reduced the release of Glu and Asp both 1 week and 1 month post‐lesion. The efflux of other neuroactive amino acids was not affected significantly. In contrast, GABA, Tau, and PEA efflux was attenuated in kainate‐lesioned striata. Glu and Asp release was also reduced under these conditions, and a smaller decrease in extracellular Gln was noted. These data suggest that GABA, Glu, and Asp are released primarily from their transmitter pools during severe hypoglycemia. The releasable pools of Tau and PEA appear to be located in kainate‐sensitive striatal neurons. The significance of these results is discussed with regard to the excitotoxic theory of hypoglyce‐mic cell death.
'%3e%3cpath fill='%23012169' d='M0 0v30h60V0z'/%3e%3cpath stroke='%23fff' stroke-width='6' d='m0 0 60 30m0-30L0 30'/%3e%3cpath stroke='%23C8102E' stroke-width='4' d='m0 0 60 30m0-30L0 30' clip-path='url(%23b)'/%3e%3cpath stroke='%23fff' stroke-width='10' d='M30 0v30M0 15h60'/%3e%3cpath stroke='%23C8102E' stroke-width='6' d='M30 0v30M0 15h60'/%3e%3c/g%3e%3c/svg%3e)
