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Neurons of the rat spinal cord were stained using the Golgi impregnation method. Successfully impregnated neurons from laminae II, III, and VI were subjected to fractal and nonfractal analyses. Fractal analysis was performed using length-related techniques. Since an application of fractal methods to the analysis of dendrite arbor structures requires caution, we adopted as appropriate a nonfractal method proposing a generalized power-law model with two main nonfractal parameters: (i) the anfractuosity, characterizing the degree of dendritic deviation from straight lines; and (ii) an estimate of the total length of arbor dendrites. The anfractuosity can distinguish between two sets of drawings where the fractal methods failed. We also redefine some basic concepts of fractal geometry, present the ruler-counting method, and propose a new definition of fractal dimension.

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The effects of Mg 2+ on Ni 2+-induced epileptiform bursting activity and input membrane resistance during this activity of leech Retzius neurons were examined using intracellular recordings. To induce epileptiform activity, 3 mmol/l NiCl 2 was added into superfusing Ringer (Ri) saline. To test for dose-dependence of the effects of Mg 2+ on the induced epileptiform activity, MgCl 2 was added in concentrations from 1 mmol/l to 20 mmol/l Mg 2+ to the Ni 2+-containing Ri saline. Input membrane resistance (IMR) was measured in standard Ri, Ni 2+ Ri and 20 mmol/l Mg 2+ Ni 2+ Ri saline. Superfusion with Ni 2+ Ri induced epileptiform bursting activity characterized by generation of paroxysmal depolarization shifts (PDSs). Parameters of epileptiform activity including PDS frequency, PDS duration, PDS amplitude and the number of spikes/PDS were measured. Magnesium suppressed Ni 2+-induced epileptiform activity, significantly reducing values of all parameters observed in a concentration-dependent manner. The highest concentration applied of 20 mmol/l Mg 2+ completely eliminated epileptiform activity. To test for the effect of Mg 2+ on membrane conductance during bursting, IMR was measured. Magnesium significantly increased IMR during bursting suppression.

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