Electrical characteristics of sensory neurons of Hirudo medicinalis

During intracellular polarization of identified sensory neurons of the leech by square pulses of hyperpolarizing current electrical parameters of the cell membranes were determined: input resistance of the neuron Rn, time constant of the membrane τ, the ratio between conductance of the cell processes and conductance of the soma ρ, the resistance of the soma membrane rs, the input resistance of the axon r a , capacitance of the membrane Cs, and resistivity of the soma membrane Rs. The results obtained by the study of various types of neurons were subjected to statistical analysis and compared with each other. Significant differences for neurons of N- and T-types were found only between the values of τ, Cs, and Rs (P<0.01). These parameters also had the lowest coefficients of variation. The surface area of the soma of the neurons, calculated from the capacitance of the membrane (the specific capacitance of the membrane was taken as 1 µF/cm2) was 7–10 times (N-neurons) or 4–6 times (T-neurons) greater than the surface area of a sphere of the same diameter. The resistivity of the soma membrane Rs was 35.00 kΘ·cm2 for cells of the N-type and 19.50 kΘ·cm2 for T-neurons. The reasons for the relative stability of this parameter compared with the input resistance of the cell (coefficient of variation 22–7 and 53–31% respectively) are discussed. The possible effects of electrical characteristics on the properties of repeated discharges in neurons of different types also are discussed.