Journal of Neurophysiology, Vol 54, Issue 4 807-817, Copyright © 1985 by APS
Electrotonic parameters of neurons following chronic ethanol consumption
D. Durand and P. Carlen
The electronic parameters of nerve cells in the dentate gyrus following
long-term ingestion of ethanol were studied in vitro. The ethanol was
administered in a liquid diet for a period of 20 wk followed by a 3-wk
withdrawal period. A control group received a similar diet with the ethanol
replaced by maltose-dextrins. Intracellular recordings were obtained from
44 neurons, and the voltage decays following current injections were
analyzed with a recent electrical model of granule cells to take into
account a somatic shunt already detected in previous studies. The new model
accurately accounted for the fast voltage transients and showed that the
membrane time constant in the dendrites is, on average, five times larger
than the somatic time constant. Injection of horseradish peroxidase into
the neurons for the morphological analysis showed that neurons in the
ethanol group have a longer dendritic tree than neurons in the control
group. Estimation of the membrane surface area showed that the membrane
area in the dendrites is at least 60% greater (in both control and ethanol
groups) when the membrane foldings and irregularities are taken into
account. The results of the modeling analysis showed that the membrane time
constant and the input resistance are not affected by ethanol. However, the
membrane resistance is significantly increased in the ethanol group (6,632
versus 18,460 omega X cm2), and the capacitance is significantly decreased
(4.48 versus 1.71 microF/cm2). The electrotonic length is also increased by
chronic ethanol treatment (0.85 versus 0.94). Higher values of membrane
specific resistance (Rm) mean larger transmission coefficients. However,
since the neurons from the ethanol group are on average longer than neurons
in the control group, it is suggested that the change in Rm compensates for
the increase in the length of the dendrites, thereby maintaining a value of
the electrotonic length under 1.0. The observed changes in the passive
parameters are in opposite direction from the recently measured effect of
acute doses of ethanol on hippocampal neurons. These results support a
model of chronic alcohol intake where homeostatic adaptive changes lead to
the development of long-term changes in cellular physiology.
