Journal of Neuroscience, Vol 2, 448-462, Copyright © 1982 by Society for Neuroscience
Electrophysiology and morphology of the developing hippocampus of fetal rabbits
PA Schwartzkroin and DD Kunkel
The pyramidal neurons of fetal rabbit hippocampus were studied using
intracellular electrophysiological techniques in in vitro slice
preparations. Correlative light and electron microscopic analyses were
carried out on hippocampus during the 21st through the 29th day of fetal
gestation. In intracellular experiments, neurons with all-or-none action
potentials and near-adult level resting potentials were found even in the
youngest preparations. Synaptic activity, however, was rare until about 24
days of gestation. CA1 neurons showed primarily excitatory synaptic
potentials during fetal development, whereas CA3 neurons displayed both
inhibitory and excitatory postsynaptic potentials at early stages.
Anatomical studies suggested that pyramidal cell precursors were still
dividing and migrating at 21 days; by 29 days, cellular migration was
completed, and cellular intercommunication in the form of synapses was
increasing. These experiments demonstrate that fetal central nervous system
(CNS) material can be studied electrophysiologically without growing tissue
in culture. Our results suggest that the newly differentiated hippocampal
neurons have a limited repertoire of activities. Such data may provide a
link between in vivo studies of postnatal CNS development and cell and
tissue culture investigations of the properties of immature neurons.