DORSAL ROOT AFFERENT FIBER TERMINATION IN THE SPINAL CORD OF THE TURTLE TESTUDO HORSFIELDI AND 3-DIMENSIONAL
RECONSTRUCTION OF THE SENSORY-MOTONEURON CONNECTION
N. M. Chmykhova,1 O. A. Karamian,1 V. M. Kozhanov,1 N. P. Vesselkin,1
X.-P. Clemann 2
1 I. M. Sechenov Institute RAS, St. Petersburg, Russia, and 2 Institute of Physiology, University of Bern, Switzerland;
1 e-mail: nchmykhova@mail.ru
HRP tracing methods and computer reconstruction were used to study the structural organization of senso-ry-motoneuron connections in the turtle. HRP was
applied through suction electrodes to thin dorsal and ventral root filaments of superfused isolated lumbar spinal cord of the turtle Testudo horsfieldi. Single
motoneurons were labeled iontophoretically with the use of intracellular glass microelectrodes. Labeled elements were examined by light microscopy. The Eutectic
Neuron Tracing System and its associated program were used for 3-D reconstructions and morphometry. The distribution of dorsal root afferent fibers and their
terminations were presented in a new scheme in which, beside the well known zones, new ones were shown in the Lissauer zone, motor nuclei, ventrolateral
funiculus and in the contralateral medial gray matter (IV-V laminae). Unlike in the frog, the motoneuron dendritic field in the turtle was restricted to an ellipsoid space
having a short axis in the rostro-cau-dal direction (300-500 μm). The dorsal root afferent fibers connected to motoneurons produced very short branches
(50-70 μm) in a restricted rostro-caudal direction. One dorsal root fiber collateral had about 80 synapselike enlargements (approximately 10-fold fewer than in the
frog). The putative sensory-motoneuron contacts were found on the I-VII order dendritic segments of the dorsal and ventromedial dendritic trees. It was shown that in
the turtle only one first order collateral of the dorsal root fiber participated in the sensory-motoneuron connection with a small number (about 4) of putative contacts,
which was also less than in the frog by a factor of 10. The simplicity of the synapse structure in the turtle is likely to be compensated through the higher efficiency
of the signal transmission which is comparable to that in mammals.
Key words: spinal motoneurons, dorsal root afferent fibers, horseradish peroxidase, 3-dimensional reconstruction, sensory-motoneuron
connection, turtle
Back
Contents
Main
|
