Journal of Neurophysiology, Vol 70, Issue 4 1585-1592, Copyright © 1993 by APS
Monosynaptic EPSPs in primate lumbar motoneurons
J. S. Carp
Wadsworth Center for Laboratories and Research, New York State Department of Health, Albany 12201-0509.
1. Homonymous and heteronymous monosynaptic composite excitatory
postsynaptic potentials (EPSPs) were evaluated by intracellular recordings
from 89 motoneurons innervating triceps surae (n = 59) and more distal (n =
30) muscles in 14 pentobarbital-anesthetized monkeys (Macaca nemestrina).
2. Homonymous EPSPs were found in all motoneurons tested. The mean values
+/- SD for maximum EPSP amplitude of triceps surae motoneurons were 2.5 +/-
1.3, 1.8 +/- 1.3 and 4.5 +/- 2.0 mV for medial gastrocnemius, lateral
gastrocnemius, and soleus motoneurons, respectively. Heteronymous EPSPs
were almost always smaller than their corresponding homonymous EPSPs. 3.
Triceps surae EPSP amplitude was larger in motoneurons with higher input
resistance. However, this relationship was weak, suggesting that factors
related to input resistance play a limited role in determining the
magnitude of the EPSP. 4. The mean ratio +/- SD of the amplitude of the
EPSP elicited by combined stimulation of all triceps surae nerves to the
amplitude of the algebraic sum of the three individual EPSPs was 0.95 +/-
0.05. This ratio was greater in motoneurons with lower rheobase. 5. Some
patterns of synaptic connectivity in the macaque are consistent with
previously reported differences between primates and cat (e.g.,
heteronymous EPSPs elicited by medial gastrocnemius nerve stimulation in
soleus motoneurons are small in macaque and other primates but large in
cat). However, no overall pattern emerges from a comparison of the
similarities and differences in EPSPs among species in which they have been
studied (i.e., macaque, baboon, and cat). That is, there are no two species
in which EPSP properties are consistently similar to each other, but
different from those of the third species.(ABSTRACT TRUNCATED AT 250 WORDS)
