POSTSYNAPTIC POTENTIALS IN TOAD'S SPINAL MOTONEURONS DUE TO MUSCLE AFFERENT VOLLEYS

Publisher Website
Google Scholar
Abstract
Synaptic activities in the rostral segments (II, III and IV) of toad''s spinal cord in situ were investigated by recording intracellular potentials of motoneurons. In response to an afferent volley in the ipsilateral nerve branch to triceps or biceps muscle there appeared in some motoneurons a monosynaptic EPSP [excitatory post-synaptic potential] from which a spike discharge occurred in some instances, without any superposition of delayed PSP''s. Some other motoneurons responded with a typical IPSP [inhibitory post-synaptic potential], while the rest with EPSP''s or insignificant undulatory changes of membrane potential, all starting at longer latencies than the monosynaptic delay. Measured from the arrival of afferent volleys at the surface of the cord, the latencies of the monosynaptic EPSP''s and the earliest IPSP''s were 154 [plus or minus] 0.042 msec. and 3.06 [plus or minus] 0.113 msec. respectively (22-24cC). The latter is reasonably regarded to involve an extra synaptic delay. EPSP and IPSP were nearly equal in their time course. The rise time and the time constant of decay of EPSP are 2.10 [plus or minus] 0.026 msec, and 8.0 [plus or minus] 0.6 msec, respectively, and those of IPSP are 2.15 [plus or minus] 0.211 msec. and 8.0 [plus or minus] 0.97 msec. (22-24[degree]C). Observations were also made on the equilibrium potential of IPSO which was found to be 10 to 20 mV more hyperpolarized than the normal resting potential.