[A light microscopic study of the axonal collaterals of the lumbar motoneurons in the spinal cord of the frog Rana ridibunda].

By using intracellular injection of horseradish peroxidase into the lumbar motoneurones of the isolated spinal cord of the frog Rana ridibunda the structure of axon collaterals was studied. It was shown that about 50% of the HRP-stained cells had mainly one axon collateral of the 1st order. The subsequent branching patterns of the collaterals showed considerable variations. The number of swellings in various collaterals was from 10 up 100. The mean diameter of swellings varied from 0.8 up 10.0 microns. It is believed that the axon collateral swellings from contacts on the dendrites of the nerve cells mainly. Apparent axosomatic contacts were revealed on the motoneurons and small nerve cells. As in the cat, collateral swellings were found on the dendrites of the parent motoneuron. Obtained morphological data the structure of motor axon collaterals in the frog are compared with those in the cat. Functional significance of the axon collateral in the frog is discussed.