The organization of the electromotor nucleus and extraocular motor nuclei in the stargazer (Astroscopus y-graecum).

The organization of the oculomotor and electromotor systems was examined in the stargazer, a teleost. The electromotor system in these animals is a derivative of the oculomotor system. The extraocular motor nuclei and nerves consist of approximately equal numbers of motoneurons and axons (about 100 per muscle). In contrast, the electromotor axons appear to branch several times within the intracranial portion of the IIIrd nerve. The topographical organization of the motoneurons was examined using retrograde transport of horseradish peroxidase injected into the electric organ or eye muscles. Electromotor and oculomotor neurons form distinct populations. Each electric organ receives a strong ipsilateral and a weak contralateral innervation. Individual eye muscles receive unilateral innervations with the expected laterality. Within the oculomotor nucleus there is some topographical separation of motoneurons innervating each muscle. Antidromic field potentials confirm the identity of the electromotor nucleus.