Electron microscopic observations on the retino-preoptic pathway of Rana temporaria L.

Electron microscopic observations confirm the presence of optic terminals of retinal origin in the preoptic area of Rana temporaria. After unilateral section of the optic nerve, degenerating axon terminals were observed among the neurosecretory cells of the preoptic nucleus, both ipsilaterally and contralaterally. The retino-preoptic terminals apparently establish axo-dendritic synapses with non-neurosecretory neurons. Many more degenerating fibres were seen in the ipsilateral preoptic nucleus than in the contralateral nucleus. These are presumed to pass through and to cross in the dorsal posterior part of the optic chiasm.