Some mammalian retinae lack FMRF-amide-like immunoreactive efferents.

The retinae of a monkey, cat, rat and mouse were examined for FMRF-amide immunoreactivity, a marker for efferent fibers in the retinae of lower vertebrates. No FMRF-amide immunoreactive retinal fibers were found despite their presence in the rat CNS. Therefore, we conclude that efferent fibers, if present in mammalian retinae, are immunologically different from efferent fibers in lower vertebrates.