Insulin-like immunoreactivity in the brain of two hagfishes, Eptatretus stouti and Myxine glutinosa.

Immunocytochemical investigation of the brains of hagfish Myxine glutinosa and Eptatretus stouti with antisera raised against salmon insulin revealed the presence of groups of immunoreactive cells discretely localized in the mid- and hindbrain of both species. Subpopulations of these cells reacted weakly with antisera against Myxine islet insulin and equivocally with anti-bovine insulin serum. Extracts prepared from Myxine brain were subject to gel filtration and were found by radioimmunoassay to contain two forms of insulin-like material, one of large molecular weight (less than 66 kDa) and another smaller molecule (6 kDa). The relationship of these molecules to the insulin-related growth factor family of neurohormonal peptides is discussed and their potential function assessed in terms of a possible homology with Muller-type cells and involvement in axonal regeneration phenomena.