Effect of insulin, proinsulin and pancreatic extract on myelination and remyelination in organotypic nerve tissue in culture.

The effect of insulin, proinsulin and crude pancreatic extract was studied in organotypic nerve tissue cultures, principally in relation to the development of myelin. Cultures were exposed to media supplemented with these substances beginning on the first day of explantation. By 4 days in vitro, there was a good neuritic outgrowth from all the fragments. That from the insulin and pancreatic extract-fed were more profuse and extended further than from the control group. By 8-12 days in vitro it was also possible to observe more myelinated axons in these treated groups. The pattern of changes in the myelin associated enzyme activity, 2',3'-cyclic nucleotide 3'-phosphohydrolase (CNPase) paralleled the differential increase in myelination. Insulin-fed cultures showed a more rapid increase in CNPase activity, which, after 21 days in vitro reached a plateau about 30-50% over that of the controls. Cultures treated with pancreatic extract showed a similar pattern of increased activity, while in proinsulin-treated explants the activity was only significantly higher after 21 days in vitro. To study the effect of these substances on remyelination, well myelinated cultures were completely demyelinated by exposure to anti-white matter antiserum and were subsequently exposed to the same normal control or supplemented media. The amount of myelin and concomitantly the CNPase activity increased rapidly and in the same proportion between the various groups as was observed previously during primary myelination. Insulin as well as crude pancreatic extract and, to some extent, proinsulin demonstrated a marked effect on the time of onset and principally on the total amount of myelin developed by treated cultures as compared to those maintained in normal nutrient medium.