| Abstract: | Elevated levels of 3′5′ adenosine monophosphate (cyclic AMP) stimulate a wide variety of cellular events including aggregation, differentiation, morphological expression, pigment migration, and secretion. The role of cyclic AMP in these events prompted our present study of embryonic chick dorsal root ganglia. Test substances were applied to cultures during the routine feeding procedure. Their development was quantitatively evaluated on the basis of explant size, length of glial-like outgrowth, distribution of growth, neurite number, length, diameter, and degree of arborization. These parameters were all shown to be independent of each other. The high variability of in vitro neurite development necessitated the use of over 100 cultures per treatment group. Cultures treated with 5′ AMP exhibited no significant differences from controls. Those treated with cyclic AMP, dibutyryl cyclic AMP, or Nerve Growth Factor (NGF) exhibited statistically significant increases in area of outgrowth, the number of neurites per culture, and in diameters, lengths, and degree of neurite arborization. The growth promoting activity of dibutyryl cyclic AMP and NGF were greater than those of cyclic AMP. Electron microscopic study shows neurites formed under the influence of cyclic AMP or its dibutyryl derivative to resemble those grown in NGF. These studies suggest the possibility that cyclic AMP stimulates neurite growth by mediating the process of microtubule (MT) assembly. They further prompt us to speculate that one way NGF enhances neurite development is by stimulating MT assembly via a “Second Messenger System”. |
