RESPONSES OF MATURE AND AGED SYMPATHETIC NEURONS TO LAMININ AND NGF -AN IN-VITRO STUDY

Whilst the potent effects of NGF and laminin on developing neurons are well documented, relatively little is known about the effects of, or altered availability of or altered responsiveness to, these substances on the growth of adult neurons. We have therefore examined this quest ion using explant cultures of sympathetic neurons from the superior ce rvical ganglion (SCG) of mature and aged rats. Explants were grown on substrata containing different doses of laminin, either with or withou t added NGF in culture medium containing FCS. Individually, laminin an d NGF had relatively small. effects on neurite outgrowth and length, w hich tended to be reduced in old neurons. In contrast, laminin in the presence of exogenous NGF exerted a powerful effect on nerve growth wh ich was substantially greater than the sum of the effects of the indiv idual factors. This synergy was evident in all experimental groups and was greatest in old explants at high doses of laminin, where growth w as comparable to that of mature neurons. The dose-response curve of ol d neurons to laminin in the presence of added NGF indicated reduced re sponsiveness. These results suggest that variations in the availabilit y of laminin and/or exogenous NGF, together with altered patterns of n euronal responsiveness, may contribute to impaired neuronal plasticity in old age.