ENHANCEMENT OF CHOLINE-ACETYLTRANSFERASE ACTIVITY IN COCULTURE OF RATSEPTAL AND HIPPOCAMPAL-NEURONS

We report that choline acetyltransferase (ChAT) activity and neuronal survival were enhanced in rat septal neurons cocultured with hippocamp al neurons. The enhancement of ChAT activity also occurred as a result of the addition of hippocampal conditioned medium (HpCM). When septal neurons from embryonic day 17 (E17) rats were cocultured with hippoca mpal neurons, ChAT activity was increased 2-fold compared with homogen eous culture of septal neurons. By contrast, no increase in ChAT activ ity was observed in coculture of septal and neocortical neurons. Treat ment with HpCM obtained from cultured E19 rat hippocampal neurons enha nced the ChAT activity of E17 rat septal neurons. The enhancement of C hAT activity caused by coculture with hippocampal neurons and that cau sed by the addition of HpCM were not blocked by the addition of anti-n erve growth factor (NGF) antibody, suggesting that NGF, which is known to increase the ChAT activity of septal neurons both in vivo and in v itro, did not participate in the increase of ChAT activity. These find ings indicate that possible target-derived neurotrophic factor(s), oth er than NGF, from hippocampal neurons enhance(s) the ChAT activity of septal neurons.