DOPAMINE REGULATION OF NEURITE OUTGROWTH FROM IDENTIFIED LYMNAEA NEURONS IN CULTURE

1. An identified dopaminergic interneuron (RPeD1) of the snail Lymnaea stagnalis, makes specific synaptic connections with a number of targe t (VI and VJ) but not non-target (VF and RPB) neurons in vivo. When cu ltured in vitro with both target and non-target cells, RPeD1 re-establ ishes synapses with target cells only. 2. To test whether exogenous do pamine exerts effects on the neurite outgrowth of both target and non- target neurons respectively, these cells were cultured in conditioned media (CM) in the presence of dopamine (10(-5) M). The growth of the n on-target cells was severely restricted and retarded in the presence o f dopamine. These data suggest that dopamine may regulate neurite outg rowth of non-target cells in culture. 3. The growth regulatory effects of dopamine on the non-target cells were blocked in the presence of a dopamine receptor antagonist (R(+) SCH-23390, 10(-4) M). These result s indicate that dopamine-induced growth regulation of the non-target c ells is mediated via dopamine receptors on these cells. 4. In the abse nce of conditioned media, dopamine was not sufficient to exert growth promoting effects on either target or non-target cells. 5. Taken toget her, our data show that dopamine differentially regulates growth of id entified Lymnaea neurons in culture. Dopamine alone, however, is not s ufficient to initiate and support neurite outgrowth from these cells. Rather, it functions to suppress the neurite outgrowth of the non-targ et cells, initiated by the conditioned media.