An identified dopaminergic interneuron (RPeD1) of the snail Lymnaea stagnalis, makes specific synaptic connections with a number of target (VI and VJ) but not non-target (VF and RPB) neurons in vivo. When cultured in vitro with both target and non-target cells, RPeD1 re-establishes synapses with target cells only. 2. To test whether exogenous dopamine 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 non-target cells was severely restricted and retarded in the presence of dopamine. These data suggest that dopamine may regulate neurite outgrowth 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 results indicate that dopamine-induced growth regulation of the non-target cells is mediated via dopamine receptors on these cells. 4. In the absence of conditioned media, dopamine was not sufficient to exert growth promoting effects on either target or non-target cells. 5. Taken together, our data show that dopamine differentially regulates growth of identified Lymnaea neurons in culture. Dopamine alone, however, is not sufficient to initiate and support neurite outgrowth from these cells. Rather, it functions to suppress the neurite outgrowth of the non-target cells, initiated by the conditioned media.
