Abstract
We previously reported that trophic factors and neurotransmitters in concert regulate survival of cultured cerebellar Purkinje cells. In particular, excitatory amino acid (EAA) transmitters and NGF increased survival, whereas neither alone was effective. In the present studies, we sought to identify molecular mechanisms through which EAAs participate in the survival-promoting interaction. Initially, we characterized the potential role of ionotropic EAA receptors by exposing cultures to the antagonists MK-801, D-2-amino-5- phosphonovaleric acid, and 6,7-dinitroquinoxalinedione. Each increased cell number, suggesting that endogenous ionotropic activity decreased survival. To determine whether metabotropic EAA receptor stimulation modulates survival, the metabotropic agonist ACPD ([1S,3R]-1- aminocyclopentane-1,3-dicarboxylic acid; 1 microM) was tested. ACPD alone had no effect on survival. However, simultaneous exposure to ACPD and NGF significantly increased Purkinje number. Moreover, this increase in survival was blocked by L-AP3 [L(+)-2-amino-3- phosphonopropionic acid; 1 microM], a putative antagonist of certain metabotropic responses. L-AP3 also reduced cell number in the absence of exogenous EAA. Thus, endogenous metabotropic stimulation is normally necessary for survival. In sum, these studies reveal a novel mechanism whereby an excitatory neurotransmitter shapes neural development by simultaneous trophic and regressive actions that are, respectively, mediated by metabotropic and ionotropic EAA receptors.