Transient expression of an atypical D1-like dopamine receptor system during avian retina differentiation

Intact cultured retina cells from chick embryos at stage E9C5 (cultures initiated with retinae from 9-day old embryos followed by 5 days in culture), preincubated with 2 nM unlabelled SCH 23390 (R(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrochloride) for 20 to 60 min at 37 degrees Celsius and then washed 5 to 25 times (approximately 1.5 min/wash) with 2 ml SCH 23390 free medium, responded to dopamine with cAMP accumulation that corresponded to 30-50 per cent of the dopamine-promoted cAMP accumulation observed in untreated cells or in cells exposed to the inactive isomer of SCH 23390. Therefore, 50 to 70 per cent of the dopamine response of SCH 23390-pretreated cells was inhibited after extensive washings of the cultures. At E9C12 the fraction of the dopamine response that remained inhibited by SCH 23390 after the washings declined to 30 per cent of the control cultures or the cultures exposed to the SCH 23390 enantiomer. Cultures at stage E9C5 treated with SCH 23390 followed by extensive washings as above and then used for measuring the number of [3H]-SCH 23390 specific binding sites revealed that 60 per cent of the sites did not interact with the tritiated compound when compared to untreated cultures or to cultures preincubated with the inactive isomer of SCH 23390. When E9C12 cultures were subjected to the same experimental protocol less than 10 per cent of D1-like sites did not interact with [3H]-SCH 23390 after the cells had been exposed to the unlabelled compound. Dissociated cells prepared from intact retinae obtained from 12-13-day old embryos also displayed a subpopulation of D1-like sites that interacted irreversibly with SCH 23390 in a stereospecific way. These sites corresponded to 25 per cent of the total number of D1-like sites present in the retina at this developmental stage. In retina cells obtained from one-day old posthatched chicks these sites were no longer detected. These data show that cultured retina cells as well as cells obtained from retina developing in ovo display two populations of D1-like receptors. One interacts irreversibly with SCH 23390 and is present only in the undifferentiated tissue or in cells at the early stages of culture and the other has a lower affinity for SCH 23390 with which its interaction follows reversible kinetics. These sites are present throughout the differentiation stages studied.

Domoic acid induces neurotoxicity and ip3 mobilization in cultured cells of embryonic chick retina

Domoic acid (DOM), 1 to 50 µM, a glutamate agonist responsible for several neurological effects such as loss of memory and confusion, induced the death of cultured neurons of chick embryonic retina, in a concentration- and Ca2+ -dependent manner. This effect was blocked by 100 µM CNQX, a competitive antagonist of the non-NMDA receptor, but not by 10 µM MK-801, a non-competitive antagonist of the NMDA receptor. DOM also induced inositol triphosphate (ip3) accumulation 4 to 7 times above basal levels. This effect was also dependent on external Ca2+ and was entirely blocked by 100 µM CNQX, but not by 10 µM MK-801. These results suggest that DOM interaction with non-NMDA glutamate receptors mediates signal transduction with ip3 accumulation and cell death