Photochemical and pharmacological evaluation of 7-nitroindolinyl-and 4-methoxy-7-nitroindolinyl-amino acids as novel, fast caged neurotransmitters

Reagents capable of rapid and efficient release of neuroactive amino acids (L-glutamate, GABA and glycine) upon flash photolysis of thermally stable, inert precursors have been elusive. 7-Nitroindolinyl (NI)-caged and 4-metho xy-7-nitroindolinyl (MNI)-caged compounds that fulfil these criteria are ev aluated here. These caged precursors are highly resistant to hydrolysis. Ph otolysis is fast (half time less than or equal to 0.26 ms) and the conversi on achieved with a xenon flashlamp is about 15% for the NI-caged L-glutamat e and about 35% for the MNI-caged L-glutamate. A procedure is described for calibration of photolysis in a microscope-based experimental apparatus. NI -caged L-glutamate itself showed no agonist or antagonist effects on AMPA a nd NMDA receptors in cultured neurones, and had no effect on climbing fibre activation of Purkinje neurones. A control compound with identical photoch emistry that generated an inert phosphate upon photolysis was used to confi rm that the intermediates and by-products of photolysis have no deleterious effects. MNI-caged L-glutamate is as stable and fast as NI-caged L-glutama te and similarly inert at glutamate receptors, but about 2.5 times more eff icient. However, NI-caged GABA is an antagonist at GABAA receptors and Nl-g lycine an antagonist at glycine receptors. The results show the utility and limitations of these fast and stable caged neurotransmitters in the invest igation of synaptic processes. (C) 2001 Elsevier Science B.V. All rights re served.