The Journal of Neurophysiology Vol. 78 No. 1 July 1997, pp. 63-75
Copyright ©1997 The American Physiological Society

Metabotropic Glutamate Receptor Agonists Alter Neuronal Excitability and Ca²⁺ Levels via the Phospholipase C Transduction Pathway in Cultured Purkinje Neurons

Jeffrey G. Netzeband, Kathy L. Parsons, Dan D. Sweeney, and Donna L. Gruol

Department of Neuropharmacology and Alcohol Research Center, The Scripps Research Institute, La Jolla, California 92037

Netzeband, Jeffrey G., Kathy L. Parsons, Dan D. Sweeney, and Donna L. Gruol. Metabotropic glutamate receptor agonists alter neuronal excitability and Ca²⁺ levels via the phospholipase C transduction pathway in cultured Purkinje neurons. J. Neurophysiol. 78: 63-75, 1997. Selective agonists for metabotropic glutamate receptor (mGluR) subtypes were tested on mature, cultured rat cerebellar Purkinje neurons (21 days in vitro) to identify functionally relevant mGluRs expressed by these neurons and to investigate the transduction pathways associated with mGluR-mediated changes in membrane excitability. Current-clamp recordings (nystatin/perforated-patch method) were used to measure the membrane response of Purkinje neurons to brief microperfusion pulses (1.5 s) of the group I (mGluR1/mGluR5) agonists (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid (300 µM), quisqualate (5 µM), and (R,S)-3,5-dihydroxyphenylglycine (50-500 µM). All group I mGluR agonists elicited biphasic membrane responses and burst activity in the Purkinje neurons. In addition, the group I mGluR agonists produced alterations in the active membrane properties of the Purkinje neurons and depressed the OFF response after hyperpolarizing current injection. In parallel microscopic Ca²⁺ imaging experiments, application of the group I mGluR agonists to fura-2-loaded cells elicited increases in intracellular Ca²⁺ in both the somatic and dendritic regions. The group II (mGluR2/mGluR3) agonist (2S,3S,4S)--(carboxycyclopropyl)-glycine (10 µM) and the group III (mGluR4/mGluR6/mGluR7/mGluR8) agonists L(+)-2-amino-4-phosphonobutyric acid (1 mM) and O-phospho-L-serine (200 µM) had no effect on the membrane potential or intracellular Ca²⁺ levels of the Purkinje neurons. The cultured Purkinje neurons, but not granule neurons or interneurons, showed immunostaining for mGluR1 in both the somatic and dendritic regions. All effects of the group I mGluR agonists were blocked by (+)--methyl-4-carboxyphenylglycine (1 mM), an mGluR antagonist. Furthermore, the phospholipase C inhibitor 1-[6-((17-3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl]-1H-pyrrole-2,5-dione (2 µM) blocked the group I mGluR agonist-mediated electrophysiological response and greatly attenuated the Ca²⁺ signal elicited by group I mGluR agonists, particularly in the dendrites. The inactive analogue1-[6-((17-3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl]2,5-pyrrolidine-dione (2 µM) was relatively ineffective against the electrophysiological response and Ca²⁺ signal. These results indicate that functional group I mGluRs (but not group II or III mGluRs) can be activated on mature Purkinje neurons in culture and result in changes in neuronal excitability and intracellular Ca²⁺ mediated through phospholipase C. These data obtained from a defined neuronal type, the Purkinje neuron, confirm biochemical and molecular studies on the transduction mechanisms of group I mGluRs and show that this transduction pathway is linked to neuronal excitability and intracellular Ca²⁺ release in the Purkinje neurons.

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