INCREASED PERINUCLEAR CA2-RECEPTOR ACTIVATION IN RAT HIPPOCAMPAL-NEURONS( ACTIVITY EVOKED BY METABOTROPIC GLUTAMATE)

The effect of metabotropic glutamate receptor activation on intracellu lar Ca2+ activity (aCa(1)) of rat hippocampal pyramidal neurones in vi tro was examined using ratiometric confocal laser scanning microscopy with the Ca2+-sensitive fluorescent probe indo-1 AIM. 2. Metabotropic receptors were selectively activated with 1S,3R-1 -aminocyclopentane-1 ,3-dicarboxylic acid (1S,3R-ACPD; 100 mu M) in the presence of D-2-ami no 5-phosphonovaleric acid (D-APV), 6-cyano-7-nitroquinoxaline-2,3-dio ne (CNQX) and CdCl2. Most pyramidal neurones (77/84) responded with an elevation in Ca2+ activity, maximal after 3-5 min. Fluorescence ratio responses were concentration dependent (EC(50) approximate to 10 mu M ) and were blocked by prior application of the antagonist (RS)-4-carbo xy-3-hydroxyphenylglycine (RS-CHPG, 300 mu M). 3. Responses to 1S,3R-A CPD (100 mu M) also caused acidification of the neurones, from estimat ed control pH 7.2 to pH 6.6 (measured with the pH-sensitive dye SNAFL- calcein). The correction factor for indo-1 determination of Ca2+ was e stimated to be x 1.4. 4. Elevations in aCa(1) were greater within the perinuclear region (>1000 nM), than in thecytoplasm (similar to 200 nM ). This region was devoid of staining by the endoplasmic reticulum sta ining dye 3,3'-dihexyloxacarbocyanine iodide (DiOC(6)(3)). 5. It is co ncluded that activation of metabotropic receptors in immature rat hipp ocampal pyramidal neurones leads to a large increase in perinuclear Ca 2+ which would be well positioned to interact with the genome.