1. The effect of metabotropic glutamate receptor activation on intracellular Ca2+ activity (alpha Cai) of rat hippocampal pyramidal neurones in vitro was examined using ratiometric confocal laser scanning microscopy with the Ca(2+)‐sensitive fluorescent probe indo‐1 AM. 2. Metabotropic receptors were selectively activated with 1S,3R‐1‐aminocyclopentane‐1,3‐dicarboxylic acid (1S,3R‐ACPD; 100 microM) in the presence of D‐2‐amino 5‐phosphonovaleric acid (D‐APV), 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (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 (EC50 approximately 10 microM) and were blocked by prior application of the antagonist (RS)‐4‐carboxy‐3‐hydroxyphenylglycine (RS‐CHPG, 300 microM). 3. Responses to 1S,3R‐ACPD (100 microM) also caused acidification of the neurones, from estimated 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 estimated to be x 1.4. 4. Elevations in alpha Cai were greater within the perinuclear region (> 1000 nM), than in the cytoplasm (approximately 200 nM). This region was devoid of staining by the endoplasmic reticulum staining dye 3,3'‐dihexyloxacarbocyanine iodide (DiOC6(3)). 5. It is concluded that activation of metabotropic receptors in immature rat hippocampal pyramidal neurones leads to a large increase in perinuclear Ca2+ which would be well positioned to interact with the genome.

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