Neurotoxic glutamate treatment of cultured cerebellar granule cells induces Ca2+ -dependent collapse of mitochondrial membrane potential and ultrastructural alterations of mitochondria

Rhodamine 123 staining and electron microscopy were used to reveal a correlation between the ultrastructural and functional state of cultured cerebellar granule cells after short glutamate treatment. Glutamate exposure (15 min, 100 microM) in Mg2+-free solution caused considerable ultrastructural alterations in a granule cell: clumping of the chromatin, swelling of the endoplasmic reticulum and mitochondria, and disruption of the mitochondrial cristae. After glutamate treatment, the mitochondria of the neurons lost their ability to sequester rhodamine 123. Both the N-methyl-D-aspartate receptor channel blocker MK-801 (30 microM) and cobalt chloride (2 mM) prevented the deteriorative effects of glutamate. These data suggest that glutamate-induced Ca2+ overload of the neurons can lead to non-specific permeability of the inner mitochondrial membrane, resulting in neuronal death.

The M1 antagonist pirenzepine suppresses heterosynaptic STD in the CA1 region

The effect of the muscarinic M1 and M2 antagonists (pirenzepine and gallamine) on heterosynaptic short-term depression (HSTD) of the CA1 population spike was studied in rat hippocampal slices. HSTD was evoked by a train of 30-50 pulses at 5 Hz (theta-like stimulation; TLS) delivered to the stratum oriens. Bath-applied pirenzepine (10(-6)-3 x 10(-6) M) significantly suppressed the magnitude of HSTD in the tested radiatum input (56 +/- 26% of control, p < 0.05). In contrast, gallamine (10(-6)-10(-5) M) did not suppress HSTD (102 +/- 7%). An enhancement of HSTD during application of eserine was also antagonized by pirenzepine (71 +/- 18%, p < 0.01), but not by gallamine (152 +/- 85%). These data suggest that acetylcholine synaptically released during TLS of the stratum oriens significantly contributes to HSTD in the CA1 region by activation of the M1 muscarinic receptor subtype.