The subcellular localization of the mGlu4a metabotropic glutamate rece
ptor was investigated in rat cerebellum. At the light microscopical le
vel, strong mGlu4a immunoreactivity was found in the molecular layer.
A post-embedding immunogold method for electron microscopy revealed go
ld particles at the presynaptic sites of synapses made by parallel fib
er terminals with dendritic spines of Purkinje cells. These observatio
ns support electrophysiological evidence indicating an autoreceptor fu
nction of mGlu4 receptors at these synapses.