RT Journal Article
SR Electronic
T1 GABA Spillover from Single Inhibitory Axons Suppresses Low-Frequency Excitatory Transmission at the Cerebellar Glomerulus
JF The Journal of Neuroscience
JO J. Neurosci.
FD Society for Neuroscience
SP 8651
OP 8658
DO 10.1523/JNEUROSCI.20-23-08651.2000
VO 20
IS 23
A1 Simon J. Mitchell
A1 R. Angus Silver
YR 2000
UL http://www.jneurosci.org/content/20/23/8651.abstract
AB GABA type B receptors (GABAB-Rs) are present on excitatory terminals throughout the CNS, but surprisingly little is known about their role in modulating neurotransmission under physiological conditions. We have investigated activation of GABAB-Rs on excitatory terminals within the cerebellar glomerulus, a structure where glutamatergic excitatory and GABAergic inhibitory terminals are in close apposition and make axodendritic synapses onto granule cells. Application of the GABAB-R agonist baclofen depressed evoked mossy fiber EPSCs by 54% at 1 Hz. The amplitude of miniature EPSCs recorded in tetrodotoxin was unchanged in the presence of baclofen, but the frequency was significantly reduced, indicating a purely presynaptic action of baclofen under our recording conditions. At physiological temperature (37°C) presynaptic GABAB-Rs were not tonically activated by spontaneous GABA release from Golgi cells, which fire at ∼8 Hz in slices at this temperature. However, tonic activation could be induced by blocking GABA uptake or by lowering temperature. GABAB-Rs were activated at physiological temperature when Golgi cell firing was increased above the basal level by stimulating a single inhibitory Golgi cell input at 50 Hz, suppressing the mossy fiber-evoked EPSC by 24% at 1 Hz. Furthermore, glutamate release was selectively inhibited at low-frequency mossy fiber inputs (<10 Hz) during Golgi cell stimulation. Our findings suggest that GABA spillover in the glomerulus modulates sensory input to the cerebellar cortex.