Caffeine Modulates Vesicle Release and Recovery at Cerebellar Parallel Fibre Terminals, Independently of Calcium and Cyclic AMP Signalling.
BACKGROUND
Cerebellar parallel fibres release glutamate at both the synaptic active zone and at extrasynaptic sites-a process known as ectopic release. These sites exhibit different short-term and long-term plasticity, the basis of which is incompletely understood but depends on the efficiency of vesicle release and recycling. To investigate whether release of calcium from internal stores contributes to these differences in plasticity, we tested the effects of the ryanodine receptor agonist caffeine on both synaptic and ectopic transmission.


METHODS
Whole cell patch clamp recordings from Purkinje neurons and Bergmann glia were carried out in transverse cerebellar slices from juvenile (P16-20) Wistar rats.


RESULTS
Caffeine caused complex changes in transmission at both synaptic and ectopic sites. The amplitude of postsynaptic currents in Purkinje neurons and extrasynaptic currents in Bergmann glia were increased 2-fold and 4-fold respectively, but paired pulse ratio was substantially reduced, reversing the short-term facilitation observed under control conditions. Caffeine treatment also caused synaptic sites to depress during 1 Hz stimulation, consistent with inhibition of the usual mechanisms for replenishing vesicles at the active zone. Unexpectedly, pharmacological intervention at known targets for caffeine--intracellular calcium release, and cAMP signalling--had no impact on these effects.


CONCLUSIONS
We conclude that caffeine increases release probability and inhibits vesicle recovery at parallel fibre synapses, independently of known pharmacological targets. This complex effect would lead to potentiation of transmission at fibres firing at low frequencies, but depression of transmission at high frequency connections.
School of Life Sciences, University of Nottingham, Medical School, Queen's Medical Centre, Nottingham, United Kingdom.
Katharine L
KL
Dobson
Laboratory for Molecular Signalling, Babraham Institute, Babraham, Cambridge, United Kingdom.
Claire
C
Jackson
Laboratory for Molecular Signalling, Babraham Institute, Babraham, Cambridge, United Kingdom; Institute of Neuro & Sensory Physiology, Humboldtallee-23, Goettingen, Germany.
Saju
S
Balakrishnan
School of Life Sciences, University of Nottingham, Medical School, Queen's Medical Centre, Nottingham, United Kingdom; Laboratory for Molecular Signalling, Babraham Institute, Babraham, Cambridge, United Kingdom.
Tomas C
TC
Bellamy
D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D002110:Caffeine / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D002531:Cerebellum / Q000187:drug effects / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D009411:Nerve Endings / Q000187:drug effects / Q000378:metabolism*; D009457:Neuroglia / Q000187:drug effects / Q000378:metabolism; D009994:Osmolar Concentration; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D011689:Purkinje Cells / Q000187:drug effects / Q000378:metabolism; D017208:Rats, Wistar; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D009435:Synaptic Transmission / Q000187:drug effects; D013572:Synaptic Vesicles / Q000187:drug effects / Q000378:metabolism*
D010726:Phosphodiesterase Inhibitors; D002110:Caffeine; D000242:Cyclic AMP; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D000262:Adenylyl Cyclases; D002118:Calcium