Synaptojanin 1 contributes to maintaining the stability of GABAergic transmission in primary cultures of cortical neurons.
Inhibitory synapses in the CNS can exhibit a considerable stability of neurotransmission over prolonged periods of high-frequency stimulation. Previously, we showed that synaptojanin 1 (SJ1), a presynaptic polyphosphoinositide phosphatase, is required for normal synaptic vesicle recycling (Cremona et al., 1999). We asked whether the stability of inhibitory synaptic responses was dependent on SJ1. Whole-cell patch-clamp recordings of unitary IPSCs were obtained in primary cortical cultures between cell pairs containing a presynaptic, fast-spiking inhibitory neuron (33.5-35 degrees C). Prolonged presynaptic stimulation (1000 stimuli, 2-20 Hz) evoked postsynaptic responses that decreased in size with a bi-exponential time course. A fast component developed within a few stimuli and was quantified with paired-pulse protocols. Paired-pulse depression (PPD) appeared to be independent of previous GABA release at intervals of >/=100 msec. The characteristics of PPD, and synaptic depression induced within the first approximately 80 stimuli in the trains, were unaltered in SJ1-deficient inhibitory synapses. A slow component of depression developed within hundreds of stimuli, and steady-state depression showed a sigmoidal dependence on stimulation frequency, with half-maximal depression at 6.0 +/- 0.5 Hz. Slow depression was increased when release probability was augmented, and there was a small negative correlation between consecutive synaptic amplitudes during steady-state depression, consistent with a presynaptic depletion process. Slow depression was increased in SJ1-deficient synapses, with half-maximal depression at 3.3 +/- 0.9 Hz, and the recovery was retarded approximately 3.6-fold. Our studies establish a link between a distinct kinetic component of physiologically monitored synaptic depression and a molecular modification known to affect synaptic vesicle reformation.
Luthi
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Section of Neurobiology, Department of Cell Biology, Yale University, School of Medicine, New Haven, Connecticut 06510, USA. anita.luthi@unibas.ch
Di Paolo
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G
Cremona
O
O
Daniell
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L
De Camilli
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P
McCormick
D A
DA
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D000831:Animals, Newborn; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D004558:Electric Stimulation; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology; D018756:GABA Antagonists / Q000494:pharmacology; D051379:Mice; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D009433:Neural Inhibition / Q000502:physiology; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D010716:Phosphatidylinositols / Q000378:metabolism; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism*; D026941:Sodium Channel Blockers; D013569:Synapses / Q000187:drug effects / Q000502:physiology; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology*; D013572:Synaptic Vesicles / Q000378:metabolism; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D018691:Excitatory Amino Acid Antagonists; D018756:GABA Antagonists; D009419:Nerve Tissue Proteins; D010716:Phosphatidylinositols; D026941:Sodium Channel Blockers; D005680:gamma-Aminobutyric Acid; C097702:synaptojanin; D010744:Phosphoric Monoester Hydrolases