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Volumn 274, Issue 5289, 1996, Pages 972-976

Maturation of a central glutamatergic synapse

Author keywords

[No Author keywords available]

Indexed keywords

CELLS; GENES; GROWTH KINETICS; NEUROLOGY; PHYSICAL PROPERTIES; PHYSIOLOGY; PROTEINS;

EID: 0030575870     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: 10.1126/science.274.5289.972     Document Type: Article
Times cited : (469)

References (41)
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    • note
    • B responses were completely blocked. Responses were filtered (1 kHz) and amplified with an Axopatch 1D, digitized (3 to 10 kHz), and stored on computer for later analysis. In about half the neurons recorded, the pipette solution also included Lucifer yellow, to allow reconstruction of the neuronal morphology at the end of the recording session. A low-magnification brightfield image of the tectum was taken to record the relative position of the cell body within the tectum.
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    • M. Rastaad, Eur. J. Neurosci. 7, 1882 (1995). In general (18/20 recordings), the minimal stimulus required to produce a postsynaptic response was the same for depolarized and hyperpolarized holding potentials.
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    • Rastaad, M.1
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    • note
    • AMPA EPSC amplitudes were determined by measuring the amplitude of the response at -60 mV during a 2- to 5-ms window that included the peak response, and subtracting the amplitude of the response immediately before a stimulus. For estimation of the NMDA component, the amplitude of the response during a 10-ms window (⋯ 20 ms after the response onset) is measured at +55 mV, and a baseline value obtained immediately before a stimulus is subtracted. At 20 ms after response onset, the AMPA component has decreased so that it contributes <5% of the total current (Fig. 2A).
  • 29
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    • For recordings of spontaneous mEPSCs, 1 μM tetrodotoxin was added to the bathing solution. mEPSCs were detected with a program as described [N. Otmakhov, A. M. Shirke, R. Malinow, Neuron 10, 1101 (1993)].
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    • Otmakhov, N.1    Shirke, A.M.2    Malinow, R.3
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    • d). The difference in failure rate at -60 mV and at +55mV was eliminated by 100 μM APV (failure rate at hyperpolarized potentials = 0.55 ± 0.08, at depolarized potentials = 0.23 ± 0.07, and at depolarized potentials with APV = 0.54 ± 0.09: n = 4), Pure NMDA responses can be attributed to the existence of synapses with only functional NMDA receptors (7-9). It is unlikely that the absence of AMPA responses at some synapses is due to greater electrotonic filtering of the faster AMPA response, because immature cells are more compact and yet have more, not less, synapses with only NMDA responses (Fig. 4G).
    • (1991) Science , vol.252 , pp. 722
    • Malinow, R.1
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    • d). The difference in failure rate at -60 mV and at +55mV was eliminated by 100 μM APV (failure rate at hyperpolarized potentials = 0.55 ± 0.08, at depolarized potentials = 0.23 ± 0.07, and at depolarized potentials with APV = 0.54 ± 0.09: n = 4), Pure NMDA responses can be attributed to the existence of synapses with only functional NMDA receptors (7-9). It is unlikely that the absence of AMPA responses at some synapses is due to greater electrotonic filtering of the faster AMPA response, because immature cells are more compact and yet have more, not less, synapses with only NMDA responses (Fig. 4G).
    • (1993) J. Physiol. , vol.471 , pp. 481
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    • S. Hestrin, Nature 357, 686 (1992).
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    • note
    • Vaccinia virus constructs (20) were injected into the brain ventricle of stage 44 to 45 tadpoles (22). Three days later, when the animal was at stage 47 to 48, the brain was dissected and used for recordings. Animals infected at the same time were stained in wholemount with X-Gal to test for β-Gal expression. Infection of amphibian cells with vaccinia virus does not result in decreased cell density (14, 22), arguing against a cytotoxic action of the virus in this species.
  • 38
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    • note
    • Only two cells had all evoked responses mediated by only NMDA receptors. This paucity can be explained if a single axon makes a number of contacts onto each postsynaptic cell. The gradual change in fraction of pure NMDA responses across the RC axis then reflects addition of AMPA receptor function to individual contacts already showing NMDA receptor function. An alternative interpretation is that pure NMDA responses are due to spill-over of transmitter from nearby synapses. In this instance, during development there must be a decrease in spillover (to account for the lower fraction of pure NMDA responses) and a compensating increase in probability of release (to maintain NMDA transmission constant). Furthermore, postsynaptic increase in CaMKII must also decrease spillover and increase probability of transmitter release (to explain similar changes in caudal cells infected with tCaMKII-VV). However, rostral cells infected with tCaMKII-VV showed no change in failure rates (either hyperpolarized or depolarized) (26), further arguing against this spillover model. Rostral cells infected with tCaMKII-VV did show an increase in AMPA receptor transmission with little change in NMDA receptor transmission. This result likely reflects the fact that rostral neurons in these animals continued to develop throughout the tadpole stage of development.
  • 40
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    • Sources of the depolarization in the most caudal region of tectum, where the neurons have predominantly NMDA responses, could be intrinsic membrane oscillations or depolarizing GABAergic inputs [E. Cherubini, J. L. Gaiarsa, Y. Ben Ari, Trends Neurosci. 14, 515 (1991)].
    • (1991) Trends Neurosci. , vol.14 , pp. 515
    • Cherubini, E.1    Gaiarsa, J.L.2    Ben Ari, Y.3
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    • note
    • Supported by the NIH (R.M.), and the National Science Foundation, NIH, and National Down Syndrome Society (H.T.C.). We thank J. Lisman for comments on the manuscript, and members of the labs for helpful discussions.


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