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Slow IPSC kinetics, low levels of α1 subunit expression and paired‐pulse depression are distinct properties of neonatal inhibitory GABAergic synaptic connections in the mouse superior colliculus
Author(s) -
Jüttner René,
Meier Jochen,
Grantyn Rosemarie
Publication year - 2001
Publication title -
european journal of neuroscience
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.346
H-Index - 206
eISSN - 1460-9568
pISSN - 0953-816X
DOI - 10.1046/j.0953-816x.2001.01587.x
Subject(s) - gabaergic , inhibitory postsynaptic potential , postsynaptic potential , postsynaptic current , neurotransmission , neuroscience , biology , superior colliculus , excitatory postsynaptic potential , receptor , biochemistry
Remodelling of visual maps in the superior colliculus (SC) depends on neuronal activity. Synaptic inhibition could contribute to this process because spontaneous spike discharge in the SC was modulated by GABA A receptor activation at postnatal days (P) 1–3. To investigate the functional capacity of GABAergic synaptic transmission at this early stage of development, whole‐cell patch‐clamp recordings were made from wide field neurons (WFNs) in horizontal slices comprising the superficial grey layer of the SC. Focal stimulation in the vicinity of WFNs evoked tetrodotoxin‐sensitive stimulus‐locked inhibitory postsynaptic currents (eIPSCs). The failure rate of eIPSCs was low (≈ 0.2), and the maximal amplitude of evoked unitary eIPSCs exceeded the amplitude of average miniature IPSCs (mIPSCs) by a factor of 4–5, suggesting that action potential‐mediated GABA release was more effective than spontaneous release. Some of the properties of GABAergic synaptic transmission in the neonatal SC were age‐specific. In contrast with eIPSCs in the more mature SC at P20–22, neonatal eIPSCs decayed more slowly, preferentially fluctuated in duration, not amplitude, and mostly lacked temporal summation, due to depression at shorter intervals. The paired‐pulse ratio (eIPSC 2 : eIPSC 1 ) was inversely related to the duration of eIPSCs. PCR analysis showed, in addition, that the ratio of α1 : α3 subunit expression was lower in the neonatal SC. Together, these results suggest that, at a young age, efficacy of GABAergic synaptic transmission is primarily constrained by the slow kinetics and the saturation of postsynaptic GABA A receptors.