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Volume 16, Number 16,
Issue of August 15, 1996
pp. 4835-4845
Copyright ©1996 Society for Neuroscience
Characterization of Functional GABAergic Synapses Formed between
Rat Hypothalamic Neurons and Pituitary Intermediate Lobe Cells in
Coculture: Ca2+ Dependence of Spontaneous IPSCs
Received March 29, 1996; revised May 7, 1996; accepted May 14, 1996.
Pierrick Poisbeau,
Frédérique René,
Christophe Egles,
Jean-Marc Félix,
Paul Feltz, and
Rémy Schlichter
Laboratoire de Neurophysiologie et de Neurobiologie des
Systèmes Endocrines, 67084 Strasbourg Cedex, France
Rat hypothalamic neurons and endocrine cells from the intermediate
lobe of the pituitary were grown in dissociated coculture. Neurons
positively stained with an antibody against glutamate decarboxylase
established apparent contacts with the  -melanocyte-stimulating
hormone-positive endocrine cells. These sites of contact were intensely
labeled with an antibody against the synaptic protein synapsin I and
displayed ultrastructural features characteristic of synapses. Using
patch-clamp recordings, we have demonstrated that these contacts
correspond to functional GABAergic synapses. The synaptic currents were
blocked reversibly by bicuculline (5 µM) and
SR95531 (5 µM), two competitive antagonists of
the GABAA receptor. At a holding potential of
 60 mV, spontaneously occurring IPSCs (s-IPSCs) had small amplitudes
(10-100 pA), whereas electrically evoked IPSCs (ee-IPSCs) had
amplitudes up to 1 nA. The rise times of both types of IPSCs were fast
( 1 msec), and their decaying phases were fitted in most cases with a
single exponential function (time constant, 50 msec). The amplitude
distribution of s-IPSCs did not reveal clear, equally spaced peaks and
was little affected by tetrodotoxin, suggesting that most s-IPSCs were
miniature IPSCs. Reduction of extracellular calcium concentration to
0.3 mM induced a marked decrease in s-IPSC
frequency and revealed a single amplitude peak at 10 pA, suggesting
that a single quantum of GABA activates 8-10
GABAA channels. Thus, our preparation might be an
interesting model to study different aspects of synapse formation
between a central neuron and its target as well as the fundamental
mechanisms of synaptic transmission at central synapses.
Key words:
inhibitory postsynaptic currents;
synaptic transmission;
synaptogenesis;
hypothalamo-hypophyseal coculture;
neuroendocrine
interaction;
GABA
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