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The Journal of Neurophysiology Vol. 86 No. 2 August 2001, pp. 717-723
Copyright ©2001 by the American Physiological Society
Division of Neuroscience, John Curtin School of Medical Research, Australian National University, Canberra, ACT 2601, Australia
Delaney, Andrew J. and
Pankaj Sah.
Pathway-Specific Targeting of GABAA Receptor Subtypes
to Somatic and Dendritic Synapses in the Central Amygdala. J. Neurophysiol. 86: 717-723, 2001. Neurons in the central amygdala express two distinct types of
ionotropic GABA receptor. One is the classical
GABAA receptor that is blocked by low
concentrations of bicuculline and positively modulated by
benzodiazepines. The other is a novel type of ionotropic GABA receptor
that is less sensitive to bicuculline but blocked by the
GABAC receptor antagonist
(1,2,5,6-tetrohydropyridine-4-yl) methylphosphinic acid (TPMPA) and by
benzodiazepines. In this study, we examine the distribution of these
two receptor types. Recordings of GABAergic miniature inhibitory
postsynaptic currents (mIPSCs) showed a wide variation in amplitude.
Most events had amplitudes of <50 pA, but a small minority had
amplitudes >100 pA. Large-amplitude events also had rise times faster
than small-amplitude events. Large-amplitude events were fully blocked
by 10 µM bicuculline but unaffected by TPMPA. Small amplitude events
were partially blocked by both bicuculline and TPMPA. Focal application
of hypertonic sucrose to the soma evoked large-amplitude mIPSCs,
whereas focal dendritic application of sucrose evoked small-amplitude
mIPSCs. Thus inhibitory synapses on the dendrites of neurons in the
central amygdala express both types of GABA receptor, but somatic
synapses expressed purely GABAA receptors.
Minimal stimulation revealed that inhibitory inputs arising from the
laterally located intercalated cells innervate dendritic synapses,
whereas inhibitory inputs of medial origin innervated somatic
inhibitory synapses. These results show that different types of
ionotropic GABA receptors are targeted to spatially and functionally
distinct synapses. Thus benzodiazepines will have different modulatory
effects on different inhibitory pathways in the central amygdala.
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