The Journal of Neuroscience, April 1, 2003, 23(7):2549
Contribution of NR2B Subunits to Synaptic Transmission in
Amygdaloid Interneurons
Csaba
Szinyei,
Oliver
Stork, and
Hans-Christian
Pape
Institute of Physiology, Medical School, Otto-von-Guericke
University, 39120 Magdeburg, Germany
Synaptic responses of interneurons in the rat lateral amygdala (LA)
to electrical microstimulation of putative cortical and thalamic
afferents were studied in slice preparations in situ. The EPSPs at both thalamic and cortical inputs were composed of two major components that were sensitive to
6,7-dinitroxaline-2,3-dione and
DL-2-amino-5-phosphonovaleric acid (APV), indicating
mediation through AMPA and NMDA receptors. NMDA receptor activation
contributed to basal synaptic transmission, as evidenced through a
reduction of EPSP amplitudes and integrals by APV. NMDA
receptor-mediated postsynaptic currents showed magnesium-regulated
voltage dependence, and current-voltage relationships displayed a
region of negative slope conductance negative to resting potential.
Deactivation of NMDA receptor-mediated currents followed a two
exponential time course, with both components being significantly
reduced by ifenprodil (10 µM), an antagonist of the NR2B
subunit of NMDA receptors. Significant differences were not observed
between NMDA currents or ifenprodil effects at thalamic and cortical
inputs. Furthermore, recordings from a sample of projection neurons in the LA provided additional evidence for the existence of
ifenprodil-sensitive components of thalamically and cortically evoked
NMDA receptor-mediated responses. Immunohistochemical double-labeling
and combined in situ hybridization/immunohistochemistry
demonstrated that GABA-immunoreactive as well as GABA-negative cells
express the NR2B subunit. Overall, these results show that GABAergic
interneurons in the LA express functional NMDA receptors, which
participate in basal synaptic transmission at both thalamic and
cortical inputs. The finding that NR2B subunits are critically involved
in NMDA receptor-mediated signaling at the two major input pathways to
interneurons and projection cells in the LA is particularly interesting
in the light of previous observations that NR2B antagonists interfere with plastic changes in the LA related to associative fear conditioning.
Key words:
lateral amygdala; projection neuron; interneuron; inhibition; NMDA receptors; NR2B subunit
Copyright © 2003 Society for Neuroscience 0270-6474/03/2372549-08$05.00/0
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