| PROPAGATING EXCITATORY POTENTIALS WITHIN THE FEAR
CONDITIONING CIRCUIT OF THE LATERAL AMYGDALA. |
| L.R. Johnson1*; V. Doyere1,2;
H.A. Alphs1; J.E. LeDoux1 |
| 1. Ctr Neural Sci, NYU, NY, NY, USA |
| 2. NAMC, Univ Paris-Sud, Orsay, France |
|
In the Hebbian postulate, transiently
reverberating cellular ensembles can sustain activity to facilitate
temporal coincidence detection. Auditory fear conditioning is believed
to be formed in the lateral amygdala (LA), by way of plasticity
at auditory input synapses on principal neurons. To evaluate the
contribution of LA cellular ensembles in the formation of conditioned
fear memories, we investigated the LA micro-circuitry by electrophysiological
and anatomical approaches. Polysynaptic field potentials evoked
in the LA by stimulation of auditory thalamus(MGm/PIN) or auditory
cortical (TE3) afferents were analyzed in vitro and in vivo. In
vivo, two potentials were identified following stimulation of either
pathway. In vitro, these multiple potentials were revealed by adding
75uM Picrotoxin or 30uM Bicuculine, with the first potential peaking
at 15-20 ms, followed by two additional potentials at 20  25 and 30 35 ms, respectively.
These data show single stimulation events can result in multiple
synchronized excitatory events within the lateral amygdala. In order
to determine underlying mechanisms of auditory signal propagation,
LA principal neuron axon collateral trajectory patterns and morphology
were analyzed. Neurons were found to have local axon collaterals
that are topographically organized. Each axon collateral within
the LA totaled 14.1 
2.73mm, had 29.8 9.1 branch points and 1870.8 1035 boutons (n=9).
Electrophysiological and anatomical data show that a network of
extensive axon collaterals within the LA may facilitate preservation
of auditory afferent signals.
Supported by: MH58911, MH38774, MH46516 and NARSAD.
|
|