LeDoux Lab 2011 SfN Abstracts

Program#/Poster#:	663.16/G10
Title:	Learning and the tripartite synapse: Appearance of synapses without astrocytes during consolidation of fear conditioning
Location:	Hall A-C
Presentation Time:	Tuesday, Nov 15, 2011, 4:00 PM - 5:00 PM
Authors:	*L. OSTROFF1, M. MANZUR1, C. K. CAIN1,2, J. E. LEDOUX1,2; 1Ctr. for Neural Sci., New York Univ., New York, NY; 2Nathan Kline Inst., Orangeburg, NY
Abstract:		Astrocytic processes are present at the synaptic cleft in many central synapses, and are believed to regulate synaptic function and possibly plasticity. Synapses in the lateral amygdala (LA) are involved in fear learning, and learning induces morphological changes at these synapses. We reconstructed adult rat LA synapses after fear learning using serial section transmission electron microscopy (ssTEM) and examined them with respect to the presence and degree of astrocytic contact. Fear conditioning induced an increase in the frequency of synapses with no astrocytic contact, while the frequency of synapses with astrocytic contacts was unchanged. There was a specific increase with fear conditioning of synapses lacking astrocyte on spines containing both polyribosomes and a spine apparatus. Since astrocytes may buffer glutamate at synapses, we measured the perimeter of each synapse and its degree of astrocyte coverage. The amount of synapse perimeter surrounded by astrocyte did not scale with synapse size, meaning that large synapses have a disproportionately large astrocyte-free perimeter. Thus overall, fear conditioning resulted in an increase in the total unbuffered synapse perimeter length in the neuropil, but no change in the length of synapse buffered by astrocyte. Our results indicate that synapses added to the population during learning lack astrocyte presence, which may occur only at stabilized synapses.