[Abstract Title]. - Society for Neuroscience

these cultures. Together, these findings suggest that granule cell dispersion, in addition to
disrupting the normally compact granule cell body layer, also disrupts granule cell dendritic
structure. Moreover, these findings demonstrate in principal, that recurrent basal dendrites can
form by movement of pre-existing apical dendrites. Whether similar cellular changes underlie
granule cell pathology in patients with epilepsy remains to be determined.
Disclosures: B.L. Murphy, None; C. Walter, None; S.C. Danzer, None.
Poster
239. Structural Plasticity at Synapses I
Time: Sunday, November 16, 2008, 1:00 pm - 5:00 pm
Program#/Poster#: 239.25/E22
Topic: B.08.i. Structural plasticity
Support: Cincinnati Children's Hosp.
Title: Structure and complexity of CA3 pyramidal cell thorny excrescences
Authors: *S. L. BRONSON 1,2 , B. L. MURPHY 1,2 , C. WALTER 1 , S. C. DANZER 1,2,3 ;
1 Dept. of Anesthesia, Cincinnati Children's Hosp., Cincinnati, OH; 2 Program in Neurosci.,
3 Departments of Anesthesia and Pediatrics, Univ. of Cincinnati, Cincinnati, OH
Abstract: Hippocampal dentate granule cell - CA3 pyramidal cell synapses constitute one part
of the classic hippocampal “trisynaptic circuit”. This synaptic pathway is structurally and
functionally unique. The presynaptic terminals making up this pathway are known as “giant
mossy fiber boutons”, so named because of their unusually large size, which is five to ten times
greater than typical presynaptic terminals in the CNS. These giant boutons contact CA3
pyramidal cell postsynaptic spines termed “thorny excrescences”. Most dendritic spines of the
CNS exhibit a simple structure of only one, or occasionally a few, spine heads per spine neck. In
contrast, thorny excrescences exhibit multitudes of spine heads attached to the trunk dendrite by
a single neck. The increased size and complexity of both presynaptic and postsynaptic structures
at this synapse reflects its potency. Firing of a single granule cell is sufficient to fire its target
pyramidal cell. Until recently, however, the complexity of CA3 pyramidal cell thorny
excrescences has made it difficult to characterize their structure and plasticity. Here, we
demonstrate that these structures can be quantified by combining high resolution confocal
microscopy with the Thy1-GFP expressing mouse line. In this mouse line, a subset of CA3
pyramidal cells is labeled with green fluorescent protein (GFP). Using this approach, it has
become clear that thorny excrescences are even more complicated than previously appreciated.
Specifically, thorny excrescences made up of more than thirty individual spine heads have been