Weizmann Institute Department of Neurobiology 

Dendritic Spines

Another major focus of research in our laboratory is the subcellular organelle where synaptic interactions and plasticity take place, the dendritic spine.
The spine is a small protrusion, less than a mm in length, onto which synapses are made. The great variety of dendirtitic spine shapes, sizes, and
density of distribution on the parent dendrites of a single neuron and the apparent persistence of spines throughout the life of the neurons suggest that
the spine is the unitary locus of memory formation and storage. While this view prevailed throughout the 20th century supporting evidence for this
notion is rather scarce, due to the fact that the small size of the spine prevents systematic electrophysiological analysis.
Our studies, therefore, focused on rapid changes in calcium concentration within the spines as a function of synaptic activity. In collaboration with Dr. Hana
Parnas of the Hebrew University, we developed a 3D model of the dendritic spine showing that dendritic spines represent independent calcium compartments
in  cultured hippocampal neurons. This characteristic of dendritic spines may allow a local rise in [Ca+2]in needed for activation of plasticity-related signaling
molecules. We also found that ongoing electrical activity can modulate the density of spines on dendrites, i.e., enhanced activity increases spine
density and vice versa.
*Further information on the subject of dendritic spines may be found in lab publications.




     
 
Long and short spines differ in the degree of their effect on dendritic [Ca+2]:
 (a) Dendritic segment taken from a cell that has been stained with the indicator 
 calcium green. Arrows point to two spines, a long one (red arrow) and a short 
 one (blue arrow) that are being compared. In both spines, fast line-scans 
 allowed detection of transient [Ca+2] changes as a result of local synaptic 
 activity. (b) There was a large difference in the response of the parent 
 dendrite to the two transients in the spines: the dendrite adjacent to the short 
 spine showed a large and fast [Ca+2] transient (blue), while the dendrite next to
 the long spine showed only a small and slow change in [Ca+2] (red). (c) shows
 the independence of [Ca+2] transients in a long spine and its parent dendrite 
 with a 3D imaged top-to-bottom line-scan thru the dendrite and spine. The scan
 illustrates two events: one occurring in the dendrite [top right, red indicates a 
 large DF/F (net fluorescence)], which is not seen in the spine, and one occurring 
 in the spine (bottom left), which is transferred only partially to the dendrite. 
 Scale bar in (a), 1 mm.

 
 
 
 
 
 
 
 

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