Excitatory Spinule Bearing Boutons of the Adult Rat Hippocampus

Carlos Delgado and Dr. Marc Nahmani

References

Introduction Results

For more information

Please contact crdelga@uw.edu

Special Thanks to

The University of Washington Tacoma Division of Science and Mathematics for providing a fun and welcoming environment in which to learn and grow.

Dr. Nahmani for the opportunity and guidance.

Methods

Determining the origin of spinules is key to understanding neuroplasticity of the brain. Although spinules have been observed to perforate between synaptic densities, much of the purpose and function of these spine protrusions remains unknown.

Previous studies have proposed that spinules might aid in circuit building through selective chemical signaling between neurons (Spacek and Harris 2004).

We found that out of a total of 94 excitatory presynaptic boutons, 27.8% contained spinules. Of the spinules identified 55.3% were post-synaptic spines, 14.9% were from an adjacent axons, 38.3% were from an adjacent spines and 29.6% were from an adjacent dendrites.

Preliminary Conclusions

These data suggest that a significant proportion of the excitatory synapses in hippocampus contain spinules, which may function as to enhance synaptic stability and extra-synaptic communication.

Micrographs of adult rat hippocampus at a resolution of 5x5x5µm (Lucchi et al.). 163 images were analyzed. Figure A (above) shows dark, narrow density adjacent to vesicles indicating an excitatory synapse (circled in blue). Figure B (above right) shows a developing invagination of a presynaptic density (red) by a postsynaptic spine (yellow). Figure C (right) shows a spine (yellow) enveloped through a presynaptic density.

Figure D (below) shows another spine from a postsynaptic density (right) penetrating a presynaptic density (left). Figure E (bottom) shows the resulting spine in the presynaptic density further in the series (Lucchi et al.).

ObjectiveIdentify spinule bearing boutons in micrograph cross sections to determine ratio of spinule bearing boutons from all synapses observed. Determine the origin of the spinule structure.

• Spacek J, Harris KM. Trans-Endocytpsis via Spinules in Adult Rat Hippocampus. The Journal of Neuroscience . 2004;24(17):4233–4241.

• Lucchi A, Li Y, Becker C, Fua P. Electron Microscopy Dataset. CVLAB. [accessed 2020 Dec 1]. https://www.epfl.ch/labs/cvlab/data/data-em/

Data

Spinule origin was determined (pie chart above) from all excitatory spinule bearing boutons (SBBs). From the total SBBs analyzed, 55.3% contained spinules from post-synaptic spines (PSs), 14.9% off SBBs contained an adjacent axon spinule (AdjAx), 38.3% of spinules originated from adjacent spines (AdjS), and 29.6% were from adjacent dendrites (AdjD). From all excitatory synapses analyzed, ~29% were spinule bearing (SBBs), while 71% of synapses analyzed did not contain a spinule (non-SBB).

% E

xcita

tory

Syn

apse

s

SBBs

Non-SBBs

55.3

38.3

29.6

14.9

PSs PSd AdjS AdjD