UC San Diego

Dendritic spines are primary sites of excitatory postsynaptic inputs in the CNS and changes in their number, size, and shape are linked to cognitive functions such as learning and memory. Spines influence diffusion of chemical signals along dendrites, which contributes to transmission and information processing within signal transduction pathways. Spines have also been thought to act as a trapping mechanism to slow intracellular diffusion in dendrites. Previous studies revealed a wide range in Purkinje cell spine density, making it difficult to draw conclusions about the cell morphology of this particular neuron. Differences in spine density reported in previous studies may be due to variations in animal species, imaging method, or sample preparation. It is challenging to count spines because they fall between the resolution gaps in light microscopy (LM) and electron microscopy (EM) ; they are too small to resolve completely using LM and too large for EM without 3D reconstruction. In this investigation, correlated LM/EM imaging was used on identical rat Purkinje dendrites to compare spine density and address discrepancies in spine quantification at these two different microscopic scales. Dendritic segments were chosen from several areas within the dendritic tree to limit sampling bias and explore effects of dendritic segment diameter, distance from soma, and branch order on spine density estimations. Spine density was 40% lower in LM compared to EM. This is likely due to improvements in resolution in EM techniques. Additionally, little to no relationship was found between spine density and diameter, distance from soma, or branch order