Comparison of hippocampal neuron spine densities in acute and perfusion‐fixed slices using the lipophilic dye DiI

Abstract

The hippocampus is a key brain structure involved in learning and memory. Hippocampal acute slices are widely used in ex vivo electrophysiological experiments to study cellular mechanisms of synaptic transmission and plasticity. Many approaches have been used to optimize slice viability and to maintain accurate in vivo physiological conditions during experimental procedures. Several different variables such as the age of the animal, the composition of the artificial cerebrospinal fluid (aCSF), the maintenance conditions in recording chambers, temperature and slice cutting methodology, among others, can affect hippocampal slices features. Specifically, by using electron microscopy and two‐photon microscopy it has been previously reported that dendritic spines, crucial neuronal structures that receive most of the excitatory synaptic inputs in the brain, show increased numbers in acute hippocampal slices compared to perfusion‐fixed sections. These alterations in dendritic spines could be one of the underlying mechanism explaining differences in ex vivo and in vivo electrophysiological experiments, as for instance success rates in long‐term depression (LTD) induction protocols. In our experiments, we have compared dendritic spine density in the cornu ammonis 1 (CA1) and dentate gyrus (DG) between hippocampal acute slices and aldehyde perfusion‐fixed hippocampi of Sprague‐Dawley (both males and females) using the lipophilic carbocyanine dye 1,1′‐Dioctadecyl‐3,3,3′,3′‐Tetramethylindocarbocyanine Perchlorate (DiI). We observed an increase in a range of 37–68% in dendritic spine density in the acute hippocampal slices when compared to aldehyde perfusion‐fixed sections independent of sex. These data suggest that spine plasticity in ex vivo electrophysiological experiments may not be reflective of the in vivo situation and interpretation of data should take this into account.Support or Funding InformationCanadian Institutes of Health ResearchNatural Sciences and Engineering Research CouncilThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.