Elsevier

Neuroscience

Volume 138, Issue 2, 2006, Pages 403-409
Neuroscience

Cellular neuroscience
Density and morphology of dendritic spines in mouse neocortex

https://doi.org/10.1016/j.neuroscience.2005.11.038Get rights and content

Abstract

Dendritic spines of pyramidal cells are the main postsynaptic targets of cortical excitatory synapses and as such, they are fundamental both in neuronal plasticity and for the integration of excitatory inputs to pyramidal neurons. There is significant variation in the number and density of dendritic spines among pyramidal cells located in different cortical areas and species, especially in primates. This variation is believed to contribute to functional differences reported among cortical areas. In this study, we analyzed the density of dendritic spines in the motor, somatosensory and visuo-temporal regions of the mouse cerebral cortex. Over 17,000 individual spines on the basal dendrites of layer III pyramidal neurons were drawn and their morphologies compared among these cortical regions. In contrast to previous observations in primates, there was no significant difference in the density of spines along the dendrites of neurons in the mouse. However, systematic differences in spine dimensions (spine head size and spine neck length) were detected, whereby the largest spines were found in the motor region, followed by those in the somatosensory region and those in visuo-temporal region.

Section snippets

Preparation of material and cell injections

C57BL/6 mice (n=2 males, 2 months old) were anesthetized by administering a lethal i.p. injection of sodium pentobarbitone and they were then perfused intracardially with 4% paraformaldehyde in 0.1M phosphate buffer. All experiments were performed in accordance with the guidelines established by the European Union regarding the use and care of laboratory animals. The brains were removed from each animal and the cortex of the right hemisphere was flattened between two glass slides before

Density and total number of spines on the basal dendrites

We first compared the structure of dendritic trees between different cortical areas. Plotting the results of the Sholl 2-D analysis and the 3-D analysis revealed that on average, pyramidal cell dendrites in M2 had more branches than those in S2. Furthermore, on average those in S2 had more branches than those in V2L/TeA (Fig. 3A). Similarly, the peak branching complexity in the basal dendritic trees of pyramidal cells in M2 was higher than that in S2 and V2L/TeA. An analysis of variance of the

Discussion

This study has generated two major findings. Firstly, we found no significant differences in spine density at the corresponding distances along the basal dendrites of layer III pyramidal cells between the M2, S2 and V2L/TeA regions of mice. In contrast, we did observe appreciable differences in our estimates of the total number of spines in the basal dendritic trees of pyramidal neurons between these three regions. Secondly, we found significant differences in the head size and neck length of

Acknowledgments

We thank the members of our laboratories for their assistance, especially to J. Arellano for the discussions regarding statistics. This work was supported by the Spanish Ministry of Education and Science (BFI2003-02745), the Comunidad de Madrid (grant 08.5/0027/2001), the National Health and Medical Research Council of Australia (G.N.E.) and the National Eye Institute and the Human Frontiers Science Project (R.Y.). I.B.-Y. is research fellowship of the Spanish Ministry of Education and Science

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