Measurements of neuron soma size and density in rat dorsal striatum, nucleus accumbens core and nucleus accumbens shell: differences between striatal region and brain hemisphere, but not sex

Abstract

Both hemispheric bias and sex differences exist in striatal-mediated behaviors and pathologies. The extent to which these dimorphisms can be attributed to an underlying neuroanatomical difference is unclear. We therefore quantified neuron soma size and density in the dorsal striatum (CPu) as well as the core (AcbC) and shell (AcbS) subregions of the nucleus accumbens to determine whether these anatomical measurements differ by region, hemisphere, or sex in adult Sprague-Dawley rats. Neuron soma size was larger in the CPu than the AcbC or AcbS. Neuron density was greatest in the AcbS, intermediate in the AcbC, and least dense in the CPu. CPu neuron density was greater in the left in comparison to the right hemisphere. No attribute was sexually dimorphic. These results provide the first evidence that hemispheric bias in the striatum and striatal-mediated behaviors can be attributed to a lateralization in neuronal density within the CPu. In contrast, sexual dimorphisms appear mediated by factors other than gross anatomical differences.

Figure 1

Neuron soma size and density differed between the CPu, AcbC and AcbS. A) Neuron soma size was significantly increased in the CPu compared to the AcbC and AcbS (p<0.0001 for both). B) Neurons were denser in the AcbS compared to both the CPu and the AcbC (p<0.001 for both), and in the AcbC compared to the CPu (p<0.001).

Figure 2

Neuron soma size did not differ by sex or hemisphere. For all subpanels: Left: Neuron soma size compared by sex. Middle: Neuron soma size compared between hemispheres in males. Right: Neuron soma size compared between hemispheres in females. A) CPu. B) AcbC. C) AcbS. For all comparisons p>0.05.

Figure 3

Neuron density was lateralized in the CPu but otherwise did not vary by sex or hemisphere. For all subpanels: Left: Neuron density compared by sex. Middle: Neuron density compared between hemispheres in males. Right: Neuron density compared between hemispheres in females. A) CPu. Neurons were significantly denser in the left hemisphere compared to the right in both males and females (p=0.037). B) AcbC. C) AcbS. Except for that noted above, for all comparisons p>0.05.