Dendritic Spines in the Spinal Cord: Live Action Pain

Abstract

Dendritic spines are microscopic protrusions on neurons that house the postsynaptic machinery necessary for neurotransmission between neurons. As such, dendritic spine structure is intimately linked with synaptic function. In pathology, dendritic spine behavior and its contribution to disease are not firmly understood. It is well known that dendritic spines are highly dynamic in vivo. In our recent publication, we used an intravital imaging approach, which permitted us to repeatedly visualize the same neurons located in lamina II, a nociceptive processing region of the spinal cord. Using this imaging platform, we analyzed the intravital dynamics of dendritic spine structure before and after nerve injury-induced pain. This effort revealed a time-dependent relationship between the progressive increase in pain outcome, and a switch in the steady-state fluctuations of dendritic spine structure. Collectively, our in vivo study demonstrates how injury that leads to abnormal pain may also contribute to synapse-associated structural remodeling in nociceptive regions of the spinal cord dorsal horn. By combining our live-imaging approach with measures of neuronal activity, such as with the use of calcium or other voltage-sensitive dyes, we expect to gain a more complete picture of the relationship between dendritic spine structure and nociceptive physiology.

Keywords: 2-photon microscopy; Dendritic spines; dorsal horn; intravital imaging; nerve injury; pain.

Figure 1.

In vivo imaging of superficial spinal cord neurons: (A) Design of custom 3D printed gimbal imaging stage. Glass windows are implanted over the lumbar region of the surgically exposed spinal cord, which permits imaging of 3D volumes of the dorsal horn (WM; white matter, GM; gray matter). (B) Intravital captured image of a dorsal spinal cord neuron with dendritic spines. Adjacent panel (right) shows a magnified image of the dendritic branch region denoted by * (left). Scale bars in (B) are both 10 µm. Source: Images adapted from Benson et al.