Functional magnetic resonance imaging of the spinal cord during sensory stimulation in diabetic rats

Abstract

Purpose: To determine if differences exist between control and diabetic rats in functional magnetic resonance imaging (fMRI) activity of the spinal cord and if fMRI can provide a means of early detection of diabetic neuropathy.

Materials and methods: fMRI of the spinal cord, using noxious electrical stimulation (15 V ( approximately 8 mA), 0.3 msec, 3 Hz) of the hind paw, was performed in groups of control and streptozotocin (STZ)-induced type 1 diabetic rats.

Results: Diabetic rats were lighter, hyperglycemic, and had lower blood pH than controls. fMRI activity at the lumbar enlargement of the spinal cord was identified in the dorsal horn ipsilateral to stimulus of all animals. Signal intensity changes across the lumbar spinal cord during periods of activity were not significantly different between control and diabetic rats, with a trend toward greater signal changes in controls. When specific regions of the spinal cord were analyzed, control rats exhibited significantly increased blood-oxygen level-dependent (BOLD) fMRI activity in both ipsilateral and contralateral dorsal horn compared to diabetic rats.

Conclusion: The results of this study are consistent with reports that primary afferent input to the spinal cord is diminished by diabetes, and suggest that BOLD fMRI may be useful in early detection of diabetic neuropathy.

Figure 1

Averaged time courses of fMRI signal response to noxious electrical stimulation in diabetic (n=9) and control (n=9) rats. Data are group mean (N=9/group) ± SEM. Black horizontal bars represent periods of electrical stimulation with a total duration of approximately 36 seconds. Each data point represents a summation of signal collected over a 6 second imaging period. See text for details of the stimulation and imaging paradigm.

Figure 2

Combined fMRI activity maps of lumbar segments L1 through L6 in a) control and b) diabetic animals following noxious electrical stimulation of the right hind paw. Pixels are labeled as active only if a minimum of 3 of the 9 animals displayed fMRI activity at a level of p < 0.01 in each individual analysis. The colour coding demonstrates greater overlap of activity within the group increasing from yellow through red in the colour spectrum. The right side of the image is the right side of the animal.