Repeated amphetamine treatment alters spinal magnetic resonance signals and pain sensitivity in mice

• Repeated amphetamine declined the reactivity to thermal stimulus in mice.
• Manganese-enhanced MR signals were collected from the spinal dorsal horn of mice.
• Repeated amphetamine concurrently reduced pain responses and increased MR signals.

Manganese-enhanced magnetic resonance imaging (MEMRI) has been extensively used in studying the structural and functional features of the central nervous system (CNS). Divalent manganese ion (Mn2+) not only enhances MRI contrast, but also enters cells via voltage-gated calcium channels or ionotropic glutamate receptors, which represents an index of neural activities. In the current mouse model, following the repeated amphetamine (Amph) treatment, a reduction of reactivity to thermal pain stimulus was noticed. Since the spinal dorsal horn is the first relay station for pain transmission in CNS, we examined the changes of neural activity in the dorsal spinal cord, particularly the superficial dorsal horn, by analyzing manganese-enhanced T1-weighted MR images (T1WIs). Our data revealed a temporal correlation between reduced pain sensitivity and increased MEMR signals in the spinal dorsal horn subsequent to repeated Amph treatments.