'Mirror pain' in the formalin test: behavioral and 2-deoxyglucose studies.
Subcutaneous injection of a dilute formaldehyde solution (5 or 10%) into a hind paw induced, in the majority of rats, the appearance of 'mirror pain': licking the contralateral untreated hind paw 10-60 min after injection. Contralateral licking activity was much less frequent than the ipsilaterally directed one, but the overall intensities of the two responses were positively correlated. Qualitatively, the two behaviours were similar. Functional activity levels of the lumbar spinal cord, as revealed by the 2-deoxyglucose (2-DG) technique, were increased bilaterally over the first hour after unilateral hind limb formalin injection in unanesthetized, freely moving rats. The enhancement of the [14C]2-DG uptake could be detected both in dorsal and ventral horns, as well as in the gray matter surrounding the central canal, and the anterolateral and dorsolateral funiculi. These metabolic changes may reflect an enhancement of the functional activity of both interneuronal pools and units projecting to supraspinal centers, giving rise to a referred contralateral pain.
Aloisi
Anna Maria
AM
Istituto di Fisiologia Umana, Universitá di Siena, I-53100 SienaItaly Dipartimento di Scienze e Tecnologie Biomediche, Università di Udine, I-33100 UdineItaly Clinica Neurologica, Università di Modena, 1-41100 ModenaItaly Istituto di Fisiologia Umana, Università di Modena, 1-41100 ModenaItaly.
Porro
Carlo Adolfo
CA
Cavazzuti
Milena
M
Baraldi
Patrizia
P
Carli
Giancarlo
G
D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects*; D003847:Deoxyglucose; D005557:Formaldehyde; D006120:Grooming / Q000187:drug effects; D008297:Male; D009474:Neurons / Q000187:drug effects / Q000502:physiology; D010147:Pain Measurement / Q000187:drug effects*; D051381:Rats; D017207:Rats, Sprague-Dawley; D017208:Rats, Wistar; D013116:Spinal Cord / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D014726:Vestibular Nuclei / Q000187:drug effects / Q000378:metabolism
D005557:Formaldehyde; D003847:Deoxyglucose