Painful conditioning stimuli of the craniofacial region evokes diffuse noxious inhibitory controls in men and women

Abstract

Aims: To compare the modulatory effects of tonic mechanical or thermal craniofacial painful conditioning stimuli on pain sensitivity in craniofacial and spinal test sites in healthy men and women.

Methods: Mechanical and cold headbands were developed and tested on 12 healthy men and 12 age-matched women (mean +/- SEM: 27 +/- 1.5 years). The pressure applied by the mechanical headband around the skull above the eyebrows could be adjusted over time via feedback from a 0 to 10 electronic visual analog scale (VAS) to maintain the pain intensity at a given level for 10 minutes (3 to 7 on VAS). The cold headband consisted of a series of plastic bags filled with antifreeze water having a temperature of approx 3 degrees C. During the 10 minutes of application, the subjects were asked to rate the pain intensity on a 10-cm VAS. Pressure pain thresholds (PPT) were recorded over the right and left masseter muscles (MAR, MAL), right splenius muscle (neck), right elbow (elbow), and right middle finger (finger) by a pressure algometer (1-cm2 area probe). The PPTs at each of the five sites were determined at baseline and during the mechanical or cold-induced pain. The two sessions with mechanical or cold headbands were performed at an interval of 30 minutes.

Results: Women had significantly lower absolute PPT values than men at most test sites (Unpaired t-test: P < .027). The mechanical headband caused pain in both men (peak pain mean +/- SEM: 4.7 +/- 0.4 cm) and women (4.9 +/- 0.4 cm) (P = .455). A significant PPT elevation was found at MAR, MAL, neck, and finger in men (11% to 17%; P < .031) and at MAR, MAL, and neck in women (15% to 22%; P < .020) during the mechanical-induced pain. The cold headband caused pain in both men (4.0 +/- 0.4 cm) and women (4.5 +/- 0.4 cm) (P = .285). During the cold-induced pain, a significant PPT elevation was found at all test sites in men (P < .023) and at all sites (P < .021) except for the finger in women. The relative changes in PPT values were not significantly different between men and women at any test site (unpaired t-test: P > .446).

Conclusion: This study has documented that mechanical and thermal painful tonic stimuli applied to the craniofacial region can evoke diffuse noxious inhibitory control (DNIC)-like effects in the craniofacial region as well as spinally innervated areas, but without sex differences.