ABSTRACT
Low-power, soft, or low-level laser irradiation has been successfully used to provide analgesia in injured or diseased tissues. In this study, we tested the possible antinociceptive effect of laser irradiation when applied to a normal tissue before the onset of a painful stimulus. Male Wistar rats (350-380 g) were used. A 1.5% formalin solution (50 microL s.c., diluted in saline) was injected into the right upper lip of the test animals (n = 9) immediately after 10 min of low-power Er:YAG laser irradiation (wavelength: 2.94 microm; energy: 0.1 J/cm(2)/pulse at 10 Hz). Control animals (n = 9) were restrained for 10 min without laser application. The nociceptive response, i.e., the amount of time the rats spent rubbing the formalin injected area, was measured by an investigator blind to whether the animals had been laser irradiated or not. On laser irradiated rats, significantly less nociceptive behavior was observed only during the late phase (12-39 min) of the test. This result is similar to that reported for nonsteroid antiinflammatory drugs (NSAIDs) and other peripherally acting antiinflammatory agents. We conclude that low-power laser irradiation have a tonic antinociceptive effect on inflammatory pain even when applied before tissue injury.
Subject(s)
Facial Pain/chemically induced , Facial Pain/radiotherapy , Formaldehyde , Low-Level Light Therapy , Animals , Male , Pain Measurement/methods , Rats , Rats, Wistar , Time FactorsABSTRACT
Response properties of nociceptors in the temporomandibular joint (TMJ) and surrounding area under experimental inflammation were investigated using an in vitro TMJ-nerve preparation in the rat. Nociceptive units (receptor and innervating nerve fiber) were classified into the following subtypes: Adelta-high-threshold mechanonociceptor (HTM), Adelta-polymodal nociceptor (POLY), C-HTM and C-POLY. In the inflamed joint, mechanical thresholds tended to be lower; however, the reaction to bradykinin was not identified as clearly as in control. Experimentally induced inflammation increased the proportion of heat-sensitive units and lowered heat threshold significantly. These results suggest that inflammation may sensitize nociceptors in the temporomandibular joint, and cause hyperalgesia and allodynia.
Subject(s)
Arthralgia/physiopathology , Arthritis/physiopathology , Nociceptors/physiology , Sensory Receptor Cells/physiology , Temporomandibular Joint Disorders/physiopathology , Temporomandibular Joint/innervation , Action Potentials/drug effects , Action Potentials/physiology , Animals , Arthralgia/chemically induced , Arthralgia/pathology , Arthritis/chemically induced , Arthritis/pathology , Bradykinin/pharmacology , Carrageenan/pharmacology , Disease Models, Animal , Hyperalgesia/pathology , Hyperalgesia/physiopathology , Kaolin , Mechanoreceptors/drug effects , Mechanoreceptors/physiology , Nerve Fibers, Myelinated/drug effects , Nerve Fibers, Myelinated/physiology , Nerve Fibers, Unmyelinated/drug effects , Nerve Fibers, Unmyelinated/physiology , Nociceptors/drug effects , Pain Threshold/drug effects , Pain Threshold/physiology , Physical Stimulation , Rats , Rats, Wistar , Sensory Receptor Cells/drug effects , Temporomandibular Joint/pathology , Temporomandibular Joint/physiopathology , Temporomandibular Joint Disorders/chemically inducedABSTRACT
Response properties of nociceptors in the rat's temporomandibular joint (TMJ) were investigated using an in vitro TMJ-nerve preparation. Recordings were obtained from 33 nociceptive units that responded to mechanical, chemical, and/or thermal stimuli. According to both characteristics of nociceptors and afferent fibers, nociceptive units in the TMJ area were classified into the following four subtypes: Adelta-high-threshold mechanonociceptor (HTM) (12.1%), Adelta-polymodal nociceptor (POLY) (36.4%), C-HTM (12.1%), and C-POLY (39.4%). The mean mechanical threshold of the Adelta units was significantly lower than that of the C units. Bradykinin increased the discharge of Adelta- and C-POLY units. No significant differences of thermal thresholds between Adelta and C units were found. The percentage of Adelta units was 47.2% and of C units was 52.8%, respectively. In the TMJ area, POLY units were predominant (75.8%), suggesting that inflammatory reactions can easily evoke pain sensation.
