CAPSAICIN APPLICATION TO THE TEMPOROMANDIBULAR-JOINT ALTERS CALCITONIN-GENE-RELATED PEPTIDE LEVELS IN THE TRIGEMINAL GANGLION OF THE RAT

The aim of this investigation was to determine the temporal effect of an intra-articular injection of capsaicin to the temporomandibular joi nt on the levels of calcitonin gene-related peptide-like immunoreactiv ity (CGRP-ir) in the trigeminal ganglion of the rat. The semporomandib ular joints of 26 adult female rats were injected on one side with cap saicin and contralaterally with a control vehicle. Another 8 animals s erved as nn untreated control group and received Mo injections. Animal s were sacrificed at time intervals of 4 hours, 48 hours, 10 days, and 21 days following treatment. The trigeminal ganglia were extirpated, and CGRP-ir-levels were quantified using a radioimmunoassay. Results d emonstrated that when the capsaicin-treated side and the vehicle-treat ed side were compared, CGRP-ir levels decreased initially at 4 hours a nd increased at 48 hours. Ar 10 days, CGRP-ir levels had again dropped below control levels, followed by an increase at 21 days. CGRP-ir lev els for the first two time periods investigated which simulate an acut e Inflammatory state, mimic results observed in studies using limb joi nts, while the other rime periods, which represent an intermediate and a chronic condition?, respectively, suggest a more complex, interacti on with capsaicin-sensitive primary afferents.