OXIDATIVE CAPACITY OF RAT MASSETER MUSCLE AFTER IMPLANTATION OF THYROTROPIN-RELEASING-HORMONE MICROSPHERES IN PROXIMITY TO TRIGEMINAL MOTONEURONS

Earlier work has shown that two important consequences of implanting t hyrotropin-releasing hormone (TRH) microspheres near motoneurones with in the trigeminal motor nucleus of actively growing rats are increased muscle mass and a darkening of the implant-side masticatory muscles. These phenomena have been associated with altered neuromuscular activi ty patterns and biomechanical forces that directly influence craniofac ial growth and development. Now, whether the implantation of TRH micro spheres in proximity to trigeminal motoneurones would affect the oxida tive capacity of the implant-side masseter muscles was investigated. C ytochrome C oxidase (COX) assays were carried out for both implant- an d non-implant-side masseters of TRH (n = 5) and blank microsphere (n = 6) Sprague-Dawley rats after stereotactic surgery at 35 days of age. Analyses of both groups at 14 days post-implantation revealed that the COX activity levels of implant-side masseters in TRH-implanted rats w as significantly (P less than or equal to 0.05) greater than that of n on-implant-side masseters; rats implanted with blank microsphere exhib ited no significant difference between implant- and non-implant-side m asseter COX activity levels. The stated null hypothesis was therefore rejected. These data suggest that TRH implants in proximity to trigemi nal motoneurones effect increased oxidative capacity of the masseter m uscle as measured by COX activity. (C) 1998 Elsevier Science Ltd. All rights reserved.