CRANIOFACIAL AND TMJ EFFECTS AFTER GLUTAMATE AND TRH MICROSPHERE IMPLANTATION IN PROXIMITY TO TRIGEMINAL MOTONEURONS OF GROWING RATS

The sequelae of sustained, in vivo delivery of two important neurotran smitter substances, glutamate and thyrotropin-releasing hormone (TRH), upon craniofacial growth and development have previously not been inv estigated. Our purpose was to document and compare the relative effect s of glutamate and TRH microspheres stereotactically placed in proximi ty to trigeminal motoneurons within the trigeminal motor nucleus. The following null hypotheses were tested: (1) TRH microspheres in proximi ty to trigeminal motoneurons have no significant effect upon the crani ofacial skeleton, and (2) there are no significant differences between the relative effects of chronic, long-term delivery of glutamate and TRH upon the neuromusculoskeletal system of growing rats. Forty male S prague-Dawley rats were divided into 4 experimental groups (glutamate microspheres, TRH microspheres, blank microspheres, sham surgeries) an d underwent stereotactic neurosurgery at 35 days; 5 rats of each group were killed at 14 and 21 days for data collection. Histology revealed that implants were clustered in the pontine reticular formation, clos e to the ventrolateral tegmental nucleus. Both glutamate and TRH rats had implant-side deviation of their facial skeleton and snout regions; 4 x 2 ANOVA and post hoc t-tests revealed significant (P less than or equal to 0.05, 0.01) differences between groups and sides for motoneu ron count, muscle weight, and osteometric data. TRH rats also demonstr ated larger implant-side TMJ discs and mandibular fossae in comparison with the other groups. The stated null hypotheses were therefore reje cted.