Increased in vivo levels of neurotransmitters to trigeminal motoneurons: effects on craniofacial bone and TMJ

Morphological analysis of the enamel organ in rats treated with fluoxetine

PURPOSE

Previous studies have evaluated the presence of serotonin in the dental epithelia and mesenchyme during odontogenesis, suggesting its participation in tooth development.

MATERIALS AND METHODS

Here, we used fluoxetine, a selective serotonin re-uptake inhibitor, at a dose of 10 mg/kg, administered for 20 days during pregnancy in 12 Wistar rats to examine the influence of this drug on the development of the enamel organ of the upper first molars of rat fetuses at 17 days of intra-uterine life (i.u.l.), and at one, five and ten days postpartum. The pregnant rats were anesthetized with xylazine at 10 mg/kg and ketamine at 25 mg/kg. The fetuses were removed and beheaded; their jaws were removed, and the upper jaws were exposed. The tissues were fixed in Bouin's fixative, decalcified in 5% nitric acid for 4 - 12 h, conventionally processed for microscopy, and embedded in paraffin. Serial sections of approximately 5 mum were obtained and stained with hematoxylin and eosin, as well as periodic acid-Schiff.

RESULTS AND CONCLUSION

Morphological analysis showed no structural changes in the experimental group compared to the controls, suggesting that, at the dose used, fluoxetine does not interfere with serotonin-mediated development of the enamel organ or the process of amelogenesis.

Effects of post-natal serotonin levels on craniofacial complex

Although the role of serotonin (5-hydroxytryptamine or 5-HT) in pre-natal craniofacial growth and development has been studied, no research has been done on the effects of serotonin on post-natal craniofacial growth and development. The following experimental question was tested: What effect does increasing in vivo serotonin levels adjacent to trigeminal motoneurons have on post-natal craniofacial structures in young, actively growing rats? Forty male Sprague-Dawley rats were divided into 4 experimental groups (10% serotonin microspheres, 15% serotonin microspheres, blank microspheres, sham surgeries) and underwent stereotactic neurosurgery at post-natal day 35; 5 rats of each group were killed at 14 and 21 post-surgical days for data collection. Statistical analyses by mixed-model, 4 x 2 repeated-measures ANOVA, and post hoc Fisher LSD tests revealed significant (P < or = 0.05, 0.01) differences between groups and sides for muscle weight, cranial dimension, and TMJ dimension data. Data described here indicate that significant alterations of post-natal craniofacial structures can be caused by altered in vivo levels of serotonin adjacent to trigeminal motoneurons.