Development of trigeminal motoneuron

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Feeding behavior of mammals changes from relatively simple sucking to complicated mastication during development. It should be very important that development of central neural mechanisms for feeding behavior is coordinated with the development of organs in oro-facial area. Trigeminal motoneurons play an important role in converting centrally organized masticatory drive to jaw movements. In the present study, we investigated developmental change of physiological properties of trigeminal motoneurons in rats age by using intracellular or patch clamp recordings. As we previously reported, application of 200 μM 5-HT suppressed the mAHP.Application of 25-200 μM 8-OH-DPAT, 5-HT_<1A> and 5-HT_7 receptor agonist, inhibited the mAHP dose-dependently. Application of pindolol, 5-HT_<1A> receptor antagonist failed to block 8-OH-DPAT-induced attenuation of the mAHP, whereas clozapine, dopamine D_2, 5-HT_<2A/2C> and 5-HT_7 receptor antagonist, antagonized both 5-HT- and 8-OH-DPAT-induced suppression of the mAHP.Ritanserin, 5-HT_<2A/2C> and 5-HT_7 receptor antagonist, also blocked 8-OH-DPAT-induced suppression of the mAHP.α-methyl-5-HT, 5-HT_<2A/2C> receptor agonist, did not attenuate the mAHP.The 8-OH-DPAT-induced suppression of the mAHP could be also antagonized by protein kinase A (PKA) inhibitor, H89. These results suggest that 5-HT-induced attenuation of the mAHP is mediated by 5-HT_7 receptors through activation of PKA in young adult rats. In contrast application of 10-100 μM 5-HT to trigeminal motoneurons of neonatal rats modulates low voltage activated (LVA) calcium currents. 5-HT lowered activation threshold, increases peak amplitude and decreases time to peak and τ_m of LVA currents. 8-OH-DPAT and 5-CT, a 5-HT_7 agonist, did not mimic the effects of 5-HT.We conclude that trigeminal motoneurons are modulated differently by 5-HT according to their age.