Single axon tracing from Locus Coeruleus to Mesencephalic Trigeminal Nucleus

Objectives: The mesencephalic trigeminal nucleus has synapses with several different peptides, however, little is known on the origin of these afferents. To study whether the mesencephalic trigeminal nucleus receives projections from the locus coeruleus, we injected a small amount of biotinylated dextran amine (BDA) into the locus coeruleus.

Methods: Rats were deeply anesthetized with pentobarbital and were mounted in a stereotaxic apparatus. Then a small amount of BDA (0.1~0.5ul) was injected into the locus coeruleus through a glass micropipette.

Results: Labeled neurons were identified in the locus coeruleus using a phase contrast microscope. Only a few locus coeruleus neurons were labeled, and the labeled axon were traced to the mesencephalic trigeminal nucleus. We found labeled terminal swellings on the neural cell bodies of the mesencephalic trigeminal nucleus.

Conclusion: The mesencephalic trigeminal nucleus receives direct projection from the locus coeruleus. We thus suggest that, when animals are put into noxious situations, the activity of the locus coeruleus increases and modulates the response of the mesencephalic trigeminal nucleus.

Supported by the Ministry of Education, Culture, Sports, Science and Technology of Japan (Open Research Center subsidy (H18) to S.S and Grants-in-Aid for Scientific Research(C) 18591912 to H.N.)