Abstract
The trigeminal subnucleus caudalis (Vc), which has been designated as the “medullary dorsal horn”- analogous to the spinal dorsal horn (DH), relays noxious input from the orofacial region to higher brain centers. Recent work in our lab has demonstrated numerous developmental differences in dissociated cultures of Vc and DH neurons. When compared with DH neurons, the growth of neurons located in the Vc was significantly slower, and glutamate receptor activity was relatively low. Detailed studies using Hoechst 33342 and TUNEL imaging assays, suggested that when compared with DH neurons, more mature neurons in Vc underwent cell death. Co-culture with DH cells remarkably improved the neuronal growth and increased the incidence of mEPSCs in Vc, while DH neurons co-cultured with Vc cells apparently exhibited slowed growth rate and a reduced incidence of mEPSCs. Recent work has also shown that blockade of P2X7 channels or 11â-hydroxysteroid dehydrogenase type 2 (HSD2), which catalyzes the conversion of corticosterone to an inactive metabolite, significantly promoted neuronal growth in both Vc and DH cultures. Using the conditioned medium from dissociated and organotypic slice cultures, we isolated several factor(s) using size exclusion column chromatography from both Vc and DH tissues. One of the factor(s) in the Vc conditioned medium, Vc-NF2, caused a decrease in live cells when applied to dissociated cortical neurons, while one of the factor(s) in the DH conditioned medium, DH-NF1, caused an increase in live cells when applied to dissociated cortical neurons. Based on the above findings, we conclude that the development of Vc neurons may be region-specifically regulated by locally released factor(s). These studies will provide novel insights into the mechanisms of Vc neuronal development, which could ultimately lead to better analgesic craniofacial regimes for infants or adults.
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