In vitro analysis of the centripetal migration mechanisms of developing LHRH neurons

This study was designed to gain insight into the underlying mechanisms of the centripetal migration of developing LHRH neurons. The medial wall of the nasal pit (NAP) of 12.5-day-old rat embryos (E12.5) was cultured singly or together with the E12.5 medial-basal wall of the forebrain vesicles (mFV) or with the E14.5 median eminence-arcuate complex (ME-Arc). Further, the NAP was cultured with the mFV and ME-Arc or with the mFV and nasal mesenchyme (NM), which lay between the mFV and the NAP, of E12.5 embryos (triple culture). The NAP gave rise first to fibers labeled with anti-neural cell adhesion molecules (NCAM) and then to LHRH neurons. In co-cultures, NAP- and brain-derived NCAM fibers connected the NAP and brain cultures, and frequently linked with each other to form knots at the periphery. LHRH neurons migrating along the NAP-derived fibers directly or indirectly entered brain cultures. In the latter case, the cells strayed along the way from the NAP-derived fibers to the brain-derived fibers at the knots and migrated retrogradely along the latter fibers to enter into the brain tissues; this occurred most frequently into the E14.5 ME-Arc. In triple cultures, abundant NCAM fibers emerging from the NAP were only found when the NM lay between the NAP and mFV; the fibers converged further to the mFV. These findings help elucidate the mechanisms underlying the centripetal LHRH cell migration from the NAP to the hypothalamus.