HISTOCHEMICAL AND IMMUNOCYTOCHEMICAL STUDY OF THE MIGRATION OF NEURONS FROM THE RAT OLFACTORY PLACODE

Immunocytochemical and histochemical methods have been used to describ e the neuronal population migrating from the rat olfactory placode and to analyze the spatio-temporal evolution of this neuronal migration d uring development. Several neuronal markers, such as binding to the le ctin Ulex europaeus (UEA I) and the presence of neuron-specific enolas e (NSE), olfactory marker protein (OMP), and luteinizing hormone-relea sing hormone (LHRH), have been tested in order to determine whether mi grating neurons originate from both the medial and the lateral parts o f the placode and whether they all express LHRH. Our data show that a large population of differentiated migrating neurons can be identified with an antibody against NSE from the 14th day of gestation and with UEA I one day later. Migrating neurons are closely associated with bot h the vomeronasal axon fascicles emerging from the medial pit and the olfactory axons originating from the lateral pit. However, the neuron migration from the lateral pit appears to be more discrete than that f rom the medial pit. No LHRH immunoreactivity has been detected among n eurons migrating from the lateral pit. Some neurons accompanying the o lfactory axon fascicles exhibit a high level of maturation as shown by their OMP-positivity. Numerous neurons positive for both NSE and UEA I have also been observed within the presumptive olfactory nerve layer in early embryonic stages.