INTRACELLULAR INJECTIONS OF LUCIFER-YELLOW INTO LIGHTLY FIXED MITRAL CELLS REVEAL NEURONAL DYE-COUPLING IN THE DEVELOPING RAT OLFACTORY-BULB

We report that intracellular injections of Lucifer Yellow into lightly fixed mitral cells revealed dye-coupling between mitral cells and bet ween mitral and granule cells in the form of discrete, radially orient ed cell clusters. Dye-coupling was observed in animals as early as pos tnatal day 10 (P10) and at least until P30. In P10 rats, a mean of 2.5 dye-coupled mitral cells and 27 granule cells were observed per colum n. Mean column depth and width were 169 mu m and 86 mu m respectively. Most of the dye-filled granule cells were found within 150 mu m of th e mitral cell layer. No significant changes were found at P2O. By P30, the mean number of granule cells per column increased to 42 and the a ddition of granule cells occurred in areas proximal to the mitral cell layer. Immunocytochemical results indicate that the developing bulb c ontains a large concentration of the gap junction protein Connexin 43 (Cx43). Cx43-like immunoreactivity was found at all ages examined, wit h the most intense staining in the nerve and glomerular layers. Less i ntense Cx43-like immunoreactivity was found in both the mitral and gra nule cell layers, with Cx43-like immunoreactive puncta observed betwee n and around cell body profiles. Freeze-fracture analysis revealed the presence of gap junction-like plaques on mitral cells, further sugges ting that the dye-coupling occurred across interneuronal gap junctions . Neuronal coupling during development could provide an inter-cellular pathway for the passage of relevant developmental signals which could influence the formation and/or strengthening of synaptic contacts. Th e coupling could also be involved in the synchronization of neuronal a ctivity, which may be important for olfactory coding.