Gap junctions in the chicken pineal gland

The chicken pineal gland, which contains a heterogeneous cell population, s ustains a circadian rhythm of activity. Synchronization of cellular activit y of heterogeneous cells might be facilitated by gap junctional intercellul ar channels which are permeable to ions and second messengers. To test this possibility, we looked for morphologically identifiable gap junctions betw een the different pineal cells, used antibodies and cDNA probes to screen f or the presence of connexins, and tested for functional intercellular coupl ing. By transmission electron microscopy and immunocytochemistry, gap junct ions and connexins were observed between pinealocyte cell bodies, stromal c ells, astrocytes, and astrocyte and pinealocyte processes. Two gap junction al proteins, connexin43 and connexin45, were detected by immunocytochemistr y, immunoblotting and RNA blot analysis. Functional intercellular coupling was observed in the gland by transfer of low molecular weight dyes. Dye tra nsferred between homologous and heterologous cells. These data suggest that homologous and heterologous gap junctions may provide a mechanism for coor dination of the cellular responses of the elements of the biological clock which are induced by lighting cues to produce the circadian rhythm of pinea l activity. (C) 2000 Elsevier Science B.V. All rights reserved.