Gap junction modulation by extracellular signaling molecules: the thymus model

Gap junctions are intercellular channels which connect adjacent cells and a llow direct exchange of molecules of low molecular weight between them. Suc h a communication has been described as fundamental in many systems due to its importance in coordination, proliferation and differentiation. Recently , it has been shown that gap junctional intercellular communication (GJIC) can be modulated by several extracellular soluble factors such as classical hormones, neurotransmitters, interleukins, growth factors and some paracri ne substances. Herein, we discuss some aspects of the general modulation of GJIC by extracellular messenger molecules and more particularly the regula tion of such communication in the thymus gland. Additionally, we discuss re cent data concerning the study of different neuropeptides and hormones in t he modulation of GJIC in thymic epithelial cells. We also suggest that the thymus may be viewed as a model to study the modulation of gap junction com munication by different extracellular messengers involved in non-classical circuits, since this organ is under bidirectional neuroimmunoendocrine cont rol.