The first part of this contribution reviews the current knowledge about endocrine and neuromodulatory actions of somatostatin. These biological actions are exerted according to endocrine, paracrine and autocrine modes of action and involve five distinct types of membrane receptors belonging to the 'super-family' of G-protein-coupled receptors. A new concept concerning a juxtacrine mode of action has recently been introduced to refer to the intervention of cytokines and growth factors in direct, cell-to-cell communication. The evidence in favor of juxtacrine actions of somatostatin will be presented in the second part of this review and illustrated by our own results on macrophage-lymphocyte T interactions in the immune system and spermatogonia -Sertoli cell interactions in mammalian testis. Another phenomenon such as ligand-induced somatostatin receptor homo-and hetero-dimerization resulting in 'poly'-receptors (with characteristics different from those of each of the two receptors forming the complex) is also at the origin of a novel mode of somatostatin action. The latter will be illustrated by the data obtained on human pituitary adenomas with somatostatin analogs specific for either 'poly'-receptor or relevant individual receptors. The arguments in favor of the analogous mode of actions among different families of chemical messengers such as peptides, cytokines and growth factors are discussed in the concluding section. The emerging unifying concepts on such functional analogies might provide a useful basis for the development of synthetic analogs not only for bioactive peptides but also for other types of chemical messengers.European Journal of Endocrinology 151 643-655

Collapsin-response mediator proteins (CRMPs) are highly expressed in the developing brain where they take part in several aspects of neuronal differentiation. CRMPs are still present postnatally, but their function remains speculative in the adult brain. We studied the expression and localization of CRMP1, CRMP2 and CRMP5 in two areas of the nervous system with persistent neurogenesis in adult mice, the olfactory mucosa and the olfactory bulb. In the olfactory mucosa, we have established that CRMP expression is restricted to postmitotic cells of the olfactory neurons lineage. CRMP5 is coexpressed with growth associated protein of 43 kDa (GAP43) in immature olfactory neurons and is down-regulated in olfactory marker protein-positive mature neurons. In contrast, CRMP1 and CRMP2 persist at all stages of differentiation from immature GAP43-positive to fully mature olfactory neurons. In the olfactory bulb, CRMP1, CRMP2 and CRMP5 are abundant in neuronal progenitors of the subependymal layer and in differentiating interneurons. In both areas, the subcellular distribution of CRMP1 or CRMP2 is different in mature vs. immature neurons, suggesting that these proteins are sequentially involved in various cellular events during neuronal lifetime. The variations of CRMP expression following axotomy are consistent with their differential localization and functional involvement in immature vs. mature neurons of the olfactory system. Our data bring new insight to the putative functions of CRMPs within areas of the adult nervous system with permanent neurogenesis, some related to differentiation of newly generated neurons but others occurring in mature neurons with a limited lifespan.

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