Morphologic and functional peculiarities of the visceral protoneuron reexamined in light of recent data

The recent works showing the richness and complexity of the sensory innervation of viscera raise various questions which are of general interest for modern physiology. 1 - The primary afferent neurons are much more numerous and heterogeneous than it was usually expected. Moreover, another category of neurones, namely the sensory intrinsic neurons, must be taken in consideration. These neurones end either in the intrinsic plexuses of viscera or in the prevertebral ganglia. 2 - Another major question concerns the mechanisms responsible for the functional diversity of interoceptors including the chemoreceptors. Several hypothesis have been proposed involving the presence of membrane receptors, the release of neurotransmitters by chromaffin cells and the deformation of tissue. In any way, the functional characteristics of interoceptors do not result in morphological differentiation since free endings are mainly found in the visceral area. 3 - Does the functional properties of primary afferent neurons are related to their morphological (diameter of fibres, size of cell bodies) or their biochemical (type of neurotransmitters) characteristics? So far, it is not possible to answer this question. Nevertheless the available data suggest that a such relationship partly exists. 4 - The visceral afferents are largely implicated in various physiological mechanisms involving visceral motility, homeostasis and behaviour. Therefore, their role in pain appear relatively less important than previously expected. Conversely, the nervous mechanisms induced by the interoceptor activation play a major part in that they prepare and potentialize the effects produced by the other mechanisms.     

Multiple effects of differentiation-inducing factor on prespore differentiation and cyclic-AMP signal transduction in Dictyostelium

Abstract. The effects of the differentiation inducing factor (DIF) on several CAMP-induced responses in Dictyostelium were investigated. It was found that DIF reduces the apparent affinity of cell-surface cAMP receptors. DIF does not affect the CAMP-induced cGMP response, but it is a potent inhibitor of the CAMP-relay response. DIF also inhibits the induction of prespore differentiation by cAMP in aggregation-competent cells. We also compared the effects of DIF on CAMP-induced responses with those of the relay inhibitor, caffeine, and the morphogen, adenosine.