Opioid peptide levels in brain after prenatal alcohol in the rat

In Drosophila, as in all arthropods, sensory neurons differentiate in the periphery; their axons grow over the peripheral epidermal cells or their associated extracellular material in towards the CNS. Based on the study of wing receptors in wild type flies, in mutants which produce supernumerary, ectopic receptors, and in mutants which block receptor differentiation, we suggest the following picture: (i) Each peripheral sensory neuron, like each epidermal cell, belongs to either the anterior or the posterior compartment of its segment. However, its compartmental location, and thus its lineage, does not directly govern the path which its axon takes to the CNS. (2) The axons of ectopic receptors of mutant flies grow with consistently correct polarity only at the sites of normal nerves; elsewhere they grow in a variety of directions. Thus, they do not obtain polarity information for directed axon growth from the general epidermis. (3) The sequence of differentiation of neurons, both in normal and in mutant flies, suggests that early-formed axons guide later-formed ones. Preliminary evidence from mosaic animals, in which specific neurons are deleted genetically, is consistent with this interpretation° Thus, the location and sequence of differentiation of neurons are dominant factors in peripheral neurogenesia, though other factors, including mechanical ones, may certainly make significant contributions.