EXCESS NERVE GROWTH-FACTOR IN THE PERIPHERY DOES NOT OBSCURE DEVELOPMENT OF WHISKER-RELATED PATTERNS IN THE RODENT BRAIN

We have addressed the issue of whether or not peripherally expressed n erve growth factor (NGF) influences the formation of whisker-specific patterns in the brain by regulating the survival of sensory neurons. T ransgenic mice that overexpress an NGF cDNA in the skin were examined. In these animals, excess NGF expression is controlled by promoter and enhancer sequences of a keratin gene, thus restricting the higher lev els of NGF expression to basal keratinocytes of the epidermis. Twice t he number of trigeminal sensory neurons survive in transgenic mice as in normal animals, and a corresponding hyperinnervation of the whisker pad is noted, both around the vibrissa follicles and along the interv ibrissal epidermis. However, the increased survival of sensory neurons and the enhanced peripheral projections do not interfere with the dev elopment of whisker-specific patterns in the trigeminal brainstem, in the ventrobasal thalamic complex or in the face-representation region of the primary somatosensory (SI) cortex. These results demonstrate th at vibrissa-related central patterns are able to form in the virtual a bsence of trigeminal ganglion cell death and suggest that mechanisms o ther than a selective elimination of sensory neurons control the devel opment of whisker-specific neural patterns in the brain. (C) 1996 Wile y-Liss, Inc.