Increased insulin-like growth factor-I (IGF-I) expression during early postnatal development differentially increases neuron number and growth in medullary nuclei of the mouse

Morphometric analyses of the medulla were performed in transgenic mice that overexpress insulin-like growth factor-I (IGF-I) postnatally and in non-tr ansgenic littermates. The total volume of the medulla was increased in tran sgenic mice at all postnatal ages studied: 14 days (18%), 21 days (23%), 28 days (23%), and 35 days (27%). By 35 days of age, the volumes of individua l medullary nuclei were also increased: nucleus of the tractus solitarius ( NTS, 59%), dorsal motor nucleus of the vagus (DMV, 84%), hypoglossal nucleu s (HN, 29%) and facial nucleus (FN, 21%). Neuron number in transgenic mice was significantly greater in NTS (50%) and DMV (53%), but not in the HN or the FN. Motor neurons in DMV, HN and FN of transgenic mice exhibited increa ses in mean profile areas of the soma and decreased numerical densities, su ggesting increases in neuritic outgrowth. These results point to IGF-I acti ons in promoting neuron survival and growth, and suggest that IGF-I has dif ferential effects on distinct neuron populations, possibly depending upon i ts time of expression. (C) 1999 Elsevier Science B.V. All rights reserved.