XXXX induces serotonergic axon sprouting in cerebral cortex of newborn @entity35 .

@entity35 @entity2955 @entity750 @entity15582
Newborn @entity35 were administered the neurotoxin @entity2955 ( @entity2955 ) to determine whether neonatal ablation of the noradrenergic (NE) innervation produces augmented growth (i.e., sprouting) of serotonergic ( @entity750 ) raphe-cortical axons. Following NE denervation at birth, the density of @entity750 axons in motor cortex ( @entity15582 ) was determined at 4 days postnatal. Using a computer microscope system, the positions of all @entity750 -positive axons were mapped in radial strips of cortex from treated and control @entity35 . Cumulative axon length, expressed as a function of area inspected, was used as a parameter of innervation density. Following @entity2955 , the cumulative length of @entity750 axons in motor cortex increases by 32% (P less than 0.05) while cortical @entity750 levels measured by HPLC concomitantly increase by 29% (P less than 0.005). The combined increases in @entity750 axon density and in neurotransmitter levels indicate that NE denervation produces increased growth of the cortical @entity750 innervation by the 4th postnatal day. The amount of transmitter stored per unit length of @entity750 axons appears unchanged. In @entity2955 -treated @entity35 , @entity750 axons exhibit augmented growth in all layers of motor cortex. In the treated @entity35 , the relative density of @entity750 axons in each cortical layer is roughly proportional to the normal innervation density. Accordingly, in motor cortex, the magnitude of @entity750 axon sprouting is greatest in layer VI, which normally receives a dense @entity750 innervation, and is less in layer V, which has a lower innervation density. Qualitative assessment of other cortical areas following @entity2955 reveals that @entity750 axon density appears increased in cortical zones that normally receive a dense @entity750 innervation, while the density remains low in zones with sparse innervation. The absence of axonal sprouting is particularly striking in those zones which receive a dense NE innervation but are sparsely innervated by @entity750 axons. Thus, while @entity750 axons undergo sprouting, they do not appear to replace ablated NE terminals in areas with a sparse @entity750 innervation. Hence, normal laminar and regional specificity of @entity750 axons is preserved despite ablation of NE afferents. These data indicate that, while NE denervation may trigger serotonergic sprouting, competition between NE and @entity750 fibers for the same postsynaptic sites is not the main factor that regulates postnatal growth of these axonal projections. The present findings demonstrate that the early development of raphe-cortical projections is influenced by NE cortical innervation.(ABSTRACT TRUNCATED AT 400 WORDS)
