Collateral sprouting

It was of interest that, in spite of the recovery of serotonin uptake sites to control levels, the content of serotonin in the same brain region remained markedly (40 to 50 percent) below age-matched controls for as long as 1 year after MDMA administration. It is unclear from these data whether there is a regeneration of axons that have previously undergone degeneration or whether the increased density of uptake sites is a consequence of increased collateral sprouting of neurons unaffected by the drug treatment. 

It is also possible that axonal regeneration and collateral sprouting arc associated with considerably greater densities of uptake sites per neuron, thereby making it more difficult to assess neuronal recovery from this index. The fact that serotonin levels remain 40 to 50 percent below age-matched controls for up to 1 year in spite of normal levels of serotonin uptake sites indicates that, following lesion by MDMA, the serotonin... 

Tassin J., Lavielle S., Herve D. et al. (1979). Collateral sprouting and reduced activity of the rat mesocortical dopaminergic neurons after selective destruction of the ascending noradrenergic bundles. Neuroscience 4, 1569-82. 

NGF infusions into the ventral hippocampus promoted axonal regeneration from the septum into the dorsal hippocampal formation, but did not induce sprouting of the nonlesioned cholinergic pathway that projects to the ventral hippocampal formation.164 Thus, as was also mentioned in Section 9.4.1.1, it is possible that NGF or other neurotrophic factors only or predominantly promote regeneration of lesioned axons in the adult brain. If so, the side effects of such treatments may not include or have limited effect on aberrant collateral sprouting of noninjured axons. One important question, which has not been resolved, is whether or how the neurotropic and guidance effects of NGF can be harnessed or even circumvented to allow a normal pattern of reinnervation and the formation of appropriate synaptic reconnections. 

Van der Zee, C. E., Fawcett, J., and Diamond, J., Antibody to NGF inhibits collateral sprouting of septohippocampal fibers following entorhinal cortex lesion in adult rats, J. Comp. Neurol., 326, 91, 1992. 

Cronin J, Dudek FE. Chronic seizures and collateral sprouting of dentate mossy fibers after kainic acid treatment in rats. Brain Res 1988 474 181-184. 

Diamond, J., Coughlin, M., MacIntyre, L., Holmes, M. and Visheau, B. (1987) Evidence that endogenous betanerve growth factor is responsible for the collateral sprouting, but not the regeneration of nociceptive axons in adult rats. Proc. Natl. Acad. Sci. USA 84 6596-6600. 

Corticospinal tract ( Collateral sprouting Newborn Schnell et al., 1994... 

At the site of the neuromuscular junction, each motor neuron forms collateral sprouts (Figure 25.2) and innervates several muscle fibers distributed almost evenly within an elliptical or circular region ranging from 2 to 10 mm in diameter. The motor neuron and the muscle fibers it innervates constitute a functional unit, the motor unit. The cross section of muscle occupied by a motor unit is called the... 

IGF-II mRNAs in muscle are transiently increased during regeneration (Glazner et al., 1993b). Thus, it is not surprising that collateral and terminal sprouts are transiently observed when regenerating motor axons reach muscle (Brown and Ironton, 1978 Taxt, 1983). 

In a study of the effects of hyperthyroidism on the developing granule cell-pyramidal cell pathway (Lauder and Mugnaini, 1977, 1980) we found that thyroxine could stimulate the growth of the mossy fibers, in a dose-dependent manner, causing them to sprout collaterals which grew down into the infrapyramidal region and synapsed with the basal dendrites of pyramidal cells. Normally, the mossy fibers innervate only the apical pyramidal cell dendrites where they synapse on... 

---