Response of facial and rubrospinal neurons to axotomy: changes in mRNA expression for cytoskeletal proteins and GAP-43

Abstract

Neurons confined within the mammalian CNS usually do not regenerate after axonal injury, while axonal regeneration is the rule in the PNS. It has been hypothesized that this may be related to differences in the microenvironment of the PNS versus CNS and to differences in the neuronal response to injury. In order to test the latter hypothesis, we compared changes in gene expression after axotomy in two populations of neurons: rat facial motoneurons and rat rubrospinal neurons. In situ hybridization with cDNA probes for the medium and light neurofilament protein revealed a reduced mRNA content in both facial and rubrospinal neurons at all times investigated (i.e., 1, 2, and 3 weeks after axotomy). On the other hand, mRNAs for actin and tubulin were increased in both neuronal populations during the first week after axotomy. While this increase was sustained in facial motoneurons for several weeks, total tubulin mRNA and actin mRNA were decreased in rubrospinal neurons at 2 and 3 weeks after axotomy, coincident with their atrophy. The developmentally regulated T alpha 1 tubulin mRNA, which was previously shown to be reexpressed in facial motoneurons after axotomy, was elevated severalfold in axotomized rubrospinal neurons, and increased levels persisted in some rubrospinal neurons as late as 7 weeks after axotomy. Similarly, the developmentally regulated GAP-43 mRNA increased in both axotomized facial and rubrospinal neurons, and increased levels were sustained in some axotomized rubrospinal neurons for at least 7 weeks. The response of rubrospinal neurons to axotomy in the cervical spinal cord is, in the first week, qualitatively similar to the response of facial motoneurons. However, by 2 weeks after axotomy there is a generalized reduction in mRNA levels for all three cytoskeletal proteins that is associated with neuronal atrophy. During this period, mRNA levels for the two specific markers of the growth state, T alpha 1 tubulin and GAP-43, remain elevated. Thus, axotomy of rubrospinal neurons appears to set in motion two independent events. First, an axotomy signal initiates a cell-body reaction similar to that of PNS neurons, including increased mRNA levels for T alpha 1 tubulin and GAP-43. Later, a generalized cellular atrophy and decrease in mRNA levels occur without reversing the specific responses of T alpha 1 and GAP-43 to axotomy. We conclude that the failure of rubrospinal neurons to regenerate is not due to a failure to initiate gene-expression changes characteristic of regenerating peripheral neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

Fate of rubrospinal neurons after unilateral section of the cervical spinal cord in adult macaque monkeys: Effects of an antibody treatment neutralizing Nogo-A

“…Cervical cord (C3) hemisection in rat induced, beside other molecular changes, a reduction of neurofilament mRNA in RS neurons (Tetzlaff et al, 1991). This is probably also the case in RS neurons in monkey as the labelling on the contralesional side was fainter than on the ipsilesional side.…”

“…In the rat, after a spinal cord lesion at cervical levels, axotomized reticulospinal (RS) neurons shrink and display modification in the expression of various molecules (Egan et al, 1977;Kwon et al, 2002Kwon et al, , 2004Novikova et al, 2000;Tetzlaff et al, 1991). In this species, the RNm regains a normal aspect if brain derived neurotrophic factor (BDNF) is provided (Kwon et al, 2002;Liu et al, 1999;Novikova et al, 2000).…”

Selective temporal and regional alterations of Nogo-A and small proline-rich repeat protein 1A (SPRR1A) but not Nogo-66 receptor (NgR) occur following traumatic brain injury in the rat

“…Adult neuronal populations upregulate regenerationassociated genes (RAGs) after axotomy (Tetzlaff et al, 1991;Schaden et al, 1994;Bonilla et al, 2002;Tanabe et al, 2003;Fischer et al, 2004), and axonal sprouting following CNS injury, including TBI, may be accompanied by reinduction of genes ordinarily associated with developmental axonal growth (Emery et al, 2000;Abankwa et al, 2002;Emery et al, 2003;Mason et al, 2003). Over-expression of SPRRR1A can promote axonal outgrowth in vitro (Bonilla et al, 2002), and following FP brain injury, we observed an increased expression of SPRR1A(+)/NeuN (+) neurons in injured cortex and, to lesser extent, CA3 of the hippocampus although frequent SPRR1A (+)/MAP-2 (−) cells were also evident.…”

Axotomy-induced alterations in the red nucleus revealed by monoclonal antibody, Py, following a low thoracic spinal cord lesion in the adult rat

“…Tetzla and colleagues have observed a precipitous reduction of actin and total tubulin mRNA which occurs between 7 and 14 days po in axotomised rubrospinal neurons following lesions at cervical levels. 21 The reduction of Py-IR was restricted to the ventrolateral portion of the red nucleus. This observation is consistent with the topographical organisation of the red nucleus, the dorsomedial and ventrolateral components projecting to cervical/upper thoracic and lumbar/lower thoracic regions of the spinal cord respectively.…”