Regeneration in the central nervous system: concepts and facts

Short- and long-term changes in striatal neurons and astroglia after transient forebrain ischemia in rats

BACKGROUND AND PURPOSE

The striatum is one of the regions most sensitive to transient forebrain ischemia. After 30-minute ischemia, areas of massive neuronal degeneration are clearly detectable a few hours after the insult and attain their maximal extension 24 hours after the insult. However, for most cellular and neurochemical parameters it is not known whether some recovery occurs at later times. We examined certain cell populations in the caudate putamen at different times after transient ischemia.

METHODS

Adult male Sprague-Dawley rats were subjected to 30-minute forebrain ischemia (four-vessel occlusion model). Six experimental groups were considered: control animals and ischemic animals killed 4 hours, 1 day, 7 days, 40 days, and 8 months after reperfusion. Three striatal cell populations were examined by means of immunocytochemistry coupled to computer-assisted image analysis: vulnerable medium spiny neurons, resistant aspiny neurons, and reactive astrocytes, labeled for their content of dopamine- and cAMP-regulated phosphoprotein mr32 (DARPP-32), somatostatin and neuropeptide Y, and glial fibrillary acidic protein, respectively.

RESULTS

(1) The area containing DARPP-32 immunoreactive neurons was markedly decreased (15% to 20% of control caudate putamen area) at 1 day after reperfusion and partially recovered at the following times (40% to 50% at 7 days and 50% to 60% at 40 days and 8 months after reperfusion). (2) The appearance of reactive astrocytes was precocious (4 hours to 1 day after ischemia) in the medial caudate putamen, the region in which DARPP-32 recovered within 40 days after ischemia, and late (7 to 40 days after ischemia) in the lateral caudate putamen, where no DARPP-32 recovery was detected. (3) Neuropeptide Y/somatostatin-containing neurons resisted the ischemic insult and could be detected in areas devoid of DARPP-32 immunoreactive neurons as long as 8 months after reperfusion.

CONCLUSIONS

The present results show a marked recovery of DARPP-32-positive neurons within 40 days after 30-minute forebrain ischemia in the medial, but not the lateral, caudate putamen. Medial caudate putamen also contains a high density of reactive astrocytes on the first day after ischemia, suggesting that astrocytic support has an important role in the spontaneous recovery of ischemic neurons.

The effect of the platelet derived wound healing formula and the nerve growth factor on the experimentally injured spinal cord

The main purpose of this study is to investigate the effect of platelet derived wound healing formula (PDWHF) and nerve growth factor (NGF) in the treatment of experimental spinal cord injury. PDWHF is a conglomerate of growth factors which include platelet derived growth factor (PDGF), platelet derived angiogenesis factor (PDAF), transforming growth factor-beta (TGF beta) and platelet factor IV (PF4). Complete spinal cord transection was performed at T12 in rats and the treatment of the spinal cord injury was achieved by filling the dead space with type 1 collagen gel impregnated with PDWHF, or with 2.5S-NGF. Controls were treated with only type 1 collagen gel. Animals were sacrificed at 1, 2 or 3 months. Histopathologically, tissue autolysis and cavity formation by phagocytosis expanded 1-3 mm into the cord stumps and the volume of cavitation was less in the two treated groups. In the NGF group, a greater number of surviving nerve cells were observed in this region. Most of the control animals formed only thin, short axonal bundles, however, increased axonal regrowth was noted in animals treated with trophic factors, especially in the NGF group. The NGF group formed thick axonal bundles and abundant neuroma. Increased angiogenesis was observed in the collagen gel matrix and the injured spinal cord parenchyma, in the PDWHF group. Recent studies have shown that mammalian adult CNS possesses the ability for structural and/or functional plasticity following injury under appropriate circumstances. In this in vivo study, exogenous NGF appeared to induce axomal outgrowth and nerve cell survival. PDWHF produced notable angiogenesis which seemed to improve the extracellular microenvironment. This may be important for the delivery of exogenous trophic factors, nutrients and for the changes of extracellular matrices to support nerve cells and axons.

The concept of trophic units in the central nervous system

The present paper proposes that trophic interplay among cells may represent the final common pathway for both genetic and environmental influences, and hence new criteria for the understanding of central nervous system (CNS) connectivity can be suggested. In particular, trophic signals may make up the common "language" through which genetic and epigenetic influences mold the CNS during development and the adult life. Furthermore, it will put forward the hypothesis that the developmental trophic interplay among cells leads to the formation of trophic units in the adult brain. A trophic unit is defined as the smallest set of cells, within the CNS, which act in a complementary way to support each other's trophism. The trophic units consist of neurons, glial cells, blood vessels, extracellular matrix (ECM). In particular, ECM gives support to the thin elongated cell processes and gives rise to selective chemical bridges between cell surfaces or between cell surfaces and the extracellular milieu. The trophic unit is a plastic device that not only assures neuronal survival, but also operates to adapt neuronal networks to new tasks by controlling extension of neuronal processes, synapse turnover and ECM characteristics. These plastic responses depend on the interplay of all the elements that constitute the trophic units. The concept of trophic unit may help to understand some features of neurodegenerative diseases, for example, the clustering of tangles in the neocortex and in the entorhinal cortex of Alzheimer's patients [corrected].

Arterial bridging for repair of peripheral nerve gap: a comparative study

A new experimental model was designed in which the regeneration of rat femoral nerve across a 8 mm excised gap was investigated after insertion of the distal and proximal stumps into the anatomically and functionally intact femoral artery (AIAB). This model was compared with groups of free artery and autologous nerve grafting. After a period of 12 weeks, a histological and electrophysiological analysis was carried out, which demonstrated that the AIAB and autologous nerve grafting group had a significantly higher percentage of regeneration compared with the free artery-graft group. The nerve regeneration and intraneural vascular reconstruction that occurred within AIAB group were more successful than those that occurred in the artery and nerve-grafting groups.

Effects of polyamine synthesis blockade on neuronal loss and astroglial reaction after transient forebrain ischemia

Polyamines and ornithine decarboxylase, the polyamine biosynthetic enzyme, have been demonstrated to increase in the early phase of several types of brain lesion. However, their role in the pathogenesis of tissue damage is still debated. In the present paper the effects of treatments with alpha-difluoromethylornithine, a suicide inhibitor of ornithine decarboxylase, have been investigated in a model of transient forebrain ischemia. Three treatment schedules were used: alpha-difluoromethylornithine treatment was either started 3 hr before and repeated 1 hr after the insult, or started at the time of the insult and continued for 3 or 7 days after post-ischemic reperfusion. The rats were sacrificed 4 hr, 7 or 40 days after reperfusion, respectively. The acute experiment demonstrated that alpha-difluoromethylornithine can reduce the increase of glial fibrillary acid protein immunoreactivity, an early marker of astroglial reaction, in ischemic striatum. Subchronic and chronic alpha-difluoromethylornithine treatments induced a worsening of the morphological outcome of the ischemic lesion. In caudate-putamen a trend for an increase of the area of neuronal loss was present after both treatments. In the hippocampal formation, a significant increase in the severity of neuronal lesion was observed in the mildly lesioned CA3 field. In addition, other alterations of lesioned tissue were observed in alpha-difluoromethylornithine-treated animals, including increases of non-neuronal cells at 7 and especially 40 days post-lesion in striatum and CA3 hippocampal field. In conclusion, present data indicate that ornithine decarboxylase activation after ischemic lesion is a crucial factor for survival of mildly lesioned neurons and proper tissue reaction to the ischemic lesion. The experiment on acute alpha-difluoromethylornithine treatment suggests that these effects may be, at least in part, related to putrescine-induced activation of astroglial cells in the early post-lesion period.

Evidence for a protective action of the vigilance promoting drug Modafinil on the MPTP-induced degeneration of the nigrostriatal dopamine neurons in the black mouse: an immunocytochemical and biochemical analysis

Based on the observations that the psychostimulant drug amphetamine in combination with physiotherapy can promote recovery of brain function after brain injury, we have studied the ability of the vigilance promoting drug Modafinil to counteract 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-(MPTP)-induced degeneration of the nigrostriatal dopamine (DA) neurons of the black mouse. MPTP was given s.c. in a dose of 40 mg/kg and the mice were sacrificed 2 weeks later. The effects of acute and chronic treatment with Modafinil were studied on MPTP-induced DA neurotoxicity. The substantia nigra and neostriatum were taken to both biochemical and histochemical analysis of presynaptic parameters of the nigrostriatal DA neurons, the latter in combination with image analysis. In separate experiments in rats in vivo tests for DA uptake blocking activity were made using intrastriatal microdialysis to study superfusate levels of DA and its metabolites and the 4-alpha-dimethylmetatyramine (H77/77) model to test for a possible ability of Modafinil to protect against H77/77-induced depletion of forebrain DA stores. Chronic treatment with Modafinil in doses of 10 to 100 mg/kg counteracted the MPTP-induced disappearance of nigral TH IR nerve cell body profiles and neostriatal TH IR nerve terminal profiles as evaluated after 2 weeks with image analysis. Chronic treatment with Modafinil (10-100 mg/kg) also dose-dependently counteracted the MPTP-induced disappearance of striatal DA uptake binding sites as evaluated at the same time interval. Also in the dose range 10-100 mg/kg Modafinil counteracts the MPTP-induced depletion of DA stores both in the neostriatum and the substantia nigra. In the acute experiments Modafinil (30 mg/kg) protected against the MPTP-induced depletion of striatal DA, dihydrophenylacetic acid (DOPAC) and homovanillic acid (HVA) levels both when given 15 min before, at the same time and 3 h following the MPTP injection. In the substantia nigra, however, these protective actions of Modafinil were only observed when the drug was coadministered with MPTP. Experiments with microdialysis in intact rats failed to demonstrate any increases of superfusate DA levels in neostriatum with 30 mg/kg of Modafinil. Modafinil in high doses of 2 x 50 mg/kg, however, significantly counteracted the H77/77 induced DA depletion of striatal DA stores. Thus, morphological and biochemical evidence has been obtained that Modafinil in the dose range 10-100 mg/kg protects against MPTP-induced degeneration of the nigrostriatal DA neurons of the black mouse.(ABSTRACT TRUNCATED AT 400 WORDS)