Denervation-induced enhancement of graft survival and growth. A trophic hypothesis

Intracerebral grafting of catecholamine producing cells and reconstruction of disturbed brain function

The objective of neural transplantation is to improve and reconstruct deteriorated brain function through an intracerebral implant of neural or paraneural tissues. In the last decade, basic research in this field has made great progress and brought magnificent results. Recently, the clinical application for treatment of Parkinson's disease has started and some fruitful effects are seen. Neural transplantation, on the other hand, is a useful tool in neurobiology to study the attention attracting themes, i.e., regeneration, development, plasticity, gene expression, neuroimmunology, trophic factor, etc. In this review, the functional recovery, mechanism, trophic factor, and clinical applications will be discussed pertaining to intracerebral grafting of catecholamine producing cells.

Restoration of ascending noradrenergic projections by residual locus coeruleus neurons: compensatory response to neurotoxin-induced cell death in the adult rat brain

There is clinical and experimental evidence that monoamine neurons respond to lesions with a wide range of compensatory adaptations aimed at preserving their functional integrity. Neurotoxin-induced lesions are followed by increased synthesis and release of transmitter from residual monoamine fibers and by axonal sprouting. However, the fate of lesioned neurons after long survival periods remains largely unknown. Whether regenerative sprouting may contribute significantly to recovery of function following lesions which induce cell loss has been questioned. We have previously analyzed the response of locus coeruleus (LC) neurons to systemic administration of the noradrenergic (NE) neurotoxin N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4) to adult rats. This drug causes ablation of nearly all LC axon terminals within 2 weeks after administration, followed by a profound loss of LC cell bodies 6 months later. The present study was conducted to determine the fate of surviving LC neurons and to characterize their potential for regenerative sprouting during a 16 month period after DSP-4 treatment. The time-course and extent of LC neuron degeneration were analyzed quantitatively in Nissl-stained sections, and the regenerative response of residual neurons was characterized by dopamine-beta-hydroxylase immunohistochemistry. The results document that LC neurons degenerate gradually after DSP-4 treatment, cell loss reaching on average 57% after 1 year. LC neurons which survive the lesion exhibit a vigorous regenerative response, even in those animals in which cell loss exceeds 60-70%. This regenerative process leads progressively to restoration of the NE innervation pattern in the forebrain, with some regions becoming markedly hyperinnervated. In stark contrast to the forebrain, very little reinnervation takes place in the brainstem, cerebellum and spinal cord. These findings suggest that regenerative sprouting of residual neurons is an important compensatory mechanism by which the LC may regain much of its functional integrity in the presence of extensive cell loss. Furthermore, regeneration of LC axons after DSP-4 treatment is region-specific, suggesting that the pattern of reinnervation is controlled by target areas. Elucidation of the factors underlying recovery of LC neurons after DSP-4 treatment may provide insights into the compensatory mechanisms of central neurons after injury and in disease states.

Nerve growth factor can influence growth of cortex cerebri and hippocampus: evidence from intraocular grafts

The effects of nerve growth factor and antiserum against nerve growth factor on cortical cholinergic projection areas in the central nervous system and cerebellum were evaluated using intraocular grafts of cortex cerebri, hippocampus and cerebellum in rat hosts receiving injections into the anterior chamber of the eye of nerve growth factor (at transplantation, 5 and 10 days after transplantation) or antiserum to nerve growth factor (every 5 days). The controls received cytochrome c or preimmune serum. Growth of grafts was followed by repeated observations directly through the cornea of the host using a stereomicroscope. Nerve growth factor-treated grafts of cortex cerebri and hippocampus grew significantly smaller as compared to the corresponding control grafts. In one experiment, growth of cytochrome c and saline-treated cortex cerebri was compared and no difference in growth was found. Growth of nerve growth factor-treated cerebellar grafts did not differ significantly from growth of cytochrome c-treated grafts. Morphological analysis using Nissl-staining, antibodies to glial acidic fibrillary protein to evaluate the degree of gliosis and antiserum to neurofilament as a neuronal marker did not reveal any marked differences between nerve growth factor- and cytochrome c-treated grafts. Cortical grafts receiving anti-nerve growth factor antiserum by injection or by immunizing host rats against nerve growth factor showed similar growth to the controls. Similarly, grafts of fetal hippocampus to rats immunized with nerve growth factor were not significantly different from grafts to host rats immunized with cytochrome c. We conclude that exogenous nerve growth factor affects the development of grafted cortex cerebri and hippocampus. The fact that these cortical areas stop growing earlier in the presence of nerve growth factor without the grafts showing evidence of disturbed glial or neuronal populations compared to control grafts indicates that nerve growth factor acts to induce overall/premature differentiation and maturation. The mechanism for this whether or not it is receptor-mediated and which cells are primarily affected by nerve growth factor is not yet known.