The Release of Excitatory Amino Acids, Dopamine, and Potassium following Transplantation of Embryonic Mesencephalic Dopaminergic Grafts to the Rat Striatum, and Their Effects on Dopaminergic Neuronal Survival In Vitro

Abstract

A major limitation to the effectiveness of grafts of fetal ventral mesencephalic tissue for parkinsonism is that about 90-95% of grafted dopaminergic neurones die. In rats, many of the cells are dead within 1 day and most cell death is complete within 1 week. Our previous results suggest that a major cause of this cell death is the release of toxins from the injured CNS tissue surrounding the graft, and that many of these toxins have dissipated within 1 h of inserting the grafting cannula. In the present experiments we measured the change over time in the concentration of several potential toxins around an acutely implanted grafting cannula. We also measured the additional effect of injecting suspensions of embryonic mesencephalon, latex microspheres, or vehicle on these concentrations. Measurements of glutamate, aspartate, and dopamine by microdialysis showed elevated levels during the first 20-60 min, which then declined to baseline. In the first 20 min glutamate levels were 10.7 times, aspartate levels 5 times, and dopamine levels 24.3 times baseline. Potassium levels increased to a peak of 33 +/- 10.6 mM 4-5 min after cannula insertion, returning to baseline of <5 mM by 30 min. Injection of cell suspension, latex microspheres, or vehicle had no significant effect on these levels. We then assayed the effect of high concentrations of glutamate, aspartate, dopamine, and potassium on dopaminergic neuronal survival in E14 ventral mesencephalic cultures. In monolayer cultures only dopamine at 200 microM showed toxicity. In three-dimensional cultures only the combination of raised potassium, dopamine, glutamate, and aspartate together decreased dopaminergic neuronal survival. We conclude that toxins other than the ones measured are the main cause of dopaminergic cell death after transplantation, or the effects of the toxins measured are enhanced by anoxia and metabolic challenges affecting newly inserted grafts.

Both apoptosis and necrosis occur early after intracerebral grafting of ventral mesencephalic tissue: a role for protease activation

“…2002), while other modes of cell death have been addressed less systematically (Cicchetti et al . 2002; Zietlow et al . 2002).…”

Past, present, and future of cell replacement therapy for parkinson’s disease: a novel emphasis on host immune responses

“…Indeed, previous studies have shown that neuronal survival markedly increased when the injection of dopaminergic cell suspension was delayed for more than one hour following cannula insertion. 160,161 Regulatory T (T REG ) cells play a vital role in maintaining immunological tolerance and homeostasis. 162,163 They are implicated in numerous autoimmune and inflammatory diseases and have been clinically utilized to improve survival rates in various organ transplantations through adoptive transfer after ex vivo expansion.…”

New Therapeutic Approaches to Parkinson’s Disease Including Neural Transplants

“…202 This suggests that at the time of implantation, there are factors relating to the traumatic delivery of the cells to the CNS, which compromises the viability and survival of the transplanted dopaminergic cells. Indeed, it is known that at the time of surgery, there is a brief surge of excitatory amino acid (EAA: glutamate and aspartate in this review), dopamine, and potassium, 203 and thus the cell loss during phase 3 may have an excitotoxicity basis. Normally the cytosolic calcium homeostasis is maintained by active mechanisms that store calcium in the mitochondria or power its extrusion out of the plasma membrane.…”

“…207 On the other hand, brief exposure to high-level EAA elicits cytotoxicity on embryonic dopaminergic neurons in vitro, and elevated dopamine and potassium concentrations in the culture medium further enhance the neuronal vulnerability to EAA treatment. 203,[208][209][210] Treatment with NMDA and AMPA receptor antagonists can protect cultured embryonic dopaminergic neurons against oxidative stress and block glutamate-induced neurotoxicity in vitro. 208,211 However, EAA inhibitors have yet to be shown to rescue dopaminergic neurons in embryonic mesencephalic grafts subject to EAA challenge.…”