Striatal neural transplants in the ibotenic acid-lesioned rat neostriatum. Cellular and functional aspects

Behavioral Effects of Neural Transplantation

Considerable evidence suggests that transplantation of fetal neural tissue ameliorates the behavioral deficits observed in a variety of animal models of CNS disorders. However, it is also becoming increasingly clear that neural transplants do not necessarily produce behavioral recovery, and in some cases have either no beneficial effects, magnify existing behavioral abnormalities, or even produce a unique constellation of deficits. Regardless, studies demonstrating the successful use of neural transplants in reducing or eliminating behavioral deficits in these animal models has led directly to their clinical application in human neurodegenerative disorders such as Parkinson's disease. This review examines the beneficial and deleterious behavioral consequences of neural transplants in different animal models of human diseases, and discusses the possible mechanisms by which neural transplants might produce behavior recovery.

Neural Transplantation for Huntington's Disease: Experimental Rationale and Recommendations for Clinical Trials

Huntington's disease (HD) is a neurodegenerative disorder affecting motor function, personality, and cognition. This paper reviews the experimental data that demonstrate the potential for transplantation of fetal striatum and trophic factor secreting cells to serve as innovative treatment strategies for HD. Transplantation strategies have been effective in replacing lost neurons or preventing the degeneration of neurons destined to die in both rodent and nonhuman primate models of HD. In this regard, a logical series of investigations has proven that grafts of fetal striatum survive, reinnervate the host, and restore function impaired following excitotoxic lesions of the striatum. Furthermore, transplants of cells genetically modified to secrete trophic factors such as nerve growth factor protect striatal neurons from degeneration due to excitotoxicity or mitochondrial dysfunction. Given the disabling and progressive nature of HD, coupled with the absence of any meaningful medical therapy, it is reasonable to consider clinical trials of neural transplantation for this disease. Fetal striatal implants will most likely be the first transplant strategy attempted for HD. This paper describes the variable parameters we believe to be critical for consideration for the design of clinical trials using fetal striatal implants for the treatment of HD.

Glutamatergic regulation of long-term grafts of fetal lateral ganglionic eminence in a rat model of Huntington's disease

Transplanting fetal striatal tissue is currently considered to be an important alternative strategy in the treatment of Huntington's disease. Although grafted striatal tissue differentiates and shows certain structural and neurochemical features of the normal striatum and receives host afferents, it is not clear whether host-derived afferent inputs can modulate the activity of neurotransmitter receptors and their signaling in the graft. An intricate interaction between dopaminergic and glutamatergic systems is pivotal for striatal function. In the present study, the modulation of D(2) receptors in the graft by host-derived glutamatergic afferents via NMDA receptors was investigated using haloperidol-induced c-Fos expression. The results indicate that haloperidol induces c-Fos in a large number of neurons in the P-zones of the graft and this induction is significantly suppressed by pretreatment with the NMDA receptor antagonist, MK-801. Therefore, the NMDA receptor-mediated modulation of D(2) receptor function seen in the normal striatum is established in the striatostriatal grafts.

Effects of lateral parabrachial nucleus lesions in chronic renal hypertensive rats

Neuroanatomic studies describing forebrain projections to the lateral parabrachial nucleus suggest a central integrative role in cardiovascular regulation. We performed this study to examine the role of this pontine nucleus in the maintenance of one-kidney, figure-8 renal-wrap hypertension. Bilateral ibotenic acid ablation of the lateral parabrachial nucleus was performed 4 weeks after induction of hypertension or sham operation. In hypertensive rats, ablation produced a significant reduction in mean arterial pressure from 160 +/- 4 to 118 +/- 2 mm Hg and a transient but significant increase in heart rate from 381 +/- 5 to 408 +/- 8 beats per minute on the first day after ablation; arterial pressure returned to preablation values by day 5 after ablation. In sham-operated, normotensive animals, arterial pressure was not altered by ablation, and a transient but significant increase in heart rate from 384 +/- 8 to 419 +/- 7 beats per minute was again observed. Before ablation, trimethaphan administration produced a significantly greater drop in arterial pressure in hypertensive (delta-72.8 +/- 4.6 mm Hg) versus normotensive (delta-55.7 +/- 4.1 mm Hg) animals. This effect was eliminated on day 1 after ablation yet returned on day 4 after ablation. In blood samples obtained before ablation and on days 1 and 4 after ablation, circulating plasma catecholamine concentrations in both groups remained unchanged. These observations suggest that, because of possible alternate neural compensatory mechanisms, lateral parabrachial nucleus ablation produces a significant yet transient reversal of renal-wrap hypertension. Thus, the lateral parabrachial nucleus may contribute to the increased sympathetic nervous system function associated with this model.