Adrenal medullary autograft transplantation into the striatum of patients with Parkinson's disease

Dopaminergic Cell Replacement for Parkinson's Disease: Addressing the Intracranial Delivery Hurdle

Parkinson's disease (PD) is an increasingly prevalent neurological disorder, affecting more than 8.5 million individuals worldwide. α-Synucleinopathy in PD is considered to cause dopaminergic neuronal loss in the substantia nigra, resulting in characteristic motor dysfunction that is the target for current medical and surgical therapies. Standard treatment for PD has remained unchanged for several decades and does not alter disease progression. Furthermore, symptomatic therapies for PD are limited by issues surrounding long-term efficacy and side effects. Cell replacement therapy (CRT) presents an alternative approach that has the potential to restore striatal dopaminergic input and ameliorate debilitating motor symptoms in PD. Despite promising pre-clinical data, CRT has demonstrated mixed success clinically. Recent advances in graft biology have renewed interest in the field, resulting in several worldwide ongoing clinical trials. However, factors surrounding the effective neurosurgical delivery of cell grafts have remained under-studied, despite their significant potential to influence therapeutic outcomes. Here, we focus on the key neurosurgical factors to consider for the clinical translation of CRT. We review the instruments that have been used for cell graft delivery, highlighting current features and limitations, while discussing how future devices could address these challenges. Finally, we review other novel developments that may enhance graft accessibility, delivery, and efficacy. Challenges surrounding neurosurgical delivery may critically contribute to the success of CRT, so it is crucial that we address these issues to ensure that CRT does not falter at the final hurdle.

Regenerative Therapies for Parkinson's Disease: An Update

Parkinson's disease is the second most common neurodegenerative disorder. It is characterised by a typical movement disorder that occurs in part because of the selective degeneration of the dopaminergic neurons of the substantia nigra pars compacta. Current treatment for the motor disorder of Parkinson's disease consists of dopaminergic medications, but these come with significant adverse effects, themselves an important part of the clinical course of Parkinson's disease, particularly in advanced stages. Therefore, treatment is needed that can restore dopaminergic tone in the striatum in a physiological and targeted manner to avert these side effects. A number of potential regenerative treatments have been developed with a view to achieving this. Following decades of optimisation and development of stem-cell-based treatments and viral gene delivery, clinical trials are on the horizon. For these treatments to be widely useful, they must be clinically effective, cost efficient and safe, and a number of practical aspects regarding storage and delivery of treatment must be optimised. Many barriers have been overcome, and the field of regenerative medicine for Parkinson's disease is now increasingly focussed on how these treatments will be delivered, demonstrating the significant progress that has been made and the optimism surrounding these approaches.

Emerging Treatment Approaches for Parkinson's Disease

Parkinson’s disease (PD) is the second most common neurodegenerative disease, manifesting as a characteristic movement disorder with a number of additional non-motor features. The pathological hallmark of PD is the presence of intra-neuronal aggregates of α-synuclein (Lewy bodies). The movement disorder of PD occurs largely due to loss of dopaminergic neurons of the substantia nigra, resulting in striatal dopamine depletion. There are currently no proven disease modifying treatments for PD, with management options consisting mainly of dopaminergic drugs, and in a limited number of patients, deep brain stimulation. Long-term use of established dopaminergic therapies for PD results in significant adverse effects, and there is therefore a requirement to develop better means of restoring striatal dopamine, as well as treatments that are able to slow progression of the disease. A number of exciting treatments have yielded promising results in pre-clinical and early clinical trials, and it now seems likely that the landscape for the management of PD will change dramatically in the short to medium term future. Here, we discuss the promising regenerative cell-based and gene therapies, designed to treat the dopaminergic aspects of PD whilst limiting adverse effects, as well as novel approaches to reducing α-synuclein pathology.

L-DOPA for Parkinson's disease-a bittersweet pill

3,4-dihydroxy-L-phenylalanine (L-DOPA) is the gold standard treatment for Parkinson's disease. It has earned that title through its highly effective treatment of some of the motor symptoms in the early stages of the disease but it is a far from perfect drug. The inevitable long-term treatment that comes with this chronic neurodegenerative condition raises the risk significantly of the development of motor fluctuations including disabling L-DOPA-induced dyskinesia. Being unsurpassed as a therapy means that understanding the mechanisms of dyskinesia priming and induction is vital to the search for therapies to treat these side effects and allow optimal use of L-DOPA. However, L-DOPA use may also have consequences (positive or negative) for the development of other interventions, such as cell transplantation, which are designed to treat or repair the ailing brain. This review looks at the issues around the use of L-DOPA with a focus on its potential impact on advanced reparative interventions.

Neural Transplantation: Prospects for Clinical use

Neural transplantation has been extensively applied in Parkinson's disease, including numerous clinical studies, studies in animal models, and related basic research on cell biology. There is evidence that the clinical trials of both adrenal medulla transplantation and fetal substantia nigra transplantation have produced a detectable clinical effect, although it is not yet clear whether the clinical benefit is sufficient to justify a more widespread application of these procedures. Studies of long-term outcome and quantitative tests are important in assaying the degree of benefit produced by transplantation procedures in Parkinson's disease and for developing improved and refined procedures. Other disease-related applications of neural transplantation are beginning to be developed. These include Huntington's disease, chronic pain, epilepsy, spinal cord injury, and perhaps even demyelinating diseases and cortical ischemic injury. Although most of these applications lie in the future, it is not too soon to begin to consider the scientific justification that should be required for initiation of human clinical trials.

Cell-based therapies for Parkinson disease—past insights and future potential

Parkinson disease (PD) is characterized by loss of the A9 nigral neurons that provide dopaminergic innervation to the striatum. This discovery led to the successful instigation of dopaminergic drug treatments in the 1960s, although these drugs were soon recognized to lose some of their efficacy and generate their own adverse effects over time. Despite the fact that PD is now known to have extensive non-nigral pathology with a wide range of clinical features, dopaminergic drug therapies are still the mainstay of therapy, and work well for many years. Given the success of pharmacological dopamine replacement, pursuit of cell-based dopamine replacement strategies seemed to be the next logical step, and studies were initiated over 30 years ago to explore the possibility of dopaminergic cell transplantation. In this Review, we outline the history of this therapeutic approach to PD and highlight the lessons that we have learned en route. We discuss how the best clinical outcomes have been obtained with fetal ventral mesencephalic allografts, while acknowledging inconsistencies in the results owing to problems in trial design, patient selection, tissue preparation, and immunotherapy used post-grafting. We conclude by discussing the challenges of bringing the new generation of stem cell-derived dopamine cells to the clinic.

An Appraisal of Ongoing Experimental Procedures in Human Spinal Cord Injury

Clinicians and scientists in the field of spinal cord injury research and medicine are poised to begin translating promising new experimental findings into treatments for people. Advances in experimental regeneration research have led to several transplantation strategies that promote axonal regrowth and partial functional recovery in animal models of injury. In this review, we summarize current knowledge regarding various invasive experimental treatments that have been or are now being applied clinically. Various questions about the timeliness, safety, and benefits of the procedures are under discussion within the spinal cord injury (SCI) research community. We also describe guidelines for carrying out optimal clinical trials and efforts to establish specific international guidelines to translate preclinical treatment strategies into clinical trials in SCI. The clinical trial process and the role that clinical professionals have in advising individuals regarding participation in experimental procedures also is discussed.

New developments in the surgery for Parkinson's disease

Despite optimization of medical therapy, a large number of patients with Parkinson's disease continue to be disabled. For this group, alternate treatment strategies such as neurosurgical intervention can be considered. Recent advances in neurosurgical techniques and in understanding the pathophysiology of motor disturbances in PD have made surgery safer and more effective. Functional neurosurgical procedures to lesion or electrically modulate dysfunctional basal ganglia circuits or to protect or restore dopaminergic transmission are being increasingly used. These procedures are having a profound impact on the motor disturbances of PD and are producing important improvements in quality of life of patients.

Orphan neurones and amine excess: the functional neuropathology of Parkinsonism and neuropsychiatric disease

The aetiology and treatment of Parkinsonism is currently conceptualised within a dopamine (DA) deficiency-repletion framework. Loss of striatal DA is thought to cause motor impairment of which tremor, bradykinaesia and rigidity are prominent features. Repletion of deficient DA should at least minimise parkinsonian signs and symptoms. In Section 2, based on extensive pre-clinical and clinical findings, the instability of this approach to Parkinsonism is scrutinised as the existing negative findings challenging the DA deficiency hypothesis are reviewed and reinterpreted. In Section 3 it is suggested that Parkinsonism is due to a DA excess far from the striatum in the area of the posterior lateral hypothalamus (PLH) and the substantia nigra (SN). This unique area, around the diencephalon/mesencephalon border (DCMCB), is packed with many ascending and descending fibres which undergo functional transformation during degeneration, collectively labelled 'orphan neurones'. These malformed cells remain functional resulting in pathological release of transmitter and perpetual neurotoxicity. Orphan neurone formation is commonly observed in the PLH of animals and in man exhibiting Parkinsonism. The mechanism by which orphan neurones impair motor function is analogous to that seen in the diseased human heart. From this perspective, to conceptualise orphan neurones at the DCMCB as 'Time bombs in the brain' is neither fanciful nor unrealistic [E.M. Stricker, M.J. Zigmond, Comments on effects of nigro-striatal dopamine lesions, Appetite 5 (1984) 266-267] as the DA excess phenomenon demands a different therapeutic approach for the management of Parkinsonism. In Section 4 the focus is on this novel concept of treatment strategies by concentrating on non-invasive, pharmacological and surgical modification of functional orphan neurones as they affect adjacent systems. The Orphan neurone/DA excess hypothesis permits a more comprehensive and defendable interpretation of the interrelationship between Parkinsonism and schizophrenia and other related disorders.

Neural transplantation in Parkinson's disease

Parkinson's disease is a neurodegenerative disorder that affects about 1% of Canadians between the ages of fifty and seventy. The medical management for these patients consists of drug therapy that is initially effective but has limited long term benefits and does not alter the progressive course of the disease. The recalcitrance of longstanding Parkinson's disease to medical management has prompted the use of alternative surgical therapies. Many neurosurgical procedures have been utilized in order to improve the disabling symptoms these patients harbour. Although most of the current procedures involve making destructive lesions within various basal ganglia nuclei, neural transplantation attempts to reconstitute the normal nigrostriatal pathway and restore striatal dopamine. The initial success of neural transplantation in the rodent and primate parkinsonian models has led to its clinical application in the treatment of parkinsonian patients. Currently, well over one hundred patients throughout the world have been grafted with fetal tissue in an effort to ameliorate their parkinsonian symptoms. Although the results of neural transplantation in clinical trials are promising, a number of issues need to be resolved before this technology can become a standard treatment option. This review focuses on the current status of neural transplantation in Parkinson's disease within the context of other surgical therapies in current use.

Adrenal medulla and Parkinson's disease

Parkinson's disease has been described as a multisystem disorder that includes alterations in the function of the autonomic nervous system. The activity of the adrenal medulla in this disease has not been thoroughly investigated. Previous reports are reviewed that demonstrate that the adrenal medullae of parkinsonian patients are compromised, having a decreased content of all catecholamines and several neuropeptides. An animal model was used to investigate whether the observations made in human patients were related to extended treatment with antiparkinsonian medications or were a natural concomitant of the disease. Administration of L-dopa and/or carbidopa to C57BL mice for 4-16 weeks had no significant effect on the level of any of the adrenal medullary catecholamines. Treatment with MPTP 4-16 weeks prior to sacrifice did not deplete adrenal medullary catecholamines in these animals, thus not fully mimicking Parkinson's disease in this animal model. The only significant effect was an interaction between group (MPTP or control) and treatment with antiparkinsonian medications; L-dopa, in the absence and presence of carbidopa, had opposite effects in the two groups. Based primarily on the lack of effect of antiparkinsonian medications on adrenal medullary catecholamines, it was concluded that the adrenal medullary depletion observed in human patients was a peripheral concomitant of Parkinson's disease.

Adrenal medulla in neural grafting and neural plasticity

The recent history of neural transplantation using the adrenal medulla parallels an evolution in our thinking about neural grafting as a therapeutic approach to treat neurodegenerative diseases such as Parkinson's disease. Initially, neural grafting was an approach to study development and regeneration. With the discovery that adrenal chromaffin cell grafts would ameliorate some of the motor deficits associated with the loss of striatal dopamine, adrenal grafts were used to provide dopamine to the dopamine-depleted striatum. However, subsequent studies showed poor chromaffin cell survival unless trophic factors were present at the site of transplantation. These experiments lead to the appreciation of the complex interactions between neurotrophic factors, inflammatory cytokines, the grafted tissue, and the host brain's response. Thus, we find ourselves again using neural transplantation as an approach to help us better understand central nervous system plasticity and the features this plasticity shares in common with development and regeneration.

The adrenal medulla and Parkinson's disease

This paper reviews the literature describing the condition of the adrenal medulla in Parkinson's disease. Parkinson's disease is a neurodegenerative disorder that is characterized primarily by the loss of dopaminergic neurons in the substantia nigra. Clinical observations have revealed that Parkinson's disease is also frequently accompanied by a variety of autonomic symptoms. The adrenal medulla is a major component of the autonomic nervous system. However, until recently this organ has not been of particular interest in Parkinson's disease. Early studies found histologic abnormalities in adrenal medullary cells, and several groups measured urinary and plasma catecholamines to determine general autonomic status. In the late 1980s adrenal medullary tissue was first transplanted to the caudate nucleus in an attempt to augment the decreased levels of dopamine, and thus treat the symptoms of Parkinson's disease. At this time the status of the adrenal medulla in this disease became clinically important. We measured the total catecholamine content of the parkinsonian adrenal medulla in tissue collected both at autopsy and in conjunction with adrenal-caudate transplants. Adrenal medullary catecholamines and several neuropeptides were severely depressed in parkinsonian glands. Thus, the adrenal medulla appears to be a target of the peripheral manifestations of Parkinson's disease.

Cerebral transplantation for Parkinson's disease: current progress and future prospects

Cerebral transplantation has received considerable attention from both the medical community and lay press as a potential treatment for Parkinson's disease. Animal models have demonstrated feasibility, although the experience in subhuman primates was very limited when the first human trials were initiated in the mid-1980s. The dramatic success reported for adrenal-to-brain transplantation in some initial trials could not be consistently replicated by other centers. Occasionally, however, patients benefited. Failure of the adrenal medullary graft to survive may have been a major factor in the poor outcomes. Recently, several US and European centers reported substantial clinical improvement after fetal dopaminergic mesencephalon was grafted into the striatum of patients with Parkinson's disease. Although many outcomes were impressive, in some cases the improvement was marginal; in no case was the condition completely reversed, and all but one patient still required levodopa therapy. Before this technique can be considered for routine use, further refinement is necessary, and many technical issues must be addressed. Certain animal studies have suggested that transplantation-related improvement may be derived from graft neurotrophic factors rather than from secretion of dopamine into the dopamine-depleted brain of patients with Parkinson's disease. Preliminary investigations in animals indicate that several other tissues, besides fetal mesencephalon, may also prove appropriate for grafting. Ultimately, advances in molecular biology may allow either transplantation of genetically engineered cells or direct modification of existing brain cells by transfection with viral vectors. The favorable preliminary experience with cerebral transplantation in patients with Parkinson's disease has resulted in the consideration of this strategy for other neurologic disorders.

Neurotransplantation: a clinical update

The use of grafts to correct neurological disorders has great promise. The progress toward this goal, as it relates to Parkinson's disease, is briefly reviewed. Although there are a number of questions that remain unanswered, recent reports of improvement in parkinsonian symptoms are very encouraging. In order to successfully evaluate the clinical trials, multicenter and/or standardized reporting techniques will be required. Future studies will need to concentrate on improving the graft survival and ability of the graft to reinnervate the host. Eventually alternative tissues may alleviate the need for fetal tissue. The use of neurotrophic factors should prove an important adjuvant to the repair and restoration of lost neurological function. As this technology is applied to other neurological diseases, it will be important to evaluate the appropriateness of grafting through extensive animal model studies and to balance the potential benefits of such therapy against the degree of risk from surgery and the severity of the disease.

Grafts in the treatment of Parkinson's disease: animal models

Long-term treatment of parkinsonian patients with L-DOPA leads to a loss of efficacy over time and the appearance of important side effects such as dyskinesias. Grafts of chromaffin cells of the adrenal medulla or fetal ventral mesencephalic neurons bring behavioral improvement in animal models of Parkinson's disease. These improvements are likely to be related to the secretion of dopamine by the grafted cells and/or to the reinnervation of the host tissue. In addition, a leak in the blood-brain barrier may allow peripheral catecholamines to gain access to the brain. Lack of clear effects of grafts in parkinsonian patients may be due to their poor survival in the human brain. Improvement of grafting techniques as well as the addition of neurotrophic factors to grafts may help increase their survival and improve behavioral effects. Recently, genetic techniques have allowed the creation of genetically modified cell lines which can produce L-DOPA and these cells may be grafted in the brain. Interestingly, these cell lines may be encapsulated in permselective membranes which can protect them from immunological rejection and avoid the uncontrolled cell growth of these mitotically active cells. Grafting techniques seem to be an interesting alternative to treat parkinsonian patients. Improvement of grafting procedures may help increase survival of grafts and thus enhance behavioral improvements. Moreover, genetic modification of well-known tumor cell lines or patient's own cells such as astrocytes may help avoid the low availability as well as ethical and immunological problems linked to the use of fetal human tissue.

Sustained release of nerve growth factor from biodegradable polymer microspheres

Although grafted adrenal medullary tissue to the striatum has been used both experimentally and clinically in parkinsonism, there is a definite need to augment long-term survival. Infusion of nerve growth factor (NGF) or implantation of NGF-rich tissue into the area of the graft prolongs survival and induces differentiation into neural-like cells. To provide for prolonged, site-specific delivery of this growth factor to the grafted tissue in a convenient manner, we fabricated biodegradable polymer microspheres of poly(L-lactide)co-glycolide (70:30) containing NGF. Biologically active NGF was released from the microspheres, as assayed by neurite outgrowth in a dorsal root ganglion tissue culture system. Anti-NGF could block this outgrowth. An enzyme-linked immunosorbent assay detected NGF still being released in vitro for longer than 5 weeks. In vivo immunohistochemical studies showed release over a 4.5-week period. This technique should prove useful for incorporating NGF and other growth factors into polymers and delivering proteins and other macromolecules intracerebrally over a prolonged time period. These growth factor-containing polymer microspheres can be used in work aimed at prolonging graft survival, treating experimental Alzheimer's disease, and augmenting peripheral nerve regeneration.

Long-term follow-up of adrenal medullary transplantation for Parkinson's disease

Long-term follow-up of eight patients who underwent stereotactic grafting of adrenal medullary tissue into unilateral or bilateral caudate nuclei is presented. We demonstrate that this procedure can be performed with minimal risk. Our results show little benefit when the group as a whole is analyzed. A subgroup of four patients was identified who responded to the procedure, as evidenced by a reduction in motor scores, reduction in medication requirements, and greater "on" time. Three of these patients continue to accrue benefit after 2 years. No characterization of a responder profile was evident. We conclude that a modest benefit is derived from this procedure that may persist for as long as 2 years. Future clinical studies to evaluate grafting procedures are encouraged.

Neural transplantation for Parkinson's disease: a critical appraisal

The medical treatment of severe Parkinson's disease is presently problematical and neural transplantation has been proposed as an additional therapy. While functional improvement in animal models of Parkinson's disease has been reported following neural grafting, the treatment of human Parkinsonian patients by adrenal medulla autografting into the neostriatum has produced little clinical improvement overall, and is associated with significant morbidity. Although recent grafting of human foetal dopaminergic neurons has shown more promise, many of the case reports lack rigorous assessment and long term follow-up. Further laboratory experimentation in animal models, particularly primates, to ascertain the mechanism of action of the grafts, the optimal sites for grafting, and the immunological responses to grafting, is essential. The future success of neural transplantation for Parkinson's disease may depend on the development of novel strategies such as the use of growth factors to aid cell survival, regulate neurotransmitter levels and promote connectivity. However, at present, the clinical application of neural transplantation for Parkinson's disease is premature.

Reduced D2 dopamine and muscarinic cholinergic receptor densities in caudate specimens from fluctuating parkinsonian patients

Binding of spiperone and 3-quinuclidinyl benzilate (QNB), both labeled with hydrogen 3 (3H), were measured in caudate tissue obtained from 8 living parkinsonian patients at the time of cerebral transplantation. This was clinically homogeneous group of patients. All remained predominantly responsive to levodopa, although with marked disability secondary to clinical fluctuations (short-duration responses) and medication-induced dyskinesias; all were receiving substantial doses of levodopa and 6 of the 8 patients were additionally receiving bromocriptine or pergolide. Binding densities of dopamine D2 receptors, as measured by [3H]spiperone binding, were reduced in this group of patients, compared to caudate specimens from autopsy control subjects. This findings may reflect medication-induced receptor downregulation. Parallel changes occurred with muscarinic cholinergic receptors; [3H]QNB binding was significantly reduced, compared to autopsy control values. This reduction of muscarinic receptors might be due to loss of nigrostriatal terminals that are known to contain muscarinic receptors. Alternatively, muscarinic receptors may have been downregulated by increased corticostriatal glutamatergic input to cholinergic cells, inferred to be present based on the prominent levodopa-induced dyskinesias. Finally, receptor deficits could have been a reflection of more widespread degenerative cerebral disease, although levodopa-refractory symptoms were generally not pronounced in these patients.

Long-term evaluation of hemiparkinsonian monkeys after adrenal autografting or cavitation alone

Autografts of adrenal medulla were implanted into preformed cavities in the caudate nuclei of four rhesus monkeys with hemiparkinsonism induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Five other hemiparkinsonian monkeys underwent caudate cavitation, but received no tissue implant. All of the animals had marked bradykinesia of the affected arm and stable apomorphine-induced turning before cavitation or implantation. Moderate behavioral recovery was seen in all five monkeys with cavitation and two of the three monkey with long-term adrenal autografts (the fourth adrenal recipient was sacrificed 10 days after grafting). The improvement occurred months after the procedure and was not as early or as complete as that seen after fetal dopaminergic grafts. Surviving adrenal tissue was found only in the animal that showed no behavioral recovery. The other two adrenal autograft recipients (with no surviving adrenal medulla) and all of the animals with cavitation had ingrowth of dopaminergic fibers from the area olfactoria and nucleus accumbens into the caudate, oriented toward the cavity. These findings show that the mechanism of improvement after adrenal medullary implants for parkinsonism is not dopamine secretion by chromaffin cells, but may be related to the sprouted host fibers. The results also indicate that the limited recovery after adrenal implants in parkinsonian patients may be a result of the cavitation, and not necessarily the result of tissue implantation.

NGF-like trophic support from peripheral nerve for grafted rhesus adrenal chromaffin cells

Autopsy results on patients and corresponding studies in nonhuman primates have revealed that autografts of adrenal medulla into the striatum, used as a treatment for Parkinson's disease, do not survive well. Because adrenal chromaffin cell viability may be limited by the low levels of available nerve growth factor (NGF) in the striatum, the present study was conducted to determine if transected peripheral nerve segments could provide sufficient levels of NGF to enhance chromaffin cell survival in vitro and in vivo. Aged female rhesus monkeys, rendered hemiparkinsonian by the drug MPTP (n-methyl-4-phenyl-1,2,3,6 tetrahydropyridine), received autografts into the striatum using a stereotactic approach, of either sural nerve or adrenal medulla, or cografts of adrenal medulla and sural nerve (three animals in each group). Cell cultures were established from tissue not used in the grafts. Adrenal chromaffin cells either cocultured with sural nerve segments or exposed to exogenous NGF differentiated into a neuronal phenotype. Chromaffin cell survival, when cografted with sural nerve into the striatum, was enhanced four- to eightfold from between 8000 and 18,000 surviving cells in grafts of adrenal tissue only up to 67,000 surviving chromaffin cells in cografts. In grafts of adrenal tissue only, the implant site consisted of an inflammatory focus. Surviving chromaffin cells, which could be identified by both chromogranin A and tyrosine hydroxylase staining, retained their endocrine phenotype. Cografted chromaffin cells exhibited multipolar neuritic processes and numerous chromaffin granules, and were also immunoreactive for tyrosine hydroxylase and chromogranin A. Blood vessels within the graft were fenestrated, indicating that the blood-brain barrier was not intact. Additionally, cografted chromaffin cells were observed in a postsynaptic relationship with axon terminals from an undetermined but presumably a host origin.

Adrenal medullary transplantation into the brain for treatment of Parkinson's disease: clinical outcome and neurochemical studies

Transplantation of adrenal medulla into the caudate nucleus as treatment for Parkinson's disease was performed in eight patients. Although our previous 6-month follow-up revealed early modest improvement, an extension of that follow-up to 1 year disclosed no additional gains in any patient. At the end of 1 year, only one patient could be categorized as moderately improved; three patients were mildly improved, and four patients were unimproved. The rationale for transplanting adrenal medulla was to reestablish a physiologic source of dopamine to the striatum. We measured cerebrospinal fluid (CSF) and plasma catecholamines and metabolites before and after transplantation. Conjugated dopamine (the predominant form of dopamine found in the CSF) and homovanillic acid (the major dopamine metabolite) were modestly and inconsistently increased in the CSF. Conjugated and free epinephrine and norepinephrine, as well as 3-methoxy-4-hydroxyphenylglycol concentrations were not increased in CSF after graft placement, an indication that the adrenal chromaffin cells were no longer producing high levels of these nondopamine catecholamines and metabolites. CSF cortisol concentrations were not increased after transplantation, compared with values from controls, consistent with low numbers of functioning adrenal cortical cells contaminating the graft (or poor survival). Posttransplantation CSF did not induce a neurotrophic effect in cell cultures of 15-day embryonic rat dorsal root ganglion or PC12 (rat pheochromocytoma) cell lines. Survival of samples of patients' adrenal medullary tissue for 2 weeks in tissue culture attested to the viability of the graft at the time of transplantation. The relative concentrations of dopamine to epinephrine or norepinephrine increased in these cultured adrenal medullary cells, presumably because of loss of the glucocorticoid influence on catecholamine synthesis. A wide variety of factors could have contributed to our failure to replicate the earlier impressive results of adrenal-to-brain transplantation reported by others. Continued transplantation studies in animal models of parkinsonism are necessary for better elucidation of these factors.