Adrenal chromaffin cells as transplants in animal models of Parkinson's disease.

The field of neural transplantation has moved rapidly forward in the last decade. Initially, fetal cells were used as implants to investigate their potential to ameliorate deficits in animal models of Parkinson's disease. However, because of the moral and legal problems associated with the use of fetal tissues in humans, alternative sources of donor tissue were sought which possessed the structural and functional characteristics needed to improve motor function in Parkinsonian patients. To date, one of the most promising tissues being investigated is the adrenal medulla, whose chromaffin cells possess an inherent plasticity of form and function. Transplanted chromaffin cells currently are being studied by a variety of approaches, including electron microscopy, in mouse, rat, and primate models of Parkinson's disease. An overview of the role of the chromaffin cell in this exciting and clinically important arena is briefly reviewed, with an emphasis on the fine structure of implanted chromaffin cells.

Fine structural correlates of vascular permeability of chromaffin cell transplants in CNS pain modulatory regions.

Adrenal medullary tissue, bovine chromaffin cells, and PC12 cells were transplanted into the pain modulatory regions of the rat midbrain periaqueductal gray (PAG) or dorsal spinal cord. Fine structural studies of vascular permeability of these grafts revealed that in all three cases, the capillary endothelium of the graft vasculature was attenuated and fenestrated, unlike that of the surrounding host CNS tissue. The intravascular injection of the protein marker, horseradish peroxidase (HRP), enters the grafted tissue parenchyma and is found in the extracellular space of the surrounding host CNS. In contrast, control gelfoam transplants, which become vascularized, do not contain vessels with fenestrated endothelium and do not leak HRP. Since cell suspension implants do not contain endothelial cells, the vasculature of the grafts must be derived from the host. However, as their morphological characteristics are similar to those of the in situ adrenal medulla, it appears that the tissue environment of the graft influences the permeability properties of the vascular bed. The increased permeability to HRP is apparently permanent and most likely is due to the passage through endothelial cell fenestrae.

Pharmacologic consequences of the vascular permeability of chromaffin cell transplants in CNS pain modulatory regions.

The transplantation of peripheral neural tissue into the CNS has been shown to alter blood-brain barrier (BBB) permeability to intravascularly injected proteins such as horseradish peroxidase. The pharmacological consequences of such BBB alterations following the transplantation of adrenal medullary tissue, isolated bovine chromaffin cell suspensions, or PC12 cell suspensions into the pain modulatory regions of the periaqueductal gray (PAG) or subarachnoid space of the lumbar spinal cord were studied using agents that normally do or do not readily pass the BBB. The injection of nicotine in animals with adrenal medullary or chromaffin cell transplants produces potent analgesia, most likely due to the stimulated release of opioid peptides and catecholamines from the transplanted cells. This analgesia could be blocked by nicotinic antagonist mecamylamine, which normally passes the BBB, but not by nicotinic antagonist hexamethonium, which normally does not readily pass the BBB. Furthermore, quaternary nicotinic agonists tetramethylammonium and 1,1-dimethyl-phenyl-piperazinium had no effect on pain sensitivity in animals with adrenal medullary implants. The Met-enkephalin peptide analog, D-Ala-Met-enkephalinamide, which normally does not alter pain sensitivity when injected systemically due to limited penetration to the CNS, produced analgesia in animals with adrenal medullary, bovine chromaffin cell, and PC12 cell implants in the PAG, but not in control gelfoam-implanted animals. This analgesia, as well as analgesia induced by nicotine, was completely blocked by naloxone pretreatment, but not by naloxone methobromide, a quaternary derivative of naloxone that does not normally pass the BBB.(ABSTRACT TRUNCATED AT 250 WORDS)

Organization, fine structure, and viability of the human adrenal medulla: considerations for neural transplantation.

Recent reports of adrenal medullary autografts in patients with Parkinson's disease raise several important questions with respect to the cell types actually being transplanted as well as the potential for chromaffin cell banking prior to neural transplantation. In this study, we determined the general morphological characteristics of the human adrenal medulla and assessed factors important for the maintenance of cultured chromaffin cells for later use as transplants. The human adrenal medulla contained islands of cortical cells scattered throughout the gland as well as Schwann cells, nerve endings, endothelial cells, pericytes, isolated ganglionic neurons, and connective tissue elements such as fibroblasts and smooth muscle cells. Because many of these cell types are mitotically active, transplantation of medullary fragments that contain these cells could have far-reaching consequences. One approach that could circumvent the problems arising from multiple cell types in the medulla is differential plating of chromaffin cells prior to transplantation. Differential plating yielded relatively pure populations of chromaffin cells that demonstrated excellent viability if processed within 2 hours after cessation of the gland's circulation. Chromaffin cells cultured in the presence of nerve growth factor exhibited a neuronal phenotype, possessed catecholamine histofluorescence, and displayed tyrosine hydroxylase- and dopamine beta-hydroxylase-like immunoreactivity. The sex and age of the donor did not affect cell viability or morphological characteristics.

Analgesia induced by isolated bovine chromaffin cells implanted in rat spinal cord.

Chromaffin cells synthesize and secrete several neuroactive substances, including catecholamines and opioid peptides, that, when injected into the spinal cord, induce analgesia. Moreover, the release of these substances from the cells can be stimulated by nicotine. Since chromaffin cells from one species have been shown to survive when transplanted to the central nervous system of another species, these cells are ideal candidates for transplantation to alter pain sensitivity. Bovine chromaffin cells were implanted into the subarachnoid space of the lumbar spinal region in adult rats. Pain sensitivity and response to nicotine stimulation was determined at various intervals following cell implantation. Low doses of nicotine were able to induce potent analgesia in implanted animals as early as one day following their introduction into the host spinal cord. This response could be elicited at least through the 4 months the animals were tested. The induction of analgesia by nicotine in implanted animals was dose related. This analgesia was blocked by the opiate antagonist naloxone and partially attenuated by the adrenergic antagonist phentolamine. These results suggest that the analgesia is due to the stimulated release of opioid peptides and catecholamines from the implanted bovine chromaffin cells and may provide a new therapeutic approach for the relief of pain.

Differentiation and transdifferentiation of adrenal chromaffin cells of the guinea pig. III. Transplants under the kidney capsule.

Histochemical, ultrastructural and biochemical studies (quantitative determinations of catecholamines (CA) and phenylethanolamine N-methyltransferase (PNMT) activity) were carried out on autologous transplants of adult guinea-pig adrenal medulla under the kidney capsule, in order to investigate the specific influences of a virtually nerve-free environment in comparison to those mediated by a densely innervated one such as in the iris (cf. Unsicker et al. 1981). Three weeks after transplantation chromaffin cells survived well, most cells maintaining their morphological identity in terms of adrenaline (A) storage, although biochemically measured A and PNMT had dramatically decreased. Chromaffin cells in transplants extended neurite-like processes in an identical fashion as seen in transplants to the anterior chamber of the eye and in culture. Chromaffin cells were frequently connected by synaptoid contacts, but did not receive cholinergic synapses as observed in transplants to the iris. It may be concluded that the growth factor(s) eliciting neurite outgrowth from transplanted chromaffin cells are rather ubiquitously present, independent of whether the transplantation site is sparsely or richly innervated.

[Experimental model with the additional source of endogenous serotonin]. / Eksperimental'naia model's dopolnitel'nym istochnikom éndogennogo serotonina.

The only experimental approach to the increase in the body serotonin level is a pharmacological one that has a number of shortcomings. The authors suggest an experimental model with additional source of endogenous serotonin (ASS-model) which occurs after embryonal gastrointestinal tract transplantation beneath the skin of adult syngeneic mice. The developing transplants showed significant amounts of serotonin and serotonin-producing enterochromaffin cells. The ASS-model provides long-term and selective increase in the blood serotonin content (by 40% on the average) with no changes being detected in the brain. This model may be used for studies on the role of serotonin in peripheral regulation of the physiological systems.