Morphological and functional correlates of chromaffin cell transplants in CNS pain modulatory regions

One-Year Chromaffin Cell Allograft Survival in Cancer Patients with Chronic Pain: Morphological and Functional Evidence

The control of chronic pain through transplantation of chromaffin cells has been reported over the past few years. Analgesic effects are principally due to the production of opioid peptides and catecholamines by chromaffin cells. Clinical trials have been reported with allografts consisting of whole-tissue fragments implanted into the subarachnoid space of the lumbar spinal cord (14,19,36). In the present study, allogeneic grafts were successfully used to control chronic pain in two patients over a period of 1 yr based on patient reported pain scores, morphine intake, and CSF levels of Met-enkephalin. Macroscopic examination at autopsy located the transplanted tissue fragments in the form of multilobulated nodules at the level of the spinal axis and cauda equina. Immunocytochemical microscopy showed neuroendocrine cells are positive for chromagranin A (CGA), and enzymes tyrosine hydroxylase (TH) and dopamine-β-hydroxylase (DβH). The results suggest that there is a relationship between analgesic effect, Met-enkephalin levels in CSF, and the presence of chromaffin cells surviving in spinal subarachnoid space.

In vivo administered reserpine increases piecemeal degranulation in rat adrenal chromaffin cells

The effects of the amine-depletory agent reserpine have been evaluated by transmission electron microscopy in chromaffin cells of the rat adrenal glands. The drug has been injected intraperitoneally in the animals at a dose of 0.5 mg/kg body weight in two administrations at 24-hr interval. The observed ultrastructural changes closely reminded of piecemeal degranulation (PMD), a slow and long-lasting secretory process previously described in normal and tumor pheochromocytes. Both adrenaline- and noradrenaline-storing cells presented the following microscopic features: high granule polymorphism, due to coexistence in the same cell of normal resting granules, granules with partially mobilized components, and large empty containers; absence of granule fusion; characteristic "haloed" pattern of residual secretory contents; great amount of 30-150 nm diameter, membrane-bound, electron-dense and -lucent vesicles, free in the cytoplasm or attached to granules; and multiple vesicles budding from the granule-limiting membranes. Morphometric analysis revealed that the frequency of all these microscopic parameters was found to be significantly increased in adrenal chromaffin cells from reserpinized rats in comparison to cells from control animals. These data suggest that reserpine, besides blocking the inward transport of catecholamines in chromaffin granules, might also stimulate a complex secretory reaction, which shares many common passages with bona fide PMD.

Secretion without membrane fusion: porocytosis

We have recently proposed a mechanism to describe secretion, a fundamental process in all cells. That hypothesis, called porocytosis, embodies all available data and encompasses both forms of secretion, i.e., vesicular and constitutive. The current accepted view of exocytotic secretion involves the physical fusion of vesicle and plasma membranes; however, that hypothesized mechanism does not fit all available physiological data. Energetics of apposed lipid bilayers do not favor unfacilitated fusion. We consider that calcium ions (e.g., 10(-4) to 10(-3) M calcium in microdomains when elevated for 1 ms or less), whose mobility is restricted in space and time, establish salt bridges among adjacent lipid molecules. This establishes transient pores that span both the vesicle and plasma membrane lipid bilayers; the diameter of this transient pore would be approximately 1 nm (the diameter of a single lipid molecule). The lifetime of the transient pore is completely dependent on the duration of sufficient calcium ion levels. This places the porocytosis hypothesis for secretion squarely in the realm of the physical and physical chemical interactions of calcium and phospholipids and places mass action as the driving force for release of secretory material. The porocytosis hypothesis that we propose satisfies all of the observations and provides a framework to integrate our combined knowledge of vesicular and constitutive secretion.

Porcine chromaffin cells, culture, and transplant for antinociceptive effects in rodents and primates

It has been shown that xenografts and allografts of spinally transplanted adrenal chromaffin cells produce antinociception in animals and pain relief in patients with cancer pain. As there is a very limited availability of human adrenal tissue to serve as allografts, the clinical need for xenogeneic chromaffin cells as transplants is obvious. Bovine adrenal glands as a steady source of chromaffin cells have been extensively studied. There is however concern about the possible infection in humans with retrovirus following transplantation. The purpose of this study is to use the pig as a preferred donor animal species for xenotransplantation into rat and monkey. As pigs have been cloned, this opens the door to gene-targeted technologies and allows for genetic modifications, which possibly could improve the efficacy and safety of chromaffin cell transplantation. Porcine chromaffin cells were isolated from adrenal glands of 6-8-month-old pigs. After culturing cells for 1 week in a medium containing serum, the release of met-enkephalin and norepinephrine from the cells was detected by high-performance liquid chromatography and radioimmunoassay with nicotine stimulation, lasting approximately 3 weeks. Transplantation of these cells into the subarachnoid space of rats produced antinociceptive effects on Adelta and C fiber-mediated responses lasting 2-3 weeks. Similar findings were observed in studies with macaque monkeys. Compared with the same number of bovine chromaffin cells, porcine chromaffin cells showed a more robust and longer antinociceptive effect, and could be a better source of cells for human transplantation.

Neurotrophic factors for the investigation and treatment of movement disorders

Neurotrophic factors (NFs) are proteins that enhance neuronal survival, differentiation, neurotransmitter function and resistance to neurotoxins and lesions. For these reasons the NFs are considered as a new potential therapeutic tool for the treatment of neurodegenerative disorders, a group of diseases that produce the most important cause for disability in the Western world. Some NFs prevent or even reverse the behavioral, biochemical, pharmacological and histological abnormalities observed in several in vitro and in vivo models of neurodegenerative disorders, namely Parkinson's disease. Several NFs have been investigated in primate models of neurological disorders and some of them have been used for patients with these diseases. The results so far obtained in humans have been disappointing for several reasons, including technical problems for delivery, unbearable side effects or lack of efficacy. Future approaches for the use of NFs in humans should include the following: (1) Investigation of the putative compounds in animal models more related to the pathophysiology of each disease, such as in genetic models of neurodegenerative diseases; (2) New methods of delivery including genetic engineering by viral vectors and administration through implantable devices; (3) More precise methods of continuous response evaluation, including the novel neuroimaging techniques; (4) Investigation of the effects of behavioral stimulation and conventional pharmacotherapy on the metabolism of NFs.

No detectable analgesic effects in the formalin test even with one million bovine adrenal chromaffin cells

The present experiments were conducted to identify analgesic agents for transfection into immortalized adrenal chromaffin cell lines to maximize their analgesic potential. Analgesic agents known to be produced by adrenal chromaffin cells were infused intrathecally at a low dose (0.2 microg) which might conceivably be attained by adrenal chromaffin cell transplants. Numerous agents, administered individually and in two-factor combinations, produced significant analgesic effects in the formalin test. Before assessing the potential additive or synergistic effects of these analgesic agents with adrenal chromaffin cells, studies were conducted to demonstrate analgesic effects with adrenal chromaffin cells alone. Analgesic effects were previously reported in the literature with 80-100k intrathecal bovine adrenal chromaffin (BAC) cells; but in the present study 500k purified BAC cells failed to produce detectable analgesic effects. One million purified BAC cells also failed to produce analgesic effects in the formalin test. In a final study, even nicotine-stimulated release from one million purified BAC cells failed to produce analgesic effects in the formalin test. The fact that even one million nicotine-stimulated BAC cells failed to demonstrate therapeutic potential in these blinded experiments under conditions which were clearly sensitive to the analgesic agents produced by BAC cells, raises serious questions about the clinical utility of this experimental treatment.

Human chromaffin cell graft into the CSF for cancer pain management: a prospective phase II clinical study

A number of pre-clinical studies have demonstrated the value of adrenal medullary allografts in the management of chronic pain. The present longitudinal survey studied 15 patients transplanted for intractable cancer pain after failure of systemic opioids due to the persistence of undesirable side-effects. Before inclusion, all the patients had their pain controlled by daily intrathecal (I-Th) morphine administration. The main evaluation criteria of analgesic activity of the chromaffin cell allograft was the complementary requirement of analgesics and in particular the consumption of I-Th morphine required to maintain effective pain control. Out of the 12 patients who profited from enhanced analgesia with long-term follow-up (average 4.5 months), five no longer required the I-Th morphine (with prolonged interruption of systemic opioids as well), two durably decreased I-Th morphine intake and five were stabilized until the end of their follow-up. Durable decline and stabilization were interpreted as indicative of analgesic activity by comparison with the usual dose escalation observed during disease progression. In most cases, we noted a relationship between analgesic responses and CSF met-enkephalin levels. The results of this phase II open study demonstrate the feasibility and the safety of this approach using chromaffin cell grafts for long-term relief of intractable cancer pain. However, while analgesic efficacy was indicated by the reduction or stabilization in complementary opioid intake, these observations will need to be confirmed in a controlled trial in a larger series of patients.

Comparison of tyrosine hydroxylase and preproenkephalin expression in rat adrenal medullary explants in vitro and transplanted into subarachnoid space

When adrenal medullary cells are cultured in vitro, tyrosine hydroxylase (TH) mRNA, preproenkephalin (PPEnk) mRNA, and methionine enkephalin (Mek) immunoreactivity was markedly increased compared with intact adrenal medullary cells in situ, suggesting an increased biosynthesis of catecholamines and enkephalin-containing peptides. In transplanted adrenal medullary cells in vivo, TH mRNA and TH immunoreactivity are still apparent for at least 1 year after transplantation, indicating continued capacity for catecholamine biosynthesis. PPEnk mRNA levels in surviving adrenal medullary grafted cells increased, particularly in the first week after transplantation, and remained above levels found in the intact adrenal gland for at least 1 year after transplantation. These results support other studies in our laboratory, suggesting that adrenal medullary transplants reduce pain by synthesis and secretion of both catecholamines and enkephalin-containing peptides. The differences in expression of TH mRNA and PPEnk mRNA in the adrenal medulla in situ, in explants in culture and in transplants in the spinal subarachnoid space, indicate that the mechanisms regulating the expression of neurohumoral factors depend upon environmental factors extrinsic to the medullary cells themselves.

Fine structure of host-graft relationships between transplanted chromaffin cells and CNS

Our laboratory studies have shown that transplantation of adrenal medullary tissue or isolated chromaffin cells into central nervous system (CNS) pain modulatory regions (i.e., periaqueductal gray and subarachnoid lumbar spinal cord) can reduce pain sensitivity of rats in both acute and chronic pain. The analgesia produced by these transplants is thought to result from release of both opiate peptides and catecholamines. Morphologically, these animal studies also suggest that there is no development of tolerance over long periods of time, and the transplanted chromaffin cells appear to be robust and well integrated with the host tissue. In our initial clinical studies, where allografts of adrenal medullary tissue were transplanted intrathecally to relieve intractable cancer pain, patients obtained significant and long-lasting pain relief. Increased cerebrospinal fluid (CSF) levels of metenkephalin were correlated with the decreased pain scores. Histology of autopsy tissue obtained from two patients with 1 year transplants revealed viable transplanted chromaffin cells. Because of the limited availability of human adrenal glands, sources of xenogeneic chromaffin cells will need to be identified if effective transplantation therapy for chronic pain is to be developed further.

Non-autologous transplantation with immuno-isolation in large animals--a review

Transplantation has become a successful method for the management of functional failure of a variety of tissues or organs. However, the majority of clinical transplantations use non-autologous allogeneic donor tissue implanted from one human to another. In order to prevent rejection of the allogeneic tissue, methods to overcome the immune barrier are necessary. Although prevention of organ rejection is currently achieved with pharmacological immune suppression, the undesirable side effects of this method have incited interest in novel methods to overcome the immune barrier. One such novel method of preventing immune reaction is immuno-isolation, in which the non-autologous tissues are physically isolated from the host tissues by placement in devices with perm-selective membranes. The membranes of these devices allow release of the therapeutic product required from the transplanted tissues, as well as diffusion of nutrients and waste necessary for survival of the non-autologous tissues. The membranes also prevent host immune mediators from contacting the non-autologous cells, thus preventing immune rejection. This technology has been tested for efficacy in large animal models, and is currently in the process of clinical trials in humans. This review will discuss the progress made in using immuno-isolation of non-autologous tissues in large animals. Immuno-isolation can be subdivided into two major areas of interest based on whether the non-autologous tissue used in the immuno-isolation device is genetically altered (gene therapy) or not. Studies using non-genetically altered non-autologous cells for immune-isolation have been dominated by the use of pancreatic islet cells for the treatment of diabetes. This work has been tested in large animal models of diabetes, including canine and primate model animals, and human clinical trials are underway. As well, there has also been work on treatment of neurological disorders such as Parkinson's disease or chronic pain using non-autologous immuno-isolated adrenal chromaffin cells or dopaminergic PC12 cells in large animals such as sheep and primates. This work will be reviewed in detail as to the types of disorders, immuno-isolation devices used and the type of large animals involved. Immune-isolation for gene therapy is a more recently developed field of research. In this case, the non-autologous cells used are first genetically altered to secrete a recombinant therapeutic product before placement in the immune-isolation devices. Genetic engineering of the non-autologous cells is beneficial, as it allows the use of a cell type that tolerates well the environment of the immune-isolation device, while still delivering the therapeutic product of interest. This form of gene therapy has been tested in our laboratory for delivery of marker products such as human growth hormone to canines. As several large animal models of human genetic disorders are available, such as canines affected with hemophilia or the lysosomal storage disease mucopolysaccharidosis, testing the efficacy of immuno-isolation for gene therapy in large animal models is an important prelude to human clinical trials. This review will discuss the topics outlined above, as well as some further considerations of the usefulness of large animal models in studying immune-isolation for non-autologous transplantation. Large animals may be more appropriate model organisms than rodents in which to study immune-isolation, as issues such as biocompatibility and immune response in a larger animal can be addressed. As well, large animal studies of immune isolation may provide data that are more relevant than rodent studies to the eventual application to human clinical trials.

Human fetal tissue research: practice, prospects, and policy

Tissue from human fetal cadavers has long been used for medical research, experimental therapies, and various other purposes. Research within the last two decades has led to substantial progress in many of these areas, particularly in the application of fetal tissue transplantation to the treatment of human disease. As a result, clinical trials have now been initiated at centers around the world to evaluate the use of human fetal tissue transplantation for the therapy of Parkinson's disease, insulin-dependent diabetes mellitus, and a number of blood, immunological and, metabolic disorders. Laboratory studies suggest a much wider range of disorders may in the future be treatable by transplantation of various types of human fetal tissue. A combination of characteristics renders fetal tissue uniquely valuable for such transplantation, as well as for basic research, the development of vaccines, and a range of other applications. Although substitutes for human fetal tissue are being actively sought, for many of these applications there are at present no satisfactory alternatives. Important issues remain unresolved concerning the procurement, distribution, and use of human fetal cadaver tissue as well as the effects of such use on abortion procedures and incidence. These issues can be addressed by the introduction of appropriate guidelines or legislation, and need not be an impediment to legitimate research and therapeutic use of fetal tissue.

Antinociception following implantation of mouse B16 melanoma cells in mouse and rat spinal cord

B16 F1C29 melanoma cells, which are thought to contain and release catecholamines, were implanted in mouse and rat spinal subarachnoid space. B16 F1C29 cell implants augmented the antinociceptive effect of morphine in tail-flick test, and this interaction was blocked by either the alpha 2-adrenergic antagonist idazoxan or the opioid antagonist naloxone. B16 F1C29 cell implants also augmented the antinociceptive effect of the catecholamine re-uptake blocker desipramine. Substance P-induced biting and scratching behaviors were inhibited in mice receiving B16 F1C29 cell implants, and this effect of B16 F1C29 cell implants was blocked by the alpha 2-adrenergic antagonist idazoxan. Mice receiving B16 F1C29 cell implants showed tolerance to intrathecal administration of the alpha 2-adrenergic agonist UK 14304. These results suggest that B16 cell implant-induced antinociception was mediated by catecholamines secreted from the cell implants and acting at spinal alpha 2-adrenergic receptors. Spinal implantation of catecholamine-releasing cells may provide an alternative approach for the therapy of chronic intractable pain and a useful model to study alpha 2-adrenergic receptor tolerance.

The biology and behaviour of intracerebral adrenal transplants in animals and man

The catecholamine containing chromaffin cells of the adrenal medulla have recently been employed as intracerebral grafts in man and animals with lesions of the nigrostriatal dopaminergic system. This review outlines the basic biology of the chromaffin cell with reference to its efficacy as a source of dopamine in the grafted state. This is followed by an evaluation of the use of these grafts in experimentally lesioned animals and in patients with Parkinson's disease.

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.

Lack of potent antinociceptive activity by substance P antagonist CP-96,345 in the rat spinal cord

Substance P (SP) binds to the NK-1 receptor and has been implicated in the transmission of pain as well as in physiological responses such as salivary gland secretion and neurogenic inflammation. Studies in this field have been limited due to the lack of specific antagonists that are not degraded rapidly and are not neurotoxic. However, a recently developed non-peptide SP antagonist, CP-96,345, is specific for the NK-1 receptor. The purpose of this study was to assess the effects of this antagonist on nociception. The tail flick, paw pinch and hot plate tests were used to assess nociception in rats. Following baseline determination of tail skin temperature and analgesiometric tests, the rats received intrathecal injections of various doses of CP-96,345, and pain sensitivity was assessed at several time intervals up to two hours after injection. The ability of CP-96,345 to inhibit SP induced biting and scratching was also assessed. Results from the analgesiometric tests indicated that there were no significant elevations in the latency of tail flick test or the paw pinch thresholds even at 240 micrograms of CP-96,345. The hot plate latency was elevated at the highest dose of antagonist. In addition, there was a significant dose-related elevation in latency on the hot plate test. CP-96,345 also produced a dose-related decrease in tail skin temperature. CP-96,345 did not block SP induced biting and scratching. CP-96,345 and SP were evaluated for their ability to displace 125I-Tyr8-SP from rat spinal cord, brain and submandibular gland membrane fractions. It was found that although the affinity of CP-96,345 was 56 fold lower than that of SP in the brain, the antagonist was nearly as potent as SP in the spinal cord and submandibular gland. The results of this study suggest that, while CP-96,345 binds to the NK-1 receptor in the spinal cord, this receptor is most likely not involved in mediating some types of nociception at the spinal cord level.

New aspects of neurotransplantation

We have examined the possibility of promoting axonal regeneration within lesioned neural tissue using grafted artificial gel matrices. Polymeric matrices which feature a three-dimensional crosslinked macromolecular network were implanted into preformed lesions of the central nervous system (CNS). The host response consisted of matrix invasion by glial elements and the deposition of newly synthesized extracellular molecules. This rearrangement of the brain scarring process into an organized cellular coating promoted axonal regeneration into the gels. Entrapment of embryonic neurons and embryonal carcinoma (EC)-derived neurons, within the gels, was performed to explore the possibility of using polymer brain implants as neural graft microcarriers. Our results suggest that this approach will be useful for the delivery of cells and the promotion of axonal elongation required for successful neurotransplantation.

Dibutyryl cAMP stimulates analgesia in rats bearing a ventricular adrenal medulla transplant

In the present study, a significant increase in pain threshold (current to elicit vocalization to tail shock) was found 15 and 60 min after injection of dibutyryl cyclic AMP (db cAMP) (30 micrograms) into the lateral ventricle in rats bearing a transplant of fetal adrenal medulla (AM). By contrast, no effect on pain threshold was observed in rats bearing an AM transplant but receiving no db cAMP, or in rats receiving db cAMP but not bearing an AM transplant. In primary cultures of rat fetal chromaffin cells, db cAMP increased the number of neuron-like cells that showed both vasoactive intestinal polypeptide (VIP)- and tyrosine hydroxylase (TH)-like immunoreactivity. These findings indicate that db cAMP exerts a pharmacological modulation of the functional activity (i.e. elevation in pain thresholds) of fetal adrenal AM transplants, and induces phenotypic changes in cultured chromaffin cells with expression of a peptide that elevates pain threshold.

Subarachnoid spinal cord transplantation of adrenal medulla suppresses chronic neuropathic pain behavior in rats

Several weeks after transection of the sciatic and saphenous nerves, rats respond by self-injury of the denervated limb ('autotomy'). This behavior serves as a model of neuropathic pain. In this study we allografted fragments of rat adrenal medulla into the subarachnoid space of other rats, at lumbar spinal cord level, in an attempt to suppress autotomy behavior. The results show that autotomy was reduced by an average of 63% throughout the 8 week observation period. Catecholamine (CA) histofluorescent staining performed up to 120 days postoperatively (P0) revealed viable transplants in 75% of the rats. Transplant viability correlated with suppression of autotomy. This suggests that medullary chromaffin cells function as a local, long-lasting source of anti-nociceptive agents at the spinal segments which process input from the injured nerves.

Adrenal medullary implants in the rat spinal cord reduce nociception in a chronic pain model

Previous work in this laboratory has indicated that the transplantation of adrenal medullary tissue into the subarachnoid space of the rat spinal cord can reduce pain sensitivity to acute noxious stimuli, particularly following stimulation by nicotine. This most likely results from the stimulated release of opioid peptides and catecholamines from the transplanted chromaffin cells. However, chronic pain models may more closely resemble human clinical pain, and the arthritic rat model has been used for screening potential therapeutic strategies. The purpose of the present study was to assess the potential for adrenal medullary tissue implanted into the spinal subarachnoid space to alleviate chronic pain. Adrenal medullary tissue was implanted into adjuvant-induced arthritic rats, and changes in body weight and vocalization responses were monitored over the 10 week course of the disease. Results indicate that the severe weight reduction normally associated with this inflammatory arthritis was attenuated by adrenal medullary, but not control, implants. In addition, vocalizations were reduced in animals implanted with adrenal medullary, but not control tissue following nicotine stimulation. This reduction was blocked by the opiate antagonist, naloxone, and partially attenuated by the alpha-adrenergic antagonist, phentolamine. Together, these results suggest that the transplantation of adrenal medullary tissue into the subarachnoid space of the spinal cord may provide a local source of opioid peptides and catecholamines for the reduction of chronic pain.

Transplantation of adrenal tissue into the central nervous system

Adrenal medullary tissue can survive transplantation to the central nervous system. Such survival has been obtained experimentally with grafts to the anterior eye chamber, to the brain and to the spinal cord, using medullary tissue from the recipient animal or unrelated animals of the same or, in some cases, different species. Appropriately placed grafts have been shown, under certain conditions, to interact with the host nervous system, exerting behavioral effects including amelioration of experimentally-induced parkinsonian symptoms. Such effects may be enhanced by administration of nerve growth factor to the grafts. On the basis of such findings, adrenal medullary tissue has been grafted to the brain of Parkinson's disease patients. Both animal and human experiments raise important questions about mechanisms of graft action and about factors that influence the outcome of these procedures.

Immunocytochemical and ultrastructural studies on allografts of the pituitary neurointermediate lobe in the third cerebral ventricle of the rat

Neurointermediate lobes from adult or 10-day-old rats were implanted by a stereotaxic procedure into the third ventricle of adult male rats, in an area close to the paraventricular nucleus. They were examined, using immunocytochemical and ultrastructural techniques, at times ranging from 1 week to 8 months. All grafts were recovered in a healthy condition although some rejection of the tissue was detected at the 1- and 2-week stages. In the neural lobe, clusters of pituicytes were scattered among the loose network of capillaries, most of which had a fenestrated endothelium. The intermediate lobe remained organized in compact avascular lobules. Axons similar to those projecting into the neurointermediate lobe in situ, but also axons of other types (e.g., somatostatinergic, enkephalinergic) penetrated the grafts. Synapses with melanotrophic cells in the intermediate lobe and neurohaemal contacts in the neural lobe were frequent from 2 1/2 months after transplantation. Immunocytochemical and ultrastructural characteristics indicated intense secretory stimulation of the melanotrophic cells in the early stages. All cells enclosed in a same glandular lobule reacted in a similar manner. In later stages, when re-innervation occurred, the cells recovered their initial characteristics. The overall effect of the re-innervation of the intermediate lobe grafted in this location is inhibitory, as in the lobe in situ.

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)

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.