Biomedical subjects

C E Sortwell

Publications and source records attributed to C E Sortwell.

9 recordsLinked to original sources

PubMed1998

Co-grafted embryonic striatum increases the survival of grafted embryonic dopamine neurons.

To enhance the current therapeutic benefit of dopamine (DA) neuron grafts in Parkinson's disease, strategies must be developed that increase both DA neuron survival and fiber outgrowth into the denervated striatum. Previous work in our laboratory has demonstrated that dopaminergic neurons grow to greater size when co-grafted with striatal cell suspensions and display extensive tyrosine hydroxylase-positive (TH+) projections, but no conclusion could be reached concerning enhancement of survival of grafted DA neurons. The aim of the present study was to characterize further the potential trophic effects of striatal co-grafts on grafted mesencephalic DA neuron survival. Unilaterally lesioned male Fischer 344 rats were grafted with either a suspension of mesencephalic cells or with both mesencephalic and striatal cell suspensions. Co-grafts were either mixed together or placed separately into the striatum. Lesioned rats receiving no graft served as controls. Rotational behavior was assessed following amphetamine challenge at 2 weeks prior to grafting and at 4 and 8 weeks following grafting. Only rats receiving co-grafts of nigral and striatal suspensions separated by a distance of 1 mm showed significant behavioral recovery from baseline rotational asymmetry. Both mixed and separate striatal co-grafts were associated with a doubling of DA neuron survival compared with solo mesencephalic grafts. In the mixed co-graft experiment, DA neurite branching appeared enhanced and TH-rich patches were observed, whereas with co-grafts that were separated, TH+ innervation of the intervening host striatum was increased significantly. These results provide the first evidence suggesting that nigral-striatal co-grafts, particularly those placed separately and in proximity to each other, increase both DA neuron survival and neurite extension from the mesencephalic component of the grafts.

Animals↗

PubMed1998

Pattern of synaptophysin immunoreactivity within mesencephalic grafts following transplantation in a parkinsonian primate model.

The majority of investigations into the degree of restoration of neural circuitry following transplantation of the embryonic ventral mesencephalon to the striatum have focused upon the particular neurochemical subtypes of the fibers exchanged between graft and host. Visualization of neurites of specific neurotransmitter type while informative regarding the specificity of graft-host interactions, vastly underrepresents overall synaptogenesis as it may occur in the grafting situation. The present approach of using a molecular marker characteristic of all normal, functional synapses provides broader information about the synaptic remodeling that occurs after tissue grafting. Synaptophysin (SY), an integral membrane protein of the synaptic vesicle, is a reliable marker of nerve terminal differentiation. Immunohistochemical staining with antibodies directed against SY and the dopamine synthetic enzyme tyrosine hydroxylase (TH) was used to assess overall synaptic differentiation as well as the relationship between SY immunoreactivity and the distribution of grafted dopamine (DA) neurons and processes in mesencephalic grafts and mesencephalic-striatal co-grafts implanted in the striatum of MPTP-treated African green monkeys. Grafted embryonic cerebellar tissue was used as a comparison graft type that does not normally exchange prominent direct projections with striatum. Dense pericellular arrays of SY-positive terminals were associated with TH-positive neurons in mesencephalic grafts. In mixed mesencephalic-striatal co-grafts, TH-positive fiber patches within the striatal portion of the graft demonstrated a high degree of correspondence with SY immunoreactivity. In contrast, grafts of cerebellar tissue did not display the same pattern of prominent pericellular arrays of SY staining. These observations suggest that functional synapses are abundantly present within grafted mesencephalon, and that these contacts are enriched in areas of the graft occupied by DA neurons. Implantation of an inappropriate striatal target, the cerebellum, results in visibly diminished innervation. The pattern of SY labeling observed suggests that tissue grafts are extensively innervated, probably both from extrinsic and intrinsic sources, and that the pattern and density of this innervation corresponds to the appropriateness of the graft-host interaction.

Animals↗

PubMed1997

Agonist-induced morphologic decrease in cellular D1A dopamine receptor staining.

The distribution of D1A dopamine (DA) receptor proteins was assessed by using subtype specific antireceptor antisera after acute DA exposure. The immunofluorescent staining of D1A DA receptor protein expression was examined in (1) stably transfected Chinese hamster ovary (CHO) cells, (2) primary striatal cell cultures, and (3) rat striatal brain slices. After agonist exposure as brief as 2 min and as long as 60 min, profound loss of immunofluorescent D1A receptor protein staining occurred in each paradigm. Additionally in the tissue slice, immunofluorescent neuropil staining for the receptor protein also was attenuated. The DA-induced alteration in receptor protein staining was blocked by the antagonist (+)-butaclamol and by the selective D1-family antagonist SCH 23390. Receptor staining patterns reverted back to the control immunofluorescent distribution within 15 min after removing the agonist from the bath. Immunofluorescence for the second-messenger cyclic AMP increased at all DA exposure times in the three experimental paradigms, was blocked by D1-family antagonists, and decreased to basal staining after brief recovery periods. This demonstrated the functional integrity of the D1A receptor in target cells. Pretreatment with the mitogenic plant lectin concanavalin A blocked the immunofluorescent decrease in receptor staining but not the elevation of the second messenger, indicating a morphologic distinction in these two events, parallel to other biochemical reports. The data suggested that a morphologic basis of acute homologous D1A DA receptor desensitization may be transposition of membrane-surface receptors to a transiently unavailable, intracellular compartment. This finding is supported by specific fluorescence incorporation of FM1-43, used as a marker of endocytosis, in CHO cells treated with DA.

Animals↗

PubMed1995

Chromaffin cell xenografts in the rat neocortex can produce antidepressive activity in the forced swimming test.

Adrenal medullary allografts, as well as other monoaminergic tissues, have been demonstrated in our laboratory to increase antidepressive activity when transplanted into the frontal neocortex of rats. Refinement in the optimal parameters for xenograft viability has indicated that isolated bovine chromaffin cells may be an improved source of graft donor tissue. The aim of the present study was to determine whether isolated bovine chromaffin cell grafts to the rat frontal neocortex could provide an alternative source of catecholamines for antidepressant activity. Isolated bovine chromaffin cells, isolated bovine fibroblasts, or an equal volume of vehicle were unilaterally implanted into the right or left frontal cortex or right visual cortex. All rats were assessed before and 6 weeks after transplantation using the forced swimming test, a popular measure of antidepressant activity. Bovine chromaffin cell grafts in either the right or left frontal cortex produced significant increases in antidepressant activity compared to grafts of bovine fibroblasts and sham-operated or nontransplanted rats. In contrast, bovine chromaffin cells transplanted to the visual cortex did not affect antidepressant activity. Bovine fibroblast grafts in the frontal cortex also induced slight increases in antidepressant activity, although significantly less than chromaffin cell grafts. Morphological analysis revealed robust survival of tyrosine hydroxylase-positive chromaffin cells that retained their in situ ultrastructure and occasionally formed synaptic connections with the host parenchyma. These results suggest that xenografted isolated bovine chromaffin cells can provide a viable source of catecholamines for antidepressive activity.

Adrenal Medulla↗

PubMed1995

Pharmacologic specificity of antidepressive activity by monoaminergic neural transplants.

Previous studies in our laboratory have demonstrated the ability of monoaminergic transplants in the rat frontal cortex to produce antidepressive activity in both the learned helplessness model and the forced swimming test, as well as to increase monoamine levels in the implanted frontal cortex. These findings implicate increased cortical levels of norepinephrine (NE) and serotonin (5-HT) in the antidepressive activity of monoaminergic transplants. The goal of the present study was to characterize the pharmacologic mechanisms involved in the monoaminergic graft-induced antidepressive activity. Immobility scores in the forced swimming test (FST) were assessed after transplantation of 5-HT-containing pineal gland tissue, NE-containing adrenal medullary tissue, a combination of both tissues, or sciatic nerve (control) into the rat frontal cortex and compared to non-transplanted and chronic imipramine-treated rats. Monoaminergic transplants and imipramine treatment significantly reduced immobility scores in the FST in contrast to control transplanted or untreated animals. All groups were assessed pharmacologically with the adrenergic antagonists phentolamine (alpha) and propranolol (beta), and serotonergic antagonists metergoline (5-HT1/5-HT2) and pirenperone (5-HT2). Serotonergic antagonists, particularly the 5HT2 antagonist, blocked the reduction in FST immobility induced by the pineal implants. Adrenergic antagonists not only blocked FST immobility reductions in adrenal medullary grafted animals, but over-compensated for the adrenal transplants, producing a large increase in immobility. The FST reduction induced by pineal and adrenal cografts was blocked by all four monoaminergic antagonists. FST immobility scores in control transplanted and non-transplanted animals were not altered by any of the antagonists. The immobility reduction produced by chronic imipramine treatment was blocked significantly only by propranolol.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal Glands↗

PubMed1994

In vivo release of catecholamines from xenogeneic chromaffin cell grafts with antidepressive activity.

Previous studies in our laboratory have demonstrated that allografts of adrenal medullary tissue and xenografts of isolated bovine chromaffin cells to the rat frontal cortex can increase antidepressive activity in two separate animal models. Biochemical and pharmacological evidence suggest that the most likely mechanism of these antidepressive effects is via local release of catecholamines into the surrounding cortical parenchyma. The aim of the present study was to directly characterize the antidepressive mechanism of chromaffin cell xenografts by utilizing in vivo microdialysis to measure extracellular catecholamine levels from bovine chromaffin cell and control implanted rat frontal cortex. Following transplantation, only bovine chromaffin cell grafted rats displayed significant increases in antidepressive activity, as assessed by the forced swimming test, compared to rats with grafts of bovine adrenal medullary fibroblasts or nontransplanted rats. In vivo microdialysis results revealed remarkably elevated levels of epinephrine (EPI) and norepinephrine (NE), but not dopamine, in dialysates from bovine chromaffin cell-transplanted frontal cortex. The most likely source of these enhanced EPI and NE levels is the grafted xenogeneic chromaffin cells. The results of this study directly demonstrate that xenografts of bovine chromaffin cells to the rat frontal cortex provide a releasable pool of catecholamines for antidepressive activity.

Animals↗

PubMed1993

Induction of antidepressive activity by monoaminergic transplants in rat neocortex.

To assess the ability of monoaminergic transplants to reduce immobility in the forced swimming test (FST), either adrenal medullary tissue, pineal gland tissue, or equal volumes of sciatic nerve were transplanted into the rat frontal neocortex. In the FST the duration of immobility is thought to indicate the level of antidepressant activity, as immobility times are reliably reduced by antidepressant therapies. Immobility times were reduced in rats with adrenal medullary grafts and pineal grafts to the rat frontal neocortex. In contrast, immobility times were not reduced in control sciatic nerve tissue grafts. Biochemical analysis using HPLC revealed that pineal-grafted neocortex contained higher levels of serotonin (5-HT) and adrenal medullary-grafted neocortex contained higher levels of norepinephrine (NE) than sciatic nerve-grafted or nongrafted controls. Immunocytochemical studies showed that the monoaminergic grafts survived well and continue to produce high levels of monoamines. These results support an important role for neocortical 5-HT and NE transmission in antidepressant activity and suggest that transplants of monoaminergic-containing tissue can reduce biochemical deficits in depression.

Adrenal Medulla↗

PubMed1990

Monoaminergic neural transplants prevent learned helplessness in a rat depression model.

Current theories of the etiology of depression implicate disturbances and imbalances in the function of monoaminergic systems, particularly involving serotonin and norepinephrine. Neural transplantation is a potential approach towards restoring balanced functioning in the central nervous system. The purpose of the present study was to determine the utility of transplanting monoamine-producing cells into the brain to alleviate behavioral depression. Serotonin-containing pineal gland tissue, catecholamine-containing adrenal medullary tissue, a combination of both, and a control of striated muscle tissue were implanted into the frontal neocortex of adult rats. The ability of these grafts to prevent the development of learned helplessness, a widely accepted model for depression, was assessed 6-8 weeks following transplantation. The monoamine-containing transplants, but not the control transplants, were able to prevent the development of learned helplessness. Immunocytochemical and ultrastructural studies revealed that the grafted monoaminergic tissues survived and continued to produce high levels of monoamines. These results suggest that neural transplants may provide a long-term local source of monoamines as a potentially new approach for alleviating some forms of depression.

Adrenal Medulla↗

PubMedDate not supplied

Comparison of neurotoxicity following repeated administration of l-dopa, d-dopa and dopamine to embryonic mesencephalic dopamine neurons in cultures derived from Fisher 344 and Sprague-Dawley donors.

Levodopa is the most efficacious and widely used symptomatic drug for Parkinson's disease (PD). There is currently, however, a great deal of interest focused on the possibility that levodopa-induced increases in dopamine (DA) turnover may increase oxidative damage derived from the breakdown of DA. Increased oxidative damage following levodopa may contribute to the progressive degeneration of remaining host nigral neurons as well as interfere with development and function of embryonic nigral neurons in neural grafting trials. There is abundant evidence that levodopa is toxic to embryonic nigral DA neurons in both cell culture and neural grafting models. These findings have prompted a number of studies on mechanisms of levodopa toxicity to identify effective means of ameliorating potential oxidative stress related to levodopa in PD. In the current study we have utilized cultures of embryonic nigral DA neurons to address the fundamental question of whether levodopa-induced toxicity is related to DA production or whether dopa itself contributes to cell death. We compared the degree of nigral DA cell death following chronic administration of: 1) levodopa (e.g.: l-dopa); 2) its less active stereoisomer d-dopa; and 3) DA. We examined the rank order of toxicity of these compounds in two species of rats, Fisher 344 (F344) and Sprague-Dawley (SD). Results indicate a toxicity profile of: DA > l-dopa >> d-dopa. In addition, although there was no difference in response of F344 and SD cultures to l-dopa, the SD cultures were significantly more susceptible to the neurotoxic effects of DA. Taken collectively, these results suggest that levodopa-induced toxicity is related primarily to DA production rather than oxidation of dopa to toxic metabolites, and that some strain related differences do exist.

Animals↗