Search PubMed⌕ Search

Biomedical subjects

T Cowen

Publications and source records attributed to T Cowen.

At least 55 records · Page 3Linked to original sources
PubMed1995

Regulation of rat sympathetic nerve density by target tissues and NGF in maturity and old age.

Previous studies in our laboratory using a transplantation model have shown that target tissues of some autonomic neurons, including cerebral blood vessels, exert a controlling influence on nerve fibre loss in old age. The present study was undertaken in order to discover whether the influence of targets extends to controlling age changes in specific populations of nerves. In old rats, we have demonstrated a significant decrease of approximately 50% in the sympathetic innervation of middle cerebral arteries, using tyrosine hydroxylase-like immunoreactivity. Following transplantation, tyrosine hydroxylase-like immunoreactive nerve density on both young and old implanted middle cerebral arteries mirrored the nerve densities seen in normal, non-transplanted vessels. Furthermore, implanted tissue from old donors became reinnervated with a nerve density approximately 50% less than that of young implanted vessels. Treatment of transplants with nerve growth factor, however, was able to reverse these age changes and restore the sympathetic innervation of aged middle cerebral arteries to levels above those seen in young middle cerebral arteries. These results suggest that the pattern and density of sympathetic innervation that the middle cerebral artery receives is determined by the target rather than by the neurons supplying the tissue. The ability of nerve growth factor to induce regrowth in sympathetic neurons innervating ageing target tissues implies that age-related neuronal atrophy may be due to reduced synthesis or availability of target-derived neurotrophic factors.

Aging↗
PubMed1995

Reduced laminin immunoreactivity in the blood vessel wall of ageing rats correlates with reduced innervation in vivo and following transplantation.

Changes in extracellular matrix composition and/or organization, and in particular in the ratio of axonal growth-promoting components such as laminin to growth-inhibiting molecules, could contribute to the degenerative changes observed in the innervation of some peripheral tissues in old age. We have investigated this issue by evaluating laminin content or accessibility at various locations on blood vessels where we had previously studied age-related alterations in innervation density. We have employed a morphological approach, measuring laminin immunoreactivity by a densitometric application of confocal microscopy, because more conventional biochemical techniques would have been unable to distinguish specific, localized changes in laminin at sites accessible to nerves from heterogeneous changes in other areas of the vessel wall, such as the endothelial basal lamina. We found that in 24-month-old rats laminin immunoreactivity is decreased by 50% at the medial-adventitial border in association with the outer layer of smooth muscle cells, where a parallel decrease is observed in innervation density. Axonal terminals were shown to have access to laminin in this region of the blood vessel wall by double staining with laminin and a general neuronal marker. Changes in laminin immunoreactivity were region-specific on the same blood vessel, thus excluding the possibility of a generalized decrease in immunoreactivity in old age. For example, in the basilar artery intensity of laminin immunoreactivity decreased in old age at the medial-adventitial border, but showed no change in endothelial cell basal lamina and in the adventitia. Moreover, we performed in oculo transplants of blood vessels displaying differences in laminin immunoreactivity and found that the density of innervation correlated with the intensity of laminin staining, thus lending further support to the hypothesis that laminin might play a role in nerve fibre atrophy in old age.

Aging↗
PubMed1995

Neuropeptides in the skin of patients with atopic dermatitis.

There is increasing evidence that neuropeptides may be involved in the pathogenesis of atopic dermatitis (AD). This study examines whether neuropeptide distribution in the skin of patients with AD differs from normal controls. The distribution and density of several neuropeptides were examined in lesional and non-lesional skin of AD patients (n = 5) and in normal controls (n = 4) using indirect immunofluorescence and image analysis. Cholinergic innervation was studied using cholinesterase histochemistry. Staining with the general neuronal marker protein gene product 9 x 5 showed a subepidermal network of nerves with fibres penetrating the epidermis, and nerves around blood vessels, sweat glands and hair follicles. Image analysis of nerves around sweat glands showed a significantly higher nerve density in non-lesional compared with both normal controls and lesional skin (P < 0.05); lesional compared with control skin showed no significant difference. In the epidermis the density of nerves was not significantly greater in non-lesional compared with lesional skin and controls. Calcitonin gene-related peptide immunoreactivity was similar in all subjects except in three of the AD patients, where more nerves appeared to penetrate the epidermis. Substance P immunoreactivity in the papillary dermis was seen in all AD patients but no controls. Vasoactive intestinal polypeptide and neuropeptide Y staining were similar in all groups. Acetylcholinesterase-positive nerves were found around sweat glands in all subjects, the staining being greatest in non-lesional and least in lesional skin. Occasional nerves were seen in the papillary dermis in lesional skin of two out of the four patients. We have demonstrated quantitative differences in nerve growth in clinically normal skin of AD patients, and altered cutaneous neuropeptide expression in these patients which may contribute to the pathogenesis of AD. The cause of atopic dermatitis (AD) has not been fully established but it is believed that there is a complex interaction between genetic susceptibility, precipitating environmental factors and disordered immune responsiveness. There is increasing evidence that neuropeptides may be involved in the pathogenesis of AD. Exacerbations of the disease can be provoked by stress, scratching and sweating which may be the result of neurogenic inflammation. One of the first features of an exacerbation is flushing of the affected skin and pruritus. Several neuropeptides that have been identified in human skin are potent inducers of vasodilation and may induce pruritus. Substance P (SP), calcitonin gene-related peptide (CGRP) and vasoactive intestinal polypeptide (VIP) all cause vasodilation when injected intradermally, and SP and CGRP have been shown to be mediators of the weal and flare reaction. Spantide, a competitive antagonist of SP, has been shown to inhibit immediate and delayed-type hypersensitivity reactions. Part of these responses may be due to release of histamine and indeed elevated concentrations of histamine have been found in vivo in the skin and plasma of patients with AD. In this study the distribution and density of several neuropeptides were examined in lesional and nonlesional skin of AD patients and in normal controls using indirect immunofluorescence and image analysis. Cholinergic innervation was studied using cholinesterase histochemistry. Because many afferent fibres do not express CGRP or SP, the general neuronal marker protein gene product (PGP 9 x 5) was used to assess the overall nerve supply to the skin.

Acetylcholinesterase↗
PubMed1994

Nerve growth factor enhances the dendritic arborization of sympathetic ganglion cells undergoing atrophy in aged rats.

We have investigated whether dendritic growth can be induced from sympathetic neurons of aged rats by the application of exogenous nerve growth factor to their target tissues. A previous study showed that significant dendritic atrophy (19%) occurs during aging in the sympathetic neurons innervating the middle cerebral artery and that dendritic atrophy correlated with loss of axon collaterals in the same population of neurons. Using retrograde tracing in conjunction with intracellular injection of fixed tissue and confocal microscopy, we now demonstrate that infusion of nerve growth factor over the peripheral processes of the same neurons from aged rats induces significant dendritic (45%) and cell body (60%) growth. However, not all aspects of the dendritic arborization were affected. Primary dendrites and branch points were not altered by nerve growth factor. In contrast, nerve growth factor induced a significant increase in the number of primary dendrites and branch points (100%) of neurons from young adults. Our results demonstrate that sympathetic neurons undergoing dendritic atrophy during aging can exhibit significant dendritic growth in response to the in vivo infusion of nerve growth factor, although the lack of regenerative response displayed by some parts of the dendritic tree leads us to believe that these neurons also show signs of reduced plasticity.

Aging↗
PubMed1994

The effect of age on dendrites in the rat superior cervical ganglion.

Intracellular injection of a biotinylated probe in fixed superior cervical ganglia followed by confocal microscopy was used to investigate the effects of age on the dendritic arborisation of sympathetic neurons in rats aged 6 wk (young adult), 7 months (fully grown adult) and 24 months (aged). In accordance with other studies considerable dendritic growth was observed during postnatal development. However, in old age dendritic growth did not continue, and significant atrophy was observed. Quantitation of neuronal morphology showed significant reductions in soma size, total dendritic length, number of branch points and total area of dendritic arborisation in old age. Unexpectedly, significant reductions in the numbers of primary dendrites were observed in maturity and in old age. Concomitant with this atrophy there was an increase in age-related morphological abnormalities. The similarities between the atrophy and dendritic abnormalities shown by our aged neurons and those seen in other studies of young adult sympathetic neurons following axotomy or trophic factor deprivation are discussed.

Aging↗
PubMed1994

In vivo infusion of NGF induces the organotypic regrowth of perivascular nerves following their atrophy in aged rats.

The aim of this study was to investigate whether NGF could reverse the nerve fiber atrophy exhibited by some neurons in old age. We used quantitative immunohistochemical techniques to investigate how the autonomic nerves that supply different blood vessels are affected by aging. Age changes in the nerve plexus were not widespread but were specific to particular vascular targets. Furthermore, where nerve fiber atrophy did occur, it affected different populations of nerves; specifically, sympathetic nerve fibers were lost from the middle cerebral artery while nonsympathetic nerves were lost from the tail vein. Peripheral target tissues have been shown to have a trophic influence on the pattern and density of their innervation, which declines in old age (Gavazzi et al., 1992), possibly as a result of decreased availability of neurotrophic factors such as NGF. Consequently, in an attempt to reverse nerve fiber atrophy, we used miniosmotic pumps to infuse NGF for 2 weeks over involuting nerve fibers in the middle cerebral artery of freely moving aged rats. Our results show that exogenous NGF can induce organotypic neurite outgrowth from aged neurons undergoing nerve fiber atrophy. Moreover, NGF can induce a change in the pattern of the old nerve plexus to one similar to that seen in young animals. NGF had different effects on the extent and manner of neurite outgrowth in young and aged nerves. NGF induced greater nerve growth in old compared to young nerves, causing old nerves to grow within existing nerve bundles and to sprout new nerve fibers, in contrast to young nerves, which tended to grow only within existing nerve bundles. In conclusion, this study shows the potential of exogenous NGF to reverse age-related changes in neuronal morphology.

Aging↗
PubMed1993

Differential regulation of tyrosine hydroxylase protein and activity in rabbit sympathetic neurones after long-term cold exposure: altered responses in ageing.

The aim of this study was to investigate the response of sympathetic neurones to prolonged neural stimulation, using cold exposure as a non-invasive experimental paradigm. We examined the effects of prolonged (8 days and 4 wk) cold exposure on tyrosine hydroxylase (TH) protein and activity and neuropeptide Y (NPY) levels in sympathetic neurones of the superior cervical ganglion (SCG), together with NPY levels in the ear artery from young and aged rabbits. The main findings were as follows. In young rabbits, TH levels and TH activity were differentially regulated in response to prolonged cold exposure. TH levels rose whilst TH activity tended to decline. Decentralization of SCG from young animals before cold exposure abolished the rise in TH levels. TH activity in SCG from young rabbits was reduced by decentralization whilst cold exposure resulted in an increase in TH activity. Thus, TH activity was induced in the SCG in the absence of pre-ganglionic input, demonstrating a non-synaptic regulatory mechanism. In old rabbits, cold-induced changes were either delayed or failed to occur, indicating that the responses of sympathetic neurones to cold stress are impaired in old age.

Aging↗
PubMed1993

NGF can induce a 'young' pattern of reinnervation in transplanted cerebral blood vessels from ageing rats.

Peripheral target tissues can determine age-related changes in their density and pattern of innervation. We have shown previously that middle cerebral arteries from young and old rats transplanted in oculo in young hosts become reinnervated with a density and pattern of innervation that is typical of the age of the donor, i.e., the density of reinnervation on old transplants is 50% lower than on young transplants. The alterations in the target tissues responsible for their decreased innervation in old age are still unknown. We have investigated the possibility that increasing the availability of nerve growth factor (NGF) might restore the pattern and density of perivascular nerves on old blood vessels to levels of innervation typical of young tissues. Old middle cerebral transplants were therefore treated with NGF or vehicle by three weekly transscleral injections. NGF treatment markedly increased the reinnervation of old transplants, restoring the density and pattern of innervation to one characteristic of young animals. NGF produced an equivalent increase in nerve growth on young and old transplants, thus confirming that the receptivity of old blood vessels to reinnervation is not impaired. Control experiments were performed by treating transplants with saline, bovine serum albumin, or cytochrome c. Unexpectedly, bovine serum albumin was shown to promote axonal growth, although to a lesser extent and with a different pattern than NGF.

Aging↗
PubMed1993

Axonal regeneration from transplanted sympathetic ganglia is not impaired by age.

Changes occur with age in several areas of the nervous system, including autonomic ganglia and the target tissues of some sympathetic neurons where signs of neuronal degeneration have been shown in old age. In this study, we have employed an intraocular grafting technique to examine whether age changes occur in sympathetic neurons of the superior cervical (SCG) and stellate ganglia that might explain the reduced innervation of some of their target tissues in old age. Ganglia taken from young and old rats were implanted in oculo for 4 or 6 weeks in young hosts whose irises had been previously sympathetically denervated. The extent, pattern, and time course of reinnervation of the host iris was studied by catecholamine histochemistry followed by image analysis. We did not observe any difference in the pattern and time course of reinnervation between ganglia taken from young and old donors. If anything, the extent of reinnervation was greater in irises implanted with SCG taken from 25-month-old animals. Moreover, we did not observe any difference in ability to reinnervate the host iris between ganglia that normally project to the iris (SCG) and ganglia that normally do not project to the iris (stellate), regardless of the age of the donor animal. Our results suggest that sympathetic neurons from aged rats have unimpaired capability of regeneration and retain plasticity, as shown by their ability to reinnervate an inappropriate target. We hypothesize that the decreased innervation observed in some sympathetic targets in old age might be caused by changes in the target tissues themselves rather than being the result of degenerative changes in the neurons.

Aging↗
PubMed1993

Ageing in the autonomic nervous system: a result of nerve-target interactions? A review.

There are few generalisations that can be made regarding the changes that occur in autonomic nerves during ageing. Old age has different effects, including loss of neurones, loss of axon branches and alterations in neurotransmitters and other intracellular features. However, these age-related events are associated with particular and often small groups of neurones and are frequently species specific. Changes occur at different periods during development and maturity without any obvious age-stage at which neurodegenerative changes come to predominate. Some of the observations regarding neuronal changes in old age can be interpreted as the result of altered interactions between neurones and their peripheral target tissues. Recent studies in my laboratory support this contention. The neurotrophic theory has been used to explain such interactions during early development and it seems possible that, for example, alterations in the access of neurones to target-derived growth factors may underlie some of the changes that have been observed in old age. Plasticity in the mature autonomic nervous system may also be governed by similar relationships between nerves and their target tissues.

Aging↗
PubMed1992

Immunohistochemical, morphological and functional changes in the peripheral sudomotor neuro-effector system in elderly people.

Age-related changes in the human peripheral sudomotor neuro-effector system have been investigated in six 80-year-olds and six young adults. Histochemical and immunohistochemical studies on forearm skin biopsies showed diminished vasoactive intestinal polypeptide (VIP) and calcitonin gene related peptide (CGRP)-like immunoreactivity and a virtual absence of acetylcholinesterase in the elderly sudomotor nerve endings compared to the young. Reduced size of nerve bundles and decreased density of sympathetic nerve endings adjacent to the sweat glands of old people were shown by the neuronal marker, protein gene product (PGP 9.5), and by electron microscopy. Image analysis techniques were also used to demonstrate a marked regression in secretory coil size with age. Functional decrements accompanying the neurochemical and morphological changes in the neuro-effector system were measured in ten 80-year-olds by local quantitative nicotine axon reflex responses and compared with 12 young adults. These studies demonstrate marked regressive changes in both the nerve endings and target cells in old age and appear to express a significant loss of vigour in trophic interactions.

Acetylcholinesterase↗
PubMed1992

GAP-43 immunoreactivity is widespread in the autonomic neurons and sensory neurons of the rat.

GAP-43 is a membrane-bound phosphoprotein generally associated with axon growth during development and regeneration. Using immunohistochemical and immunoblotting techniques this study shows that GAP-43 is expressed extensively in the unperturbed adult autonomic nervous system. Strong immunoreactivity was seen in the developing and mature enteric subdivision of the autonomic nervous system and in nerves of the iris and various blood vessels. The presence of GAP-43 immunoreactivity in varicose nerve fibres, and a comparison of the labelling pattern of GAP-43 with the nerve associated marker PGP 9.5 suggests that GAP-43 is present in most or all autonomic nerve fibres in these organs. Immunoblotting of gut samples on 10% polyacrylamide gels revealed a single band of approximately 45,000 mol. wt that co-migrated with pure central nervous system GAP-43. Surgical sympathectomy experiments resulting in almost complete elimination of sympathetic fibres did not markedly affect the pattern of GAP-43 immunoreactivity in the iris, indicating that GAP-43 is expressed not only in sympathetic nerves but also in parasympathetic and sensory fibres. These findings show that GAP-43 is expressed extensively in autonomic nerves of the adult rat, at levels comparable to those seen during development. High levels of GAP-43 are not therefore restricted to development and regeneration in this part of the nervous system.

Animals↗
PubMed1992

Influence of target tissues on their innervation in old age: a transplantation study.

Age-related changes in the nervous system might be intrinsic to the neurons or secondary to changes in the target tissues they supply. We have investigated this question by transplanting old and young vascular muscle into contact with young host nerves in oculo and observing the reinnervating nerve fibres. The density and pattern of reinnervation were those typical of the age of the target tissue, thus old transplants imposed an 'old' pattern of reinnervation on young host nerves. Our findings strongly support the hypothesis that target tissues determine the pattern and density of their innervation in old age.

Aging↗
PubMed1991

Image analysis quantification of peptide-immunoreactive nerves in the skin of patients with Raynaud's phenomenon and systemic sclerosis.

Image analysis quantification was used to assess the results of immunocytochemistry for a neuronal marker and neuropeptides in digital skin biopsies from Raynaud's phenomenon (RP) and systemic sclerosis (SS) patients, to verify the possibility of a selective quantitative abnormality of immunoreactive nerves. The field area of specific immunostaining and nerve counts were evaluated on coded specimens, and the data compared by statistical analysis. Nerves immunoreactive for protein gene product 9.5 (PGP), a marker for neuronal elements, were decreased significantly in epidermal and subepidermal layers of digital skin in RP patients (P less than 0.0001). This change was paralleled by a decrease of calcitonin gene-related peptide (CGRP) immunoreactive nerves in the epidermis and around capillaries in the dermal papillae (P = 0.005). In the skin of RP patients, these changes were readily demonstrated by image analysis, although they were not always apparent on visual screening. In digital skin of SS patients, there was a generalized and very significant decrease of PGP, CGRP, and VIP immunoreactivities in all areas (P less than 0.0001). These results demonstrate that neuropeptide-containing nerves are involved in the digital pathology of RP and SS, and that image analysis quantification is an accurate and sensitive method for assessing morphological changes in pathological samples.

Adult↗
PubMed1991

Streptozotocin-induced diabetes in rats causes neuronal deficits in tyrosine hydroxylase and 5-hydroxytryptamine specific to mesenteric perivascular sympathetic nerves and without loss of nerve fibers.

The aim of this study was to investigate the possibility that inadequate venous return to the heart in diabetes is the result of a neuropathy which affects autonomic nerves supplying the splanchnic vasculature. Mesenteric veins from rats with streptozotocin-induced diabetes were markedly dilated in vivo compared to veins from control animals. Dilation appeared to be the result of loss of muscle tone rather than hypertrophy or hyperplasia of the vessel wall. Using quantification by image analysis and double-labeling immunohistochemistry on mesenteric veins, significant reductions in the density of nerve plexuses staining for 5-hydroxytryptamine (5-HT) and tyrosine hydroxylase (TH) were shown in vessels from diabetic rats compared to controls. No reductions were observed in the density of nerve plexuses stained for the neuronal marker, PGP 9.5, or for substance P (SP), a marker for afferent nerve fibers. These results indicate neurochemical deficits in experimentally induced diabetes which are specific to perivascular noradrenergic nerves and which, within the time-scale of our experiments, do not involve loss of nerve fibers. These deficits may contribute to an increase in venous pooling of blood in the splanchnic vasculature of diabetic rats and thus to inadequate venous return to the heart.

Animals↗
PubMed1991

Identification of neural profiles containing vasoactive intestinal polypeptide, acetylcholinesterase and catecholamines in the rat thymus.

Sympathetic and parasympathetic innervation of the rat thymus is described using immunohistochemical, fluorescence histochemical and histochemical methods. Sympathetic innervation was found to enter the gland with the vasculature and to be distributed mainly in the subcapsular and corticomedullary junctional areas of the cortex. The parasympathetic innervation was also found to enter the gland with the vasculature, but was distributed to both cortex and medulla. Acetylcholinesterase-positive staining cells were seen in the medulla. Ideas about the function of thymus innervation are discussed.

Acetylcholinesterase↗
PubMed1990

Cerebrovascular nerves in old rats show reduced accumulation of 5-hydroxytryptamine and loss of nerve fibres.

The effect of old age on the net accumulation of 5-hydroxytryptamine (serotonin) into cerebrovascular nerves of rats was studied using a new, densitometric application of image analysis of immunohistochemical staining. The results showed evidence of reduced accumulation in old animals in nerves supplying arteries of the circle of Willis. Measurements of the density of nerves stained with an antibody to the neuronal marker, PGP9.5, showed that loss of nerve fibres may occur in some cerebral vessels in old age.

Adrenergic Fibers↗