Biomedical subjects

A Seiger

Publications and source records attributed to A Seiger.

At least 73 records · Page 4Linked to original sources

PubMed1992

Eighteen-month course of two patients with grafts of fetal dopamine neurons for severe Parkinson's disease.

Two patients with advanced Parkinson's disease were followed for 6 months before, and 18 months after, receiving stereotaxic grafts of fetal mesencephalic tissue from aborted human fetuses. Parameters studied included a series of standardized tests of movement, response to levodopa, electrophysiological recording of the motor readiness potential, and positron emission tomography (PET) with ligands based upon levodopa and upon the dopamine reuptake inhibitor nomifensine. The patients each received stereotaxic implantation of ventral mesencephalic tissue containing midbrain dopamine neurons from aborted human fetuses of 8 to 10 weeks gestational age into the caudate and putamen of one hemisphere. Throughout their 18-month course, the patients were treated with cyclosporine, azathioprine, and glucocorticoids to minimize the risk of graft rejection. There were no significant complications from the procedure, but there was also no major change in their assessment of impairment on the Hoehn and Yahr scale. However, significant changes were observed in clinical, electrophysiological, and PET measures. Changes in these parameters, apparent at 6 months postoperatively, were described in detail in a previous report. The purpose of this present report is to provide follow-up data from the subsequent year with an emphasis on longitudinal evaluation methodology. Standardized clinical testing showed a small but long-term improvement in the first of the two patients. Following the operation, she was able to walk in "off" periods, which she had not been able to do preoperatively. This improvement was accompanied by increased walking speed and reduction in the time necessary to perform a series of pronation and supination movements using both hands. Although these improvements have continued throughout the postoperative period, they have not alleviated her basic neurological impairment. The second patient showed similar improvement during the first 6 months; she then reverted to her preoperative status at the end of the 18-month follow-up period. The electrophysiological recordings were consistent with the clinical findings. Both patients had significant changes in the motor readiness (bereitschafts) potential amplitude, which was greatest 5 to 7 months postoperation. The amplitude of the potential declined subsequently for both patients, but remained significantly elevated over the preoperative baseline for patient 1. The analysis of the PET scans was somewhat compromised by technical problems in the preoperative scans. However, they are also consistent with the clinical data. In comparisons of the operated and the unoperated sides, fluoro-dopa showed increased uptake in the caudate nucleus of patient 1 at 6 months and at 13 months.(ABSTRACT TRUNCATED AT 400 WORDS)

Brain Tissue Transplantation↗

PubMed1992

Transient spinal cord ischemia induces temporary hypersensitivity of dorsal horn wide dynamic range neurons to myelinated, but not unmyelinated, fiber input.

1. The activity of 197 single dorsal horn neurons was recorded extracellularly in the spinal cord of decerebrate, spinalized, unanesthetized rats. The response properties of 174 wide dynamic range (WDR) neurons to electrical, mechanical, and thermal stimulation in three groups of rats were studied:normal, 1-4 days after transient spinal cord ischemia induced photochemically by laser irradiation when the rats exhibited behavioral hypersensitivity to mechanical stimuli (allodynia), and 10-20 days after spinal ischemia when the allodynia had ceased. 2. In normal rats, the responses of dorsal horn WDR neurons to suprathreshold electrical stimulation of their receptive fields consisted of a short-latency (A) and a long-latency (C) response. In 77% of the neurons (57/74), there was a separation between the A- and C-fiber responses. The response threshold (defined as 20% increase in neuronal discharges above background activity) to mechanical stimulation applied with calibrated von Frey hairs was 13.8 g, and the discharges of these neurons to graded stimulation increased linearly. 3. In 68% of WDR neurons in allodynic rats (38/56), the response to suprathreshold electrical stimuli was a single burst with no separation between A- and C-fiber responses. The magnitude and duration of the response were significantly increased compared with those recorded in normal rats. The sensitivity of these neurons to mechanical stimulation was also greatly increased, expressed by a lowered threshold (2.1 +/- 0.3 g, mean +/- SE) and a shift to the left of the nonlinear stimulus-response curve. The background activity of the neurons and the size of the receptive fields were, however, unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

Baclofen reverses the hypersensitivity of dorsal horn wide dynamic range neurons to mechanical stimulation after transient spinal cord ischemia; implications for a tonic GABAergic inhibitory control of myelinated fiber input.

1. In the companion paper, we described a state of hypersensitivity that developed in dorsal horn wide dynamic range (WDR) neurons in rats after transient spinal cord ischemia. Thus the WDR neurons exhibited lower threshold and increased responses to low-intensity mechanical stimuli. The response pattern of these neurons to suprathreshold electrical stimulation was also changed. Notably, the response to A-fiber input was increased. No change in response to thermal stimulation was found before and after spinal cord ischemia. 2. In normal rats, the gamma-aminobutyric acid (GABA)B agonist baclofen (0.1 mg/kg ip) administered 1-3 h before neuronal recording suppressed the responses of WDR neurons to high-intensity mechanical pressure without influencing the threshold and the responses to lower-intensity stimuli. 3. In allodynic rats, similar pretreatment with baclofen totally reversed the hypersensitivity of the WDR neurons to mechanical stimuli and normalized the response pattern of neurons to electrical stimulation. 4. The GABAA receptor agonist muscimol (1 mg/kg ip) did not influence the response of WDR neurons in either normal or allodynic animals. 5. The present results demonstrated that the GABAB agonist baclofen is effective in reversing the hypersensitivity of dorsal horn WDR neurons to low-intensity mechanical stimulation after transient spinal cord ischemia, indicating that dysfunction of the GABAergic inhibitory system may be responsible for the development of neuronal hypersensitivity. 6. It is suggested that GABAergic interneurons exert a tonic presynaptic inhibitory control, through baclofen-sensitive B-type GABA receptors, on input from low-threshold mechanical afferents, and that disruption of this control may result in painful reaction to innocuous stimuli (allodynia).

Animals↗

PubMed1992

Systemic mexiletine relieves chronic allodynialike symptoms in rats with ischemic spinal cord injury.

We have recently reported a chronic allodynialike symptom in rats after ischemic spinal cord injury. This pain-related behavior is resistant to a number of pharmacologic treatments, including morphine, clonidine, carbamazepine, baclofen, and muscimol. In the present report, we present evidence indicating that systemic mexiletine, a local anesthetic and antiarrhythmic agent, effectively relieves the allodynia-like symptoms at doses of 15 and 30 mg/kg in these rats without inducing major side effects. It is suggested that systemically applied mexiletine may be useful in treating central pain in patients with spinal cord injury.

Animals↗

PubMed1991

Hypersensitivity of dorsal horn wide dynamic range neurons to cutaneous mechanical stimuli after transient spinal cord ischemia in the rat.

The responsiveness of dorsal horn wide dynamic range (WDR) neurons to cutaneous mechanical stimuli was studied in decerebrate, spinalized, unanesthetized rats before and after transient photochemically induced spinal cord ischemia. In normal rats, the discharges of dorsal horn WDR neurons to the graded mechanical stimuli applied with calibrated von Frey hairs increase linearly. One to four days after spinal ischemia, when the rats exhibit a strong allodynia-like behavioral reaction to cutaneous stimuli, the sensitivity of dorsal horn WDR neurons to mechanical pressure is greatly increased. There is a significant decrease in the threshold pressure to evoke neuronal discharges and the exponential stimulus-response curve is shifted to the left. Thus, transient ischemia of the spinal cord results in hyperexcitability of dorsal horn WDR neurons, which may underly the allodynia-like sensory abnormalities observed in behaving animals. The present results may contribute to understanding the mechanism of the development of chronic central pain in patients after central nervous system injury involving ischemia.

Animals↗

PubMed1991

The excitatory amino acid receptor antagonist MK-801 prevents the hypersensitivity induced by spinal cord ischemia in the rat.

Protection by the NMDA receptor antagonist MK-801 against transient spinal cord ischemia-induced hypersensitivity was studied in rats. The spinal ischemia was initiated by vascular occlusion resulting from the interaction between the photosensitizing dye Erythrosin B and an argon laser beam. The hypersensitivity, termed allodynia, where the animals reacted by vocalization to nonnoxious mechanical stimuli in the flank area, was consistently observed during several days after induction of the ischemia. Pretreatment with MK-801 (0.1-0.5 mg/kg, iv) 10 min before laser irradiation dose dependently prevented the occurrence of allodynia. The neuroprotective effect of MK-801 was not reduced by maintaining normal body temperature during and after irradiation. There was a significant negative correlation between the delay in the administration of MK-801 after irradiation and the protective effect of the drug. Histological examination revealed slight morphological damage in the spinal cord in 38% of control rats after 1 min of laser irradiation without pretreatment with MK-801. No morphological abnormalities were observed in rats after pretreatment with MK-801 (0.5 mg/kg). The present results provide further evidence for the involvement of excitatory amino acids, through activation of the NMDA receptor, in the development of dysfunction following ischemic trauma to the spinal cord.

Amino Acids↗

PubMed1991

Effects of glutamate and gamma-aminobutyric acid on spontaneously active intraocular spinal cord graft neurons.

Pieces of fetal rat lumbar spinal cord were transplanted into the anterior eye chamber of adult rat hosts. At least seven months later, extracellular single-unit recordings of spontaneously active graft neurons were made prior to and during the superfusion of either glutamate or gamma-aminobutyric acid (GABA). Superfusion of glutamate produced an increase (five cells), decrease (three cells), or had no effect (two cells) on the firing rate of neurons tested. Superfusion of GABA decreased the firing rate of all twelve neurons tested, while superfusion of the GABA receptor antagonist bicuculline increased the firing rates of all eight neurons tested. The latency and magnitude of the responses to glutamate and GABA were not related to depth of the recording electrode below the graft surface. Together, these data suggest that the intraocular spinal cord graft is suitable for the in vivo study of GABA and glutamate neuropharmacology.

Animals↗

PubMed1990

Regulation of adrenergic receptors in intraocular hippocampal transplants: role of noradrenergic innervation.

Hippocampal tissue transplanted into the anterior chamber of the eye offers a unique system in which development can be studied in the absence of the noradrenergic innervation. This system was used to determine the extent to which noradrenergic innervation regulates the development of adrenergic receptors. In addition to examining single denervated transplants, transplants grown with innervation from the superior cervical ganglia of the host rat or from locus coeruleus cotransplants were also examined to determine whether the source of norepinephrine and extent of innervation in oculo regulate the development and density of adrenergic receptors. In vitro autoradiographic analysis of ligand binding to both alpha 1- and beta-adrenergic receptors with 125I-BE 2254 and 125I-pindolol, respectively, was used to characterize adrenergic receptors in the intraocular transplants. Quantitative analysis of the receptors showed an up-regulation of both alpha 1- and beta-adrenergic receptors in tissue grown in the absence of norepinephrine, but in general there was not a high degree of correlation between norepinephrine content and receptor density. Although high-performance liquid chromatography (HPLC) analysis of catecholamines revealed higher than normal amounts of norepinephrine in hippocampal transplants innervated by the superior cervical ganglia or a locus coeruleus cotransplant, the density of alpha 1 and beta receptors was quite comparable with values found in the literature for normal adult hippocampus. These results suggest that the relationship between receptor number and density of innervation may differ significantly from what is observed in response to pharmacological manipulation of norepinephrine systems in the adult brain.

Adrenergic alpha-Antagonists↗

PubMed1990

Intraocular grafts of fetal rat spinal cord: a Golgi study of neuronal morphology and organization.

A modified Golgi staining technique was used to study the neuronal morphology and organization of the fetal rat spinal cord which had developed in the anterior eye chamber of adult rat hosts. Individual neurons in spinal cord grafts displayed profiles which were strikingly similar to previously described spinal cord neurons stained in situ. Further, for the population of 464 graft neurons studied, the distributions of average cell body diameters and numbers of primary dendrites were comparable to those of previously published in situ studies. An internal organization of graft neurons was also observed. Similar-shaped neurons were grouped together, which made it possible to identify different regions within a graft, such that a comparison could be made with normal spinal cord morphology. These observations provide further evidence that the intraocular spinal cord graft is a suitable model for studying spinal cord growth, development, and plasticity and indicate that the Golgi stain may be useful for the quantitative study of concomitant changes in neuronal morphology.

Animals↗

PubMed1990

Behavioral and electrophysiological correlates of human mesencephalic dopaminergic xenograft function in the rat striatum.

While human fetal xenografts placed into immunocompromised animal hosts have been shown to survive and grow, their ability to function and influence the host tissue has not been fully examined. Therefore, we implanted grafts of human fetal mesencephalic tissue intracranially into rats with unilateral 6-hydroxydopamine lesions of their nigrostriatal dopaminergic innervation and tested the rats behaviorally for reductions in apomorphine-induced rotations. The purpose of this study was to test the ability of these grafts to provide a functional reinnervation by comparing the behavioral changes with the morphology and presence of electrophysiologically active dopaminergic neurons within the graft and with firing rates of host striatal neurons. Adult Sprague-Dawley rats that had been unilaterally lesioned and that showed a stable two peak pattern of apomorphine-induced rotations received grafts of human fetal mesencephalic tissue placed directly into the lesioned striatum. These rats were then further tested each month for five months for reductions in their turning behavior. At 5 to 6 months postgrafting, electrophysiological recordings were made of cells within the graft and within the host striatum. The rats were then examined immunohistochemically to evaluate graft survival and extent of reinnervation of the host tissue. The rats receiving mesencephalic dopaminergic grafts demonstrated a 79% reduction in their apomorphine-induced rotations. Electrophysiological recordings revealed spontaneously active dopaminergic neurons within the graft as well as host striatal cell firing rates consistent with those of dopamine-innervated cells. Furthermore, immunohistochemical studies confirmed graft survival and revealed marked fiber outgrowth from the graft into and throughout the striatum. Taken together these findings provide evidence that grafts of human fetal mesencephalic tissue are able to produce behavioral improvements in lesioned animals which are associated with the presence of dopaminergic neurons within the graft and are consistent with normal host striatal cell activity levels.

Animals↗

PubMed1990

Electrophysiologic effects of ethanol in human brain xenografts in oculo: antagonism by Ro15-4513.

Human cortex cerebri and cerebelli xenografts from first-trimester fetal tissue fragments were used to study the effects of ethanol on single human central neurons. Transplants were placed into the anterior eye chamber of athymic nude rats and allowed to develop for 3 to 11 months. Immunohistologic analysis revealed graft structures that stained positively for a number of neuronal, transmitter-related, glial and vascular markers. Superfusion of ethanol (EtOH) elicited a reversible and dose-dependent depression of action potential discharge. At least two populations of neurons could be identified--a more sensitive group with an EC50 of 3.0 mM and a less sensitive group with an EC50 of 22.4 mM. These EtOH levels are within the range eliciting behavioral signs of intoxication in humans. EtOH-induced depressions could be antagonized by administration of the benzodiazepine inverse agonist Ro 15-4513. This study represents the first demonstration, to our knowledge, of the electrophysiologic actions of EtOH on single neurons from human brain, and provides dose-response data collected with known concentrations of EtOH as well as evidence for the blockade of these EtOH effects by the Roche compound.

Animals↗

PubMed1989

In vitro electrophysiological analysis of mature rat hippocampal transplants in oculo.

We have investigated the maturation of isolated rat hippocampus grafted into the anterior chamber of the eye. Electrophysiological responses from transplants were compared to those recorded from the in vitro hippocampal slice preparation. Intracellular recording demonstrated that the passive membrane characteristics of intraocular hippocampal neurons were similar to those of the CA1 pyramidal cells in the in vitro slice preparation. However, the slow after-hyperpolarization which normally follows depolarization-induced action potentials was reduced or completely absent in the intraocular transplants, and the excitatory postsynaptic potential (EPSP) evoked by local stimulation was prolonged. The duration of the EPSP was reduced by perfusion with D-aminophosphonovaleric acid (2.5-50 microM), an N-methyl-D-aspartate receptor antagonist. Normal levels of glutamate decarboxylase (a marker for gamma-aminobutyric acidergic neurons) were found in the transplants, and responses to adenosine, bicuculline, and norepinephrine were similar in the in oculo transplants and in vitro slices. The data suggest that although many properties of hippocampal neurons are intrinsically determined, other aspects of the physiology of mature hippocampus either fail to develop, or develop abnormally in the absence of external inputs in oculo.

2-Amino-5-phosphonovalerate↗

PubMed1989

Restricted fiber growth from substance P-immunoreactive brain neurons grafted to the anterior eye chamber of the rat.

Substance P (SP)-immunoreactive cell groups from fetal rat brain were homografted to the anterior eye chamber and left there for 2 months to mature, to elucidate their capacity to form nerve fibers in this ectopic environment. All grafts survived well, were rapidly revascularized from the host iris and proliferated to final sizes 2- to 4-fold the volume at transplantation. In spite of a rich SP fiber innervation of the transplant neuropil, no or almost no SP-positive fibers reached out from the transplant on to the iris. Monoamine histochemical analysis of the same locus coeruleus transplants revealed abundant fluorescent locus-derived nerve fibers of the host irides. Thus, a marked difference in growth behavior between noradrenergic and SP-immunoreactive neurons from the same brainstem region was found.

Animals↗

PubMed1989

Age-related alterations in noradrenergic input to the hippocampal formation: structural and functional studies in intraocular transplants.

Intrinsic versus extrinsic determinants of age-related alterations in hippocampal noradrenergic transmission were investigated using intraocular allografts in rats. Three groups of animals were examined: young hippocampal transplants in young hosts, old transplants in old hosts and young transplants in old hosts. Postsynaptic sensitivity to noradrenaline (NA) was measured by extracellular recordings of spontaneous activity and superfusion with known concentrations of catecholamines in the anterior chamber of the eye. Hill plots demonstrated that the dose-response relationships of NA-induced depressions were linear and parallel in the 3 groups. Aged hippocampal grafts displayed a highly significant subsensitivity to NA of one order of magnitude. The EC50 for this group was 203.1 microM as compared to 29.2 in young grafts. Young intraocular grafts in old hosts responded similarly to transplants in young hosts, with an EC50 of 32.4 microM for the depressant actions of NA. Collaterals of the host iris sympathetic ground plexus invaded the hippocampal grafts. The density of this noradrenergic innervation was estimated by immunohistochemistry for tyrosine hydroxylase. A slightly increased density and fluorescence intensity of the noradrenergic fibers were observed in the old transplants as compared to the young transplants in young and old hosts. This was correlated with a significantly (P less than 0.01) increased content of NA in old transplants, as measured with high performance liquid chromatography. The old transplants also contained a large number of autofluorescent lipofuchsin granules, which were absent in the young transplants, regardless of the recipient age. Taken together, these results suggest the existence of alterations in pre- as well as postsynaptic noradrenergic mechanisms in the aging hippocampus. These changes were dependent on transplant age rather than host age, thus suggesting an involvement of intrinsic rather than extrinsic determinants in this model system.

Action Potentials↗

PubMed1989

Human fetal dopamine neurons grafted into the striatum in two patients with severe Parkinson's disease. A detailed account of methodology and a 6-month follow-up.

By using stereotaxic surgical techniques, ventral mesencephalic tissues from aborted human fetuses of 8 to 10 weeks' gestational age were implanted unilaterally into the striata in two patients with advanced Parkinson's disease. The patients were treated with a cyclosporine, azathioprine, and steroid regimen to minimize the risk for graft rejection. They were examined for 6 months preoperatively and 6 months postoperatively and continued to receive the same doses of antiparkinsonian medication. There were no significant postoperative complications. No major therapeutic effect from the operation was observed. However, in the clinical tests, both patients showed small but significant increases of movement speed for repeated pronation-supination, fist clenching, and foot lifting. The rate of walking also increased in the one patient tested. For both patients, there was an initial worsening postoperatively, followed by improvement vs preoperative performance at 1 to 3 months. Both patients also showed significant improvement in the magnitude of response to a single dose of levodopa (L-dopa), but there was no increase in the duration of drug action. The motor readiness potential increased in both patients postoperatively, primarily over the operated hemisphere. Neurophysiological measurements also showed a more rapid performance of simple and complex arm and hand movements on the side contralateral to transplantation in one patient at 5 months postoperatively. Positron emission tomography demonstrated no increased uptake of 6-L-(18F)-fluorodopa in the transplanted striatum at 5 and 6 months. Taken together, these results suggest that the fetal nigral implants may have provided a modest improvement in motor function, consistent with the presence of small surviving grafts. Although our results support further scientific experimentation with transplantation in Parkinson's disease, widespread clinical trials with this procedure are probably not warranted at this time.

Contingent Negative Variation↗

PubMed1989

Human ventral mesencephalic xenografts to the catecholamine-depleted striata of athymic rats: ultrastructure and immunocytochemistry.

On the basis of animal studies, grafts of fetal human dopaminergic cells have been suggested as a therapy for Parkinson's disease. The purpose of this study was to characterize the ultrastructure and immunocytochemistry of human ventral mesencephalic xenografts placed into the catecholamine-depleted striata of athymic "nude" rats. Human fetal tissue was obtained from tissue fragments derived from elective abortions during the first trimester of pregnancy. Small pieces of the basal mesencephalon were grafted into the catecholamine-depleted striata of four athymic nude rats. The rats were allowed to survive from 3 to 6 months after grafting; following fixation, the striatal tissue containing the grafts was labeled with antibodies against tyrosine hydroxylase and serotonin. Immunocytochemistry revealed tyrosine-hydroxylase-like-immunoreactive (THLI) and serotoninlike-immunoreactive (5HTLI) cell bodies within the human grafts. Both 5HTLI and THLI fibers crossed the graft-host interface and innervated the previously lesioned striatum. Both types of fibers also entered the host cortex from the adjacent human graft. At the ultrastructural level, THLI and 5HTLI fibers and synaptic terminals were observed in the host neuropil. THLI and 5HTLI dendrites and axon terminals were also observed in the neuropil of the grafts themselves. THLI axon terminals are not normally present in the substantia nigra. The results of our study indicate that human xenografts can survive in the neuropil of the host striatum and form morphologically appropriate synapses within the host brain.

Animals↗

PubMed1989

Human fetal spinal cord xenografts survive in the eye of athymic nude rat hosts.

Human fetal spinal cord tissue was recovered from elective abortions and grafted to the anterior chamber of the eye of adult athymic nude rats. The transplants slowly became vascularized from the host iris during the first months. There was a clear cut stage-dependent survival and growth along a more "human" time-table. Fetal spinal cord tissue from embryos younger than gestational week 8 showed a much better survival and growth than tissue from older stages. Using laminin immunohistochemistry blood vessels could be visualized in the grafts. The pattern of vascularization was, however, clearly abnormal; there were fewer vessels which had abnormally thick walls as compared to those in the normal spinal cord. Similar to rat spinal cord allografts the human spinal cord xenografts displayed a relative gliosis and were surrounded by a glial layer visualized with antibodies against glial fibrillary acidic protein. Neurofilament-immunoreactive fibres were found inside the glial layer. A variety of neurons were found including large polygonal motoneuron-shaped cells, albeit with CGRP and AChE negative cell bodies. Both Substance P and enkephalin-immunoreactive cells and fibres were found. It is concluded that xenografted fetal human spinal cord survives, grows and may provide a useful model for experimental studies of human spinal cord development and connectivity.

Animals↗

PubMed1989

Detection of nerve growth factor and its mRNA by separate and combined immunohistochemistry and in situ hybridization in mouse salivary glands.

Intense labelling of secretory cells in the male mouse submandibular gland was observed after in situ hybridization using mouse nerve growth factor (NGF) cDNA probes. Under the same conditions, sparse less intensely labelled cells were also found in the sublingual gland. Hybridization to a chicken NGF cDNA probe gave weak labelling on the glands in accordance with a weak cross-hybridization between mouse NGF mRNA and chicken NGF cDNA probes, whereas no labelling was seen using pUC9 DNA as a hybridization probe. A combination of in situ hybridization and immunohistochemistry was also carried out on the same sections of submandibular gland. A good correlation was seen between actively synthesizing and intensely immunoreactive cells in the gland. The technique described here allows the detection of individual cells synthesizing relatively low levels of NGF. The combination of in situ hybridization and immunocytochemistry on the same section should be particularly useful in cases where NGF is transported away from its site of synthesis.

Animals↗