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Biomedical subjects

G A Brook

Publications and source records attributed to G A Brook.

35 records · Page 2Linked to original sources
PubMed1998

A novel early component of the cell body response in axotomized Clarke's nucleus neurons revealed by monoclonal antibody Py.

The monoclonal antibody Py was initially developed as a tool for the identification of subpopulations of hippocampal neurons. Recently it has also been demonstrated to be a useful marker for other populations of midbrain and spinal cord neurons in which the antigen showed a strong colocalization with cytoskeletal elements. To assess the possible usefulness of Py as a tool for studying lesion-induced cell body changes, densitometric analysis of altered Py-immunoreactivity (Py-IR) has been compared with that of microtubule-associated protein 2 (MAP2) in Clarke's nucleus following axotomy. One week after a unilateral transection of the dorsal spinocerebellar tract at Th9-10, Py-IR in the Clarke's nucleus ipsilateral and caudal to the lesion was reduced by approximately 40%. By 21 days, Py-IR was reduced by approximately 50% (a near maximal reduction) and remained constant up to 5 months after the lesion (the longest survival time studied). Alterations of MAP2-IR in Clarke's nucleus were later in onset, slower to develop, and less marked. The differential distribution of the Py antigen in the CNS and its rapid and long lasting loss indicate that the Py antibody is a sensitive tool for studying novel early alterations of the cytoskeleton which may be important molecular events in axotomy-induced pathological processes.

Animals↗
PubMed1998

Distribution of B-50(GAP-43) mRNA and protein in the normal adult human spinal cord.

B-50(GAP-43) is a phosphoprotein mainly found in the nervous system which plays a major role in neurite growth during development and regeneration as well as in synaptic remodelling. In the mature intact central nervous system, intense B-50 immunoreactivity (B-50-IR) can still be detected in regions which maintain residual capacity for structural re-organization. B-50 expression has been studied extensively in laboratory animals; however, its distribution and regulation in the human spinal cord is largely unknown. As a first step to analyze lesion-induced structural alterations, we investigated the distribution of B-50 protein and mRNA in the normal adult human spinal cord and dorsal root ganglia. Intense B-50-IR was localized to the superficial laminae of the dorsal horn at all segmental levels, the intermediolateral nucleus at thoracic levels and Onuf's nucleus at sacral levels. Scattered neurons, particularly in the ventral horn of lumbar and sacral segmental levels (and occasionally also in Clarke's nucleus) displayed intense B-50-IR in close apposition to the perikaryal and proximal dendritic surfaces. Nonradioactive in situ hybridization indicated that B-50 mRNA could also be detected in neurons of the ventral horn and also in the intermediolateral nucleus. The distribution of B-50 mRNA and protein in the normal human spinal cord shows a marked similarity to that reported in experimental animals, including the selective labelling of Onuf's nucleus. However, the strong B-50-IR on the surface of some large anterior horn motor neurons has not been observed in other mammals. This finding might reflect a particular state of readiness for synaptic plasticity.

Aged↗
PubMed1998

Dynamics of microglial activation in the spinal cord after cerebral infarction are revealed by expression of MHC class II antigen.

Microglial reactivity associated with induction of MHC class II (HLA-DR) antigen is a sensitive indicator for pathological events in the CNS. To assess the response of glial cells after lesions of supraspinal descending tracts, HLA-DR, CD68 and GFAP were studied immunohistochemically on spinal cord tissue of 5 patients who died after unilateral infarction of the middle cerebral artery territory, and 5 control cases. In patients who died shortly after a stroke (4-14 days) increased HLA-DR-immunoreactivity (HLA-DR-IR) could be observed in the intermediate grey matter and in the ventral horn. The CD68-IR was much less intense. After longer survival times (5 weeks to 4 months). HLA-DR-IR in the grey matter was clearly lower than that observed in the spinal cord of short survival times, but very abundant in the dorsolateral funiculus, specifically within the corticospinal tract. In white matter areas, CD68-IR was almost identical to the HLA-DR-IR. Within the grey matter, CD68-IR was similar to the control tissue. A moderate increase of GFAP-positive astrocytes could be seen only in the grey matter after longer survival times. It seems probable, that the dynamics of HLA-DR-positive microglia reflect the early phagocytosis of presynaptic terminals by microglia in target regions of descending fibre tracts. In the white matter, the removal of degenerating axons by phagocytosing microglia expressing HLA-DR and CD68 antigens is a slower process which occurs over a period of months.

Adult↗
PubMed1997

Differential distribution of immunoreactivity in the adult rat spinal cord revealed by the monoclonal antibody, Py: a light and electron microscopic study.

The monoclonal antibody Py has previously been shown to be a useful marker for subpopulations of neurons in the rat brain. However, the distribution of Py immunoreactivity in other regions of the CNS and PNS is not known. Here, we present a light and electron microscopic investigation into the distribution of Py immunoreactivity in the adult rat spinal cord, dorsal root ganglia, and peripheral nerves. Py immunoreactivity was associated with cytoskeletal elements in the cell body and dendrites of large-diameter neurons (particularly motoneurons, Clarke's nucleus neurons, and some dorsal root ganglion cells). Small-diameter neurons of lamina II (substantia gelatinosa) were Py negative. Py immunoreactivity was also detected in some populations of nerve fibers, notably axons located in the corticospinal tract, axons in the region of the white matter bordering the gray matter (presumably propriospinal axons), and also motor axons of the ventral root, but not in peripheral nerve. Dorsal roots were largely unstained. The present observations suggest a possible involvement of the Py antigen in the function or maintenance of the cytoskeleton of some populations of neurons and that the antibody may be a potentially useful tool for studying lesion-induced cytoskeletal alterations, particularly in alpha-motoneurons and Clarke's nucleus neurons.

Animals↗
PubMed1997

Axotomy-induced alterations in the red nucleus revealed by monoclonal antibody, Py, following a low thoracic spinal cord lesion in the adult rat.

The monoclonal antibody Py was previously developed as a tool for the identification of subpopulations of hippocampal neurons. Here, the differential distribution of Py immunoreactivity in the mid-brain is described showing that Py also serves as a useful marker for other populations of neurons. Medium to strong immunoreactivity was observed in the cell body and dendrites of neurons of the oculomotor nucleus, superior colliculus and substantia gelatinosa reticulata. However, particularly intense Py-immunoreactivity was identified in the magnocellular neurons in the caudal pole of the red nucleus. Unilateral transection of the rubrospinal tract at Th9-10 induced a marked reduction of Py immunoreactivity in the ventrolateral territory of the caudal pole of the axotomised red nucleus. A small but statistically significant reduction of Py-immunoreactivity was first seen at 7 days after surgery and a maximal loss of immunoreactivity (reduced to 66% of control levels) was observed by 21 days after surgery. Immunoreactivity in the axotomised red nucleus was reduced for the duration of the experiment but at the longer survival times studied (3 and 6 months) a small degrees of recovery of staining was observed in small-medium diameter atrophic neurons. These results indicate that monoclonal antibody Py, may be a useful novel and sensitive tool for investigating the cell body reaction of particular populations of axotomised CNS neurons following spinal cord injury.

Animals↗
PubMed1996

Transient decrease of acetylcholinesterase in ventral horn neurons caudal to a low thoracic spinal cord hemisection in the adult rat.

Light microscopic enzyme histochemistry was employed to study the alterations of acetylcholinesterase (AChE) within lumbosacral ventral horn neurons at survival times of 1, 4, 7, 14, 28, 60, and 90 days after low thoracic spinal cord hemisection in adult rats. The intensity of histochemical staining was quantified using densitometric techniques. Virtually all ventral horn neurons of sham-operated and unoperated animals, which served as controls, displayed intense AChE staining. Hemisection of the spinal cord induced a transient ipsilateral decrease of AChE staining in most neuronal cell bodies and in the neuropil of lamina IX at all segmental levels caudal to the lesion. Quantitative analysis of representative segments revealed a reduction of AChE in the ventral horn during a postoperative (p.o.) period of 1 to 28 days followed by a phase of recovery over the next two months. AChE activity still remained slightly reduced, even at 90 days p.o. The transient decrease in AChE is a well-known metabolic response of axotomized motoneurons. However, the observed changes of AChE reactivity in intact motoneurons ipsilateral and caudal to the hemisection are presumably induced by the interruption of supraspinal descending pathways. These metabolic changes may functionally affect the whole motor unit and be involved in the disturbances of motor function following spinal cord injury.

Acetylcholinesterase↗
PubMed1995

B-50 (GAP-43) in the rat spinal cord caudal to hemisection: lack of intraspinal sprouting by dorsal root axons.

The controversial hypothesis that intraspinal sprouting by dorsal root axons promotes reinnervation of partially denervated neurons caudal to a low thoracic cord hemisection was re-investigated in rats using quantitative immunohistochemical analysis of the neural specific growth-associated protein B-50 (GAP-43) at postoperative survival times of 3, 10, 21, 42, and 90 days. The lack of increase in B-50-immunoreactivity in all segments below the hemisection at all survival times does not support the concept of intraspinal sprouting following the removal of supraspinal descending pathways.

Animals↗
PubMed1995

Structural changes of anterior horn neurons and their synaptic input caudal to a low thoracic spinal cord hemisection in the adult rat: a light and electron microscopic study.

Structural changes in lumbosacral ventral horn neurons and their synaptic input were studied at 3, 10, 21, 42, and 90 days following low thoracic cord hemisection in adult rats by light microscopic examination of synaptophysin immunoreactivity (SYN-IR) and by electron microscopy. There was an ipsilateral transient decrease in SYN-IR at the somal and proximal dendritic surfaces of anterior horn neurons which extended caudally from the site of injury over a postoperative (p.o.) period of 42 days. Concomitantly, at 21 days p.o., perineuronal SYN-IR started to recover in upper lumbar segments. By 90 days p.o., a normal staining pattern of SYN was noted in upper and mid lumbar segments, but the perineuronal SYN-IR was still slightly below normal levels in low lumbar and sacral segments. Electron microscopy revealed ultrastructural changes coincident with the alterations in SYN-IR. At 3 days p.o., phagocytosis of degenerating axon terminals by activated microglial cells was observed at the somal and proximal dendritic surfaces of ventral horn neurons. These changes were most prominent up to two segments caudal to the lesion. At 10 days p.o., advanced stages of bouton phagocytosis were still detectable in all lumbosacral motor nuclei. Additionally, abnormal axon terminals, with a few dispersed synaptic vesicles and accumulations of large mitochondria, appeared at the scalloped somal surfaces of anterior horn neurons. At 21 days p.o., several large lumbosacral motoneurons had developed chromatolysis-like ultrastructural alterations and motoneuronal cell bodies had become partially covered by astrocytic lamellae. At 42 days p.o., there was a transient appearance of polyribosomes in some M-type boutons. In addition, at 42 and 90 days p.o., a few degenerating motoneurons were detected in all lumbosacral segments, but most displayed normal neuronal cell bodies contacted by numerous intact synapses as well as by astrocytic processes. In contrast to these striking alterations of synaptic input at somal and proximal dendritic surfaces of motoneurons, relatively few degenerating boutons were detected in the neuropil of motor nuclei at all the p.o. times studied. We suggest that the preferential disturbance of the predominantly inhibitory axosomatic synapses on ventral horn neurons may be involved in the mechanisms which influence the well-established increase in motoneuronal excitability after spinal cord injury.

Animals↗
PubMed1994

Extrusion transplantation of Schwann cells into the adult rat thalamus induces directional host axon growth.

In a previous study we found that Schwann cells microtransplanted into the central nervous system rapidly dispersed from the transplantation site and became intimately associated with host grey and white matter. We have now investigated whether this migratory behavior of the donor Schwann cells is compatible with the production of stable, continuous anatomical cell tracks and whether such tracks can induce directional host axon growth. During the gradual withdrawal of a micropipette, highly purified suspensions of cultured adult peripheral nerve Schwann cells were continuously extruded to form a vertical column of cells extending for up to 4 mm through the thalamus and across the choroid fissure into the hippocampus of adult rat hosts. The donor Schwann cells were identified by immunohistochemistry for low-affinity nerve growth factor receptor, vimentin, and Rat 401. Although donor Schwann cells migrated into the host tissues, a large number remained along the axis of the injection track to form a column which was maintained for up to 3 weeks. From 4 days, increasing numbers of parallel, unbranching host RT97-positive axons entered the Schwann cell column in alignment with the long axis of the Schwann cells in the vertical tracks. The axons did not fasciculate directly with each other, but mingled diffusely with the Schwann cells. The Schwann cell tracks were able to convey host axons out of the dorsal thalamus, across the extracellular space of the choroid fissure, and into the ventral hippocampus. Thus, Schwann cells, transplanted in the form of elongated tracks, can establish bridges across boundary membranes in the brain and carry substantial numbers of nerve fibers from one area to another.

Animals↗
PubMed1993

Monoclonal antibody G10 which recognises microtubule-associated protein 1x identifies growing axons of neurons microtransplanted into adult rat hippocampus.

Monoclonal antibody G10 recognises an epitope on microtubule-associated protein 1x, a developmentally regulated cytoskeletal protein expressed in immature axons of the central and peripheral nervous systems. Here we report that G10 can be used to identify the axonal projections of syngeneic embryonic (E14-E15) hippocampal cells microtransplanted by a minimally traumatic technique into intact adult host hippocampus.

Animals↗
PubMed1993

Morphology and migration of cultured Schwann cells transplanted into the fimbria and hippocampus in adult rats.

Schwann cells cultured from neonatal rat peripheral nerve were injected into the fimbria and hippocampus of syngeneic adult rats by a microtransplantation technique which causes minimal disturbance to the host brain structure at the site of implantation, and thus allows the grafted cells to come into immediate contact with intact host tissue. Numerous Schwann cells could be identified for up to 6 weeks (and with decreasing frequency for up to 3 months) by intense immunoreactivity for low affinity nerve growth factor receptor. The transplanted cells adopted a distinctive elongated form, with a central, ovoid nucleus flanked by processes which were up to 300 microns long, and which ranged from swollen segments with a diameter as large as 12 microns down to thread-like fibres of 1 micron or less. This morphology is different from that of any of the host cells. The transplanted Schwann cells migrated freely into the host tissue along blood vessels and according to the position of the grafts, they either entered the hippocampal neuropil, or migrated (for distances of up to 2 mm) along the longitudinal axis of the fimbria, where they were interspersed in parallel with the interfascicular glial rows and axons. The host astrocytes did not appear to impede the migration of the donor Schwann cells. Although the host astrocytic processes became hypertrophic, with increased glial fibrillary acidic protein and vimentin expression, the predominant longitudinal orientation of the astrocytic tract processes was maintained. The transplanted Schwann cells did not form peripheral myelin (as detected by P0 immunoreactivity), and it is not clear whether they survive beyond the period at which we detect them.

Animals↗
PubMed1993

Schwann cells transplanted into the CNS.

A small volume of purified Schwann cells, cultured from early postnatal rat sciatic nerve, was injected into the hippocampus or fimbria of syngeneic adult hosts. The procedure caused minimal structural disturbance at the transplantation site, with close graft-host contact and maximal opportunity for integration. The donor Schwann cells were identified by a combination of light and electron microscopic features (which include characteristic deep and complex infoldings of a well marked nuclear envelope), antigenic profile (especially low affinity nerve growth factor receptor immunoreactivity), uptake of fluorescent latex microspheres and autoradiography of [3H]thymidine-labelled dividing cells. The donor Schwann cells adopted a distinctive elongated form, with a central, ovoid nucleus flanked by processes which were up to 300 microns long, and which ranged from swollen segments with a diameter as large as 12 microns down to thread-like fibres of 1 microns or less with growth cone-like expansions. Transplanted cells migrated from the graft, particularly along blood vessels and could permeate all cytoarchitectonic regions of the adjacent host hippocampal neuropil. Donor Schwann cells also migrated along the longitudinal axis of the fimbria, where they were interspersed in parallel with the interfascicular glial rows and axons. The grafted cells induced a transient but marked host astrocytic hypertrophy, which did not appear to impede the migration of the donor Schwann cells. The transplanted Schwann cells did not form peripheral myelin (as detected by P0 immunoreactivity), and it is not clear whether they survive beyond the period at which we detect them.

Animals↗
PubMed1990

End-plates, transmission and contractile characteristics of muscles without spindles in the hereditary sensory neuropathy of the Sprawling mouse.

In the mutant mouse Sprawling, a deficiency of sensory ganglion cells is associated with a failure of the development of spindles and tendon organs particularly affecting muscles of the hindleg. Electrophysiological and morphological investigations were made on nerve, muscle and the neuromuscular junction of soleus and extensor digitorum longus (EDL). It was found that the absence of sensory innervation had no effect on the development of muscle bulk, on the fibre diameters or on histochemical profiles. The elimination of polyneuronal innervation proceeded at the normal rate and was complete by 3 wks of age. The strength of contractile responses and the number of motor units were normal in both muscles. End-plate areas were measured and the size distribution found to be normal in soleus. In EDL, however, there was a preponderance of small end-plates and a relative deficiency of large ones. This was associated with an abnormally low frequency of miniature end-plate potentials and of the mean quantal content of transmission. There was also a reduction in the complexity of the postsynaptic specialization at end-plates in the EDL. Localized axonal swellings packed with neurofilaments were observed in preterminal motor nerve fibres, which suggested an abnormality of axonal transport. There was no evidence of denervation of muscle fibres. The contractile characteristics of soleus and EDL were still distinguishable as slow and fast-twitch, respectively, despite the abnormalities found, and it seems likely that impulse traffic in the lower motoneuron is only marginally affected, if at all. An abnormality of axonal transport may be responsible for the inability of motoneurons to maintain large end-plates in fast-twitch muscles.

Animals↗
PubMed1988

Changes in denervated skeletal muscle of amiodarone-fed mice.

Prolonged dosing of mice with amiodarone produced a myopathy characterized by autophagic vacuolation and phospholipid inclusions. A previous morphological study had shown that amiodarone did not affect the rate of nerve regeneration after sciatic nerve crush. In the present study, reinnervation was assessed by the reappearance of miniature endplate potentials that confirmed that axonal regeneration and motor reinnervation was not affected by amiodarone. However, there was a marked delay in the recovery of motor function in the amiodarone-treated mice. Denervation was found to induce an extensive necrosis of muscle fibers in the deeper parts of fast-twitch muscles. Histochemical studies showed that type 1 fibers were spared, necrosis affecting mainly type 2 fibers with relatively high oxidative enzyme activity (fast-twitch oxidative fibers). Biochemical studies showed a significant increase in the amount of amiodarone and its metabolite in denervated muscle of amiodarone-treated mice when compared with contralateral, normally innervated muscles.

Amiodarone↗
PubMed1987

Effects of phospholipase of Enhydrina schistosa venom on nerve, motor end-plate and muscle of the mouse.

Phospholipase A2 from Enhydrina schistosa (sea snake) venom was administered intravenously or intramuscularly to mice. The effects on the contractile responses and neuromuscular transmission were studied in soleus (a slow-twitch muscle) and extensor digitorum longus (e.d.l.--a fast-twitch muscle). These muscles were also studied by morphological methods which included light and electron microscopy and enzyme histochemistry. There was a rapid and irreversible reduction of resting membrane potentials of muscle fibres of soleus which then failed to contract in response to direct or indirect stimulation. The e.d.l. was less severely affected. Spontaneous and evoked release of transmitter remained detectable at almost all end-plates tested and there was no apparent reduction in the sensitivity of the post-synaptic membrane. Most muscle fibres of soleus but only about 50% of those in e.d.l. became necrotic, the histochemical fibre types 1 and 2A being affected. Electron microscopy showed that in the acute phase (up to 24 h) there were lesions of the plasmalemma and severe disorganization of the internal structure of muscle fibres. In contrast, motor nerve terminals remained intact as did myelinated axons in the intramuscular nerves. There was a transient increase in the number of omega-shaped profiles in the axolemma and of coated vesicles in nerve terminals at 1-3 h, but by 24 h motor nerve terminals were normal in appearance. In regenerated muscle, post-synaptic folds at motor end-plates were reduced in depth and number.

Adenosine Triphosphatases↗