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T P Powell

Publications and source records attributed to T P Powell.

At least 19 recordsLinked to original sources
PubMed1991

Clustering of ipsilateral cortico-cortical projection neurons to area 7 in the rhesus monkey.

The distribution within individual cytoarchitectonic areas of the cells of origin of ipsilateral cortico-cortical fibres to area 7 of the parietal lobe of the monkey has been studied. After injections of horseradish peroxidase into area 7, labelled cells in a variety of cortical areas were plotted and their distribution along the length of the cortex analysed. Significant clustering of labelled cells was seen wherever their numbers were sufficient for meaningful statistical analysis. In most cases, further analysis using correlation techniques revealed a significant banding of labelled cells across the cortex. Typical bands varied from 500-800 microns in width, and formed an irregular branching and rejoining pattern across the cortex. The intra-area distribution of cortico-cortical projection neurons is comparable to the distribution of neurofibrillary tangles in the cortex in Alzheimer's disease.

Alzheimer Disease↗
PubMed1991

Neuronal hypertrophy in the pars reticulata of the substantia nigra in Parkinson's disease.

The size of neurons in the pars reticulata of the substantia nigra in patients dying with Parkinson's disease has been compared with that in non-parkinsonian control cases. Parkinson's disease is accompanied by a significant (+53%) hypertrophy of reticulata neurons. This is similar to changes seen in experimental rats with ipsilateral damage of the striatum. It is suggested that the enlargement seen in Parkinson's disease, similar to that in the rat, is indicative of plasticity in the GABA-ergic reticulata neurons, and may be associated with increased inhibitory flux in pathways arising from the pars reticulata to the superior colliculus and thalamus.

Adult↗
PubMed1990

The connections of area PG, 7a, with cortex in the parietal, occipital and temporal lobes of the monkey.

The cortico-cortical connections of area PG, 7a, in the parietal, occipital and temporal lobes have been studied after injections of HRP in this area and in certain of the areas connected with it. After such injections in PG there are labelled cells in architectonic areas OA and PE (visual area PO), the cingulate and retrosplenial areas situated medial to PG; posteriorly labelled cells are present in OA, visual areas MST, MT, V2, V3, V4 and in the walls and floor of the lower part of the superior temporal sulcus. Injections in PE and V4 show that these connections are reciprocal. Small injections in PG result in cell labelling in different parts of the areas connected to PG, suggesting that the connections are well organized and that there may be an ordered representation of the visual field in PG. In the lower wall of the lower part of the superior temporal sulcus there is overlap of the two visual pathways in the cortex, that to the temporal lobe with that to the parietal lobe; and in a restricted part of this sulcus there is convergence and overlap of the sequences of cortico-cortical connections related to the visual, somatic and auditory sensory systems. There may be certain common principles in the sequences of cortical connections to the parietal and temporal lobes from the primary visual and somatic sensory areas; in both there are well organized hierarchical and parallel pathways, and both are related to the superior temporal sulcus and to the cingulate cortex.

Animals↗
PubMed1990

The ipsilateral cortico-cortical connections of area 7b, PF, in the parietal and temporal lobes of the monkey.

The cortico-cortical connections of area 7b (or PF) in the parietal and temporal lobes of the monkey have been studied with the method of axoplasmic transport of horseradish peroxidase (HRP). Area 7b is reciprocally and precisely connected with area 5, the second somatic sensory area (SII), the retroinsular area, the granular insular area (Ig), area 23 of the cingulate cortex and with the cortex in the walls of the superior temporal sulcus. Area 7b is not interconnected with area 7a (PG) nor with any of the prestriate visual areas. After injections of HRP into area PF the labelled cells in all these areas, except the granular insular area, are mainly in layer III and these cells are considered to be the origin of 'feed-forward' type connections; in the granular insular area most of the cell labelling is in layer V, interpreted to be the origin of 'feed-back' connections. Between SI and area PF there are two sequences of connections in parallel with each other, one through area 5 and the other through SII. In all areas the labelled cells are in clusters of 500-2000 microns width on individual sections and in bands of these widths on planar reconstructions.

Animals↗
PubMed1990

The ipsilateral corticocortical connections of area 7 with the frontal lobe in the monkey.

The corticocortical connections between area 7 and the frontal lobe have been studied in the monkey. Injections of HRP were made into area 7 of the parietal lobe or into area 46 in the walls of the principal sulcus. The two subdivisions of area 7, 7a or PG and 7b or PF, are connected with different parts of the frontal lobe, and each subdivision is connected with two distinct areas. Area 7b, PF, is connected in a well organized and somatotopic manner with the lower premotor area and with the lower part of area 46, below the fundus of the principal sulcus. Area 7a, PG, is connected with area 8a and with the upper part of area 46, above the fundus of the principal sulcus; it is suggested that the lower part of area 8a and the posterior part of area 46 are related to the central visual field, while the medial part of area 8a and the anterior part of area 46 are related to the periphery of the visual field. The corticocortical connections between area 7 and the frontal lobe are reciprocal and those passing from area 7 to the frontal lobe are 'feed-forward' and those to area 7 are 'feed-back'.

Animals↗
PubMed1990

A quantitative study of the neurofibrillary tangles and the choline acetyltransferase activity in the cerebral cortex and the amygdala in Alzheimer's disease.

A quantitative study has been made of the number of neurofibrillary tangles and of the choline acetyltransferase activity in several sites in the cerebral hemispheres of eight patients who had had Alzheimer's disease. The neurofibrillary tangles were maximal in structures in the medial temporal lobe (uncus, amygdala, hippocampus and parahippocampal gyrus), severe in the neocortex on the lateral surface of the temporal lobe, moderate in the "association cortex" of the parietal and frontal lobes and minimal in primary somatic and visual sensory areas. There was a significant decrease in choline acetyltransferase activity in almost all areas, and the means of the percentage decreases for the different groups of areas correlate well with the counts of the neurofibrillary tangles. These results support the hypothesis that the pathological process in Alzheimer's disease may spread along a sequence of corticocortical connections between the main sensory areas and the hippocampal formation. The disease process may also spread along the reciprocal connections between the amygdala and the neocortex because the numbers of tangles in different areas of the neocortex closely parallel the density of their connections and the amygdala.

Aged↗
PubMed1988

Experiments to study recovery of lateral geniculate nucleus cell size following monocular lid closure and reverse suture in infant monkeys.

Following monocular eyelid closure at birth in macaque monkeys, reverse suture at 3 weeks of age cancels the difference in size between deprived and undeprived parvocellular lateral geniculate nucleus (LGN) cells by causing hypertrophy of the initially deprived cells. This means that two weeks after reversal cells in both initially deprived and initially undeprived parvocellular laminae are approximately 15% larger than normal. However, long term survival shows that there is a second phase of change during which all parvocellular cells shrink, but particularly the initially undeprived cells which become considerably smaller than the initially deprived cells. Reopening the secondarily closed eye after a short period of reversal resulted in normal cell sizes in one animal, but two animals developed marked squints and had very small parvocellular cells in all laminae, and one animal developed bilateral amblyopia. Simply reopening the eye of two animals after two months of late closure started at 7 months of age reversed the shrinkage of all parvocellular cells which is caused by late closure.

Animals↗
PubMed1988

A comparison of cell size changes in central and pericentral representations within the primate lateral geniculate nucleus following early monocular deprivation.

Mean cell areas have been measured in the most posterior part of the lateral geniculate nucleus containing the representation of central retina in 8 normal monkeys (Macaca mulatta) and in 5 monkeys following monocular closure from birth. Comparisons with cell size changes at a more anterior level, where pericentral retina is represented, show that size changes of parvocellular cells at the posterior level are significantly less, being only between half and two-thirds of those more anteriorly. The undeprived cells undergo less initial hypertrophy than cells at a more anterior level and subsequently the deprived cells show less shrinkage. There is no comparable difference for magnocellular cells.

Animals↗
PubMed1988

The cortico-cortical connections within the parieto-temporal lobe of area PG,7a, in the monkey.

After injections of HRP into area PG(7a) labelled cells have been found in architectonic areas OA, PE, the cingulate and retrosplenial areas medial to area PG; posteriorly areas MST, OA (V4), V2, V3 and the cortex in the walls and floor of the superior temporal sulcus have also been labelled. Small injections placed in PG have resulted in different parts of these areas being labelled, suggesting that these cortico-cortical connections are well organized and raising the possibility of an ordered representation of the visual field in PG. It is suggested that the vertical meridian is around the boundary and the horizontal meridian passes antero-posteriorly across about the middle of its medio-lateral extent; the central part of the visual field is in the depths of the intraparietal sulcus, and the periphery is on the surface of the inferior parietal lobule and in the anterior wall of the upper part of the superior temporal sulcus. The lower visual field is medial and the upper field is lateral.

Animals↗
PubMed1988

The organization of the cortico-cortical connections between the walls of the lower part of the superior temporal sulcus and the inferior parietal lobule in the monkey.

After injections of HRP into area 7a,PG, in the monkey labelled cells have been found in the walls and floor of the lower part of the superior temporal sulcus; the part of area 7a,PG, in the posterior wall of the intraparietal sulcus is connected with the floor and posterior wall of the superior temporal sulcus, and the part of 7a,PG on the surface of the inferior parietal lobule with the floor and anterior wall. Area 7b,PF is related to a restricted part of the floor of the superior temporal sulcus.

Animals↗
PubMed1987

The cortico-cortical connections of area 7b, PF, in the parietal lobe of the monkey.

The cortico-cortical connections of area 7b (or PF) in the parietal lobe of the monkey have been studied with the method of axoplasmic transport of horseradish peroxidase or with the method of axonal terminal degeneration. Area 7b is reciprocally and precisely connected with area 5, the second somatic sensory area (SII), area 23 of the cingulate cortex, the retroinsular area (Ri), the granular insular area (Ig), and with the cortex in the walls of the superior temporal sulcus.

Animals↗
PubMed1987

Increase in immunohistochemical staining of GABAergic axons in the superior colliculus and thalamus of the rat following damage of the ipsilateral striatum and frontal cortex.

The superior colliculus and ventromedial nucleus of the thalamus have been examined in rats following damage of the frontal cortex and underlying striatum with immunohistochemical staining using an antiserum directed against gamma-aminobutyric acid (GABA). Following such lesions, at a time when the cell bodies of the neurones in the ipsilateral pars reticulata of the substantia nigra are known to be significantly enlarged, there is substantially more immunostaining of GABAergic fibres in both sites when compared with the contralateral side and with normal littermate control animals. The increase in immunoreactivity may indicate sprouting of the axons of the enlarging pars reticulata neurones or an increase in immunoreaction of existing fibres.

Animals↗
PubMed1987

The cholinergic nuclei of the basal forebrain of the rat: normal structure, development and experimentally induced degeneration.

The normal morphology and distribution of the cholinergic neurones of the basal forebrain of the rat have been studied qualitatively and quantitatively after staining immunohistochemically with a monoclonal antibody to choline acetyl transferase (ChAT). This was done in order to provide an adequate control for the changes found in these cells on both sides of the brain in the experimental investigation of the reaction of the cells to damage of their axons. The cholinergic cells form a more or less continuous anteroposterior band, but they can be subdivided into distinct nuclear groups on the basis of the size and form of the cell bodies and dendrites, their position and arrangement. these nuclei conform closely to previous descriptions of Nissl-stained material: the medial septal nucleus, the vertical and horizontal nuclei of the diagonal band and the basal nucleus. Quantitative measurements of the cross-sectional areas of the cells in the different nuclei confirmed the conclusions drawn from the qualitative examination. Measurements of the ChAT cells at different ages showed that in all nuclei they are significantly larger in size in infancy than in the adult, and they shrink to the mature size by 46 days. The cells in the various cholinergic nuclei show distinctly different reactions to damage of their terminal axonal fields. After removal of a large part of the neocortex by removal of the overlying pia-arachnoid mater the cells in the basal nucleus in the operated hemisphere underwent retrograde cellular degeneration, being swollen and paler-staining up to 14 days, and thereafter shrinking by 20-30% (as compared with those in the brains of age- and sex-matched littermate controls). The degree of shrinkage was appreciably greater when the animals were operated upon at the neonate stage. No cell loss was found, qualitatively or quantitatively, in the basal nucleus. After removal of the hippocampus there is marked loss of cholinergic neurones in the medial septal nucleus and in the vertical nucleus of the diagonal band, and with severe shrinkage of the remaining cells. Removal of the olfactory bulb results in only slight shrinkage of the cells, and no cell loss, in the horizontal nucleus of the diagonal band.(ABSTRACT TRUNCATED AT 400 WORDS)

Age Factors↗
PubMed1987

The cholinergic nuclei of the basal forebrain of the rat: hypertrophy following contralateral cortical damage or section of the corpus callosum.

After damage of the neocortex of one hemisphere by removal of the pia-arachnoid mater, the cholinergic cells of the basal nucleus of the unoperated hemisphere show a marked increase in their cross-sectional areas. This hypertrophy reaches a maximum of 25% by 3 weeks after operation and persists indefinitely. The cell bodies appear normal in shape, are often paler-staining and the hypertrophy includes the proximal dendrites. The hypertrophy is confined to the part of the basal nucleus corresponding to that which shows shrinkage on the operated side. The enlargement is greatest in animals operated upon on the first day after birth (+31%), is less in adult animals (mean +22%) but occurs at all ages up to 496 days, the oldest animal used. After unilateral removal of the hippocampus or section of the fimbria there is hypertrophy of the cholinergic neurones of the contralateral medial septal nucleus (+24%) and vertical nucleus of the diagonal band (+18%). Removal of the olfactory bulb on one side had no apparent effect upon the cholinergic neurones in the contralateral horizontal nucleus of the diagonal band. Damage of the neocortex by exitotoxic amino acids did not result in hypertrophy of the cholinergic cells of the contralateral basal nucleus despite marked shrinkage of the neurones in the basal nucleus on the operated side. After section of the corpus callosum the neurones throughout the basal nucleus of both sides are significantly larger than in the normal animal; the hypertrophy has occurred by 20 days after operation and persists indefinitely.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1987

Bilateral morphological changes in the substantia nigra of the rat following unilateral damage of the striatum.

The effects of damage of the striatum and globus pallidus of one side on the size of cells in the pars reticulata and pars compacta of the substantia nigra on both sides and in the contralateral globus pallidus have been examined. Cellular cross-sectional areas have been compared with those for neurons in the same nuclei in normal age and sex matched littermate control animals. One week after removal of the left striatum and globus pallidus and overlying cortex, the cells in the ipsilateral pars compacta are significantly shrunken (15%). This decrease in size gets progressively more marked with longer survival times reaching 50% 112 days after operation, the longest survival time examined. The shrinkage is accompanied by marked cell loss. Neurons in the contralateral pars compacta show an initial significant hypertrophy of their cell bodies (20%) in the first week after the operation, and later show a shrinkage of 20% at 35 days. The degree of this contralateral shrinkage gradually declines to 12% at 112 days. The changes in the pars compacta are accompanied by a significant enlargement (33%) of the cells in the pars reticulata of the substantia nigra on the side of the damage. This hypertrophy is present by 35 days after operation and persists at least until 112 days. Similar hypertrophy occurs in the ipsilateral globus pallidus in the one case where this could be examined. There are no significant changes in the contralateral pars reticulata, but there is significant enlargement (23%) of the neurons in the contralateral globus pallidus.

Animals↗
PubMed1987

Effects of enucleation at different ages on the sizes of neurons in the lateral geniculate nucleus of infant and adult monkeys.

Cell areas have been measured in the lateral geniculate nucleus following enucleation in 7 infant and 3 adult monkeys. Deafferented cells showed rapid transneuronal degeneration. Following enucleation at birth non-deafferented parvocellular LGN cells underwent hypertrophy which was followed by a delayed return to normal size. Enucleation at 7 months of age caused marked shrinkage of non-deafferented parvocellular cells. These changes in the non-deafferented cells are similar to those following monocular lid closure at the same ages. Sizes of non-deafferented cells were unchanged following enucleation of adult monkeys.

Aging↗
PubMed1987

Changes in the size of cells in the monocular segment of the primate lateral geniculate nucleus during normal development and following visual deprivation.

Cell areas have been measured in the monocular segment of the lateral geniculate nucleus in a series of 18 normal rhesus monkeys and in 27 following monocular or binocular lid closure or monocular enucleation. Cells in the parvocellular monocular segment shrank by 16% during the later period of normal development, between about 3 and 18 months of age, in contrasts to cells in the binocular segment which did not. Monocular closure at birth caused hypertrophy of cells in the undeprived monocular segment whereas long-term closure started later caused shrinkage of both deprived and undeprived parvocellular cells additional to that occurring during normal development. In both these instances cells in the monocular segment related to the undeprived eye are undergoing changes indicating some form of binocular interactions even in the monocular segment, but these interactions are considerably weaker than in the binocular part of the nucleus. Enucleation caused marked transneuronal degeneration of cells in the contralateral monocular segment of both infant and adult monkeys.

Animals↗