Biomedical subjects

P Cornwell

Publications and source records attributed to P Cornwell.

At least 19 recordsLinked to original sources

PubMed2001

Role of the superior colliculus in analyses of space: superficial and intermediate layer contributions to visual orienting, auditory orienting, and visuospatial discriminations during unilateral and bilateral deactivations.

The superior colliculus (SC) has been implicated in spatial analyses of the environment, although few behavioral studies have explicitly tested this role. To test its imputed role in spatial analyses, we used a battery of four spatial tasks combined with unilateral and bilateral cooling deactivation of the upper and intermediate layers of the superior colliculus. We tested the abilities of cats to orient to three different stimuli: (1) moving visual, (2) stationary visual, (3) stationary white-noise aural. Furthermore, we tested the ability of the cats to discriminate the relative spatial position of a landmark. Unilateral cooling deactivation of the superficial layers of the SC induced a profound neglect of both moving and stationary visual stimuli presented in, and landmark objects located within, the contralateral hemifield. However, responses to auditory stimuli were unimpaired. Unilateral cooling deactivation of both the superficial and intermediate layers induced a profound contralateral neglect of the auditory stimulus. Additional and equivalent deactivation of the opposite SC largely restored orienting to either moving visual or auditory stimuli, and restored landmark position reporting to normal levels. However, during bilateral SC deactivation, orienting to the static visual stimulus was abolished throughout the entire visual field. Overall, unilateral SC deactivation results show that the upper and intermediate layers of the SC contribute in different ways to guiding behavioral responses to visual and auditory stimuli cues. Finally, bilateral superior colliculus deactivations reveal that other structures are sufficient to support spatial analyses and guide visual behaviors in the absence of neural operations in the superior colliculus, but only under certain circumstances.

Acoustic Stimulation↗

PubMed1998

Streptozotocin-induced diabetes increases gamma-glutamyltranspeptidase activity but not expression in rat liver.

Earlier work describing increased biliary excretion of the acetaminophen-cysteine conjugate advanced the hypothesis that streptozotocin-induced diabetes increases gamma-glutamyltranspeptidase (GGT) expression in Sprague-Dawley rats. To test this hypothesis, rats were divided into control, diabetic, and insulin-treated diabetic groups. Diabetes was induced by intravenous injection of 45 mg streptozotocin/kg body weight and was effectively controlled by insulin treatment in the appropriate group. Densitometric quantification demonstrated that hepatic GGT activity in diabetic rats was significantly increased when compared to normal and insulin-treated diabetic controls. Histochemical staining of liver was greater in female than in male rats, and staining increased in female rat liver as the duration of diabetes lengthened from 30 to 90 days. GGT activity was increased by diabetes in liver canalicular-enriched and basolateral-enriched membrane preparations, and it was unchanged in renal brush border-enriched membranes. Total mRNA isolated from diabetic and insulin-treated diabetic rat livers did not conclusively demonstrate an elevation of GGT mRNA relative to normal. Western blot analysis showed no differences in the amount of GGT in diabetic versus normal rat livers. These data indicate that streptozotocin-induced diabetes does not alter the expression of, but does increase the activity of, GGT in liver.

Animals↗

PubMed1998

Dissociation of visual and auditory pattern discrimination functions within the cat's temporal cortex.

In ablation-behavior experiments performed in adult cats, a double dissociation was demonstrated between ventral posterior suprasylvian cortex (vPS) and temporo-insular cortex (TI) lesions on complex visual and auditory tasks. Lesions of the vPS cortex resulted in deficits at visual pattern discrimination, but not at a difficult auditory discrimination. By contrast, TI lesions resulted in profound deficits at discriminating complex sounds, but not at discriminating visual patterns. This pattern of dissociation of deficits in cats parallels the dissociation of deficits after inferior temporal versus superior temporal lesions in monkeys and humans.

Analysis of Variance↗

PubMed1998

Effect of acute exercise on plasma homocysteine.

BACKGROUND: The aim this work was to study the effects of acute exercise on plasma homocysteine level. METHODS: Twenty healthy, physically active males aged 24-39 (X = 29) ran on treadmill at an intensity of 70% of their maximal heart for 30 minutes. Blood was taken before, immediately following and 30 minutes following the exercise bout. RESULTS: There was no statistically significant relationship between pre-exercise plasma homocysteine levels and VO2 max (r = -0.05). Plasma homocysteine significantly increased 11.5% from the pre-exercise to 11.6 +/- 3.3 mumol.L-1 immediate post exercise levels. Thirty minutes postexercise plasma homocysteine was still elevated from pre-exercise levels, however the mean of 11.2 +/- 2.9 mumol.L-1 was not statistically different from pre-exercise values. The increase in homocysteine that occurred with 30 minutes of exercise is thought to be the result of hemoconcentration as indicated by changes in plasma albumin. Plasma albumin likewise paralleled the changes observed for homocysteine. Mean pre-exercise plasma albumin values were 42.9 +/- 2.9 g.L-1. Plasma albumin significantly increased 6.9% to 45.8 +/- 2.4 g.L-1 immediately post-exercise. Thirty minutes post exercise plasma albumin was still elevated from pre-exercise levels at 44.8 +/- 5.4 g.L-1. When the homocysteine plasma levels were adjusted for changes in plasma albumin, there was no statistical difference between any of the time points. CONCLUSIONS: It was concluded that acute exercise does not have any effect on plasma homocysteine in young healthy men aged 24-39.

Adult↗

PubMed1996

Learning and recall of form discriminations during reversible cooling deactivation of ventral-posterior suprasylvian cortex in the cat.

Extrastriate visual cortex of the ventral-posterior suprasylvian gyrus (vPS cortex) of freely behaving cats was reversibly deactivated with cooling to determine its role in performance on a battery of simple or masked two-dimensional pattern discriminations, and three-dimensional object discriminations. Deactivation of vPS cortex by cooling profoundly impaired the ability of the cats to recall the difference between all previously learned pattern and object discriminations. However, the cats' ability to learn or relearn pattern and object discriminations while vPS was deactivated depended upon the nature of the pattern or object and the cats' prior level of exposure to them. During cooling of vPS cortex, the cats could neither learn the novel object discriminations nor relearn a highly familiar masked or partially occluded pattern discrimination, although they could relearn both the highly familiar object and simple pattern discriminations. These cooling-induced deficits resemble those induced by cooling of the topologically equivalent inferotemporal cortex of monkeys and provides evidence that the equivalent regions contribute to visual processing in similar ways.

Animals↗

PubMed1996

Evidence for greater sight in blindsight following damage of primary visual cortex early in life.

This review compares the behavioral, physiological and anatomical repercussions of lesions of primary visual cortex incurred by developing and mature humans, monkey and cats. Comparison of the data on the repercussions following lesions incurred earlier or later in life suggests that earlier, but not later, damage unmasks a latent flexibility of the brain to compensate partially for functions normally attributed to the damaged cortex. The compensations are best documented in the cat and they can be linked to system-wide repercussions that include selected pathway expansions and neuron degenerations, and functional adjustments in neuronal activity. Even though evidence from humans and monkeys is extremely limited, it is argued on the basis of known repercussions and similarity of visual system organization and developmental sequence, that broadly equivalent repercussions most likely occur in humans and monkeys following early lesions of primary visual cortex. The extant data suggest potentially useful directions for future investigations on functional anatomical aspects of visual capacities spared in human patients and monkeys following early damage of primary visual cortex. Such research is likely to have a substantial impact on increasing our understanding of the repercussions that result from damage elsewhere in the developing cerebral cortex and it is likely to contribute to our understanding of the remarkable ability of the human brain to adapt to insults.

Adaptation, Physiological↗

PubMed1994

Reversible inactivation of visual processing operations in middle suprasylvian cortex of the behaving cat.

Extrastriate visual areas on the banks of the middle suprasylvian sulcus were inactivated by cooling to assess the behavioral contribution of this cortical region to the extraction of a stationary figure from a moving mask. Cooling blocked figure-ground separation when the mask was moving but had no influence when the mask was static. This difference provides strong evidence that the areas bounding the middle suprasylvian sulcus contribute to the neural separation of stationary from moving visual stimuli.

Action Potentials↗

PubMed1994

System-wide repercussions of damage to the immature visual cortex.

Damage of the primary visual cortex in mammals, including humans, severely disrupts vision by disconnecting much of the cognitive-processing machinery of extrastriate cortex from its source of visual signals in the retina. Studies of the anatomical consequences of damage to the immature primary visual cortex in cats reveal system-wide repercussions on neural circuitry that includes the retina, thalamus, midbrain and extrastriate cortex. The repercussions modify circuits that support relatively normal signal processing and the sparing of certain visually guided behaviors such as aspects of complex-pattern recognition and orienting to novel stimuli introduced into the visual field. These studies have implications for understanding the consequences of damage to the visual cortex in infant monkeys and humans, and for devising therapeutic strategies to attenuate defects in vision induced by cortical lesions.

Animals↗

PubMed1993

Capacity of the retinogeniculate pathway to reorganize following ablation of visual cortical areas in developing and mature cats.

The purpose of the present study was to determine the pattern and density of retinal projections to the dorsal lateral geniculate nucleus (dLGN) following ablation of visual cortical areas in developing cats of different postnatal ages and in mature cats. The terminations of retinal projections to the dLGN were evaluated following the injection of tritiated amino acids into one eye. Regardless of age, a visual cortical ablation of areas 17 and 18 induces massive death of neurons within the regions of the dLGN that are linked topographically to the cortical areas removed. However, the pattern of retinal projections to these degenerated regions of the dLGN differs depending upon whether the cortical lesion is incurred early in postnatal life or in adulthood. Following ablation on the day of birth (P1), virtually all surviving cells were found in the C-complex of dLGN with only a token number in the A-laminae. Correspondingly, retinal projections were maintained to the C-complex of the nucleus and were barely detectable in the degenerated A-laminae. However, in cats in which areas 17 and 18 had been removed in adulthood (> or = 6 months of age) retinal projections were maintained to the A-laminae even though nearly all neurons in those laminae had degenerated. Moreover, a subgroup of animals that incurred area 17 and 18 ablations at P1 showed that the modification of retinal projections to the A-laminae occurs within the first postnatal month, and an additional subgroup showed that retinal projections become increasingly resistant to the degenerative events in the dLGN that follow ablation of areas 17 and 18 at progressively older ages during the first postnatal month. Furthermore, retinal inputs also respond, in an age-dependent way, to degeneration of neurons in the C-complex induced by extension of the cortical ablation to include extrastriate visual areas.

Age Factors↗

PubMed1993

Differential sparing of depth perception, orienting, and optokinetic nystagmus after neonatal versus adult lesions of cortical areas 17, 18, and 19 in the cat.

Performance by cats with lesions of the visual cortex made in infancy or adulthood was examined on tasks of visually guided behavior that do not require specific training. Cats with lesions confined to areas 17, 18, and 19 made during the 1st postnatal week showed more sparing of function on a visual cliff, at orienting to targets suddenly appearing in the visual field, and at optokinetic nystagmus than did cats with equivalent damage incurred as adults. Cats with lesions that included areas 17, 18, 19 and most of the contiguous visual areas were severely impaired at all tasks whether the lesions were incurred neonatally or in adulthood. These findings suggest that sparing of vision after neonatal lesions of cortical areas 17, 18, and 19 is not confined to pattern learning tasks and that remaining lateral cortical visual areas are importantly involved in such sparing.

Aging↗

PubMed1989

Selective sparing after lesions of visual cortex in newborn kittens.

Previous findings are discordant regarding the effects of perinatal lesions of Cortical Areas 17 and 18 on visual discrimination learning in cats. Three potential determinants of such sparing were investigated: age at lesion (4 or 181 days), age at testing (3 or 9 months), and stimulus complexity. Age at testing was not significant, but performance varied with stimulus complexity and cortical damage, and there was an interaction between stimulus complexity and age at lesion. Both operated groups were transiently impaired in discriminating objects and subsequently learned to discriminate simple 2-dimensional patterns as well as done by controls, but the lesion groups were permanently impaired in discriminating similar patterns circumscribed by irrelevant lines. The age-at-lesion groups differed, however, in discriminating patterns masked by superimposed lines. The group lesioned at 181 days was severely impaired at both acquisition and subsequent intercurrent performance; the group lesioned at 4 days was impaired only at intercurrent performance. This study suggests that sparing after early postnatal damage of Areas 17 and 18 occurs only under limited circumstances.

Animals↗

PubMed1989

Visual discrimination by cats given lesions of visual cortex in one or two stages in infancy or in one stage in adulthood.

Sparing of visual function was studied in cats with bilateral cortical damage to Areas 17 and 18 and most of Area 19. Cats with lesions made in 2 stages, on Postnatal (P) Days 3 and 6, in 1 stage on P6, or in 1 stage in adulthood were compared with sham-operated controls on 10 visual discrimination tasks. On some tasks, both groups of cats that underwent surgery as infants showed considerable sparing of function compared with cats that had surgery as adults; the latter group showed a marked impairment. However, on several of the discriminations, 2-stage lesions permitted almost total sparing of pattern vision, whereas 1-stage lesions made neonatally were almost as debilitating as those incurred in adulthood. The findings suggest that differential behavioral consequences can follow physiological or anatomical changes, or both, that occur within a 4-day neonatal interoperative period.

Aging↗

PubMed1988

Neocortical connections in fetal cats.

The major extrinsic projections to and from visual and auditory areas of cerebral cortex were examined in fetal cats between 46 and 60 days of gestation (E46-E60) using axonal transport of horseradish peroxidase either alone or in combination with tritiated proline. Projections to visual cortex from the dorsal lateral geniculate nucleus and lateral-posterior/pulvinar complex exist by E46, and those from the contralateral hemisphere, claustrum, putamen, and central lateral nucleus of the thalamus are present by E54-E56. In addition, cells in the medial geniculate nucleus project to auditory cortex by E55. At E54-E56 efferent cortical projections reach the contralateral hemisphere, claustrum, putamen, lateral-posterior/pulvinar complex and reticular nucleus of the thalamus. Cells in visual cortex also project to the dorsal and ventral lateral geniculate nuclei, pretectum, superior colliculus and pontine nuclei, and cells in auditory cortex project to the medial geniculate nucleus. Except for interhemispheric projections, all pathways demonstrated are ipsilateral, and projections linking cerebral cortex with claustrum, dorsal lateral geniculate nucleus and lateral-posterior/pulvinar complex are reciprocal. The reciprocal projections formed with the dorsal lateral geniculate nucleus, lateral-posterior/pulvinar complex and the claustrum show a greater degree of topological organization compared to the projections formed with the contralateral hemisphere and superior colliculus, which show little or no topological order. Therefore, the results of the present study show that the major extrinsic projections of the cat's visual and auditory cortical areas with subcortical structures are present by the eighth week of gestation, and that the origins and terminations of many of these projections are arranged topologically.

Animals↗

PubMed1984

Extrinsic visual and auditory cortical connections in the 4-day-old kitten.

The major extrinsic projections to and from the visual and auditory cortical areas were examined in 4-day-old kittens using axonal transport of horseradish peroxidase (HRP) and/or tritiated proline. Six different afferent and seven different efferent systems were studied; all 13 were present by postnatal day 4 as revealed by either HRP, or autoradiography alone, or these two techniques combined. Topographical projections were found for the corticopetal pathways from the thalamus and claustrum and for the corticofugal pathways to the thalamus, claustrum, striatum, and tectum, as well as for the inter- and intrahemispheric pathways. No topographical relations were seen in projections to the cortex from the basal ganglia or the lower brainstem. The results of the present study indicate that most or all of the major extrinsic connections of the kitten's visual and auditory cortical areas are present neonatally, and that both the cells of origin and the axonal targets are arranged topographically much like those of adult cats. However, the origins of callosal projections from visual cortex are more widespread in newborn kittens than in adult cats. In addition, the laminar arrangements of the kitten's corticocortical connections differ from those of adult cats in a number of details. The results suggest that the sparing of some visual and auditory functions after neonatal lesions occurs despite the fact that the cortical areas removed have formed extrinsic connections.

Age Factors↗

PubMed1984

Transneuronal degeneration of beta retinal ganglion cells in the cat.

Transneuronal retrograde degeneration of retinal ganglion cells was investigated following neonatal visual cortex ablation in the cat. After a survival time of at least 18 months, retinal ganglion cells projecting to the thalamus were labelled by retrograde transport of horseradish peroxidase. Filled ganglion cells were classified into alpha, beta and gamma types on the basis of dendritic morphology. In normal cats, alpha cells made up 8-10% of the total population in the sample area, beta cells made up 64-67% and gamma cells made up 23-27%. In retinae of visual cortex-ablated cats, normal numbers of alpha and gamma cells were present, but the beta cell population was depleted by 90% of normal. Thalamic projections of surviving retinal ganglion cells were investigated by anterograde transport of tritiated proline injected into the eye. In these animals, ablation of visual cortex resulted in almost complete degeneration of laminae A and A1 of the dorsal lateral geniculate nucleus. In the radioautographic material, projections from the retina to the degenerated parts of laminae A and A1 were barely detectable. Survival of some ganglion cell populations and death of others after neonatal visual cortex ablation may be explained in terms of the pattern of projections of the different cell types. We conclude that the majority of beta cells degenerate following visual cortex ablation because of removal of cells in the dorsal lateral geniculate nucleus which form their sole or principal target. Alpha and gamma cells and 10% of beta-cells survive because of extensive collateral projections to targets other than cells of the laminae A and A1 of dorsal lateral geniculate nucleus.

Animals↗

PubMed1981

Transneuronal retrograde degeneration in the cat retina following neonatal ablation of visual cortex.

Bilateral removal of the cortical visual area in newborn cats produces degeneration of retinal ganglion cells. Measurements of over 4,000 cells and calculation of neuron densities from sample areas of retina in the adult show that the medium sized cell population in peripheral retina is reduced by 68%, whereas the populations of small and large cells are not affected. The degeneration is greater in peripheral retina than in area centralis.

Animals↗

PubMed1981

Visual discrimination defects in cats with temporal or occipital decortications.

Performance on visual discrimination problems by seven control (C) cats, eight cats with lesions in the posterior temporal (PT) cortex, and eight with destruction of the central 3 degrees-20 degrees of the retina's projection to the marginal (M) gyrus was investigated as a function of three variables: discriminanda (objects and patterns, type of pattern), learning requirement (acquisition, transfer, retention), and stimulus-response contingency (simultaneous, successive, concurrent discrimination). Group PT was impaired on 7/11 initial learning and transfer tests and on 0/3 retention tests, with pattern stimuli; it was inferior to Group C on 1/7 object discrimination tasks. No discrimination contingency was more likely than the others to reveal a significant deficit in Group PT. Group M was not impaired relative to Group C on any individual discrimination task. However, it made significantly more total errors on seven discriminations between complex patterns (embedded or masked figures) than Group C. On three discriminations between simple patterns (unmasked figures), Group M made fewer errors than Group C. This pattern of loss is qualitatively similar to, but milder than, that observed in previous cats with M lesions, very probably because the present M lesions were relatively small. The findings indicate that M and PT ablations produce differential impairments in cats, a selective difficulty in differentiating complex patterns after M lesions and a nonselective disruption of pattern discrimination learning after PT lesions.

Animals↗

PubMed1981

Behavioral effects of early rearing conditions and neonatal lesions of the visual cortex in kittens.

Kittens with neonatal lesions of the marginal and posterolateral gyri, along with unoperated controls, were reared either in an enriched environment or in laboratory cages. Kittens with lesions were inferior to controls at learning mazes and at discriminating forms and gratings, whether they were raised in enriched or impoverished conditions. Enrichment did not facilitate form or grating discrimination by either normal or operated cats, although such experience facilitated maze learning by both groups. It is concluded that early enrichment of sensorimotor experience was probably not the cause of the complete sparing of pattern vision after neonatal damage of the visual cortex reported in earlier studies. Discussion centers on task variables and completeness of the lesions as reasons for sparing of vision.

Animals↗