Search PubMed⌕ Search

Biomedical subjects

C A Chapman

Publications and source records attributed to C A Chapman.

At least 37 records · Page 2Linked to original sources
PubMed1997

Converging inputs to the entorhinal cortex from the piriform cortex and medial septum: facilitation and current source density analysis.

Converging inputs to the entorhinal cortex from the piriform cortex and medial septum: facilitation and current source density analysis. J. Neurophysiol. 78: 2602-2615, 1997. The entorhinal cortex receives sensory inputs from the piriform cortex and modulatory inputs from the medial septum. To examine short-term synaptic facilitation effects in these pathways, current source density (CSD) analysis was used first to localize the entorhinal cortex membrane currents, which generate field potentials evoked by stimulation of these afferents. Field potentials were recorded at 50-micron intervals through the medial entorhinal cortex in urethan-anesthetized rats and the one-dimensional CSD was calculated. Piriform cortex stimulation evoked a surface-negative, deep-positive field potential component in the entorhinal cortex with mean onset and peak latencies of 10.4 and 18.4 ms. The component followed brief 100-Hz stimulation, consistent with a monosynaptic response. CSD analysis linked the component to a current sink, which often began in layer I before peaking in layer II. A later, surface-positive field potential component peaked at latencies near 45 ms and was associated with a current source in layer II. Medial septal stimulation evoked positive and negative field potential components which peaked at latencies near 7 and 16 ms, respectively. A weaker and more prolonged surface-negative, deep-positive component peaked at latencies near 25 ms. The early components were generated by currents in the hippocampal formation, and the late surface-negative component was generated by currents in layers II to IV of the entorhinal cortex. Short-term facilitation effects in conscious animals were examined using electrodes chronically implanted near layer II of the entorhinal cortex. Paired-pulse stimulation of the piriform cortex at interpulse intervals of 30 and 40 ms caused the largest facilitation (248%) of responses evoked by the second pulse. Responses evoked by medial septal stimulation also were facilitated maximally (59%) by a piriform cortex conditioning pulse delivered 30-40 ms earlier. Paired pulse stimulation of the medial septum caused the largest facilitation (149%) at intervals of 70 ms, but piriform cortex evoked responses were facilitated maximally (46%) by a septal conditioning pulse 100-200 ms earlier. Frequency potentiation effects were maximal during 12- to 18-Hz stimulation of either the piriform cortex or medial septum. Occlusion tests suggested that piriform cortex and medial septal efferents activate the same neurons. The CSD analysis results show that evoked field potential methods can be used effectively in chronically prepared animals to examine synaptic responses in the converging inputs from the piriform cortex and medial septum to the entorhinal cortex. The short-term potentiation phenomena observed here suggest that low-frequency activity in these pathways during endogenous oscillatory states may enhance entorhinal cortex responsivity to olfactory inputs.

Animals↗
PubMed1997

Isoluminance and contingent color aftereffects.

In the typical induction of the orientation-contingent color aftereffect (CCAE), the stimuli are composed of elements that differ in both color and luminance. Three experiments are reported that show that chromatic contrast between stimulus elements is insufficient for the induction of the orientation-CCAE and that luminance contrast is necessary. These experiments expand on previous research concerned with the role of luminance contrast in the induction of orientation-CCAEs by eliminating alternative explanations.

Adult↗
PubMed1996

Neurobehavioral profiles of children with neurofibromatosis 1 referred for learning disabilities are sex-specific.

We compared neurobehavioral profiles of 10 children with neurofibromatosis 1 (NF-1) referred for evaluation of learning disabilities (NF/LD) to those to learning disabled children without known genetic disease (LD), matched for age, sex, and estimated IQ. It was hypothesized that the NF/LD children would exhibit a neurobehavioral profile diagnostic of compromise of frontal/subcortical brain systems while those of the case controls would be heterogeneous. Records from a clinical data base were reviewed retrospectively for the neurological and neuropsychological components of an interdisciplinary learning disabilities evaluation. Neurological abnormalities were more frequent in the NF/LD group, involving gross and fine motor coordination, praxis, and megencephaly. As predicted, clinical neuropsychological diagnostic ratings and composite neurobehavioral observation scores were consistent with compromise of frontal systems in the NF/LD group. An unanticipated finding was that outcomes in the NF/LD group were sex dependent: Megencephaly was observed in females only; and the frontal/subcortical neurobehavioral profile was more consistently observed in females. Females with NF-1 with megencephaly may be at increased risk for a neurobehavioral syndrome contributing to LD that is consistent with compromise of frontal/subcortical brain systems.

Attention↗
PubMed1996

Neurologic findings in children and adults with Williams syndrome.

Twenty-four children with Williams syndrome underwent systematic neurologic evaluations. Abnormalities of mental status, motor coordination, tone, and gait were most prevalent. Tone abnormalities varied as a function of age, with younger children frequently exhibiting decreased tone and older subjects almost exclusively having increased tone. The gait and coordination abnormalities persisted among older subjects, indicating that they were not simply maturational problems. Physicians caring for such youngsters need to be aware that a variety of neurologic abnormalities are common in Williams syndrome and may change or progress over time. Neurologic examinations that reveal findings beyond the typical pattern that we report may raise suspicion for added neurologic insult and warrant further investigation.

Adolescent↗
PubMed1995

Post-activation potentiation in the neocortex. III. Kindling-induced potentiation in the chronic preparation.

Previous experiments have shown the neocortex to be very resistant to the induction of long-term potentiation in chronic preparations. We show here that kindling-induced potentiation effects can be reliably produced in the neocortex of awake, freely moving rats. These effects develop rather slowly. In sites contralateral to the stimulation electrode, potentiation effects did not become clear until the animals had received about 5 days or more of stimulation. Ipsilateral sites required even longer (approximately 10 days), and both sites required more than 13 days to reach asymptotic levels of potentiation. Both monosynaptic and polysynaptic components were present in the neocortical field potentials. When population spikes were absent, the surface negative monosynaptic EPSP component tended to show a potentiation effect. If population spikes were present, they were generally enhanced while the monosynaptic population EPSP tended to be depressed. Consequently, the apparent depression may have been due to competing field currents. The later polysynaptic components (15-28 ms latency to peak) always showed a potentiation effect with 5 or more kindling stimulations and is presumed to result from activation of cortico-cortical associational fibers. All of these effects were long-lasting, showing little decay over a period of several weeks.

Animals↗
PubMed1995

Post-activation potentiation in the neocortex. IV. Multiple sessions required for induction of long-term potentiation in the chronic preparation.

The neocortex in chronically prepared rats is very resistant to the induction of long-term potentiation (LTP). In the first of two experiments described in this paper, we tried unsuccessfully to induce neocortical LTP within one session by coactivating basal forebrain cholinergic and cortical inputs to our neocortical recording site. In the second experiment, we tested a new procedure which involved the application of repeated conditioning sessions over several days. This procedure was suggested by our finding that kindling-induced potentiation (KIP) of cortical field potentials could be reliably triggered but was slow to develop. We administered 30 high frequency trains per day to the corpus callosum for 25 days. LTP in callosal-neocortical field potentials became clear after about 5 days of stimulation and reached asymptotic levels by about 15 days. After the termination of treatment, LTP persisted for at least 4 weeks, the duration of our post-stimulation test period. As in previous experiments on kindling-induced potentiation, the potentiation effects were clear in both early population spike components and in a late (probably disynaptic) component. The monosynaptic EPSP component was often depressed, but this may have been due to competing field currents generated by the enhanced population spike activity. We discuss these results in the context of theories emphasizing slower but more permanent memory storage in neocortex compared to the hippocampus.

Animals↗
PubMed1995

A nerve growth factor peptide retards seizure development and inhibits neuronal sprouting in a rat model of epilepsy.

Kindling, an animal model of epilepsy wherein seizures are induced by subcortical electrical stimulation, results in the upregulation of neurotrophin mRNA and protein in the adult rat forebrain and causes mossy fiber sprouting in the hippocampus. Intraventricular infusion of a synthetic peptide mimic of a nerve growth factor domain that interferes with the binding of neurotrophins to their receptors resulted in significant retardation of kindling and inhibition of mossy fiber sprouting. These findings suggest a critical role for neurotrophins in both kindling and kindling-induced synaptic reorganization.

Animals↗
PubMed1995

Habitat, annual, and seasonal effects on positional behavior in red colobus monkeys.

Positional behavior in adult red colobus monkeys (Colobus badius) was examined in a variety of ecological contexts. Using a focal-animal methodology, we assessed how data collected by different observers, in different years, in different seasons, and in different forests affected estimates of positional behavior. In all, 23,000 bouts were recorded. Variation in frequency is greatest in the common behaviors, especially arboreal quadrupedalism. Significant behavioral differences occur more often in the context of different forests than in annual or seasonal comparisons. The activity of feeding exhibits the largest frequency changes across positional behavior and ecological context. In all, red colobus monkeys exhibit substantial amounts of flexibility in positional behavior across different ecological contexts.

Animals↗
PubMed1995

Positional behavior in five sympatric Old World monkeys.

Observations of positional behavior and habitat use were recorded on focal individuals of five species of Old World monkeys at Kibale Forest, Uganda, through the dry season of 1990 and 1991. Cercopithecus ascanius, Cercopithecus mitis, Cercocebus albigena, Colobus badius, and Colobus guereza commonly utilize five similar types of positional behavior (i.e., quadrupedalism, leaping, climbing, sitting, and standing), but in varying frequencies and situations. As a group, colobines use oblique supports and leap more often, and cover greater linear distances during leaps than do cercopithecines. Colobines also prefer to sit (about 90% of all postures), while cercopithecines stand more frequently. Body size differences between the sexes of a species are not reflected in positional behavior. The two small-bodied species climb more and leap less often than the three larger species, which is the reverse of what we would expect. Leaping is the most common method of crossing open spaces within the canopy; but most spatial gaps and leaps are over short distances, usually one meter or less. All five species, regardless of body size or the availability of forest supports, prefer medium-sized supports. Incorporating our work from Uganda with previous investigations of positional behavior reveals few consistent trends with respect to body size or habitat use across primates.

Animals↗
PubMed1995

Neurobehavioral and neurologic outcome in long-term survivors of posterior fossa brain tumors: role of age and perioperative factors.

We evaluated the neuropsychological and neurologic outcome of 15 long-term survivors of posterior fossa tumors who were treated between 1970 and 1984 with cranial irradiation (n = 15) and surgery (n = 14). The interval between diagnosis and evaluation ranged from 4 to 20 years (median = 10 years). Earlier age at diagnosis (< 6 years) was associated with an increased incidence of severe neurologic and neuropsychological sequelae. Hydrocephalus, obtundation, and tumor extension outside the vermis also were more prevalent in the younger group. Poor neurobehavioral outcomes in young children with posterior fossa tumors may be related to more aggressive tumor growth or complications of the initial therapy and not solely due to toxicity from craniospinal irradiation.

Adolescent↗
PubMed1994

Motor cortex and pyramidal tract axons responsible for electrically evoked forelimb flexion: refractory periods and conduction velocities.

Double-pulse methods are used here to measure the refractory periods and conduction velocities of the pyramidal tract axons which cause forelimb flexion in pentobarbital anesthetized rats. In the refractory period experiments, conditioning and test pulses were delivered to the motor cortex, the ipsilateral internal capsule, or the ipsilateral pyramid, and the maximum force exerted by the contralateral forelimb was measured at various conditioning-test intervals. The movements increased as conditioning-test interval increased from 0.5 to 1.0 ms in pyramid sites, from 0.6 to 1.5 in internal capsule sites, and from 0.6 to 2.0 ms in surface cortical sites, suggesting longer refractory periods for the substrates at more rostral sites. In cortical sites, as the conditioning-test interval increased from 4.0 to 20.0 ms, the movements decreased gradually to the single-pulse level, suggesting decreasing temporal summation at longer conditioning-test intervals. In the collision experiments, when conditioning pulses were delivered to one site and test pulses to a second site, the movements increased at conditioning-test intervals that were longer by 0.5-1.3 ms than the refractory periods in either site. This suggests that collisions occurred between orthodromic and antidromic action potentials in the pyramidal tract axons responsible for the limb movement. The collision-like increase was greater between internal capsule and pyramid than between cortex and pyramid, or between cortex and internal capsule. The estimated conduction times were 0.9-1.5 ms between cortex and pyramid, 0.4-0.8 ms between cortex and internal capsule, and 0.5-0.8 ms between internal capsule and pyramid. The range of conduction velocities, therefore, was quite narrow between all pairs (8.8-16.8 m/s). The largest pyramidal tract axons appear to be responsible for most of the force of forelimb flexion in pentobarbital anesthetized rats.

Animals↗
PubMed1994

Contrasting chimpanzees and bonobos: nearest neighbor distances and choices.

In an effort to understand factors underlying differences in the social organization of Pan troglodytes and P. paniscus, we measured the nearest neighbor distances and choices for chimpanzees in Kibale National Park, Uganda, and for bonobos in Lomako Forest, Zaire. We assume that the spatial organization of a set of individuals should reflect the underlying relationships between them. Bonobos were found to have smaller nearest neighbor distances than chimpanzees. The distribution and variability of the distances suggested that chimpanzees have a more restricted range of nearest neighbor distances than bonobos, avoiding situations of very close proximity. Selection of the sex of the nearest neighbor by a focal animal differed between the species. For example, male bonobos rarely had another male as their nearest neighbor, while male chimpanzees frequently did. Similarly, male bonobos tended to move apart when observed together, while it was female chimpanzees who tended to move apart when together. These observations are considered with respect to the nature of the social interactions in these species.

Animals↗
PubMed1993

Axons and synapses mediating startle-like responses evoked by electrical stimulation of the reticular formation in rats: symmetric and asymmetric collision effects.

A new method for determining the locations, directions of transmission and transmission times of synapses mediating electrically evoked responses is proposed here. Electrical stimulation of pontine or medullary reticular formation with one 0.1-ms pulse evokes a short-latency startle-like response. Two pulses were delivered to single sites at various interpulse intervals and the currents required to evoke a criterion startle response were measured. The results suggest that the startle-evoking substrates have absolute refractory periods that range from 0.25-0.6 ms. When one pulse was delivered to a caudal pontine site and a second pulse was delivered to a an ipsilateral medulla site, decreases in required current were observed as interpulse interval increased from +0.4 to +0.8 ms or as interpulse interval decreased from -0.4 to -0.8 ms. These collision-like effects, being symmetric around an interpulse interval of 0, suggest that electrically evoked startle is mediated by fast axons that pass longitudinally through medulla. When one pulse was delivered to the rostral pons and a second pulse to the ipsilateral medulla, however, required currents decreased sharply as interpulse intervals increased from +0.4 to 1.0 ms and as interpulse intervals decreased from +0.2 to -0.2 ms. These asymmetric collision-like effects suggest that strong synapses in the caudal pons, transmitting from pons to medulla, mediate electrically evoked startle. The 0.3-ms asymmetry suggests that the transmission time (i.e., from presynaptic stimulus to postsynaptic action potential) averaged 0.3 ms via monosynaptic connections. The short duration of collision (0.7 ms) suggests that only one postsynaptic action potential was produced with high probability for each presynaptic action potential. From the localization of these effects and the short refractory periods, we estimate that < 60 giant cells on each side of the ventral pontine reticular formation mediate the startle reflex in the rat.

Animals↗
PubMed1993

Crossed reticular formation connections that mediate the startle reflex in rats.

The startle response is a bilateral response even when elicited by unilateral acoustic or tactile stimuli. Similarly, unilateral electrical stimulation of the reticular formation also elicits a bilateral startle-like response. To examine whether crossed reticular formation connections can distribute the effects of unilateral stimulation across the midline, we delivered one pulse to the caudal pontine (RPC) or medullary reticular formation (MRF) and a second pulse to the opposite side of the brain, at various interpulse intervals. The symmetric collision effects suggest that axons which produce at least 37% (range 23-53%) of the startle response efficacy cross from RPC to RPC with a mean conduction velocity of 13 m/s. Similar collision effects were observed between RPC and MRF sites but at shorter conduction times. To examine which axons might cause these collision effect, the axonally transported label DiI was injected post mortem into 37 RPC sites. Many coarse axons were observed to cross in fascicles between bilateral RPC sites and then separate in the contralateral RPC. The fiber diameters and trajectories of these DiI-labelled axons are consistent with the conduction velocities and trajectories of the substrates mediating the startle-like response determined in collision tests.

Animals↗
PubMed1991

The significance of fibrous foods for Kibale Forest chimpanzees.

Four categories of plant food dominated the diet of chimpanzees in Kibale Forest, Uganda: non-fig tree fruits, fig tree fruits, herbaceous piths and terrestrial leaves. Fruit abundance varied unpredictably, more among non-figs than figs. Pith intake was correlated negatively with fruit abundance and positively with rainfall, whereas leaf intake was not influenced by fruit abundance. Piths typically have low sugar and protein levels. Compared with fruits and leaves they are consistently high in hemicellulose and cellulose, which are insoluble fibres partly digestible by chimpanzees. Herbaceous piths appear to be a vital resource for African forest apes, offering an alternative energy supply when fruits are scarce.

Animals↗
PubMed1990

Dietary differences between neighboring Cebus capucinus groups: local traditions, food availability or responses to food profitability?

The feeding patterns of three neighboring groups of Cebus capucinus were documented over a 3-year period in Santa Rosa National Park, Costa Rica. We describe the diets of the three groups and examine whether dietary differences between groups could be attributed to environmental differences in food abundances, to differences in the profitability of what was available or to learned local traditions. Diets were variable among groups; group A primarily ate fruit (81.2% of feeding time) and spent little time eating insects (16.9%), while group C was more heavily reliant on insects (44.3%) and ate less fruit (53.0%). Group B had a diet that was somewhat intermediate (69.8% fruit, 29.0% insects). By measuring the densities of all major plant foods, we were able to determine that many of the dietary differences between groups could not be attributed to simple measures of food abundance, but we could not distinguish between the food profitability hypothesis and local tradition hypothesis.

Animals↗