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At least 109 records · Page 6Linked to original sources

PubMed1987

Long-lasting potentiation of synaptic potentials in the motor cortex produced by stimulation of the sensory cortex in the cat: a basis of motor learning.

A long-lasting increase in the efficiency of synaptic transmission in the central nervous system has been thought to be one of the bases of learning and memory. To explore the possibility that the motor cortex (area 4 gamma) itself is involved in motor learning, the existence of long-term potentiation (LTP) was examined by recording excitatory postsynaptic potentials (EPSPs) from motor cortical neurons. Short tetanic intracortical microstimulation (ICMS) of the somatic sensory cortex produced a marked potentiation of the EPSPs in a small group of motor cortical neurons. The results raised the possibility that the input from the sensory cortex participates in motor learning and retention of the learned motor skills.

Animals↗

PubMed1993

Monoamine concentrations in rat prefrontal cortex and other mesolimbocortical structures in response to partial neonatal lesions of the medial prefrontal cortex.

In an earlier study it was found that partial neonatal lesions of the medial prefrontal cortex (mPFC) resulted in an increased dopaminergic innervation in the remaining part of mPFC along with functional sparing. The present study assessed whether this response is restricted to this part of the cortex or whether also other structures of the mesolimbocortical system are involved. Furthermore, it was investigated whether the other monoaminergic systems were affected by neonatal mPFC lesions. In 6-day-old rats, the mPFC was partially ablated or a sham operation was made. The concentrations of dopamine (DA) and its metabolites increased to 250-350% in the remaining part of the mPFC compared to the sham-operated controls. The response was most prominent in this part of the cortex; no other mesolimbocortical structure showed such major changes of DA and its metabolites. In addition, a small increase in the concentrations of noradrenaline, serotonin and their metabolites was also spotted in the remaining mPFC and some other mesolimbocortical structures of the lesioned animals. The present data support the suggested involvement of DA in the neural mechanism of sparing of function, and this DA response seems to be most prominent in the remaining mPFC. However, the responses of the noradrenergic and serotonergic systems may also be important for sparing of function to occur.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1996

Normal development of tyrosine hydroxylase and serotonin immunoreactive fibers innervating anterior cingulate cortex and visual cortex in rabbits exposed prenatally to cocaine.

Anterior cingulate cortex develops abnormally in rabbits exposed to cocaine in utero but visual cortex is normal. The interactions of cocaine with the dopamine, norepinephrine and serotonin systems makes each a potential candidate for influencing these developmental effects. Here, we report no differences in the distribution and density of serotonin and tyrosine hydroxylase-immunoreactive fibers in the anterior cingulate cortex in postnatal rabbits exposed prenatally to cocaine or saline. Because the pattern and extent of cortical innervation by these systems appears normal, the data suggest that the effects of prenatal exposure to cocaine may involve changes in monoamine signaling distinct from morphological reorganization of the cortical afferents.

Animals↗

PubMed1987

Effects of early environments on monkey cortex neuroanatomical changes following somatomotor experience: effects on layer III pyramidal cells in monkey cortex.

Sixteen infant stumptail monkeys were reared to 6 months under four conditions. Behaviors and cortical neuroanatomy were compared. Earlier studies showed effects on stellate cell dendrites. Here are reported the results in six cortical areas on basilar dendrites of layer III pyramidal cells. Basilar dendrites show significantly larger numbers (p less than .05) of branching for motor I cortex under condition 3 associated with the greatest skills and amount of activity in climbing, swinging, and grasping of objects. Visual cortex was not significantly altered by the rearing conditions, but the basilar dendrites showed less branching than in the five other areas of cortex sampled. It is concluded that genetic factors are responsible for the major growth patterns and that environmental factors contribute to quantitative increases or decreases in the branching of dendrites and therefore the finer tuning of neural interconnections.

Animals↗

PubMedDate not supplied

Information cascade from primary auditory cortex to the amygdala: corticocortical and corticoamygdaloid projections of temporal cortex in the rat.

Corticocortical and corticoamygdaloid connections of temporal cortext and perirhinal cortex (PRh) were examined in the rat with the anterograde tracer Phaseolus vulgaris leucoagglutinin (PHA-L). Iontophoretic injections of PHA-L into area TE1 resulted in columnar axonal terminations in surrounding and contralateral regions of temporal neocortex and in the striatum, but not in the amygdala. Within temporal neocortex, labeled fibers were present locally in adjacent regions of TE1, as well as in TE2d, TE1v, TE3v, and TE2c. Injection of cortical areas TE1v, TE3v, and TE2c, which received projections from TE1, or injections of perirhinal periallocortex, which received projections from TE1v, TE2v, and TE3v, resulted in projections to the amygdala. The pattern of corticocortical and corticoamygdaloid projections differed among the divisions of auditory cortex. TE1 exhibited extensive ipsilateral and contralateral projections to temporal cortical regions and no projections to the amygdala. In contrast, areas of temporal neocortex ventral and posterior to TE1, including TE1v, TE3v, TE2c, and PRh, had more limited ipsi- and contralateral corticocortical projections but had an increased connectivity with the subcortical forebrain, especially the lateral nucleus of the amygdala (AL). There was a topographic organization to the AL afferents. The dorsal subdivision of AL received projections from TE1v, TE3v, TE2c, and PRh, while the ventrolateral division received projections from TE3v, TE2c, and PRh. The ventromedial division received projections only from PRh, which, unlike other temporal cortical areas, also projected to the basolateral and basomedial nuclei of the amygdala. These findings define the complete sequence of connections linking primary auditory cortex with the amygdala in the rat. In addition, the findings indicate that the ventral portion of TE1, designated TE1v, has connections that distinguish it from dorsal TE1, namely, dense projections to AL and a diminished number of corticocortical projections ipsilaterally and contralaterally. Finally, the results suggest a topographic organization to the cortical terminations within the amygdala.

Amygdala↗

PubMed1995

Functional magnetic resonance imaging at 1 T: motor cortex, supplementary motor area and visual cortex activation.

Functional activation of the brain has been visualized using magnetic resonance imaging (MRI). Early studies used echo planar imaging and magnetic fields of 2 T and above. However, recent studies have successfully shown the activation of visual and motor areas of the brain using conventional clinical 1.5 T MRI systems. The purpose of the present study was to replicate these studies at a lower field strength. Eight motor and two visual activation studies were performed using a 1 T clinical scanner. Activation was seen in the contralateral motor cortex during motor stimulation in six of the eight volunteers. Activation was also documented within the contralateral supplementary motor area in four of the six volunteers with motor cortex activation. The supplementary motor area was located in the posteromedial aspect of the superior frontal gyrus. Both volunteers subjected to photic stimulation showed activation within the visual cortex. Results show that functional imaging can be successfully carried out with a 1 T clinical scanner. The size of the image intensity on activation change suggests that contrast may not be due solely to susceptibility changes.

Brain Mapping↗

PubMed1987

Fetal frontal cortex transplanted to injured motor/sensory cortex of adult rats. I. NADPH-diaphorase neurons.

Fetal frontal cortex from 18-d-old embryonic rat brain was transplanted into cavities of juvenile host motor/sensory cortex. Two to seven months later, sections were reacted for NADPH-diaphorase (NADPH-d) enzyme histochemistry. NADPH-d-positive neurons survived in 11 of 13 grafts. All but one of the transplants had reduced numbers of these neurons, although in 3 transplants the reductions were moderate and not statistically significant. The distribution and morphology of NADPH-d neurons within most grafts was comparable to that of NADPH-d neurons in normal host cortex. At the margin of the 2 transplants with no NADPH-d neuronal perikarya, NADPH-d fibers crossed from host to transplant as far as a millimeter into the transplant, and on rare occasions, the host neurons that gave rise to these fibers were identified. This suggests that host-transplant interactions are possible. One transplant had an abnormally large number of NADPH-d-positive neurons and fibers, possibly due to selective survival of these neurons. The data reported here for NADPH-d in cortical transplants may also apply to neuropeptide Y (NPY), since nearly all neocortical NPY neurons also contain NADPH-d.

Animals↗

PubMed1984

Transplantation of human cortex with Alzheimer's disease into rat occipital cortex; a model for the study of Alzheimer disease.

Senile dementia of the Alzheimer type (SDAT) is a major problem in the human senescent population. As this pathology cannot be reproduced in animals, research into its development is greatly impeded. The technique of implantation of the nervous tissue has been utilized in order to establish an animal model and to test the possible existence of a transmissible agent. When human temporal cortex with Alzheimer's disease is implanted in the occipital cortex of 7-week-old rats, human cerebral tissue containing abundant tangles induces in the receiver cortex a reactive fibrous gliosis. In the processes of the astrocytes, twisted filaments are evident among bundles of normal filaments. These alterations could be induced by the metabolising of abnormal filament subunits or by some infectious agent introduced by the implant.

Aged↗

PubMedDate not supplied

Plastic reorganizations of the receptive fields of neurons of the auditory cortex and the medial geniculate body induced by microstimulation of the auditory cortex.

The receptive fields of neurons (RFs) whose activity was simultaneously recorded at several loci of the auditory cortex (AC) and in the medial geniculate body (MGB) were investigated before and after intracortical microstimulation (ICMS). Three types of neurons of the AC and MGB were distinguished on the basis of the character of the RFs: mono-, bi-, and polymodal. The RFs of the neighboring neurons in the AC (or in the MGB) could differ, while the RFs of remote neurons of the AC could be similar. The microstimulation of the AC could lead to changes in the RFs of neurons in the stimulated locus and neighboring loci of the AC, as well as in the loci of the MGB tonotopically associated with them. It is hypothesized that long-term modification of the efficiency of synaptic transmission between different elements of the cortex-thalamus-cortex circuit which arises as the result of the circulation of impulses along this chain during ICMS may be the mechanism underlying the observed changes in the RFs of AC and MGB neurons.

Animals↗

PubMed1995

Intrauterine cocaine exposure of rabbits: persistent elevation of GABA-immunoreactive neurons in anterior cingulate cortex but not visual cortex.

The effects of prenatal cocaine exposure on the development of the rabbit cerebral cortex were studied. Two cortical areas were compared: primary visual cortex (VC) and anterior cingulate cortex (ACC). ACC was selected because behavioral deficits observed in cocaine-exposed infants suggest the involvement of ACC. In addition, ACC receives dense dopaminergic innervation and cocaine's action in inhibiting the re-uptake of dopamine is believed to underly the rewarding properties of cocaine. VC was selected as a control area because there is no evidence of behavioral deficits associated with visual perception in cocaine-exposed infants, and because VC receives minimal dopaminergic innervation. Two aspects of cortical development were studied: (i) cortical morphology, growth and cytoarchitectonic organization; and (ii) the development of the GABAergic neurotransmitter system. Measures of postnatal cortical growth, including cortical lamination, cell number and soma size, were compared in cocaine-exposed or control (saline) rabbits aged P5-P60. There was no difference between cocaine and saline animals in any of these parameters, and cortical cytoarchitecture appeared normal. However, despite the absence of major abnormalities in cortical development, we found that the number of GABA-immunoreactive neurons in cocaine-exposed animals was significantly higher than normal in ACC. This effect was highly consistent, was present in all laminae and at all ages studied, and persisted into maturity (P60). In contrast, in VC, the number of GABA-immunoreactive neurons in cocaine-exposed animals did not differ from normal. We suggest that increased GABA immunoreactivity may reflect a compensatory response to excessive excitatory input to ACC. A change in the balance of excitation and inhibition in ACC, reflecting 'noisy' or dysfunctional intracortical circuitry, may underly the emotional lability and attentional deficits characteristically described in infants exposed in utero to cocaine.

Animals↗

PubMed1991

Contribution of striate cortex and the superior colliculus to visual function in area MT, the superior temporal polysensory area and the inferior temporal cortex.

We studied the visual responses of single neurons in three extra-striate visual areas of the macaque following lesions of striate cortex, lesions of the tecto-pulvinar system or both. After striate lesions, there was (a) considerable specific activity remaining in area MT including direction selectivity, (b) only non-specific activity in the superior temporal polysensory area (STP), and (c) no visual responsiveness at all in inferior temporal cortex (IT). In animals with striate lesions, interruption of the tecto-pulvinar pathway eliminated the residual visual activity in MT and STP that survived the striate lesions. Interruption of the tecto-pulvinar pathway alone had little or no effect on visual evoked activity in any of the three areas. These results are related to the relative dependence of visual responsiveness in MT, STP and IT on striate cortex and the superior colliculus, to differences between the dorsal and ventral cortical processing streams, and to neural mechanisms underlying blind sight.

Animals↗

PubMed1979

Loss of hybridizable ribosomal DNA from human post-mitotic tissues during aging: II. Age-dependent loss in human cerebral cortex--hippocampal and somatosensory cortex comparison.

DNA was isolated from the hippocampal and from the somatosensory cortex of 13 humans (at autopsy). In both the cortex and hippocampus, the loss of ribosomal DNA (rDNA), as measured through hybridization in the liquid phase, approximates about 0.9% per year. The r value for somatosensory cortex was about -0.7 and that for the hippocampus was about -0.91. The correlation coefficient between the sets of two samples derived from the same individual (two different areas) in +0.945. These results are consistent with those reported concurrently for human myocardium and with earlier studies conducted with beagle dogs, in which only post-mitotic tissues (brain, heart and skeletal muscle) showed measurable decrements in these key genes. To the degree that the synthesis of new proteins is essential for sustained mental activity, these results are consistent with the observations that Nissl substance is more slowly replenished, following exhaustive work by motor cortical cells, and the fact that many older persons experience mental fatigue during continuous mental work at earlier times than do younger persons. The mechanism of loss is not certain, but may well be related to inadequacies in DNA repair systems, thereby allowing deletion of tandemly duplicated genes through cross-over "episome" formation, followed by degradation of the excised DNA segments. The ratio of loss of rDNA hybridizability in human and dogs in about 1 to 7, which approximates the relative ratios of their lifespans (reciprocals).

Adolescent↗

PubMed1993

Comparisons of hemi-inattention produced by unilateral lesions of the posterior parietal cortex or medial agranular prefrontal cortex in rats: neglect, extinction, and the role of stimulus distance.

Neglect in human and non-human primates has been demonstrated following unilateral lesions of both posterior parietal and prefrontal areas. While it has now been well established that a unilateral lesion of the rodent analog of dorsolateral prefrontal cortex, medial agranular cortex (AGm), results in neglect, the effects of unilateral damage restricted to rodent posterior parietal cortex (PPC) have not been examined in detail. The current study assessed rats with unilateral lesions of PPC or AGm on their ability to orient to unilateral and bilateral stimulation. Since it has been proposed in both the primate and rodent literatures that frontal areas may be responsible for the perception of near space while parietal areas may be responsible for far space, stimuli were presented at two different distances. Lesions of PPC and AGm resulted in severe neglect relative to control operates, with both PPC and AGm operates manifesting severe hemi-inattention and allesthesia relative to control operates. After behavioral recovery from neglect there was no evidence of extinction to bilateral simultaneous stimulation. While neglect to visual stimuli predominated in unilateral PPC operates, unilateral AGm operates had severe neglect in all modalities. In addition, while both left and right PPC operates showed contralesional neglect, AGm operates demonstrated the lateralized differences in neglect reported in previous studies. All groups demonstrated an approximately equivalent level of neglect to stimuli presented at the two different distances, and thus failed to support the suggestion of a peripersonal-extrapersonal dichotomy between frontal and parietal areas in rodents.

Animals↗

PubMed1994

Lack of effect of lesions in the anterior cingulate cortex and retrosplenial cortex on certain tests of spatial memory in the rat.

The effects of cytotoxic lesions in either the anterior cingulate cortex or the retrosplenial cortex were compared with those of fornix lesions on three tests of spatial memory. Two of the tasks, delayed nonmatching-to-position and spatial reversal learning, were tested in an automated apparatus. The third task, forced alternation, was tested in a T-maze. Neither anterior cingulate nor retrosplenial cortex damage produced any significant impairment on the three tasks. In contrast, rats with fornix lesions (hippocampal system damage) were markedly impaired on all three tasks. The results, which were considered in the light of proposals for a hippocampal--anterior thalamic--cingulate system that is important for spatial memory, suggest that neither of the cingulate regions involved in this study form a critical subcomponent of this proposed system. It is therefore assumed that the cingulate cortices are only critical for certain classes of spatial problem. It is also suggested that in some previous studies the effects of inadvertent damage to the cingulum bundle may have contributed to the apparent effects of cingulate lesions.

Animals↗

PubMed1994

Efferents of frontal or occipital cortex grafted into adult rat's motor cortex.

Phaseolus vulgaris leucoagglutinin (PHA-L) was used to examine the efferent connectivity of embryonic (E16) frontal (homotopic) or occipital (heterotopic) neocortical transplants placed into--or in the vicinity of--lesion cavities made in the frontal cortex of adult recipients. Homotopic transplants projected towards the host sensorimotor cortex and, in most cases, into the lateral caudate-putamen (CPu). Heterotopic transplants projected into the anterior cingulate cortex and, in most cases, distributed terminals into the medial CPu. It is suggested that embryonic neocortical tissue placed into a damaged cortical site of an adult recipient develops a pattern of efferents corresponding to its cortical origin.

Animals↗

PubMed1987

Dopaminergic innervation of the primary visual cortex in the rat, and some correlations with human cortex.

Dopaminergic terminals have been identified in the primary visual cortex with three techniques; immunocytochemistry with an anti-dopamine antiserum, retrograde axonal transport techniques using unconjugated wheat germ agglutinin and HPLC determination of catecholamines and metabolites in microdissected sub-regions of occipital cortex in the rat. The results demonstrate a specific dopaminergic innervation, arising from the ventral tegmental area, which is found mainly in laminae VI and V, but with minor innervation also in lamina I. Dopaminergic innervation to adjacent cortical regions is also described. Neurochemical data from post-mortem human material suggests that a similar innervation exists in man. An analysis of the distribution of dopaminergic fibres in relation to the known connections and possible functions of the deep laminae of visual cortex suggests that dopaminergic axons may participate in the corticofugal control of visual afferent pathways.

Aged↗

PubMed1988

Layer V in rat auditory cortex: projections to the inferior colliculus and contralateral cortex.

This study compares the form and distribution within layer V of cells projecting to the inferior colliculus with that of commissural cells of origin in adult rat auditory cortex after horseradish peroxidase injections in the ipsilateral inferior colliculus or auditory cortex. The goal of this work was to determine whether every part of layer V participates equally in both projections, and if the cortical neurons in each pathway were similar. The types of neurons were defined in Golgi-Cox preparations and matched with the profiles of retrogradely labeled cells from architectonically defined cortical area 41. Inferior colliculus and commissural neurons form two populations that differ in their distribution in layer V, in somatic area, and in the form of their apical dendritic arbors. Corticocollicular neurons include the largest pyramidal cells, whose robustly filled apical dendrites ascend into layer II or farther. Commissural cells are smaller and have a more heterogeneous form. Their apical dendrites do not usually extend above layer IV, and a few of these cells may be non-pyramidal. Small pyramidal cells and inverted pyramidal cells project to the opposite cortex, but not to the inferior colliculus. Medium-sized pyramidal cells project in both systems. In addition, certain callosal cells of origin in layers V and III were morphologically similar. More than one-third of the commissural cells originate in the superficial part of layer V, where only 7% of the inferior colliculus projection neurons arise. Most corticocollicular cells lie deeper in layer V, where there are fewer commissural neurons. These findings suggest that the efferent systems projecting to telencephalic and mesencephalic targets are morphologically distinct and spatially segregated in layer V. However, the commissural projection includes similar cells in different cortical layers. The types of these efferent neurons may be more closely related to their target than to their laminar origin.

Animals↗

PubMed1983

Neonatal hemidecortication or frontal cortex ablation produces similar behavioral sparing but opposite effects on morphogenesis of remaining cortex.

Rats with complete removal of the neocortex of one hemisphere (hemidecorticate) or of the cortex anterior to bregma in both hemispheres (frontal cortex) in adulthood were compared behaviorally and neuroanatomically with rats with similar removals at 7 days of age. Neonatal ablation of the frontal cortex produced partial sparing of performance on the Morris water task and reduced the thickness of the remaining neocortex. Neonatal hemidecortication produced similar sparing of function on the water task but increased the thickness of the contralateral neocortex. These results imply that behavioral sparing following neonatal cortical lesions is independent of the gross morphogenesis of the remaining neocortex.

Age Factors↗