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PubMed1990

The prevalence of amyloid (A4) protein deposits within the cerebral and cerebellar cortex in Down's syndrome and Alzheimer's disease.

The extent of amyloid deposition within the cerebellum and the cerebral cortex was assessed and compared, using anti-amyloid protein (A4) immunostaining and a novel methenamine silver method, in 20 patients aged between 60 and 77 years with Alzheimer's disease (AD), 29 patients aged between 13 and 71 years with Down's syndrome (DS), 26 demented patients with disorders other than AD and DS and in 20 non-demented elderly individuals of age range 60-102 years. In AD, amyloid deposits were noted in the cerebellar cortex in 90% of patients and in the meningeal vessels of the cerebellum in 80% of patients. In DS, amyloid deposits were seen in the cerebellar cortex in 82% of patients over 30 years of age and was universal in patients over 50 years of age. Overall, in DS, amyloid deposits were present in the meningeal vessels of the cerebellum in 79% of patients, but were present in 94% of those patients over 50 years of age. The sites of amyloid deposition in the cerebellar cortex were (poorly) detected by lectin histochemistry (Concanavalin A binding) in only 40% of patients with AD and 43% of all patients with DS (69% of those over 50 years of age). No amyloid deposits were seen in either the cerebellar cortex or its meningeal vessels in any of the 20 non-demented elderly individuals nor in any of the non-Alzheimer demented patients. The cerebellar amyloid deposits were never associated with a neuritic change [i.e. as characterised by the presence of (tau-positive) paired helical filaments (PHF)] and neurofibrillary tangles were seen only in a few cells of the dentate nucleus in a single patient with AD and in three of the elderly DS patients. Amyloid deposits were numerous in the cerebral cortex of all patients with AD and in all, except the 13-year-old patient, with DS. In all the AD patients and in most of the DS patients over 30 years of age, many of the cerebral cortical amyloid deposits were associated with neurites and were strongly recognised by lectin histochemistry. Amyloid deposits were present within the meningeal vessels of the cerebral cortex in 75% patients with AD and 72% of patients, over 30 years of age, with DS (82% of those over 50 years of age). These data indicate that the process of amyloidosis in AD and in elderly DS patients is not restricted to the cerebral cortex and may affect other grey matter regions, particularly the cerebellum.(ABSTRACT TRUNCATED AT 400 WORDS)

Adolescent↗

PubMed1992

Cortical connections of the inferior arcuate sulcus cortex in the macaque brain.

Injections of the retrograde/anterograde tracers Wheat Germ Agglutinin-Horseradish peroxidase (WGA-HRP) into the cortex along the banks of the inferior limb of the arcuate sulcus in the cortex of 4 macaque monkeys (Macaca fascicularis) were used to investigate its cortico-cortical connections. All injections produced transported label within the sulcus principalis, the ventral lateral prefrontal cortex, the anterior cingulate sulcus and the dorsal insular cortex. The distribution of label within each of these areas differed slightly depending on the injection site. Injections along the caudal bank of the inferior arcuate sulcus label premotor, supplementary motor, and precentral motor areas but produce relatively sparse prefrontal labeling. Posteriorly label is transported to the inferior parietal cortex and the dorsal opercular bank of the Sylvian fissure. Injections along the rostral bank of the sulcus do not label motor areas but produce labeling in dorsal, lateral and orbital prefrontal areas, and in cortex along the ventral bank of the superior branch of the arcuate sulcus. Posteriorly label is transported to cortical areas in the superior temporal gyrus including the dorsal bank of the superior temporal sulcus. The more dorsal rostral bank injection produced both superior temporal and some sparse inferior parietal labeling and the more ventral rostral bank injection produced extensive superior temporal labeling but no parietal labeling. No labeling was ever seen in cortex ventral to the fundus of the superior temporal sulcus. Although other auditory recipient prefrontal areas have been reported, this is the first demonstration of a region chiefly devoted to auditory connections within the ventral frontal cortex. Its adjacency to areas associated with vocal muscle movement, and its connections to midline cortical areas associated with vocal functions in both primates and humans may provide important clues to the organization of Broca's language area.

Animals↗

PubMed1994

Posterior piriform and perirhinal cortex relay seizures evoked from the area tempestas: role of excitatory and inhibitory amino acid receptors.

The functional relationship between the area tempestas (AT), an epileptogenic site within the deep prepiriform cortex, and the regions in the posterior piriform cortex which are innervated by AT, were studied in the rat. The GABAA receptor agonist, muscimol (390 pmol) was microinjected unilaterally into the posterior piriform cortex and adjacent regions in the same hemisphere from which seizures were evoked by focal application of bicuculline into AT. Pretreatment with muscimol into either the ventral posterior piriform cortex or perirhinal cortex, protected against the bilateral clonic seizures evoked from the ipsilateral AT. No seizure protection was obtained when muscimol was placed into adjacent areas of amygdala, entorhinal cortex, neocortex and ventral hippocampus. Seizure protection was also obtained when kynurenic acid, but not 2-amino-7-phosphonoheptanoic acid, was microinjected into the ventral posterior piriform cortex, suggesting that glutamate transmission mediated via non-N-methyl-D-aspartate (non-NMDA) receptors is required for the relay of seizure discharge through this region. Our data indicate that a specific region of the temporal cortex, the posterior piriform and perirhinal area, functions as a critical link in the propagation of limbic seizures evoked from AT.

2-Amino-5-phosphonovalerate↗

PubMed1988

Role of auditory cortex in the acquisition of differential heart rate conditioning.

Previous findings from our laboratory indicate that lesions of the auditory cortex disrupt the retention of differentially conditioned bradycardiac responses to tonal stimuli in rabbits. In the present experiment, the effect of lesions of the auditory cortex on the acquisition of differential bradycardiac conditioning was examined. The effect of lesions in the auditory cortex were compared to the effect produced by control lesions in the visual cortex. After 7 days of recovery, animals received 7 days of differential Pavlovian bradycardiac conditioning in which one tone (CS+) was paired with the unconditioned stimulus, and another tone (CS-) was never paired with the unconditioned stimulus. All animals demonstrated differential conditioning during the first 3 days of conditioning. On days 4-7, however, auditory cortex lesioned animals did not exhibit significant differential heart rate (HR) conditioning, whereas control animals with lesions in the visual cortex showed no loss of conditioning during this period. The loss of differential conditioning in animals with lesions in the auditory cortex appears to be due to an increase in the magnitude of the response to the CS-. These data support the hypothesis that the auditory cortex serves to inhibit the response to the CS- in differential conditioning of bradycardia to acoustic stimuli, and that the inhibition may be mediated by a descending corticothalamic or corticolimbic pathway.

Animals↗

PubMed1982

Bilateral [14C]2-deoxyglucose uptake by motor pathways after unilateral neonatal cortex lesions in the rat.

The left sensorimotor (SM) cortex was removed in 1-day-old and 30-day-old rats. At 90 days of age [14C]2-deoxyglucose (2DG) was injected and the right motor (MI) cortex was electrically stimulated to produce predominantly left vibrissae movements. Animals were sacrificed and their brains autoradiographed. Right motor cortex (MI) stimulation activated subcortical structures bilaterally in 3 of 5 neonatally lesioned rats. Right MI stimulation activated most subcortical structures unilaterally in 30-day lesioned rats. This implies that a critical period for SM cortex injury may occur between 1 and 30 days of age. We suggest that removal of left SM cortex at 1 day of age occurs before or during the critical period and this induces right MI cortex to form bilateral subcortical connections. The bilateral 2DG uptake increases imply the bilateral connections are functional. The unilateral subcortical activation in 2 of 5 neonatally lesioned animals may have been due to differences in size of the lesion, parameters of stimulation, or perhaps due to the time of the lesion being near the critical period. We also suggest that removal of left SM cortex at 30 days of age occurs after the critical period, but that this does not affect the predominantly ipsilateral subcortical connections from MI cortex which have previously formed during normal development.

Aging↗

PubMed1994

Regional difference in the neurotoxicity of ochratoxin A on the developing cerebral cortex in mice.

Pregnant mice were treated intraperitoneally with 3 mg/kg of ochratoxin A on day 10 of gestation. They were allowed to give birth and the offspring were killed at 6 weeks of age for observation. Prenatal exposure to ochratoxin A caused microcephaly in offspring. Their body weight, brain weight, cortical thickness and numerical densities of neurons and synapses in somatosensory and visual cortex were examined. The mice exposed in utero to ochratoxin A showed a significant deficit in brain weight compared to the age-matched control, but there was no significant difference in body weight between these two groups. The cortical thickness showed a significant decrease in both somatosensory and visual cortex. Normal control mice had about 66,000 neurons/mm3, while age-matched ochratoxin A-treated mice had about 91,000 neurons/mm3 in somatosensory cortex. There was a significant increase in OA-treated group. However, there was no significant difference in the numerical density of neurons in visual cortex. On the other hand, there was no significant difference in the numerical density of synapses in both somatosensory and visual cortex. The somatosensory cortex of control mice had about 13,000 synapses per neuron, whereas ochratoxin A-treated mice had about 9,400 synapses per neuron. In the visual cortex, no significant difference was seen in synapse-to-neuron ratios. The discrepancy in the numerical density of neurons and synapse-to-neuron ratios between the somatosensory and visual cortex might derive from a time difference in cortical neurogenesis.

Aging↗

PubMed1997

Effects of dorsal noradrenergic bundle lesions on recovery after sensorimotor cortex injury.

Several lines of evidence suggest that the recovery of the ability of rats to traverse a narrow beam after unilateral injury to the sensorimotor cortex is noradrenergically mediated. We tested the hypotheses that the influence of norepinephrine on beam-walking recovery occurs, at least partially, through effects in the contralateral and/or ipsilateral cerebral cortex. Rats had either a selective left or right 6-hydroxydopamine lesion or sham lesion of the dorsal noradrenergic bundle (DNB) 2 weeks before suction-ablation or sham injury of the right sensorimotor cortex. The rats' abilities to perform the beam-walking task were measured over the 10 days following cortex surgery. DNB lesions did not affect the initial severity of the beam-walking deficit and had no effect on the performance of the task in rats with sham cortex injuries. Lesions of the contralateral but not ipsilateral DNB significantly impaired recovery. Further, in cortically lesioned rats with contralateral DNB lesions, norepinephrine content in the cerebral cortex opposite to the sensorimotor cortex lesion was significantly correlated with recovery. These data suggest that the effect of norepinephrine on recovery of beam-walking ability may be partially exerted in the cerebral cortex contralateral to the injury.

Animals↗

PubMedDate not supplied

Rewiring of transcortical projections to middle suprasylvian cortex following early removal of cat areas 17 and 18.

Retrograde tracers were injected into middle suprasylvian (MS) cortex of two groups of experimental adult cats that had incurred removal of visual areas 17 and 18 on either the day of birth (P1), or at 1 month of age (P28). Tracers were also injected into the same region of intact and adult ablated control cats. The locations and numbers of labeled neurons in the experimental and control groups were compared. Following lesions on P1, but at no other age, increased numbers of neurons projected to MS cortex. Virtually all of the additional neurons were located in the superficial layers of the ventral posterior suprasylvian (vPS) cortex. These results demonstrated that (1) neurons with ipsilateral transcortical axons have the potential to reconfigure their projections after early, localized cortical damage elsewhere in the cortex of the same hemisphere; (2) this reconfiguration involves expansion of specific projections and is not a generalized capacity of all cortical neurons; (3) the expansion is modality specific; and finally, (4) the ability of cortical neurons to reorganize projections is limited in time. The expanded projection from vPS to MS cortex may contribute to neuronal compensations and the sparing of visually guided behaviors previously demonstrated in cats with neonatal visual cortex damage, and is a testament to the latent capacities immature cerebral cortex neurons possess to establish new projections following restricted damage to the cerebral cortex early in life.

Animals↗

PubMed2004

The motor cortex and facial expression: new insights from neuroscience.

BACKGROUND: For more than a century, unusual and complex deficits in facial expression have been known to occur following localized brain damage. Some brain injuries leave the face with pronounced alterations in affect whereas others result in movement disorders such as blepharospasm and Meige syndrome. There is also a historic trail of clinical observations that document deficits in either voluntary or emotional control of the facial muscles following central nervous system damage. REVIEW SUMMARY: Recent studies in the nonhuman primate cerebral cortex reveal the existence of multiple cortical facial representations in the frontal lobe and adjacent anterior cingulate cortex. These comprise the facial representation of the primary motor cortex (M1), ventral lateral premotor cortex (LPMCv), supplementary motor cortex (M2), rostral cingulate motor cortex (M3), and caudal cingulate motor cortex (M4). Homologous facial representations reside in the human brain based on observations following cortical stimulation, functional neuroimaging, and localized surgical resection. In the nonhuman primate, all these facial representations have been found to be directly interconnected through topographically organized corticocortical connections, and each facial area has also been found to send direct corticobulbar projections to the facial motor nucleus. The facial representations of M2 and M3 are both located on the medial wall of the hemisphere, in the vascular territory of the anterior cerebral artery. Both preferentially give rise to bilateral projections to parts of the facial nucleus that innervate the upper facial musculature as demonstrated in the monkey. The facial representation of M1, LPMCv, and M4 preferentially give rise to contralateral axonal projections ending in parts of the facial nucleus that innervate the lower facial musculature. The facial representation of M1 and LPMCv both reside in the vascular territory of the middle cerebral artery (MCA). The classic clinical presentation of paralysis in the contralateral lower facial musculature and intact bilateral upper facial musculature following typical MCA in infarction in the human parallels this mapping pattern of corticobulbar connections found in the nonhuman primate. CONCLUSIONS: Facial movements are undoubtedly under the powerful influence of the cerebral cortex and are essential for the appropriate execution of many important functions such as mastication, swallowing, and social interaction, including speech and nonverbal communication. This information provides a theoretic template for interpreting the clinical effects of neuropathologic disease and localized cortical trauma on facial movements.

Animals↗

PubMed1979

Effect of visual experience on tubulin synthesis during a critical period of visual cortex development in the hooded rat.

1. In some species, restriction of visual experience in early life may affect normal functional development of visual cortical cells. The purpose of the present study was to determine if visual deprivation during post-natal development in the hooded rat also affects the production in brain cells of certain molecular components such as tubulin, that are needed for growth and maintenance of synapses and neurites. 2. Norwegian black hooded rats were reared under a variety of conditions of visual deprivation. At various stages of development the animals were killed and the rate of synthesis of tubulin in visual and motor cortex determined. Tritiated colchicine was used to assay tubulin and L-[14C]leucine injected into the brain ventricles 2 hr before death was used to measure rate of tubulin synthesis. 3. In rats reared in normal light there is a marked elevation in visual cortex tubulin synthesis that spans the period from eye-opening (13 days) until approximately 35 days. This elevation in tubulin synthesis is absent in animals reared in darkness from birth or deprived of pattern vision by eyelid suture. Also the effect of visual deprivation on tubulin synthesis was specifically confined to visual cortex and was not found for the motor cortex. Similarly, the incorporation of L-[14C]leucine into total protein in visual cortex was unaffected by dark rearing. Hence the stimulation of tubulin synthesis by visual experience in rat visual cortex is not attributable to a general non-specific stimulation of protein synthesis. 4. Rats that were dark-reared from birth and then exposed to a lighted environment for 24 hr during a certain critical period that extends from eye-opening (13 days) until approximately 35 days, displayed a significant increase in visual cortex tubulin rats that were brought into the light later than 35 days showed no significant increase in tubulin synthesis when compared with their continuously dark-rearer controls. 5. It is suggested that the number of synapses and cytoplasmic processes that a developing cell can maintain depends on the size of the tubulin pool available to that cell. Tubulin in brain only has a half-life of about 4 days, so when the level of tubulin drops this could result in competition between different synapses for the limited supply of tubulin needed for their maintenance, a factor which may contribute to the structural plasticity of the visual cortex during the critical period.

Aging↗

PubMed1984

Experiments on functional role of peripheral input to motor cortex during voluntary movements in the monkey.

The functional role of sensory input to the motor cortex was studied by interrupting two major input pathways. One was the dorsal column, which sends the input directly through the thalamus to the motor cortex, and the other was the sensory cortex, which transfers its input through association fibers. Removal of the sensory cortex produced very little motor disturbances and the function recovered within a week. Section of the dorsal column produced some motor deficit, but the deficit was not severe and the animals recovered nearly completely within 2 wk. Combination of dorsal column section and sensory cortex removal produced severe motor deficits. These consisted of loss of orientation within extrapersonal space and loss of dexterity of individual fingers. These deficits never recovered within the duration of observation, which lasted 4-5 wk. It is concluded that the direct sensory input from the thalamus plays an important role in the control of voluntary movements, but loss of its function can be compensated by the input from the sensory cortex. The possible neuronal basis for the observed motor deficits is discussed and it is proposed that the sensory input functions by selectively changing the excitability of cortical efferent zones before and during the execution of voluntary movements. Recovery of motor function following dorsal column section occurred in parallel with the recovery of sensory input to the motor cortex. The recovered function and sensory input disappeared again following section of the association fibers from the sensory cortex. Neuronal mechanism for this observation is also discussed.

Afferent Pathways↗

PubMed1993

Projection from the sensory to the motor cortex is important in learning motor skills in the monkey.

1. The projection from the somatosensory cortex to the primary motor cortex has been proposed to play an important role in learning novel motor skills. This hypothesis was examined by studying the effects of lesions to the sensory cortex on learning of new motor skills. 2. We used two experimental paradigms to reveal the effects of lesions on learning of new motor skills. One task was to catch a food pellet falling at various velocities. The other task was to catch a food pellet from a rotating level. Both tasks required acquisition of novel motor skills. 3. The training was started after a lesion of the hand area in the somatosensory cortex of one hemisphere. In both tasks, monkeys had severe difficulty in learning the new skills with the hand contralateral to the ablated somatosensory cortex, compared with the hand contralateral to the intact hemisphere. 4. After acquisition of the motor skill in the hand contralateral to intact hemisphere, lesion of the somatosensory cortex hand area did not abolish the learned motor skill. 5. In control experiments, monkeys were trained to pick up a food pellet from a rotating board. This task did not necessitate acquisition of new motor skills, but could be performed by utilizing existing motor skills. Lesion in the somatosensory cortex before or after the training did not affect the execution of this task by either hand. 6. It is concluded that the corticocortical projection from the somatosensory to the motor cortex plays an important role in learning new motor skills, but not in the execution of existing motor skills.

Afferent Pathways↗

PubMed2000

Impairments in prehension produced by early postnatal sensory motor cortex activity blockade.

This study examined the effects of blocking neural activity in sensory motor cortex during early postnatal development on prehension. We infused muscimol, either unilaterally or bilaterally, into the sensory motor cortex of cats to block activity continuously between postnatal weeks 3-7. After stopping infusion, we trained animals to reach and grasp a cube of meat and tested behavior thereafter. Animals that had not received muscimol infusion (unilateral saline infusion; age-matched) reached for the meat accurately with small end-point errors. They grasped the meat using coordinated digit flexion followed by forearm supination on 82.7% of trials. Performance using either limb did not differ significantly. In animals receiving unilateral muscimol infusion, reaching and grasping using the limb ipsilateral to the infusion were similar to controls. The limb contralateral to infusion showed significant increases in systematic and variable reaching end-point errors, often requiring subsequent corrective movements to contact the meat. Grasping occurred on only 14.8% of trials, replaced on most trials by raking without distal movements. Compensatory adjustments in reach length and angle, to maintain end-point accuracy as movements were started from a more lateral position, were less effective using the contralateral limb than ipsilateral limb. With bilateral inactivations, the form of reaching and grasping impairments was identical to that produced by unilateral inactivation, but the magnitude of the reaching impairments was less. We discuss these results in terms of the differential effects of unilateral and bilateral inactivation on corticospinal tract development. We also investigated the degree to which these prehension impairments after unilateral blockade reflect control by each hemisphere. In animals that had received unilateral blockade between postnatal weeks (PWs) 3 and 7, we silenced on-going activity (after PW 11) during task performance using continuous muscimol infusion. We inactivated the right (previously active) and then the left (previously silenced) sensory motor cortex. Inactivation of the ipsilateral (right) sensory motor cortex produced a further increase in systematic error and less frequent normal grasping. Reinactivation of the contralateral (left) cortex produced larger increases in reaching and grasping impairments than those produced by ipsilateral inactivation. This suggests that the impaired limb receives bilateral sensory motor cortex control but that control by the contralateral (initially silenced) cortex predominates. Our data are consistent with the hypothesis that the normal development of skilled motor behavior requires activity in sensory motor cortex during early postnatal life.

Age Factors↗

PubMed1996

Mitochondrial distribution in visual and auditory cerebral cortex of the harbour porpoise.

The distributions of mitochondria and synapses in two areas of harbour porpoise cerebral cortex were examined by quantitative electron microscopy of sections stained for cytochrome oxidase. The distribution of cytochrome oxidase-positive and total mitochondria in the visual cortex of the lateral gyrus and in the auditory cortex of the temporal operculum was related closely to that of total cytochrome oxidase staining seen by light microscopy in the relevant areas. There were two peaks of mitochondrial numerical density in visual cortex: in layer III and the upper part of layer I. Mitochondrial distribution was more uniform in temporal cortex, where the numbers of mitochondria in layers VI, V and lower I were similar to those in visual cortex, but fewer were present in layers III, II and upper I. The laminar distribution of axodendritic synapses in both cortices was relatively uniform, and there was not such a large difference between the two areas. As large numbers of mitochondria have been described in the layers of cat visual cortex showing dark staining for cytochrome oxidase and receiving thalamic afferent input, we regard our data as suggestive of the existence of two main thalamorecipient zones in cetacean cortex: one in layer III and the other in upper layer I.

Animals↗

PubMedDate not supplied

Location of the sensorimotor cortex: functional and conventional MR compared.

PURPOSE: To determine the value of functional MR imaging to supplement conventional MR imaging for locating the rolandic cortex. METHODS: Parasagittal MR images acquired in conjunction with functional MR images were reviewed. The central sulcus was identified on the MR images by conventional parcellation methods. In the functional MR images, the sensorimotor cortex (rolandic cortex) was identified by the activation secondary to finger and thumb movement or tactile stimulation of the palm. The location of the central sulcus and rolandic cortex was compared. RESULTS: In 18 of 23 studies, the central sulcus selected by anatomic criteria coincided exactly or approximately with the cortex activated by the motor or sensory tasks. In two cases of tumor, the rolandic cortex could be located by means of the activation, but the central sulcus was not identified because of severe distortion of anatomic landmarks. In two volunteers, the central sulcus identified by anatomic landmarks did not coincide with the activated cortex. CONCLUSION: This study demonstrates that functional imaging supplements anatomic imaging in locating the sensorimotor cortex. Functional MR imaging may be a useful adjunct to conventional MR imaging to determine noninvasively the proximity of eloquent brain to focal brain lesions.

Adult↗

PubMed1996

Topography, architecture, and connections of somatosensory cortex in opossums: evidence for five somatosensory areas.

Microelectrode maps of somatosensory inputs were related to cortical architecture and patterns of cortical connections to provide evidence for five subdivisions of the somatosensory or sensorimotor cortex in North American opossums (Didelphis marsupialis). Microelectrode recordings revealed three systematic representations of the body surface. A large mediolaterally oriented representation was identified as the primary somatosensory area (S1) by its relative position, somatotopy, architecture, and connections. S1 represented the hindlimb, trunk, forelimb, and face in a mediolateral sequence. Two additional representations of cutaneous receptors were found caudolateral to S1, each with face representations adjacent to the border of lateral S1 and other body-part representations progressing more caudally toward the auditory cortex. We identified the more dorsal field as the second somatosensory area (S2) and the more ventral field as the parietal ventral area (PV). Tracers injected into S1 labeled neurons and terminals in architectonically distinct fields rostral and caudal to S1, the somatosensory caudal area (SC) and the somatosensory rostral area (SR). Movements could be evoked by microstimulation from sites scattered over S1, SR, and the frontal cortex, but thresholds were high and uncharacteristic of motor cortex. S2 and PV merged caudally with the cortex responsive to auditory stimuli, possibly A1, and neurons in some caudal recording sites in PV were activated by both auditory and cutaneous stimuli. Primary (V1) and secondary (V2) visual areas were also identified by microelectrode mapping, architecture, and connections. In addition, at least part of the cortex between V2 and the somatosensory cortex had visual connections. Thus, most of the dorsolateral cortex of opossums appears to be somatosensory, auditory, or visual.

Animals↗

PubMed1996

Development of local connections in ferret somatosensory cortex.

Ferrets have become recognized as a useful and interesting model for study of neocortical development. Because of their immaturity at birth, it is possible to study very early events in the ontogeny of the brain. We used living slices of ferret somatosensory cortex to study the formation and development of intrinsic elements within the neocortex. A small number of fixed, hemisected brains injected with 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI) were also used. The slices were obtained from ferret kits aged postnatal day (P)1 to P62 and maintained in a chamber; each slice received injections of fluorescent-labeled dextrans. The injections were made at different ages in several distinct sites, which included the proliferative ventricular zone, the intervening white matter (or intermediate zone), and different sites of developing cortex, including the deeper cortical plate, which incorporated the subplate in young animals, and more superficial cortical sites depending on the age of the animal. Several animals also received injections into the ventrobasal thalamus. Injections into young animals (P1-7) produced a dominant radial pattern that extended from the ventricular zone into the cortex. Injections into the ventricular zone labeled many cells that appeared morphologically like radial glia as well as presumptive neurons. Although the predominant pattern was radial, injections in the ventricular zone often produced tangentially oriented cells and horizontally arranged fibers at the outer edge of the proliferative zone. These cells and fibers may provide a substrate for tangential dispersion of neurons within the neocortex. More superficial injections within the slice labeled lines of cells that appeared to be stacked upon one another in a radial pile in the cortex; the cortical plate received very few lateral projections. Data obtained from more mature slices indicated that although the overall pattern of staining remained radial, the precise character of the pattern changed to include more lateral spread into surrounding cortex, which eventually refined and developed into distinct patches by P28, when the overall cortical architecture appeared adult like. The data involving thalamocortical connections were more limited, but they indicated that the thalamus projects precisely to the somatosensory cortex in a point-to-point fashion from the earliest date studied (P0) and that the ventrobasal nucleus terminates upon the somatosensory cortex in a patchy manner during the early postnatal days of development. This study of the development of the somatosensory cortex confirms the ubiquitous nature of column-like connections throughout the neocortex and provides a novel view of the radial nature of early neocortical maturation.

Animals↗

PubMed1998

Anatomical comparison of the macaque and marsupial visual cortex: common features that may reflect retention of essential cortical elements.

This study identifies fundamental anatomical features of primary visual cortex, area V1 of macaque monkey cerebral cortex, i.e., features that are present in area V1 of phylogenetically distant mammals of quite different lifestyle and features that are common to other regions of cortex. We compared anatomical constituents of macaque V1 with V1 of members of the two principal marsupial lines, the dunnart and the quokka, that diverged from the eutherian mammalian line over 135 million years ago. Features of V1 common to both macaque and marsupials were then compared with anatomical features we have previously described for macaque prefrontal cortex. Despite large differences in overall area and thickness of V1 cortex between these animals, the absolute size of pyramidal neurons is remarkably similar, as are their specific dendritic branch patterns and patterns of distribution of intrinsic axons. Pyramidal neuron patchy connections exist in the supragranular V1 in both the marsupial quokka and macaque as well as in macaque prefrontal cortex. Several specific types of aspinous interneurons are common to area V1 in both marsupial and macaque and are also present in macaque prefrontal cortex. Spiny stellate cells are a common feature of the thalamic-recipient, mid-depth lamina 4 of V1 in all three species. Because these similarities exist despite the very different lifestyles and evolutionary histories of the animals compared, this finding argues for a highly conserved framework of cellular detail in macaque primary visual cortex rather than convergent evolution of these features.

Anatomy, Artistic↗