PubMed Health⌕ Search

Biomedical subjects

T Manzoni

Publications and source records attributed to T Manzoni.

At least 19 recordsLinked to original sources
PubMed2001

Posterior corpus callosum and interhemispheric transfer of somatosensory information: an fMRI and neuropsychological study of a partially callosotomized patient.

Interhemispheric somatosensory transfer was studied by functional magnetic resonance imaging (fMRI) and neuropsychological tests in a patient who underwent resection of the corpus callosum (CC) for drug-resistant epilepsy in two stages. The first resection involved the anterior half of the body of CC and the second, its posterior half and the splenium. For the fMRI study, the hand was stimulated with a rough sponge. The neuropsychological tests included: Tactile Naming Test (TNT), Same-Different Recognition Test (SDRT), and Tactile Finger Localization Test (intra- and intermanual tasks, TFLT). The patient was studied 1 week before and then 6 months and 1 year after the second surgery. Before this operation, unilateral tactile stimulation of either hand activated contralaterally the first (SI) and second (SII) somatosensory areas and the posterior parietal (PP) cortex, and SII and PP cortex ipsilaterally. All three tests were performed without errors. In both postoperative sessions, somatosensory activation was observed in contralateral SI, SII, and PP cortex, but not in ipsilateral SII and PP cortex. Performance was 100% correct in the TNT for the right hand, but below chance for the left; in the other tests, it was below chance except for TFLT in the intramanual task. This case provides the direct demonstration that activation of SII and PP cortex to stimulation of the ipsilateral hand and normal interhemispheric transfer of tactile information require the integrity of the posterior body of the CC.

Adult↗
PubMed2001

Taste laterality in the split brain.

Two patients with corpus callosum resection, one complete and the other sparing the genu and the rostrum, were tested for discrimination of three basic taste stimuli (sour, bitter, salty) applied to the right or left sides of the tongue. Responses were made by pointing with either hand to written words or images of visual objects corresponding to the stimuli, a language-based discrimination. In both patients, response accuracy was significantly above chance for both hemitongues but there was a significant advantage for the left side. Reaction time was shorter for left stimuli than for right stimuli but the difference was not significant. Eight normal controls matched for age with the patients performed equally well with right and left hemitongue stimuli and so did a third callosotomy patient with sparing of the posterior callosum, including the splenium. Tactile and visual tests showed that the left hemisphere was responsible for language-based responses in the first two patients. The results confirm and extend previous findings in another callosotomy patient, indicating that: (i) taste information from either side of the tongue can reach the left hemisphere in the absence of the corpus callosum; (ii) the ipsilateral input from the tongue to the left hemisphere is more potent functionally than the contralateral input and (iii) in the normal brain, the corpus callosum, specifically its posterior part including the splenium, appears to equalize the effects of the ipsilateral and contralateral gustatory inputs on the left hemisphere. Taken together with evidence about lateralized taste deficits following unilateral cortical lesions, the results also suggest that the gustatory pathways from tongue to cortex are bilaterally-distributed with an ipsilateral predominance that may be subject to individual variations.

Adult↗
PubMed1999

Role of the corpus callosum in the somatosensory activation of the ipsilateral cerebral cortex: an fMRI study of callosotomized patients.

To verify whether the activation of the posterior parietal and parietal opercular cortices to tactile stimulation of the ipsilateral hand is mediated by the corpus callosum, a functional magnetic resonance imaging (fMRI, 1.0 tesla) study was performed in 12 control and 12 callosotomized subjects (three with total and nine with partial resection). Eleven patients were also submitted to the tactile naming test. In all subjects, unilateral tactile stimulation provoked a signal increase temporally correlated with the stimulus in three cortical regions of the contralateral hemisphere. One corresponded to the first somatosensory area, the second was in the posterior parietal cortex, and the third in the parietal opercular cortex. In controls, activation was also observed in the ipsilateral posterior parietal and parietal opercular cortices, in regions anatomically corresponding to those activated contralaterally. In callosotomized subjects, activation in the ipsilateral hemisphere was observed only in two patients with splenium and posterior body intact. These two patients and another four with the entire splenium and variable portions of the posterior body unsectioned named objects explored with the right and left hand without errors. This ability was impaired in the other patients. The present physiological and anatomical data indicate that in humans activation of the posterior parietal and parietal opercular cortices in the hemisphere ipsilateral to the stimulated hand is mediated by the corpus callosum, and that the commissural fibres involved probably cross the midline in the posterior third of its body.

Adult↗
PubMed1999

Localization of the first and second somatosensory areas in the human cerebral cortex with functional MR imaging.

BACKGROUND AND PURPOSE: Our objective was to map by means of a conventional mid-field (1.0 T) MR imaging system the somatosensory areas activated by unilateral tactile stimulation of the hand, with particular attention to the areas of the ipsilateral hemisphere. METHODS: Single-shot echo-planar T2*-weighted imaging sequences were performed in 12 healthy volunteers to acquire 10 contiguous 7-mm-thick sections parallel to the coronal and axial planes during tactile stimulation of the hand. The stimulation paradigm consisted of brushing the subjects' palm and fingers with a rough sponge at a frequency of about 1 Hz. RESULTS: Stimulation provoked a signal increase (about 2% to 5%) that temporally corresponded to the stimulus in several cortical regions of both hemispheres. Contralaterally, activation foci were in the anterior parietal cortex in an area presumably corresponding to the hand representation zone of the first somatosensory cortex, in the posterior parietal cortex, and in the parietal opercular cortex forming the upper bank of the sylvian sulcus and probably corresponding to the second somatosensory cortex. Activation foci were also observed in the frontal cortex. Ipsilaterally, activated areas were in regions of the posterior parietal and opercular cortices roughly symmetrical to those activated in the contralateral hemisphere. The same activation pattern was observed in all subjects. CONCLUSION: The activated areas of the somatosensory cortex described in the present study corresponded to those reported in other studies with magnetoelectroencephalography, positron emission tomography, and higher-field functional MR imaging. An additional area of activation in the ipsilateral parietal operculum, unnoticed in other functional MR imaging studies, was also observed.

Adult↗
PubMed1998

The cerebral ventricles, the animal spirits and the dawn of brain localization of function.

This paper reviews the early history of brain localization of function. It analyses the doctrines professed in ancient times by philosophers and physicians, who believed that brain functions were carried out in the cerebral ventricles by the psychic pneuma, or animal spirit, a sort of special and light substance endowed with the power to perform sensory, motor and mental activities. This theory, conceived in the Classic Age and called "ventricular-pneumatic doctrine", evolved in the 4th-5th centuries A.D. into the "three-cell theory", according to which each cerebral ventricle was the seat of a specific function, and contained a unique type of spirit with the power to perform that function. The three-cell theory represents the earliest attempt to localize different mind functions in separate brain sites and was held true by Byzantine, Arabian and Western Latin scholars well beyond the Renaissance. The paper is subdivided into an Introduction and eight sections. The first two sections report a brief history of the philosophical and medical doctrines about the pneuma as mediator of all vital functions, the ventricular-pneumatic doctrine elaborated by Galen of Pergamon, and his theory of nerve physiology based on the assumption that the pneuma, set in motion by active brain movements and flowing in the hollow nerves, could transfer sensations from the sense organs to the anterior ventricles, and motor commands from the posterior ventricle to the muscles. The third and fourth sections trace the ways in which these doctrines were transmitted to the Byzantine physicians and then to the Arabs, until they reached the Latin West. Here, throughout the Middle Ages they not only formed the background of medical and natural philosophy, but also influenced Christian theologians. The fifth section is devoted to the ventricular localization of mind faculties, called internal senses by Arabian and Western Latin scholars. Most authors recognized three basic internal senses: imagination, cognition and memory, and generally localized imagination in the anterior ventricle, cognition in the middle and memory in the posterior one, while other scholars adopted complex lists including up to seven faculties, each carried out by a specific type of animal spirit and localized, or sub-localized, in different ventricular sites according to complex topographical patterns. This section reports more than sixty patterns of ventricular localization from various authors (summarized in a Table), the rationale of complex ventricular localization, and the naive interpretations of Medieval physicians and surgeons of the impairment of the internal senses caused by brain disease and trauma. The sixth section deals with the decline of the three-cell theory, which was first challenged in the early 16th century and then drastically revised by several Renaissance and post-Renaissance experimentalists, anatomists and philosophers, although some remnants of the Galenic pneumatic neurophysiology survived in medicine until the 18th century. The penultimate section analyses bibliographical data on the earliest localizationists and shows that, independently of chronological priority, Nemesius of Emesa was the source of the pattern of ventricular localization of function adopted by later Byzantines and by the Arabs, and then transmitted to Latin Western scholars. The last section discusses the legacy of the three-cell theory to later generations of neuroscientists.

Animals↗
PubMed1996

Glutamate decarboxylase immunoreactivity in corticocortical projecting neurons of rat somatic sensory cortex.

Combined retrograde tracing and immunocytochemical experiments were carried out on rats to ascertain whether corticocortical projecting neurons in the somatic sensory areas are immunoreactive to an antiserum against glutamate decarboxylase. Injections of a retrograde tracer (colloidal gold-labelled wheat germ agglutinin conjugated to enzymatically inactive horseradish peroxidase) in the first somatic sensory area labelled neurons in the injected area, in the second somatic sensory area, and in the parietoventral area of the ipsilateral hemisphere. The topographical and laminar distribution of these retrogradely-labelled corticocortical neurons in the first and second somatic sensory areas and in the parietoventral area was in line with a previous description (Fabri M. and Burton H. (1991b) J. comp. Neurol. 311, 405-424). In sections processed for the simultaneous visualization of the retrograde tracer and glutamate decarboxylase immunoreactivity, a number of neurons were double-labelled. Double-labelled neurons were most numerous in the first somatic sensory cortex, where they accounted for 5% of all retrogradely-labelled neurons. Outside this region, double-labelled cells were observed in the second somatic sensory cortex and in the parietoventral cortex, where they amounted respectively to 2.8% and 2.3% of all corticocortical neurons labelled in these two areas. Glutamate decarboxylase-immunopositive corticocortical neurons were mainly concentrated in the infragranular layers (73.8% of all double-labelled neurons in the first somatic sensory area, 81.7% in the second somatic sensory area, and 76.5% in the parietoventral area). The results indicate the presence of a small but significant contingent of GABAergic inhibitory neurons in the associative connections of the somatic sensory areas.

Animals↗
PubMed1995

Laminar pattern of termination of the ipsilateral cortical projection from SII to SI in cats.

The present light and electron microscopic experiments were carried out on the first somatic sensory area (SI) of cats to determine the laminar distribution of axon terminals from the ipsilateral second somatic sensory area (SII) and to identify the types of synapses between these terminals and the neuronal elements of SI. Phaseolus vulgaris-leucoagglutinin (PHA-L) was iontophoretically injected into multiple sites and at different cortical depths of the forepaw representation zone of SII. Fixed brain blocks containing the injected SII and ipsilateral SI were cut into slices and processed immunocytochemically to stain PHA-L-filled fibers and terminals. Light microscopic examination of SI revealed patches of anterograde labeling in the forepaw representation zone, concentrated mainly in supragranular layers. In these layers, thin immunolabeled fibers branched extensively and formed a dense plexus that was more prominent in layers II and I. Conversely, the infragranular layers contained fragments of vertically oriented thick fibers that rarely emitted axon collaterals. PHA-L-labeled axons had numerous swellings along their course, interpreted as boutons en passant, and stalked boutons. Of 19,661 labeled terminals (17,833 beads and 1,828 stalked boutons), 84.74% were observed in supragranular layers, with the highest concentration in layer II (33.15%) and lower in layers I (26.27%) and III (25.30%). The proportion of terminals was lower in layers IV (6.49%) and V (5.45%) and lowest in layer VI (3.32%). These counts also showed that boutons en passant were the majority (90.70%) and stalked boutons, the minority (9.30%). The ratio of these two types of presynaptic specializations was similar (9:1) in all six layers. Electron microscopic examination of the labeled regions of SI showed that both axon swellings and stalked boutons formed synapses of the asymmetric type with SI neuronal elements. The majority (85.37%) of a sample of 130 labeled terminals synapsed on SI neurons in layers I-III. The identified postsynaptic profiles were dendritic spines (61.11%) or medium-sized and small dendrites (38.89%). These results are discussed in relation to those of a companion study on the laminar pattern of the projection from SI to SII of cats (P. Barbaresi, A. Minelli, and T. Manzoni, 1994, J. Comp. Neurol. 343:582-596). Based on the anatomical organization of these reciprocal connections, there seems to be no clear hierarchicalal relationship between SI and SII in cats.

Animals↗
PubMed1994

Topographical relations between ipsilateral cortical afferents and callosal neurons in the second somatic sensory area of cats.

Experiments were carried out on the second somatic sensory area (SII) of cats to study 1) the laminar distribution of axon terminals from the ipsilateral first somatic sensory cortex (SI); and 2) the topographical relations between their terminal field and the callosal neurons projecting to the contralateral homotopic cortex. To label simultaneously in SII both ipsilateral cortical afferents and callosal cells, cats were given iontophoretic injections of Phaseolus vulgaris-leucoagglutinin (PHA-L) in the forepaw zone of ipsilateral SI, and pressure injections of horseradish peroxidase (HRP) in the same zone of contralateral SII. The possibility that ipsilateral cortical axon terminals synapse callosal neurons was investigated with the electron microscope by combining lesion-induced degeneration with retrograde HRP labelling. Fibers and terminations immunolabelled with PHA-L from ipsilateral SI were distributed in SII in a typical patchy pattern and were mostly concentrated in supragranular layers. Labelled fibers formed a very dense plexus in layer III and ramified densely also in layers I and II. Labelled axon terminals were both en passant and single-stalked boutons. Counts of 8,303 PHA-L-labelled terminals of either type showed that 82.40% were in supragranular layers. The highest concentration was in layer III (43.99%), followed by layers II (30.32%) and I (8.09%). The remaining terminals were distributed among layers IV (6.96%), V (4.93%), and VI (5.68%). The same region of SII containing anterogradely labelled axons and terminals also contained numerous neurons retrogradely labelled with HRP from contralateral SII. Callosal projection neurons were pyramidal, dwelt mainly in layer III, and were distributed tangentially in periodic patches. Patches of anterograde and retrograde labelling either interdigitated or overlapped both areally and laminarly. In the zones of overlap, numerous PHA-L-labelled axon terminals were seen in close apposition to HRP-labelled pyramidal cell dendrites. Combined HRP-electron microscopic degeneration experiments showed that in SII axon terminals from ipsilateral SI form asymmetric synapses with HRP-labelled dendrites and dendritic spines pertaining to callosal projection neurons. These results are discussed in relation to the layering and function of the SI to SII projection, and to the evidence that SII neurons projecting to the homotopic area of the contralateral hemisphere have direct access to the sensory information transmitted from ipsilateral SI.

Animals↗
PubMed1992

Substance P-containing pyramidal neurons in the cat somatic sensory cortex.

Light and electron microscopic immunocytochemical methods were used to verify the possibility that neocortical pyramidal neurons in the first somatic sensory cortex of cats contain substance P. At the light microscopic level, substance P-positive neurons accounted for about 3% of all cortical neurons, and the vast majority were nonpyramidal cells. However, 10% of substance P-positive neurons had a large conical cell body, a prominent apical dendrite directed toward the pia, and basal dendrites, thus suggesting they are pyramidal neurons. These neurons were in layers III and V. At the electron microscopic level, the majority of immunoreactive axon terminals formed symmetric synapses, but some substance P-positive axon terminals made asymmetric synapses. Labelled dendritic spines were also present. Combined retrograde transport-immunocytochemical experiments were also carried out to study whether substance P-positive neurons are projection neurons. Colloidal gold-labelled wheat germ agglutinin conjugated to enzymatically inactive horseradish peroxidase was injected either in the first somatic sensory cortex or in the dorsal column nuclei. In the somatic sensory cortex contralateral to the injection sites, a few substance P-positive neurons in layers III and V also contained black granules, indicative of retrograde transport. This indicates that some substance P-positive neurons project to cortical and subcortical targets. We have therefore identified a subpopulation of substance P-positive neurons that have most of the features of pyramidal neurons, are the probable source of immunoreactive axon terminals forming asymmetric synapses on dendritic spines, and project to the contralateral somatic sensory cortex and dorsal column nuclei. These characteristics fulfill the criteria required for classifying a cortical neuron as pyramidal.

Amino Acid Sequence↗
PubMed1992

Thalamic connections of the second somatic sensory area in cats studied with anterograde and retrograde tract-tracing techniques.

The thalamic connections of the second somatosensory area in the anterior ectosylvian gyrus of cats have been investigated using the retrograde tracer horseradish peroxidase and the anterograde tracer Phaseolus vulgaris leucoagglutinin. Horseradish peroxidase was injected iontophoretically in several somatotopic zones of the second somatosensory area map of six cats. Sites of horseradish peroxidase delivery were identified preliminarily by recording with microelectrodes the responses of neurons to skin stimulation. Phaseolus vulgaris leucoagglutinin was iontophoretically injected within the ventrobasal complex (one cat) or in the posterior complex (one cat). Horseradish peroxidase injections into cytoarchitectonic area SII retrogradely labeled neurons in the ipsilateral ventrobasal complex and in the posterior complex. Counts of labeled neurons from the ipsilateral thalamus showed that the overwhelming majority of horseradish peroxidase-labeled neurons were in the ventrobasal complex (96.3-96.9%) and few were in the posterior complex (3.1-3.7%). Neurons labeled in the ventrobasal complex were observed throughout the anteroposterior extent of the nucleus, while their mediolateral distribution varied with the site of horseradish peroxidase delivery in the body map of the second somatosensory area, which indicates that the projections from the ventrobasal complex to the second somatosensory area are somatotopically organized. In the cat in which the horseradish peroxidase injection involved both the second somatosensory area proper and the second somatosensory area medial, which lies in the lower bank of suprasylvian sulcus, labeled neurons were almost as numerous in the ventrobasal complex as in the posterior complex. Phaseolus vulgaris leucoagglutinin injected in the ventrobasal complex anterogradely labeled thalamocortical fibers in the ipsilateral anterior ectosylvian gyrus. In this case, patches of labeled fibers and terminals were distributed exclusively within the cytoarchitectonic borders of the second somatosensory area proper. Labeled terminals were numerous in layer IV and lower layer III, but terminal boutons and fibers with axonal swellings, probably forming synapses en passant, were frequently observed also in layers VI and I. Injection of Phaseolus vulgaris leucoagglutinin in the posterior complex labeled thalamocortical fibers in two distinct regions in the ipsilateral anterior ectosylvian gyrus, one lying laterally and the other medially, which correspond, respectively, to the fourth somatosensory area and the second somatosensory area medial. In both areas the densest plexus of labeled fibers and axon terminals was in layer IV and lower layer III, but numerous labeled fibers and terminals were also observed in layer I. In this case, only rare fragments of labeled fibers were present in second somatosensory area proper, but no labeled terminals could be observed.

Animals↗
PubMed1990

Matching of receptive fields in the association projections from SI to SII of cats.

Anatomical and electrophysiological experiments were performed on cats to investigate the pattern of divergence and convergence in the association projections from the first (SI) to the second (SII) somatic sensory cortex and to ascertain whether diverging and converging fibre components from SI have receptive fields (RFs) matching those of target neurons in SII. In the first group of six cats, a single deposit of horseradish peroxidase (HRP) was iontophoretically placed (2-4 microA for 20 minutes) into an electrophysiologically identified site of the SII map: the digit (3 cats), forepaw (2 cats), and arm (1 cat) zones. The forelimb representation in ipsilateral SI was subsequently explored with microelectrodes and RFs from small clusters of neurons systematically mapped. Planar maps of this area were reconstructed with the aid of a computer from serial sections, to correlate on the tangential plane the topographical distribution of retrogradely labelled association neurons with the physiological map of the forelimb. Since diverging projections were observed from a zone of SI to multiple zones of SII, double-labelling experiments were carried out in a second group of three cats, in which two retrograde fluorescent dyes (diamidino yellow and fast blue) were injected by pressure into two different sites of the SII map, to ascertain whether SI sends diverging projections by branching axons. HRP injections in SII retrogradely labelled a discrete number of association neurons in SI. Their distribution area was several tens of times wider than that covered by the injection site. This suggests that a remarkable amount of divergence and convergence exists in the association projections from SI to SII. Despite the substantial difference in the extent of the injected and labelled areas, RFs of afferent and target neurons corresponded closely. Injections covering a small region within a single digit zone of SII labelled neurons throughout the entire representation of the same digit in SI, while neurons labelled in somatotopically inappropriate zones were rare. RFs mapped from several sites of the labelled region in SI were individually smaller than the RF mapped from the injection site in SII, but the overall size of afferent RFs encompassed that of target neurons. Divergence and convergence in the SI projections to SII zones representing more proximal portions of the forelimb may be even greater since HRP injections in the forepaw and arm zones of SII labelled a number of neurons also in the digit zone of SI, providing the RFs mapped from the injection sites were sufficiently wide to include the digits.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗
PubMed1989

Glutamate-positive neurons and axon terminals in cat sensory cortex: a correlative light and electron microscopic study.

Immunocytochemical methods were used to perform a correlative light and electron microscopic study of neurons and axon terminals immunoreactive to the antiglutamate (Glu) serum of Hepler et al. ('88) in the visual and somatic sensory areas of cats. At the light microscopic level, numerous Glu-positive neurons were found in all layers except layer I of both cortical areas. On the basis of the dendritic staining of Glu-positive cells, two major morphological categories were found: pyramidal cells, which were the most frequent type of immunostained neuron, and multipolar neurons, which were more numerous in layer IV of area 17 than in any other layer. A large number of Glu-positive neurons, however, did not display dendritic labelling and were considered unidentified neurons. Counts of labelled neurons were performed in the striate cortex; approximately 40% were Glu-positive. Numerous lightly stained punctate structures were observed in all cortical layers: the majority of these Glu-positive puncta were in the neuropil. After resectioning the plastic sections for electron microscopy it was observed that: 1) the majority of neurons unidentifiable at light microscopic level were indeed pyramidal neurons except in layer IV of area 17, where many stained cells were probably spiny stellate neurons. Some Glu-positive neurons, however, exhibited clear ultrastructural features of nonspiny nonpyramidal cells; 2) all synaptic contacts made by Glu-positive axon terminals were of the asymmetric type, but not all asymmetric synaptic contacts were labelled. The vast majority of postsynaptic targets of Glu-positive axons were unlabelled dendritic spines and shafts. The present results provide further evidence that Glu (or a closely related compound) is probably the neurotransmitter of numerous excitatory neurons in the neocortex.

Animals↗
PubMed1989

Callosal connections of the somatic sensory areas II and IV in the cat.

The homotopic and heterotopic callosal connections in the forelimb representations of the second (SII) and fourth (SIV) somatic sensory areas of cats were investigated by means of the axonal transport of horseradish peroxidase (HRP) in conjunction with microelectrode recording. The tracer was injected in the electrophysiologically identified hand and/or digit zone of SII (six cats) or SIV (four cats). The homotopic area in the contralateral hemisphere was explored with microelectrodes in five animals (three injected in SII and two in SIV) to map neuronal receptive fields. The aim was to correlate in the same experimental case the topography of labelled callosal neurons with the physiological map of the forelimb. Labelled cells and recording sites were plotted on planar maps reconstructed with the aid of a computer from serial coronal sections from the anterior ectosylvian gyrus. After SII injections, labelled callosal neurons were observed throughout the forelimb representation in the contralateral area, but in the tangential plane their distribution was uneven. Each somatotopic zone composing the forelimb map, that is, the arm, hand, and digit zones, contained several subzones in which callosal neurons were either dense or rare. Microelectrode explorations showed that receptive fields mapped from callosal and relatively acallosal subzones representing the same body part were similar in extent and location. After SIV injections, labelled callosal neurons were observed throughout the forelimb and proximal body representation of the contralateral area. Although slight regional variations in the density of labelled cells were apparent, no subzones bare of callosal labelling were observed in SIV. In both SII and SIV, callosal neurons were concentrated mainly in layer III, but a significant number was also evident in the infragranular layers. After HRP injections in the digit zone of SII or SIV, labelled cell bodies were also observed in heterotopic areas of the contralateral hemisphere. Most of these neurons were clustered in the medial bank of the coronal sulcus and in two other heterotopic cortical regions lying, respectively, in the anterior suprasylvian sulcus and in the lateral branch of the ansate sulcus. Some callosal cells interconnecting SII and SIV were also labelled. The results show that the distal forelimb zones in SII and SIV are callosally connected with the respective homotopic zones and with several somatosensory fields located heterotopically in the contralateral hemisphere.

Afferent Pathways↗
PubMed1988

Immunocytochemical evidence for glutamatergic cortico-cortical connections in monkeys.

Retrograde transport of horseradish peroxidase and immunocytochemical visualization of glutamate (Glu) were combined to investigate the neurotransmitter used by cortico-cortical neurons in the first (SI) and second (SII) somatic sensory areas of macaque monkeys. The majority of association and callosal neurons in SI and SII were immunoreactive for an antiGlu serum: evidence was therefore obtained in support of a role for Glu, or a closely related compound, as the synaptic transmitter used by cortico-cortical fibers.

Animals↗
PubMed1988

Demonstration of glutamate-positive axon terminals forming asymmetric synapses in cat neocortex.

Electron microscopic examination of sections immunocytochemically processed with an anti-glutamate serum reveals that many asymmetric synapses in the cat neocortex contain elevated levels of immunodetectable glutamate. These labelled axon terminals are likely to use glutamate as neurotransmitter. Axon terminals forming symmetric contacts were never labelled. Since glutamate is known to exert potent excitatory effects on neocortical neurons, the present finding gives immunocytochemical evidence that asymmetric synapses are excitatory.

Animals↗