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PubMed1994

[The effect of age and disease on the MR imaging T2 low signal intensity area in the cerebral cortex].

We retrospectively studied magnetic resonance (MR) images of the brain in 139 patients (16 cases of Alzheimer's disease, 8 cases of Parkinson's disease, 53 cases of multiple cerebral infarct, 33 cases of other central nervous diseases, and 29 cases of peripheral neuropathy) between the age of 6 and 85 years old with a mean age of 60.6 +/- 18.5 to examine the appearance of T2 low signal intensity areas (T2CLIA) in the cerebral cortex. Motor, occipital, sensory or other cortices were evaluated with long repetition time/echo time (TR/TE) spin-echo sequences and staged into three grades in the motor cortex: none, partial, and whole; and two grades in the others: none or present. In general, T2CLIA was not seen in any cortex in patients less than 50 years old, then after 50 years old T2CLIA increased with age. Over 70 years of age T2CLIA appeared in 50.9% of patients in the whole motor cortex, 88.7% in either whole or partial motor cortex, 47.2% in the occipital cortex, and 20.8% in the sensory cortex. T2CLIA was not observed in other cortices. The incidence of T2CLIA appearance in the motor cortex was significantly higher in all central nervous diseases than in cases of peripheral neuropathy over 70. T2-CLIA showed a correlation with temporal lobe atrophy and white matter lesions in the motor cortex. In the sensory cortex, T2CLIA correlated with white matter lesions. These results suggest that T2-CLIA may correlate with age or accumulation of nonheme iron in the cortex associated with central nervous diseases.

Adolescent↗

PubMed1998

Nitric oxide synthase and the acetylcholine receptor in the prefrontal cortex: metasynaptic organization of the brain.

Nitric oxide synthase (NOS) and the nicotinic acetylcholine receptor (nAChR) immunoreactivity of the cerebral cortex was studied in adult Macaca fascicularis monkeys at light- and electron microscopic levels. NOS was located by means of the polyclonal antibodies developed by Transduction Laboratories (Lexington, KY, USA), as primary serum, in a dilution of 1:1000, and nAChR was located by means of biotinylated alpha-bungarotoxin (BTX) obtained from Molecular probes (Eugene, Oregon, USA) in a dilution of 1:2000. While endothelial eNOS outlined blood vessels in the brain, brain-derived (neural) bNOS labelled three well-defined cell types in area 46 of the prefrontal cortex, viz. (a) bipolar cells, scattered through layers III to V, equipped with long dendrites which pass over the thickness of the cortex in a right angle to the pial surface, establishing dendritic bundles closely reminiscent of a columnar organization; (b) large multipolar cells, located mainly in layers V and VI, with axons which interconnect dendritic bundles of the bipolar cells and establish synapses with dendritic shafts and spines of the former; and (c) stellate cells, located in lamina II and III, which establish an axonal network in lamina zonalis (lamina I). This arrangement is most characteristic in area 46 of the prefrontal cortex; areas 10 and 12 display similar features. In contrast, the primary visual cortex (area 17), is lacking any sign of columnar organization. Localization of bNOS immunoreactivity is at marked variance to that of NADPH-diaphorase which labels large pyramidal cells in the primate cortex. Binding of alpha-bungarotoxin (BTX) which labels the alpha 7 subunit of nAChR is located in somata, dendrites and axons of interneurons scattered over the entire width of the prefrontal cortex; on the other hand, the monoclonal antibody mAb 35 which labels subunits alpha 1, alpha 3 and alpha 5 in the main immunogenic region of the receptor, visualizes apical dendritic shafts similar to those like bNOS. Strategic localization of bNOS in the primate prefrontal cortex fulfills criteria of producing a freely diffusing retrograde messenger molecule operative in signal transduction routes subserving topography and columnar organization of the cortex, as well as long-term potentiation and long-term depression phenomena underlying mnemonic and gnostic functions. Common occurrence of bNOS and nAChR in identical or similar structures in the prefrontal cortex suggests that interactions between nitrogen oxide and presynaptically released acetylcholine might be involved in the metasynaptic organization of the cerebral cortex, operating in a non-synaptic manner in maintaining optimal performance on cognitive tasks.

Animals↗

PubMed2001

Endogenous serotonin contributes to a developmental decrease in long-term potentiation in the rat visual cortex.

The primary visual cortex shows synaptic plasticity during a postnatal "critical period," and its plasticity declines with development. Indeed, we found a developmental decrease in the induction of long-term potentiation (LTP) in the rat visual cortex. In visual cortex slices obtained from 2- to 3-week-old rats, tetanic stimulation (100 Hz for 1 sec, twice at an interval of 30 sec) of the white matter reproducibly induced LTP of field potentials in layer II/III. However, in slices from 5-week-old rats, the same tetanic stimulation failed to induce LTP. We hypothesized that endogenous serotonin (5-HT) is responsible for the developmental decrease in visual cortex LTP, because the induction of visual cortex LTP was suppressed by the addition of exogenous 5-HT (10 microm) and because the amount of 5-HT in the visual cortex increased during development. To test this hypothesis, we investigated the effect of methysergide, a 5-HT receptor antagonist, on the induction of visual cortex LTP. When visual cortex slices from 5-week-old rats were perfused with 50 microm methysergide, tetanic stimulation of the white matter induced robust LTP in layer II/III. Furthermore, serotonergic neurons were lesioned by intracerebroventricular injection of 5,7-dihydroxytryptamine (5,7-DHT). LTP was induced in visual cortex slices from 5,7-DHT-treated, 5-week-old rats. These results suggest that the induction of visual cortex LTP in 5-week-old rats is suppressed by endogenous 5-HT. 5-HT may be a factor that determines a critical period for synaptic plasticity in the rat visual cortex.

5,7-Dihydroxytryptamine↗

PubMed1996

Non-uniform distribution of the NMDAR1 receptor subunit in kitten visual cortex at the peak of the critical period.

PURPOSE: The development of columnar systems in the visual cortex, in particular ocular dominance columns, is dependent on experiential activity in conjunction with NMDA-mediated plasticity mechanisms. Recent experiments, however, have shown that certain aspects of the columnar organization of the visual cortex, such as the spacing of columns, are not changed by manipulations that affect the pattern of retinal activity. This raises the possibility that features intrinsic to the visual cortex may play a crucial role in the development of cortical columns and that a non-uniform distribution of NMDA receptors in the developing visual cortex could form the link between activity and intrinsic cortical modularity. METHODS: To examine this possibility we used immunohistochemical techniques to label the NMDAR1 receptor subunit protein in kitten visual cortex. The arrangement of the NMDAR1 subunit was visualized (using a monoclonal antibody) in flattened and coronal sections through visual cortex. The tangential and laminar distributions of NMDAR1 immunoreactivity (NMDAR1ir) were studied at the peak of the critical period for plasticity (4-5 weeks of age) in the developing kitten visual cortex. RESULTS: At the ages examined there was a non-uniform distribution of NMDAR1 immunoreactivity in the visual cortex. These patches of darker NMDAR1 label were found in layers 2/3 and extended up into layer 1. Thus, during development neurons expressing the NMDAR1 receptor subunit were distributed in a patchy fashion in the upper layers of the kitten visual cortex. CONCLUSIONS: This suggests that NMDA-mediated activity-dependent plasticity may not occur uniformly across the tangential extent of the visual cortex, and raises the possibility that the arrangement of NMDAR1 patches may guide the emergence of nascent columns in the developing visual cortex.

Animals↗

PubMed2000

The organization of somatosensory cortex in the short-tailed opossum (Monodelphis domestica).

The organization of neocortex in the short-tailed opossum (Monodelphis domestica) was explored with multiunit microelectrode recordings from middle layers of cortex. Microelectrode maps were subsequently related to the chemoarchitecture of flattened cortical preparations, sectioned parallel to the cortical surface and processed for either cytochrome oxidase (CO) or NADPH-diaphorase (NADPHd) histochemistry. The recordings revealed the presence of at least two systematic representations of the contralateral body surface located in a continuous strip of cortex running from the rhinal sulcus to the medial wall. The primary somatosensory area (S1) was located medially while secondary somatosensory cortex (S2) formed a laterally located mirror image of S1. Auditory cortex was located in lateral cortex at the caudal border of S2, and some electrode penetrations in this area responded to both auditory and somatosensory stimulation. Auditory cortex was outlined by a dark oval visible in flattened brain sections. A large primary visual cortex (V1) was located at the caudal pole of cortex, and also consistently corresponded to a large chemoarchitecturally visible oval. Cortex just rostral and lateral to V1 responded to visual stimulation, while bimodal auditory/visual responses were obtained in an area between V1 and somatosensory cortex. The results are compared with brain organization in other marsupials and with placentals and the evolution of cortical areas in mammals is discussed.

Animals↗

PubMed1995

Projections from the anterodorsal and anteroventral nucleus of the thalamus to the limbic cortex in the rat.

The present study characterized the projections of the anterodorsal (AD) and the anteroventral (AV) thalamic nuclei to the limbic cortex. Both AD and AV project to the full extent of the retrosplenial granular cortex in a topographic pattern. Neurons in caudal parts of both nuclei project to rostral retrosplenial cortex, and neurons in rostral parts of both nuclei project to caudal retrosplenial cortex. Within AV, the magnocellular neurons project primarily to the retrosplenial granular a cortex, whereas the parvicellular neurons project mainly to the retrosplenial granular b cortex. AD projections to retrosplenial cortex terminate in very different patterns than do AV projections: The AD projection terminates with equal density in layers I, III, and IV of the retrosplenial granular cortex, whereas, in contrast, the AV projections terminate very densely in layer Ia and less densely in layer IV. Further, both AD and AV project densely to the postsubicular, presubicular, and parasubicular cortices and lightly to the entorhinal (only the most caudal part) cortex and to the subiculum proper (only the most septal part). Rostral parts of AD project equally to all three subicular cortices, whereas neurons in caudal AD project primarily to the postsubicular cortex. Compared to AD, neurons in AV have a less extensive projection to the subicular cortex, and this projection terminates primarily in the postsubicular and presubicular cortices. Further, the AD projection terminates in layers I, II/III, and V of postsubiculum, whereas the AV projection terminates only in layers I and V.

Animals↗

PubMed2001

Evidence for a direct projection from the postrhinal cortex to the subiculum in the rat.

Behavioral data indicate that three of the areas which form the parahippocampal region in the rat, i.e., the entorhinal, perirhinal, and postrhinal cortices, have different, although related functions that also differ from those of the hippocampal formation. These functional differences might be related to differences in connectivity, on the one hand with parts of the association cortex, and on the other with the hippocampal formation. In a previous study, we showed the existence of both a direct and an indirect projection from the perirhinal cortex to areas CA1 and subiculum of the hippocampus. Here we present the result of a second study, demonstrating a similarly organized projection from the postrhinal cortex to the subiculum, comprising both a direct and an indirect route. Electrical stimulation of the postrhinal cortex in vivo evoked field potentials throughout the subiculum and the dentate gyrus. Current source density analysis in both the subiculum and dentate gyrus revealed the presence of sink-source pairs, indicative of a synaptic termination. Based on comparison with the sink-source pairs found after stimulation of the medial entorhinal cortex, we conclude that the connection between the postrhinal cortex and the dentate gyrus most likely is formed by a polysynaptic pathway mediated via the medial entorhinal cortex, while the pathway from the postrhinal cortex to the subiculum is likely monosynaptic. In order to substantiate these findings, we carried out several tracer experiments. Anterograde tracer injections in the postrhinal cortex resulted in labeled fibers in limited parts of the subiculum, but no anatomical evidence for a projection of the postrhinal cortex to the dentate gyrus was found. Additional retrograde tracer injections in the subiculum also showed evidence for a direct postrhinal-to-subiculum projection with a strong topological organization. Based on these combined anatomical and electrophysiological data, we conclude that the postrhinal cortex indeed can reach the subiculum via both a direct and an indirect pathway.

Action Potentials↗

PubMed1987

Immunocytochemical localization of dopamine in the prefrontal cortex of the rat at the light and electron microscopical level.

In the present study the dopaminergic innervation of the prefrontal cortex was studied by means of a recently developed anti-dopamine serum. This method can demonstrate endogenous dopamine in a specific way, and offers the opportunity to study the distribution of dopaminergic fibres in the cortex in detail in counterstained sections. Furthermore, dopaminergic nerve endings can be visualized at the electron microscopic level. Light microscopic observations demonstrated that the highest density of dopaminergic fibres in the frontal cortex is found in the prefrontal cortex and the infralimbic cortex. Within the prefrontal cortex, a good correlation is found between regional differences in distribution of dopaminergic fibres and the cytoarchitectonic parcellation of this part of the cortex. Outside the prefrontal cortex dopaminergic fibres were observed in adjacent frontal areas, the cortex surrounding the entire rhinal sulcus and the retrosplenial cortex. Electron microscopic observations demonstrated dopaminergic terminals through all cortical layers. The majority of dopaminergic terminals in the prefrontal cortex from synaptic contacts with dendritic processes. The synaptic profiles were usually symmetric and were characterized by the presence of many clear vesicles and an occasional dense-core vesicle.

Animals↗

PubMed1994

The distribution of tyrosine hydroxylase-immunoreactive fibers in the human entorhinal cortex.

The entorhinal cortex plays an important role in learning and memory, and it has been implicated as a site of dysfunction in some neuropsychiatric disorders such as schizophrenia. The organization of many components of the neural circuitry of this region, including dopaminergic afferents, has not been studied in detail. Using immunohistochemical techniques, we examined the density and laminar distribution of axons immunoreactive for tyrosine hydroxylase, the rate limiting enzyme in catecholamine biosynthesis, in the entorhinal cortex of eight control human brains. The density of tyrosine hydroxylase-containing axons decreased from rostral to caudal regions of entorhinal cortex. In addition, there was a prominent medial to lateral gradient of increasing fiber density. This gradient extended into the adjacent transentorhinal cortex, which contained the highest density of labeled axons of the regions studied. The laminar distribution of tyrosine hydroxylase-containing fibers also differed among the subdivisions of the entorhinal cortex. A bilaminar pattern of labeled axons in layers deep I-superficial II and in deep layer VI was present in the intermediate and caudal subdivisions of entorhinal cortex. In contrast, the olfactory and rostral subdivisions, as well as portions of the transentorhinal region, contained a trilaminar pattern, with a high density of tyrosine hydroxylase-immunoreactive axons in layers deep I-superficial II, deep III-IV and deep VI. In addition, radially-oriented bands of labeled fibers were observed extending between deep layer I and layer III, particularly in the rostral subdivision of the entorhinal cortex. In summary, tyrosine hydroxylase-containing afferents to the human entorhinal cortex are distributed in a characteristic regional and laminar pattern, and the lateral regions of the entorhinal cortex and the adjacent transentorhinal cortex are particularly densely innervated. These data contribute to the understanding of the normal circuitry of the human entorhinal cortex, and are of potential relevance to the pathophysiology of certain neuropsychiatric disorders, such as schizophrenia.

Adult↗

PubMed1999

Emotional and behavioral correlates of the anterior cingulate cortex during associative learning in rats.

Neuronal activity was recorded from the anterior cingulate cortex of behaving rats during discrimination and learning of conditioned stimuli associated with or without reinforcements. The rats were trained to lick a protruding spout just after a conditioned stimulus to obtain reward (intracranial self-stimulation or sucrose solution) or to avoid aversion. The conditioned stimuli included both elemental (auditory or visual stimuli) and configural (simultaneous presentation of auditory and visual stimuli predicting reward outcome opposite to that predicted by each stimulus presented alone) stimuli. Of the 62 anterior cingulate neurons responding during the task, 38 and four responded differentially and non-differentially to the conditioned stimuli (conditioned stimulus-related neurons), respectively. Of the 38 differential conditioned stimulus-related neurons, 33 displayed excitatory (n = 10) and inhibitory (n = 23) responses selectively to the conditioned stimuli predicting reward. These excitatory and inhibitory differential conditioned stimulus-related neurons were located mainly in the cingulate cortex areas 1 and 3 of the rostral and ventral parts of the anterior cingulate cortex, respectively. The remaining 20 neurons responded mainly during intracranial self-stimulation and/or ingestion of sucrose (ingestion/intracranial self-stimulation-related neurons). Increase in activity of the ingestion/intracranial self-stimulation-related neurons was correlated to the first lick to obtain rewards during the task, suggesting that the activity reflected some aspects of motor functions for learned instrumental behaviors. These ingestion/intracranial self-stimulation-related neurons were located sparsely in cingulate cortex area 1 of the rostral part of the anterior cingulate cortex and densely in frontal area 2 of the caudal and dorsal parts of the anterior cingulate cortex. Analysis by the multidimensional scaling of responses of 38 differential conditioned stimulus-related neurons indicated that the anterior cingulate cortex categorized the conditioned stimuli into three groups based on reward contingency, regardless of the physical characteristics of the stimuli, in a two-dimensional space; the three conditioned (two elemental and one configural) stimuli predicting sucrose solution, the three conditioned (two elemental and one configural) stimuli predicting no reward, and the lone conditioned stimulus predicting intracranial self-stimulation. The results suggest that the anterior cingulate cortex is organized topographically; stimulus attributes predicting reward or no reward are represented in the rostral and ventral parts of the anterior cingulate cortex, while the caudal and dorsal parts of the anterior cingulate cortex are related to execution of learned instrumental behaviors. These results are in line with recent neuropsychological studies suggesting that the rostral part of the anterior cingulate cortex plays a crucial role in socio-emotional behaviors by assigning a positive or negative value to future outcomes.

Acoustic Stimulation↗

PubMed2004

[Effect of propofol on the activation of nuclear factor-kappa B and expression of inflammatory cytokines in cerebral cortex during transient focal cerebral ischemia-reperfusion: experiment with rats].

OBJECTIVE: To investigate the effect of propofol on the activation of nuclear factor-kappa B (NF-kappa B) and the expression of inflammatory cytokines, such as interleukin-1 (IL-1), tumor necrosis factor-alpha (TNF-alpha), and intercellular adhesion molecule-1 (ICAM-1) in cerebral cortex during transient focal cerebral ischemia-reperfusion, and to discuss the probable mechanism of its protective effect. METHODS: Ninety male Wistar rats were randomly divided into 3 equal groups: sham operation group undergoing sham operation; ischemia/reperfusion (I/R) group undergoing thread embolism of the left middle cerebral artery occlusion (MCAO) to cause focal ischemia for 2 hours and then undergoing reperfusion; and propofol group undergoing peritoneal injection of propofol 2 hours before the ischemia-reperfusion of MCAO. Then the rats in the 3 groups were re-divided into subgroups of 5 rats, totally 18 subgroups, to be decapitated 2, 3, 6, 12, 24, and 72 hours after reperfusion for the latter 2 groups, and their brains were taken out and fixed. Immunohistochemistry was used to detect the translocation of NF-kappaB in the neurons and the expression of IL-1, TNF-alpha, and ICAM-1 in the brain. Western blotting was used to detect the expression of NF-kappa B. The opposite non-ischemic cortexes were used as controls. RESULTS: Two to 24 hours after the reperfusion NF-kappaB was significantly translocated from the cytoplasm into the nucleus; however, NF-kappa B remained in the cytoplasm of bilateral cortexes in the sham operation groups, and the nonischemic cortexes in the I/R and protofol groups. The translocation of NF-kappa B from cytoplasm into nucleus was significantly inhibited in the ischemic cortex of the propofol group. The expression values of NF-kappa B in the nuclei of ischemic cortexes in the I/R group 2 to 24 hours after reperfusion were significantly higher than those in the sham operation group and the nonischemic cortexes of the I/R and propofol groups (all P < 0.01). The expression values of NF-kappa B in the ischemic cortex of the propofol group 2 to 24 hours after reperfusion was significantly lower than that of the I/R group (all P < 0.05). The expression values of IL-1, TNF-alpha, and ICAM-1 in the ischemic cortexes were significantly higher than that in the cortex of the sham operation group and those in the nonischemic cortexes of the I/R group and propofol group (P < 0.01 or P < 0.05) and the expression values of IL-1, TNF-alpha, and ICAM-1 in the propofol group were all significantly lower than those in the I/R group (all P < 0.05). CONCLUSION: Propofol inhibits the inflammatory reaction by inhibiting the NF-kappa B activation during focal ischemia-reperfusion which may be one of the mechanisms of its neuroprotective function.

Animals↗

PubMed1997

Organization of somatosensory cortex and distribution of corticospinal neurons in the eastern mole (Scalopus aquaticus).

The somatotopic organization of somatosensory cortex of the eastern mole (Scalopus aquaticus) was explored with multiunit microelectrode recordings from middle layers of cortex. The recordings revealed the presence of at least parts of two systematic representations of the body surface in the lateral cortex. One of the representations appears to be primary somatosensory cortex (S1), and it contained cytochrome oxidase dark regions, separated by light septa that formed isomorphs with some body parts. The rostral portion of this presumptive S1 cortex contained a face representation with a series of barrel-like cytochrome oxidase dark ovals that corresponded to the vibrissae on the snout. In caudolateral S1, light septa outline the palm and digits of the forepaw. Cortex caudal to S1, in the expected region of auditory cortex, responded to vibration, suggesting a modification of auditory cortex. Injections of wheat germ agglutinin-horseradish peroxidase into the cervical enlargement of the spinal cord revealed two dense foci of cortical cells that project to the spinal cord. The focus medial to the face region in S1 may correspond to primary motor cortex (M1). The second focus was coextensive with the somatosensory representation of the forelimb and the trunk in S1. The dense corticospinal projections from the forelimb representation of S1 and motor cortex may reflect sensorimotor specializations related to digging behaviors in moles.

Animals↗

PubMed1997

Reevaluation of ipsilateral corticocortical inputs to the orofacial region of the primary motor cortex in the macaque monkey.

An anatomical approach to possible areas in the cerebral cortex involved in somatic motor behavior is to analyze the cortical areas containing neurons that connect directly to the primary motor cortex (MI). To define the cortical areas related to orofacial movements, we examined the distribution of cortical neurons that send their axons to the orofacial region of the MI in the macaque monkey. Injections of retrograde tracers into the electrophysiologically identified orofacial region of the MI revealed that labeled neurons were distributed in the following cortical areas: the orbital cortex (area 12), insular cortex, frontoparietal operculum (including the deep part of the cortical masticatory area and the secondary somatosensory cortex), ventral division of the premotor cortex (especially in its lateral part), orofacial region of the supplementary motor area, rostral division of the cingulate motor area (CMA), and CMA on the ventral bank. A number of labeled neurons were also seen in the MI around the injection sites and in the parietal cortex (including the primary somatosensory cortex and area 7b). No labeled neurons were found in the dorsal division of the premotor cortex. Fluorescent retrograde double labeling further revealed virtually no overlap of distribution between cortical neurons projecting to the orofacial and forelimb regions of the MI. Based on the present results, we discuss the functional diversity of the cortical areas related to orofacial motor behavior and the somatotopical organization in the premotor areas of the frontal cortex.

Animals↗

PubMed2005

Differential connections of the perirhinal and parahippocampal cortex with the orbital and medial prefrontal networks in macaque monkeys.

Previous anatomical studies indicate that the orbital and medial prefrontal cortex (OMPFC) of monkeys is organized into an "orbital" network, which appears to be related to feeding and reward, and a "medial" network, related to visceral control and emotion. In this study, we examined the connections of the orbital and medial prefrontal networks with the perirhinal (areas 35 and 36) and parahippocampal (areas TF and TH) cortex with anterograde and retrograde axonal tracers. The perirhinal cortex is reciprocally connected with orbital network areas Iapm, Iam, Ial, 13m, 13l, 12r, and 11l. In contrast, the parahippocampal cortex is reciprocally connected with the medial network, especially areas around the corpus callosum (areas 24a/b, caudal 32, and 25), and with area 11m. Projections from the parahippocampal cortex also extend to areas 10m, 10o, Iai, and rostral area 32, as well as to dorsolateral areas 9 and 46. In addition, both the perirhinal and parahippocampal cortex are reciprocally connected with areas that are intermediate between the orbital and medial networks (areas 13a, 13b, and 14c) and with the supracallosal area 24a'/b'. Outside the frontal cortex, the perirhinal cortex and the orbital prefrontal network are both interconnected with the ventral part of the temporal pole (TG), area TE and the ventral bank and fundus of the superior temporal sulcus (STS), and the dysgranular insula. In contrast, the parahippocampal cortex and the medial prefrontal network are connected with the dorsal TG, the rostral superior temporal gyrus (STG) and dorsal bank of STS, and the retrosplenial cortex.

Animals↗

PubMed1990

Areal and laminar organization of corticocortical projections in the rat somatosensory cortex.

The present study examines patterns of connectivity between the primary somatosensory cortex of the rat (SI) and surrounding cortical areas also implicated in the processing of somatosensory information. The impetus for the study was the recent reports of major differences in the organization of cortex lateral and caudal to the SI in two other rodent species; the mouse (Carvell and Simons, '86: Somatosens. Res. 3:213-237; '87: J. Comp. Neurol. 265:409-427) and the grey squirrel (Krubitzer et al., '86: J. Comp. Neurol 250: 403-430). Corticocortical connections between the somatosensory areas of the rat parietal cortex were examined by using the combined retrograde and anterograde transport of horseradish peroxidase as well as the retrograde transport of fluorescent tracers. Tracer injections were made into different locations within SI and dysgranular cortex as well as into more lateral regions of parietal cortex. The tangential patterns of distribution both of callosal connections and of cytochrome oxidase activity together provided points of reference in determining the relation between injection sites and the resultant patterns of label. The results indicate that two distinct somatosensory areas, SI and the dysgranular cortex, are interconnected with a further lateral somatosensory area referred to as the second somatosensory area (SII). These projections are organized in a topographic fashion, which we interpret as evidence for a single representation of the body surface in SII. The three somatosensory areas each exhibit unique laminar patterns of ipsilateral corticocortical projection neurons and terminations. In SI, projection neurons are found mainly in layers II, III, and Va, and terminations are largely restricted to the infragranular layers. In the dysgranular cortex, projection neurons and terminations are found in all layers except layer I in which only terminal label is detectable and layer Vb in which notably fewer neurons are labelled. In SII, projection neurons and terminations are found in all layers except layer I and are particularly dense in lower layer III and layer IV. Further, whereas the laminar and areal distributions of ipsilateral and contralateral corticocortical projections largely overlap in both SI and the dysgranular cortex, in SII they tend to be areally segregated. Neurons projecting bilaterally to both ipsilateral and contralateral somatosensory cortex were equally rare in all three somatosensory areas. These results are discussed in relation to the organization of SII in other rodent species, and it is concluded that in the rat, like the mouse, cortex lateral and caudal to SI contains a single representation of the body surface.

Animals↗

PubMed1985

Responses of cat motor cortex neurons to cortico-cortical and somatosensory inputs.

Intracellular techniques were used to investigate a cortico-cortical path from sensory cortex to motor cortex of cats. Cortico-cortical epsps were evoked in motor cortex neurons by microstimulation of area 3a. Epsps with latencies between 1.2 and 2.4 ms were identified as monosynaptic. These short latency cortico-cortical effects were recorded in layers II through VI of the motor cortex. Neurons with monosynaptic cortico-cortical epsps also received excitatory inputs from forelimb nerves, usually from both muscle and cutaneous afferent fibers. The epsps evoked from forelimb nerves in motor cortex neurons were preceded by neural activity in somatosensory cortex. Time delays between arrival of inputs in sensory cortex and in motor cortex were compared to the latencies of cortico-cortical epsps in the same motor cortex neurons. It was apparent that the timing was appropriate for the identified cortico-cortical path to have relayed some sensory inputs to motor cortex.

Animals↗

PubMed1992

Transition from developing to mature patterns of acetylcholinesterase activity in rat visual cortex: implications for the time-course of geniculocortical development.

Patterns of acetylcholinesterase (AChE) histochemical staining in cortical area 17 differ in infant and mature rats. In infants, intense AChE activity is seen as a band corresponding to layer IV and deep layer III of the visual cortex, and this staining is associated with terminal fields of geniculocortical neurons. In adult animals, AChE activity is densest in deep layer IV and layer V and is associated with projections originating in the basal forebrain. The present study investigated the transition from developing to mature patterns of AChE staining in visual cortex. Unilateral lesions were placed in either the lateral geniculate body or the basal forebrain of rats postnatal days 8 (P8) to adulthood; the effects of these lesions on patterns of AChE activity in visual cortex were studied with histochemical techniques and optical densitometry. Lesions involving the lateral geniculate body markedly reduce AChE activity in visual cortex of P12 rats, had moderate effects in P20 rats, and had no apparent effect on AChE activity of visual cortex of rats aged P40 and older. Lesions of basal forebrain had little effect on AChE activity in visual cortex of P12 animals, increasing effect in P15-35 rats, and eliminated much of AChE staining in visual cortex of adults. The period of transition from developing to mature patterns of AChE activity in visual cortex of animals bilaterally enucleated at birth was not different from the period of transition in normally sighted animals. These data indicate that mature patterns of AChE activity in visual cortex are not achieved until well into the second month of life. If transient AChE expression is characteristic of geniculocortical neurons during the period of time in which axons are proliferating within visual cortex, then these data indicate that geniculocortical connections may be forming well into the second month of life in the rat.

Acetylcholinesterase↗

PubMed1991

Distribution of the calcium-binding proteins parvalbumin and calbindin-D28k in the sensorimotor cortex of the rat.

This study examined and compared the immunocytochemical distribution of the two calcium-binding proteins parvalbumin and calbindin-D28k in the primary motor and somatosensory areas of the rat neocortex. Parvalbumin-immunoreactive cells were found in all layers of the cortex except layer 1 and reached their peak density in the middle layers. The two cortical areas differed markedly in the number, cell size and morphology of immunoreactive cells. Parvalbumin-positive cells were more than twice as numerous in the somatosensory cortex compared to the motor cortex. In addition, the average size of their cell bodies was 25-30% larger in the somatosensory area. Parvalbumin cells in the motor area represented several classes of nonpyramidal cells, while the somatosensory cortex contained in addition many large cells with thick vertically oriented primary dendrites. Some of these cells resembled regular or inverted pyramidal neurons. Punctate neuropil labeling was much heavier in the upper layers of the somatosensory than in the motor cortex and was especially heavy in layer 4. Dense parvalbumin-positive perisomatic puncta surrounded large, unstained pyramidal cells in layer 5B of the motor cortex. Calbindin-D28k neuronal staining in both areas was confined to two populations. The most prominent was darkly labeled, small nonpyramidal cells confined to two bands in layers 2/3 and 5/6. There was also a lighter stained population composed of many pyramidal cells distributed throughout layers 2 and 3. In addition, the motor area contained a band of lightly stained, large pyramidal cells in layer 5B. Calbindin-D28k neuropil labeling was heaviest in layers 1 to 3. In contrast to parvalbumin, we found only minor differences in distribution, size and morphology of calbindin-D28k cell body or neuropil staining in the two cortical areas. Double-labeling immunocytochemistry showed that the large majority of immunoreactive cells contained only calbindin-D28k or parvalbumin, but a distinct population of multipolar cells in the upper layers of the somatosensory cortex contained both. The clear parcellation of parvalbumin immunoreactivity in the rat neocortex suggests that parvalbumin is preferentially associated with specific neuronal populations and terminals in the somatosensory cortex. The more general and homogeneous labeling of the upper layers of the cortex indicates that calbindin-D28k could be related to the relatively high density of calcium channels or N-methyl-D-aspartate receptors in the superficial layers of the rat cortex.

Animals↗