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PubMed1987

Behavioural and anatomical studies of the posterior parietal cortex in the rat.

Primates have an area of posterior cortex characterized by multimodal sensory projections to and from the frontal association cortex and a clear behavioural syndrome resulting from lesions to this zone. The posterior association cortex of the rat was examined in two series of experiments, one anatomical and one behavioural, to see if an analogous region could be found. The anatomical connections of Krieg's area 7 in the rat were examined by placing the retrograde tracer, True blue, into the frontal or posterior cortex, and the behaviour of rats with this cortex removed was studied on a variety of tasks. This area appears to be a multimodal sensory association region. It receives projections from striate (area 17), extrastriate (areas 18a and 18b), and somatosensory cortex (area 3). It is also reciprocally connected with the posterior cingulate cortex and two frontal association zones in the medial frontal cortex, namely the anterior cingulate cortex and the frontal eye fields. Lesions produced deficits on tasks of tactile discrimination, and walking a narrow beam, two tasks requiring animals to navigate accurately to a point in space, and a task requiring the association of two spatially discontiguous cues. The animals were not impaired at navigating to a cue or in opening puzzle latches. Overall, the results show that the rat has a sensory association zone that may be analogous to the posterior parietal cortex of primates.

Animals↗

PubMed1984

Corticocortical projections to the prefrontal cortex in the rhesus monkey investigated with horseradish peroxidase techniques.

The corticocortical afferents innervating the prefrontal cortex in the monkey were studied by means of the retrograde axonal transport of horseradish peroxidase. After injection of small amounts (0.3-0.5 microliter) of this enzyme into various parts of the prefrontal cortex, many labeled neurons (mostly pyramids of 15-25 microns in diameter) were found in various cortical regions of the ipsilateral hemisphere. A small part of the prefrontal cortex received fibers from other parts of the same cortex. For example, area 8 receives many fibers from both the rostral part of area 9 and a small area adjacent to the inferior branch of the arcuate sulcus. On the other hand, area 9 in the inferior prefrontal convexity receives fibers from localized parts of areas 8 and 9 in the dorsolateral convexity as well as from area 6. It is also apparent that association connections from the dorsolateral to the inferior convexity are stronger than those going in the opposite direction. The prefrontal afferents from other cortical regions include many fibers originating from the posterior association cortex as well as some fibers arising in the cingulate and orbital gyri. The prefrontal cortex does not receive direct corticocortical fibers from the motor and "primary" sensory cortices. There is a topographic pattern in the prefrontal projections from the cortical walls (STs area) surrounding the superior temporal sulcus. Thus, the caudal half of the STs area projects to area 8 and a small adjacent part of area 9. The dorsal wall of the rostral half of the STs area projects to areas 9-12, the fundus to the inferior convexity, and the ventral wall only to the caudal part of the convexity. Projections from the circumjacent association cortex of the STs area to the prefrontal cortex as well as to the STs area are likewise found to be topographically organized. This suggests that certain parts of the posterior association cortex projecting to particular areas of the prefrontal cortex, also send fibers to those parts of the STs area which project to the same prefrontal areas.

Animals↗

PubMed2000

Kindling causes persistent in vivo changes in firing rates and glutamate sensitivity of central piriform cortex neurons in rats.

The present experiments were undertaken to study whether amygdala kindling induces persistent alterations in the functional status of neurons of the central piriform cortex, a subregion of the piriform cortex identified previously as a site involved in the kindling process. Extracellular, single-unit recordings of piriform cortex neurons were made in anesthetized fully kindled rats at an interval of at least five weeks after the last seizure. Electrode implanted but not kindled rats served as sham controls. An additional group of non-implanted rats was used as naive controls. Spontaneously firing piriform cortex neurons were characterized in all groups by smooth, sharp, biphasic (i.e. positive/negative) action potentials with a duration of 0.8-1.8 ms, and were primarily located at the border between piriform cortex layers II and III. In kindled rats, neurons in the central piriform cortex exhibited a significantly higher firing rate compared to controls. Based on median group values, the increase in basal activity in kindled rats averaged about 90%. The responsiveness of piriform cortex neurons to neurotransmitters was tested by microiontophoretic application of glutamate, N-methyl-D-aspartate and GABA. Piriform cortex neurons of kindled rats exhibited a significantly lower responsiveness to the excitatory effect of glutamate than naive controls. A lowered glutamate responsiveness was also seen in sham controls. No significantly altered transmitter sensitivities of piriform cortex neurons from kindled rats were seen with N-methyl-D-aspartate or GABA. The data indicate that amygdala kindling causes persistent interictal changes in both basal activity and glutamate responsiveness of central piriform cortex neurons which could contribute to the abnormal hyperexcitability characteristic of kindling.

Action Potentials↗

PubMed1998

Increased glomerular capillary pressure and size mediate glomerulosclerosis in SHR juxtamedullary cortex.

To gain insight into the mechanisms in the development of glomerulosclerosis in juxtamedullary cortex, the degree of glomerulosclerosis, glomerular tuft diameter, glomerular capillary pressure (Pgc), and local renal blood flow (RBF) autoregulation were measured in superficial and juxtamedullary cortex of 10- and 70-wk-old spontaneously hypertensive rat (SHR), using aged matched Wistar-Kyoto (WKY) rats as controls. Pgc was measured after corticotomy by direct micropuncture of glomeruli in superficial and juxtamedullary cortex. Total RBF was measured by a transit-time flowmeter (Transonic) and local blood flow by use of laser-Doppler flowmetry. The degree of glomerulosclerosis measured by a semiquantitative histological technique was significantly increased in juxtamedullary compared with superficial cortex in all groups. The difference was most pronounced in the juxtamedullary cortex of 70-wk-old SHR. Pgc was significantly increased in juxtamedullary cortex compared with superficial cortex in 70-wk SHR (57.1 +/- 2.7 vs. 46.5 +/- 0.5 mmHg, P < 0.01). The corresponding data set from 70-wk WKY was 45.5 +/- 0.43 vs. 41.6 +/- 1.5 (P < 0.05). The Pgc in juxtamedullary cortex of 10-wk SHR was slightly higher than in superficial cortex (45.1 +/- 2.3 vs. 50.1 +/- 1.2 mmHg, P = 0.05), whereas there was no difference in 10-wk WKY. Glomerular diameter was larger in juxtamedullary cortex in old animals but not significantly different in 10-wk WKY rats and 10-wk SHR. Total RBF was reset to higher perfusion pressures in hypertensive rats. Juxtamedullary and superficial blood flow autoregulation were not significantly different from total RBF autoregulation in all groups. These results suggest that hypertrophy as well as increased Pgc might contribute to the development of manifest glomerulosclerosis. Changes in local blood flow autoregulation do not seem to play a major role in the development of glomerulosclerosis.

Animals↗

PubMed1996

Kindling-induced epileptiform potentials in piriform cortex slices originate in the underlying endopiriform nucleus.

1. Previous studies in vivo and in vitro have shown that kindling from several locations in the limbic system induces the onset of epileptiform activity in the piriform (olfactory) cortex in the rat. In the present study we tested the hypothesis that kindled epileptiform events in piriform cortex are initiated in the underlying endopiriform nucleus. The experiments were performed in slices taken from rats that were previously kindled by conventional means. 2. Both stimulus-evoked and spontaneous interictal-like epileptiform events were observed in most slices from the anterior piriform cortex, but in few slices from the posterior piriform cortex. These events resembled those described in unanesthetized and urethan-anesthetized rats in previous studies. 3. Findings in support of the hypothesis were as follows. Epileptiform events in the endopiriform nucleus preceded those in the piriform cortex. Epileptiform events could occur in endopiriform nucleus alone, but were only observed in the piriform cortex following occurrence in the endopiriform nucleus. A buildup in population activity preceded the onset of all-or-none epileptiform events in the endopiriform nucleus. Epileptiform events could be triggered by local application of glutamate in the endopiriform nucleus and adjacent claustrum, but not from the piriform cortex. Finally, local application of Co2+ in the endopiriform nucleus, but not in the piriform cortex or elsewhere in the slices, blocked the occurrence of epileptiform events. 4. Additional experiments were performed to further characterize the generation process. 6,7-Dinitroquinoxaline-2,3-dione (DNQX) blocked epileptiform events and the preceding accelerating buildup in multiunit activity at a concentration below that required to block the monosynaptic excitatory postsynaptic potential (EPSP). This suggests that EPSPs mediated by alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors underlie epileptiform events in slices of piriform cortex, and that multisynaptic interactions within the endopiriform nucleus are required for generation of these epileptiform EPSPs. By contrast, block of N-methyl-D-aspartate (NMDA) receptors decreased the amplitude of epileptiform EPSPs but did not block their occurrence, indicating that NMDA receptors contribute to generation but are not required. When membrane potential was depolarized to increase driving force, fast inhibitory postsynaptic potentials were found to consistently accompany the buildup process and epileptiform EPSPs. This indicates that if initiation of epileptiform activity in the endopiriform nucleus results from a compromise in feedback inhibition, this compromise is partial rather than complete. 5. Epileptiform EPSPs in slices of piriform cortex from kindled rats displayed similarities in properties, locus of origin, and mechanism of generation to those previously studied in slices from normal rats in which epileptiform activity was induced by a brief period of bursting activity. These similarities suggest that study of bursting-induced epileptiform EPSPs may provide insight into certain aspects of kindling-induced epileptogenesis.

Amygdala↗

PubMed2000

The promoting effect of eucommiol from Eucommiae cortex on collagen synthesis.

The effect of a methanol extract of Eucommiae Cortex on collagen synthesis was investigated in false aged model rats. Granuloma formation and collagen synthesis were significantly increased by the administration of the methanol extract of Eucommiae Cortex. The effective component of Eucommiae Cortex was then discussed by fractionating the methanol extract of Eucommiae Cortex. Eucommiol, a main component in the water fraction of the methanol extract, was found to be an effective compound. In our previous paper, we reported the promoting effect of Eucommia ulmoides OLIVER leaf on collagen synthesis, and found geniposidic acid and aucubin were the main effective compounds in the leaf. Based on our data in this paper, we clarified that the main effective components of the Eucommia ulmoides OLIVER leaf and Eucommiae Cortex were different. Geniposidic acid and aucubin were reported to be contained at a high concentration in the fresh cortex of Eucommia ulmoides OLIVER, but during the drying process and storage, most of them were destroyed by enzymes in the cortex and very little remained in the Eucommiae Cortex. Therefore, we investigated the effect of the methanol extract of fresh cortex of Eucommia ulmoides OLIVER. A stronger effect than Eucommiae cortex was shown, and geniposidic acid, aucubin and geniposide were concluded to be the main effective components. Although geniposide was found to be an effective compound, when the dose was higher than 50 mg/kg/d, toxicity was shown. The pharmaceutical effect of eucommiol was reported for the first time.

Aging↗

PubMedDate not supplied

[Functional activity of auditory cortex studied with SPECT: methodology validation and application in bilateral profound deafness].

To evaluate the differences in the functional activity of the auditory cortex between normal hearing and profound deafness, a perfusion single photon emission tomography (SPECT) study was designed. SPECT stereotaxic localisation of the auditory cortex was previously validated in 2 brains by means of an anatomical study of the macroscopic localisation and cytoarchitecture of the auditory cortex. Additionally, 15 controls with normal hearing and 30 patients with profound bilateral deafness were scanned using external anatomical point sources (glabela, ineon) for stereotaxic location of the auditory cortex. The normal controls were scanned in auditive deprivation and, in 10 cases, during a monoaural tonal stimulation. Cerebral blood flow relative to cerebellum (relCBF) was assessed in the auditory cortex. The anatomical study showed that mean differences between the true auditory cortex size and the measured SPECT value were less than 2.5 mm. Nevertheless, only the caudal aspect of this area corresponded to the primary auditory cortex in the cytoarchitectonic study. During tonal stimulation, control subjects presented a significant increase of relCBF in the auditory cortex bilaterally, with significant differences in the asymmetry index (contralateral to the side of stimulation). The relCBF in the auditory cortex of controls in deprivation conditions was significantly higher than in deaf patients. There were no significant differences between groups of deaf patients, however the highest values were seen after cochlear implant. SPECT is a suitable method for studying changes in auditory cortex activity relative to different functional conditions, with a possible role in cochlear implant candidates in predicting the future benefit of the implantation.

English Abstract↗

PubMed2001

Temporary inactivation of the retrosplenial cortex causes a transient reorganization of spatial coding in the hippocampus.

The ability to navigate accurately is dependent on the integration of visual and movement-related cues. Navigation based on metrics derived from movement is referred to as path integration. Recent theories of navigation have suggested that posterior cortical areas, the retrosplenial and posterior parietal cortex, are involved in path integration during navigation. In support of this hypothesis, we have found previously that temporary inactivation of retrosplenial cortex results in dark-selective impairments on the radial maze (Cooper and Mizumori, 1999). To understand further the role of the retrosplenial cortex in navigation, we combined temporary inactivation of retrosplenial cortex with recording of complex spike cells in the hippocampus. Thus, behavioral performance during spatial memory testing could be compared with place-field responses before, and during, inactivation of retrosplenial cortex. In the first experiment, behavioral results confirmed that inactivation of retrosplenial cortex only impairs radial maze performance in darkness when animals are at asymptote levels of performance. A second experiment revealed that retrosplenial cortex inactivation impaired spatial learning during initial light training. In both experiments, the normal location of hippocampal "place fields" was changed by temporary inactivation of retrosplenial cortex, whereas other electrophysiological properties of the cells were not affected. The changes in place coding occurred in the presence, and absence, of behavioral impairments. We suggest that the retrosplenial cortex provides mnemonic spatial information for updating location codes in the hippocampus, thereby facilitating accurate path integration. In this way, the retrosplenial cortex and hippocampus may be part of an interactive neural system that mediates navigation.

Action Potentials↗

PubMed1997

Effect of treatment with the neuroactive peptide posatirelin on microanatomical changes of frontal cortex and hippocampus caused by lesions of the locus coeruleus.

The influence of monolateral and bilateral lesions of the Locus coeruleus (LC) on the number of nerve cell and glial fibrillary acidic protein (GFAP)-immunoreactive astrocyte profiles, on silver-gold impregnated fibres and on tyrosine hydroxylase (TH) immunoreactivity was assessed in the rat frontal cortex and hippocampus. The influence of treatment for 4 and 8 weeks with a 10 mg/kg/day dose of the neuroactive peptide posatirelin on the above parameters was also investigated. Lesions of the LC decreased the number of nerve cell profiles in the frontal cortex 8 weeks after lesioning and were without effect on nerve cell profiles in the frontal cortex 4 weeks after lesioning and in the hippocampus at both 4 and 8 weeks after LC lesioning. Glial fibrillary acidic protein (GFAP)-immunoreactive astrocytes were not affected by lesions of LC. Silver-gold impregnated fibres were decreased in the frontal cortex but not in the hippocampus of LC-lesioned rats at 8 weeks after lesioning. TH immunoreactivity, which was localized in nerve fibre-like structures both in the frontal cortex and in the hippocampus was decreased in the frontal cortex and in the hippocampus from the 4th week after LC lesioning. Treatment with posatirelin was without effect on the number of nerve cell and of GFAP-immunoreactive astrocyte profiles at both 4 and 8 weeks after LC lesioning, with the exception of nerve cells of the frontal cortex in monolaterally-lesioned rats which were increased 8 weeks after lesioning. The compound increased silver-gold impregnated fibres in the frontal cortex of monolaterally lesioned rats after 8 weeks of treatment, but did not affect TH immunoreactivity both in the frontal cortex or in the hippocampus. The above results suggest that treatment with posatirelin exerts a neuroprotective effect on the frontal cortex consisting of the partial restoration of some microanatomical changes caused by lesions of LC. The possible significance of this effect is discussed.

Animals↗

PubMed1981

The laminar distribution and ultrastructure of fibers projecting from three thalamic nuclei to the somatic sensory-motor cortex of the opossum.

The projections of the ventrobasal complex (VB), the ventrolateral complex (VL), and the central intralaminar nucleus (CIN) to the somatic sensory-motor (SSM) cortex of the Virginia opossum were studied with light and electron microscopic autoradiographic methods. VB, VL, and CIN have overlapping projections to SSM cortex and each one also projects to an additional cortical area. Unit responses to somatic sensory stimulation and the areal and laminar distribution of axons in cortex is different for VB, VL, and CIN, but the axons from each form similar round asymmetrical synapses, predominantly with dendritic spines. As in other mammals, VB units in the opossum have discrete, contralateral cutaneous receptive fields. VB projects somatotopically to SSM cortex and also projects to the second somatic sensory representation. Within the cortex, VB axons terminate densely in layer IV and the adjacent part of layer III. A few axons also terminate in the outermost part of layer I and the upper part of layer VI. Most VB axons terminate upon dendritic spines (86.6%), but they also contact dendritic shafts (10%) and neuronal cell bodies (3%). Neurons in VL have no reliable response to somatic stimulation under our recording conditions. VL projects to the SSM cortex and to the posterior parietal area. Throughout this entire projection field VL fibers terminate in layers I, III, and IV most densely, and sparsely in the other cortical layers. The density of termination in the mid-cortical laminae is quite sparse compared to VB, but the projection to layer I is considerably greater. Nearly all (93%) of VL axons contact dendritic spines, the remainder (7%) end on dendritic shafts. CIN is a thalamic target of ascending medial lemniscal, cerebellar, spinal, and reticular formation axons. Neurons in CIN respond to stimulation restricted to a particular body part, but typically responses may be evoked from larger areas and at longer latencies than neurons in VB that are related to the same body part. CIN neurons require a firm tap or electrical stimulation within their receptive field to elicit a response in the anesthetized preparation. CIN axons terminate throughout the entire parietal cortex, but unlike VB and VL, CIN fibers end almost exclusively in the outer part of layer I. Approximately 21% of CIN fibers contact dendritic shafts in layer I, which is twice the percentage of shafts contacted by VL or VB axons. All of the other CIN synapses are formed with dendritic spines. These experiments demonstrate three different pathways to SSM cortex. The results suggest that each projection has a unique role in controlling the patterns of activity of neurons within the SSM cortex.

Animals↗

PubMed1983

Afferent and efferent pathways of the vibrissal region of primary motor cortex in the mouse.

The afferent and efferent connections of the vibrissal representation within the mouse primary motor cortex (MsI) were identified by using the retrograde transport of horseradish peroxidase (HRP) and the anterograde transport of tritiated amino acids injected into MsI. Following aldehyde perfusion brains were frozen-sectioned at 40 microns and reacted for HRP using the 3-3' diaminobenzidine-cobalt chloride technique of Adams ('77). Alternate HRP reacted sections were processed for autoradiography. HRP-filled pyramidal cell somata and concentrations of developed silver grains above background levels were observed in both the vibrissal area of primary somatosensory cortex (SmI) cortex (i.e., the posteromedial barrel subfield; PMBSF cortex) and in the face region of SmII (area 40). In both regions labeled somata occurred predominantly in cortical layers II-III and V. Autoradiographic label was superimposed over the regions containing labeled somata but exhibited a less distinct laminar organization. A dense reciprocal projection connected the injection site with the homotopic area in contralateral MsI; somata occurred for the most part in layers III and V. Developed silver grains were uniformly dispersed over the area containing labeled cell bodies. HRP-labeled pyramidal somata were noted in contralateral PMBSF cortex, but no silver grains occurred in this region. Reciprocal projections linked MsI cortex with the ipsilateral thalamic nuclei: ventralis pars lateralis (VL) and centralis pars lateralis (CL) and with the zona incerta (ZI). Labeled cell bodies and developed silver grains were more dense in VL than in CL. The ipsilateral striatum and thalamic reticular nucleus (NRT) received afferents from the motor cortex but did not project to it. Thus, the vibrissal area of primary motor cortex is connected with a number of cortical and subcortical structures, each of which has been shown to play a role in motor performance. Identification of the afferent and efferent pathways of MsI cortex will now enable further investigation of the ultrastructural and synaptic organization of the vibrissal area of MsI.

Afferent Pathways↗

PubMed1988

Organization and synaptic relationships of the projection from the primary sensory to the primary motor cortex in the cat.

It is known from previous studies that fibers originating from cells in area 2 of the cat primary somatosensory cortex project topographically to area 4 of the motor cortex and that they terminate preferentially in the caudal region of the cruciate sulcus. We examined this pathway to determine more precisely the distribution pattern of fibers and the laminar arrangement of axon terminals in the motor cortex. The recently developed technique of PHA-L staining enabled us to label anterogradely the axons that form this projection. Iontophoretic injections of PHA-L were made into the rostral bank of the ansate sulcus (area 2). After 7 days the cats were perfused and the tissue was processed immunohistochemically to stain the PHA-L filled fibers. Light microscopic examination revealed that a small cluster of cells in the sensory cortex gave rise to multiple foci of labeled axons in area 4. The labeled fibers formed columnlike arrays, which were located for the most part in the posterior bank of the cruciate sulcus and were separated by irregular intervals of cortex devoid of labeled fibers. Clusters of labeled fibers were also found in the anterior region of the cruciate sulcus in some of the animals. The dimensions of the labeled areas and the small number of cells that gave rise to each group of fibers suggested that axonal branches of cells within the injection site formed the multiple foci. Variations in the immunohistochemical staining enabled us to study the laminar distribution of sensory cortex axon terminals with the electron microscope. Whereas some PHA-L labeled terminals were found in the deep cortical layers, the majority (82%) were spread throughout layers I-III. Differences in the laminar distribution of sensory cortex afferents that formed axodendritic or axospinous synapses were noted. Synapses formed with dendritic shafts were relatively sparse (28%) and were confined to the superficial layers. Some of the more numerous axospinous synapses, which accounted for 72% of identified synapses, were found in layers V and VI, although most were in layers I-III. The distribution pattern of terminals showed little variation between columns in different areas of the motor cortex, including that in the anterior cruciate region. The pattern of termination of the sensory to motor cortex projection is discussed in relation to the physiological characteristics of this pathway.

Animals↗

PubMed1994

Interconnections between the prefrontal cortex and the premotor areas in the frontal lobe.

We examined interconnections between a portion of the prefrontal cortex and the premotor areas in the frontal lobe to provide insights into the routes by which the prefrontal cortex gains access to the primary motor cortex and the central control of movement. We placed multiple injections of one retrograde tracer in the arm area of the primary motor cortex to define the premotor areas in the frontal lobe. Then, in the same animal, we placed multiple injections of another retrograde tracer in and around the principal sulcus (Walker's area 46). This double labeling strategy enabled us to determine which premotor areas are interconnected with the prefrontal cortex. There are three major results of this study. First, we found that five of the six premotor areas in the frontal lobe are interconnected with the dorsolateral prefrontal cortex. Second, the major site for interactions between the prefrontal cortex and the premotor areas is the ventral premotor area. Third, the prefrontal cortex is interconnected with only a portion of the arm representation in three premotor areas (supplementary motor area, the caudal cingulate motor area on the ventral bank of the cingulate sulcus, and the dorsal premotor area), whereas it is interconnected with the entire arm representation in the ventral premotor area and the rostral cingulate motor area. These observations indicate that the output of the prefrontal cortex targets specific premotor areas and even subregions within individual premotor areas.

Amidines↗

PubMed1996

Regional differences in the ontogeny of the serotonergic projection to the cerebral cortex.

We used light and electron microscope immunocytochemistry to compare the development of the pattern of innervation and synaptic organization of the serotonin (5-HT) afferent system in sensory (visual and somatosensory) and motor areas of the rat cerebral cortex. Serotonin-labeled fibers were present in all cortical areas at birth appearing as two tangential streams, one above and one below the cortical plate. These fibers gradually arborized sending branches into all cortical layers in an "inside-out" sequence that broadly paralleled the gradient of neurogenesis and differentiation in the cortex. A striking feature at the early stages of postnatal development of the visual and somatosensory cortex was the transient presence of a dense accumulation of 5-HT fibers in layer IV. In agreement with earlier reports, transient aggregations of serotonergic axons characterized sensory but not motor areas of the cortex. The innervation pattern characteristic of the adult cortex was attained by the end of the 3rd postnatal week. Electron microscopic analysis of the developing visual cortex showed that 5-HT-containing axonal varicosities formed synaptic contacts, predominantly of the asymmetrical variety, throughout postnatal life. The proportion of varicosities forming synapses increased gradually from birth to reach a peak at the end of the 2nd week, then declined markedly in the subsequent week before rising again at later stages. It appears that the formation of exuberant synapses by 5-HT axons coincides with the period of maturation of the neuronal circuitry of this cortical area. When quantitative analysis was restricted only to layer IV, the proportion of varicosities forming synapses reached a peak at the end of the 1st week of life, when transient innervation was most prominent in this layer. These results suggest that the effects of this dense band of serotonergic axons may be mediated through axodendritic synapses. The types of postsynaptic elements involved in the formation of synapses varied according to age, suggesting progressive morphological differentiation of cortical target neurons or, alternatively, a continuous process of removal and establishment of new connections by 5-HT axons in the visual cortex. In contrast, analysis in the motor cortex revealed a continuous increase in the proportion of 5-HT varicosities engaged in synaptic contacts from birth to the late sages of development. The results presented here provide anatomical evidence for a differential role of 5-HT in the maturation of the cerebral cortex.

Age Factors↗

PubMed1979

Peripheral input pathways projecting to the motor cortex in the cat.

The possibility that the motor cortex receives peripheral input directly from the thalamus was examined using the evoked potential method and the following results were obtained. Potentials in the motor cortex evoked by stimulation of superficial radial (SR) or group II deep radial (DR) nerve were neither abolished nor delayed by ablation of the sensory cortex. Potentials in the motor cortex evoked by stimulation of group II DR nerve were most severely reduced by interruption of the spinocervcial tract. Potentials evoked by stimulation of SR nerve were more severely reduced in the sensory cortex than in the motor cortex by section of the dorsal funiculus or cooling of the cuneate nucleus. The size of evoked potentials in the motor cortex increased rapidly when stimulus intensity to DR nerve exceeded the threshold to group II fibers. The results suggest that some inputs from the SR and group II DR nerves reach the motor cortex without a relay through the sensory cortex.

Animals↗

PubMedDate not supplied

Laminar, tangential and regional organization of the noradrenergic innervation of monkey cortex: dopamine-beta-hydroxylase immunohistochemistry.

An antiserum directed against human dopamine-beta-hydroxylase purified from pheochromocytoma tissue was employed in an immunohistochemical study of the organization of the noradrenergic innervation of monkey neocortex. A detailed description is given of the laminar pattern of noradrenergic innervation in the dorsolateral prefrontal cortex (Brodmann areas 9 and 10) and the primary somatosensory cortex of the postcentral gyrus (Brodmann areas 3,1,2). The noradrenergic innervation of these two regions is similar in the following respects: (1) fibers are present in all six layers, (2) the innervation is dense and terminal-like in layers IV and V, and (3) layer VI is characterized by fibers oriented parallel to the pial surface which follow the contours of the subcortical white matter. However, these regions differ with respect to specific laminar patterns of fiber distribution and orientation and by virtue of the fact that the primary somatosensory cortex has a very dense noradrenergic innervation, while the density of innervation in dorsolateral prefrontal cortex is low relative to the postcentral gyrus and most other neocortical areas. The laminar pattern of noradrenergic innervation in primary visual cortex differs fundamentally from both prefrontal and primary somatosensory cortices. In a separate series of experiments, dorsolateral frontal cortex lesions were used to investigate the intracortical trajectory of noradrenergic fibers. A discrete aspiration lesion confined to the grey matter of the prefrontal cortex led to a substantial loss of noradrenergic fibers in cortical regions caudal to the lesion. The decrease in density of noradrenergic innervation was particularly pronounced in the pre- and postcentral gyri. These results demonstrate that while the noradrenergic innervation of primate cortex exhibits a far greater degree of regional variation than is present in the rat cortex, the tangential intracortical trajectory that is characteristic of the lissencephalic rat brain is also a dominant feature of the noradrenergic innervation of the gyrencephalic primate brain.

Adrenergic Fibers↗

PubMed2001

Identification of the source of the bilateral projection system from cortex to somatosensory neostriatum and an exploration of its physiological actions.

Microinjections of cholera toxin B subunit were made into the area of the neostriatum that receives input from the primary somatosensory barrel cortex (SI) in the rat. Studies of the cortices then allowed retrograde identification of the cortical cells supplying the striatal input. When injections were restricted to the neostriatum, retrograde labelling was found in layer V of both SI cortices. Ipsilateral to the injection, cells were retrogradely filled with toxin in all parts of the barrel field, in adjacent parietal cortex, in the motor cortex and in prefrontal areas. A similar distribution across cortical areas was seen contralaterally; however, the stained cells in the SI were between rather than within barrel columns. An earlier anterograde study suggested two inputs from the SI to the neostriatum. The present results indicate that one input to the somatosensory area of the neostriatum arises bilaterally from neurons between the barrels of the SI, while the topographic pathway from below the barrels is present only ipsilaterally. These anatomical results indicate that separate stimulation of the two corticostriatal pathways from the barrel cortex is possible. Electrical stimulation of the contralateral cortex will activate the bilateral pathway, while electrical stimulation of the whisker pads activates the barrels and hence the topographic pathway. Neurons in the somatosensory region of the striatum responded to stimuli in the contralateral cortex and in the contralateral whisker pad. In spite of very different path lengths, stimuli via the two routes gave rise to excitatory postsynaptic potentials in the striatal cells with similar latencies. The excitatory postsynaptic potentials to whisker pad stimulation had a rapid rise time and usually resulted in at least one action potential. Responses to stimulation of the contralateral cortex rose to a peak more slowly and were more variable in latency, but also gave rise to an action potential in the majority of cases. All the neurons had the physiological characteristics of medium-sized densely spiny cells and after intracellular filling with biocytin had the appropriate morphology. In summary, we propose that two corticostriatal pathways arise from layer V cells in the barrel area of the somatosensory cortex; one is bilateral and arises from cells mainly below the septa, while a topographical pathway arises from cells below the barrels. Both pathways can raise the spiny output cells of the striatum to firing threshold. The latencies from the contralateral cortex imply slowly conducting fibres with considerably more temporal dispersion than the pathway from below the barrels, which we excited from the contralateral periphery.

Animals↗

PubMed1999

Integrity of the mesocortical dopaminergic system is necessary for complete expression of in vivo hippocampal-prefrontal cortex long-term potentiation.

The prefrontal cortex receives dopaminergic inputs from the ventral tegmental area and excitatory inputs from the hippocampus. Both afferent pathways target in close proximity dendritic spines of pyramidal cells in layer V-VI of the prefrontal cortex. In view of the prominent role of dopamine in cognitive functions we examined the effects of ventral tegmental area stimulation on the induction of long-term potentiation in the hippocampal-prefrontal cortex pathway of anesthetized rats. Stimulation of the ventral tegmental area at a frequency known to evoke dopamine overflow in the prefrontal cortex produces a long-lasting enhancement of the magnitude of the hippocampal-prefrontal cortex long-term potentiation. The role of dopamine was further examined by investigating the effects of prefrontocortical dopamine depletion induced by an electrolytic ventral tegmental area lesion. A significant correlation (r = 0.8; P < 0.001; n = 14) was obtained between cortical dopamine levels and cortical long-term potentiation amplitude, a depletion of more than 50% of cortical levels corresponding to a dramatic decrease in hippocampal-prefrontal cortex long-term potentiation. However, a recovery to normal long-term potentiation was observed 1 h after tetanic stimulation. In contrast to the effects on long-term potentiation, ventral tegmental area stimulation, when applied at low or high frequency, decreases the amplitude of the hippocampal-prefrontal cortex postsynaptic synaptic response. The present study demonstrates the importance of the integrity of the mesocortical dopaminergic system for long-term potentiation to occur in the hippocampal-prefrontal cortex pathway and suggests a frequency-dependent effect of dopamine on hippocampal-prefrontal cortex transmission.

Animals↗