摘要:

AbstractNorepinephrine has been implicated in the regulation of a number of cortical functions, yet relatively little is known about the anatomical organization of noradrenergic axons in the expanded and highly differentiated prefrontal cortex of primates. In this study, the distribution of fibers containing dopamine‐ß‐hydroxylase (DBH), the enzyme that converts dopamine to norepinephrine, was characterized immunohistochemically in the prefrontal cortical regions of Old World cynomolgus monkeys (Macaca fascicularis) and New World squirrel monkeys (Saimiri sciureus). In both species, differences in the density of DBH‐labeled fibers were detected both across and within many prefrontal cytoarchitectonic regions. In cynomolgus monkeys, area 8B had the greatest density of DBH‐immunoreactive fibers; within this region, the medial surface had a greater density of labeled processes than the dorsal surface. Areas 9 and 24 also had a high density of DBH‐labeled fibers, areas 11, 12, 13 and 25 were of intermediate density, and portions of areas 10 and 46 had the lowest density of immunoreactive fibers. Regional differences in the density of DBH‐immunoreactive fibers were also present in squirrel monkey prefrontal cortex.Despite the regional variations in the density of DBH‐immunoreactive fibers, the laminar distribution of these fibers was very similar across cytoarchitectonic areas of cynomolgus prefrontal cortex. Layer I contained a low density of labeled fibers which were primarily tangential in orientation. The predominantly radially oriented fibers in layers II‐IV were slightly higher in density. The density of both radially and tangentially oriented immunoreactive fibers increased substantially in layer V. Fiber density decreased in layer VI; a band of tangentially oriented fibers was present in the deep portion of this layer. With a few exceptions, the laminar distribution of DBH‐immunoreactive fibers in the prefrontal regions of squirrel monkey cortex was similar to that of cynomolgus monkey.Since other data suggest that anti‐DBH selectively labels noradrenergic axons in monkey neocortex, the distinctive innervation patterns exhibited by DBH‐immunoreactive fibers reveal the regions and layers that may be the principal sites of action of norepinephrine in exerting its effects on prefro

ISSN:0092-7317    

DOI:10.1002/cne.902820302

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractIn a systematic attempt to trace all projections from the brainstem and diencephalon to the pontine nuclei of the cat, implantations and injections of horseradish peroxidase‐‐wheat germ agglutinin (HRP‐WGA) or Fluoro‐Gold were placed in the pontine nuclei of 21 cats. In most of the cases there was no evidence of spread of tracer outside the pontine nuclei. Retrogradely labeled cells in the brainstem and diencephalon were carefully mapped and counted.The number of labeled cells in the brainstem and diencephalon ranged from 24 in cases with very small implantations to 3,490 in cases with large injections in the pontine nuclei (counts from every fifth section). The labeled cells are located bilaterally with an ipsilateral preponderance. After large injections, 25‐38% of the labeled cells were located in the brainstem reticular formation, 10‐16% in the pretectal nuclei, 10‐15% in the hypothalamus, 7‐9% in the zona incerta, 3‐9% in the fields of Forel, 4‐5% in the nucleus locus coeruleus, 3‐5% in the ventral lateral geniculate body, 2‐4% in the superior colliculus, 3% in the periaqueductal gray, and 14‐15% in other parts of the brainstem.Judging from cases with small tracer deposits entirely confined to the pontine nuclei, there appear to be two types of subcortical inputs: Projections from the reticular formation, the nucleus locus coeruleus, the periaqueductal gray, and the raphe nuclei are widespread, presumably reaching all parts of the pontine nuclei, while projections from a diversity of other sources are localized, reaching limited parts of the pontine nuc

ISSN:0092-7317    

DOI:10.1002/cne.902820303

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractThe corticospinal tract (CST) of the rat undergoes a prolonged period of postnatal development. Lesions of the presumptive CST pathway at birth are followed by the aberrant rerouting of the developing corticospinal axons around the lesion site through adjacent undamaged CNS tissue. This developmental plasticity becomes severely restricted by 5‐6 days of age, so the axons are no longer capable of growth around the site of injury. The aim of the current study was to determine whether altering the environment at the site of injury by filling the lesion with transplanted fetal spinal cord tissue could prolong the critical period for developmental plasticity of the corticospinal pathway. The spinal cord was damaged (overhemisection) at three stages in the development of the corticospinal (CS) pathway: 1) prior to the arrival of CS axons, 2) after the axons elongated through the cord but prior to synaptogenesis, and 3) after both axonal elongation and synaptogenesis were completed. One to 9 months later, anterograde neuronal tracing with horseradish peroxidase was used to assess the growth of the corticospinal pathway with or without a fetal transplant at the site of injury, and the pattern of labeling was compared with that observed in adult nonlesioned control animals. Our results indicate that the presence of a transplant prolongs the critical period for developmental plasticity of the CST. Transplants elicited growth of CST axons throughout the postnatal period examined. CST axons damaged prior to synaptogenesis exhibited more robust growth than those lesioned after synaptogenesis had been completed. These results suggest that both environmental and neuronal factors interact to regulate the response of immature CS neurons to injur

ISSN:0092-7317    

DOI:10.1002/cne.902820304

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractThe developing uncrossed retinocollicular projection in the Syrian hamster undergoes a characteristic set of changes during the first 2 postnatal weeks. The retinal fibres, which initially project across the whole superior colliculus, withdraw from the caudal part and their terminals become clustered into deep, discrete clumps rostrally. Coincident with these afferent changes, there is substantial retinal ganglion cell death. To examine whether neuronal activity plays a role in these changes, we made daily injections of the sodium channel blocker tetrodotoxin (TTX) into one or both eyes from postnatal day 2 or 4 up to day 12.Following TTX treatment, the uncrossed terminals retracted on schedule from the caudal and superficial parts of the superior colliculus and came to lie, as normal, in the deep layers rostrally. Within the rostral superior colliculus, however, the uncrossed terminals from TTX‐injected eyes lost their characteristic patchy distribution and were arranged diffusely. When only one eye received TTX injections, this inhibiting effect on terminal segregation was seen only in the projections from the TTX‐treated eye. The effect of TTX treatment on terminal segregation was much less severe than that of unilateral enucleation, after which uncrossed terminals persist throughout the entire superior colliculus.TTX injections appeared to have little effect on overall ganglion cell death since the total number of ganglion cells in the crossed projection from TTX‐treated eyes was similar to that in normal eyes. However, the relative distribution of uncrossed cells in temporal and nasal retina was altered. In eyes that received TTX injections, the proportion of uncrossed cells in nasal retina was about 1.6 times that in normal animals and was close to the proportion seen in unilaterally enucleated animals. This increase in the treated eye occurred whether one or both eyes were injected with TTX.We conclude that neuronal activity plays a role in the segregation of uncrossed terminals into discrete clumps in rostral colliculus and in the preferential elimination of uncrossed cells from the nasal retina. The inactive uncrossed projections from TTX‐treated eyes showed the greatest degree of disruption. The extent of the disruption was similar whether the crossed input from the other eye was active or inactive. This suggests that the activity‐driven interactions between ganglion cells within one eye are more significant than those between the two eyes in shaping the final form of the uncrossed retinocollicular p

ISSN:0092-7317    

DOI:10.1002/cne.902820305

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractThe morphology of jaw‐muscle spindle afferents in the rat has been studied by intra‐axonal injection of horseradish peroxidase. All stained axons were located in the motor root of the trigeminal nerve and could be traced dorsomedially to the vicinity of the trigeminal motor nucleus, where they divided into an ascending branch in the tract of the mesencephalic nucleus and a descending branch in the tract of Probst. Axon collaterals and swellings on fine collateral branches presumed to be synaptic boutons were located in the following regions: the trigeminal motor nucleus, the region dorsal to the trigeminal motor nucleus including the supratrigeminal nucleus, the parvicellular reticular formation immediately caudal to the trigeminal motor nucleus, the reticular formation at the level of the facial nucleus, and the caudal portion of the mesencephalic nucleus. No evidence of a projection to the cerebellum was observed. Boutons were most numerous in the region surrounding the trigeminal motor nucleus, especially dorsally. Here they were not demonstrated in close proximity to counterstained cells, and therefore it was not possible to determine how many of these contacts are located on cells in this region and how many are on the distal dendrites of trigeminal motorneurons. Boutons located within the trigeminal motor nucleus were always confined to a small portion of the nucleus and were significantly larger than those located dorsally. Some boutons were found in close apposition to trigeminal motor‐neurons and presumably make somatic contacts. These results suggest that jaw‐muscle spindle afferents make somatic and proximal dendritic contacts with only a limited number of trigeminal motorneurons and also project to masticatory interneuronal regions dorsal and caudal to the motor

ISSN:0092-7317    

DOI:10.1002/cne.902820306

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractWe have recorded from a small neuron in layer 1 of the striate visual cortex in a 34‐day‐old kitten. It had a simple, orientation‐selective receptive field that was nondirectional and showed length summation. The neuron was injected intracellularly with horseradish peroxidase. Computer‐aided reconstruction revealed that it had a dense axonal plexus confined to layer 1, elongated in the anteroposterior dimension. By means of an antibody directed against a GABA‐like antigen, and postembedding immunocytochemistry, the neuron was found to be strongly immunoreactive. The main input to soma and dendrites of the neuron was from synapses that were not GABA‐L‐immunoreactive, and probably originated from pyramidal cells. The axon of the cell formed synapses on dendritic shafts and spines, whose most likely sources were the apical tufts of pyramidal cell dendrites. These data suggest that such neurons may be involved in local circuits that contribute to the formation of pyramidal cell rec

ISSN:0092-7317    

DOI:10.1002/cne.902820307

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractThe cytoarchitecture of the prearcuate gyrus, including the region of the physiologically defined frontal eye fields (FEF), was studied in four macaque monkeys (Macaca fascicularis, M. mulatta) to determine if the FEF could be anatomically identified. Brain sections were stained with standard Nissl and, in some cases, myelin stains.Two nonstandard planes of section were used: one tangential to the prearcuate gyrus and the second normal to the most posterior bend of the prearcuate gyrus. The first plane of section was advantageous for studying the location of the FEF with reference to the entire medial‐lateral extent of the gyrus and the second allowed good comparisons of the FEF to adjacent anterior and posterior cortical areas. Frontal plane sections through the prearcuate gyrus were also examined in 15 macaque monkeys for comparison with sections cut normal to the posterior bend of the gyrus and tangential to the gyrus.Intracortical microstimulation was performed in three monkeys. The FEF was defined as the area from which low‐threshold (≤50 μA) saccades could be evoked. The area extended about 10 mm along the anterior bank of the arcuate sulcus. Within the area, saccade amplitudes were represented in a mediolateral, large‐to‐small topography. No topography of saccade direction was noted within FEF but reversals of saccade direction for any given electrode pass were found. These results confirm the results from our earlier mapping study of FEF (Bruce et al.:J. Neurophysiol. 54:714‐734, '85).Cell bodies of large pyramidal cells in layers III and V of the prearcuate gyri from three hemispheres were measured with the aid of an image‐combining computer microscope. The distribution of cells of>22 μm diameter or cross‐sectional areas of<500 μm2were plotted. In one monkey, marker lesions made at microstimulation sites within the FEF or in adjacent non‐FEF areas were also plotted. The location of the FEF appeared to coincide with the concentration of large layer V pyramidal cells in the prearcuate gyrus rather than with any previously mapped cytoarchitectonic area. The numbers of large pyramids in layer V were noticeably reduced along the lip of the prearcuate gyrus and at dorsomedial and ventrolateral locations which were outside the physiol

ISSN:0092-7317    

DOI:10.1002/cne.902820308

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractFluorescent retrograde tracing techniques were employed in a double‐labelling paradigm to determine the distribution of corticospinal, corticotectal, and corticotrigeminal projection neurons in layer Vb of the adult and neonatal rat somatosensory cortex. The double‐labelling paradigm allowed a direct comparison of the cortical distribution of neurons projecting to each target and identification of neurons projecting to more than one target.In the adult rat, each population of projection neurons was found to have a unique laminar and/or areal distribution. Corticospinal projection neurons were located throughout the width of layer Vb in the medial granular portion of somatosensory cortex, while corticotrigeminal projection neurons were distributed throughout the width of layer Vb in the more laterally located dysgranular portion of somatosensory cortex. Corticotectal projection neurons were located more superficially in layer Vb than either corticospinal or corticotrigeminal projection neurons and found scattered throughout both dysgranular and granular somatosensory cortex. Each combination of subcortical injections also resulted in double labelling a small percentage of uniquely distributed neurons. These distribution differences coupled with measurements of cell size allowed us to identify the parent population of the dual projection neurons. Subpopulations of corticotectal neurons also project to the brainstem trigeminal complex and to the spinal cord. Subpopulations of corticotrigeminal neurons also project to the spinal cord, and a proportion of corticotrigeminal neurons projects to at least two targets within the brainstem trigeminal complex (nucleus principalis and subnucleus interpolaris). In the adult rat, corticospinal neurons (as defined by either laminar position or somal size) did not appear to give off collaterals to either the superior colliculus or brainstem trigeminal complex.In the neonatal rat, double‐labelled neurons which project to both the spinal cord and the tectum are distributed throughout the full width of layer Vb, rather than restricted to the superficial portion of the layer as in the adult rat. Further, it appears as if the ontogenetic change in the laminar distribution of corticospinal and tectal projection neurons is achieved by mechanisms of selective process elimination rather than cell death.These results are discussed in terms of both the developmental factors which may contribute to the discrete distribution of cortical projection neurons found in the adult and the functional significance of bifurcating projection ne

ISSN:0092-7317    

DOI:10.1002/cne.902820309

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractIt has been reported previously that neurons in the dorsal lateral geniculate nucleus (LGN) of cats with neonatal damage to visual cortex (KVC cats) have receptive fields that are abnormally large and that the receptive fields of these neurons sometimes do not appear to conform to the normal retinotopic order in the LGN. A primary aim of this study was to determine if these physiological abnormalities are related to inappropriate patterns of retinogeniculate connections.We therefore have analyzed the terminal arbors of retinogeniculate axons in adult cats that had received a lesion of visual cortex (areas 17, 18, and 19) on the day of birth. Single retinogeniculate axons were characterized physiologically and injected intracellularly with horseradish peroxidase. Consistent with earlier reports that neonatal removal of visual cortex results in a retrograde loss of retinal X‐cells, all of the retinogeniculate axons that we recorded were from Y‐cells. While the visual responses of these Y‐cell axons were normal, the morphology of their terminal arbors in the LGN was abnormal. Retinal Y‐cell axons in KVC cats have terminal fields in the A laminae of the LGN that are as large or larger than those of normal Y‐cells. However, since the LGN in KVC cats is severely degenerated, single Y‐cell arbors occupy a proportional volume of the LGN that is 12 times greater than normal. Thus an early lesion of visual cortex produces a severe mismatch between retinogeniculate axon arbor size and target size. Also, despite the normal size of retinogeniculate axon arbors in KVC cats, the number and density of terminal boutons are greatly decreased.Thus our morphological results suggest that the unusually large receptive fields of LGN cells in KVC cats and the relative lack of retinotopic precision in the LGN are due, at least in part, to anomalies in the relative size and distribution of retinogeniculate axon arbors that develop after neonatal removal of vi

ISSN:0092-7317    

DOI:10.1002/cne.902820310

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractWe have examined the effect of restricted unilateral cochlear lesions on the orderly topographic mapping of sound frequency in the auditory cortex of adult guinea pigs. These lesions, although restricted in spatial extent, resulted in a variety of patterns of histological damage to receptor cells and nerve fibres within the cochlea. Nevertheless, all lesions resulted in permanent losses of sensitivity of the cochlear neural output across a limited frequency range. Thirty‐five to 81 days after such damage to the organ of Corti, the area of contralateral auditory cortex in which the lesioned frequency range would normally have been represented was partly occupied by an expanded representation of sound frequencies adjacent to the frequency range damaged by the lesion. The thresholds at their new characteristic frequencies (CFs) of clusters of cortical neurones in these regions were close to normal thresholds at those frequencies (mean difference across all animals was 3.8 dB). In a second series of experiments, the responses of neurone clusters were examined within hours of making similar cochlear lesions. It was found that shifts in CF toward frequencies spared by the lesions could occur, but thresholds were greatly elevated compared to normal (mean difference was 31.7 dB in five animals). The emergence of sensitive drive in such regions after prolonged recovery periods in lesioned animals thus suggests that the auditory cortical frequency map undergoes reorganization in cases of partial deafness. Some features of this reorganization are similar to changes reported in somatosensory cortex after peripheral nerve injury, and this form of plasticity may therefore be a feature of all adult sensory system

ISSN:0092-7317    

DOI:10.1002/cne.902820311

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY