摘要:

AbstractIntracellular recordings were made from frog retinal ganglion cell axons in the optic nerve. Following electrophysiological characterisation of receptive field properties, HRP was injected into the axon, and the brain and retina were subsequently stained. The morphologies of retinal ganglion cells, their dendritic domains, and their central projections were determined with light microscopy, and the optic nerve portion of the ganglion cell axon was examined with electron microscopy. This paper describes the structural and functional features of one ganglion cell class, the off units (class IV or dimming detectors) whose characteristic response is a preferential sensitivity to decreasing light intensity within the receptive field. Typical receptive field diameter of these units was about 16° with a range of 3° to more than 30°. Examination of the spatial characteristics of their receptive field centers and surrounds showed that the class IV cells could be divided into two broad categories. Linear class IV cells did not respond to phase‐reversal of a fine grating pattern. These linear cells also tended to have clear surround suppression: illumination of the surround diminished their response to light off at the center. The second group responded briskly to each reversal of the fine grating pattern, whatever its position within the receptor field center. These nonlinear class IV cells did not show surround suppression, but rather they had surround antagonism and they responded to light on in the surround. Nonlinear units were much more frequently recorded in frogs maintained in summer conditions (12‐hour days, constant 20°C temperature).In spite of this functional heterogeneity, all cells had similar morphology consisting of (1) a large ganglion cell with a large dendritic arbor (400–1,000 μm) confined to a single stratum in the outer third of the inner plexiform layer, (2) a medium‐sized axon (2.4‐μm diameter), (3) a smallish pretectal arbor, and (4) a large tectal arbor (300–7

ISSN:0092-7317    

DOI:10.1002/cne.902580402

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

年代:1987

数据来源: WILEY

摘要:

AbstractTo determine the presence and organization of kinesthetic, as compared with other mechanosensory projection zones in the thalamus of raccoons, unit‐cluster responses to mechanical stimulation of the postcranial body were mapped electrophysiologically in the thalami of 14 raccoons anesthetized with Dial‐urethane. A distinct zone of kinesthetic projections (from receptive fields in muscles, tendons, and joints) was found in the rostral and dorsal aspects of the mechanosensory projection zone. These projections are somatotopically organized: those from axial structures lie dorsalmost and those from successively more distal limb regions are successively more caudoventral. The kinesthetic forelimb representation is large and lies rostrodorsal to a large central core of cutaneous projections from the forepaw digits. A few scattered kinesthetic projections were found at the caudal edge of the sensory thalamic region.The large, spatially and somatotopically distinct kinesthetic projection zone in the thalamus parallels those seen in the cortex and medulla of raccoons. Similar findings in monkeys, and suggestions from data in cats and humans support the hypothesis of a distinct pathway to the cortex for kinesthetic information in all mamm

ISSN:0092-7317    

DOI:10.1002/cne.902580403

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

年代:1987

数据来源: WILEY

摘要:

AbstractTo determine anatomically the boundaries and internal organization of the kinesthetic and cutaneous mechanosensory regions of the ventrobasal thalamus, alternate section series from electrophysiologically mapped tissues from 14 raccoons were stained for cytochrome oxidase, myelinated fibers, acetylcholinesterase, and Nissl substance. Microelectrode tracks, along with electrolytic lesions placed as tissue markers, reveal that (1) the mechanoreceptor projection zones have higher cytochrome oxidase and lower acetylcholinesterase staining than some neighboring regions. Both these enzymatic stains reveal particularly sharp boundaries separating the mechanoresponsive region, from the lateral posterior nucleus dorsally and from the ventroposterior inferior nucleus ventrally. (2) The kinesthetic projection zone is often separated from other mechanoreceptor projections by bundles as well as laminae of myelinated fibers, similar to those separating cutaneous projections from distinct body parts. These subdivisions are particularly well marked by the cytochrome oxidase stain. The combination, in neighboring sections, of the use of the several stains adds considerably to the visible delineation of these functionally distinct regions, beyond what can be seen in Nissl‐stained section

ISSN:0092-7317    

DOI:10.1002/cne.902580404

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

年代:1987

数据来源: WILEY

摘要:

AbstractNeurons immediately adjacent to the central canal were demonstrated in the cat and monkey to be immunoreactive for the peptide vasoactive intestinal polypeptide (VIP), by means of the peroxidase antiperoxidase method. Most of the cells were found in the thoracic and sacral segments, although a few were present at each level. The thoracic neurons were multipolar and either ependymal or subependymal; they usually had a large, thick dendrite that was oriented radially toward the center of the central canal; this dendrite penetrated through the ependymal layer and ended as a large, fringed podlike process (4–5‐μm diameter) along the canal surface in contact with the cerebrospinal fluid (CSF). From the basal surface of the thoracic cell arose several small dendrites and a varicose axon. A few of the thoracic VIP neurons also contained two nuclei. In the sacral cord, the VIP neurons that lie along the central canal were of several types. They were round or multipolar and were either subependymal, within the ependyma, or supraependymal. Many had long dendrites and thin varicose axons stretching for long distances parallel to the cord surface. Other VIP neurons were smaller cells with short, highly branched, varicose processes. Most prominent in the sacral cord of the cat was a massive intricate network of intensely labelled processes extending in parallel along the canal surface. This network contained thick dendrites, highly varicose axons, and small neurons. Electron microscopy demonstrated VIP axons and varicosities containing small round clear vesicles and dense core vesicles. These processes were in desmosomal contact with ependymal cells and in direct contact with the CSF space. VIP processes were also found along the pial surface of the spinal cord at each level. In some cases single axons and bundles of axons arising from the area around the central canal could be traced to terminal fields along the ventral median fissure and the ventral and ventral lateral surface. In summary, the cat and monkey spinal canal is richly innervated by VIP neurons with elaborate processes in contact with the cerebrospinal fluid; further, some of these neurons may also extend axons to the ventral surface of the spinal cord. In these aspects, these cells resemble CSF‐containing neurons previously described in lower s

ISSN:0092-7317    

DOI:10.1002/cne.902580405

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

年代:1987

数据来源: WILEY

摘要:

AbstractAn in vitro brain slice preparation has been used to label fibers connecting the somatosensory thalamus and cortex of the mouse. In 400–800‐μm brain slices, the pathway between the ventrobasal complex and somatosensory cortex was labeled under direct vision with horseradish peroxidase crystals (HRP), HRP‐Nonidet P‐40 (NP40) detergent chips, or a solution of HRP/dimethylsulfoxide.Thalamocortical and corticofugal fibers are organized into a plexiform system of bundles that appears to be fairly constant from animal to animal. Bundles of fibers projecting from the ventrobasal complex course between regularly spaced groups of thalamic neurons. Thalamocortical axons do not invariably leave the thalamus via the fiber bundle closest to the perikarya. Thus, nearest‐neighbor relationships are abolished before these axons have even left the thalamus. The axon bundles traverse the thalamic reticular nucleus lateral to the complex. The axons then rotate about one another, analogous to the coiling of strands in rope about a central axis. This accounts for the well known 180° rotation in the mediolateral direction between thalamic and cortical maps. Laterally, fiber bundles converge and diverge within the internal capsule so that nearest‐neighbor relationships are lost. Individual thalamocortical axons do not bifurcate proximal to the subcortical white matter. After single bundles of fibers reach a point just below the subcortical white matter, their individual fibers diverge widely.Within the subcortical white matter most afferent fibers make a small dorsally concave loop prior to taking one of two possible courses: Some of the fibers ascend directly into the overlying cortex usually angled towards the dorsal surface of the brain; other fibers run in the subcortical white matter for variable distances prior to ascending into cortex. Within somatosensory cortex, smooth axons branch near their terminals in layers IV and VI. Axonal terminal and branching patterns of these axons within somatosensory cortex are similar to those found in in vivo preparations. Most axons are smooth, but other axons are beaded. Some beaded axons project to layer I.Corticofugal fibers are labeled. Fibers leaving somatosensory cortex have an angle of descent opposite to the angle of ascent for afferent fibers, and are often fasciculated in the cortex and subcortical white matter. Within the subcortical white matter efferent fibers often loop in a direction opposite to that of afferent fibers. Corticofugal fibers occasionally give off a collateral corticostriatal branch within the internal capsule. It is otherwise difficult to differentiate afferent from efferent fibers within the internal capsule. Efferent fibers course through the point of rotation; some fibers continue in the cerebral peduncle, while others enter the vertrobasal complex. Corticothalamic terminals have been identified within the ventrobasal complex.The principal findings of this study are that nearest‐neighbor relationships of third‐order afferent Fibers are abolished at many points along the thalamocortical pathway (i.e., as axons leave the ventrobasal complex, within the internal capsule, and within the subcortical white matter). Third‐order afferents “seek out” appropriate cortical targets to re‐establish nearestneighbor relationships that exist in the ventrobasal thalamus. The point of rotation, where the mediolateral inversion between thalamic and cortical maps takes place, has been demonstrated. Significant differences exist between thalamocortical and corticofugal fibers, at both ends of the pathway, which generally permits discrimination be

ISSN:0092-7317    

DOI:10.1002/cne.902580406

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

年代:1987

数据来源: WILEY

摘要:

AbstractIn anesthetized and artificially ventilated cats, the physiological and morphological properties of expiratory neurons or their axons of the Bötzinger complex (BOT) were studied using intracellular recording and intracellular HRP labeling techniques. Thirteen expiratory neurons (nine cell somata and four axons) were successfully stained. Four of them were motoneurons, having relatively large cell somata in the retrofacial nucleus (RFN) and axons without any collaterals inside the brainstem. All the motoneurons showed a plateau shape of depolarization potentials during the expiratory phase. Any of the other nine expiratory neurons exhibited augmenting type firing or membrane potential changes during the expiratory phase. In five out of nine augmenting neurons, cell somata were stained and located ventral to the RFN. In four, only axons were stained. The majority of the augmenting neurons had two major axonal branches: one traveling toward the contralateral side and the other descending ipsilaterally in the brainstem. The most striking feature of the axonal trajectory was that all of the stained augmenting expiratory neurons, including the axons, had collateral branches with synaptic boutons in the BOT area, thus indicating that BOT expiratory neurons interact with some respiratory neurons in the BOT area and its vicinity

ISSN:0092-7317    

DOI:10.1002/cne.902580407

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

年代:1987

数据来源: WILEY

摘要:

AbstractThe trigeminal region of the chick was studied with indirect immunofluorescence in order to determine whether extracellular matrix components might be distributed in such a way as to guide trigeminal axons to their peripheral targets in the mandibular arch. Tissue sections from stages 13–15 and 21/22 were immunolabeled indirectly with affinity‐purified antibodies raised against fibronectin and laminin, two extracellular matrix glycoproteins that support axon growth in vitro. Fibronectin was distributed ubiquitously throughout the head mesenchyme prior to and during initial axon growth from the brainstem (stages 13–15). Shortly after trigeminal axons reached their target tissues (stage 21/22), fibronectin immunolabeling was distributed throughout the head mesenchyme, but was present only at low levels in the trigeminal ganglion and motor nerve. Laminin immunolabeling was distributed in the lateral head mesenchyme at stage 13 as small specks and patches. At stage 14, when the motor axons first exit from the brainstem, short, linear arrays of laminin immunostaining were present from the basement membrane of the neural tube to the core of the mandibular arch, and many were parallel to the direction of axon growth. By stage 21/22 the trigeminal ganglion and motor root showed intense antilaminin immunofluorescence as did the central core of the mandibular arch. These studies suggest that the distribution of fibronectin within the head mesenchyme cannot give directional information to the growing trigeminal axons because of its homogeneous distribution. However, the initial distribution of laminin during the earliest stages of axon outgrowth may provide an extracellular matrix pathway that permits trigeminal axons to reach their ta

ISSN:0092-7317    

DOI:10.1002/cne.902580408

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

年代:1987

数据来源: WILEY

摘要:

AbstractDuring the ontogeny of the enteric nervous system, the varicosities of mature neurons contact dividing neural precursors, which persist in the developing murine gut for several weeks postnatally. This phenomenon has led to the hypothesis that the release of transmitter from mature neurons may influence the subsequent development of uncommitted neuroblasts. In order to test this hypothesis, it is necessary to know the timing of the expression of postsynaptic receptors for enteric neurotransmitters. Since serotoninergic neurons are among the earliest of enteric neurons to develop (appearing on day E12 of development in the mouse), the ontogeny of enteric neural serotonin receptors (5‐HTR) was studied. These receptors have previously been characterized in adult guinea pigs and rabbits. In the current experiments, 5‐HTR were identified in the adult murine bowel; their properties were compared with the 5‐HTR of guinea pig and rabbits; their ontogeny was followed throughout the length of the developing mouse gut; and the properties of 5‐HTR in the developing murine bowel were compared with those of the mature gut. The 5‐HTR were assayed by measuring the binding of 3H‐serotonin (3H‐5‐HT) to isolated enteric membranes by rapid filtration, and to frozen sections of bowel by radioautography. A single saturable, high affinity3H‐5‐HT binding site was found in membranes from the adult mouse gut (KD= 3.9 ± 0.5 nM; Bmax= 1.6 ± 0.3 pmoles/mg protein). Binding of3H‐5‐HT at this site was not antagonized by compounds known to be antagonists at receptors for other neurotransmitters or at the 5‐HT1or 5‐HT2class of CNS 5‐HTR. Hydroxylation of the indole ring of analogues of serotonin was required for affinity at the enteric3H‐5‐HT binding site. Binding of3H‐5‐HT was inhibited by N‐acetyl‐5‐hydroxytryptophyl‐5‐hyroxytryptophan dipeptide, a compound that has been demonstrated to antagonize those responses of myenteric neurons to serotonin that resemble slow excitatory postsynaptic potentials, but not by ICS 205–930 (Sandoz), a serotonin antagonist that does not block these responses. All of these properties of adult murine3H‐5‐HT binding sites are virtually identical of those of guinea pigs and rabbits, which have previously been shown to be 5‐HTR; therefore, murine enteric3H‐5‐HT binding sites are probably 5‐HTR as well. The 5‐HTR were found radioautographically in both enteric plexuses and in the mucosa of all regions of the adult murine bowel with the exception of the fundus (rumen) of the stomach. During ontogeny the binding of3H‐5‐HT, evaluated radioautographically, appeared for the first time on day E14, when it was found in the stomach and small intestine from the pylorus to the level of the mid‐jejunum. The3H‐5‐HT binding sites then spread proximodistally, reaching the ileocolic sphincter on day E15, the proximal colon on days E16–18, and the distal colon on day P2. The acquisition of 3H‐5‐HT binding sites by the rectum occurred entirely postnatally and was not complete until day P22. The properties of the 3H‐5‐HT binding sites of developing animals were not distinguishable from those of adults, and thus were considered to be 5‐HTR. Additional 'H‐5‐HT binding sites were found in the perianal skin of adult mice. The characteristics of 3H‐5‐HT binding sites to these cutaneous sites were similar to those of the gut, which suggests that there are 5‐HTR of the enteric type in the skin. These observations indicate that enteric neural 5‐HTR make their appearance late indevelopment than do serotoninergic neurons; however, 5‐HTR are present during the period when proliferating neural precursors are present in the enteric nervous system.It seems unlikely, therefore, that 5‐HTR on precursors are important in determining the serotoninergic phenotype. Yet, the observations are consistent with the hypothesis that serotoninergic neurons influence the development of

ISSN:0092-7317    

DOI:10.1002/cne.902580409

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

年代:1987

数据来源: WILEY

摘要:

AbstractRubral neurons sending axons to the cerebellar anterior interpositus nucleus (AIN) in the cat were identified light microscopically by labeling them with horseradish peroxidase (HRP). The synaptic organization of these rubral neurons and of their afferents from the cerebral motor cortex and the AIN was also analyzed electron microscopically by combined anterograde degeneration and retrograde HRP‐labeling techniques.In the light microscopic study, either HRP or a mixture of HRP and kainic acid was injected into the AIN. Both of the injections resulted in retrograde labeling of rubrocerebellar projection neurons in the red nucleus on the contralateral side. The labeled neurons were distributed throughout the rostrocaudal extent of the red nucleus: some lay in clusters. Most labeled neurons were small to medium‐sized, although some were large. The injection of HRP into the AIN also resulted in anterograde labeling of cerebellorubral projection fibers terminating in a wider area of the red nucleus on the contralateral side of the injection, whereas the injection of a mixture of HRP and kainic acid showed no anterograde labeling of fibers or terminals.In one set of electron microscopic observations, HRP injections into the AIN were combined with ablation of the motor cortex. Degenerating axon terminals were occasionally found to synapse with both dendrites and neuronal somata labeled with HRP retrogradely.In another set of electron microscopic observations, a mixture of HRP and kainic acid was injected into the AIN in order to label rubrocerebellar projection neurons retrogradely and to bring about degeneration in the cerebellorubral projection fibers anterogradely. Abundant degenerating axon terminals were observed to make axosomatic synaptic contacts with rubral neurons labeled with HRP retrogradely and also with unlabeled rubral neurons.These results indicate that cerebrorubrocerebellar and rubrocerebellorubral monosynaptic circuitries exist which constitute one of the cerebrocerebellar linkages, as well as those linkages via the inferior olivary complex and the pontine nuc

ISSN:0092-7317    

DOI:10.1002/cne.902580410

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

年代:1987

数据来源: WILEY

摘要:

AbstractThe localization of gamma‐aminobutyric acid (GABA)‐ and L‐glutamate 1 carboxy‐lyase (GAD)‐immunoreactive neurons was compared in the skate, frog, pigeon, chicken, rabbit, and man. Horizontal cells show both GABA and GAD immunoreactivity in the skate, frog, and bird. Certain amacrine cells show GABA and GAD immunoreactivity in all species. The distribution of GABA‐ and GAD‐immunoreactive cell bodies and cell processes was very similar, if not identical, in the skate and man. In the other species, cell populations with GAD immunoreactivity also showed GABA immunoreactivity. However, in the bird, frog, and rabbit, the GABA‐immunoreactive amacrine cells were at least twice as numerous as the GAD‐immunoreactive cells. In birds, the distributions of the GAD and GABA immunoreactivities were different in the sublayers of the inner plexiform layer. The reason for the difference is currently unknown. GABA‐immunoreactive bipolar‐like cells

ISSN:0092-7317    

DOI:10.1002/cne.902580411

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

年代:1987

数据来源: WILEY