摘要:

AbstractThe crayfish slow‐adapting abdominal stretch receptor was fixed under the relaxed or stretched condition. During this procedure action potentials of the sensory neuron were recorded by a suction electrode. The receptor organ consists of a receptor muscle and a sensory neuron with its dendrites embedded in the connective tissue zone in the receptor muscle. From the cell body of the neuron, several “primary dendrites” arise, branch successively into “dendritic branches”, and finally terminate as “dendritic tips”, which are cylindrical processes of fairly uniform diameter. In contrast to the primary dendrites and the dendritic branches, the dendritic tips have neither mitochondria nor sheaths and are embedded in the connective tissue zone or apposed to the receptor muscle with a gap of about 15 nm. Microtubules and smooth ER are seen in all parts of the dendrites. When the receptor is stretched and then fixed with 1.6% glutaraldehyde in 0.12 M phosphate buffer (total osmolarity of this solution is isosmotic with the physiological solution), dendritic tips became more parallel to the long axis of the receptor muscle and showed marked deformation consisting of alternate regions of swelling and shrinkage, resulting in a bead‐like appearance. When fixed with 1.6% glutaraldehyde in 0.2 M phosphate buffer (total osmolarity of this solution is hyperosmotic), the dendritic tips showed less tendency toward such deformation. These results suggest that the dendritic tip membrane is susceptible to stretch and might be the region where the generator potent

ISSN:0092-7317    

DOI:10.1002/cne.902000102

出版商:Alan R. Liss, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractThe crayfish slow‐adapting stretch receptor was fixed under relaxed or stretched conditions (twice the relaxed length) and then processed for freeze‐fracture study. The sensory neuron membrane had evenly distributed intramembrane particles mostly on its P face. The density of these particles was higher in the cell body than in the dendritic tips, which are the terminal portions of the dendrites. The dendritic tips were cylindrical under the relaxed condition and showed deformations with stretch stimuli. When they were fixed under the stretched condition with 1.6% glutaraldehyde in 0.12 M phosphate buffer (the total osmolarity of this fixative is isosmotic with the physiological solution), the dendritic tips showed regional swelling and shrinkage. The intramembrane particle density of the swollen parts decreased and there were particle‐free patches of membrane, whereas the particle density of the shrunken parts increased. On the other hand, when the receptor was fixed with 1.6% glutaraldehyde in 0.2 M phosphate buffer (the total osmolarity is hyperosmotic but buffer osmolarity is isosmotic), the diameter of the dendritic tips became smaller, and their membrane particle densities were almost the same as that under the relaxed condition. The sheath cells covering the sensory neuron were characterized by their sheet‐like profiles, gap junctions, and crater‐like protrusions. The receptor muscle membrane had longitudinal foldings, occasional invaginations, peripheral couplings, stringshaped particle aggregates, and band‐shaped particle

ISSN:0092-7317    

DOI:10.1002/cne.902000103

出版商:Alan R. Liss, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractThe crayfish slow‐adapting abdominal stretch receptor organ is innervated by three inhibitory and several excitatory axons. A previous study by Tisdale and Nakajima ('76) showed that under certain fixation conditions inhibitory and excitatory synapses can be distinguished on the basis of synaptic vesicle structure. Using this morphological criterion we describe six types of synapses in the receptor: (1) the inhibitory axo‐dendritic synapse, (2) the excitatory neuromuscular synapse, (3) the inhibitory neuromuscular synapse, (4) the axo‐axonic synapse which suggests presynaptic inhibition on the excitatory synapse, (5) the axo‐axonic synapse which suggests presynaptic inhibition on the inhibitory synapse, (6) the reciprocal inhibitory axo‐axonic synapse, which is a new type of synapse. The presence of these six types of synapse suggests that inhibitory and excitatory axons interact synaptically in a complicated manner, resulting in a delicate control of receptor function. In freeze fracture we have observed the presynaptic membrane structures of inhibitory and excitatory synapses. The active zone of the inhibitory synapse has ridges with loosely aggregated particles on the tops of the ridges and indentations (vesicle attachment sites) along their sides. The active zone of the excitatory neuromuscular synapse consists of bands of particle aggregates which are situated on slightly elevated membrane regions and surrounded by wide, relatively particle‐free, flat mem

ISSN:0092-7317    

DOI:10.1002/cne.902000104

出版商:Alan R. Liss, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractThe development of the pyramidal tract and other projections from the sensorimotor cortex was studied in the postnatal hamster with both (3H) proline and horseradish peroxidase (HRP) as anterograde tracers. In the 1‐day‐old animal labeled axons extend as far as the pons. Other corticofugal fibers have penetrated into the corpus striatum and the thalamus. By 2 days postnatally, the pyramidal tract has grown to midmedullary levels and there is substantial retrograde (HRP) and anterograde labeling in the thalamus. The pyramidal decussation is formed at 3 days of age and by 4 days the pyramidal tract has descended in the dorsal funiculus as far as midcervical spinal cord. Corticofugal fibers invade the pontine nuclei at 4 days and both the dorsal column nuclei and the superior colliculus at 6 days of age. At 6 days the pyramidal tract can be traced to midthoracic levels of the spinal cord, by 8 days the tract reaches lumbar levels, and by 14 days it has completed its caudal growth to the coccygeal spinal cord. Fibers first penetrate the gray matter of a given spinal cord level approximately 2 days after the tract has grown past that level in the dorsal funiculus. Pyramidal fibers continue their lateral growth into the dorsal horn at all levels of the cord throughout the third postnatal week such that by 21 days of age the pyramidal tract appears similar to that of the adult.The projections from sensorimotor cortex to the pontine nuclei, the superior colliculus, and the dorsal column nuclei appear to have a pattern similar to that of the adult soon after the fibers grow into these structures. There is a consistent delay of 2 to 3 days between the arrival of the pyramidal tract axons in the white matter adjacent to target structures and their innervation of a given terminal field. The pyramidal tract grows more quickly through the dorsal funiculus of the spinal cord than it does along the ventral surface of the medulla. Extensive elongation of pyramidal tract axons is achieved long before the growth and differentiation of the sensorimotor cortical neurons from which they originate. Finally, the pyramidal tract appears to grow as a compact bundle and not by the addition of temporally staggered groups of fibers. The relatively protracted period of innervation of the spinal cord by the pyramidal tract coupled with the immaturity of the cortical neurons at birth may be factors contributing to the significant regrowth of pyramidal tract axons severed early in developm

ISSN:0092-7317    

DOI:10.1002/cne.902000105

出版商:Alan R. Liss, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractAutoradiography of3H‐thymidine incorporation was combined with horseradish peroxidase (HRP) transport to distinguish the birthdates of motoneurons and internuclear neurons of the abducens nucleus, and of specific motor pools within the oculomotor nucleus. Motoneurons were identified by their retrograde transport of HRP from the extraocular muscles. In other experiments, internucleur neuron types may be controlled by the local environment. The motor pools ofthe oculomotor nucleus are generated sequentially. This may reflect the mechanism whereby nuclei are constructe

ISSN:0092-7317    

DOI:10.1002/cne.902000106

出版商:Alan R. Liss, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractThe localization of synaptic receptor sites for γ‐amino butyric acid (GABA) in the goldfish retina was studied by light microscopic (LM) and electron microscopic autoradiography (EM‐ARG) of3H‐muscimol and3H‐GABA binding. Sodium‐independent binding of both3H‐muscimol and3H‐GABA was localized to a uniform band throughout the inner plexiform layer (IPL) by LM‐ARG of cryostat sections incubated in these compounds. No binding was observed over the outer plexiform layer. This binding pattern differs from the uptake pattern of3H‐GABA in the IPL, which shows very heavy labeling in the most proximal IPL and little labeling throughout the rest of the IPL. Statistical analysis of EM‐ARGs of3H‐muscimol (i.e., make GABAergic synapses). Labeled amacrine‐to‐amacrine synapses are mostly concentrated in the 20–80% levels of the IPL, whereas amacrine‐to‐bipolar synapses are concentrated at about the 70–90% depth. Maximal3H‐GABA uptake, however, occurs at the 90–100% depth. This difference in the location of GABAergic synaptic binding and GABAergic uptake leads to the conclusion that the density of uptake label provides little information about the density of synaptic contacts. Thus, in order to localize GABAergic interactions, synaptic binding rather than neuronal uptake appears to pr

ISSN:0092-7317    

DOI:10.1002/cne.902000107

出版商:Alan R. Liss, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractDorsal ventricular ridge (DVR) is a thalamorecipient, subcortical telencephalic structure in reptiles and birds. Although there is a fair amount of information about sources of afferents to DVR, little is known about the relationship of projections from individual thalamic nuclei to the organization of the structure. This study examines the relationship between thalamic projections and both areal and zonal divisions of anterior DVR (ADVR; Balaban,'78a) of emydid turtles with orthograde degeneration, and horseradish peroxidase techniques.Individual thalamic nuclei contribute either a diffuse or a restricted projection to ADVR. Diffuse projections arise primarily from the dorsomedial anterior nucleus. These fine‐caliber axons distribute bilaterally over a wide region of the telencephalon via both medial and lateral thalamotelencephalic pathways. The terminal regions include septum, striatum and the medial bank of cortex caudal to the lamina terminalis. In ADVR, the fibers are distributed sparsely in zones 2–4 of dorsal, medial and ventral areas. Restricted projections to ADVR originate in nucleus rotundus, nucleus reuniens and nucleus caudalis. They ascend ipsilaterally in the lateral thalamotelencephalic pathway (lateral forebrain bundle), and enter ADVR rostral to the anterior commissure. Nucleus rotundus projects to zone 4 of dorsal area, nucleus caudalis projects to zones 2–4 of the dorsal division of medial area, and nucleus reuniens projects to zones 2–4 of both the ventral division of medial area and the ventral area.Comparison of these results with thalamotelencephalic projections in mammals suggests that diffuse and restricted thalamic projection systems are a common feature of both groups. Restricted thalamic projections in reptiles, birds and mammals, terminating in anatomically distinct regions, also appear to be associated with different sensory modalities. The significance of diffuse systems is no

ISSN:0092-7317    

DOI:10.1002/cne.902000108

出版商:Alan R. Liss, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractThis study describes some properties of the map of nucleus rotundus onto dorsal area of anterior dorsal ventricular ridge (ADVR) in emydid turtles by correlating results of anterograde and retrograde tracing experiments with observations from Golgi‐ and myelin‐stained brains. An earlier paper (Balaban and Ulinski, '81) demonstrated that this projection is restricted to zone 4 of dorsal area of ADVR. This paper indicates that the rotundal pathway is organized such that longitudinally aligned groups of neurons in nucleus rotundus project to longitudinal regions in zone 4 of dorsal area. The projection field spans the dorsoventral (or concentric) dimension of zone 4 at each transverse level. Comparisons of experimental and Golgi preparations suggest that each rotundal neuron projects, via collaterals, to the entire rostrocaudal extent of rotundorecipient zone 4. Individual terminal branches span the dorsoventral dimension of zone 4 and are confined within both sagittal and transvere planes. Lesion experiments suggest that collaterals of a single rotundal axon are also distributed over at least one‐third to one‐half of the superficial‐deep dimension of zone 4. This is also reflected in the observation that neurons from disjoint dorsal, dorsolateral and medial rotundal loci project to overlapping, concentric regions of dorsal area. Both this prominent concentric component of terminal branches and the extensive overlap of projections of neurons at distinct rotundal loci preclude the possibility of a topographic representation of either dorsoventral or mediolateral rotundal axes in zone 4 of do

ISSN:0092-7317    

DOI:10.1002/cne.902000109

出版商:Alan R. Liss, Inc.    

年代:1981

数据来源: WILEY

ISSN:0092-7317    

DOI:10.1002/cne.902000101

出版商:Alan R. Liss, Inc.    

年代:1981

数据来源: WILEY