摘要:

AbstractSamples of S1 dorsal root nerve fibers from cats of different pre‐ and postnatal ages were examined electron microscopically with regard to axon caliber and number of myelin lamellae. Each root was examined at four different cross‐sectional levels. Two levels were situated close to the spinal cord entrance on each side of the peripheral (PNS) and central nervous system (CNS) border. The third and fourth levels were located more distally. The first compact myelin lamella was observed in the CNS part of the root in a 47‐day‐old fetus. In the 53‐day‐old fetus the degree of myelination was the same in the CNS as distal in the PNS part of the root. Surprisingly, all axons appeared unmyelinated close to the PNS‐CNS border and remained so for a further 10‐day period. After this time lag, this part of the root became myelinated and showed a rapid increase in myelin sheath thickness. Calculations of axonal growth, mesaxonal length, and myelin volume indicated a maturation process that progressed discontinuously. Myelination did not proceed in a strict somatofugal direction, but was a regionally differentiated process. The maximal myelin production, expressed as the increase in myelin volume per Schwann cell, was found during the second to fourth postnatal months, i. e., very late

ISSN:0092-7317    

DOI:10.1002/cne.902090302

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

年代:1982

数据来源: WILEY

摘要:

AbstractThe internal structure of the synaptic membranes in the inner plexiform layer (IPL) of the retina of monkeys and rabbits was studied with the freeze‐fracturing technique. In ribbon synapses, the presynaptic active zone is characterized by an aggregate of P‐face particles, images of synaptic vesicle exocytosis, and forming coated vesicles which occupy distinct, contiguous membrane domains from apex to base of the synaptic ridge. The postsynaptic membrane contains a prominent aggregate of homogeneous particles which remain associated with the E‐face. In the presynaptic membrane of conventional synapses, images of synaptic vesicle exocytosis are intermingled with large P‐face particles, whereas forming coated vesicles surround the active zone. Three types of internal organization characterize the postsynaptic membrane of conventional synapses. Usually, the postsynaptic membrane exhibits the same internal structure as the surrounding nonjunctional plasmalemma. A second, less common type of conventional synapse contains a loose aggregate of heterogeneous particles which remain associated with the P‐face. Finally, synapses were exceptionally found which are macular in shape and contain an aggregate of E‐face particles within the postsynaptic membrane. The freeze‐fracture evidence suggests that the axonal endings of bipolar cells—or at least some of them—make excitatory synapses, whereas the vast majority of amacrine cell dendrites make inhibitory synapses. Additional specializations of the cell surface in the IPL include gap junctions, puncta adhaerentia, subsurface cisterns, and cell

ISSN:0092-7317    

DOI:10.1002/cne.902090303

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

年代:1982

数据来源: WILEY

摘要:

AbstractThree different pairs of double retrograde axonal tracers have been used to study the distribution of axon collaterals from individual cells in the olfactory bulb and the nucleus of the horizontal limb of the diagonal band: (1) horseradish peroxidase (HRP) and tritiated apo‐HRP (3H‐HRP), (2) HRP and125I‐wheat germ agglutinin (I‐WGA), and (3) the flurochromes true blue (TB) and bisbenzimide (BB) or nuclear yellow (NY). With each combination of tracers, paired injections were made into different parts of the olfactory system, and the olfactory bulb and the nucleus of the diagonal band were examined for the presence and arrangement of cells labeled with one or both retrograde tracers.In the olfactory bulb both single and double retrogradely labeled mitral cells were found following injections in disparate parts of the olfactory cortex. Furthermore, no consistent pattern was found in the distribution of single‐ or double‐labeled cells in the olfactory bulb; that is, the distribution of cells labeled from one area of the cortex was not consistently different from the distribution of cells labeled from other parts of the cortex. Therefore, it was concluded that individual mitral cells project to widely spaced parts of the olfactory cortex, and that there is no apparent correspondence between the location of a given cell in the olfactory bulb and the distribution of its axon in the cortex.In contrast to this, cells in the nucleus of the horizontal limb of the diagonal band were only rarely double‐labeled from nonoverlapping injections into the olfactory cortex or olfactory bulb, although overlapping injections produced a high proportion of double‐labeled cells. Cells which were single‐labeled from different injection sites were extensively intermixed within the nucleus. Therefore, in this case it was concluded that individual cells project to relatively restricted areas, although there was again no apparent correspondence between the position of a cell in the nucleus and the terminal

ISSN:0092-7317    

DOI:10.1002/cne.902090304

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

年代:1982

数据来源: WILEY

摘要:

AbstractUsing standard paraffin technique the addition of new cells in crucian carp retinas was examined. Between eye diameters 4.4 and 10.0 mm the number of ganglion cells increases from 103,000 to 205,000, INL cells from 1.5 to 3 million, cones from 250,000 to 900,000, and rods from 2 to 9 million. Concomitantly retinal area increases fivefold and the cell densities decrease by 37% for the cones, 57% for th e INL cells, and 58% for the ganglion cells, while the rod density remains stable.In relation to the rods the cell ratios at different retinal loci undergo marked changes during growth. The contributions to retinal growth by addition of new neurons and by expansion of the retina have been determined for the different retinal layers. The layer of rods grows exclusively by addition of new rod mosaic. In the cone layer 81% of growth is due to addition of new cone mosaic. In the inner nuclear layer (INL) 56% of growth is due to addition of new cells and in the ganglion cell layer 52% is due to cell addition. In each case retinal expansion accounts for the remainder of increase in retinal area.On morphological grounds six cone types can be found in the crucian carp retina. Their ratios are constant during retinal growth and at different retinal loci.

ISSN:0092-7317    

DOI:10.1002/cne.902090305

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

年代:1982

数据来源: WILEY

摘要:

AbstractThe areas of the ganglion cell dendritic trees were determined in Golgistained, flatmounted retinas of crucian carp ranging in age from one summer to 7 years. The dendritic trees of small ganglion cells (S‐GC), forming the majority of retinal ganglion cells, add new branches as the retina grows. The increase in dendritic tree area exactly compensates for the decrease in ganglion cell density during growth of the eye so that the number of dendritic trees covering a particular point remains constant. While the retinal diameter increases by a factor of 2.5, the mean diameter of the S‐GC dendritic fields increases by a factor of 1.9 and the visual angle covered by one S‐GC dendritic tree decreases from 1.6° to 1.2°.The number of branching points of the S‐GC dendrites is significantly higher in the ventral retina than in the dorsal. In general the dendrites of the S‐GCs tend to grow towards the retinal margin. Dendritic orientation patterns of large (LGC) and large displaced (LDGC) ganglion cells closely resemble those of the amacrines, being oriented parallel to the retinal margin over a wide peripheral region, while the SGCs rapidly lose their tangential orientation. The dendrites of the SGCs are restricted mainly to the proximal sublayer of the inner plexiform layer, suggesting they are ON‐cells, while LGC, LDGC, and amacrine cell dendrites are distributed in depth bimodally.As determined from Golgi‐stained sections the crucian carp has the same basic IPL organization as t

ISSN:0092-7317    

DOI:10.1002/cne.902090306

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

年代:1982

数据来源: WILEY

摘要:

AbstractThe purpose of this study was to determine the distribution of luteinizing hormone‐releasing hormone (LHRH) cells and pathways projecting to the median eminence and organum vasculosum of the lamina terminalis in the hypothalamus of the rat. Immunopositive LHRH was detected by the PAP method of immunocytochemistry on vibratome sections without embedding. Female rats were ovariectomized and treated with estradiol benzoate or implanted with estradiol capsules prior to sacrifice in order to minimize variations in LH and ultimately to maximize hypothalamic LHRH content. Immunoreactive LHRH perikarya are diffusely aggregated across several nuclear groups: nucleus of the vertical limb of the diagonal band of Broca, medial septal nucleus, medians preoptic nucleus, rostral and medial preoptic areas, anterior hypothalamic area, and lateral and basal hypothalamic areas. The aggregate of LHRH cells when projected upon a horizontal plane resembles the form of a V bisected by the third ventricle. The apex of the V is directed rostrally toward the midline nuclear groups whereas the ends of the V incline ventrally toward the base of the brain and the median eminence. The majority of LHRH cells are in the rostral portion of the V in preoptic and anterior hypothalamic areas. Few cells are present in the basal hypothalamus. The processes of LHRH cells form two diffuse fiber systems which are separated by the midline hypothalamic nuclei over most of their course and converge in the basal hypothalamus close to the median eminence. The more lateral fiber system forms part of the medial forebrain bundle, while the periventricular system is associated with the wall of the third ventricle. The dispersion of LHRH cells over many nuclear groups may allow for the integration of afferents from divergent regions of the neuraxis to mediate both tonic and phasic gonadotropin secretion in the ra

ISSN:0092-7317    

DOI:10.1002/cne.902090307

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

年代:1982

数据来源: WILEY

摘要:

AbstractTrigeminal and facial motor nuclei innervating the pigeon's jaw muscles were identified using a combination of microstimulation and EMG recording and HRP injections were made iontophoretically. The trigeminal motor nucleus receives an ipsilateral projection from sensory neurons in the trigeminal mesencephalic nucleus which forms the afferent limb of the monosynaptic stretch reflex of the jaw‐closers. Both the trigeminal and facial motor nuclei receive bilateral projections from interneurons in the intertrigeminal area and the lateral (parvocellular) reticular formation of the pons and medulla. These neurons serve as premotor elements in the control of jaw movements, mediating ascending, descending and internuclear connections. The similarity of inputs to the trigeminal and facial nuclei may reflect their common function as jaw motoneurons in this specie

ISSN:0092-7317    

DOI:10.1002/cne.902090308

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

年代:1982

数据来源: WILEY

摘要:

AbstractCentral pathways converging upon the trigeminofacial motor nuclei of the mallard were studied in order to elucidate neuroanatomically the presumed influence of primary sensory trigeminal afferents upon jaw muscle activity. The techniques used included the Fink‐Heimer I method after lesions, and axonal transport labeling following injections of3H‐leucine or of HRP for retrograde identification of the neurons of origin.A general description is given of the trigeminofacial motor complex. Jaw closer muscles are innervated by trigeminal motor neurons, and facial motor neurons innervate the jaw depressor muscles. Two afferent premotor systems, one including the mesencephalic trigeminal nucleus (MesV) and the other the rhombencephalic reticular formation, are distinguished. The proprioceptive neurons of the mesencephalic trigeminal nucleus project upon the ipsilateral trigeminal motor nucleus and upon the nucleus supratrigeminalis. The latter cell group bilaterally projects upon the dorsal and intermediate parts of the facial motor nucleus and upon part of the trigeminal motor nucleus. Exteroceptive information, relayed through the primary sensory trigeminal column (PrV and nTTD), ultimately reaches the motor nuclei via the reticular formation. The reticular formation forms the final link of three separate circuits: a telencephalic one entered through the principal trigeminal sensory nucleus, a cerebellar one via subnucleus oralis of the descending trigeminal system, and a direct one via subnucleus interpolaris. No direct connections between the principal trigeminal sensory nucleus or subnuclei of the descending trigeminal system and the motor nuclei of the trigeminal (NV) and facial (NVII) nerves have been observed, nor are such direct projections present in the outflow of the presumed telencephalic and cerebellar circuits, viz. of the archistriatum and the central cerebellar nuclei, respectively. The archistriatum projects via the occipitomesencephalic tract upon the lateral rhombencephalic reticular formation as far down as the rostral cervical cord, as well as upon the subnucleus interpolaris of the descending trigeminal system. Similarly, efferents from the central cerebellar nuclei reach the reticular formation, which in turn projects bilaterally upon the motor nuclei. Finally, commissural intermotor connections apparently are mediated by reticular cells surrounding the motor nuclei of NV or NVII, rather than emanating from these nuclei direc

ISSN:0092-7317    

DOI:10.1002/cne.902090309

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

年代:1982

数据来源: WILEY

ISSN:0092-7317    

DOI:10.1002/cne.902090301

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

年代:1982

数据来源: WILEY