摘要:

AbstractA combined analysis with the Golgi and silver‐degeneration methods and electron microscopy in the ventral nucleus of the medial geniculate body has confirmed that the Golgi type II neuron forms dendro‐dendritic synapses with the principal neuron in terminal aggregates called synaptic nests. Both types of neurons receive synaptic contacts from the afferent axons that ascend from the posterior colliculus and from those that descend from the auditory cortex. Only the principal neuron projects to the auditory cortex. The Golgi type II cells that receive endings from afferent axons send presynaptic processes to principal cells that are also contacted by the very same afferent axons. The axons of Golgi type II cells project to synaptic nests other than those supplied by the dendrites of the parent cell and link the Golgi type II cells with each other. On the surface of the Golgi type II cell there is a segregation of the different types of synaptic endings and a consistent sequence in their synaptic relationships. The endings of colliculogeniculate and Golgi type II axons predominate on the distal dendrites in the synaptic nests. Corticogeniculate endings congregate more on the soma and proximal dendrites. In the synaptic nests the Golgi type II dendrites are presynaptic to the principal cell dendrites, whereas both kinds of dendrites are postsynaptic to the very same axons, which project either from the posterior colliculus or from Golgi II cells. The endings of the Golgi type II dendrites have pale, irregular, often quite big profiles that contain large pleomorphic vesicles and make nearly symmetrical synaptic contacts. The synaptic endings of the Golgi type II axons could resemble the dendritic endings, but many of the axonal endings appear to have smaller profiles containing smaller, flatter vesicles. The endings of the colliculogeniculate axons are generally darker, often contain smaller, rounder synaptic vesicles than the dendritic endings do, and make strongly asymmetric synaptic contacts. The terminals of the corticogeniculate axons resemble the smallest colliculogeniculate endings but have darker profiles and contain some flattened vesicles. These identifications are consistent with electron microscopic observations of the synaptic degeneration following destruction of the sources of the afferent axons in the posterior colliculus and cerebral cortex.The segregation of inputs on the Golgi type II cell implies that its axon would be influenced more directly by the corticogeniculate pathway, while the dendrites of the same cell would be more directly accessible to the colliculogeniculate pathway. The Golgi type II cells might be either inhibitory or excitatory interneurons or both. As inhibitory interneurons, Golgi type II cells could provide for response patterns that would render the principal neurons particularly sensitive to stimulus onsets and to temporal changes in the afferent input. As excitatory interneurons, Golgi type II cells could provide for incremental or sustained response patterns that would tend to prolong particular signal trains. In either case the synaptic relationships of the Golgi type II cells would be critical in defining the spatial and temporal aspects of stimulus coding involved in the cortical analysis of temporal patterns and locations of sou

ISSN:0092-7317    

DOI:10.1002/cne.901620202

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

年代:1975

数据来源: WILEY

摘要:

AbstractIn order to obtain a better understanding of the microscopic structure of the cat fasciculus gracilis, entire cross‐sections of the fasciculus were examined with the electron microscope. Twenty‐five thousand, two hundred and eighty‐four fibers were encountered in one fasciculus. The fiber caliber spectra obtained from the study show that the fasciculus gracilis at cervical level has a unique fiber distribution pattern. The fiber diameters range from less than 1 μ to 15 μ, however, 97% of fibers have diameters less than 8 μ; and the majority of the fibers are in the 2

ISSN:0092-7317    

DOI:10.1002/cne.901620203

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

年代:1975

数据来源: WILEY

摘要:

AbstractTwo area specific reflexes elicited by natural stimulation of different regions of the hindlimbs ofXenopus laevishave been identified. Light or intense mechanical stimulation of the foot evokes reflex activity in the ipsilateral knee flexor nerve; moderate pressure applied to the calf evokes reflex activity predominantly in the ipsilateral knee extensor nerve. The reflex responses have been recorded electrophysiologically to overcome the limitations of behavioral observations for determining the presence of activity in particular muscles. Normal area specific reflexes are elicited in the normal ipsilateral hindlimb by stimulation of grafted supernumerary hindlimbs innervated either by hindlimb (lumbar) or by non‐limb (thoracic) spinal cord segments. The area specific reflexes can be elicited only if the limb is grafted to a host younger than stage 54–55 of Nieuwkoop and Faber ('56), the stage at which reflex movements are first observed behaviorally. Abnormal reflex responses are evoked by stimulation of supernumerary limbs innervated by either thoracic or lumbar segments when the limb buds are grafted to older larvae. Supernumerary forelimbs grafted at early stages and innervated by either thoracic or lumbar spinal cord segments generally fail to elicit area specific reflex responses in the normal hindlimb. Single‐unit recordings of afferent fibers supplying the normal and supernumerary hindlimbs show that each limb receives a separate nerve supply. No evidence for branched afferent fibers has been found. The implications of these results for theories of neuronal specification are discussed, particularly the hypothesis that peripheral tissues are able to specify the central actions of afferent fibers that innervate

ISSN:0092-7317    

DOI:10.1002/cne.901620204

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

年代:1975

数据来源: WILEY

摘要:

AbstractA three‐dimensional block model of the cochlear nucleus of the cat was constructed from histologic sections. Boundaries of various subdivisions, based on cytoarchitectonic criteria, were included in the model. Usage of the block model in correlating physiological and anatomical data is illustrated by localizing characteristic waveforms of gross evoked responses and characteristic frequencies of single unit

ISSN:0092-7317    

DOI:10.1002/cne.901620205

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

年代:1975

数据来源: WILEY

摘要:

AbstractSingle unit activity in the posteroventral cochlear nucleus (PVCN) was recorded for a variety of stimulus conditions. The units were classified according to their response characteristics. The locations of units were plotted onto a three‐dimensional block model of the cochlear nucleus. Certain types of units that responded best to the onsets of stimuli were located predominantly in the octopus cell region of the PVCN. The remainder of the PVCN, which contains a rather heterogeneous collection of small and multipolar cells, was found to contain several types of units with the dominant type being “chopper”

ISSN:0092-7317    

DOI:10.1002/cne.901620206

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

年代:1975

数据来源: WILEY

摘要:

AbstractSingle unit activity was examined in three component layers of the dorsal cochlear nucleus (DCN): the molecular layer, the fusiform cell layer, and the polymorphic layer (deep DCN). Electrophysiological units were classified into types on the basis of their activity under a variety of stimulus conditions. In the molecular layer spike activity was small and difficult to isolate. Almost all units in the fusiform cell layer could be classified as either “pauser” or “buildup” units. Classification of units in the deep DCN was sometimes difficult, but “pauser,” “chopper,” and some “on” units were found. The “on” types of units tended to be located in the more superficial part of the deep DCN. Unit locations were referred to a three‐dimensional block mode

ISSN:0092-7317    

DOI:10.1002/cne.901620207

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

年代:1975

数据来源: WILEY

ISSN:0092-7317    

DOI:10.1002/cne.901620201

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

年代:1975

数据来源: WILEY