The Journal of comparative neurology
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Topographic distributions of cortico-cortical projections from the primary (AI), anterior (A), posterior (P), ventroposterior (VP), and second (AII) auditory fields were studied in relation to tonotopic maps in combined anatomical and electrophysiological experiments. Distributions of axon terminals were determined by autoradiographic labeling with tritiated proline and leucine. Each of fields A, AI, P, and VP is connected with the other three in the same hemisphere as well as with a number of other auditory cortical areas. ⋯ Within AI, projections from contralateral fields A and AI and from ipsilateral fields A and P terminate in patches which are often elongated in a direction parallel to the low-to-high best-frequency gradient. A divergence in the projections from one field upon another is apparent in many experiments. Within fields A, AI, P, and VP, patches of label are distributed along a band of cortex oriented parallel to isofrequency lines.
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The time of origin (birthday) of Rohon-Beard cells in Xenopus laevis was studied by 3H-thymidine autoradiography. Rohon-Beard cells were selected because they are a morphologically identifiable population of neurons in which the development of chemical and electrical excitability has been studied. A single injection of a radioactive DNA precursor was given to animals in successive stages of development from blastula to late tail bud (Nieuwkoop and Faber stages 8--33/34). ⋯ By stage 27, no Rohon-Beard neuron incorporated 3H-thymidine. In addition to Rohon-Beard neurons, five other neuronal populations begin generation during gastrulation: Mauthner neurons (Vargas-Lizardi and Lyser, '74), trigeminal ganglion cells, large basal plate cells of the medulla, extramedullary neurons, and primary motor neurons. The first birthdays in any of the six populations are temporally close to but appear to be independent of the others.
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Comparative Study
Intracortical connectivity of architectonic fields in the somatic sensory, motor and parietal cortex of monkeys.
Anterograde and retrograde transport methods were used to study the corticocortical connectivity of areas 3a, 3b, 1, 2, 5, 4 and 6 of the monkey cerebral cortex. Fields were identified by cytoarchitectonic features and by thalamic connectivity in the same brains. Area 3a was identified by first recording a short latency group I afferent evoked potential. ⋯ Parts of area 5 that should be more properly considered as area 2, and other parts that receive thalamic input not from the ventrobasal complex but from the lateral nuclear complex and anterior pulvinar, are also interconnected with area 4. More posterior parts of area 5 are connected with laterally placed parts of area 6. A more medial part of area 6, the supplementary motor area, occupies a pivotal position in the sensory-motor cortex, for it receives fibers from areas 3a, 4, 1, 2 and 5 (all parts), and projects back to areas 3a, 4 and 5.
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The tract of Lissauer receives small caliber dorsal root fibers in addition to axons arising from dorsal horn neurons. The termination of Lissauer's tract and dorsal root fibers was examined in the C7 segment of the rhesus monkey spinal cord. The distribution of normal dorsal root afferents was mapped by labelling the C7 dorsal root ganglion with tritiated amino acids, and then compared with the degeneration of C7 dorsal root fibers following an intradural dorsal rhizotomy. ⋯ The tract of Lissauer consists of two populations, each containing small afferents. One population degenerates at three to five days and distributes mainly to laminae II and III (substantia gelatinosa); the other degenerates around 12 days and distributes mainly to lamina I and the outer zone of II. It is suggested that the exclusive termination of the small afferents to laminae I, II and III may be correlated with certain unique histochemical properties (e.g., high substance P and high opiate receptor binding levels) of these same dorsal horn areas...