Biomedical subjects

L C Katz

Publications and source records attributed to L C Katz.

57 records · Page 4Linked to original sources

PubMedDate not supplied

Fluorescent latex microspheres as a retrograde neuronal marker for in vivo and in vitro studies of visual cortex.

The use of retrograde axonal transport of various substances (for example, enzymes, lectins, synthetic fluorescent compounds) has yielded much information on the organization of neuronal pathways. Each type of retrograde tracer has its own set of attributes which define the scope of problems it can address. We describe here a new class of retrograde tracer, rhodamine-labelled fluorescent latex microspheres (0.02-0.2 micron diameter), which have distinct advantages over other available tracers for in vivo and in vitro applications. When injected into brain tissue, these microspheres show little diffusion and consequently produce small, sharply defined injection sites. Once transported back to neuronal somata, the label persists for at least 10 weeks in vivo and 1 yr after fixation. Microspheres have no obvious cytotoxicity or phototoxicity as assessed by intracellular recording and staining of retrogradely labelled cells in a cortical brain slice preparation. This approach was further used to visualize and compare, in cat visual cortex slices, neurones with different projection patterns, and revealed significant differences in patterns of intrinsic axons and dendrites. These properties of microspheres open new avenues for anatomical and physiological studies of identified projection neurones in slices as well as in dissociated cell cultures.

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PubMedDate not supplied

Gap junctional communication and the development of local circuits in neocortex.

In the neocortex, as well as in many other brain regions, neurons responding to similar stimulus features are usually found close to one another. Here we examine the possible role of gap junctional communication in forming and defining these local neuronal groupings, examples of which may be the columns found in the neocortex of virtually all mammalian species. We have approached this question experimentally in cortical brain slices using calcium imaging to visualize multicellular activity patterns, and tracer injections to identify the anatomical pattern of gap junction coupling in the developing neocortex. Our results suggest that dendrodendritic gap junctional communication may be involved in the formation of local connectivity, most likely by synchronizing electrical or biochemical activity among neighboring neurons.

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PubMedDate not supplied

Development of horizontal projections in layer 2/3 of ferret visual cortex.

Pyramidal cells in layer 2/3 of cat striate cortex extend long axons that form clustered projections linking iso-orientation columns. Using extracellular biocytin injections in brain slices, the formation of these projections was examined in the ferret to determine whether horizontal projections exhibit similar patterns of development in the ferret and the cat, and to relate the time course of horizontal projection formation to the onset of patterned visual experience and orientation selectivity. Soon after the first appearance of axon collaterals in layer 2/3, around postnatal day 22 (P22), pyramidal cell axons were uniformly distributed and unbranched for up to 1 mm from the cell body. By P26, axons began to form secondary branches 1-2 mm from the cell body, with little evidence for distinct clusters. The first indication of selective elaboration of secondary branches and retraction of unbranched collaterals occurred around P28. By P34, patchy regions of axon branches emerged, though unbranched collaterals were still present, followed by distinct, adult-like clusters by P45. Although the general pattern of horizontal projection formation closely resembles that seen in the cat (Callaway and Katz, 1990), the ferret circuitry matures earlier than that of the cat relative to the time of eye opening. Since eye opening in ferrets occurs between P30 and P32, this system of orientation-specific patches begins to develop in the absence of patterned visual input and when most cortical cells are not yet orientation selective, suggesting a prominent role for spontaneous activity in initiating cluster formation. The refinement of clustered connections, however, does occur synchronously with the maturation of orientation-selective responses (Chapman and Stryker, 1993).

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