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Intrinsic Connectivity of Identified Projection Neurons in Cat Visual Cortex Brain Slices


Katz, Lawrence Charles (1984) Intrinsic Connectivity of Identified Projection Neurons in Cat Visual Cortex Brain Slices. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/kahn-q578.


The mammalian primary visual cortex is a structure of remarkable physiological and morphological heterogeneity. Despite quite intensive efforts, using a variety of approaches, the relationships between neuronal form and neuronal function have remained obscure. Most previous attempts proceeded on the assumption that a cell's physiological responses to particular stimuli were the best indication of its function. In this study a different assumption was made: that since different efferent targets of area 17 neurons were presumably engaged in different sorts of neural processing, area 17 cells that project to those targets should be engaged in different intrinsic circuits. This in turn might be reflected in distinctive patterns of intrinsic axons and dendrites. This hypothesis was tested by comparing the morphology of two groups of neurons within layer VI of cat area 17: those that project to the claustrum and those that project to the lateral geniculate nucleus. Since both projections occupy the same laminar position, and therefore have potential access to the same environmental and lamina-specific influences, this projection was an excellent system to examine the role of different efferent projections in defining neuronal form, not confounded by differences in laminar position.

This study was carried out by retrogradely labeling, in vivo, one or the other of the projections with a newly developed fluorescent tracer, latex microspheres. Subsequently, in vitro brain slices were prepared from area 17, and the retrogradely labeled neurons were visualized, impaled, and intracellularly stained with a second fluorescent dye, lucifer yellow.

Comparisons of the two efferent projection classes revealed nonoverlapping patterns of distributions of intrinsic axons and dendrites between the two groups, and a remarkable degree of homogeneity within each group. Particularly dramatic was the difference in intrinsic axons: claustrum projecting cells had long, horizontally directed collaterals restricted to layer VI, whereas LGN projecting neurons had few if any collaterals within layer VI, possessing instead thick, ascending collaterals which arborized in layer IV. Additionally, claustrum projecting cells had significantly fewer, yet more extensive, basal dendritic arms than LGN projecting cells. The apical dendrites of the two groups arborized within different overlying laminae, suggesting that the two classes receive different inputs. These differences in axons and dendrites demonstrate that the two cell classes participate in different intrinsic circuits within area 17.

In addition to the two efferent projection classes, a considerable number of pyramidal cells lacking an efferent axon were observed. They resembled either one or the other of the projection classes, and may represent a substantial population of neurons that, during development, were unable to maintain an efferent projection.

These results suggest that, independent of laminar differences, at least some of the cellular heterogeneity observed in cortex may be attributed to the different informational needs of various efferent targets.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Neurobiology
Degree Grantor:California Institute of Technology
Major Option:Neurobiology
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Konishi, Masakazu
Thesis Committee:
  • Konishi, Masakazu (chair)
  • Allman, John Morgan
  • Heiligenberg, Walter F.
  • Van Essen, David C.
Defense Date:27 April 1984
Funding AgencyGrant Number
NIH5T32 GM07737-05
Jean Weigle Memorial FundUNSPECIFIED
Record Number:CaltechTHESIS:11202018-101534170
Persistent URL:
Related URLs:
URLURL TypeDescription adapted for Appendix.
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:11277
Deposited On:20 Nov 2018 21:34
Last Modified:03 Nov 2021 23:39

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