Development of individual geniculocortical arbors in cat striate cortex and effects of binocular impulse blockade

Abstract

This study analyzes the morphological changes in geniculocortical axons terminating in the primary visual cortex of the cat, during the period in which, in normal development, the terminals in layer IV undergo an eye-specific segregation. Geniculocortical afferent fibers were filled anterogradely by the Phaseolus lectin (PHA-L) injected into the main laminae of the LGN. After standard immunohistochemical procedures, single axons were serially reconstructed in two or three dimensions. Experiments were performed in normal kittens and in kittens in which retinal activity was continuously blocked by repeated intraocular injections of TTX. In normal kittens, arbors were reconstructed at four different ages (19, 23, 30-31, and 39 days postnatally) spanning the period during which the geniculocortical projection segregates into eye-specific columns in layer IV (LeVay et al., 1978). Results reveal that sparse but widely extending branches characteristic of young arbors are eliminated during normal development at the same time as selected portions of the arbor grow considerably in length and complexity. The terminal arborizations also subdivide into distinct patches of terminals, consistent with the segregation of left and right eye afferents. In TTX-treated animals, axonal arbors reconstructed at postnatal days 23, 29, and 39 show a complexity and extent of terminal arborization similar to that of normal animals, though more variable in size and degree of elaboration. No progressive changes are evident with age. Further, the majority of arbors reconstructed from TTX-treated animals lack the patchy organization typical of normal animals.

Developmental and comparative aspects of posterior medial thalamocortical innervation of the barrel cortex in mice and rats

“…We found no evidence of exuberant growth followed by regression. Such a pattern of directed growth is consistent with that described for the development of other types of circuitry, including VPM TCAs to barrel cortex (Agmon et al, 1995; Catalano et al, 1996), geniculocortical inputs to cat visual cortex (Antonini and Stryker, 1993), and intrinsic barrel cortex projections (Rhoades et al, 1996; Miller et al, 2001; Bureau et al, 2004). Nevertheless, the complexity of single POm TCA arbors in adult rats (Deschenes et al, 1998) far exceeds the typical morphology we observed at P8.…”

Brain-Derived Neurotrophic Factor Enhances Long-Term Potentiation in Rat Visual Cortex

“…The formation or segregation of ocular dominance columns in the visual cortex of kittens is suggested to be dependent on processes of consolidation of core axon terminals or retraction of exuberant terminals (Callaway and Katz, 1992;Antonini and Stryker, 1993). This suggestion seems to be consistent with the recent observations that the column formation in the visual cortex is impaired by the application of BDNF (Cabelli et al, 1995;Hata et al, 1996), because BDNF is known to increase their branching of axon terminals (Cohen-Cory and Fraser, 1995).…”

Robust emergence of small-world structure in networks of spiking neurons

“…However, there is growing evidence for a theory of development based on construction, rather than elimination (Quartz 1999). In biological networks, selective growth and elimination of connections result in a net increase in connectivity (Antonini and Stryker 1993) and structural complexity (Katz and Shatz 1996). When neurons and connections were added to a network op coupled maps, in Gong and van Leeuwen 2003, a scale-free network resulted from the current rewiring scenario.…”