The growth and formation of ocular dominance columns by deflected optic fibers in goldfish.

Abstract

Abstract In juvenile goldfish the simultaneous regeneration into tectum of ‘host’ and ‘deflected’ optic fibers was studied as a function of time after surgery. The host fibers, i.e. those normally innervating tectum were severed by a large incision made across anterior dorsal host tectum. The deflected fibers were those surgically redirected from the opposite ‘donor’ tectum and inserted into this same incision. These deflected fibers were those which normally innervate the posterior dorsal quadrant of donor tectum and in number were about 10–15% of contralateral fibers. At 13–80 days postoperatively either host or deflected fibers were labeled by an intraocular injection of tritiated proline followed by autoradiography 18 h later. At 13–14 days host and deflected fibers both filled the optic laminae in the anterior half of dorsal tectum but were largely absent from the posterior half. By 28–33 days, deflected fibers had grown through the anterior half of tectum showing little or no termination labeling there and both host and deflected fibers had invaded the posterior half of dorsal tectum. In the main optic lamina of dorsal posterior tectum, both sets of fibers overlapped extensively. Over the next 30 days, however, these fibers gradually separated from each other to form eye dominance columns, i.e. alternating columnar zones of host fiber and deflected fiber innervation. Thus regeneration mimics the sequence of overlap followed by segregation found in the normal ontogeny of mammalian cortex. Several other features of reinnervation were noteworthy. The surgical procedure caused fibers, particularly the transplanted ones, to initially enter non-optic tectal layers and even tegmentum. However, fibers quickly turned into optic lamina so that within a few hundred micrometers of the incision site, nearly all label was in the optic layers. Some deflected fibers also invaded lateral tectum, even though the host optic innervation of this region was left intact. This label remained for up to 80 days but retained a fasciculated appearance. A few host fibers grew back along the deflected fibers into donor tectum and by 30 days had spread throughout its dorsal posterior quadrant, the region denervated by the deflection. Virtually all of this label was eliminated by 60 days, and this region was instead innervated by optic fibers from neighboring regions of donor tectum.