Pamela Raymond Johns

Growth of the adult goldfish eye—I: Optics

Abstract We have measured the optical and retinal fields of goldfish eyes; the animals ranged from 6 to 20 cm in body length. Both fields are spherically symmetric, invariant with the size of the eye, and equal (retinal field = 185.3° ± 4.1°, optical field = 183.6° ± 2.7°, means ± S.D.). They are tilted with respect to one another by a few (

Horizontal compensatory eye movements in goldfish (Carassius auratus)

Summary1.Horizontal eye and head movements made by freely swimming goldfish have been recorded cinematographically and analyzed frame-by-frame.2.Most horizontal eye movements occur during turns. A binocular saccade precedes a turn, and the eyes counterrotate relative to the head as the turn progresses, thus keeping a nearly constant orientation in space. The subsequent saccades reset the eyes from an intermediate position to an extreme one.3.Both the saccades and the compensatory movements are generally unequal in the two eyes. The rotation by the eye on the outside of a turn exceeds that of the inner one, which undercompensates.4.The compensation factor, CF, defined as the ratio of (mean binocular rotation relative to the head)/(head rotation), is variable from turn to turn, but averages 0.95±0.10 (mean±2 S.E.M.).5.The slight undercompensation by the inside eye, when coupled with forward movement by the fish, results in relative visual stabilization of a region of space some tens of centimeters or less lateral to the animal. This stabilized region changes with each saccade.

Directed outgrowth of optic fibres regenerating in vitro.

THE way in which growing nerve fibres find their destined sites of termination is largely unknown, although there are supporting arguments and documentation for both local and long-range guidance mechanisms1–3. Fibres regenerating following axotomy tend to grow in the direction of the degenerating tracts, apparently guided through channels formed by debris and/or glial cells4,5. Here we present evidence that the neuritic outgrowth from goldfish retinal explants is related to the orientation of cut fibres within the explant.

Retinal Growth in Adult Goldfish

Most studies of growth and development have been done on embryonic or larval animals, and with good reason. The dramatic increase in size, rapid changes in morphology, and sudden emergence of function in the embryo are much more exciting from a developmental perspective than the relatively static adult state. A separate but related problem is how to grow while functioning, and that is the problem which adult organisms must solve. We are concerned here with growth of the nervous system, in which function is dependent on a precise, orderly set of connexions between neurons. During growth, how are new nerve cells integrated into the system without disturbing the ongoing activity?

Growth and Neurogenesis in Adult Goldfish Retina

Growth continues in adult goldfish. Cell counts and3 H—thymidine radioautography indicate that the brain and retina increase in size in part by the addition of new neurons. The retina of a large, 4-year-old fish (20 cm in length) has about 20,000,000 neurons, whereas in a small (5 cm) fish there are only about 3,000,000 retinal neurons. New cells are produced at the margins of the retina and are added appositionally at rates of up to 20,000 cells/day. Growth-related changes also occur in the older, more central regions of the retina: the eyeball expands, stretching the retina and decreasing the density of its cells. The rods alone maintain a constant density with growth, so that the proportion of rods relative to other retinal neurons increases as the fish grows. Since new rods are added only at the periphery, a shift in the position of rods with respect to their postsynaptic partners is implied. This suggests that synaptic connections may be continually broken and reformed in the functioning adult goldfish retina.