Alan D. Springer

The role of the optic tectum in various visually mediated behaviors of goldfish

Five visually mediated behaviors were assessed following ablation of one or both lobes of the optic tectum in goldfish. Three of the behaviors disappeared following tectal ablations: optomotor response (swimming with the stripes in a rotating striped drum), food pellet localization and shadow-induced deceleration of respiration. Two of the behaviors persisted following tectal ablation: optokinetic nystagmus (movement of the eyes with the stripes in a rotating striped drum) and dorsal light reflex (tilting of the vertical axis toward the brighter of two laterally placed lights). The unexpected result that lesioned fish tracked the stripes with their eyes, but did not swim after them as normal fish did, suggests that the tectum serves a pre-motor function in addition to its sensory role. In addition, the results demonstrate that selected behaviors can be used to establish whether functional tectal or non-tectal connections are made by regenerating goldfish optic nerves.

Effect of temperature on rate of goldfish optic nerve regeneration: A radioautographic and behavioral study

Optic nerve regeneration was examined in goldfish radioautographically, as well as by a variety of behavioral measures of visual function. The rate of regeneration was markedly enhanced by increasing temperature above the ambient level (20 degrees C). The earliest functional indication of recovery was the appearance of an autonomic response to a change in illumination, then the ability to localize food visually and at a still later time, an optomotor response. Even the early behavioral indications of return of function appeared some time after there was radioautographic evidence that the tectum had been reinnervated.

Bilateral tectal innervation by regenerating optic nerve fibers in goldfish: a radioautographic, electrophysiological and behavioral study.

Following unilateral enucleation and optic nerve crush in goldfish, the remaining nerve regenerates and innervates both optic tecta. Approximately 5% of the nerve fibers reach the ipsilateral optic tectum (IOT) via the ipsilateral tract at the chiasma. Comparable debris in both tracts was not sufficient to result in an IOT projection since when both nerves were crushed simultaneously the usual pattern was seen, i.e., each nerve innervated a contralateral optic tectum (COT). When the arrival of one nerve at the chiasma was delayed by staggering the nerve crushes, the nerve that first arrived at the chiasma partially innervated the Iot. In most instances the entire IOT was innervated, however, the stratigraphic distribution of fibers in the various tectal lamina was atypical. Electrophysiological analysis indicated that fibers from each area of the retina innervated the IOT visuotopically. The COT was ablated in order to determine whether the IOT projection could mediate behavior. All fish failed to respond to changes in illumination as measured by respiration and failed to swim with or against the stripes in an optomotor drum. Thus, the IOT input, possibly because of its sparseness, could not be shown to be behaviorally functional.

Anterograde and retrograde effects of electroconvulsive shock and of puromycin on memory formation in the goldfish

Electroconvulsive shock [ECS] or puromycin administered prior to training did not significantly impair acquisition of shock-avoidance in goldfish. Significant retention deficits are observed on retraining 72 hr later in groups of fish that received ECS 2.5, 1 or 0.5 hr before training as well as in groups that received ECS 0, 4 or 24 hr after training. Puromycin produces significant retention deficits on retraining when given 24, 16, 8, 4 or 0 hr prior to, or 0 or 0.25 hr following training. A temporal course of development of the retention deficit that has been seen with puromycin was not observed with ECS as the deficit was maximal at the earliest train-retrain interval examined. ECS administered before both training and retraining did not relieve the deficit. Since performance was not diminished in fish retrained just after ECS, it appears that this proactive effect of ECS reflects disruption of memory rather than state-dependent learning.

Electroconvulsive shock- or puromycin-induced retention deficits in goldfish given two active-avoidance sessions

In a factorial design, goldfish received 15 active-avoidance training trials on Days 1, 7, and 13 followed by electroconvulsive shock (ECS) or no treatment after the training session on Days 1 and 7. The final retention deficits observed when ECS was given after the first session only or after the second session only were similar. Fish given ECS after both sessions showed a cumulative deficit that approximated the sum of the two effects. Similar results were obtained with puromycin. These data support the hypothesis that ECS and puromycin impair only recent learning. Retrograde amnesia gradients confirmed that the efficacy of these amnestic agents was not altered by a second administration.

The effect of memory blocking antibiotics and their analogs on acetylcholinesterase.

The ability of antibiotics to inhibit acetylcholinesterase was measured in homogenates of goldfish brain. Puromycin aminonucleoside was the most potent inhibitor followed by puromycin, cycloheximide and acetoxycycloheximide. Puromycin effectively impaired retention of active-avoidance learning in goldfish when injected either immediately before or after training, while puromycin aminonucleoside did not regardless of injection time. These results suggest that the known amnestic effects of puromycin, cycloheximide and acetoxycycloheximide are not a consequence of interference with acetylcholinesterase.

Puromycin-induced retention deficit in goldfish as a function of attained training performance level.

Goldfish received either 20 or 50 active avoidance training trials followed by puromycin (or no-treatment) and 10 retraining trials either 1 or 7 days following training. While 50 trials resulted in significantly more training avoidances than 20 trials, the groups which received puromycin showed equivalent retention deficits on Day 7. A within-group comparison of fish whose training performance was high or low further revealed that the degree of the retention deficit was independent of achieved training performance level. These data support the hypothesis that puromycin interferes with a memory fixation process that is initiated only upon completion of the training session.