J.F. Hobbelen

The effect of continuous light exposure on the retina in albino and pigmented rats

Abstract The effect of exposure to continuous light on the electroretinogram of albino and pigmented rats was studied. Two series of animal groups, adult or new-born at the start of the exposure period, were given different light-dark regimes for different periods of time. Increase of the a- and b-wave threshold was only found in the albino rats exposed to continuous light. In none of the groups an effect on wave threshold of age at the start of the exposure or exposure duration was seen. Reduction of the amplitude of the a- and b-wave, and lengthening of the time to peak of both waves was seen in all groups exposed to the high light intensity, though the effects of overexposure were much stronger in the albino rats. Moreover the changes in ERG parameters in the albino rats after overexposure were strongest in the adult at the start of the exposure period animals. Morphological damage of the retina after exposure was only seen in albino rats after continuous light exposure.

Visual discrimination after bilateral removal of the visual cortex in the rabbit

Rabbits were trained on a brightness and a vertical vs horizontal discrimination. After bilateral removal of the visual cortex the threshold of brightness discrimination was significantly higher. In addition, there was a severe impairment of striated pattern discrimination.

Visual discrimination learning in corpus callosum sectioned rabbits

Abstract Corpus callosum-sectioned rabbits were examined on several visual discrimination tasks. The learning of either a black-white or a vertical-horizontal discrimination was found to be entirely normal in such animals. Finally they were tested on an oblique striation task where a colour filter system was used to ensure only one of the two visual patterns was available to each eye on any given trial. No learning deficit was found in cerebral-bisected animals provided the commissure section was complete and without functional side effects.

Motor behaviour and visual discrimination after neonatal and adult hemidecortication in the rabbit

In 5 groups of rabbits (0-1, 2-3, 4-5, 6-7 and 12-13 weeks old) the left frontal, parieto-temporal and occipital cortex were removed. Beginning two weeks after the operations the hopping reaction was tested during 15 weeks. It was found in the groups operated 0-1, 2-3 and 4-5 weeks after birth, that the hopping reaction developed normally. This was not the case in the animals operated 6-7 and 12-13 weeks after birth. Brightness discrimination with the left and right eye was tested in the same animals, beginning 12 weeks after the operation. Contrary to the motor system, no age-dependent recovery was found in the visual system. In all age groups, brightness discrimination with the eye contralateral to the lesion was impaired.

Monocular pattern discrimination in rabbits with unilateral lesions of the motor cortex

Abstract Rabbits with unilateral lesions of the motor cortex were trained to discriminate vertical versus horizontal striations. After reaching the training criterion with binocular vision, the performance was tested with each eye separately. It was found that performance with the eye contralateral to the lesion was markedly inferior to that with the other eye.

DESCENDING PATHWAYS AND THE HOPPING RESPONSE IN THE RABBIT

Descending pathways were studied in 5 adult rabbits by means of HRP, injected in the cervical spinal cord (in C2 and C3) at the right side. Results indicate the existence of pathways from the contralateral motor cortex, bilateral projections from the red nuclei, from the vestibular nuclei and from several nuclei in the reticular formation.

The hopping reaction in the rabbit after early and late removal of the motor cortex.

Unilateral lesions of the sensorimotor cortex were made in rabbits either 24 h or 6 months after birth. Four months after the operation the hopping reaction in the leg contralateral to the lesion was still absent in the animals operated in adulthood. In the animals operated one day after birth a normal hopping reaction was found when tested 1.5 and 4 months after the operation.

The effect of devascularization of the visual cortex on visual function in the rabbit

The role of the visual cortex in brightness and pattern vision was re-examined in the rabbit. Animals were trained on both a brightness and a horizontal-vertical striation discrimination. Bilateral removal of the dura mater overlying the entire visual cortex produced no impairments in either brightness or pattern vision. When the visual cortex was devascularized by removal of the pia mater bilaterally, total loss of pattern vision was found with no impairment of brightness discrimination ability. The significance of the finding that the effects of slowly developing degenerative lesions are the same as those of surgical ablation was discussed.

The hopping response after two-stage cortical ablation in young and adult rabbits

In a group of 14 rabbits aged between 14 and 21 days a hemidecortication was performed in the left hemisphere. A normal monopedal lateral hopping response developed in both forelegs. At adult age, 13 weeks after the first lesion, the remaining cortex on the right side was ablated. Three days afterwards the hopping response was tested again. In all animals, the hopping response remained positive in the right foreleg, contralateral to the lesioning at early age. However, in 10 out of 14 animals the response was absent on the left side, contralateral to the recent lesion. These results show that the hopping response is not mediated by corticofugal connections of the remaining hemisphere of the foreleg contralateral to the early lesion.

The Effects of Early and Late Hemidecortication on Vision and Locomotion in the Rabbit

The hemispherectomized rat and cat have been used by various investigators as a model for studying the processes underlying age-dependent recovery from brain damage.