Effect Of Unilateral Enucleation Research Articles

Changes in the Motor Asymmetry and Structure of Mauthner Neurons of the Goldfish Resulting from Unilateral Visual Deprivation

We studied the effects of unilateral enucleation of the eye on the motor asymmetry of goldfish fries and morphometric characteristics of their Mauthner neurons, MNs (data of 3D reconstruction using serial slices). Enucleation of the right or left eye in ambidextral fishes resulted in stable preference of turnings during swimming toward the side of visual deafferentation and in a shift of the initial motor asymmetry coefficient (MAC) by 25%, on average. Ipsilateral enucleation of the eye in dextral and sinistral fishes intensified the initial motor asymmetry by 20%. Contralateral enucleation of the eye in dextral and sinistral fishes induced inversion of the motor asymmetry with a decrease in the MAC by 50%, on average. All operated fishes stably (within 3 months or more) preferred to turn toward the side of the enucleated eye. Morphological measurements showed that the size of the ventral dendrite of the MN contralateral with respect to the side of enucleation noticeably decreased. At the same time, this neuron (according to a shift in the motor asymmetry of the fish) became the functionally dominant unit. These data agree with the earlier supposition on a reciprocal relation between the level of functional activity of the MN and the size of its ventral dendrite. Selective changes in the dimension of the ventral dendrite of the MN receiving visual inputs probably resulted from the action of some endogenous trophic factor. The effect of this factor was enhanced after enucleation of the eye and the corresponding dysfunction of the contralateral visual input. A specific local change in the balance of neurotransmitter influences upon the MN ventral dendrite can play the role of such a factor. From the neurophysiological aspect, a decrease in the size of the ventral MN dendrite is a primary link in the chain of events resulting in modification of behavior; it leads to intensification of the integral functional activity of the MN and a shift of the motor asymmetry of the fish compensating, in such a way, the effect of unilateral visual deprivation.

Return to work following unilateral enucleation in 34 horses (2000–2008)

REASONS FOR STUDY: The effect of unilateral enucleation on vision and potential loss of performance in horses has received little study. To evaluate the likelihood of return to prior discipline following unilateral enucleation in horses, assessing the role of age at enucleation, equine discipline, reason for enucleation, time to vision loss and eye enucleated. Unilateral enucleation has no significant effect on likelihood of return to work in horses, for both right and left eyes, across age and discipline. A retrospective review of medical records identified 92 horses that underwent unilateral enucleation at the University of Pennsylvania New Bolton Center from April 2000-April 2008. Case variables determined from the medical record included breed and sex of horse, age at enucleation, which eye was enucleated, reason for enucleation and onset of vision loss. Pre- and post operative occupations were determined by telephone interview with the owner or trainer of each horse. Based on hospital surgery logs, 92 enucleations were performed over the 8 year period and 77 records were available for review, with follow-up information available for 34 horses. Of these, 29/34 (85%) horses returned to work in pleasure or trail riding (11/13), flat racing (7/10), hunter/jumpers (4/4), dressage (3/3), group lessons (1/1), eventing (1/1), steeplechase (1/1) and as a broodmare (1/1). Four of 5 horses (4/34, or 12% sample) that did not return to work (2 pleasure and 2 racing) were retired due to anticipated or perceived decrease in performance or behaviour change following unilateral enucleation, with the remaining horse retired from racing for lameness issues unrelated to enucleation. Twenty-two of 25 horses (88%) with acute vision loss and 7/9 horses (78%) with gradual vision loss returned to their previous discipline. Horses are able to return to a variety of occupations after unilateral enucleation.

Monoamine Oxidase-A-positive Retinal Ganglion Cells Projecting to the Superior Colliculus and Dorsolateral Geniculate Nucleus of the Rat Brain

Detailed morphology and distribution of monoamine oxidase type A (MAO-A) positive retinal ganglion cells, and their synaptic terminals in the superior colliculus and the lateral geniculate nucleus, were investigated by light and electron microscopy. In addition, the differences in various retinal ganglion cells with respect to the projection site were examined by the injection of colloidal gold into the superior colliculus and the lateral geniculate nucleus. The effects of unilateral enucleation were also examined.In the retina, small, medium and large sized MAO-A-positive ganglion cells were observed; the large sized cells were distributed evenly throughout the retina, while the small and medium sized cells were most numerous in a ring surrounding the central retina and decreased in density near the optic disc and the peripheral retina. The MAO-A-positive terminals in the superior colliculus were smaller in size than those in the lateral geniculate nucleus. From colloidal gold injections, it was apparent that the MAO-A-positive ganglion cells projecting to the superior colliculus were generally smaller in size than those projecting to the lateral geniculate nucleus. Fourteen days after unilateral enucleation, the MAO-A-positive terminals in the superior colliculus and lateral geniculate nucleus contralateral to the enucleated eye had almost disappeared, whereas those in the ipsilateral regions remained unaffected. These findings demonstrate the distribution and projections of the MAO-A-positive ganglion cells.

Substance P and enkephalins in the superficial layers of the rat superior colliculus: Differential plastic effects of retinal deafferentation

In this work we studied the effects of unilateral eye enucleation on the contents and distribution of leu-enkephalin-, met-enkephalin-arg6-gly7-leu8-, and substance-P-like immunoreactivities (L-ENK-I, ENK-8-I, and SP-I, respectively) in the superficial layers of the rat superior colliculus (SC) by means of the unlabelled antibody peroxidase-antiperoxidase method. In the normal rat only a few L-ENK-I neurons appear dispersed in the stratum griseum superficiale. No immunostained somata appear in the stratum opticum. The most striking effect of unilateral enucleation was the dramatic appearance of a laminarly distributed population of L-ENK-I and/or ENK-8-I neurons in the dorsal stratum opticum of the SC contralateral to the enucleated side. This population of immunoreactive cells was observed with all the survival times examined in the present study (3, 7, 15, and 30 days) and was always accompanied by an increase in the immunostaining of L-ENK-I and/or ENK-8-I fibers in the contralateral stratum griseum superficiale. Enucleation also produced a decrease in the immunostaining of SP-I dendrites that only became obvious 15 days after enucleation. However, the number of SP-I somata or terminal-like immunoreactive structures showed no detectable changes. These results show that retinal deafferentation of the superficial layers of the rat SC has different effects on some immunohistochemically distinguishable neuronal subgroups in the SC, suggesting different functional or trophic relationships of the retinal input to these groups of neurons.

The ipsilateral retinocollicular projection in the rabbit: an autoradiographic study of postnatal development and effects of unilateral enucleation.

The postnatal development of the ipsilateral retinocollicular projection in the rabbit and the effects of unilateral enucleation (performed on the day of birth, day 0) on that development were studied by using the anterograde axonal transport of tritiated proline injected intraocularly. Material from 1-, 6-, and 10-day-old (i.e., at days 1, 6, and 10) and adult animals was examined. On day 1, autoradiographically labelled optic fibers from the ipsilateral eye formed distinct patches and bands within the superior colliculus (SC), which were restricted primarily to the lateral one-half and anterior one-third to one-half of the nucleus. At subsequent ages no major changes in the location of this projection were found for normal animals or animals enucleated on day 0 (0-DE animals). From dorsal-view reconstructions, the pattern of the ipsilateral projection appeared wedge-shaped with a broad base aligned with the lateral SC border for all normal and 0-DE animals at the various postnatal ages examined. In normal animals the surface area of this projection increased with age and maintained a constant proportion of the increasing surface area of the total SC. In 0-DE animals the surface area of the projection initially increased more rapidly than in normal animals. Thus, by day 6 the area was already within the normal adult range but did not exceed this range at later postnatal ages. The only obvious difference in the appearance of the ipsilateral retinocollicular projection between normal and 0-DE animals at corresponding ages was an enhanced radial distribution of the projection across laminae in the 0-DE animals. Taken together these findings suggest that, in the rabbit, once topographically appropriate connections are established between the SC and the ipsilateral retinal projection, they are maintained regardless of substantial postnatal growth of the SC and removal of the contralateral retinal projection to the SC.

The effect of eye enucleation on the number of fibres in the supraoptic decussation of posthatch chicks ( Gallus gallus)

In this study of the young chick we examine the effects of unilateral or bilateral eye enucleation on the number of axons in the supraoptic decussation, a major interhemispheric tract subserving visual function. On posthatch day 25, chicks underwent removal of either one or both eyes. After a survival period of 32 days, electron microscopic examination of the supraoptic decussation revealed a substantial loss of fibres. In the bilaterally enucleated group, a significant decrease in the number of axons occurred in both the dorsal and ventral aspects of the supraoptic decussation. The effect of unilateral enucleation was not as severe. The results indicate that enucleation of the precocial and functioning visual system of the chick leads to a transneuronal loss of axons. The degree of loss may reflect the amount of fibres in the crossed visual projection within the supraoptic decussation.

Postnatal development of the ipsilateral retinocollicular projection and the effects of unilateral enucleation in the golden hamster.

Anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) was used to study the normal development of the ipsilateral retinocollicular projection in golden hamsters, and to examine the effect of enucleation of the other eye at birth. In neonatal animals there were retinal fibers and sparsely distributed granular labeling in the superficial layers of the ipsilateral superior colliculus over its entire areal extent. Differences in the uncrossed projections of normal and enucleated animals first became clear at day 5. In normal animals, retinal fibers withdrew from the superficial layers of the superior colliculus, and the projection became concentrated in the stratum opticum, where denser clumps of label in the rostral part of the superior colliculus were first seen at day 5. In enucleated animals, the retinal projection persisted in the most superficial layers, and the density of labeling was higher than in normals. The very sensitive WGA-HRP technique showed retinal fibers extending to the caudal pole of the superior colliculus at all ages: even in normal animals more than 2 weeks of age some fibers reached as far as the inferior colliculus. When the shrunken size of the superior colliculus in the enucleated animals was taken into account, the total areal distribution of the ipsilateral projection was similar in normal animals and enucleates. The major difference between the two groups was in the higher density of ipsilateral labeling, especially in the caudal part of the superior colliculus, and in its more superficial laminar distribution in the enucleated animals.

Cholinergic transmission in subcortical and cortical visual centers of rats: No evidence for the involvement of primary optic system

The effect of unilateral enucleation, ablation of the visual cortex or coagulation of the lateral geniculate nucleus (LGN) upon the activity of choline acetyltransferase (ChAc) and acetylcholinesterase (AChE) in different structures of the visual system of albino rats was studied. The localization and extent of the degeneration pattern were followed up by histological silver degeneration methods. Afferents from the retina project mainly contralaterally to the dorsal and ventral LGN, the pretectal region and the superior colliculus. Afferent fibres from the dorsal LGN enter the visual cortex in area 17 only. Neurons of this area project back ipsilaterally to the LGN and the superior colliculus (SC). No significant decrease in the activity of the cholinergic marker enzyme choline acetyltransferase could be observed under any of the experimental conditions; there was rather a tendency to increased activity in the subcortical centres. AChE as a less specific marker also exhibited no gross changes in activity in the lesioned animals. The results add more direct proof to pharmacological and physiological evidence that ACh is not involved in the synaptic transmission of the direct optic projections in rats, either at the subcortical or at the cortical level.

Effect of unilateral enucleation on protein and ribonucleic acid metabolism of avian brain

The metabolic activity of brain regions at various times after unilateral eye removal has been studied in the chick where the visual pathways are totally crossed over. Protein and ribonucleic acid from cerebral hemispheres and optic lobes were assayed for radioactivity following subcutaneous injection of tritiated leucine or uridine. Cerebral hemispheres and optic lobes contralateral to the extirpated eye showed a reduction of protein and RNA synthetic rate relative to the paired ipsilateral regions. Some of these differential effects were observed in animals as early as 1 hr after enucleation and persisted during the ensuing 17 days. Results were of similar magnitude both in the optic lobes which are directly innervated by the optic nerve and in the cerebral hemispheres which receive little or no direct innervation from the optic tract. The decay rates of protein or ribonucleic acid were unaltered in the paired regions from unilaterally enucleated birds. The results suggest that rapid metabolic alterations subsequent to eye removal are not confined to directly denervated regions. A significant fall in the rate of RNA synthesis is the earliest effect noted; subsequent effects may thus be a reflection of alterations of RNA transcription at the genetic level.

Structural changes in the area striata of the mouse after enucleation.

The optic pathways of the mouse have been studied by tracing of degenerating fibers after enucleation and coagulation of the lateral geniculate nucleus. The effects of unilateral enucleation at birth in the contralateral area striata of the mouse have been studied with the Golgi method. The number of spines on three different portions of the apical dendrites of layer V pyramidal cells have been counted in the affected area striata of mice 24 and 48 days old enucleated at birth. The results were compared with the countings obtained in the area striata homolateral to the enucleated side and with controls of the same ages. The results indicated that enucleation produces, through a series of transneuronal changes, significant diminution of the number of spines in the apical dendritic segments located in layer IV. The diminution of dendritic spines is more pronounced in younger animals. Specific variations in the orientation of dendrites of stellate cells with ascending axons have been observed in enucleated animals. The significance of these findings has been discussed suggesting the existence of compensatory mechanisms which affect significantly the intrinsic organization of the area striata.

The development of the optic lobes in the frog. I. The effects of unilateral enucleation in embryonic stages

The development of the optic lobes in the frog. I. The effects of unilateral enucleation in embryonic stages