Prevention of ethambutol induced changes by memantine in optic nerve of rabbit

This study was designed to evaluate the prevention of ethambutol [EMB] induced toxicity in optic nerve by memantine. Forty optic nerve specimens were obtained from twenty New Zealand albino rabbits; these were divided into four groups, each comprising five animals. Group A, was given distilled water according to their weight, in addition to water ad libitum. Group B was treated with EMB 100 mg/kg/day and groups C and D were treated with memontine [MEM], 1 and 5 mg/kg/day respectively, in addition to EMB for four weeks which was given one hour before administering EMB. Optic nerves were removed after sacrificing the animals under anaesthesia and processed for histological examination. It was observed that the preparations from group B showed marked vacuolation of axoplasm [205.60 +/- 49.33] the difference was statistically significant when compared with groups A [2.80 +/- 0.22], C [2.80 +/- 0.98] and D [1.33 +/- 0.37], It was concluded that EMB induced vacuolar changes could be prevented by using MEM

Neuroprotective effect of memantine in a rabbit model of optic nerve ischemia

The purpose of this study was to evaluate the neuroprotective effect of memantine, a N-methyl-D-aspartate antagonist, in an experimental optic nerve ischemia. Endothelin-1 (ET-1) in a dosage of 0.1 microg/day was delivered to the perineural region of the anterior optic nerve by osmotically driven minipumps for 8 weeks in 10 rabbits. In 5 rabbits, 1 mg/kg memantine was administered concurrently by intramuscular injection once a daily. Morphologic optic nerve head changes were monitored with a confocal scanning laser ophthalmoscope. Multivariate statistical analysis showed a significant change in topometric parameters (cup area, cup depth and rim volume), indicating an increase in optic nerve head cupping and a decrease of neural rim volume in the ET-1 administered eyes (P < 0.0001). In rabbits where memantine was given concurrently with ET-1, no significant change in topometric parameters was observed after ET-1 administration (P = 0.78). The current results suggest that memantine has a neuroprotective effect in optic nerve ischemia. Memantine may potentially be useful in the management of various ischemic disorders of the optic nerve, including glaucoma.

Effect of ethambutol on the development of the retina and optic nerve of the chick embryo

The present work was concerned with the development of the retina and optic nerve of the chick embryo and the effect of ethambutol on its development together with the explanation of the possible hazards of antituberculous drugs which May occur To the foetus, if the pregnant mother is under the treatment with these drugs. Histological studies were made on the retina and optic nerve of 9,11 and 15 days chick embryos injected on the 6 th day of incubation with a dose of ethambutol equivalent to the human therapeutic dose [0.8mg/chick embryo]. It was found that ethambutol induced retardation of growth and degenerative changes in the layers of the retina associated with reduction in the size of the optic nerve. As age advenced at 15 day of incubation, regeneration of retina started and progressed gradually till full term, but its size was still less than the control embryo of the same age

Aconite induced myelo-optic neuropathy in a rabbit model

Aconite is a common remedy of herb doctors and is widely used in the Far East. Clinical aspects of the visual disturbance produced by this drug have been described, but little is known about its pathology. Tinctura aconiti (0.6 mg of total alkaloid/kg 2x) was administered intraperitoneally in rabbits to evaluate its toxic effects on the visual system. The alteration in the visual evoked potential following aconite injection consisted of a delay in the onset and peak latency. Histopathologically, there were damages to the myelin sheath of the visual pathway, spinal cord and peripheral nerves. These findings suggest that aconite may cause primarily myelo-optic neuropathy.

Visual evoked responses in tuberculous children on ethambutol therapy.

Visual evoked responses (VERs) were recorded in 47 children, aged 3-13 years with tuberculosis, treated with ethambutol (20 mg/kg/day) as a part of the antitubercular regimen. VERs were evoked by monocular whole field stimulation, the stimulus being provided by a black and white checker-board pattern reversed every 560 msec and recorded before the commencement, 2, 4, 6, 9 and 12 months of therapy and between 3 to 6 months after stopping the drug. In the first 6 months of therapy the mean values of latency ranged from 92.8 to 101.3 msec in the 3 to less than 6 years age group and 88.5 to 100.3 msec in children 6-13 years of age. Between 6-12 months of therapy the mean values of latency were between 93.3 to 101.0 msec in the 3 to less than 6 years age group and 96.0 to 101.5 msec in the older group. Between 3-6 months after stopping therapy the means of latency ranged from 92 to 96 msec. The differences were not statistically significant at any point of time. Thus, children do not seem to be at greater risk for developing ethambutol inducted optic damage as compared to adults. Ethambutol in the above stated dose may, therefore, be recommended for inclusion in antitubercular chemotherapy in pediatrics without undue fear of subclinical toxicity.