Functional and morphological effects of ß-estradiol in eyes with N-methyl-D-Aspartate-induced retinal neurotoxicity in rats.

Glutamate-mediated excitotoxicity, mainly induced by N-methyl-d-aspartate (NMDA) receptors, is known to cause retinal ganglion cell death in retinal ischemia, glaucoma, and several other retinal diseases. We evaluated the effects of ß-estradiol (E2) against a single intravitreal injection of NMDA using a functional and morphological approach. Male rats were randomly divided into 3 treatment groups: (1) Control; (2) NMDA (intravitreal injection of 5 mM NMDA); and (3) NMDA + E2 (intravitreal injection of 5 mM NMDA and pretreatment with subcutaneous E2 implantation). Seven days after NMDA injection, full-field electroretinograms (ERGs) and quantitative morphological analyses using transverse sections of the retina were conducted. In the NMDA group, full-field ERGs showed reductions in the amplitudes of the negative-scotopic threshold response, rod response b-wave, oscillatory potentials, flicker response second b-wave and cone response b-wave. Morphological evaluations of transverse sections of the retina demonstrated a reduction in the thickness of the inner plexiform layer, increases in the thickness of the outer plexiform and outer nuclear layers, and a loss of cells in the ganglion cell layer. In the NMDA + E2 group, pretreatment with E2 prevented the aggravations in the amplitudes of the ERGs except for oscillatory potential 2 (OP2); however, no morphological differences between the NMDA and NMDA + E2 groups were seen. These findings indicate that E2 can protect retinal function against NMDA-induced neurotoxicity. In addition, these indications suggested that the effect of E2 may have therapeutic benefits in NMDA related diseases, such as retinal ischemia and glaucoma.

Effect of estrogen on electroretinographic responses in streptozotocin-induced diabetic female rats.

The aim of this study is to investigate the effects of estrogen on functional changes in the retinas of streptozotocin (STZ)-induced diabetic rats by using an electroretinography. Female rats were randomly divided into four treatment groups: (1) Control (sham operation and vehicle administration); (2) STZ (sham operation and STZ administration); (3) OVX (ovariectomy and vehicle administration); and (4) OVX + STZ (ovariectomy and STZ administration). Full-field electroretinograms (ERGs) were recorded before OVX and STZ administration and 4 and 12 weeks after STZ administration. At 4 weeks after STZ administration, although there were no differences in the STZ and OVX groups compared with the Control group, the amplitude of the cone-response was significantly lower in the OVX + STZ group than in the Control group (P = 0.013). At 12 weeks after STZ administration, this response showed a similar tendency in the STZ and the OVX + STZ groups. At 12 weeks after STZ administration, the implicit times of OP3 and OP4 and of the cone-response were significantly delayed in the STZ and OVX + STZ groups (OP3: P = 0.030 and 0.050, OP4: P = 0.0060 and 0.0053, cone-response: P = 0.014 and 0.039), compared with in the Control group. Thus, the retinal functions in STZ-induced diabetic female rats were aggravated by OVX. OVX-induced estrogen deficiency resulted in earlier changes in the amplitudes of cone-response, especially in the diabetes, although this is a transient effect and it is difficult to explain. Recognizing the early neurosensory change would enable a better understanding of the effect of estrogen in the retina.

Spontaneous Ocular Abnormalities in Sprague-Dawley Rats.

We collected historical control data derived from pretreatment ophthalmologic examinations of young (4 to 7 wk of age) Sprague-Dawley (Crl:CD[SD]) male, (2033, 42 lots) and female (1322, 32 lots) rats used in toxicity studies at our facility from 2004 through 2015. Ophthalmologic examination of male and female rats by using a binocular indirect ophthalmoscope and slit lamp revealed high incidences of corneal opacity (61% and 60%, respectively), lenticular opacity (43% and 47%), persistent hyaloid artery (21% and 17%), and retinal folds (27% and 27%). All other ocular abnormalities of the globe, conjunctiva, cornea, anterior chamber, lens, iris, vitreous, and choroid or retina occurred at incidences of less than 5%. Corneal opacities were localized mainly in the corneal nasal (38% and 37%) and paracentral (32% and 33%) areas, and lenticular opacities predominantly occurred in the nuclear area (31% and 34%). We then compared the incidences of spontaneous ocular abnormalities between the first (2004 through 2009) and second (2010 through 2015) 6-y periods. Corneal opacity and persistent hyaloid artery in male and female rats occurred more frequently during the second 6-y than during the first (corneal opacity, second period: male, 68%; female, 66%; corneal opacity, first period: 49% and 51%; persistent artery, second period, 26% and 23%; persistent artery, first period; 12% and 10%). These results support the importance of updating historical control data regularly and providing useful information for toxicologists and ophthalmologists to differentiate treatment-related changes from spontaneous lesions.

Drug-induced lenticular opacity and accumulation of cholesterol-related substances in the lens cortex of dogs.

TP0446131, developed as an antidepressant agent, was found to cause lenticular opacity in a 13-week repeated-dose study in dogs. Histopathologically, the lenticular opacity was observed as a degeneration of the lens fibers, characterized by irregularity in the ordered arrangement of the fibers which is necessary to maintain the transparency of the lens, and was considered to manifest clinically as cataract. To evaluate the development mechanism of the lenticular opacity, the chemical constituents of the lens, which is known to be associated with the development of cataract, were examined. The results of liquid chromatography-tandem mass spectrometry analysis revealed an increase in the amplitudes of 3 unknown peaks in a dose- and time-dependent manner in the lens, with no remarkable changes in the other chemical components tested. In addition, the content of cholesterol, alterations of which have been reported to be associated with cataract, remained unchanged. The mass spectral data and chromatographic behavior of the 3 peaks indicated that these peaks corresponded to sterol-related substances, and that one of them was 7-dehydrocholesterol, a precursor of cholesterol biosynthesis. This finding suggested that TP0446131 exerts some effects on the cholesterol biosynthesis pathway, which could be involved in the development of the cataracts. Furthermore, increases in the levels of these sterol-related substances were also detected in the serum, and were, in fact, noted prior to the onset of the cataract, suggesting the possibility that these substances in the serum could be used as potential safety biomarkers for predicting the onset of cataract induced by TP0446131.

Full-field electroretinography obtained using a contact lens electrode with built-in high-intensity white-light-emitting diodes can be utilized in toxicological assessments in rats.

Full-field electroretinography (ERG) using contact lenses with built-in LED was performed on albino rats, and used to evaluate the visual toxicity of sodium iodate (NaIO(3)). Experiment 1 was carried out to determine the optimal conditions in rats relating to stimulus intensity, background illumination, and light adaptation period. As a result, we found that a full-field ERG was recorded under the following conditions: stimulus intensity: -3.5 log cd s/m(2) in rod response; background intensity and light adaptation period: 10 cd/m(2) and 10 min in cone and flicker responses. Experiment 2 was carried out to confirm the usefulness of full-field ERG using rats with retinal toxicities induced by NaIO(3). Male rats were given NaIO(3) intravenously at a dose of 50 mg/kg. ERG was recorded before administration and after 3, 8, 24 h, and 7 days of administration, and histopathological analysis was conducted after 8 h of administration. The rod response disappeared completely at 3 h, based on a reduced maximal response and oscillatory potentials. On the other hand, cone and flicker responses were still present at 8 h. All responses disappeared on the 7th day. These findings indicate that the retinal toxicity induced by NaIO(3) was expressed first in rods, followed by cones. There were no microscopical changes after 8 h of administration, although the rod responses had completely disappeared by this time. These results suggest that full-field ERG in rats using an LED contact lens is useful for the separate evaluation of toxic effects on rods and cones.

Evaluation of the efficacy and safety of coil occlusion for patent ductus arteriosus in dogs.

We performed a retrospective study of 56 dogs with Patent Ductus Arteriosus (PDA) to evaluate the indications for and efficacy of transarterial PDA coil embolization. Transarterial PDA coil embolization was conducted in 37 cases (66.1%) and surgical ligation was conducted in 16 cases (28.6%). Three cases (5.4%) were diagnosed as pulmonary hypertension and were excluded from surgical intervention. Although coil dislodgement was observed in the pulmonary artery in one case, no death occurred during coil embolization or surgical ligation. Echocardiography showed that fractional shortening decreased from 35.4 +/- 6.8% to 30.2 +/- 5.9% (P<0.05) after transarterial PDA coil embolization. Although slight residual shunts were observed in 18 cases, transarterial PDA coil embolization was effective treatment of PDA.