Retinoic acid (RA) plays an important role in the development of eye and increases cell differentiation of photoreceptors in the early embryonic period. The present study aimed to investigate the effect of exogenous RA during development and morphogenesis of photoreceptors of the developing chick embryo after the initial organogeny of the retina. Fertilized eggs of Gallus domesticus were injected with a single dose of 0.5 µg, 1 µg or 2 µg of RA dissolved in 1 µl of dimethylsulphoxide (DMSO). Injections were carried out after three days of incubation. RA treatment induced cell death of some photoreceptors of the developing retina of chick embryos. Semithin sections examination revealed that the abundance of photoreceptor cells in the retinae of the treated embryos was less than that of the untreated ones. Ultrastructure examination revealed disorder in the cell organoids. Nuclear chromatin was highly condensed at the nuclear envelope. The nucleus lost its oval or spherical shape and transformed into a highly lobulated form probably in a preliminary step towards fragmentation. The results support the hypothesis that high doses of exogenous RA induce cell death and degeneration of photoreceptors during morphogenesis of the retina.

Retinoic acid (RA) is an important player in the developing systems. The present study aimed to investigate the effect of exogenous RA on pattern formation of thr developing chick embryo. Fertilized eggs of Gallus domesticus were injected with a single dose of 0.5 µg, 1 µg or 2 µg of RA dissolved in 1 µl of dimethylsulphoxide (DMSO). Injections were carried out after three days of incubation. RA treatment induced teratogenic effects during the morphogenesis of the developing chick embryos. These effects included eye abnormalities such as lens dysgenesis, retinal folds and chorioretinal coloboma. The effects also included several abnormalities and hypoformations in the trunk and tail regions, fore- and hind-limb abnormalities, and anteriorly shifted hind limbs. Also, dwarfism and disappearance of limb parts were observed. The explanation of the RA effect based on the disturbance of normal pattern of expression of genes concerned with the process of morphogenesis, where the excess of the exogenous RA cause overexpression of some genes resulted in several malformations and disturbance of pattern formation in the developing embryo. Also, RA might have induced cell death in some parts of the limbs leading to disappearance of toes in some cases and syndactyly in other cases.

Retinoic acid (RA) is an important player in the developing systems. The present study aimed to investigate the effect of exogenous RA on pattern formation of thr developing chick embryo. Fertilized eggs of Gallus domesticus were injected with a single dose of 0.5 µg, 1 µg or 2 µg of RA dissolved in 1 µl of dimethylsulphoxide (DMSO). Injections were carried out after three days of incubation. RA treatment induced teratogenic effects during the morphogenesis of the developing chick embryos. These effects included eye abnormalities such as lens dysgenesis, retinal folds and chorioretinal coloboma. The effects also included several abnormalities and hypoformations in the trunk and tail regions, fore- and hind-limb abnormalities, and anteriorly shifted hind limbs. Also, dwarfism and disappearance of limb parts were observed. The explanation of the RA effect based on the disturbance of normal pattern of expression of genes concerned with the process of morphogenesis, where the excess of the exogenous RA cause overexpression of some genes resulted in several malformations and disturbance of pattern formation in the developing embryo. Also, RA might have induced cell death in some parts of the limbs leading to disappearance of toes in some cases and syndactyly in other cases.

Retinoic acid (RA) is an important player in the developing systems. The present study aimed to investigate the effect of exogenous RA on pattern formation of thr developing chick embryo. Fertilized eggs of Gallus domesticus were injected with a single dose of 0.5 µg, 1 µg or 2 µg of RA dissolved in 1 µl of dimethylsulphoxide (DMSO). Injections were carried out after three days of incubation. RA treatment induced teratogenic effects during the morphogenesis of the developing chick embryos. These effects included eye abnormalities such as lens dysgenesis, retinal folds and chorioretinal coloboma. The effects also included several abnormalities and hypoformations in the trunk and tail regions, fore- and hind-limb abnormalities, and anteriorly shifted hind limbs. Also, dwarfism and disappearance of limb parts were observed. The explanation of the RA effect based on the disturbance of normal pattern of expression of genes concerned with the process of morphogenesis, where the excess of the exogenous RA cause overexpression of some genes resulted in several malformations and disturbance of pattern formation in the developing embryo. Also, RA might have induced cell death in some parts of the limbs leading to disappearance of toes in some cases and syndactyly in other cases.

The ultrastructure of the regenerating skin of a larval stage (number 53) of the Egyptian toad, Bufo regularis Reuss was studied after transection at the prospective knee joint level. It was observed that the wound surface was covered with a thin layer of epithelial cells free of underlying basement membrane. The ultrastructure of the epithelial cells revealed typical structure arrangements of migrating cells, such as the cortical cytoplasmic zones devoid of organelles and showing pseudopodial activities. Membrane bound vesicles were found in between the basal plasma membrane and the basal lamina as a sign of detachment. The basement membrane was discontinuous and the dermis was absent during the early few days after amputation, allowing the passage of ectodermal signals from the epithelium to the underlying mesenchymal tissues to enhance blastemal formation. In late stages of regeneration, the basement membrane was continuous and firmly attached the basal plasma membranes through a large number of tonofilament bundles as anchorage sites (Figures of Eberth), which is suggested to act as a source of raw material for building cells of the regenerate after regression of the Figures. The dermis was well developed in the late stages of regeneration.

The ultrastructure of developing and differentiating retinal cells of chick embryo was studies during the early embryonic period from 33 hours old till 6 days old. At 33 hours old, the optic vesicle was 2-3 cells thick. The cells had almost the same form. At 48 hours old, the outer wall of the optic cup became thinner than the inner wall. Retinal cells of chick embryo were mitotically active during the first six days of incubation. It was impossible to distinguish photoreceptor cells from each other during the first three days of incubation. Slimming of the pigmented retina is suggested to be due to apoptosis. The first sign of differentiation was observed at the age of three days, where photoreceptors started to show up. The basal bodies of cilia were formed. The cilia were completely differentiated at the age of six days. Cilia were at the apices of photoreceptors invading the optic ventricle but not tightly attached to the pigment epithelium. Different stages of mitochondrial differentiation were seen. Mitochondriogenesis is suggested in the present study to be de nove. Not all the cells were differentiated at the age of six days. Photoreceptors and pigment epithelial cells were the first types to be observed.

N‐arylthiophene‐2‐carboxamidoxime derivatives (a‐e) were synthesized by using two methods and then subjected to thermolysis at 200–250 °C for 2 h under nitrogen atmosphere either alone or in the presence of tetralin and/or naphthalene as radical scavengers yielded imidazole, oxazole, triazine and amide derivatives. The pyrolysates from both reactions were separated with their constituents by column chromatography and analyzed then identified 1H NMR, 13C NMR and GC‐MS. A plausible mechanism is suggested through two competitive pathways involving the homolysis of N‐O and/or C‐N bonds to account for the thermolysis products.

N‐arylthiophene‐2‐carboxamidoxime derivatives (a‐e) were synthesized by using two methods and then subjected to thermolysis at 200–250 °C for 2 h under nitrogen atmosphere either alone or in the presence of tetralin and/or naphthalene as radical scavengers yielded imidazole, oxazole, triazine and amide derivatives. The pyrolysates from both reactions were separated with their constituents by column chromatography and analyzed then identified 1H NMR, 13C NMR and GC‐MS. A plausible mechanism is suggested through two competitive pathways involving the homolysis of N‐O and/or C‐N bonds to account for the thermolysis products.

N‐arylthiophene‐2‐carboxamidoxime derivatives (a‐e) were synthesized by using two methods and then subjected to thermolysis at 200–250 °C for 2 h under nitrogen atmosphere either alone or in the presence of tetralin and/or naphthalene as radical scavengers yielded imidazole, oxazole, triazine and amide derivatives. The pyrolysates from both reactions were separated with their constituents by column chromatography and analyzed then identified 1H NMR, 13C NMR and GC‐MS. A plausible mechanism is suggested through two competitive pathways involving the homolysis of N‐O and/or C‐N bonds to account for the thermolysis products.

This work is a trial to evoke hind limb regeneration by application of alternating electric current of different wave shapes; sine, square and triangular with different frequencies; 50, 500, 5000 and 50000 Hz. It was found that application of an alternating electric current with different wave shapes partially enhances limb regeneration in the prometamorphic stage (number 56) of Bufo regularis Reuss after amputation at the mid shank level. Regenerates were ranging from limbs with complete number of toes to hypomorphic limbs without toes. The enhancing effect was suggested to be due to stimulation of both the active sties of epithelial DNA, which are involved in the transcription processes. And nerve regeneration. Square and sine waves produced more enhancing effect due to being at peak maximum for periods relatively longer than triangular waves. Application of 50 Hz and 50000 Hz was more effective than that of 500 Hz and 5000 Hz, suggesting its interference with the natural regeneration current to produce the most compatible frequencies creating resonance with the stump tissues.