Loss of binocular vision as direct cause for misrouting of temporal retinal fibers in albinism.

In humans, the nasal retina projects to the contralateral hemisphere, whereas the temporal retina projects ipsilaterally. The nasotemporal line that divides the retina into crossed and uncrossed parts coincides with the vertical meridian through the fovea. This normal projection of the retina is severely altered in albinism, in which the nasotemporal line shifted into the temporal retina with temporal retinal fibers cross the midline at the optic chiasm. This study proposes the loss of binocular vision as direct cause for misrouting of temporal retinal fibers and shifting of the nasotemporal line temporally in albinism. It is supported by many observations that clearly indicate that loss of binocular vision causes uncrossed retinal fibers to cross the midline. This hypothesis may alert scientists and clinicians to find ways to prevent or minimize the loss of binocular vision that may occur in some diseases such as albinism and early squint. Hopefully, this will minimize the misrouting of temporal fibers and improve vision in such diseases.

The evolution of contralateral control of the body by the brain: is it a protective mechanism?

Contralateral control, the arrangement whereby most of the human motor and sensory fibres cross the midline in order to provide control for contralateral portions of the body, presents a puzzle from an evolutionary perspective. What caused such a counterintuitive and complex arrangement to become dominant? In this paper we offer a new perspective on this question by showing that in a complex interactive control system there could be a significant net survival advantage with contralateral control, associated with the effect of injuries of intermediate severity. In such cases an advantage could arise from a combination of non-linear system response combined with correlations between injuries on the same side of the head and body. We show that a simple mathematical model of these ideas emulates such an advantage. Based on this model, we conclude that effects of this kind are a plausible driving force for the evolution of contralateral control.

Crossing of neuronal pathways: is it a response to the occurrence of separated parts for the body (limbs, eyes, etc.) during evolution?

Most sensory and motor pathways in the central nervous system cross the midline. Comparing between different neuronal pathways in different species suggest that, fibers crossing is most probably a response to the development of separated parts for the body during the process of evolution. This hypothesis proposes direct link between the occurrence of fibers crossing and the occurrence of separated parts of the body such as lateral eyes and limbs. It is supported by many observations that clearly indicate that different neuronal pathways in different species cross the midline when they carry separated information and run ipsilaterally when they carry shared information. Carrying separated information seems to create a need for functional coordination between the two halves of the nervous system which seems to be mediated by the fibers crossing. This hypothesis may alert scientists to study certain aspects of sensory and/or motor pathways in different species. It also enable the students to remember whether a pathway is uncrossed or crossed based on whether this pathway carry shared or separated information.

Histo-functional effects of Peganum harmala on male rat's spermatogenesis and fertility.

BACKGROUND: The Peganum harmala is currently used by the Jordanian populations systemically for its antispasmodic, diuretic, sedative and analgesic effects and externally for its antirheumatic effect. OBJECTIVE: To study effects of Peganum harmala on the reproductive system and fertility using adult male albino rats. MATERIAL & METHOD: A total of 20 rats were involved in this study and were divided into two groups. Group (A) a vehicle-treated control and group (B) a treated group with aqueous extract of Peganum harmala at a dose of 300 mg/kg body weight for 60 days. RESULTS: This dose induces a significant decrease in the weight of reproductive organs (p<0.01) when compared to controls. The sperm motility and density in cauda epidydimides and testicular ducts were significantly decreased (p<0.01). Furthermore treatments have remarkably altered the histoarchitecture of testes. Spermatogenesis was inhibited at both primary and secondary spermatocyte stages. Epididymides showed reduced number of spermatozoa. Lumen of vas deferentia were devoid of sperms. The secretary activities of seminal vesicle and ventricular prostate were also reduced. Spermatocytes parameters were altered which included a significant decrease count (p<0.001). In addition counts of developing spermatocytes in treated rats showed a decrease in number of spermatocytes and spermatids (p<0.001) when compared to controls. Serum hormonal assay indicated a decrease in Testosterone and Follicular Stimulating Hormone (FSH) levels in treated rats. A decreased in number female rats impregnated by males receiving treatment was observed and demonstrated by a decrease in the implantation sites and viable fetuses number (p<0.01). CONCLUSION: The aqueous extracts of Peganum harmala might have adverse effects on the processes of spermatogenesis due to direct or indirect effects on somniferous tubules and or the pituitary testicular axis.