Hierarchies in light sensing and dynamic interactions between ocular and extraocular sensory networks in a flatworm

Light sensing has independently evolved multiple times under diverse selective pressures but has been examined only in a handful among the millions of light-responsive organisms. Unsurprisingly, mechanistic insights into how differential light processing can cause distinct behavioral outputs are limited. We show how an organism can achieve complex light processing with a simple "eye" while also having independent but mutually interacting light sensing networks. Although planarian flatworms lack wavelength-specific eye photoreceptors, a 25 nm change in light wavelength is sufficient to completely switch their phototactic behavior. Quantitative photoassays, eye-brain confocal imaging, and RNA interference/knockdown studies reveal that flatworms are able to compare small differences in the amounts of light absorbed at the eyes through a single eye opsin and convert them into binary behavioral outputs. Because planarians can fully regenerate, eye-brain injury-regeneration studies showed that this acute light intensity sensing and processing are layered on simple light detection. Unlike intact worms, partially regenerated animals with eyes can sense light but cannot sense finer gradients. Planarians also show a "reflex-like," eye-independent (extraocular/whole-body) response to low ultraviolet A light, apart from the "processive" eye-brain-mediated (ocular) response. Competition experiments between ocular and extraocular sensory systems reveal dynamic interchanging hierarchies. In intact worms, cerebral ocular response can override the reflex-like extraocular response. However, injury-regeneration again offers a time window wherein both responses coexist, but the dominance of the ocular response is reversed. Overall, we demonstrate acute light intensity-based behavioral switching and two evolutionarily distinct but interacting light sensing networks in a regenerating organism.

Cellular immunity in Hodgkin's disease

Defective cell-mediated immunity (CMI) occurs early in the course of Hodgkin's disease (HD) and may persist even two years after successful treatment. This has been confirmed by in vivo and in vitro tests performed on 51 untreated and 52 treated patients of HD. The grading of skin reponse in vivo to dinitrochlorobenzene (DNCB) correlated very well with the in vitro leukocyte migration inhibition (LMI) response against phytohemagglutinin (PHA). An inhibitory influence of HD patients' sera was demonstrated by LMI tests in vitro. The response of peripheral leukocytes from HD patients in the LMI tests could be augmented in vitro by addition of levamisole (an immuno-potentiator) to the culture medium, thus pointing to an intrinsic defect in Lymphocytes. The data indicate that defect at multiple sites in the immune system is responsible for persistent anergy in HD.