Background to work on retinoids and amphibian limb regeneration: studies on anuran tadpoles - a retrospect

Studies on the effects of exogenous vitamin A palminate on limb development and regeneration in anuran tadpoles carried out since late 1960s at the author's laboratory are reviewed and discussed. Most significant was the initial discovery that vitamin A causes regeneration of complete or nearly complete limbs instead of only the missing distal part, thus altering the P-D pattern of regeneration-a phenomenon now called proximalization. Often more than one such regenerates develop per stump. Vitamin A produces proximalizing effect on regeneration cells during their dedifferentiation and blastema formation but inhibits regeneration if given once redifferentiation begins. Shank-level blastemas from treated tadpoles grafted into orbits of previously treated/untreated host tadpoles formed complete limbs. Proximalizing effect is proportionate to vitamin A concentration, duration of treatment, amputational level and stage of tadpoles. Vitamin A produces this effect also if given only prior to amputation. Its influence persists after cessation of treatment, declining with time. Proximalizing effect is correlated with natural ability in limbs to regenerate. Vitamin A improves regenerative ability and can induce it to some extent in non-regenerating limbs. Vitamin A excess retards limb development and produces stage dependent teratogenic defects. Further development of only that limb region is prevented in which differentiation is beginning when vitamin A is given. Short treatment of tadpoles beginning with limbs at spatula/paddle stage inhibited foot development in the unoperated limbs hut promoted regeneration of complete limbs from the contra-lateral amputated limbs. These dual effects were due to cells of the former differentiating and of the latter dedifferentiating when exposed to vitamin A palmitate

Development of mouthparts in the tadpoles of Rana tigrina Daud

The morphology of the mouthparts of Rana tigrina tadpoles is studied. The development starts after hatching with distinct mouth opening and is followed by paired beaks and labial fringes. The horny teeth then start differentiating in both the labial fringes and by addition of successive rows of teeth the full complement of larval dentition is developed. The mouthparts persist upto stage 50 and by stage 51 both the beaks and teeth are shed and the labial fringes are considerably resorbed

Non-linear optimized spatial filter for single-trial identification of movement related cortical potential

To investigate the optimal filter settings for pre-processing of Movement Related Cortical Potentials (MRCP) for the detection through EEG in single trial, we have proposed a novel Non-Linear Optimized Spatial Filter (NL-SF) and compared it to the Optimized Spatial Filtering (OSF) used in literature. MRCPs from EEG recordings are emphasized, calculating the optimal non-linear combination of channels which isolates the signal of interest. The method is applied to EEG data recorded from 16 healthy patients either executing or imagining 50 self-paced upper limb movements (palmar grasp). MRCPs have been identified from the outputs of the two filters by matching with a template built by averaging responses to movement intentions in the training set. NL-SF had a median accuracy on the overall dataset of 84.6%, which is significantly better than that of OSF (i.e., 76.9%). Being a filter and feasible for self-paced applications, it could be of interest in online BCI system design

Correlation of the proximalizing effect of retinoid treatment on limb regeneration in anuran tadpoles with the normal capacity to regenerate

The unique effect of retinoids on limb regeneration in amphibians is expressed in the apperance of some or all stump structures in the regenerate; the phenomenon is described as proximalization of blastema.In the anuran larvae and urodeles the proximalized blastema forms the regenerate which may even be a complete limb and not just the part removed distal to the amputation level.Urodeles retain the normal capaciy to regenerate amputated limbs throughout life but in the developing hind limbs of anuran larvae this capacity is progressively reduced along its P-D axis and lost completely with the approach of metamorphosis. The question was whether the proximalization of limb regeneration by retinoids in anuran tadpoles is related with the presence of normal capacity to regenerate. Therefore, the frequency of the type of regenerates produced in controls (untreated) was compared with that in vitamin A treated groups after amputation across thigh, shank and ankle in young and older tadpoles of Bufo melanostictus. In young control groups, good regeneration occurred in nearly all cases at the three levels; and all regenerates were the usual type consisting of the part only distal to amputation level. In older tadpoles this capacity was reduced with regenerates developing in fewer cases, many of them being hypomorphic, and in the oldest group small spikes developed in a few cases only at the ankle level. In young vitamin A treated groups, regeneration at the three levels occurred also in nearly all cases; but all regenerates were the proximalized type and structurally perfect. In the tadpoles of a higher devlopmental stage having reduced regenerative capaity, vitamin A treatment produced both the proximalized and the usual type regenerates, the former type being fewer at thigh but much more than the latter type at shank and ankle levels. Both types were structurally well formed. In the oldest group with almost nil regenerative capacity, vitamin A treatment did promote some regeneration in many cases at all levels but only of small spikes. Results indicated that proximalization of blastema by retinoid in anuran tadpoles is positively related with the extent of the ability to regenerate present in the limbs at any stage

Abnormal hind limb regeneration in the tadpoles of the toad Bufo andersonii exposed to vitamin excess

Young tadpoles of the toad, Bufo andersoni, at a very early stage of hind limb development underwent amputation through the shanks and were exposed to 15IV of vitamin A palmitate per I ml of water. Whereas controls regenerated normal limbs, in the treated tadpoles the regenerates were retarded and highly abnormal. In 6 out of 14 cases multiple regenerates developed from the stump. In 5 cases the regenerated portion consisted of rudiments of the whole limb including thigh, shank, and foot regions, i.e. also from parts already present in the stump. It is suggested that exposure to excess vitamin A increases the potencies of the blastemas thus enabling them to overcome the restrictive influences of the stump and to form a whole'limb instead of only the distal parts actually removed by amputation

A comparitive study on the effects of palmitate and acetate forms of vitamin A on toad tadpoles

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The various effects of retinol palmitate on hind limb regeneration in Bufo melanostuctus tadpoles of different developmental stages

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The pattern of decline and loss of the capacity for hind limb regeneration in the tadpoles of Bufo melanostictus Schneider

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An ammocoete larva of Entosphenus lamottenii (Lesueur) with an accessory tail

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