[Effects of weak magnetic fields on different phases of planarian regeneration].

We analyzed the effects of weak combined magnetic fields, tuned to the cyclotron resonance condition for calcium ions, obtained in different phases of planarian regeneration. We showed that the result of regeneration in 72 hours after decapitation depends on the length of exposure, and the time between decapitation and initiation of a half-hour exposure. The experimental dependence can be explained by a multiplicity of enzymatic targets activated in different phases of the regeneration process.

[Retinoic acid as a regulator of planarian morphogenesis].

The effect of retinoic acid on regeneration of two species of asexual planarian races, Girardia tigrina and Schmidtea mediterranea, was studied. It was established that retinoic acids at physiological concentrations (10(-7)-10(-10) M) inhibit the regeneration of the head part of planarians but have no effect on tail blastema growth. It is shown that regeneration of the head part is inhibited as a result of arrest of the cell cycle of neoblasts, proliferating stem cells, during the transition from the G1/G0 to the S phase. Thus, the morphogenetic role of retinoic acids in planarians, primitive bilaterally symmetrical animals, has been demonstrated.

[Melatonin effect on the regeneration of the flatworm Girardia tigrina].

The melatonin effect on the anterior and posterior ends of a free-living flatworm Girardia tigrina was studied, as well as the variability of the mitotic activity of the stem cells (neoblasts) in the anterior and posterior postblasteme. This hormone may inhibit the regeneration of the anterior end of the animal in the physiologic-friendly concentrations of 10(-10)-10(-15) M by suppressing the mitotic activity of the neoblasts. This hormone does not affect the posterior end's regeneration; thus, its regeneration effect is significantly elective.

[Regulation of asexual reproduction in the planarian Dugesia tigrina]. / Reguliatsiia besplologo razmnozheniia planarii Dugesia tigrina.

We studied asexual reproduction of planarians under the natural and artificial photoperiodic conditions. It was shown that light inhibits the fission of planarians, while darkness stimulates it. The diurnal dynamics of the fission of planarians demonstrated a circadian rhythm. This rhythm is stable, which is expressed when the conditions are experimentally changed: constant darkness, unnatural rhythm of light-darkness succession). However, this stability is affected at the time zone change. The planarians are adapted to new conditions and begin to fission at once in correspondence with the new diurnal regime.

[The morphogenetic function of neuropeptides]. / Morfogeneticheskaia funktsiia neiropeptidov.

Morphogenetic effects of neuropeptides on the regeneration of planarians and the development of grain beetle larvae, were investigated. Macromorphological parameters and the proportions of planarian body were estimated using the technique of vital computer morphometry; the weight and moulting intensity changes were measured in larvae. Vasopressin, dalargin, somatostatin and hydra activator (morphogen) activated, sleep-inducing peptide exerted no effect, and LH-RH inhibited the planarian regeneration. The hydra morphogen and LH-RH stimulated normal development of grain beetle larvae. The dose- and structure-dependent action of neuropeptides on the morphogenesis were similar to those related to other physiological functions.

[Extracts of regenerating Planarians regulate proliferation of vertebrate cells]. / Ekstrakty regeneriruiushchikh planarii reguliruiut proliferatsiiu kletok pozvonochnykh.

The effects of extracts from intact and regenerating planarians on cell behaviour in culture were studied. The extracts were added to the culture of Chinese hamster fibroblasts and to the primary culture of human lymphocytes. Some extracts contained active agents which influenced the proliferation of fibroblasts increasing or decreasing the mitotic index. The extracts exerted no effect on the mitotic index of lymphocytes. When the extracts were added to the lymphocyte culture together with phytohemagglutinin, which induces the proliferation, the mitotic index somewhat increased. The extracts of regenerating planarians contain factors which activate and inhibit cell proliferation in culture. The active factors stimulated, rather than induced proliferation.

[Acetylcholinesterase activity in the nervous system of normal planaria and during regeneration]. / Aktivnost' atsetilkholinésterazy v nervnoi sisteme planarii v norme i pri regeneratsii.

The acetylcholine esterase (AChE) activity was studied in the nervous system of planarians in the normal state and during regeneration. During the regeneration of the cephalic body end, the AChE appears in the cells of the newly formed ganglion on the 5th day. During the regeneration of caudal body end, the AChE activity in the residual ganglion after the cut exceeds the normal level. The possible role of the ACh system in the processes of planarian regeneration is discussed.