[Regeneration of planarians: experimental object].

We discuss the expediency of using invertebrates, such as flatworms and planarians, as experimental objects. Free-living planarian flatworms (phylum Platyhelminthes, class Turbellaria) are invertebrate animals in which a bilateral symmetry appears for the first time in evolution and organs and tissues form. As the highest ecological link of the food chain--predators--these animals are characterized by a set of behavioral reactions controlled by a differentiated central nervous system. Planarians have unsurpassed ability to regenerate lost or damaged body parts. Owing to the ease of their breeding and their convenience for manipulations, these animals are used to study the influence of chemical and physical factors on the processes of life, growth, and reproduction. Currently, planarians are recognized as a model for biological research in the field of regeneration, stem cell biology, study of their proliferation and differentiation, as well as the regulatory mechanisms of morphogenetic processes. The genome of the planarian Schmidtea mediterranea was fully sequenced, which opened up the opportunity to work with this object at the molecular biological level. Furthermore, planarians are used in neurobiological and toxicological studies, in studying the evolutionary aspects of centralization of the nervous system, mechanisms of muscle contraction, and in the development of new antiparasitic drugs. This review aims to demonstrate the relevance and diversity of research conducted on simple biological objects--planarians--to awider audience to show the historical continuity of these studies and their wide geographical distribution and to focus on the studies carried out in Russia, which, as a rule, are not included in the foreign reviews on planarian regeneration.

[Modulating effect of weak combined magnetic fields on duration of mealworm beetle Tenebrio molitor metamorphosis stage].

It is shown that an exposure of pupae of the mealworm beetle Tenebrio molitor to the combined static (42 µT) and very weak alternating (250 nT) magnetic fields exerts different influence, depending on the frequency of the alternating magnetic field, on duration of metamorphosis processes in these insects. For instance, an exposure of pupae to weak combined magnetic fields, adjusted to the frequency of ion cyclotron resonance for glutaminic acid (4,4 Hz), stimulates metamorphosis process--a transitional stage from pupae to imago lasts shorter. An inhibiting effect was observed when adjusted to the frequency of ion cyclotron resonance for Ca2 (32,2 Hz). At some frequencies this effect is not seen. For instance, an exposure at a frequency of ion cyclotron resonance for K+ (16,5 Hz) exerts no noticeable effect on the duration of the pupal metamorphosis stage.

[The effect of combined magnetic fields, adjusted to ion-cyclotron resonance for Ca ions, on intensity of division in planaria].

The combination of a constant (42 mkT1) and parallel to it a changing magnetic field on a frequency of 32 Hz (it corresponds to cyclotron frequency for Ca2+ ions) is shown to have a changing magnetic field amplitude-dependent effect on intensity of division in planaria. A stimulating effect has been observed at the magnitude of a changing component equal to 100 nT, but the amount of division significantly decreased at 250 nT and no impact of the magnetic field was registered at 500 nT1.

[Formation of the photosensing system function in early development].

The function of simple prototypic eyes in two planarian species, the two ocular Girardia tigrina and the multiocular Polycelis tenuis, has been studied. When exposed to light, planarians display the light avoidance reaction known as negative phototaxis. This reaction has been investigated in intact animals and in head and tail fragments after their section in the course of eye regeneration. Specific features of the phototaxis reaction have been described in all groups of animals. The differences in light response recovery were shown between two planarian species and two regenerating fragments. No correlation between phototaxic reactions and the restoration of the eye structure, the number of eyes, the maturation of ganglion, the growth of regenerative blastema, and motor system has been found. The phototaxic response occurred two days after the recovery of the morphology of eyes and their connection with the brain. The participation of conserved and novel genes in early development of the eye function is discussed.

Effects of weak electromagnetic irradiation on various types of behavior in the mealworm Tenebrio molitor.

The effects of weak electromagnetic irradiation on simple forms of behavior were studied using adult Tenebrio molitor mealworms. The beetles' motor behavior was studied in conditions of different motivations, i.e., positive (food) and negative (avoidance of light), in otherwise identical experimental conditions. The beetles had to navigate a defined space to reach their target - potato or cover from light. Experiments consisted of one trial per day for five days. Target attainment time was measured in groups of beetles. Behavior in both cases developed as follows: an initial orientation reaction appeared and was followed by adaptation to the apparatus. Exposure to weak electromagnetic irradiation led to increases in the response time at the initial stages of the experiments. The effects of irradiation were seasonal in nature and differed in the two types of behavior.

[Regeneration processes in various species of planarians].

Blastema growth and functional maturation of the pharynx during regeneration in various planarian species were compared. The intensity of blastema growth was highest in Polycelis tenuis; the lowest, in Schmidtea mediterranea. In the sexual and asexual races of Girardia tigrina blastema growth differed inconsiderably. The function of the pharynx during the regeneration of caudal fragments lacking pharynx was manifested in G. tigrina in the usual amount of time, while in the regeneration of head fragments lacking pharynx, this function occured earlier. In other planarian species of the other two typed, the times of pharynx regeneration had no regular character and took longer compared to the same process in G. tigrina.

[Influence of weak electromagnetic field on different forms of behavior in grain beetle, Tenebrio molitor].

The influence of weak electromagnetic radiation on simple forms of behavior was studied on the model of the motor behavior of the imago grain beetle (Tenebrio molitor). Positive (feeding) and negative (illumination) motivations were created in the same experimental conditions. Beetles in a Petri dish were put to the starting point of a special container. The goal (a peace of potato or a box protected from light) was in the other fixed point of the container. Time of the goal reaching by groups of beetles was recorded in one daily trial in the course of five consecutive days. Under conditions of both motivations, behavioral phases such as orienting reaction and environmental adaptation were observed. Exposure to weak electromagnetic radiation resulted in an increase in the reaction time at the initial stage of the experiment. The effect was of a seasonal character and varied depending on the behavioral form.

[Effects of weak physical and chemical factors on morphogenetic processes in invertebrates].

Numerous data of long-term investigations of weak agents on morphogenetic processes in invertebrates (regeneration of planarians, Dugesia (Girardia) tigrina and postembryonic development of insects, the grain beetle Tenebrio molitor) have been analyzed. Weak physical and chemical factors were used: electromagnetic radiation, static, alternating, and combined magnetic fields, and low concentrations of solutions of neuropeptides. Some common features of the influence of weak factors on morphogenesis were found, namely, the instability and the opposite direction of the effect. The dependence of the effects on external conditions and the dynamics of physiological functions of objects was established.

[Effect of weak and ultraweak static magnetic fields on the intensity of fission of the planarian Dugesia tigrina].

It has been shown that, in the range of 03000 nT, a biological system differently responds to the treatment with a weak static magnetic field. Thus, at a practically complete compensation of the field (induction 5 nT), the intensity of fission of planarian does not differ from control values. As the field intensity is successively increased to 300 nT, a marked and statistically significant stimulating effect is observed (SC 1.51.8), which disappears in the intensity range of 400 and 600 nT. At intensities from 800 to 1500 nT, the stimulating effect manifests itself again. Further increase of field intensity to 3000 nT leads to the disappearance of the effect.

[Specific features of eye regeneration in multiocular planarians Polycelis tenuis].

Regeneration and negative phototaxis were studied in planarians Polycelis tenuis, in which the anterior body end is fringed with many eyes. Comparative data for the same indices are given for binocular planarians Girardia tigrina. Multiple eyes regenerated gradually with a decrease in the rate of regeneration and independently from the rate of restoration of the anterior body end, where they are located. Negative phototaxis was restored independently from the total amount of regenerated eyes. It was unstable in both planarian species.

[Effect of weak and superweak combined permanent and low-frequency alternating magnetic fields and low-intensity millimeter waves on regeneration of planaria Dugesia tigrina].

It has been shown that exposure to weak combined collinear magnetic fields (permanent component 42 mT; amplitude of alternating component 40 nT, frequency 3.7 Hz) or millimeter waves with a frequency of 36 GHz and power density of 100 mT/cm2 substantially stimulates the growth of the regeneration blastema in the tail fragment of planaria when the exposure to fields precedes the cutting of the planaria body. This effect is more clearly pronounced during the treatment of planaria with magnetic field. If the treatment with weak physical factors is carried out after the cutting of planaria, the effect of the field is two times less pronounced (exposure to magnetic waves) or is not evident at all (exposure to electromagnetic radiation).

[Asexual reproduction of planarians: metric studies].

A relationship was studied between fission and restoration of body and its individual parts under different experimental conditions in planarians of the Dugesia tigrina asexual race. The body and its fragments were studied morphomterically. After fission, the growth of planarians demonstrated topographic differences. The separated tail fragments and postpharyngeal area, in which the zone of fission is formed, were growing at the highest rate. More active growth was also noted over the long body axis. Fission and growth were more active in isolated planarians, as compared to those kept in groups.

A behavioral study of the beetle Tenebrio molitor infected with cysticercoids of the rat tapeworm Hymenolepis diminuta.

The host-parasite relationship, Tenebrio molitor-Hymenolepis diminuta, was analyzed. The learning behavior of infected and uninfected (control) beetles in a T-maze was compared. The infected beetles moved much slower in the T-maze than the controls. The infected beetles reached the same level of learning as the controls. However, they needed more trials than the controls. The effect of the infection was already distinct after the first week and even higher after the second week. This indicates that the initial phase of infection caused stress in the beetles. Longer infection did not worsen their ability to learn. Thus, the parasites clearly changed the behavior of their intermediate host and probably made them more susceptible to their final host, the rat.

[Resources of regeneration in planarians].

We studied the intensity of blastema growth in operated planarians at an early stage of regeneration as a function of the following factors: area of regenerate and its function and number of regeneration foci (volume of regeneration). There was no direct dependence between the intensity of regeneration and the size of regenerating fragment, as well as the volume of regeneration. Some specific features of the early stage of regeneration have been described, which suggest its determinate character. The behavior of neoblasts during formation of blastemas with different localization is discussed.

[Morphogenesis in planarians Dugesia tigrina]. / Morfogenez u planarii Dugesia tigrina.

We carried out computer morphometry in regenerates of planarians Dugesia tigrina. The blastema growth was analyzed in fragments of planarians after their fission and after transverse transection at different body levels. The blastema was growing at a higher rate on tail fragments than on the head fragments and the growth rate was the higher, the closer the transection was to the head end. After fission, the blastema was growing at a slower rate than after transection in the fission zone. The growth of adjacent blastemas formed on both sides after fission or transection proceeded at different rates as a function of new body polarity.

[Effect of weak electromagnetic radiation on larva development and metamorphosis of grain beetle Tenebrio molitor]. / Deistvie slabogo élektriomagnitnogo izlucheniia na razvitie lichinok i metamorfoz muchnogo khrushchaka Tenebrio molitor.

The effect of weak electromagnetic radiation (36 GHz, 100 mu W/cm2) on the development of the grain beetle Tenebrio molitor was studied. Insects were irradiated in different larval instars and at the pupal stage. It was found that weak electromagnetic radiation stimulated the molting and pupation of larvae and the metamorphosis of pupae. The stimulating effect of radiation was weak when animals were exposed in the initial period of the instar and the pupal stage and was more pronounced if the irradiation was carried out in the second half of the current instar and the pupil stage. The effect of weak electromagnetic radiation on the development of beetle can be related to the function of the hormones of metamorphosis.

[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.

[Effect of weak electromagnetic radiation on learning in the grain beetle Tenebrio monitor]. / Vliianie slabogo élektromagnitnogo izlucheniia na obuchenie zhukov muchnogo khrushchaka Tenebrio monitor.

Weak electromagnetic radiation (36 GHz, 100 MicroW/cm2) was used to study its effect on learning and memory of larvae and imago of the grain beetle Tenebrio molitor. The insects were learned to choose the direction in a T-maze. The retention was tested a month later. They were exposed to weak electromagnetic radiation before or after the learning experiments. Previous exposure to weak electromagnetic radiation stimulated learning of both larvae and imago. The effect depended on the developmental stage of the larvae. It was considerably stronger in larvae exposed to weak electromagnetic radiation immediately after their molting. It was better in the first half of the instar than in the second half. It is suggested that the effect of weak electromagnetic radiation can correlate with the function of hormones of metamorphosis.

[Dependence of effects of weak combined low-frequency variable and constant magnetic fields on the intensity of asexual reproduction of planarians Dugesia tigrina on the magnitude of the variable field]. / Zavisimost' vliianiia slabykh kombinirovannykh nizkochastotnykh peremennykh i postoiannykh magnitnykh polei na intensivnost' bespologo razmnozheniia planarii Dugesia tigrina ot velichiny peremennogo polia.

It was shown that the stimulating effect of weak combined magnetic fields (constant component 42 microT, frequency of the variable component 3.7 Hz) on the division of planarians depends on the amplitude of the variable component of the field. The effect is particularly pronounced at 40 (the main maximum), 120, 160, and 640 nT. Narrow ranges of effective amplitudes alternate in some cases with equally narrow ranges in which the system does not respond to he treatment. In the range of super weak amplitudes of the variable field (0.1 and 1 nT), the stimulating effect is poorly pronounced. The data obtained indicate the presence of narrow amplitude windows in the response of the biological systems to weak and super weak magnetic fields. In a special series of experiments, it was shown that the effect of fields on planarians is partially mediated via aqueous medium preliminarily treated with weak magnetic fields. It is noteworthy that in experiments with water treated with weak magnetic fields, there were no pronounced maxima and minima in the magnitude of the effect in the range of amplitude of the variable magnetic field from 40 to 320 nT.