[The preference for movement direction in a T-maze in planarians]

Characteristics of spatial orientation in T-maze were studied in 1768 Planaria of following types: Dugesia tigrina (sexless and sexual race), Dugesia lugubris, Ijmia tenuis, Bdellacephala punctata. It was shown that from one third to one half of individuals were characterized by asymmetry of movement direction preference. The preference of right turning was typical for Dugesia tigrina; Dugesia lugubris, Ijmia tenuis, Bdellacephala punctata preferred left turning. The asymmetry described is considered as a primitive form of species functional asymmetry.

Toxicity of selenium (Na2SeO3) and mercury (HgCl2) on the planarian Dugesia gonocephala

The toxicity of selenium (Na2SeO3) and mercury (HgCl2) was determined by using a freshwater planarian which is particularly sensitive to pollution, and belongs to a fissiparous breed of Dugesia gonocephala. The mortality and fissiparity frequency of the subjects were studied. They were exposed to intense treatments (48 hours) or for medium to long periods of time (21 days) to either the single compounds or a combination of both, and were fed or fasting. The lethal effect of sodium selenite is correlated to the food intake, whereas the toxicity of mercurous chloride is probably the result of a fixative effect which does not depend on feeding. The 21-day treatment with the first compound has a non-negligible lethal effect which is probably due to an accumulation phenomenon. At doses where an antioxidant effect prevails, fissiparity is stimulated. On the other hand, the second compound reduces reproduction frequency to half the base values. Compared to the Paracentrotus lividus, the Dugesia gonocephala offers various advantages concerning toxicological experiments; besides being easier to handle in the laboratory, it is available all year round and is not subject to seasonal cycles. It is also more susceptible to the toxic effect of mercury, which is a common and highly toxic pollutant, than the sea urchin.

Observations on planarian epithelization after wounding

Wound closure of planarian regenerates was studied by light and electron microscopy. Quick response of epidermal cells after amputation depended on muscular contraction near the open wound. Early epithelization involved both active and passive cell migration phenomena. First, the old cells from the dorsal and ventral epidermis facing the wound simultaneously spread to close the wound surface, joining first near the wound center. This was facilitated by the contraction. Cell stratification at the wound margin was the result of active cell migration at the time of amputation. Secondly, these cells were passively stretched from the wound margin so that the stratification disappeared. Partial relaxation of the wound was a causative factor for extreme elongation of the wound epidermal cells. Disappearance of hemidesmosomal attachments was initiated by the collapse of the basal lamina. This was obviously linked to cell locomotion. Further development of the wound epidermis was accomplished by the successive supplementation of precursor cells from the newly formed regeneration blastema (mainly rhabdite-forming cells).

Meiosis in Mesostoma ehrenbergii ehrenbergii. IV. Recombination nodules in spermatocytes and a test of the correspondence of late recombination nodules and chiasmata

Male meiosis in Mesostoma ehrenbergii ehrenbergii (2x = 10) is characterized by extreme restriction of chiasma formation; 3 pairs of chromosomes form bivalents at metaphase I which are associated by single very distally localized chiasma, while two pairs of chromosomes remain as unpaired univalents. Electron microscopical three-dimensional reconstruction analysis of serial sections has been applied to 20 pachytene spermatocyte nuclei. In each nucleus three short stretches of synaptonemal complex (SC) were found, confined to a localized branched lobe of the nucleus, confirming the findings of an earlier study. The majority of reconstructed nuclei show that each of the three SC segments has a single prominent recombination nodule ("late" RN) associated with it. Late RNs in this system therefore show an excellent correspondence with metaphase I chiasmata, in contrast to a previous report. M.e. ehrenbergii is therefore not an exception to the hypothesis that meiotic exchange requires a functional late RN. A few nuclei had two, one or no RNs; these presumably represent nuclei that are not at the stage of maximum RN presence. Although M. e. ehrenbergii shows pronounced chiasma localization at the light microscope level, at the ultrastructural level RNs are widely distributed along the 5-10 microns of SC formed in each bivalent, indicating that genetic exchange are not restricted to particular localized sites but occur at a large number of DNA sequence.

[Extracts of regenerating Planarians regulate proliferation of vertebrate cells]

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.

Somatostatin-like peptide and regeneration capacities in planarians

The presence of a neuropeptide immunologically related to somatostatin (SRIF) has been investigated in the neurosecretory cells of two regenerating planarian species (Dugesia lugubris and Dendrocoelum lacteum). A correlation has been shown between the discharge of the SRIF-like-immunoreactive cells during the first hours after amputation and the capacity to regenerate, and between the persistence of numerous positive cells and the lack of regeneration. These results suggest that somatostatin might play a regulatory (inhibitory) role on the cellular proliferation which leads to the blastema edification.

Absence of light response in eyeless planaria

Planaria Dugesia dorotocephala were bilaterally enucleated, decapitated caudal to the auricles, or sectioned at the level of the pharynx. None of these worms either altered or elicited any movement responses to stimulation by horizontal or overhead light even though they made such responses to mechanical stimulation. By comparison, all intact planaria responded vigorously to light stimulation but not to an elevation of water temperature. These results suggest that light receptors in these planaria might have evolved away from the body surface and are located in the ocelli.

Stimulation of cellular proliferation and differentiation in the intact and regenerating planarian Dugesia(G) tigrina by the neuropeptide substance P

The neuropeptide substance P (SP) is shown to be a potent mitogen for intact and regenerating planarians. At nanomolar concentrations, SP markedly enhances cellular proliferation causing an increase in the mitotic index and in the number of blastema cells. Moreover, albeit to a lower extent, SP enhances cellular differentiation as shown by the increases in eye and pharynx length in regenerating organisms. On the basis of these observations, we hypothesize that SP may be one of the postulated growth factors necessary for the stimulation of proliferation, and to a lesser extent differentiation of cells in intact and regenerating planarians.

Cell movement in intact and regenerating planarians. Quantitation using chromosomal, nuclear and cytoplasmic markers

One of the tenets of Wolff and Dubois' 'neoblast theory' of planarian regeneration (Wolff & Dubois, 1948) is that blastema is mainly formed by the accumulation of undifferentiated parenchymal cells (neoblasts) that can migrate, if needed, over long distances to the wound. That neoblasts migrate was claimed by these authors after partial X-irradiation, and total X-irradiation and grafting using planarian strains of different pigmentation. From this they suggested that migration of neoblasts is stimulated by the wound and directed towards it. To study the nature and extent of such 'migration' in intact and regenerating organisms, and in order to avoid the flaws of using pigmentation as a marker, we made grafts between sexual and asexual races of Dugesia(S)mediterranea that differ in a chromosomal marker, and between diploid and tetraploid biotypes of Dugesia(S)polychroa that differ in nuclear size. Also, fluorescent latex beads were used as cytoplasmic markers to follow 'migration' of differentiated cells. The hosts were irradiated or non-irradiated intact and regenerating organisms. The results show that: 1) movement of graft cells into host tissues occurs in intact organisms at a rate of approximately equal to 40 micron/day, and that this increases up to approximately equal to 75 micron/day in irradiated hosts; 2) movement of cells occurs evenly in all directions; 3) regeneration does not speed up rate of movement nor drives cells preferentially to the wound; 4) spreading of cells is mainly due to the movement of undifferentiated cells (neoblasts); and 5) higher rates of movement are correlated with higher mitotic indexes. From this, it is concluded that the so-called 'migration' of neoblasts is not a true cell migration but the result of the slow, even and progressive spreading of these cells mainly caused by random movements linked to cell proliferation. The implications of these results for blastema formation and the origin of blastema cells are discussed.

Regeneration and pattern formation in planarians. I. The pattern of mitosis in anterior and posterior regeneration in Dugesia (G) tigrina, and a new proposal for blastema formation

Mitotic activity during regeneration in the planarian Dugesia (G) tigrina shows a biphasic pattern, with a first maximum at 4-12 h, a second and higher maximum at 2-4 days, and a relative minimum in between. The first peak is mainly due to pre-existing G2 cells entering mitosis shortly after cutting, whereas the second maximum is due to cells that divide after going through the S period from the onset of regeneration. From a spatial point of view, the highest mitotic values are found in stump (postblastema) regions near the wound (0-300 micron), though regions far from it also show increased mitotic values but always lower overall values. As regeneration continues the postblastema maximum shifts slightly to more proximal regions. In contrast, no mitosis has been found within the blastema, even though the number of blastema cells increases steadily during regeneration. The results suggest that blastema in planarians forms through an early accumulation of undifferentiated cells from the stump to the base of blastema. The results obtained demonstrate that blastema formation in planarians occurs through mechanisms somewhat different to those shown to occur in the classical epimorphic models of regeneration (Annelida, Insecta, Amphibia), and suggest that planarian regeneration could represent an intermediate stage between morphallactic and epimorphic modalities of regeneration.

Epidermal cell migration during wound healing in Dugesia lugubris. Observations based on scanning electron microscopy and treatment with cytochalasin

The epidermal cells that migrate over the surface during the wound closure stage of head regeneration in Dugesia lugubris s.l. were examined by scanning electron microscopy. The effect of cytochalasin B on epidermal cell migration was also examined. During the first few hours after decapitation epidermal cells at the edges of the wound showed significant changes of shape related to the process of migration that was accomplished approximately 10 h after wounding. Flattening of the marginal cells was associated with active epidermal spreading throughout the healing period. Suitable support for migrating cells appeared to be a rhabditic network attached to the wound tissue. Epidermal cell migration was inhibited by cytochalasin B. These results demonstrate that the basis for cell movement in planarians is similar to that of many other systems.

On the phylogeny of asymmetry and spatial discrimination

We define and develop the fundamental experimental conditions required for an organism to demonstrate the capacity for spatial discrimination. It is then shown that concomitant with evolutionary progression in organisms, there is a corresponding increase in the dimensions of functional asymmetry, and in the quantity and dimensionality of spatial discrimination. It is also shown that the mismatch in asymmetry between the human body form and functional mechanism, and a demonstrated weakness in left--right discrimination, implies that the human organism is in transition between archetypal stages of phylogeny. Implications for the phenomena of mirrorimage reversal and left--right confusion are discussed. It is further argued that the development of functional asymmetry is an inherent principle of evolution.

Planarian regeneration: in vivo and in vitro effects of calcium and calmodulin on DNA synthesis

Regeneration does not occur when planarians are grown in Ca2+-free medium. The possible effect of calcium upon DNA synthesis was therefore studied using cultured planarian cells and regenerating planarian fragments. In the cultures, DNA synthesis was Ca2+-dependent and required a minimum of 10(-6) M Ca2+ in the medium. It was gradually decreased in cells grown in Ca2+-free medium. Addition of Ca2+ to these cultures raised DNA synthesis. The time lag between addition of Ca2+ and stimulation of DNA synthesis varied with culture age. The triggering effect of Ca2+ was amplified by ionophore A 23187. A calcium binding protein, ram testis calmodulin, intensified the stimulatory effect of calcium, but EGTA blocked this effect. In the presence of trifluoperazine (TFP), DNA synthesis was not stimulated by Ca2+. This inhibition by TFP was overcome by adding calmodulin to the medium. Ca2+ therefore triggered DNA synthesis in vitro, and this role might have been potentiated by calmodulin. In vivo, DNA synthesis was shown to be dependent on the Ca2+ concentration in the medium in which intact or regenerating planarians were grown. In 12-h regenerates, the Ca2+ concentration in the medium was no longer critical. Total calcium content decreased just after sectioning until completion of healing (at 6 h) and then rose significantly to a peak at 12 h which coincided with the first peak of DNA synthesis. The calmodulin content gradually diminished during the first 6 h after sectioning. After a transient rise at 12 h, calmodulin content further decreased until 48 h. The results demonstrate the crucial role of Ca2+ in triggering DNA synthesis in planarian cells in vitro and in regenerating fragments. Calmodulin, whose concentration is very low in planarians compared to vertebrates, might help to induce the first peak of DNA synthesis at 12 h after sectioning, but is probably not the main Ca2+-binding protein involved in the regeneration process.

Histochemical localization of retinochrome and rhodopsin studied by fluorescence microscopy

Retinochrome is readily reduced by sodium borohydride into an N-retinyl protein that emits visible fluorescence upon irradiation with near-ultraviolet light. Rhodopsin is also converted to a similar fluorescent product, but only when denatured with formaldehyde before reduction. Based upon this difference, retinochrome was discriminated from rhodopsin on frozen sections. The distribution of these two photopigments in various photosensitive tissues was examined by means of epifluorescence microscopy. In the octopus retina (Octopus vulgaris), the yellow-green fluorescence of reduced retinochrome was observed in both the basal regions of the outer segments and throughout the inner segments of the visual cells, while the fluorescence of reduced rhodopsin was restricted to within the rhabdomal layer of the outer segments. In the squid parolfactory vesicles (Todarodes pacificus), rhodopsin was present in the central lumen, which contains the distal processes of the photoreceptor cells, while retinochrome was detected in the myeloid bodies scattered within the vesicular wall. In the slug retina (Limax flavus), rhodopsin was found in the microvilli, and retinochrome appeared to be concentrated in the photic vesicles of the visual cells.

Effects of dopaminergic agents on monoamine levels and motor behaviour in planaria

1. Dopamine, serotonin and, in lesser amounts, norepinephrine were detected in Dugesia gonocephala using electrochemical detection coupled with liquid chromatography (LCED). 2. Treatment with L-dopa induced hyperkinesias, and a rise in dopamine, serotonin and norepinephrine content, whereas reserpine reduced motor activity and the concentrations of all three monoamines. 3. Haloperidol reduced motor activity and dopamine and norepinephrine levels. 4. Apomorphine induced hyperkinesias without altering monoamine levels.

Evidence of male germ cell redifferentiation into female germ cells in planarian regeneration

The source and fate of blastema cells are important and still unresolved problems in planarian regeneration. In the present investigation we have attempted to obtain new evidence of cell dedifferentiation-redifferentiation by using a polyploid biotype of Dugesia lugubris s.l. This biotype is provided with a natural karyological marker which allows the discrimination of triploid embryonic and somatic cells from diploid male germ cells and from hexaploid female germ cells. Thanks to this cell mosaic we previously demonstrated that male germ cells take part in blastema formation and are then capable of redifferentiating into somatic cells. In the present investigation sexually mature specimens were transected behind the ovaries and the posterior stumps containing testes were allowed to regenerate the anterior portion of the body. Along with the usual hexaploid oocytes, a small percentage (3.2%) of tetraploid oocytes were produced from regenerated specimens provided with new ovaries. By contrast only hexaploid oocytes were produced from control untransected specimens. The tetraploid oocytes are interpreted as original diploid male germ cells which following the transection take part in blastema formation and then during regeneration redifferentiate into female germ cells thus doubling their chromosome number as usual for undifferentiated cells entering the female gonad in this biotype.

Cell death and acid phosphatase activity in the regenerating planarian Polycelis tenuis Iijima

A combination of microscopical, cytochemical, and biochemical techniques have been employed to study the changes occurring during the first seven days of blastema formation and regeneration after decapitation in adult Polycelis tenuis worms. Fine structural data reveal evidence of cell fragmentation, selective cell deletion, and phagocytosis at and below the wound surface. Initially, (0-12 h regeneration) cell debris is phagocytosed by intact parenchymal and gastrodermal cells near the cut surface which is later sealed (24 h) by a stretching of marginal epidermal cells. Wound sealing is followed by a migration of newly differentiated rhabdite cells into the epithelium. Morphological evidence of a selective cell autolysis precedes evidence of an accumulation of lipid and glycogen reserves in the parenchymal and gastrodermal cells and the later (48 h regeneration time) aggregation of undifferentiated mitotically active neoblasts beneath the wound. Biochemical data reveal an early period of high acid phosphatase (p-nitrophenyl phosphatase and sodium-beta-glycerophosphatase) activity 3-12 h after injury, followed by a further intense period of activity at 44-48 h after decapitation. The coincident cytochemical data show an increased level of acid phosphatase activity associated with cell lysis and death in the wound and blastema zone and also with the digestion of phagocytosed cell debris.

Morphogenesis of regenerating fragments of Dugesia schubarti (Turbellaria tricladia)

An extensive study of regeneration processes from the point of view of the axial gradient theory and its corollary, the possibility of forming two heads from one fragment (the Janus head problem) was undertaken on the South American species Dugesia schubarti. Altogether 330 specimens were used, cut into 2,640 pieces and the regeneration of each of them was followed to the end result. Concerning the role of an axial gradient in the regeneration processes the results were not supportive. Anterior fragments often regenerated less completely (eyes and auricles without complete heads) than more posterior ones, although the differences were not sharp, due to individual variations of physiological nature. The Janus head regeneration, one of the postulates of the axial gradient theory, was analyzed both on preauricular (parts A) and postauricular fragments (part B). The regeneration of parts A was less perfect than that of parts B. ALthough a considerable number of the part A fragments regenerated normally, the majority of the cases remained incomplete for a long time and eventually disintegrated without completing the regeneration process. The only irregularity parts B proceeded more evenly and the death rate was also much lower. The only irregularity observed was a great number of cyclopic regenerates, i.e. heads with one single eye in the midline. Some of these cyclopic heads remained permanently in this condition but most of them later separated in two eyes but with a pigment between them, and in others the cyclopic eye separated in two normal eyes at the end of the regeneration. The Janus head phenomenon was never observed.

Respiration during wound regeneration and healing in the planarian worm Dendrocoelum lacteum

The intensity of respiration of the body fragments of the planarian after its division anteriorly and posteriorly to the pharynx was studied. After division anteriorly to the pharynx regeneration takes place. During regeneration of the anterior fragment respiration increases in the first day after the operation and at the differentiation stage. During regeneration of the posterior fragments the oxygen consumption is unchanged. Healing of the wound after division of the planarian posteriorly to the pharynx is accompanied by intensification of respiration during the first two days after the operation. Comparison of regeneration and healing of the wound in fragments of equal weight shows that in the initial stages the intensity of respiration was the same. A significant difference is found at the stage of differentiation of the regenerating worm, when the regenerating fragments have a higher intensity of respiration than fragments unable to regenerate.

[Variations in DNA synthesis and the activities of acid and alkaline deoxyribonucleases during regeneration of planaria (Polycelis tenuis)]

Variations of DNA synthesis were established for the first time during planarian regeneration by 32P phosphoric acid incorporation. A first peak of DNA synthesis occurred between the 10th and the 18th hour after sectioning (maximum at 12 hrs.). Subsequently, DNA synthesis increased again progressively after the 24th hour to a plateau between 48 and 72 hrs. after regeneration. Simultaneously, variations of alkaline and acid DNases were determined.

Dopamine agonist performance in Planaria after manganese treatment

Using Planaria motor performance as model, the authors confirm that Mn++ basically inhibits dopaminergic release with transitory hyper-release.

On the role of germ cells in planarian regeneration. I. A karyological investigation

Specimens from a polyploid biotype of Dugesia lugubris s.l. were used to clarify the role and fate of germ cells during planarian regeneration. These specimens provide a useful karyological marker because embryonic and somatic cells (3n = 12) can be easily distinguished from male (2n = 8) and female (6n = 24) germ cells by their chromosome number. We succeed in demonstrating how primordial germ cells participate in blastema formation and take part in rebuilding somatic tissues. This evidence was obtained by cutting each planarian specimen twice at appropriate levels. The first aimed to induce primordial germ cells to migrate to the wound. The second cut was performed after complete regeneration and aimed to obtain a blastema from a cephalic or caudal area devoid of gonads. A karyological analysis of mitotic cells present in each blastema obtained after the second cut provided evidence that cells, originally belonging to the germ lines, are still present in somatic tissues even months after complete regeneration. The role of primordial germ cells in planarian regeneration was finally discussed in relation to the phenomenon of metaplasia or transdifferentiation.

On the role of germ cells in planarian regeneration. II. Cytophotometric analysis of the nuclear Feulgen-DNA content in cells of regenerated somatic tissues

Previous findings by our group have shown how primordial male germ cells take part in regenerative blastema formation in planarians by migrating to the wound. The role of these cells in rebuilding transected tissues has been investigated in a population of Dugesia lugubris s.l. which is particularly suited for our purpose. In fact, these planarians provide a clear karyological marker to distinguish diploid male germ cells (2n = 8) from tryploid embryonic or somatic cells (3n = 12). In this study we employed the cytophotometric analysis of the nuclear Feulgen-DNA content in order to distinguish non-replicating male germ cells from reserve and somatic cells. The Feulgen-DNA content in cells from the gonad-free caudal area was measured after complete regeneration. Most non-replicating cells (94-95%) were found to have a DNA amount typical of cells previously estimated as triploid. Some (5-6%) nuclei containing a DNA amount typical of cells previously estimated as diploid male gonia were also found. These findings seem to support the view that primordial male germ cells also participate in rebuilding somatic tissues according to the field influence they encounter during regeneration. The possibility that metaplasia (or cell transdifferentiation) may occur in planarians is finally discussed.

A simple method for studying chemotaxis using sustained release of attractants from inert polymers

Chemotaxis of the bacterium Escherichia coli and the planarian Dugesia dorotocephala toward a variety of substances impregnated in sustained-release polymers has been demonstrated. Tests were carried out in soft agar and in aqueous medium with highly consistent results. The simplicity of this method may make it particularly useful for rapid qualitative screening of new wild-type and mutant strains of bacteria for chemotaxis toward nonmetabolites. The cost, ease of fabrication, and the facility with which they can be utilized in test systems suggest that these sustained-release vehicles will provide a new and general method of creating concentration gradients to study chemotaxis.

Ribonucleic acid metabolism during planarian regeneration

A method for the extraction of total RNA of the planarian Polycelis tenuis is described. This technique has been applied to the study of RNA synthesis in the course of regeneration. Synthesis of RNA begins 7 hrs after sectioning and proceeds in two phases. The first phase, from 7 to 21 hr is characterized by an increased rate of (3H) orotic acid incorporation into RNA up to the 18th after sectioning followed by a decrease between 18 and 21 hrs. The rate of precursor incorporation then had risen again in the second phase to the 30th hr and finally decreased slowly until completion of regeneration. Studies of the pool of nucleotide precursors, show that the observed variations of orotic acid incorporation into RNA reflect variations in RNA synthesis. Electrophoretic analysis of RNA labelled for 2 hrs at various times during regeneration shows that the product formed during the first phase of regeneration is mainly rRNA and low molecular weight RNA. The second phase of the regeneration process, from the 24th hr, is characterized by the appearance of both ribosomal and polydisperse RNAs. These heterogeneous RNA species are detected up to the 46th hr of regeneration, after which time rRNA again becomes predominent. The significance of the two phases of RNA metabolism of which this is the first observation during planarian regeneration is discussed in connection with other biochemical events which have been described during regeneration processes in planarians and other animals.

Localization of newly synthesized precursors of basal lamina in the regenerating planarian as revealed by autoradiography

Autoradiography has been carried out to investigate the site of synthesis of the basal lamina in the regenerating planarian, Dugesia japonica. Since the basic collagenous structures of the basal lamina rose from RR-positive amorphous precursor, [3H]proline, [3H]glucose and [35S]sodium sulphate were used as radioactive precursors of collagen, unsulphated and sulphated GAG respectively. Cytoplasm of the most regenerating epidermal cells was heavily labeled with [3H]proline during epithelization. A quantitative uptake analysis of [3H]proline indicates a progressive decline in the amount of labeled precursor in the epidermis with a corresponding increase in deposition of the labeled collagen at the presumptive basal lamina. Several myoblasts at the subepidermal region were highly labeled with both [3H]glucose and [35S]sodium sulphate. Silver grains of these labeled precursors were also present in the presumptive portion of basal lamina. These observations suggest that the regenerating epidermal cell is the only site of synthesis of the basal lamina collagen while the myoblast exclusively secretes extracellular GAG. Some of the GAG may be closely associated with the amorphous zone.

Stimulation of mitosis in Dugesia tigrina by a neurosecretory fraction

A neurosecretory fraction, isolated from regenerating Dugesia tigrina, significantly stimulates the number of cells entering mitosis in the blastema of posterior worm pieces. When this fraction was applied to regenerating worms in the presence of colchicine, a doubling of the mitotic index was observed.

The pigmentary system of planaria. II. Physiology and functional morphology

The pigmentary system of the planaria, Dugesia gonocephala s.l. (Platyhelminthes, Turbellaria, Tricladida), consists of granules contained in chromatophore cells distributed in the parenchyma tissue. The administration of MSH release-inhibiting Factor (M.I.F.) leads to an easily observable general decolouration of the animal due to the migration of the pigment granules towards the deeper-lying cell nucleus. In planarians bisected transversely through the pharyngeal region, the decolouration occurs only in the cephalic segment, and the caudal segment remains dark. When, however, the decapitated caudal segment regenerates a head region, a decolouration response occurs when exposed to M.I.F. The significance of these results is discussed, and an hypothesis on the hormonal regulation of the pigmentary system is proposed.

[The role of serotonin and catecholamines in the regeneration of the Planaria Polycelis tenvis]

During traumatic regeneration of Planaria Polycelis tenuis, determination of serotonin, noradrenaline and dopamine levels revealed important variations of serotonin and catecholamines from the time of excision. The use of specific inhibitors of these hormones delayed regeneration whereas simultaneous addition of an hormone and its antagonist restores a standard time of regeneration. Serotonin acts through adenylate cyclase system. Results allow us to assume that dopamine acts through the same mechanism. The action of noradrenaline is so far not elucidated although propranolol (beta antagonist) delays or inhibits completely regeneration.

Isolation of a neurosecretory substance which stimulates RNA synthesis in regenerating planarians

An approach to the isolation of neurosecretory material from planarians is described. This material stimulated RNA synthesis, in a dose-dependent response, in regenerating Dugesia tigrina. The data support the concept that neurosecretion plays a key role in the process of regeneration in planarians.

On the occurrence and significance of annulate lamellae in gastrodermal cells of regenerating planarians

Cytoplasmic annulate lamellae have been observed to occur only in a subset of the gastrodermal cell population of regenerating planarians. They have not been found in the gastrodermal cells of intact, non-injured worms, nor in any other somatic cell type. These observations plus the presence of numerous chromatoid bodies in the same cells are consistent with the hypothesis that these cells are altering their state of differentiation and are preparing for division. It is further suggested that these cells are the precursors to the definitive somatic stem cells, the beta cells.

Schistosoma mansoni: interference with cercarial host-finding by various aquatic organisms

Schistosoma mansonicercariae labelled with75Se-methionine were used to study host-finding capacity by determining the radioactivity of exposed mouse “target” tails. Possible interfering effects of some aquatic vertebrates and invertebrates, plants and algae and secretions and excretions of aquatic organisms were examined.

A marked interferent effect due to predatory behaviour was produced byCyclops strenuus(Copepoda),Daphnia pulexandD. longispina(Cladocera),Notodromas monachaandCypria ophthalmica(Ostracoda) andLebistes reticulatus(guppy).Bufo bufo(Amphibia) andPlanaria lugubris(Turbellaria) interfered significantly, presumably by secreting cercaricidal toxins. Several other organisms apparently produced no interference. The interferent effect of the plant speciesCeratophyllum demersum, Elodea canadensis, Lemna minor, Ranunculus aquaticus, Holcus lanatus(grass) andBotryococcus brauniiwas particularly pronounced when they were confined to the surface layer of the water. Several other species did not interfere with host-finding.

Structure and regeneration of the planarian basal lamina: an ultrastructural study

The structure and regeneration of the planarian subepidermal basement membrane or basal lamina have been electron microscopically examined, particularly in relation to the changes of extracellular products at the wounded area. The intact basal lamina consists of three structural elements; namely, an electron-lucent zone, a limiting layer and a microfibrillar layer. Ultrastructural changes during wound healing have suggested that the amorphous material secreted in the interspace between the epidermal cells and blastema contains precursors of the basal lamina. Within the amorphous zone two distinct phases of the basal lamina regeneration are observed: one is a reconstitution of the limiting layer and the other is a polymerization of the microfibrils. The limiting layer arises from areas subjacent to newly developed hemidesmosomes of epidermal cells. The unit microfibrils are formed from an accumulation of the precursors through transitional smaller microfibrils. At the late stage, individual mature microfibrils are regularly lined with the limiting layer and cell membranes of the newly differentiated muscle fibres. On the basis of these observations we suggest that the planarian basal lamina is regenerated by the interaction between epidermal cells and myoblasts.

Analysis of the progress of hormone-receptor amplification during differentiation in regenerating planarians

Planarians developing from isolated regenerates, when pretreated with epinephrine at different periods of their second regeneration, show a higher rate of sugar uptake than the controls, which were not treated with epinephrine. The hormone receptor development can be influenced most effectively by pretreatments performed during the 1--3 and 6--9 day periods, though some effect can be evoked at any time in the course of the second regeneration. The head regenerates developing from the anterior end of the original midpiece (and regenerating tails the second time, B1) were found to be most sensitive, while the similar regenerates developing from the hindpiece of the original planarian (C) showed the weakest reactivity. The experiments provide further evidence that the hormone receptors' activity can be amplified in the course of regenerative development, leading thus--at a later stage--to a more intense sugar uptake response of the cells.

The mechanism of anterior-posterior polarity control in planarians

The substance which inhibits brain formation in the regenerating planarian Dugesia etrusca was found to be a large molecule, at least in part protein, which electrophoreses as an electronegative moiety in pH 6.8 buffer. A model is presented, based on this finding and previous studies, which proposes an electrochemical mechanism for the control of polarity and possibly for the maintenance of tissue organization in planarians. It is proposed that a bioelectric field exists and moves the electronegative brain-inhibiting substance in a posterior direction, establishing polarity. This model explains the polarity reversal experiments using external fields and many of the previously unexplained classical planarian experiments. Data are presented demonstrating the existence, magnitude, and polarity of this bioelectric field, which is not greatly altered upon decapitation, all in accord with predictions of the model.

Characterization of an organ-specific differentiator substance in the planarian Dugesia etrusca

A substance which inhibits brain formation in decapitated regenerating planarians (Dugesia etrusca) was characterized and partially purified. The substance's inhibitory activity was followed during each purification procedure by adding freshly decapitated animals of a standard size to each fraction, and later measuring the resultant regenerated brain volume. The inhibitory activity remained in the supernatant after a 10000 g centrifugation of a cell-free homogenate. Most of the activity sedimented when the 10000 g supernatant was centrifuged at 32000 g. The degree of inhibitory activity increased with increased numbers of animals in the initial homogenate. The substance has an apparent molecular weight between 2 X 10(5) and 4 X 10(5) daltons. Digestion by pronase destroyed the activity, but treatment with RNase, DNase I, or lipase had no significant effect. The inhibiting substance has an isoelectric point (pI) of between 4-75 and 5-38 and migrates to the anode when electrophorezed in pH 6-8 buffer.

[Control of the regeneration of small pieces of the planarian Dugesia tigrina by cylic AMP and GMP nucleotides]

The effects on regeneration of cyclic nucleotides AMP and GMP were studied on small pieces of the planarian worm Dugesia tigrina. db cAMP, 8Br cGMP and substances acting on their metabolism were used in this work (aminophylline, insulin, imidazole). It seems that these second messengers play a role in a mechanism of regulation in which cGMP has a promotive action and cAMP an inhibitive one.