[The effect of repeated amputations on planarian regeneration in the presence of the heat-stable toxin from Bacillus thuringiensis]

The exotoxin of Bacillus thuringiensis, which is an inhibitor of RNA synthesis, inhibits Planarian regeneration. Planarians which have been cut twice at the same level are able to regenerate after the second section in the presence of the toxin. This indicates that the first amputation stimulates a synthesis of stable RNAs which thus are available for regeneration at the moment of the second section.

Cell sociology: a way of reconsidering the current concepts of morphogenesis

Research in the field of planarian regeneration on the one hand, and a general survey of embryology on the other, throw doubt upon the reality of supra-cellular controls, which are still at the basis of all modern concepts of morphogenesis. The necessity of referring to such controls, which have never been convincingly demonstrated, is probably due to the fact that two aspects of cell behaviour have been underestimated: 1) the capacity of cells to change their individualities for a time independently of other cells; 2) the social behaviour of cells, which is the consequence of the reciprocal exchange of information. Pattern formation and pattern remodeling in normal development results from readjustments of cell populations to local or global changes. The common specific syntheses and cell migration. In the young embryo these may promptly restore the unity of the injured primordium, leading to so-called restitution; this is based on a normal sequence of further readjustments in the primordium. In older organisms the same responses give rise to cell interactions which may be the starting point for further sequential readjustments (regeneration)--in some instances these are comparable to those that originally organized the primordium in question during development. The desirability of giving up the notion of morphogenetic field is discussed.

Cephalic mechanism for social control of fissioning in planarians: III. Central nervous system centers of facilitation and inhibition

Previous studies have indicated that asexual reproduction (fissioning) in the planarian Dugesia dorotocephala is socially controlled through a cephalic mechanism: Isolation releases fissioning; grouping inhibits it; decapitation, at the level of the auricles, releases it even in grouped subjects. The brain is not necessary for programming the actual events of fissioning; these are orchestrated by the segmental plexus fissioning (SPF) system. Various surgical cuts were made to ablate selected portions of the central nervous system of isolated and grouped planarians in order to ascertain the inhibitory or facilitatory effects of these in the physiological mediation of such control on the SPF system. These results were synthesized into a model of this control system; the anterior lobes and optic regions of the brain inhibit the SPF system, and the anterior and caudal segmental plexuses facilitate it. These influences are partially tonic and partially contingent upon social stimulation.

[DNA reproduction in the organism of planarians in post-injury recovery]

No mitotic figures were found during histological observations of intact as well as transsected planarians Dendrocoelum lacteum within 15 days after the operation. DNA content in intact and regenerating worms was measured. It has been shown, that the posttraumatic repair in planarians does not involve DNA synthesis or cell reproduction.

Distribution of neoblasts and mitoses during the asexual reproduction of the planarian Dugesia tigrina (Girard)

The neoblast distribution in the prepharyngeal portion of the body remains unchanged during the asexual reproduction of planaria. During the first few days after fission, the number of neoblasts decreases in the portion of the body immediately adjoining the site of daughter zooid detachment and considerably increases in the regenerative bud. Starting with the fourth day after division, there is an increase in the number of neoblasts in the region of future fission, which can be regarded as one preparatory mechanism for the next fission. The mitosis distribution pattern is just the reverse: the regions of the body with the highest neoblast density are characterized by a low mitotic index or no dividing cells at all. The neoblast and mitosis distributions in the daughter zooid during its asexual reproduction cycle duplicate those observed in the maternal zooid.

[Incorporation of 3H-5 uridine and 3H-5 leucine into cultured planarian cells, Polycelis tenuis (Iijima) in vitro]

RNA and protein synthesis in Planarian cells cultivated in vitro was studied by histoautoradiography. In the non-differentiated cells, uptake of precursor is intense from the beginning of the culture, and sensitive to addition of trophic factor known for their activating effect on mitosis and regeneration. On the contrary the rate of incorporation in differentiated cells is low and uniform, independently of the differents factors added to the medium.

Chemo-klino-kinesis in planarian food location

The effects of a homologous series of buffered fatty acid solutions on planarian behaviour were measured as the change in klino-kinetic activity. On the basis of the results obtained a model demonstrating the function of this behaviour pattern in the food-locating response was proposed. The model suggested that qualitative rather than quantitative gradients were effective in stimulating klino-kinetic orientation.

Proposal of a new model with dopaminergic-cholinergic interactions for neuropharmacological investigations

The motor system of Dugesia gonocephala shows a striking similarity with the extrapyramidal system of high vertebrates and of man with the evidence of correlations between dopaminergic and cholinergic neurons. The utilization of this model seems to be useful in testing drugs which presumably act on dopaminergic or cholinergic transmission. In this model, the quantification of animal behaviour seems considerably easier when compared with the difficulties met in other animal models commonly employed. Besides, it might be anticipated that this model, if correctly used, can display interesting perspectives also in neuroendocrinological investigations.

[Histological and cytological study of neoblasts and fixed parenchymal cells in Dendrocoelum lacteum planarians deprived of their anterior region]

On amputating either at the root of the pharynx or between the mouth and the genital pore, the posterior parts which are thereby isolated do not regenerate. However they are capable of surviving for ever a year, without feeding. The wounded region is occupied by neoblasts which degenerate within a few days after an initial secretory activity. Their degeneration is of autophagic type. The abortive blastems disappear only slowly, because the degeneration of their neoblasts is partly compensated by the continual immigration of new regeneration cells which come from the posterior region. Several months after amputation, under the effect of prolonged starvation, neoblasts and fixed parenchymal cells begin to degenerate.