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Summary
The central nervous system of earthworms comprises suprapharyngeal ganglia, also called
cerebral ganglia or “brains”, connected by circumpharyngeal connectives with subpharyngeal
ganglia, the latter forming with ventral ganglia the ventral nerve cord. Siekierska (2003a)
described the structure of neurosecretory cells in the cerebral ganglia and subpharyngeal
ganglia of adult specimens of Dendrobaena veneta.
The aim of the first part of the present thesis was to examine the development of
neurosecretory centres in the cerebral ganglia of earthworms in the first month after
hatching. It was revealed that the neurosecretory cells are active in the cerebral ganglia of D.
veneta already on the day of hatching. Within the first month after hatching, the
neurosecretion content increased in the cells and its form gradually changed from dispersed
into grainy.
Siekierska (2002a, 2007) showed that the amputation of the first six segments of adult
specimens of D. veneta resulted in a reversible degeneration of ovaries, and she suggested
that the return of oogenesis occurs in parallel to the progress of the reconstruction of
the neurosecretory system of the regenerating brains. In our preliminary study we showed that
the amputation of the first six head segments of D. veneta resulted in a temporary inhibition of
cocoon production, which started only several weeks after surgery, presumably along with the
regeneration of neurosecretory centres. A question raised, whether the same effect occurs
after surgical resection of the suprapharyngeal ganglia (the brain) of earthworms, keeping
intact the subpharyngeal ganglia and undisturbed food intake. Hence, further research focused
on earthworms regenerating surgically removed cerebral ganglia. The aim of the second part
of this thesis was to study the regeneration of surgically removed cerebral ganglia and
the concomitant changes in reproduction of D. veneta.
The surgical removal of cerebral ganglia was performed on specimens immobilized as a
result of the electrostimulation-induced expulsion of coelomic fluid which constitutes worms’
hydrostatic skeleton; that was connected with a loss of coelomocytes freely floating in
coelomic fluid, thus an additional group of earthworms was subjected to electro-stimulation
associated with the loss of coelomocytes but without the removal of the brain.
During the 18-week investigations, reproduction, reconstruction of the coelomocytes pool,
and regeneration of the cerebral ganglia were compared between the untreated control
specimens with the both experimental groups of earthworms. Apparently, the surgically
removed cerebral ganglia with their neurosecretory centers were fully regenerated within
several weeks. The removal of the brain resulted in temporary inhibition of reproductive
capacity, which gradually returned as the regeneration of the brain proceeded. The restoration
of the reproductive activity is therefore a biomarker of the regeneration of cerebral ganglia.
The number and composition of the immunocompetent coelomocytes (amebocytes and
eleocytes) and the content of riboflavin, lost due to expulsion of coelomic fluid, returned to
the level characteristic of the control earthworms faster in the specimens with untouched
brains than in specimens regenerating cerebral ganglia. Consecutive studies our team
(Molnar et al. 2015) proved that regeneration of the brain and the restoration of reproductive
ability occured faster in the specimens with retained immunological system, i.e. with brains
removed under pharmacological anaesthesia, than in the specimens from the present thesis,
regenerating simultaneously the nervous and the immunological system. The obtained results
prove the existence of close relations of the nervous, reproductive and immunological systems
of earthworms. The D. veneta earthworms are thus a convenient model for research in the
field of immunoneuroendocrinology of invertebrates.