Reorganization of the GABAergic system following brain extirpation in the earthworm (Eisenia fetida, Annelida, Oligochaeta)

Csoknya, Mária and Barna, J. and Elekes, K. (2002) Reorganization of the GABAergic system following brain extirpation in the earthworm (Eisenia fetida, Annelida, Oligochaeta). Acta Biologica Hungarica, 53 (1-2). pp. 43-58. ISSN 0236-5383

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Abstract

The reorganization of the GABAergic system was studied by means of immunohistochemistry after the symmetrical and asymmetrical (unilateral) extirpation of the brain of the annelid Eisenia fetida. GABA-immunoreactive neurons were first observed in the wound tissue on the 3rd postoperative day. Thereafter the number of labelled cells gradually increased, and by postoperative days 76–80 all GABA-immunoreactive cells (approx. 140 neurons) could be found in their final positions in the symmetrically regenerated brain. After asymmetrical brain extirpation, nearly all cells (70–75) could be detected in the regenerating hemisphere by postoperative days 50–56. In the early stages of the asymmetrical regeneration of the brain, more GABAergic cells were concentrated dorsally and laterally in the preganglion than during the symmetrical type of regeneration. In both types of regeneration, the immunoreactive neurons in the regenerated brain originated in part from undifferentiated neuroblasts situated in different parts of the body, and in part from dividing neurons localized mainly in the pharyngeal nerve plexus. Both exogenous GABA and picrotoxin, applied during the early stages (days 10–12) of brain regeneration, inhibited the development of the wound tissue and the migration of the neuroblasts and the enteric neurons. At the same time, exogenous GABA application accelerated the proliferation of the pharyngeal neurons. No effect on the process of regeneration could be demonstrated when exogenous GABA and picrotoxin were given together.

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