Organization of last-order premotor interneurons related to the protraction of tongue in the frog, Rana esculenta

Éva Rácz, Tímea Bácskai, Gábor Szabo, György Székely, Clara Matesz

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Moving visual stimuli elicit a sequence of coordinated activity of muscles including tongue protraction. Morphological and physiological studies fail to reveal any direct tectal projections to hypoglossal motoneurons suggesting that the last-order premotor interneurons (LOPI) are the direct recipients of neural activities generated in the optic tectum. The aim of this study is to analyze the topographical organization of the last-order premotor interneurons related to protractor muscles of the tongue. In Rana esculenta, biotinylated dextran amine (BDA) was injected by iontophoresis into the subnucleus of the hypoglossal nerve containing the motoneurons of protractor muscles of the tongue. For visualizing BDA, sections were treated with avidin-biotin complex and a nickel-enhanced DAB chromogen reaction. The position of labeled neurons was reconstructed with a Neurolucida equipment. Morphologically heterogeneous populations of neurons were detected bilaterally, the majority of them were distributed ipsilateral to the site of injection and extended 1200 μm in rostral and 500 μm in caudal directions. Labeled neurons were found in the rhombencephalic reticular formation, the vestibular nuclei, the nucleus prepositus hypoglossi, the nucleus of solitary tract, the spinal nucleus of trigeminal nerve and the dorsal column nuclei. Our results indicate that the majority of last-order premotor interneurons related to protractor muscles of the tongue are located in the reticular formation of the brainstem. Since this area also receives a significant input from the vestibular system and from proprioceptive fibers, the last-order premotor interneurons presented here may be the target of convergence of sensory modalities involved in prey-catching behavior.

Original languageEnglish
Pages (from-to)111-115
Number of pages5
JournalBrain research
Issue number1
Publication statusPublished - Jan 2 2008



  • Brainstem
  • Hypoglossal nucleus
  • Neuronal labeling
  • Optic tectum
  • Reticular formation

ASJC Scopus subject areas

  • Neuroscience(all)
  • Molecular Biology
  • Clinical Neurology
  • Developmental Biology

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