, Volume 144, Issue 4, pp 429-434

Prey-selective neurons in the toad's optic tectum and sensorimotor interfacing: HRP studies and recording experiments

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  1. In accordance with recent recording experiments in paralyzed toadsBufo bufo (L.) neurons have been identified between layers 6 and 8 of the optic tectum that exhibit selective responses to the configuration of moving prey dummies.

  2. Injection of HRP into the two extrinsic tongue muscles — which are the effectors of the toad's snapping response — showed that motoneurons innervating the protractor (m. genioglossus) and the retractor (m. hyoglossus) have distinct topographical distributions within the hypoglossal nucleus of the medulla oblongata.

  3. Following injection of HRP in the vicinity of the hypoglossal nucleus, retrogradely labelled fibers have been identified in (1) the dorso-lateral tegmentum, (2) the fasciculus tegmentalis, (3) ansulate commissure of the ventral tegmentum, and (4) layer 7 of the optic tectum. Retrogradely labelled cells were identified in (1) the subtectal region, (2) the nucleus antero-ventralis tegmenti mesencephali, and (3) layer 6 of the optic tectum. Labelled cells were also identified in the caudal part of the area ventrolateralis thalami, occasionally in the lateral part of the posterocentral nucleus, and in the postero-lateral nucleus of the caudal thalamus.

  4. The results are discussed with regard to the control of prey-catching behavior, and it is suggested that the toad's optic tectum contains a substrate for sensorimotor interfacing.

We are greatly obliged to Professor Dr. S.O.E. Ebbesson, Ponce, Puerto Rico, for helpful comments on the HRP technique. We also thank Ms. D. Müller, Zentrale Werkstätten University of Kassel, for the photomicrographs and Ms. U. Reichert for secretarial assistance.