Journal of Comparative Physiology A

, Volume 176, Issue 2, pp 181–192

Pretecto-tectal influences

II. How retinal and pretectal inputs to the toad's superficial tectum interact: a study of electrically evoked field potentials
  • W. W. Schwippert
  • T. W. Beneke
  • J. -P. Ewert
Original Paper

DOI: 10.1007/BF00239921

Cite this article as:
Schwippert, W.W., Beneke, T.W. & Ewert, J.P. J Comp Physiol A (1995) 176: 181. doi:10.1007/BF00239921

Abstract

(1)From the dorsal surface of the toad (Bufo b. spinosus, B. marinus) optic tectum (OT), field potentials (FP) were recorded at 9 reference sites in response to electrical stimulation of the optic nerve (ON). The FP showed 4 main components, besides an initial deflection attributed to axonal potentials: two negative waves N1, N2 (attributed to postsynaptic excitatory processes) and two positive waves P2, P3 (attributed to postsynaptic inhibitory processes). The responses across the reference sites were rather similar in different individuals. (2) Electrical stimulation of an area in the ipsilateral pretectal lateral posterodorsal and posterior (Lpd/P) thalamic region evoked tectal FPs showing mainly a negative and a positive wave. Regarding wave amplitudes, the FPs displayed disproportionalities across the reference sites. (3) Electrical stimulation of the contralateral Lpd/P evoked mainly a positive wave in the tectal FP whose disproportionality corresponded roughly to the one obtained to ipsilateral Lpd/P stimulation. (4) The inital negative wave of the tectal FP in response to ON stimulation was nearly abolished, if Lpd/P stimulation preceded ON stimulation at a delay of 17–25 ms. (5) Since FPs showed adaptation to repetitive stimulation, various experiments were carried out to distinguish adaptation phenomena from effects of neuronal interactions between Lpd/P and OT. (6) The results provide evidence that ON- and Lpd/P-mediated inputs interact in superficial tectal layers, whereby pretectotectal input suppresses retinotectal excitatory information transfer. Input of Lpd/P to the contralateral superficial OT suggests postsynaptic inhibition. This study provides no information about pretectal inputs to deeper tectal layers, which anatomically are known to exist.

Key words

Optic tectum Evoked field potentials Pretectal/tectal interaction Toad 

Abbreviations

A-I

recording sites from the dorsal tectal surface

Dt

delay between Lpd/P and ON stimulation

EPSPIPSP

excitatory and inhibitory postsynaptic potentials, respectively

FP

field potential

L

latency of FP waves

ON

optic nerve

OT

optic tectum

Lpd/P

lateral posterodorsal and posterior pretectal thalamic region

Lpv

lateral posteroventral pretectal thalamic nucleus

N, P

negative and positive waves of FPs, respectively

PRE

presynaptic axonal input

TH

pretectal thalamic neurons

Copyright information

© Springer-Verlag 1995

Authors and Affiliations

  • W. W. Schwippert
    • 1
  • T. W. Beneke
    • 1
  • J. -P. Ewert
    • 1
  1. 1.Abteilung Neurobiologie, Fachbereich Biologie/Chemie, Universität Kassel (GhK)KasselGermany