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Electrophysiological and Pharmacological Characterization of Vestibular Inputs to Identified Frog Abducens Motoneurons and Internuclear Neurons In Vitro
Author(s) -
Straka Hans,
Dieringer Norbert
Publication year - 1993
Publication title -
european journal of neuroscience
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.346
H-Index - 206
eISSN - 1460-9568
pISSN - 0953-816X
DOI - 10.1111/j.1460-9568.1993.tb00491.x
Subject(s) - neuroscience , antidromic , vestibular nuclei , excitatory postsynaptic potential , inhibitory postsynaptic potential , cnqx , chemistry , vestibular system , abducens nucleus , picrotoxin , electrophysiology , stimulation , medial vestibular nucleus , interneuron , vestibular nerve , excitatory amino acid antagonists , strychnine , ampa receptor , biology , antagonist , glutamate receptor , receptor , biochemistry
Synaptic vestibular inputs of antidromically identified motoneurons and internuclear neurons in the abducens nucleus were studied electrophysiologically and pharmacologically in the isolated brain of grass frogs ( Rana temporaria ). The prevailing response pattern of abducens motoneurons (AbMOT) following stimulation of the VIIIth nerve was crossed disynaptic excitation and uncrossed disynaptic inhibition. A few AbMOT (five of 46), however, exhibited uncrossed excitation instead of inhibition. Abducens internuclear neurons (AbINT), identified by antidromic activation following stimulation of the contralateral medial longitudinal fascicle, exhibited disynaptic response patterns to stimulation of the VIIIth nerve that were very similar in latency and rise time to those of AbMOT except for the absence of uncrossed disynaptic inhibition. Bath application of strychnine (50 μM), a glycine antagonist, blocked the uncrossed inhibitory vestibular input to AbMOT and AbINT completely and reversibly, whereas picrotoxin (100 μM), a GABA (γ‐aminobutyric acid) antagonist, had no detectable effect on these disynaptic potentials. These results suggest glycine as the transmitter of inhibitory vestibular projections onto AbMOT and AbINT. The pharmacology of the excitatory vestibular input of these neurons was studied by electrical stimulation of the vestibular nuclear complex. Crossed monosynaptic excitatory inputs in AbMOT and AbINT were blocked completely by CNQX (6‐cyano‐7‐nitroquinoxaline‐2,3‐dione) (10 μM), an antagonist of AMPA (α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid) receptors, indicating glutamatergic excitation. Comparison of these results with those in the cat suggests the presence of a basic horizontal vestibulo‐ocular reflex that is very similarly organized, and corroborates the hypothesis that major behavioural differences in the performance of compensatory eye movements between species result from the properties of supplementary networks and not from differences in a common‘three‐neuron’vestibulo‐ocular arc.