The importance of NMDA receptors for multi-modal integration in the deep
layers of the cat superior colliculus.
Binns K.E. & T.E.Salt.
Department of Visual Science, Institute of Ophthalmology, Bath street,
London, EC1V 9EL.
APStracts 2:0287N, 1995.
SUMMARY AND CONCLUSIONS
1. Many sensory events contain multi-modal information yet most sensory nuclei
are devoted to the analysis of single modality information. In the deep
superior colliculus (DSC) visual, auditory and somatosensory information
converges on individual multi-modal neurones. The responses of multi-modal
neurones are determined by the temporal and spatial correspondence properties
of the converging inputs such that stimuli arising from the same event elicit
a facilitated multi-modal response. 2. NMDA receptors may underlie the
detection of spatial and temporal coincidence and could be involved in the
generation of multi-modal facilitatory responses due to the non-linear
properties of NMDA-receptor-mediated events. In order to assess the role of
NMDA receptors in multi-modal integration, extracellular recordings were made
from single multi-sensory neurones in the DSC of the cat. 3. The responses to
visual, auditory and somatosensory stimuli alone and to multi-modal
combinations of stimuli were challenged with iontophoretically applied AP5, an
NMDA receptor antagonist. All responses to visual stimuli presented alone
(n=9) were greatly reduced. Somatosensory responses (n=25) were usually
decreased. In contrast, the responses to auditory stimulation were decreased
(n=9), unaffected (n=3) or enhanced (n=5). 4. Responses to multi-modal
stimulus presentations were consistently reduced during iontophoretic
application of AP5, irrespective of the modalities which comprised the
stimulus. The reductions of multi-modal responses were significantly greater
than the sum of the reductions of responses to single-modality stimuli. 5.The
data suggest, that for uni-modal stimuli, the importance of NMDA receptors in
synaptic transmission of sensory responses in DSC may be dependent on the
stimulus modality. Furthermore, NMDA receptors are of major importance in the
integration of input from different modalities for the generation of multi-
modal responses.
Received 13 December 1994; accepted in final form 13 September 1995.
APS Manuscript Number J780-4.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 31 October 95