Influences exerted by the frontal eye field on accessory oculomotor nuclei neurons of the rat

G. Bosco, A. Casabona, G. Giaquinta, V. Perciavalle

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Abstract

The medial agranular cortex (AGm), considered the rat's analogous to the frontal eye fields of the monkey, sends a conspicuous projection towards the accessory oculomotor nuclei (AON), i.e. the nucleus of posterior commissure (NPC), the nucleus of Darkschewitsch (NDK) and the interstitial nucleus of Cajal (INC). The nature of the synaptic influences exerted by AGm on the AON neurons and the receptor(s) which mediates these cortical-evoked effects were studied in adult rats. Electrical stimulation of a single site within the AGm elicited changes in firing rate of a significant fraction of cells belonging to the ipsilateral accessory oculomotor nuclei (50% in INC, 52.3% in NDK and 52% in NPC). In 82.9% of the cases, the responses were excitations, most of which having latencies and response characteristics compatible with a monosynaptic linkage. The remaining 17.1% of cases were inhibitions with latencies ranging between 4 and 11 ms. Extracellular field potential recordings within the accessory oculomotor nuclei were interpreted as arising from impulses propagating along excitatory axons projecting in a bundle from the cortex. Effects of exogenously applied excitatory amino acid N-methyl-D-aspartate (NMDA) receptor antagonist 2-amino-5 phosphonovaleric acid (2APV) and of selective non-NMDA receptor antagonist 6,7-dinitroquinoxaline-2,3-dione (DNQX) were examined on synaptic excitation. Monosynaptic excitations induced by the cortical stimulation were abolished by microiontophoretic application of 2APV and not of DNQX. This finding indicates that cortical inputs activate specifically NMDA receptors of AON neurons.

Original languageEnglish
Pages (from-to)305-316
Number of pages12
JournalArchives Italiennes de Biologie
Volume134
Issue number4
Publication statusPublished - Oct 1996

ASJC Scopus subject areas

  • Medicine(all)

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