Excitatory amino acid actions on membrane potential and conductance of brainstem motoneurones

Abstract

N-methyl-D-aspartate (NMDA), quisqualate and kainate receptors are widely studied in the central nervous system and their participation in synaptic transmission of different pathways has been well established [for reviews: 1–5,16,19]. Relatively little is known about the excitatory transmitters in the oculomotor system. Our earlier observations on intracellularly recorded activity indicated that L-glutamate and NMDA excited cat abducens motoneurones in different ways [8]. We report here a comparison of NMDA effects on membrane potential and conductance of these brainstem motoneurones of the rat in vivo and in a brainstem slice preparation. In vivo the excitatory amino acids (EAA) were applied by iontophoretic injections while perfusion or droplets were used in the slice preparation. The first mode of application had a local effect on the somatic region of the motoneurone. The second mode had a diffuse effect in reaching all parts of the neurone together with its microenvironment. We used two receptor antagonists (DL-aminophosphonovalerate and kynurenate) to study the involvement of EAA receptors in the synaptic responses evoked in these motoneurones.