Chapter 15 The pathways and functions of GABA in the oculomotor system

Abstract

This chapter reviews the anatomical connections involved in vertical and horizontal vestibulo-ocular reflexes, including vertical and horizontal gaze. It also cites experimental evidence to demonstrate the involvement of gamma-aminobutyric acid (GABA) as the major neurotransmitter of inhibitory premotor neurons in the oculomotor system. The chapter compares the monkey and the cat in terms of the distribution and synaptic connections of GABA-labeled neurons and presents a summary of their putative inhibitory role in eye movement. Conjugate eye movement involves coordinating the action of at least one pair of extraocular muscles in each eye. In horizontal eye movement, one muscle (for example, the medial rectus) must be excited and its antagonistic muscle (the lateral rectus) inhibited. In vertical eye movement, this reciprocal relationship includes the superior and inferior recti. GABA is the major inhibitory neurotransmitter utilized by the premotor neurons involved in vertical eye movements. By contrast, glycine is the inhibitory neurotransmitter of most premotor neurons that are related to horizontal eye movements.