Transmitter inputs to different motoneuron subgroups in the oculomotor and trochlear nucleus in monkey

Area of Science:

• Neuroscience
• Ophthalmology
• Motor Control

Background:

• Vertebrate eye movements are controlled by six extraocular muscle pairs.
• Motoneurons are categorized into singly-innervated muscle fiber (SIF) and multiply-innervated muscle fiber (MIF) groups.
• Limited data exists on transmitter inputs to SIF and MIF motoneurons.

Purpose of the Study:

• To quantitatively analyze transmitter inputs to SIF and MIF motoneurons in monkey oculomotor and trochlear nuclei.
• To elucidate differences in inhibitory control mechanisms for eye movement motoneurons.

Main Methods:

• Quantitative study of transmitter inputs to SIF and MIF motoneurons in monkey.
• Immunostaining for GABA, glutamate decarboxylase, GABA-A receptor, glycine transporter 2, glycine receptor 1, and vesicular glutamate transporters (vGlut1, vGlut2).
• Analysis of pre-labeled motoneurons within oculomotor and trochlear nuclei.

Main Results:

• Inhibitory control of SIF motoneurons for horizontal and vertical eye movements shows differences.
• Significant GABAergic input found in all SIF motoneuronal groups.
• Glycinergic input was specific to medial rectus (MR) and levator palpebrae (LP) muscle motoneurons.
• vGlut1 terminals densely innervated the supraoculomotor area (SOA), targeting MR MIF motoneurons.

Conclusions:

• Distinct GABAergic and glycinergic inhibitory pathways modulate eye movement control.
• vGlut1 input to MR MIF motoneurons in the SOA may influence near response systems like vergence and accommodation.