Facilitation of saccade initiation by brainstem cholinergic system

Area of Science:

• Neuroscience
• Systems Neuroscience
• Neurophysiology

Background:

• The mammalian superior colliculus (SC) receives cholinergic inputs from the pedunculopontine tegmental nucleus (PPTN).
• The precise role of these cholinergic inputs in SC function, particularly in visuomotor processing, remains to be fully elucidated.

Purpose of the Study:

• To investigate the action of cholinergic input on superior colliculus intermediate gray layer (SGI) neurons.
• To explore the behavioral significance of cholinergic modulation in visually guided saccade tasks.
• To analyze the activity of PPTN neurons during saccade preparation and execution.

Main Methods:

• Whole-cell patch-clamp recordings in rat SC slice preparations.
• Application of acetylcholine (ACh) and nicotine to SGI neurons.
• Microinjection of nicotine into the SC of awake monkeys performing a visually guided saccade task.
• Single unit activity recordings of PPTN neurons.

Main Results:

• Acetylcholine (ACh) application induced fast inward currents in SGI neurons via nicotinic receptors.
• Nicotine enhanced N-methyl-D-aspartate receptor-mediated EPSPs and lowered the bursting threshold in SGI neurons.
• Nicotine injection into the SC increased the frequency of express saccades in monkeys.
• A subpopulation of PPTN neurons showed increased firing preceding saccades and during the gap period.

Conclusions:

• Cholinergic input to the SC facilitates signal transmission through the visuomotor pathway.
• The brainstem cholinergic system, via PPTN and SC, plays a crucial role in the initiation of saccades.
• PPTN neurons are involved in both the preparation and execution of saccades, potentially influenced by attention or vigilance levels.