Brain stem reticular units: synaptic responses to stimulation within the ascending reticular pathways

Area of Science:

• Neuroscience
• Neurophysiology

Background:

• The ascending reticular activating system (ARAS) influences arousal and consciousness.
• Observed long-lasting effects of ARAS stimulation suggest complex neural processing.

Purpose of the Study:

• To investigate the hypothesis that interactions among reticular cells prolong stimulation effects.
• To differentiate between intrinsic distal structure responses and reticular cell network activity.

Main Methods:

• Acute experiments on cats under anesthesia.
• Recording single units with ascending axons (projecting units) in the rostral rhombencephalon.
• Stimulation of specific ARAS projection areas (midbrain, thalamus, basal forebrain).

Main Results:

• ARAS stimulation predominantly caused suppression of spontaneous activity in projecting units.
• Short-latency, single-spike synaptic excitation was observed in about half of the responses.
• Response occurrence correlated directly with the number of identified projecting axons from a stimulation site.

Conclusions:

• Prolonged effects of ARAS stimulation are unlikely due to reverberating excitatory circuits among projecting units.
• Retrograde activation of collaterals interconnecting reticular cells may explain synaptic responses.
• Reticular collateral interactions might specifically function to decrease activity in cells projecting to similar rostral targets.