Intranasal scopolamine affects the semicircular canals centrally and peripherally

Area of Science:

• Vestibular Neuroscience
• Aerospace Medicine
• Pharmacology

Background:

• Space motion sickness (SMS) is a significant challenge for astronauts, often treated with promethazine or scopolamine.
• Current scopolamine administration methods (oral, transdermal) have drawbacks.
• Intranasal scopolamine offers rapid absorption and therapeutic onset, suitable for spaceflight.

Purpose of the Study:

• To evaluate the effects of intranasal scopolamine (0.4 mg) on semicircular canals (SCCs) and otoliths.
• To investigate scopolamine's impact on vestibular functions, including the vestibulo-ocular reflex (VOR).

Main Methods:

• Double-blind, placebo-controlled study with 19 healthy male subjects.
• Evaluation of horizontal SCC function, VOR, saccular, and utricular function.
• Assessment of intranasal scopolamine's central and peripheral effects on the vestibular system.

Main Results:

• Intranasal scopolamine primarily affects SCCs centrally and peripherally, with a lesser effect on utricles.
• The medial vestibular nucleus is a likely central site of action due to muscarinic receptor density.
• Evidence suggests scopolamine suppresses peripheral vestibular system activity, potentially via muscarinic receptors.

Conclusions:

• Intranasal scopolamine demonstrates suppressive effects on the SCCs and utricles.
• Scopolamine's action may alleviate SMS by mitigating intravestibular conflict.
• Intranasal administration presents a promising route for scopolamine delivery in spaceflight settings.