Cerebral Blood Flow Responses to Trigeminal Olfactory Stimulation and Their Nicotinic Cholinergic Regulation in...

Area of Science:

• Neuroscience
• Cerebrovascular Physiology
• Sensory Systems

Background:

• The sense of smell involves both the olfactory and trigeminal nerves.
• Olfactory nerve stimulation increases cerebral blood flow (BF) in the olfactory bulb.
• Nicotinic receptor activation potentiates olfactory bulb BF responses.

Purpose of the Study:

• To compare the effects of intranasal trigeminal nerve stimulation on regional cerebral BF with olfactory nerve stimulation.
• To investigate the impact of nicotinic receptor activation on trigeminal nerve-induced BF responses.
• To determine the specific brain regions affected by trigeminal nerve stimulation.

Main Methods:

• Regional cerebral BF in the olfactory bulb and frontal cortex was measured using laser Doppler flowmetry or laser speckle contrast imaging.
• Anesthetized and artificially ventilated rats underwent electrical stimulation of the intranasal trigeminal nerve.
• The effects of intravenous nicotine administration and spinal cord transection on BF responses were assessed.

Main Results:

• Intranasal trigeminal nerve stimulation increased frontal cortical BF and arterial pressure, with a minor increase in olfactory bulb BF.
• The pressor response to trigeminal stimulation was abolished after spinal cord transection.
• Nicotine administration augmented the frontal cortical BF increase following trigeminal nerve stimulation but did not affect olfactory bulb BF.

Conclusions:

• Intranasal trigeminal nerve stimulation primarily increases frontal cortical BF, independent of significant changes in olfactory bulb BF or blood pressure.
• Nicotinic receptor activation potentiates trigeminal nerve-mediated increases in frontal cortical BF.
• These findings differentiate the vascular responses mediated by the olfactory and trigeminal nerves.