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Abstract
This study examined the effect of olfactory nerve stimulation on regional cerebral blood flow and assessed the effect of intravenous nicotine administration on this response in anesthetized rats. Regional cerebral blood flow was measured with laser Doppler flowmetry or laser speckle contrast imaging. Unilateral olfactory nerve stimulation for 5 s produced current (≥ 100 μA) and frequency-dependent (≥ 5 Hz) increases in blood flow in the olfactory bulb ipsilateral to the stimulus. The increased olfactory bulb blood flow peaked at 30 ± 7% using stimulus parameters of 300 μA and 20 Hz. Nerve stimulation did not change frontal cortical blood flow or mean arterial pressure. The intravenous injection of nicotine (30 μg/kg) augmented the olfactory bulb blood flow response to nerve stimulation (20 Hz, 300 μA) by approximately 1.5-fold (60-s area after the stimulation). These results indicate that olfactory nerve stimulation increases olfactory bulb blood flow, and the response is potentiated by the activation of nicotinic cholinergic transmission.
Highlights
The cholinergic neurons originating in the basal forebrain send projections to the neocortex, hippocampus, and olfactory bulb that contribute to cognition, memory, and olfactory function, respectively [1,2,3]
Our research group previously found in anesthetized rats that activation of basal forebrain cholinergic neurons produces an increase in regional blood flow in the neocortex [4,5,6,7] and hippocampus [8], whereas it does not influence blood flow in the olfactory bulb [9]
Blood flow response to olfactory nerve stimulation in the olfactory bulb The effects of electrical stimulation of the unilateral olfactory nerve with different stimulus intensities (Fig. 1a, b) and frequencies (Fig. 1c–e) on regional blood flow in the olfactory bulb ipsilateral to the stimulation were examined
Summary
The cholinergic neurons originating in the basal forebrain send projections to the neocortex, hippocampus, and olfactory bulb that contribute to cognition, memory, and olfactory function, respectively [1,2,3]. Our research group previously found in anesthetized rats that activation of basal forebrain cholinergic neurons produces an increase in regional blood flow in the neocortex [4,5,6,7] and hippocampus [8], whereas it does not influence blood flow in the olfactory bulb [9]. Blood flow in the olfactory bulb is reportedly increased by odor stimulation in association with neuronal activities [10,11,12,13,14]. To improve our neurophysiological understandings of olfactory bulb blood flow response to olfactory input, it is necessary to study the effect of sensory (olfactory) nerve stimulation, in addition to natural olfactory stimulation of odor inhalation. Electrical stimulation of the olfactory nerve using various stimulus parameters on olfactory bulb blood flow was tested. Blood flow in the frontal cortex and systemic arterial pressure were measured simultaneously
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