Nicotinic cholinergic regulation of olfactory bulb blood flow response in aged rats

Regional heterogeneity of cerebral blood flow immediately after the onset of ventricular pacing in anesthetized rats

Selective distribution of cerebral blood flow (CBF) to vital brain regions likely occurs during rapid severe hypotension caused by tachyarrhythmia but has not yet been demonstrated. In this study, we aimed to test the hypothesis that CBF is differentially preserved between brain regions depending on the degree of hypotension. In anesthetized rats, CBF was measured in the motor cortex (MC), medial prefrontal cortex, amygdala, thalamus, dorsal hypothalamus, hippocampus, ventral tegmental area, dorsolateral periaqueductal gray (dlPAG), and parabrachial nucleus (PB) by using laser-Doppler flowmetry. Ventricular pacing was performed for 30 s at 550-800 beats/min. The cerebrovascular CO2 response time and reactivity were evaluated during 5% CO2 exposure. During 1-4 s of ventricular pacing, mean arterial pressure (MAP) rapidly decreased, with minor changes in central venous and intracranial pressures. CBF was relatively well maintained in brain regions other than the MC (Ps ≤ 0.012) when moderate hypotension occurred (-34 mmHg ≤ ΔMAP ≤ -15 mmHg), whereas severe hypotension (-54 mmHg ≤ ΔMAP ≤ -35 mmHg) induced selective CBF distribution to regions other than the MC, thalamus, and dlPAG. The cerebrovascular CO2 response time/reactivity was rapid or high in the thalamus, dlPAG, and PB, which almost completely differed from the brain regions in which CBF was relatively maintained during pacing-induced severe hypotension. These results suggest that regional heterogeneity of CBF arises depending on the degree of tachyarrhythmia-induced hypotension. Clarifying the mechanisms and functions of CBF maintenance would be beneficial to syncope and cerebral ischemia management in patients with arrhythmia.NEW & NOTEWORTHY When lethal tachyarrhythmia occurs, survival is prioritized by counterregulating the cardiovascular system, which is driven by vital brain regions. However, whether limited cerebral blood flow is selectively distributed to vital brain regions is unknown. We demonstrated the preferential maintenance of cerebral blood flow in vital brain regions, depending on the degree of hypotension caused by ventricular pacing, in anesthetized rats. Our data may have clinical implications for syncope and cerebral ischemia management in patients with arrhythmia.

Cerebral Cortical Vasodilation via Nicotinic Receptors by Heated Tobacco Product Aerosol Extract in Rats

INTRODUCTION

Smoking increases the risk of lung cancer due to a number of components of smoke. The use of novel heated tobacco products (HTPs), alternative to conventional combustion cigarettes, has increased in recent years. However, the in vivo biological effects of HTPs are poorly understood. This study aimed to clarify the acute effects of injecting aerosol extract prepared from an HTP on regional cerebral blood flow (rCBF) in rat cortex by comparing them to the effects of injecting smoke extract prepared from conventional combustible cigarettes.

METHODS

In urethane anesthetized rats, rCBF was measured using laser speckle contrast imaging simultaneously with arterial pressure.

RESULTS

Both cigarette smoke extract and HTP aerosol extract, at a dose equivalent to 30 μg nicotine/kg, injected intravenously, increased cortical rCBF without changing arterial pressure. The magnitude and time course of the increased rCBF response to both extracts were similar throughout the cortical area, and the rCBF increases were all abolished by dihydro-β-erythroidine, an α4β2-preferring nicotinic acetylcholine receptor (nAChR) antagonist.

CONCLUSION

In conclusion, our study demonstrated that the effect of injecting aerosol extract prepared from an HTP, an acute increase in cortical rCBF, is mediated via activation of α4β2-like neuronal nAChRs in the brain.

Influence of age on nicotinic cholinergic regulation of blood flow in rat's olfactory bulb and neocortex

The olfactory bulb receives cholinergic basal forebrain inputs as does the neocortex. With a focus on nicotinic acetylcholine receptors (nAChRs), this review article provides an overview and discussion of the following findings: (1) the nAChRs-mediated regulation of regional blood flow in the neocortex and olfactory bulb, (2) the nAChR subtypes that mediate their responses, and (3) their activity in old rats. The activation of the α4β2-like subtype of nAChRs produces vasodilation in the neocortex, and potentiates olfactory bulb vasodilation induced by olfactory stimulation. The nAChR activity producing neocortical vasodilation was similarly maintained in 2-year-old rats as in adult rats, but was clearly reduced in 3-year-old rats. In contrast, nAChR activity in the olfactory bulb was reduced already in 2-year-old rats. Thus, age-related impairment of α4β2-like nAChR function may occur earlier in the olfactory bulb than in the neocortex. Given the findings, the vasodilation induced by α4β2-like nAChR activation may be beneficial for neuroprotection in the neocortex and the olfactory bulb.