Pivotal role of the ventral tegmental area in spontaneous motor activity and concomitant cardiovascular responses in decerebrate 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.

Exaggerated renal sympathetic nerve and pressor responses during spontaneously occurring motor activity in hypertensive rats

Stimulation of the mesencephalic locomotor region elicits exaggerated sympathetic nerve and pressor responses in spontaneously hypertensive rats (SHR) as compared with normotensive Wistar-Kyoto rats (WKY). This suggests that central command or its influence on vasomotor centers is augmented in hypertension. The decerebrate animal model possesses an ability to evoke intermittent bouts of spontaneously occurring motor activity (SpMA) and generates cardiovascular responses associated with the SpMA. It remains unknown whether the changes in sympathetic nerve activity and hemodynamics during SpMA are altered by hypertension. To test the hypothesis that the responses in renal sympathetic nerve activity (RSNA) and mean arterial pressure (MAP) during SpMA are exaggerated with hypertension, this study aimed to compare the responses in decerebrate, paralyzed SHR, WKY, and normotensive Sprague-Dawley (SD) rats. In all strains, an abrupt increase in RSNA occurred in synchronization with tibial motor discharge (an index of motor activity) and was followed by rises in MAP and heart rate. The centrally evoked increase in RSNA and MAP during SpMA was much greater (306 ± 110%) in SHR than WKY (187 ± 146%) and SD (165 ± 44%). Although resting baroreflex-mediated changes in RSNA were not different across strains, mechanically or pharmacologically induced elevations in MAP attenuated or abolished the RSNA increase during SpMA in WKY and SD but had no effect in SHR. It is likely that the exaggerated sympathetic nerve and pressor responses during SpMA in SHR are induced along a central command pathway independent of the arterial baroreflex and/or result from central command-induced inhibition of the baroreflex.

Increased prefrontal oxygenation prior to and at the onset of over-ground locomotion in humans

We found using wireless near-infrared spectroscopy that prefrontal oxygenation increased before the onset of arbitrary over-ground walking, whereas the preexercise increase was absent when walking was suddenly started by cue. The difference in prefrontal oxygenation between start modes (considered related to central command) preceded heart rate response variances and demonstrated a positive relationship with the difference in heart rate. The central command-related prefrontal activity may contribute to cardiac adjustment, synchronized with the beginning of over-ground walking.