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

Diencephalic and brainstem circuit mechanisms underlying autonomic cardiovascular adjustments to exercise: Recent insights from rodent studies

Autonomic cardiovascular adjustments to exercise, essential for meeting the increased metabolic demands of exercising skeletal muscle, are regulated by motor volition-driven neural activation, i.e., central command. The contribution of brain mechanisms to these adjustments has been suggested for more than a century, yet the functional brain architecture remains incompletely understood. This article discusses recent findings primarily obtained from rodent studies utilizing advanced experimental tools, particularly those enabled by genetic engineering, such as optogenetics and viral neural tracing, to elucidate the diencephalic and brainstem circuits responsible for autonomic cardiovascular adjustments during voluntary exercise. Particular attention is paid to the central neural pathways and specific neuronal populations involved in transmitting central command signals, that drive not only somatic muscular activity but also autonomic cardiovascular responses. The uncovered diencephalic and brainstem circuits are relevant to understanding the brain substrate of central command, which is essential for maintaining cellular homeostasis and enhancing physical performance. Future studies and potential subjects for further investigation to deepen our understanding of the brain mechanisms underlying autonomic cardiovascular regulation are also discussed.

Medial prefrontal cortex-periaqueductal gray circuit overcomes anxiety-like behavior in male mice following adversity

BACKGROUND

Inescapable stress leads to various long-lasting physical and mental dysfunctions. Acute stress exposure is linked to a high risk of psychological disorders, such as anxiety disorders. The medial prefrontal cortex (mPFC) and periaqueductal gray (PAG) are anatomical regions associated with social information processing and emotional valence. However, it is unclear whether mPFC projections to the PAG are involved in anxiety behavior.

METHODS

In this study, an anxiety model by an inescapable foot shock was established. And used immunofluorescence, FosTRAP strategy, specific chemogenetics, optogenetics and behavior test to reveal that the stressful event increased the anxiety behavior of mice after exposure to foot shock and activation of mPFC-PAG circuitry can improve anxiety-like behavior and the locomotor behavior of mice.

RESULTS

Notably, FosTRAP results indicated that c-Fos expression in the PAG and mPFC is increased during foot shock, but inhibiting these brain regions did not significantly alleviate anxiety behavior. Additionally, chemogenetic activation of mPFC projections to the PAG improved anxiety-like behavior and locomotor activity in mice only during stress. Optogenetic activation of the mPFC-PAG circuitry increased the total distance traveled in the open field test and slightly increased the number of entries into the center area, while optogenetic inhibition slightly increased anxiety-like behavior in control mice.

LIMITATION

The limitation of this study is that only the changes and regulations of mPFC-PAG of anxiety male animals were studied.

CONCLUSIONS

Overall, our findings suggest that the valence-encoding mPFC-PAG circuit modulates anxiety, and that these projections may be potential targets for treatment of anxiety disorders.

Orexinergic neurons contribute to autonomic cardiovascular regulation for locomotor exercise

While the hypothalamic orexinergic nervous system is established as having a pivotal role in the long-term regulation of various organismic functions, including wakefulness, metabolism and hypertensive states, whether this system contributes to the rapid autonomic cardiovascular regulation during physical activity remains elusive. This study aimed to elucidate the role of the orexinergic nervous system in transmitting volitional motor signals, i.e. central command, to drive somatomotor and sympathetic cardiovascular responses. We first found that this system is activated by voluntary locomotor exercise as evidenced by an increased expression of Fos, a marker of neural activation, in the orexinergic neurons of Sprague-Dawley rats engaged in spontaneous wheel running. Next, using transgenic Orexin-Cre rats for optogenetic manipulation of orexinergic neurons, we found that optogenetic excitation of orexinergic neurons caused sympathoexcitation on a subsecond timescale under anaesthesia. In freely moving conscious rats, this excitatory stimulation rapidly elicited exploration-like behaviours, predominantly locomotor activity, along with pressor and tachycardiac responses. Meanwhile, optogenetic inhibition of orexinergic neurons during spontaneous wheel running immediately suppressed locomotor activities and blood pressure elevation without affecting basal cardiovascular homeostasis. Taken together, these findings demonstrate the essential role of the orexinergic nervous system in the central circuitry that transmits central command signals for locomotor exercise. This study not only offers insights into the brain circuit mechanisms precisely regulating autonomic cardiovascular systems during voluntary exercise but also likely contributes to our understanding of brain mechanisms underlying abnormal cardiovascular adjustments to exercise in pathological conditions, such as hypertension. KEY POINTS: The hypothalamic orexinergic nervous system plays various roles in the long-term regulation of autonomic and endocrine functions, as well as motivated behaviours. We present a novel, rapid role of the orexinergic nervous system, revealing its significance as a crucial substrate in the brain circuit mechanisms that coordinate somatomotor and autonomic cardiovascular controls for locomotor exercise. Our data demonstrate that orexinergic neurons relay volitional motor signals, playing a necessary and sufficient role in the autonomic cardiovascular regulation required for locomotor exercise in rats. The findings contribute to our understanding of how the brain precisely regulates autonomic cardiovascular systems during voluntary exercise, providing insights into the central neural mechanisms that enhance physical performance moment-by-moment during exercise.

Regional difference in prefrontal oxygenation before and during overground walking in humans: a wearable multichannel NIRS study

Using wireless multichannel near-infrared spectroscopy, regional difference in cortical activity over the prefrontal cortex (PFC) was examined before and during overground walking and in response to changes in speed and cognitive demand. Oxygenated-hemoglobin concentration (Oxy-Hb) as index of cortical activity in ventrolateral PFC (VLPFC), dorsolateral PFC (DLPFC), and frontopolar cortex (FPC) was measured in 14 subjects, whereas heart rate was measured as estimation of exercise intensity in six subjects. The impact of mental imagery on prefrontal Oxy-Hb was also explored. On both sides, Oxy-Hb in VLPFC, DLPFC, and lateral FPC was increased before the onset of normal-speed walking, whereas Oxy-Hb in medial FPC did not respond before walking onset. During the walking, Oxy-Hb further increased in bilateral VLPFC, whereas Oxy-Hb was decreased in DLPFC and lateral and medial FPC. Increasing walking speed did not alter the increase in Oxy-Hb in VLPFC but counteracted the decrease in Oxy-Hb in DLPFC (but not in lateral and medial FPC). Treadmill running evoked a greater Oxy-Hb increase in DLPFC (n = 5 subjects). Furthermore, increasing cognitive demand during walking, by deprivation of visual feedback, counteracted the decrease in Oxy-Hb in DLPFC and lateral and medial FPC, but it did not affect the increase in Oxy-Hb in VLPFC. Taken together, the profound and localized Oxy-Hb increase is a unique response for the VLPFC. The regional heterogeneity of the prefrontal Oxy-Hb responses to natural overground walking was accentuated by increasing walking speed or cognitive demand, suggesting functional distinction within the PFC.

Investigating Cortical Buffering Effects of Acute Moderate Intensity Exercise: A cTBS Study Targeting the Left Dorsolateral Prefrontal Cortex

Background: The beneficial effects of both single-session bouts of aerobic exercise and therapeutic exercise interventions on the cortical regions associated with top-down attentional control [i.e., prefrontal cortex (PFC)] have been well documented. However, it remains unclear whether aerobic exercise can be used to buffer against suppressive influences on the dorsolateral PFC (dlPFC). Objective: The current study sought to determine whether a single session of moderate intensity aerobic exercise can offset the expected suppressive effects of continuous theta burst stimulation (cTBS) targeting the dorsolateral prefrontal cortex (dlPFC). Methods: Twenty-two right-handed participants (aged 19-30) completed a 20-minute movement-only control session [10% heart rate reserve (HRR)] and moderate intensity (50% HRR) exercise in a counterbalanced order. Following each exercise session, participants received active cTBS to the left dlPFC. Changes in executive functions were quantified using a Flanker paradigm employed at baseline, post-exercise and post-cTBS time points. Additionally, EEG was used to measure changes in event-related potential components related to inhibitory control (i.e., N2) and attentional control (i.e., P3) during the flanker task. Results: Behavioral results from the flanker task revealed a significant improvement in task performance following an acute bout of moderate intensity exercise. Furthermore, the effect of cTBS in both the movement-only control and moderate intensity conditions were non-significant. Similarly, EEG data from P3b and N2 ERP components revealed no changes to amplitude across time and condition. P3b latency data revealed a significant effect of time in both the moderate intensity and movement-only conditions, such that P3b latencies were significantly shorter across time points. Latency data within the N2 ERP component revealed no significant interactions or main effects. Conclusion: The findings of the current study provide tentative support for the hypothesis that both moderate and light intensity exercise promote cortical buffering against the suppressive effects of cTBS targeting the dlPFC. However, in the absence of a no-movement control, a lack of expected suppressive effects of cTBS cannot be ruled out.

Central command-related increases in blood velocity of anterior cerebral artery and prefrontal oxygenation at the onset of voluntary tapping

The anterior cerebral artery (ACA) supplies blood predominantly to the frontal lobe including the prefrontal cortex. Our laboratory reported that prefrontal oxygenated-hemoglobin concentration (Oxy-Hb) increased before and at exercise onset, as long as exercise is arbitrarily started. Moreover, the increased prefrontal oxygenation seems independent of both exercise intensity and muscle mass. If so, mean blood velocity of the ACA (ACA_BV) should increase with "very light motor effort," concomitantly with the preexercise and initial increase in prefrontal Oxy-Hb. This study aimed to examine the responses in ACA_BV and vascular conductance index (ACA_VCI) of the ACA as well as prefrontal Oxy-Hb during arbitrary or cued finger tapping in 12 subjects, an activity with a Borg scale perceived exertion rating of 7 (median). With arbitrary start, ACA_BV increased at tapping onset (14 ± 9%) via an elevation in ACA_VCI. Likewise, prefrontal Oxy-Hb increased at the onset of tapping with a time course resembling that of ACA_BV. A positive cross correlation between the initial changes in ACA_BV and prefrontal Oxy-Hb was found significant in 67% of subjects, having a time lag of 2 s, whereas a positive linear regression between them was significant in 75% of subjects. When tapping was forced to start by cue, the initial increases in ACA_BV, ACA_VCI, and prefrontal Oxy-Hb were delayed and blunted as compared with an arbitrary start. Thus, active vasodilatation of the ACA vascular bed occurs at tapping onset, as long as tapping is arbitrarily started, and contributes to immediate increases in blood flow and prefrontal oxygenation.NEW & NOTEWORTHY Anterior cerebral artery blood velocity and vascular conductance index along with prefrontal oxygenated-hemoglobin concentration all increased at the onset of finger tapping, peaking immediately after tapping onset, as long as tapping was arbitrarily started. Positive cross correlation and linear regression between the increases in ACA_BV and prefrontal Oxy-Hb were significant in 67%-75% of subjects. Active vasodilatation of the ACA vascular bed occurs with arbitrary tapping onset and contributes to increased ACA_BV and prefrontal oxygenation.