Simultaneous measurement of central amygdala neuronal activity and sympathetic nerve activity during daily activities in rats.

NEW FINDINGS: What is the central question of this study? The functional relationships between central amygdala neuronal activity (CeANA) and sympathetic nerve activity in daily activities remain unclear. We aimed to measure CeANA, renal and lumbar sympathetic nerve activity (RSNA and LSNA, respectively), heart rate (HR) and arterial pressure simultaneously in freely moving rats. What is the main finding and its importance? The CeANA was significantly related to RSNA and LSNA and HR in a behavioural state-dependent and regionally different manner; meanwhile, CeANA was tightly associated with RSNA and HR across all behavioural states. Thus, it is likely that the amygdala is a component of neural networks generating regional differences in RSNA and LSNA. ABSTRACT: The central amygdala (CeA) is involved in generating diverse changes in sympathetic nerve activity (SNA) in response to changes in daily behavioural states. However, the functional relationships between CeA neuronal activity (CeANA) and SNA in daily activities are still unclear. In the present study, we developed a method for simultaneous and continuous measurement of CeANA and SNA in freely moving rats. Wistar rats were chronically instrumented with multiple electrodes (100-µm-thick stainless-steel wire) for the measurement of CeANA, renal SNA (RSNA) and lumbar SNA (LSNA), and electroencephalogram, EMG and ECG electrodes, in addition to catheters for measurement of arterial pressure (AP). During the transition from non-rapid eye movement sleep to quiet wakefulness, moving and grooming states, a significant linear relationship was observed between CeANA and RSNA (P < 0.0001), between CeANA and LSNA (P = 0.0309), between CeANA and heart rate (HR) (P = 0.0123) and between CeANA and EMG (P = 0.0089), but no significant correlation was observed between CeANA and AP (P = 0.5139). During rapid eye movement sleep, the relationships between CeANA and RSNA, LSNA, HR, AP and EMG deviated from the previously observed linear relationships, but the time course of RSNA and HR changes was the mirror image of that of CeANA, whereas the time course of changes in LSNA and AP was not related to that of CeANA. In conclusion, CeANA was related to RSNA, LSNA and HR in a behavioural state-dependent and regionally different manner, and CeANA was tightly associated with RSNA and HR across all behavioural states.

Regional Differences in Sympathetic Nerve Activity Are Generated by Multiple Arterial Baroreflex Loops Arranged in Parallel.

In this review, by evaluating the responses during freezing, rapid eye movement (REM) sleep, and treadmill exercise, we discuss how multiple baroreflex loops arranged in parallel act on different organs to modulate sympathetic nerve activity (SNA) in a region-specific and coordinated manner throughout the body. During freezing behaviors, arterial pressure (AP) remains unchanged, heart rate (HR) persistently decreases, renal SNA (RSNA) increases, and lumbar SNA (LSNA) remains unchanged. The baroreflex curve for RSNA shifts upward; that for LSNA remains unchanged; and that for HR shifts to the left. These region-specific changes in baroreflex curves are responsible for the region-specific changes in RSNA, LSNA, and HR during freezing. The decreased HR could allow the heart to conserve energy, which is offset by the increased RSNA caused by decreased vascular conductance, resulting in an unchanged AP. In contrast, the unchanged LSNA leaves the muscles in readiness for fight or flight. During REM sleep, AP increases, RSNA and HR decrease, while LSNA is elevated. The baroreflex curve for RSNA during REM sleep is vertically compressed in comparison with that during non-REM sleep. Cerebral blood flow is elevated while cardiac output is decreased during REM sleep. To address this situation, the brain activates the LSNA selectively, causing muscle vasoconstriction, which overcomes vasodilation of the kidneys as a result of the decreased RSNA and cardiac output. Accordingly, AP can be maintained during REM sleep. During treadmill exercise, AP, HR, and RSNA increase simultaneously. The baroreflex curve for RSNA shifts right-upward with the increased feedback gain, allowing maintenance of a stable AP with significant fluctuations in the vascular conductance of working muscles. Thus, the central nervous system may employ behavior-specific scenarios for modulating baroreflex loops for differential control of SNA, changing the SNA in a region-specific and coordinated manner, and then optimizing circulatory regulation corresponding to different behaviors.

Differential shifts in baroreflex control of renal and lumbar sympathetic nerve activity induced by freezing behaviour in rats.

NEW FINDINGS: What is the central question of this study? Is the arterial baroreflex involved in causing patterned, region-specific changes in sympathetic nerve activity during freezing behaviour in conscious rats? What is the main finding and its importance? Freezing behaviour is accompanied by differential shifts in the baroreflex control of renal and lumbar sympathetic nerve activity and heart rate. It is noteworthy that baroreflex pathways may be discretely separated, allowing differential modification of baroreflex curves that may generate differential changes in sympathetic nerve activity during freezing behaviour. ABSTRACT: The present study was designed to test whether the baroreflex stimulus-response curves for renal sympathetic nerve activity (RSNA), lumbar sympathetic nerve activity (LSNA) and heart rate (HR) were shifted in a regionally specific manner during freezing behaviour in conscious rats. Male Wistar rats were chronically instrumented with electrodes and arterial and venous catheters for measurement of RSNA, LSNA and electrocardiogram. After a 60-min control period, freezing behaviour in conscious rats was induced by exposure to loud white noise (90 dB) for 10 min. The baroreflex curves for RSNA, LSNA and HR were generated by changing systemic arterial pressure using rapid intravenous infusions of vasoactive drugs and then fitted to an inverse sigmoid function curve. During the freezing behaviour, the baroreflex curve for RSNA was expanded upward with a significant (P < 0.001) increase (by 153% compared with the control level) in the upper plateau (maximum capacity of RSNA drive), whereas the baroreflex curve for LSNA remained unchanged. Conversely, the baroreflex curve for HR was shifted leftward with a significant (P = 0.004) decrease (by 11 mmHg relative to the control level) in the midpoint pressure. Our results indicate that baroreflex curve shifts for RSNA, LSNA and HR occur in a regionally specific manner during freezing behaviour. This indicates that baroreflex pathways may be discretely separated, allowing differential modification of baroreflex curves that may generate differential changes in sympathetic nerve activity during freezing behaviour.

Renal and Lumbar Sympathetic Nerve Activity During Development of Hypertension in Dahl Salt-Sensitive Rats.

To study the contribution of sympathetic nerve activity (SNA) to the development of hypertension, experiments were designed to continuously and simultaneously measure renal (RSNA) and lumbar SNA (LSNA) during the development of hypertension induced by 8% salt loading in Dahl salt-sensitive (DS) rats. Male DS and salt-resistant rats were instrumented with bipolar electrodes to record RSNA and LSNA and a telemeter to record arterial pressure (AP). AP increased during the first 3 days after the onset of salt loading by ≈10 mm Hg in both DS and Dahl salt-resistant rats. AP continued to increase progressively from day 4 to day 14 of salt loading by 33±1 mm Hg in DS rats, while it remained the same in Dahl salt-resistant rats. RSNA and LSNA increased in the initial few days by 6% to 8%, and decreased gradually thereafter, suggesting that increases in neither RSNA nor LSNA are directly linked with the progressive increase in AP induced by salt loading in DS rats. After the cessation of salt loading, AP pressure returned to the presalt loading level in both DS and Dahl salt-resistant rats. RSNA increased significantly by 32±3% after the cessation of salt loading, while LSNA remained the same in DS rats, suggesting that salt-sensitive mechanisms respond to a loss of sodium, not a gain, and selectively activate RSNA in DS rats. In summary, RSNA and LSNA are not likely to be a primary trigger to initiate the progressive increase in AP induced by 8% salt loading in DS rats.