Blockade of insulin receptor signaling in the medullary cardiovascular centers impairs open‐loop arterial baroreflex function via attenuated neural arc in healthy male rats

Figures

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  FIGURE 1. The area of insulin receptor (IR), c‐Fos, and 4′,6‐diamidino‐2‐phenylindole (DAPI) expression, and the overlap area between IR, c‐Fos, and DAPI expression in the nucleus tractus solitarius (NTS), caudal ventrolateral medulla (CVLM), rostral ventrolateral medulla (RVLM), and spinal trigeminal nucleus (Vsp) in control and baroreflex stimulation (BARO) treated rats. Representative image of the expression of IR, c‐Fos, and DAPI and co‐localization with IR, c‐Fos, and DAPI in the NTS, CVLM, RVLM, and Vsp (A). The sections of the NTS (10 sections each rat), CVLM (3 sections each rat), RVLM (3 sections each rat), and Vsp (5 sections each rat) were collected from three control and three BARO‐treated rats. In the BARO‐treated group, carotid sinus pressure (CSP) was changed stepwise under open‐loop conditions, while control rats were rested under closed‐loop conditions (CSP was matched to arterial pressure by using a servo‐pump system). The magnification is ×10. The white scale bar is 100 μm. The data were analyzed by an unpaired t‐test or the Mann–Whitney U‐test (B). Data are shown as mean ± SD.

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  FIGURE 2. Distribution of insulin receptor (IR), c‐Fos, and 4′,6‐diamidino‐2‐phenylindole (DAPI) expression, and the overlap area between IR, c‐Fos, and DAPI expression at each bregma level of the nucleus tractus solitarius (NTS) in control and baroreflex stimulation (BARO) treated rats. In the BARO treated group, carotid sinus pressure (CSP) was changed stepwise under open‐loop conditions while control rats were rested under closed‐loop conditions (CSP was matched to arterial pressure by using a servo‐pump system). Sections of the NTS (10 sections each rat) were serially collected from three control and three BARO treated rats. The data were analyzed by a two‐way repeated measures ANOVA (group‐by‐coordinate) followed by Bonferroni's multiple comparison test. *p < .05 vs. control group. † p < .05 vs. −13.6 mm to the bregma. The gray dashed and solid lines show individual data from the control and the BARO treated groups, respectively. Data are shown as the mean ± SD.

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  FIGURE 3. Representative recordings of arterial pressure (AP), renal sympathetic nerve activity (RSNA), and heart rate (HR) responses to stepwise carotid sinus pressure (CSP) input before and 30, 60, 90, and 120 min after intracerebroventricular injection of artificial cerebrospinal fluid (control) and insulin receptor antagonist (GSK1838705). Gray and black lines in the RSNA show rectified raw data and normalized data, respectively.

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  FIGURE 4. Open‐loop static characteristics of the neural arc, peripheral arc, total reflex arc, and heart rate (HR) control before and 30, 60, 90, and 120 min after intracerebroventricular injection of artificial cerebrospinal fluid (control) and insulin receptor antagonist (GSK1838705). CSP, carotid sinus pressure; RSNA, renal sympathetic nerve activity; AP, arterial pressure. The data were analyzed by a two‐way repeated measures ANOVA (time‐by‐CSP) followed by Bonferroni's multiple comparison test. a, b, c, and d show significant differences between before and 30, 60, 90, or 120 min, respectively (p < .05). Since the x‐axis in the peripheral arc was RSNA, which varied between animals, a two‐way repeated measures ANOVA was not performed for the peripheral arc. Data are shown as the mean ± SD.

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  FIGURE 5. The baroreflex equilibrium diagram (A) and operating‐point arterial pressure (AP) and renal sympathetic nerve activity (RSNA) (B) before and 120 min after intracerebroventricular (ICV) injection of artificial cerebrospinal fluid (control) and insulin receptor antagonist (GSK1838705). The baroreflex equilibrium diagram was constructed from the fitted neural (sigmoid curve) and peripheral (linear regression line) arcs (A). In this diagram, the open and filled circles indicate operating‐point AP and RSNA before and 120 min after ICV injection of control and insulin receptor antagonist, respectively. The open (Before) and filled (120 min) circles represent individual data (B). The data were analyzed by a two‐way repeated measures ANOVA (solution‐by‐time) followed by Bonferroni's multiple comparison test. Data are shown as the mean ± SD.

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  FIGURE 6. Open‐loop static characteristics of the neural arc, peripheral arc, total reflex arc, and heart rate (HR) control before and 30, 60, 90, and 120 min after intracerebroventricular injection of a 50% dimethyl sulfoxide solution. CSP, carotid sinus pressure; RSNA, renal sympathetic nerve activity; AP, arterial pressure. The open (Before) and filled (120 min) circles represent individual data. The data were analyzed by a two‐way repeated measures ANOVA (time‐by‐CSP). Since the x‐axis in the peripheral arc was RSNA, which varied between animals, a two‐way repeated measures ANOVA was not performed for the peripheral arc. Data are shown as the mean ± SD.

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  FIGURE 7. Baroreflex equilibrium diagram simulation under hypertensive (A) and hypotensive (B) stresses before and 120 min after intracerebroventricular injection of artificial cerebrospinal fluid (control) and insulin receptor antagonist (GSK1838705). The operating‐point arterial pressure (AP) under hypertensive/hypotensive stress was simulated by the intersection of the neural and peripheral arcs, whose intercept was shifted upward (+5, +10, +15, and +20 mmHg [hypertensive stress]) and downward (−5, −10, −15, and −20 mmHg [hypotensive stress]) in the baroreflex equilibrium diagram. Δoperating‐point AP; the difference in operating‐point AP from before to after hypertensive and hypotensive stresses. The data were analyzed by a two‐way repeated measures ANOVA (time‐by‐pressure or solution‐by‐pressure) followed by Bonferroni's multiple comparison test. Data are shown as the mean ± SD.