Journal: Journal of Cerebral Blood Flow & Metabolism
Article Title: Stroke-prone salt-sensitive spontaneously hypertensive rats show higher susceptibility to spreading depolarization (SD) and altered hemodynamic responses to SD
doi: 10.1177/0271678X221135085
Figure Lengend Snippet: Body weight (BW), body temperature and mean arterial pressure (MAP) in stroke-prone spontaneously hypertensive rats (SHRsp) and Wistar-Kyoto rats (WKY) on either regular or Japanese diet. (a) Evolution of BW in SHRsp and WKY on regular or Japanese diet at weeks 9, 10, 11, and 12 before experiments conducted at weeks 12-14. For the statistical analysis, we used a two-way repeated-measures analysis of variance (ANOVA) on ranks with post-hoc Bonferroni t-tests [SHRsp on Japanese diet ( n = 19) versus SHRsp on regular diet ( n = 16) versus WKY on Japanse diet ( n = 11) versus WKY on regular diet ( n = 28) as factor A and age in weeks as factor B]. As early as week 9 before starting the Japanese diet in two groups, BW was significantly higher in WKY than SHRsp ( p ≤ 0.05). At week 12, all 4 groups were significantly different from each other ( p ≤ 0.05). Within all 4 groups, there was a significant difference between BW at week 9 and week 12 ( p ≤ 0.05). That is, there was significant weight loss in both strains under Japanese diet and significant weight gain under regular diet, which suggests some degree of malnutrition under Japanese diet. (b) When experiments were pooled linear regression found that BW immediately before the experiments and body temperature after surgery significantly correlated both in SHRsp and WKY. The relationship between body weight and body temperature observed here is related to the so-called Bergmann's rule. Thus, as the volume of an object decreases, the ratio of its surface area to its volume increases. In other words, the smaller an animal is, the higher the surface area-to-volume ratio. These animals lose heat relatively quickly and cool down faster. (c) Immediately before the experiments at the age of 12–14 weeks, WKY rats on regular diet had a significantly higher median BW than WKY on Japanese diet, SHRsp on regular diet, or SHRsp on Japanese diet [Kruskal-Wallis One Way Analysis of Variance on Ranks (KW-ANOVA) and post-hoc Dunn’s tests (phD)]. In addition, SHRsp on regular diet had a significantly higher median BW than SHRsp on Japanese diet. (d) Body temperature before the start of the experiments was significantly higher in WKY on regular diet than in either WKY on Japanese diet or SHRsp on Japanese diet (KW-ANOVA and phD). In addition, body temperature was significantly higher in SHRsp on regular diet than in either WKY or SHRsp on Japanese diet. SD susceptibility is known to correlate positively with body temperature. Because the body temperature of SHRsp tended to be lower than that of WKY, it can be excluded that changes in body temperature were responsible for the higher SD susceptibility of SHRsp and (e) MAP before the start of experiments was significantly higher in SHRsp on regular diet than in WKY on either regular diet or Japanese diet (KW-ANOVA and phD). In addition, MAP was significantly higher in SHRsp on Japanese diet than WKY on Japanese diet. The whiskers (error bars) above and below the boxes indicate the 90th and 10th percentiles.
Article Snippet: Systemic mean arterial pressure (MAP, Pressure Monitor BP-1, World Precision Instruments, Berlin, Germany) and expiratory pCO 2 (Heyer CO 2 Monitor EGM I, Bad Ems, Germany) were continuously monitored.
Techniques:
![Body weight (BW), body temperature and <t>mean</t> <t>arterial</t> <t>pressure</t> (MAP) in stroke-prone spontaneously hypertensive rats (SHRsp) and Wistar-Kyoto rats (WKY) on either regular or Japanese diet. (a) Evolution of BW in SHRsp and WKY on regular or Japanese diet at weeks 9, 10, 11, and 12 before experiments conducted at weeks 12-14. For the statistical analysis, we used a two-way repeated-measures analysis of variance (ANOVA) on ranks with post-hoc Bonferroni t-tests [SHRsp on Japanese diet ( n = 19) versus SHRsp on regular diet ( n = 16) versus WKY on Japanse diet ( n = 11) versus WKY on regular diet ( n = 28) as factor A and age in weeks as factor B]. As early as week 9 before starting the Japanese diet in two groups, BW was significantly higher in WKY than SHRsp ( p ≤ 0.05). At week 12, all 4 groups were significantly different from each other ( p ≤ 0.05). Within all 4 groups, there was a significant difference between BW at week 9 and week 12 ( p ≤ 0.05). That is, there was significant weight loss in both strains under Japanese diet and significant weight gain under regular diet, which suggests some degree of malnutrition under Japanese diet. (b) When experiments were pooled linear regression found that BW immediately before the experiments and body temperature after surgery significantly correlated both in SHRsp and WKY. The relationship between body weight and body temperature observed here is related to the so-called Bergmann's rule. Thus, as the volume of an object decreases, the ratio of its surface area to its volume increases. In other words, the smaller an animal is, the higher the surface area-to-volume ratio. These animals lose heat relatively quickly and cool down faster. (c) Immediately before the experiments at the age of 12–14 weeks, WKY rats on regular diet had a significantly higher median BW than WKY on Japanese diet, SHRsp on regular diet, or SHRsp on Japanese diet [Kruskal-Wallis One Way Analysis of Variance on Ranks (KW-ANOVA) and post-hoc Dunn’s tests (phD)]. In addition, SHRsp on regular diet had a significantly higher median BW than SHRsp on Japanese diet. (d) Body temperature before the start of the experiments was significantly higher in WKY on regular diet than in either WKY on Japanese diet or SHRsp on Japanese diet (KW-ANOVA and phD). In addition, body temperature was significantly higher in SHRsp on regular diet than in either WKY or SHRsp on Japanese diet. SD susceptibility is known to correlate positively with body temperature. Because the body temperature of SHRsp tended to be lower than that of WKY, it can be excluded that changes in body temperature were responsible for the higher SD susceptibility of SHRsp and (e) MAP before the start of experiments was significantly higher in SHRsp on regular diet than in WKY on either regular diet or Japanese diet (KW-ANOVA and phD). In addition, MAP was significantly higher in SHRsp on Japanese diet than WKY on Japanese diet. The whiskers (error bars) above and below the boxes indicate the 90th and 10th percentiles.](https://pub-med-central-images-cdn.bioz.com/pub_med_central_ids_ending_with_3222/pmc09903222/pmc09903222__10.1177_0271678X221135085-fig3.jpg)
![Differences in spreading depolarization (SD) threshold and propagation speed between stroke-prone spontaneously hypertensive rats (SHRsp) and Wistar-Kyoto rats (WKY) on regular diet. (a) We found that the median electrical threshold of SD was significantly lower in SHRsp than WKY [Mann-Whitney U test (MWU)]. (b) The median propagation speed of SD was significantly faster in SHRsp than WKY (MWU). (c) In series 1A, the amplitude of the epidural negative DC shift was not different between SHRsp and WKY (MWU). (d) In series 1B, the amplitude of the subdural negative DC shift in the window area was not different between SHRsp and WKY (MWU). (e) In series 1A, the peak of the laser-Doppler flowmetry (LDF)-determined hyperemia was not significantly different between SHRsp and WKY (MWU). (f) In series 1B, we determined the median of 5 regions of interest (ROI) in the window area for each animal. We found that the laser speckle contrast analysis (LASCA) imaging-determined hyperemia was significantly higher in SHRsp than WKY (MWU). (g) Scatterplot SD propagation speed versus mean arterial pressure (MAP). SHRsp and WKY are marked in different colors. SHRsp and WKY appear as two distinct clusters. (h) Scatterplot SD threshold versus MAP. No statistically significant correlation was found. (i) Scatterplot SD propagation speed versus body weight (BW). SHRsp and WKY appear as two distinct clusters. The higher speeds in the lower body weight animals fit well with previous findings in malnourished rodents. Guedes discussed three main factors as possibly causative: (i) reduction in brain myelin content, (ii) impairment of glial function, and (iii) increase in the cell packing density with reduction of the extracellular space. and (j) Scatterplot SD threshold versus BW. The statistical relationship in the pooled data is based on the influence of the SHRsp. For the 23 SHRsp alone, the Spearman coefficient was 0.69 ( p ≤ 0.001), while no significant relationship between SD threshold and BW was found for the 22 WKY [Spearman coefficient: −0.12 ( p = 0.589)]. The whiskers (error bars) above and below the boxes indicate the 90th and 10th percentiles.](https://pub-med-central-images-cdn.bioz.com/pub_med_central_ids_ending_with_3222/pmc09903222/pmc09903222__10.1177_0271678X221135085-fig4.jpg)
![In series 2, brain topical application of artificial cerebrospinal fluid (aCSF) containing the nitric oxide synthase (NOS) inhibitor N G -nitro-L-arginine (L-NNA) and increased K + concentration ([K + ] aCSF ) induced spreading ischemia. (a) Original recording of an experiment in a stroke-prone spontaneously hypertensive rat (SHRsp) on Japanese diet of series 2. Trace 1 from top to bottom shows the mean arterial pressure (MAP). Traces 2 and 3 demonstrate the depressive effect of the spreading depolarizations (SD) on the spontaneous brain activity as assessed in the higher frequency band [alternating current (AC)-electrocorticography (ECoG), bandpass: 0.5–45 Hz] of the subdural (Sub) recordings. Trace 4 gives the direct current (DC)/AC-ECoG recordings (bandpass: 0–45 Hz) at the subdural electrode within the cranial window. The SDs are observed as negative DC shifts. Traces 5 and 6 demonstrate the depressive effect of the SDs on the spontaneous brain activity as assessed with the recordings of the epidural (Epi) electrode outside the window area. Trace 7 gives the DC/AC-ECoG at the epidural electrode. In traces 4 and 7, the time period is outlined in yellow for which laser speckle contrast analysis (LASCA) imaging-recorded regional cerebral blood flow (rCBF) in two regions of interest (ROI) in the window area is shown in (b). (b) shows rCBF traces typical for SD-induced spreading ischemias with a prolonged initial hypoperfusion followed by hyperperfusion. In principle, the two events each consist of two SDs, each leading to an initial hypoperfusion due to a vasocontrictive response. , Time points a-h in (b) correspond to LASCA perfusion maps a-h in (c). The two circles in (c) show the two ROIs for which rCBF is shown in (b). (d) The left panel shows the linear relationship between duration of initial hypoperfusion and duration of negative DC shift during SD-induced spreading ischemia for the pooled experiments from series 2. The right panel shows that higher blood pressure correlated with prolonged SD-induced spreading ischemia when the experiments from series 2 were pooled. (e) The negative DC shift of SD was always significantly longer when SD in series 2 induced spreading ischemia than when SD in series 1B or 3 induced normal spreading hyperemia (Mann-Whitney Rank Sum Tests).](https://pub-med-central-images-cdn.bioz.com/pub_med_central_ids_ending_with_3222/pmc09903222/pmc09903222__10.1177_0271678X221135085-fig6.jpg)