Fig. 9
Inhibition of P2X7R prevented IS-induced nociceptive behavior and cognitive deficits. a-c Nociceptive behaviors were assessed using periorbital withdrawal threshold and the number of head-scratching within 1 h. (a) Baseline periorbital withdrawal thresholds measured before the first drug administration were not significantly different among the four groups. (b-c) The sham-VEH, sham-BBG and IS-BBG mice had higher post-treatment periorbital withdrawal thresholds measured 1-h after the last drug administration (b) and less head-scratching within 1-h measured immediately after the last drug administration (c) than IS-VEH mice, indicating the IS-induced nociceptive behaviors were partially prevented by pretreatment with BBG. d-f Non-spatial recognition memory was assessed using novel object recognition test. (d) Schematic illustration of the novel object recognition test. (e) All mice showed similar explorations of two identical objects at day 2 (training stage). (f) The sham-VEH, sham-BBG and IS-BBG mice showed a higher discrimination ratio than IS-VEH mice, indicating the IS-induced impairment of non-spatial recognition memory was improved by pretreatment with BBG. (Discrimination Ratio = Tnovel – Told / Tnovel + Told). g-i Spatial learning and memory was assessed using Morris water maze test. Average latency to find visible platform on day 1 and hidden platform in target quadrant on day 2–5. All mice exhibited similar average latency to find a visible platform on day 1 (g), suggesting the similar vision and motor ability of all mice. From day 2 to day 5 (learning period), the escape latency gradually decreased in all mice and the slope of the decrease was not significantly different among the four groups (g), suggesting the similar spatial learning ability of all mice. On day 6 (probe trial), IS-VEH mice displayed a shorter time spent in target quadrant (h) and less platform crossings (i) than sham-VEH mice, suggesting the impaired spatial memory retention in IS-VEH mice. Although IS-BBG mice displayed a trend with a longer time spent in target quadrant (h) and more platform crossings (i) than IS-VEH mice, the difference did not reach statistical levels. n = 10 mice per group. *p < 0.05, **p < 0.01 and ***p < 0.001 as compared to sham-VEH mice; +p < 0.05, ++p < 0.01 and +++p < 0.001 as compared to IS-VEH mice. Repeated-measures ANOVA with Tukey’s multiple comparisons was performed for datasets in (g); the other datasets were analyzed using one-way ANOVA with Tukey’s multiple comparisons or Kruskal–Wallis with Dunn’s multiple comparisons test. Data are represented as mean ± SEM. Abbreviations: IS, inflammatory soup; BBG, brilliant blue G; VEH, vehicle; Tnovel, time spent in exploring the novel object; Told, time spent in exploring the old object