The arterial blood gas analyses
In the experiment, all rats in each group survived until the end of the experiment. We observed that the animals’ skin was ruddy and that the respiration was smooth. There were no significant changes in the pH, pCO2 and pO2 in any groups (Table 3).
Table 3
The arterial blood gases analyse (6 animals per group)
Parameter | group Ⅰ | group Ⅱ | group Ⅲ | group Ⅳ | group Ⅳ |
pH | 7.39 ± 0.02 | 7.41 ± 0.03 | 7.41 ± 0.03 | 7.42 ± 0.04 | 7.42 ± 0.04 |
PCO2a (mmHg) | 39.3 ± 1.4 | 39.1 ± 1.7 | 38.0 ± 2.1 | 40.0 ± 2.3 | 39.8 ± 2.6 |
PO2b (mmHg) | 168.0 ± 3.1 | 166.0 ± 4.4 | 163.3 ± 4.5 | 164.8 ± 5.1 | 162.2 ± 4.0 |
a Pco2 pressure carbon dioxide. |
b Po2 pressure oxygen. |
The effects of ketamine on the proliferation and differentiation of NSCs in the SVZ
According to our previous studies, BrdU immunofluorescence was used to evaluate the proliferation capacity of NSCs in the SVZ. When 100 mg/kg BrdU was injected immediately after anesthesia in PND-7 rats, we observed a drastic reduction in the number of BrdU+ cells per SVZ in the ketamine group (median [IQR]: 28900 [26500–30750]) compared to that in the control group (median [IQR]: 44435 [42450–47408], shown in Fig. 1A and 1B, n = 8, p < 0.01). It was suggested that neonatal ketamine exposure inhibited NSC proliferation in the SVZ.
NSCs have the ability to differentiate into neurons, and the early neuronal marker associated with differentiation is β-tubulin III. BrdU+ cells coexpressing the neuronal marker β-tubulin III were used to present the neuronal differentiation of NSCs. In this study, we found that the proportion of β-tubulin III+/BrdU+ cells to BrdU+ cells in the ketamine group (median [IQR]: 19.05% [18%-19.725%]) was increased compared to that in control animals (median [IQR]: 13.15% [12.475%-13.7%]) at 24 h after BrdU injection (Fig. 2A and 2B, n = 8, p < 0.01).
The proportion of BrdU+ cells coexpressing GFAP was introduced to show astrocytic differentiation of NSCs. The proportion of GFAP+/BrdU+ cells to BrdU+ cells at 24 h after BrdU injection was significantly greater in control rats (median [IQR]: 16.3% [15.925%-16.925%]) than in ketamine-anesthetized rats (median [IQR]: 11.35% [10.775%-11.975%], shown in Fig. 3A and 3B, n = 8, p < 0.01). It was suggested that neonatal ketamine exposure significantly promoted neuronal differentiation and attenuated the astrocytic differentiation of NSCs in the SVZ.
Dexmedetomidine protects NSCs from ketamine-induced injury
Next, we investigated the impact of dexmedetomidine (DEX) on the ketamine-induced disturbance of the proliferation and differentiation of NSCs in the SVZ. As shown in Fig. 1D and 1E, our findings suggested that pretreated with 5 µg/kg DEX or 10 µg/kg DEX before ketamine anesthesia could significantly increase the number of BrdU+ cells per SVZ compared to that in the ketamine group (median [IQR]: 35900 [35025–36950] in the 5 µg/kg DEX plus ketamine group, median [IQR]: 41100 [38925–43368] in the 10 µg/kg DEX plus ketamine group, vs. median [IQR]: 28900 [26500–30750] in the ketamine group, n = 8, p < 0.01).
Moreover, compared with the ketamine group, we found that pretreated with 5 µg/kg DEX or 10 µg/kg DEX before ketamine anesthesia significantly decreased the proportion of β-tubulin III+/BrdU+ cells in the SVZ compared with ketamine treatment (median [IQR]: 15.6% [14.85%-16.05] in the 5 µg/kg DEX plus ketamine group, median [IQR]: 13.85 [13.125–14.175] in the 10 µg/kg DEX plus ketamine group, vs. median [IQR]: 19.05% [18%-19.725%] in the ketamine group, n = 8, p < 0.01, Fig. 2A and 2B). In addition, pretreated with DEX could dose-dependently improve the reduction in the proportion of GFAP+/BrdU+ cells in the SVZ under ketamine anesthesia (median [IQR]: 13.7% [12.88%-13.98] in the 5 µg/kg DEX plus ketamine group, median [IQR]: 15.35 [14.93–15.68] in the 10 µg/kg DEX plus ketamine group, vs. median [IQR]: 11.35% [10.775%-11.975%] in the ketamine group, n = 8, p < 0.01, Fig. 3A and 3B). However, 1 µg/kg DEX pretreatment had no protective effect on the disturbance of proliferation and differentiation of NSCs induced by ketamine (p > 0.05, Fig. 1F, Fig. 2B and 3B).
In summary, these results suggest that moderate and high-dose DEX pretreatment may alleviate the disturbance in the proliferation and differentiation of NSCs in the SVZ induced by ketamine.