Laboratory of Physiology of Reticular Formation, National Institute of Neurology and Neurosurgery, INNN, Insurgentes Sur 3877, Col. La Fama, C.P. 14269, Mexico City, Mexico.
Laboratory of Neurochemistry, National Institute of Neurology and Neurosurgery, INNN, Insurgentes Sur 3877, Col. La Fama, C.P. 14269, Mexico City, Mexico.
Radiat Oncol. 2020 Nov 23;15(1):269. doi: 10.1186/s13014-020-01716-y.
Whole-brain radiotherapy is a primary treatment for brain tumors and brain metastasis, but it also induces long-term undesired effects. Since cognitive impairment can occur, research on the etiology of secondary effects has focused on the hippocampus. Often overlooked, the hypothalamus controls critical homeostatic functions, some of which are also susceptible after whole-brain radiotherapy. Therefore, using whole-brain irradiation (WBI) in a rat model, we measured neurotransmitters and receptors in the hypothalamus. The prefrontal cortex and brainstem were also analyzed since they are highly connected to the hypothalamus and its regulatory processes.
Male Wistar rats were exposed to WBI with 11 Gy (Biologically Effective Dose = 72 Gy). After 1 month, we evaluated changes in gamma-aminobutyric acid (GABA), glycine, taurine, aspartate, glutamate, and glutamine in the hypothalamus, prefrontal cortex, and brainstem according to an HPLC method. Ratios of Glutamate/GABA and Glutamine/Glutamate were calculated. Through Western Blott analysis, we measured the expression of GABAa and GABAb receptors, and NR1 and NR2A subunits of NMDA receptors. Changes were analyzed comparing results with sham controls using the non-parametric Mann-Whitney U test (p < 0.05).
WBI with 11 Gy induced significantly lower levels of GABA, glycine, taurine, aspartate, and GABAa receptor in the hypothalamus. Also, in the hypothalamus, a higher Glutamate/GABA ratio was found after irradiation. In the prefrontal cortex, WBI induced significant increases of glutamine and glutamate, Glutamine/Glutamate ratio, and increased expression of both GABAa receptor and NMDA receptor NR1 subunit. The brainstem showed no statistically significant changes after irradiation.
Our findings confirm that WBI can affect rat brain regions differently and opens new avenues for study. After 1 month, WBI decreases inhibitory neurotransmitters and receptors in the hypothalamus and, conversely, increases excitatory neurotransmitters and receptors in the prefrontal cortex. Increments in Glutamate/GABA in the hypothalamus and Glutamine/Glutamate in the frontal cortex indicate a neurochemical imbalance. Found changes could be related to several reported radiotherapy secondary effects, suggesting new prospects for therapeutic targets.
全脑放疗是脑肿瘤和脑转移的主要治疗方法，但也会引起长期的不良影响。由于认知障碍可能发生，因此对继发性效应病因的研究集中在海马体上。然而，经常被忽视的下丘脑控制着关键的体内平衡功能，其中一些功能在全脑放疗后也很容易受到影响。因此，我们使用全脑照射（WBI）在大鼠模型中测量了下丘脑的神经递质和受体。还分析了前额叶皮层和脑干，因为它们与下丘脑及其调节过程高度相关。
雄性 Wistar 大鼠接受 11 Gy（生物有效剂量= 72 Gy）的 WBI。照射 1 个月后，我们根据 HPLC 方法评估了下丘脑、前额叶皮层和脑干中γ-氨基丁酸（GABA）、甘氨酸、牛磺酸、天冬氨酸、谷氨酸和谷氨酰胺的变化。计算了谷氨酸/ GABA 和谷氨酰胺/谷氨酸的比值。通过 Western Blott 分析，我们测量了 GABAa 和 GABAb 受体以及 NMDA 受体的 NR1 和 NR2A 亚单位的表达。使用非参数 Mann-Whitney U 检验（p<0.05）将结果与假对照进行比较，分析变化。
11 Gy 的 WBI 导致下丘脑 GABA、甘氨酸、牛磺酸、天冬氨酸和 GABAa 受体的水平显著降低。此外，照射后下丘脑的谷氨酸/ GABA 比值升高。在前额叶皮层中，WBI 导致谷氨酰胺和谷氨酸、谷氨酰胺/谷氨酸比值显著增加，GABAa 受体和 NMDA 受体 NR1 亚单位的表达增加。照射后脑干没有统计学上的显著变化。
我们的研究结果证实，WBI 可以对大鼠大脑区域产生不同的影响，并为进一步研究开辟了新的途径。照射 1 个月后，WBI 降低了下丘脑的抑制性神经递质和受体，而相反，增加了前额叶皮层的兴奋性神经递质和受体。下丘脑谷氨酸/ GABA 比值和前额叶皮层谷氨酰胺/谷氨酸比值的增加表明神经化学失衡。发现的变化可能与几种报道的放射治疗继发性效应有关，为治疗靶点提供了新的前景。
