125I-iomazeniI binding shows stress- and/or diazepam-induced reductions in mouse brain: Supporting data for123I-iomazenil SPECT study of anxiety disorders

Effects of repeated swim stress on the binding of¹²⁵I-iomazenil were examined in the brains of diazepam-treated and non-treated mice. The mice were orally administered diazepam or vehicle (0.5% ethylene glycol) and subjected to daily swim stress (at 20°C for 10 min) for seven consecutive days. The distribution and the amount of¹²⁵I-iomazenil binding were analyzed autoradiographically afterin vivo andin vitro binding experiments. Repeated swim stress decreased thein vivo binding in the hippocampus (p < 0.05) and cerebral cortex (p < 0.05) of vehicle-treated mice but caused no significant changes in diazepam-treated mice. Subchronic treatment with diazepam decreased thein vivo binding approximately 50% in all brain regions examined (p < 0.01). Thein vitro experiment, however, revealed no significant changes except in the hippocampus, where a small but significant decrease in the binding was observed after subchronic treatment with diazepam (p < 0.01). The stress- or diazepam-induced reductions seem to represent alterations in thein vivo environment related to¹²⁵I-iomazenil binding. These results suggest that we can investigate the pathophysiology of stress and anxiety with¹²³I-iomazenil SPECT. Care must be taken concerning the effects of benzodiazepines.     

Effects of diazepam on125I-iomazenil-benzodiazepine receptor binding and epileptic seizures in the El mouse

OBJECTIVE: To investigate changes in free benzodiazepine receptor density in response to repeated, long-term administration of diazepam in epilepsy, we assessed 125I-iomazenil (125I-IMZ) binding in a mouse model. METHODS: El mice were divided into two groups of 12 mice each which received either no diazepam (E1(D[-]) group) or 2 mg/kg of diazepam per week (El(D[+]) group). Nine ddY mice were used as a control. Once each week from the age of 5 to 19 weeks, the El mice received stimulation to produce epileptic seizures 20 minutes after receiving intraperitoneal injections. At 20 weeks of age, a total dose of 0.37 MBq of 125I-IMZ was injected in all mice and their brains were rapidly removed 3 hours later. The incidence of epileptic seizures at the age of 19 weeks and the autoradiograms of the brain were compared. RESULTS: The incidence of epileptic seizures in response to weekly stimulation was significantly lower in the E1(D[+]) group than in the E1(D[-]) group (p < 0.001). The percent injected doses of 125I-IMZ per gram of tissue in the cortex, hippocampus and amygdala were significantly lower in the E1(D[+]) group than in the E1(D[-]) group (p < 0.05). CONCLUSION: The results suggest that diazepam binds competitively to 125I-IMZ as an agonist to free benzodiazepine receptor sites in the cortex, hippocampus and amygdala and shows anticonvulsant effect in E1 mice.     

125I-iomazenil - benzodiazepine receptor binding and serum corticosterone level during psychological stress in a rat model

To test the hypothesis that benzodiazepine receptor density decreases in response to stress, we correlated (125)I-iomazenil ((125)I-IMZ) binding with serum corticosterone levels in a rat model. Wistar male rats were divided into four groups; control group (CON, 10 rats), no physical or psychological stress; and one-, three-, and five-day stress groups of 12 rats each (1-DAY, 3-DAY, and 5-DAY, respectively), receiving psychological stress for the given number of days. Psychological stress were given to rats with a communication box. The standardized uptake value (SUV) of (125)I-iomazenil of the 3-DAY and 5-DAY showed that (125)I-iomazenil-benzodiazepine receptor binding was significantly reduced in the cortices, accumbens nuclei, amygdala and caudate putamen (p<0.05). Serum corticosterone level ratio appeared to be slightly elevated in 3-DAY and 5-DAY, although this elevation was not significant. These data suggest that (125)I-IMZ is a useful radioligand to reflect received stress and its binding in the cortices, accumbens nuclei, amygdala and caudate putamen is strongly affected by psychological stress.     

Experience with 123I-iomazenil SPECT in acute cerebral infarction

Neuronal cells are susceptible to cerebral ischaemia. As gamma-aminobutyric acid(A) (GABA(A)) receptors are specific for neurones, functional receptor imaging using I-iomazenil (IMZ), a ligand to the GABA benzodiazepine receptor, has been proposed as an imaging modality for the assessment of neuronal integrity. However, there is only limited experience with IMZ in patients with acute cerebral infarction. Therefore, the aim of this study was to evaluate IMZ single photon emission computed tomography (SPECT) in patients with acute cerebral ischaemia. IMZ SPECT was performed in 21 patients with acute cerebral infarction 7-10 days after stroke onset. Eleven patients underwent systemic thrombolysis within 6 h after symptom onset (group 1), whereas 10 patients were treated conservatively (group 2). IMZ (150-200 MBq) was injected intravenously and imaging was performed using a dedicated four-head SPECT camera at 5 min (perfusion) and 90 min (receptor distribution) post-injection, with an acquisition time of 50 min each. Images were analysed by visual inspection. Four patients showed normal IMZ distribution, and 17 patients showed abnormalities of IMZ uptake on both early and late images. In six patients with regional uptake deficits, a crossed cerebellar diaschisis was observed on early images. Cerebellar inhomogeneity of tracer uptake was absent at the time of late images in all six patients. In eight patients, areas of hypoperfusion corresponded exactly to the regions of receptor deficiency (match). In five patients, preserved neuronal integrity was present in hypoperfused areas (mismatch). In four patients, normally or even hyperperfused areas exhibited regional receptor deficiency (inverse mismatch). In conclusion, IMZ SPECT demonstrated differences between regional perfusion and receptor distribution in about one-half of patients 7-10 days after acute cerebral ischaemia. Interesting patterns between the early phase (perfusion) and the late phase (receptor distribution) were found. These patterns are indicative of the heterogeneous development of cerebral ischaemia where, even days after stroke onset, areas of hypoperfusion but preserved neuronal integrity may be present. However, the evaluation of the potential clinical and therapeutic impact of individual IMZ distribution patterns requires further investigation.     

Benzodiazepine effect of (125)I-iomazenil-benzodiazepine receptor binding and serum corticosterone level in a rat model

To test the change in free or unoccupied benzodiazepine receptor (BZR) density in response to diazepam, we investigated (125)I-iomazenil ((125)I-IMZ) binding and serum corticosterone levels in a rat model. Wistar male rats, which received psychological stress using a communication box for 5 days, were divided into two groups according to the amount of administered diazepam: no diazepam [D (0)] group and 10 mg/kg per day [D (10)] group of 12 rats each. The standardized uptake value (SUV) of (125)I-IMZ of the D (10) group were significantly lower (P < .05) than those of the D (0) group in the frontal, parietal and temporal cortices, globus pallidus, hippocampus, amygdala and hypothalamus. The serum corticosterone level ratio in the D (10) group was significantly lower than that in the D (0) group (P < .05). From the change in serum corticosterone levels, diazepam attenuated the psychological stress produced by the physical stress to animals in adjacent compartments. From the reduced binding of (125)I-IMZ, it is clear that diazepam competed with endogenous ligand for the free BZR sites, and the frontal, parietal and temporal cortices, globus pallidus, hippocampus, amygdala and hypothalamus are important areas in which (125)I-IMZ binding is strongly affected by administration of diazepam.     

Assessment of outcome by EC/IC bypass with123I-iomazenil brain SPECT

We report two patients with occlusive cerebrovascular disease who were examined by means of benzodiazepine receptor SPECT(BZR-SPECT) with 123I-iomazenil (IMZ) before extracranial-intracranial bypass surgery (EC/IC bypass). Preoperative low perfusion areas detected by cerebral blood flow SPECT (CBF-SPECT) were divided into two parts on BZR-SPECT images. In the low perfusion areas where the BZR were preserved, regional cerebral blood flow (rCBF) increased on postoperative CBF-SPECT, but where the BZR were not preserved, rCBF did not increase on postoperative CBF-SPECT. On visual inspection, the SPECT images of postoperative CBF-SPECT appeared similar to those of preoperative BZR-SPECT. For evaluation of the ischemic brain condition itself, instead of the cerebral metabolism, the distribution and activity of cerebral neurons indicated by BZR-SPECT with IMZ might be utilized.     

In vivo imaging of GABAA receptors using sequential whole-volume iodine-123 iomazenil single-photon emission tomography

Using a brain-dedicated triple-headed single-photon emission tomography (SPET) system, a sequential whole-volume imaging protocol has been devised to evaluate the regional distribution of iodine-123 iomazenil binding to GABA_A receptors in the entire brain. The protocol was piloted in eight normal volunteers (seven males and one female; mean age, 24.8±3.9 years). The patterns obtained were largely compatible with the known distribution of GABA_A receptors in the brain as reported in autoradiographic studies, with cerebral cortical regions, particularly the occipital and frontal cortices, displaying the highest¹²³I-iomazenil uptake. Measures of time to peak uptake and tracer washout rates presented with the same pattern of regional variation, with later times to peak and slower washout rates in cortical regions compared to other brain areas. Semiquantitative analysis of the data using white matter/ventricle regions as reference demonstrated a plateau of specific¹²³I-iomazenil binding in neocortical and cerebellar regions from 60–75 min onwards. These data demonstrate the feasibility of sequential, dynamic whole-volume¹²³I-iomazenil SPET imaging. The protocol may be particularly useful in the investigation of neuropsychiatric conditions which are likely to involve more than one focus of GABA abnormalities, such as anxiety disorders and schizophrenia.     

Decrease in benzodiazepine receptor binding in a patient with Angelman syndrome detected by iodine-123 iomazenil and single-photon emission tomography

A receptor mapping technique using iodine-123 iomazenil and single-photon emission tomography (SPET) was employed to examine benzodiazepine receptor binding in a patient with Angelman syndrome (AS). AS is characterized by developmental delay, seizures, inappropriate laughter and ataxic movement. In this entity there is a cytogenic deletion of the proximal long arm of chromosome 15g11–q13, where the gene encoding the GABA_A receptor3 subunit (GABRB3) is located. Since the benzodiazepine receptor is constructed as a receptor-ionophore complex that contains the GABA_A receptor, it is a suitable marker for GABA-ergic synapsis. To determine whether benzodiazepine receptor density, which indirectly indicates changes in GABA_A receptor density, is altered in the brain in patients with AS, we investigated a 27-year-old woman with AS using¹²³I-iomazenil and SPET. Receptor density was quantitatively assessed by measuring the binding potential using a simplified method. Regional cerebral blood flow was also measured withN-isopropyl-p-[¹²³I]iodoamphetamine. We demonstrated that benzodiazepine receptor density is severely decreased in the cerebellum, and mildly decreased in the frontal and temporal cortices and basal ganglia, a result which is considered to indicate decreased GABA_A receptor density in these regions. Although the deletion of GABRB3 was not observed in the present study, we indirectly demonstrated the disturbance of inhibitory neurotransmission mediated by the GABA_A receptor in the investigated patient.¹²³I-iomazenil with SPET was useful to map benzodiazepine receptors, which indicate GABA_A receptor distribution and their density.     

125I-iomazenil-benzodiazepine receptor binding during psychological stress in rats

OBJECTIVE: We investigated the changes in 125I-iomazenil (125I-IMZ) benzodiazepine receptor (BZR) binding with psychological stress in a rat model. METHODS: Six male Wistar rats were placed under psychological stress for 1 hour by using a communication box. No physical stress was not received. 1.85 MBq of 125I-IMZ was injected into the lateral tail vein and the rat was killed 3 hours later. Twenty-micrometer-thick sections of the brain were collected and % injected dose per body weight (%ID/BW) of eleven regions (frontal, parietal, temporal, occipital cortices, caudate putamen, accumubens nuclei, globus pallidus, amygdala, thalamus, hippocampus and hypothalamus) were calculated by autoradiography. The %ID/BW of rats which were placed under psychological stress was compared with that of 6 control rats. RESULTS: The %ID/BW of rats which were placed under psychological stress diffusely tended to show a reduction in 125I-IMZ-BZR binding. A significant decrease in BZR binding was observed in the hippocampus of the rats which were placed under psychological stress. CONCLUSION: 125I-IMZ-BZR binding tended to decrease throughout the brain.     

骨髓基质干细胞移植对脑挫伤大鼠神经行为学和Bax表达的影响

目的 探讨骨髓基质干细胞(bone morrow stromal cells,BMSCs)移植对脑挫伤大鼠神经功能的影响,并探讨其分子机制。方法 24只SD大鼠按随机数字表法分为假手术组、脑挫伤组（采用自由落体砸伤制备大鼠运动皮质区脑损伤模型）和BMSCs移植组（将培养纯化的BMSCs移植入损伤位点周围）,每组8只大鼠。术后对动物进行神经损伤严重程度评分(neurological severity scores,NSS);14 d后取脑组织观察移植细胞在体内存活、迁移情况;用RT - PCR技术检测宿主脑组织内凋亡基因Bax的表达变化。结果 脑挫伤组NSS为(12±3)分,较BMSCs移植组NSS(7±1)分明显升高(P＜0.05)。移植的BMSCs能在宿主脑内存活并迁移;RT - PCR显示BMSCs移植组凋亡基因Bax表达（0.9±0.1）较脑挫伤组(1.1±0.2)明显减少(P＜0.05)。结论 BMSCs移植能有效促进脑挫伤大鼠神经功能恢复,其作用机制可能与抑制促凋亡基因Bax表达有关。     

Renal accumulation and excretion of radioiodinated 3-iodo-α-methyl-<Emphasis Type="SmallCaps">L</Emphasis>-ty rosine

OBJECTIVE: We investigated mechanisms of renal accumulation of radioiodinated 3-iodo-alpha-methyl-L-tyrosine (IMT), which has been used clinically for tumor imaging and as an amino acid transport marker in studies of brain and pancreas function. METHODS: In this study, we used 125I- or 123I-labeled IMT ([125I]IMT or [123I]IMT) as the transport marker. Partition coefficients of [125I]IMT were determined for hypothetic urine at pH ranging from 5 to 8. The examination of uptake and inhibition of [125I]IMT was performed using normal human renal proximal tubule epithelial cells (RPTEC), which are characteristic of the proximal convoluted tubule. The plasma protein binding ratio of [125I]IMT was determined using rats. In the in vivo experiments using mice, we examined biodistribution and excretion inhibition, and performed whole body autoradiography. Also, renal SPECT using [123I]IMT was performed using a normal canine. RESULTS: Very low lipophilicity of [125I]IMT in hypothetic urine suggests that a carrier-mediated pathway contributes to its marked kidney accumulation. [125I]IMT uptake into RPTEC was significantly inhibited by 2-aminobicyclo[2,2,1]heptane-2-carboxylic acid (BCH) in a sodium-dependent manner, suggesting reabsorption mainly via system B0 in apical membrane of proximal tubule. Plasma protein binding ratio of IMT was 45.4 +/- 5.6%. At 6 hr after administration of IMT to mice, excretion via urinary tract was 77.51% of injected dose, and excretion into feces was 0.25%. Furosemide, ethacrynic acid and probenecid inhibited tubular secretion of [125I]IMT in mice. We obtained very clear autoradiographs of mouse renal cortex and a canine renal SPECT image (S2-like region). CONCLUSIONS: We believe that [123I]IM-T is useful for kidney imaging. In future studies, we plan to examine the use of [123I]IMT in diagnosis of disease.     

锁阳水提物PartⅢ对缺氧小鼠心、脑蛋白含量及病理形态的影响

目的：研究锁阳水提物PartⅢ对缺氧小鼠物质代谢和心脑细胞结构的影响。方法：BALB／C小鼠40只，分为空白对照组、缺氧模型组、缺氧＋锁阳PartⅢ组和缺氧＋人参皂苷组，每组10只。给药组和阳性对照人参皂苷组剂量均为300mg／（kg·d）×7，空白对照组和缺氧模型组给予同体积的蒸馏水。于末次灌胃后1h，模拟高原（7000m）减压缺氧6h。处死小鼠采集血液和心脑组织，测定大脑含水量及脑组织和心肌组织蛋白含量，并制作心脑HE切片。正常对照组置常氧室温低氧装置附近（海拔1520m）。结果：锁阳水提物PartⅢ可减轻缺氧小鼠脑水肿程度，增加心肌蛋白含量；能够有效保护缺氧时小鼠心脑组织细胞的结构。结论：锁阳PartⅢ可改善缺氧小鼠脑水肿和增强心肌功能。     

MR and cerebrospinal fluid enzymes as sensitive indicators of subclinical cerebral injury after open-heart valve replacement surgery.

PURPOSETo evaluate MR imaging and lumbar cerebrospinal fluid enzymes as potential sensitive indicators of cerebral injury after open-heart valve replacement surgery.METHODSThirty-four patients with cardiac valvular disease were prospectively entered into this study and then underwent valve replacement or repair under cardiopulmonary bypass using a membrane oxygenator. In 26 patients, MR head images were obtained 12 to 24 hours before surgery; repeat MR images were obtained between 1 and 2 weeks after surgery. In 18 patients, lumbar puncture cerebrospinal fluid was analyzed 24 to 48 hours after surgery; the analyses included measurement of lactic dehydrogenase, creatine phosphokinase, adenylate kinase, and neuron-specific enolase.RESULTSAfter surgery, MR imaging showed new ischemic lesions in 15 (58%) of 26 patients: 7 with deep white matter hyperintense lesions; 5 with brain stem, caudate, cerebellar, or thalamic/basal ganglia infarcts; 1 with intraparenchymal hemorrhage; 1 with a subdural hematoma and cortical infarct; and 1 with a corpus callosum lesion consistent with calcium or air. These new ischemic lesions seen on MR images were associated with a focal neurologic deficit in only 4 (27%) of the 15 patients. Neuron-specific enolase and lactic dehydrogenase were abnormally elevated after surgery in 5 (28%) of 18 patients. Adenylate kinase and creatine phosphokinase (brain isozymes) were elevated in one (67%) of the patients. Two (40%) of the five patients with abnormally high neuron-specific enolase or lactic dehydrogenase after surgery also showed a new focal neurologic deficit.CONCLUSIONSMR imaging is a sensitive measure of subclinical cerebral ischemia after cardiac valve replacement under cardiopulmonary bypass. Cerebrospinal fluid neuron-specific enolase and lactic dehydrogenase are less sensitive than MR imaging for detecting subclinical cerebral ischemia, but these values were elevated after surgery more frequently than was adenylate kinase in our patients.     

应用Fluoro-Jade C评价匹罗卡品模型中新大脑皮质神经变性

目的 应用Fluoro-Jade C(FJC)在小鼠匹罗卡品癫痫模型中探测新大脑皮质结构中神经元的变性情况.方法 雄性昆明种小鼠10只(对照组5只,匹罗卡品处理组5只).对照组给予阿托品、生理盐水腹腔注射;匹罗卡品处理组给予阿托品、匹罗卡品腹腔注射诱发癫痫持续状态.在癫痫持续状态后12 h,通过经心灌注固定处死匹罗卡品处理组小鼠.对照组小鼠处死时间及方法同匹罗卡品处理组.在各新大脑皮质水平切制冠状切片,行FJC染色,在荧光显微镜下,观察FJC阳性细胞的形态和在新大脑皮质中的整体分布情况.结果 在匹罗卡品处理组,许多新大脑皮质出现呈亮黄绿色荧光的FJC阳性细胞,而对照组未见.结论 在小鼠匹罗卡品癫痫模型中,运用FJC染色技术在新大脑皮质中显示发生了大量神经元变性,有利于更好地理解颞叶癫痫的长期病理变化和自发反复发作的癫痫机制.     

<Superscript>11</Superscript>C-NMSP/<Superscript>18</Superscript>F-FDG microPET to monitor neural stem cell transplantation in a rat model of traumatic brain injury

PURPOSE: To investigate whether (11)C-N-methylspiperone ((11)C-NMSP) microPET could be used for imaging neural stem cells (NSCs) transplantation in a rat model of traumatic brain injury. METHODS: NSCs were induced to express dopamine receptor type 2 (DRD(2)), then confirmed by RT-PCR, Western blotting and immunocytochemistry. Eighteen rats were subjected to focal traumatic brain injury in the right parietal lobe and then assigned randomly to the transplantation group and the control group. NSCs labeled with 5-bromo-2-deoxyuridine (BrdU) were transplanted into the cerebral lesion of the transplatation group. MicroPET scan using (11)C-NMSP and (18)F-FDG were performed to detect the DRD(2) expression of transplanted NSCs and the regional glucose metabolism in the cerebral lesion, respectively. Behavioral neurological function of rats were also tested. RESULTS: Histological analysis identified viable NSCs. Western blotting and immunofluorescence showed high level of NSCs-induced DRD(2) expression. Immunostaining demonstrated high levels of survived BrdU+ and DRD(2)+ donor cells in the cerebral lesion 2 weeks after transplantation. The lesion-to-normal contralateral ratio (L/N ratio) of (11)C-NMSP in the cerebral lesion decreased significantly from 97% to 68% after injury and increased dramatically to 137% 1 day after the transplantation and then decreased gradually. Glucose metabolism showed a decrease of 35% in the cerebral lesion 1 day after injury and recovered to 87% 2 weeks after transplantation. The behavioral neurological function of the transplantation group was significantly improved compared with the control group. CONCLUSIONS: This study verified that (11)C-NMSP microPET can be used to assess the NSCs-induced DRD(2) expression in rat model.     

MRI-based correction for partial-volume effect improves detectability of intractable epileptogenic foci on 123I-iomazenil brain SPECT images.

(123)I-Iomazenil brain SPECT has been used for the detection of epileptogenic foci, especially when surgical intervention is considered. Although epileptogenic foci exhibit a decrease in (123)I-iomazenil accumulation, normal cerebral cortices often exhibit similar findings because of thin cortical ribbons, gray matter atrophy, or pathologic brain structures. In the present study, we created (123)I-iomazenil SPECT images corrected for gray matter volume using MRI and tested whether the detectability of the epileptogenic foci improved. METHODS: Seven patients (1 male patient and 6 female patients; mean age +/- SD, 34 +/- 17 y) with intractable epilepsy were surgically treated by resecting the cerebral cortex after surface electroencephalography. Histopathologic examination of the resected specimens and a good outcome after surgery indicated that the resected lesions were epileptogenic foci. These patients underwent (123)I-iomazenil SPECT and 3-dimensional T1-weighted MRI examinations before their operations. Each SPECT image was coregistered to the corresponding MR image, and its partial-volume effect (PVE) was corrected on a voxel-by-voxel basis with a smoothed gray matter distribution image. Four nuclear medicine physicians visually evaluated the (123)I-iomazenil SPECT images with and without the PVE correction. The SPECT count ratio of the suspected focus to the contralateral cerebral cortex was evaluated as an asymmetry index (%) based on the volume of interest. RESULTS: The sensitivity, specificity, and accuracy of focus detection by visual assessment were higher after PVE correction (88%, 99%, and 98%, respectively) than before correction (50%, 92%, and 87%, respectively). The mean asymmetry index for the surgically resected lesions was significantly higher on the PVE-corrected SPECT images (22%) than on the PVE-uncorrected ones (16%) (P = 0.006). CONCLUSION: MRI-based PVE correction for (123)I-iomazenil brain SPECT improves the sensitivity and specificity of the detection of cortical epileptogenic foci in patients with intractable epilepsy.     

Iodo-QNB cortical binding and brain perfusion: effects of a cholinergic basal forebrain lesion in the rat

This study deals with the question of whether in vivo application of [125I]iodo-quinuclidinyl-benzilate (QNB) is able to demonstrate changes in cortical muscarinic receptor density induced by a cholinergic immunolesion of the rat basal forebrain cholinergic system, and whether the potential effects on IQNB distribution in vivo are also associated with effects on regional cerebral perfusion. Immunolesioned and control animals were injected with (R,S) [125]iodo-QNB and with [99mTc]-d,l-hexamethylpropyleneamine oxime (HMPAO). The cerebral distribution of both tracers was imaged using double tracer autoradiography. Impaired cholinergic transmission was paralleled by a 10-15% increase of [125I]iodo-QNB binding in the regions of cortex and hippocampus. The local cerebral blood flow remained unchanged after cholinergic lesion.     

Effect of chronic (-)-nicotine treatment on rat cerebral benzodiazepine receptors

The purpose of this study was to clarify the effect of (-)-nicotine on cerebral benzodiazepine receptors (BzR) with radiotracer methods. The effect of (-)-nicotine on BzR was examined in in vitro studies using chronic (-)-nicotine-treated rats using 3H-diazepam. The in vitro radioreceptor assay showed a 14% increase in the maximum number of binding sites of BzR in chronic (-)-nicotine-treated rats in comparison with the control rats. Moreover, a convenient in vivo uptake index of 125I-iomazenil was calculated and a higher uptake of the radioactivity was observed in the chronic (-)-nicotine-treated group than in the control group. Although further studies of the mechanism of (-)-nicotine on such BzR changes are required, an increase in the amount of BzR in the cerebral cortex was found in rats that underwent chronic (-)-nicotine treatment, and this result contributed to the understanding of the effects of (-)-nicotine and smoking on neural functions.     

Sensitivity to radiation-induced apoptosis and neuron loss declines rapidly in the postnatal mouse neocortex

Therapeutic brain irradiation can cause progressive decline in cognitive function, particularly in children, but the reason for this effect is unclear. The study explored whether age-related differences in apoptotic sensitivity might contribute to the increased vulnerability of the young brain to radiation. Postnatal day 1 (P1) to P30 mice were treated with 0 – 16 Gy whole-body X-irradiation. Apoptotic cells were identified and quantified up to 48 h later using the TdT-UTP nick end-labelling method (TUNEL) and immunohistochemistry for activated caspase-3. The number of neuron-specific nuclear protein (NeuN)-positive and -negative cells were also counted to measure neuronal and non-neuronal cell loss. Significantly greater TUNEL labelling occurred in the cortex of irradiated P1 animals relative to the other age groups, but there was no difference among the P7, P14 and P30 groups. Irradiation decreased the %NeuN-positive cells in the mice irradiated on P1, whereas in P14 animals, irradiation led to an increase in the %NeuN-positive cells. These data demonstrate that neocortical neurons of very young mice are more susceptible to radiation-induced apoptosis. However, this sensitivity decreases rapidly after birth. By P14, acute cell loss due to radiation occurs primarily in non-neuronal populations.     

Sensitivity to radiation-induced apoptosis and neuron loss declines rapidly in the postnatal mouse neocortex

Therapeutic brain irradiation can cause progressive decline in cognitive function, particularly in children, but the reason for this effect is unclear. The study explored whether age-related differences in apoptotic sensitivity might contribute to the increased vulnerability of the young brain to radiation. Postnatal day 1 (P1) to P30 mice were treated with 0-16 Gy whole-body X-irradiation. Apoptotic cells were identified and quantified up to 48 h later using the TdT-UTP nick end-labelling method (TUNEL) and immunohistochemistry for activated caspase-3. The number of neuron-specific nuclear protein (NeuN)-positive and -negative cells were also counted to measure neuronal and non-neuronal cell loss. Significantly greater TUNEL labelling occurred in the cortex of irradiated P1 animals relative to the other age groups, but there was no difference among the P7, P14 and P30 groups. Irradiation decreased the %NeuN-positive cells in the mice irradiated on P1, whereas in P14 animals, irradiation led to an increase in the %NeuN-positive cells. These data demonstrate that neocortical neurons of very young mice are more susceptible to radiation-induced apoptosis. However, this sensitivity decreases rapidly after birth. By P14, acute cell loss due to radiation occurs primarily in non-neuronal populations.