BACKGROUND Delayed post hypoxic leukoencephalopathy syndrome(DPHLS),also known as Grinker’s myelinopathy,is a rare but significant neurological condition that manifests days to weeks after a hypoxic event.Characteriz...BACKGROUND Delayed post hypoxic leukoencephalopathy syndrome(DPHLS),also known as Grinker’s myelinopathy,is a rare but significant neurological condition that manifests days to weeks after a hypoxic event.Characterized by delayed onset of neurological and cognitive deficits,DPHLS presents substantial diagnostic and therapeutic challenges.AIM To consolidate current knowledge on pathophysiology,clinical features,diagnostic approaches,and management strategies for DPHLS,providing a comprehensive overview and highlighting gaps for future research.METHODS Following the Preferred Reporting Items for Systematic Reviews and Meta-Analyzes guidelines,we systematically searched PubMed,ScienceDirect and Hinari databases using terms related to delayed post-hypoxic leukoencephalopathy.Inclusion criteria were original research articles,case reports,and case series involving human subjects with detailed clinical,neuroimaging,or pathological data on DPHLS.Data were extracted on study characteristics,participant demographics,clinical features,neuroimaging findings,pathological findings,treatment,and outcomes.The quality assessment was performed using the Joanna Briggs Institute critical appraisal checklist.RESULTS A total of 73 cases were reviewed.Common comorbidities included schizoaffective disorder,bipolar disorder,hypertension,and substance use disorder.The primary causes of hypoxia were benzodiazepine overdose,opioid overdose,polysubstance overdose,and carbon monoxide(CO)poisoning.Symptoms frequently include decreased level of consciousness,psychomotor agitation,cognitive decline,parkinsonism,and encephalopathy.Neuroimaging commonly revealed diffuse T2 hyperintensities in cerebral white matter,sometimes involving the basal ganglia and the globus pallidus.Magnetic resonance spectroscopy often showed decreased N-acetylaspartate,elevated choline,choline-to-creatinine ratio,and normal or elevated lactate.Treatment is often supportive,including amantadine,an antioxidant cocktail,and steroids.Hyperbaric oxygen therapy may be beneficial in those with CO poisoning.Parkinsonism was often treated with levodopa.Most of the patients had substantial recovery over the course of months and many cases had some residual neurocognitive deficits.CONCLUSION DPHLS remains a complex and multifaceted condition with various etiologies and clinical manifestations.Early recognition and appropriate management are crucial to improving patient outcomes.Future research should focus on standardizing diagnostic criteria,using advanced imaging techniques,and exploring therapeutic interventions to improve understanding and treatment of DPHLS.Conducting prospective cohort studies and developing biomarkers for early diagnosis and monitoring will be essential to advance patient care.展开更多
Objective:To evaluate the changes of brainstem auditory evoked potential (BAEP) in patients with delayed encephalopathy after acute carbon monoxide poisoning. Methods: BAEPs were performed in 32 controls and 40 patien...Objective:To evaluate the changes of brainstem auditory evoked potential (BAEP) in patients with delayed encephalopathy after acute carbon monoxide poisoning. Methods: BAEPs were performed in 32 controls and 40 patients. Wave Ⅰ , Ⅱ , Ⅲ ,Ⅳ, Ⅴ latencies and Ⅰ-Ⅲ , Ⅲ-Ⅴ , Ⅰ-Ⅴ interpeak latencies were measured, respectively. Results: Abnormalities of BAEPs in 13 patients (13/40, 32 ％). Among the13 abnormal BAEPs, 3 displayed prolongation of latency to waves in one side, no potential in another side; 5 displayed a similar abnormality which was bilateral prolongation of latency to waves ;and another 5 displayed unilateral latency delay. Compared wave Ⅰ , Ⅱ , Ⅲ , Ⅳ, Ⅴ latencies and Ⅰ-Ⅲ , Ⅲ-Ⅴ , Ⅰ-Ⅴ interpeak latencies in the patients and the controls, there were no significant differences (P＞0.05). Conclusion: BAEPs can be used for evaluating the diagnostic and prognostic values in the cases of delayed encephalopathy after acute carbon monoxide poisoning.展开更多
Subdural hematoma is often secondary to brain trauma and other diseases.The onset is hidden and the condition is critical.Timely detection and early treatment are particularly important.The patient denied a history of...Subdural hematoma is often secondary to brain trauma and other diseases.The onset is hidden and the condition is critical.Timely detection and early treatment are particularly important.The patient denied a history of trauma,but had a history of consciousness loss after charcoal burning.The clinical symptoms were progressive cognitive impairment.The initial diagnosis was delayed encephalopathy caused by carbon monoxide poisoning.However,computed tomography(CT)scan of the brain showed a large area of subdural hematoma on the left side and the formation of a cerebral hernia,which was life-threatening.The patienfs symptoms gradually improved after an emergency operation.展开更多
Objective:To study the influence of mouse nerve growth factor (mNGF) combined with hyperbaric oxygen on serum cytokines and cognitive function in patients with delayed encephalopathy after carbon monoxide poisoning (D...Objective:To study the influence of mouse nerve growth factor (mNGF) combined with hyperbaric oxygen on serum cytokines and cognitive function in patients with delayed encephalopathy after carbon monoxide poisoning (DEACMP).Methods: 218 patients with DEACMP who were treated in our hospital between June 2012 and September 2016 were chosen as research subjects and retrospectively divided into the control group (n=100) who underwent hyperbaric oxygen treatment and the observation group (n=118) who underwent mouse nerve growth factor combined with hyperbaric oxygen treatment. Serum contents of nerve injury indexes and inflammatory mediators were compared between two groups of patients and cognitive function was assessed.Results:Before treatment, differences in serum levels of nerve injury indexes and inflammatory mediators, total MMSE score and each dimension score were not statistically significant between two groups of patients. After treatment, serum contents of nerve injury indexes creatine kinase-BB (CK-BB), neuron-specific enolase (NSE), S-100β protein (S-100β) and lactate (Lac) in observation group were lower than those in control group;serum contents of inflammatory mediators interleukin-6 (IL-6), interleukin-10 (IL-10), interleukin-18 (IL-18), hypersensitive C-reactive protein (hs-CRP) and tumor necrosis factor (TNF-α) were lower than those in control group;total MMSE score and each dimension score were higher than those of control group.Conclusion:mNGF combined with hyperbaric oxygen treatment of DEACMP is helpful to reduce the nerve injury and systemic inflammatory response, and improve the cognitive function.展开更多
Objective： To evaluate the diagnostic and prognostic values in patients with delayed encephalopathy after acute carbon monoxide poisoning. Methods： The tibial nerve somatosensory evoked potentials （SEPs）, vision e...Objective： To evaluate the diagnostic and prognostic values in patients with delayed encephalopathy after acute carbon monoxide poisoning. Methods： The tibial nerve somatosensory evoked potentials （SEPs）, vision evoked potentials （VEPs）, and brain stem audition evoked potentials（BAEPs） were performed in 32 healthy adults and 43 patients with delayed encephalopathy after acute carbon monoxide poisoning. Results： This paper indicated abnormalities of tibial nerve SEPs in 31 patients （31/43, 72.1%）, VEPs in 17 patients （17/28, 60.7%）, and BAEPs in 14, patients （14/43, 32.6%）. These results showed that the greatest diagnostic value was SEPs, followed by VEPs and, BAEPs with the lowest sensitivity. Conclusion： Multimodality evoked potentials （EPs） can be used for evaluating the diagnostic and prognostic values in cases of delayed encephalopathy after acute carbon monoxide poisoning.展开更多
Currently, there is no known optimal therapy for carbon monoxide （CO） poisoning and CO-associated delayed neu- rological sequelae. Hyperbaric oxygen therapy （HBOT） is a well-known treatment method, but its use for...Currently, there is no known optimal therapy for carbon monoxide （CO） poisoning and CO-associated delayed neu- rological sequelae. Hyperbaric oxygen therapy （HBOT） is a well-known treatment method, but its use for CO poison- ing patients is controversial to use due to lack of evidences regarding its efficacy. Thus, it is unlikely that HBOT alone will be accepted as the standard treatment method. In this article, current and potential treatment methods of CO poi- soning are presented as well as the tentative multi-factorial pathophysiology. A series of treatments are suggested for use as a bundle therapy, with targeted temperature management as the base treatment method. Such a therapy holds a great potential, especially for the cases where HBOT is not readily available. We suggest further investigations for elucidating the effects of these suggested treatments and their roles in terms of the complex pathophysiology of CO poisoning. Future ac- ceptance of this therapy based on the improved scientific and clinical knowledge may result in injury prevention and mini- mization of the signs and the symptoms in CO poisoning.展开更多
Objective In vivo Proton Magnetic Resonance Spectroscopy （1H-MRS） can be used to evaluate the levels of specific neurochemical biomarkers of pathological mechanisms in the brain. Methods We conducted T2-Weighted Mag...Objective In vivo Proton Magnetic Resonance Spectroscopy （1H-MRS） can be used to evaluate the levels of specific neurochemical biomarkers of pathological mechanisms in the brain. Methods We conducted T2-Weighted Magnetic Resonance Imaging （MRI） and 1H-MRS with a 3.0-Tesla animal MRI system to investigate the early microstructural and metabolic profiles in vivo in the striatum of rats following carbon monoxide （CO） poisoning. Results Compared to baseline, we found significant cortical surface deformation, cerebral edema changes, which were indicated by the unclear gray/white matter border, and lateral ventricular volume changes in the brain. A significant reduction in the metabolite to total creatine （Cr） ratios of N-acetylaspartate （NAA） was observed as early as 1 h after the last CO administration, while the lactate （Lac） levels increased marginally. Both the Lac/Cr and NAA/Cr ratios leveled off at 6 h and showed no subsequent significant changes. In addition, compared to the control, the choline （Cho）/Cr ratio was slightly reduced in the early stages and significantly increased after 6 h. In addition, a pathological examination revealed mild cerebral edema on cessation of the insult and more severe cerebral injury after additional CO poisoning. Conclusion The present study demonstrated that 1H-MRS of the brain identified early metabolic changes after CO poisoning. Notably, the relationship between the increased Cho/Cr ratio in the striatum and delayed neuropsychologic sequelae requires further research.展开更多
BACKGROUND Delayed neurological sequelae(DNS)caused by carbon monoxide(CO)intoxication poses considerable treatment challenges for clinical practitioners.In this report,we used nuclear medicine imaging and the Mini-Me...BACKGROUND Delayed neurological sequelae(DNS)caused by carbon monoxide(CO)intoxication poses considerable treatment challenges for clinical practitioners.In this report,we used nuclear medicine imaging and the Mini-Mental State Examination(MMSE)to evaluate the effectiveness of intravascular laser irradiation of blood(ILIB)therapy for the management of DNS.CASE SUMMARY A 51-year-old woman presented to our medical center experiencing progressive bradykinesia,rigidity of limbs,gait disturbance,and cognitive impairment.Based on her neurological deficits,laboratory tests and imaging findings,the patient was diagnosed with delayed neurological sequelae of CO intoxication.She received intensive rehabilitation and ILIB therapy during 30 sessions over 2 mo after diagnosis.Brain single-photon emission computed tomography was performed both prior to and after ILIB therapy.The original hypoperfusion area in bilateral striata,bilateral frontal lobe,right parietal lobe,and bilateral cerebellum showed considerable improvement after completion of therapy.The patient’s MMSE score also increased markedly from 6/30 to 25/30.Symptoms of DNS became barely detectable,and the woman was able to carry out her daily living activities independently.CONCLUSION ILIB therapy could facilitate recovery from delayed neurological sequelae in patients with CO intoxication,as demonstrated by improved cerebral blood flow and functional outcomes in our patient.展开更多
This study examined a 24-year-old patient with delayed encephalopathy, who was admitted to hospital with complaints of headache and visual impairment 1 week after acute carbon monoxide poisoning. The results of a visu...This study examined a 24-year-old patient with delayed encephalopathy, who was admitted to hospital with complaints of headache and visual impairment 1 week after acute carbon monoxide poisoning. The results of a visual field assessment, electroencephalography and head magnetic resonance imaging indicated damage to the cerebral cortex. After a 2-week treatment period, the patient had recovered from the visual impairment, but exhibited digit- and letter-reading difficulty. The Chinese aphasia battery and the number and letter battery supplement were conducted. The results revealed that the patient exhibited digit and letter alexia, while the ability to read Chinese characters was preserved. In contrast, the patient exhibited a deficit in Chinese character writing, while number and letter writing remained intact. Following treatment, reading and writing ability was improved and electroencephalographic abnormalities were ameliorated. Overall, our experimental findings demonstrated that delayed encephalopathy following acute carbon monoxide poisoning was characterized by digit and letter alexia.展开更多
Objective To research the expression of hypoxia-inducible factor-1 alpha(HIF-1α)and heme oxygenase-1(HO-1)in hippocampus of rats with delayed encephalopathy after acute carbon monoxide poisoning(DEACMP)and its functi...Objective To research the expression of hypoxia-inducible factor-1 alpha(HIF-1α)and heme oxygenase-1(HO-1)in hippocampus of rats with delayed encephalopathy after acute carbon monoxide poisoning(DEACMP)and its functions.Methods One hundred and fiftysix rats were selected and randomly divided into展开更多
文摘BACKGROUND Delayed post hypoxic leukoencephalopathy syndrome(DPHLS),also known as Grinker’s myelinopathy,is a rare but significant neurological condition that manifests days to weeks after a hypoxic event.Characterized by delayed onset of neurological and cognitive deficits,DPHLS presents substantial diagnostic and therapeutic challenges.AIM To consolidate current knowledge on pathophysiology,clinical features,diagnostic approaches,and management strategies for DPHLS,providing a comprehensive overview and highlighting gaps for future research.METHODS Following the Preferred Reporting Items for Systematic Reviews and Meta-Analyzes guidelines,we systematically searched PubMed,ScienceDirect and Hinari databases using terms related to delayed post-hypoxic leukoencephalopathy.Inclusion criteria were original research articles,case reports,and case series involving human subjects with detailed clinical,neuroimaging,or pathological data on DPHLS.Data were extracted on study characteristics,participant demographics,clinical features,neuroimaging findings,pathological findings,treatment,and outcomes.The quality assessment was performed using the Joanna Briggs Institute critical appraisal checklist.RESULTS A total of 73 cases were reviewed.Common comorbidities included schizoaffective disorder,bipolar disorder,hypertension,and substance use disorder.The primary causes of hypoxia were benzodiazepine overdose,opioid overdose,polysubstance overdose,and carbon monoxide(CO)poisoning.Symptoms frequently include decreased level of consciousness,psychomotor agitation,cognitive decline,parkinsonism,and encephalopathy.Neuroimaging commonly revealed diffuse T2 hyperintensities in cerebral white matter,sometimes involving the basal ganglia and the globus pallidus.Magnetic resonance spectroscopy often showed decreased N-acetylaspartate,elevated choline,choline-to-creatinine ratio,and normal or elevated lactate.Treatment is often supportive,including amantadine,an antioxidant cocktail,and steroids.Hyperbaric oxygen therapy may be beneficial in those with CO poisoning.Parkinsonism was often treated with levodopa.Most of the patients had substantial recovery over the course of months and many cases had some residual neurocognitive deficits.CONCLUSION DPHLS remains a complex and multifaceted condition with various etiologies and clinical manifestations.Early recognition and appropriate management are crucial to improving patient outcomes.Future research should focus on standardizing diagnostic criteria,using advanced imaging techniques,and exploring therapeutic interventions to improve understanding and treatment of DPHLS.Conducting prospective cohort studies and developing biomarkers for early diagnosis and monitoring will be essential to advance patient care.
基金Supported by the Department of Education in Henan (2000320042)
文摘Objective:To evaluate the changes of brainstem auditory evoked potential (BAEP) in patients with delayed encephalopathy after acute carbon monoxide poisoning. Methods: BAEPs were performed in 32 controls and 40 patients. Wave Ⅰ , Ⅱ , Ⅲ ,Ⅳ, Ⅴ latencies and Ⅰ-Ⅲ , Ⅲ-Ⅴ , Ⅰ-Ⅴ interpeak latencies were measured, respectively. Results: Abnormalities of BAEPs in 13 patients (13/40, 32 ％). Among the13 abnormal BAEPs, 3 displayed prolongation of latency to waves in one side, no potential in another side; 5 displayed a similar abnormality which was bilateral prolongation of latency to waves ;and another 5 displayed unilateral latency delay. Compared wave Ⅰ , Ⅱ , Ⅲ , Ⅳ, Ⅴ latencies and Ⅰ-Ⅲ , Ⅲ-Ⅴ , Ⅰ-Ⅴ interpeak latencies in the patients and the controls, there were no significant differences (P＞0.05). Conclusion: BAEPs can be used for evaluating the diagnostic and prognostic values in the cases of delayed encephalopathy after acute carbon monoxide poisoning.
文摘Subdural hematoma is often secondary to brain trauma and other diseases.The onset is hidden and the condition is critical.Timely detection and early treatment are particularly important.The patient denied a history of trauma,but had a history of consciousness loss after charcoal burning.The clinical symptoms were progressive cognitive impairment.The initial diagnosis was delayed encephalopathy caused by carbon monoxide poisoning.However,computed tomography(CT)scan of the brain showed a large area of subdural hematoma on the left side and the formation of a cerebral hernia,which was life-threatening.The patienfs symptoms gradually improved after an emergency operation.
文摘Objective:To study the influence of mouse nerve growth factor (mNGF) combined with hyperbaric oxygen on serum cytokines and cognitive function in patients with delayed encephalopathy after carbon monoxide poisoning (DEACMP).Methods: 218 patients with DEACMP who were treated in our hospital between June 2012 and September 2016 were chosen as research subjects and retrospectively divided into the control group (n=100) who underwent hyperbaric oxygen treatment and the observation group (n=118) who underwent mouse nerve growth factor combined with hyperbaric oxygen treatment. Serum contents of nerve injury indexes and inflammatory mediators were compared between two groups of patients and cognitive function was assessed.Results:Before treatment, differences in serum levels of nerve injury indexes and inflammatory mediators, total MMSE score and each dimension score were not statistically significant between two groups of patients. After treatment, serum contents of nerve injury indexes creatine kinase-BB (CK-BB), neuron-specific enolase (NSE), S-100β protein (S-100β) and lactate (Lac) in observation group were lower than those in control group;serum contents of inflammatory mediators interleukin-6 (IL-6), interleukin-10 (IL-10), interleukin-18 (IL-18), hypersensitive C-reactive protein (hs-CRP) and tumor necrosis factor (TNF-α) were lower than those in control group;total MMSE score and each dimension score were higher than those of control group.Conclusion:mNGF combined with hyperbaric oxygen treatment of DEACMP is helpful to reduce the nerve injury and systemic inflammatory response, and improve the cognitive function.
基金The Department of Education in Henan (2000320042)
文摘Objective： To evaluate the diagnostic and prognostic values in patients with delayed encephalopathy after acute carbon monoxide poisoning. Methods： The tibial nerve somatosensory evoked potentials （SEPs）, vision evoked potentials （VEPs）, and brain stem audition evoked potentials（BAEPs） were performed in 32 healthy adults and 43 patients with delayed encephalopathy after acute carbon monoxide poisoning. Results： This paper indicated abnormalities of tibial nerve SEPs in 31 patients （31/43, 72.1%）, VEPs in 17 patients （17/28, 60.7%）, and BAEPs in 14, patients （14/43, 32.6%）. These results showed that the greatest diagnostic value was SEPs, followed by VEPs and, BAEPs with the lowest sensitivity. Conclusion： Multimodality evoked potentials （EPs） can be used for evaluating the diagnostic and prognostic values in cases of delayed encephalopathy after acute carbon monoxide poisoning.
文摘Currently, there is no known optimal therapy for carbon monoxide （CO） poisoning and CO-associated delayed neu- rological sequelae. Hyperbaric oxygen therapy （HBOT） is a well-known treatment method, but its use for CO poison- ing patients is controversial to use due to lack of evidences regarding its efficacy. Thus, it is unlikely that HBOT alone will be accepted as the standard treatment method. In this article, current and potential treatment methods of CO poi- soning are presented as well as the tentative multi-factorial pathophysiology. A series of treatments are suggested for use as a bundle therapy, with targeted temperature management as the base treatment method. Such a therapy holds a great potential, especially for the cases where HBOT is not readily available. We suggest further investigations for elucidating the effects of these suggested treatments and their roles in terms of the complex pathophysiology of CO poisoning. Future ac- ceptance of this therapy based on the improved scientific and clinical knowledge may result in injury prevention and mini- mization of the signs and the symptoms in CO poisoning.
基金supported by the National Natural Science Foundation of China,‘Study on the pathogenic effect of HO-1/CO in the delayed encephalopathy after acute CO poisoning’,(Grant No.81101024)
文摘Objective In vivo Proton Magnetic Resonance Spectroscopy （1H-MRS） can be used to evaluate the levels of specific neurochemical biomarkers of pathological mechanisms in the brain. Methods We conducted T2-Weighted Magnetic Resonance Imaging （MRI） and 1H-MRS with a 3.0-Tesla animal MRI system to investigate the early microstructural and metabolic profiles in vivo in the striatum of rats following carbon monoxide （CO） poisoning. Results Compared to baseline, we found significant cortical surface deformation, cerebral edema changes, which were indicated by the unclear gray/white matter border, and lateral ventricular volume changes in the brain. A significant reduction in the metabolite to total creatine （Cr） ratios of N-acetylaspartate （NAA） was observed as early as 1 h after the last CO administration, while the lactate （Lac） levels increased marginally. Both the Lac/Cr and NAA/Cr ratios leveled off at 6 h and showed no subsequent significant changes. In addition, compared to the control, the choline （Cho）/Cr ratio was slightly reduced in the early stages and significantly increased after 6 h. In addition, a pathological examination revealed mild cerebral edema on cessation of the insult and more severe cerebral injury after additional CO poisoning. Conclusion The present study demonstrated that 1H-MRS of the brain identified early metabolic changes after CO poisoning. Notably, the relationship between the increased Cho/Cr ratio in the striatum and delayed neuropsychologic sequelae requires further research.
文摘BACKGROUND Delayed neurological sequelae(DNS)caused by carbon monoxide(CO)intoxication poses considerable treatment challenges for clinical practitioners.In this report,we used nuclear medicine imaging and the Mini-Mental State Examination(MMSE)to evaluate the effectiveness of intravascular laser irradiation of blood(ILIB)therapy for the management of DNS.CASE SUMMARY A 51-year-old woman presented to our medical center experiencing progressive bradykinesia,rigidity of limbs,gait disturbance,and cognitive impairment.Based on her neurological deficits,laboratory tests and imaging findings,the patient was diagnosed with delayed neurological sequelae of CO intoxication.She received intensive rehabilitation and ILIB therapy during 30 sessions over 2 mo after diagnosis.Brain single-photon emission computed tomography was performed both prior to and after ILIB therapy.The original hypoperfusion area in bilateral striata,bilateral frontal lobe,right parietal lobe,and bilateral cerebellum showed considerable improvement after completion of therapy.The patient’s MMSE score also increased markedly from 6/30 to 25/30.Symptoms of DNS became barely detectable,and the woman was able to carry out her daily living activities independently.CONCLUSION ILIB therapy could facilitate recovery from delayed neurological sequelae in patients with CO intoxication,as demonstrated by improved cerebral blood flow and functional outcomes in our patient.
基金supported by National Natural Science Foundation of China (No. 81072242)Natural Science Foundation of Guangdong Province (No. S2011010004708)+2 种基金the Fundamental Research Funds for the Central Universities,Funds for Pearl River Science & Technology Star of Guangzhou CityNatural Science Foundation of Guangdong Province (No.10151130001000001)Science and Technology Project of Guangzhou (No. 2010Y1-C191)
文摘This study examined a 24-year-old patient with delayed encephalopathy, who was admitted to hospital with complaints of headache and visual impairment 1 week after acute carbon monoxide poisoning. The results of a visual field assessment, electroencephalography and head magnetic resonance imaging indicated damage to the cerebral cortex. After a 2-week treatment period, the patient had recovered from the visual impairment, but exhibited digit- and letter-reading difficulty. The Chinese aphasia battery and the number and letter battery supplement were conducted. The results revealed that the patient exhibited digit and letter alexia, while the ability to read Chinese characters was preserved. In contrast, the patient exhibited a deficit in Chinese character writing, while number and letter writing remained intact. Following treatment, reading and writing ability was improved and electroencephalographic abnormalities were ameliorated. Overall, our experimental findings demonstrated that delayed encephalopathy following acute carbon monoxide poisoning was characterized by digit and letter alexia.
文摘Objective To research the expression of hypoxia-inducible factor-1 alpha(HIF-1α)and heme oxygenase-1(HO-1)in hippocampus of rats with delayed encephalopathy after acute carbon monoxide poisoning(DEACMP)and its functions.Methods One hundred and fiftysix rats were selected and randomly divided into
