Persistent working memory dysfunction following traumatic brain injury: evidence for a time-dependent mechanism

The prefrontal cortex is highly vulnerable to traumatic brain injury (TBI) resulting in the dysfunction of many high-level cognitive and executive functions such as planning, information processing speed, language, memory, attention, and perception. All of these processes require some degree of working memory. Interestingly, in many cases, post-injury working memory deficits can arise in the absence of overt damage to the prefrontal cortex. Recently, excess GABA-mediated inhibition of prefrontal neuronal activity has been identified as a contributor to working memory dysfunction within the first month following cortical impact injury of rats. However, it has not been examined if these working memory deficits persist, and if so, whether they remain amenable to treatment by GABA antagonism. Our findings show that working memory dysfunction, assessed using both the delay match-to-place and delayed alternation T-maze tasks, following lateral cortical impact injury persists for at least 16 weeks post-injury. These deficits were found to be no longer the direct result of excess GABA-mediated inhibition of medial prefrontal cortex neuronal activity. Golgi staining of prelimbic pyramidal neurons revealed that TBI causes a significant shortening of layers V/VI basal dendrite arbors by 4 months post-injury, as well as an increase in the density of both basal and apical spines in these neurons. These changes were not observed in animals 14 days post-injury, a time point at which administration of GABA receptor antagonists improves working memory function. Taken together, the present findings, along with previously published reports, suggest that temporal considerations must be taken into account when designing mechanism-based therapies to improve working memory function in TBI patients.

Visualization of mRNA expression in CNS using 11C-labeled phosphorothioate oligodeoxynucleotide

Antisense phosphorothioate oligodeoxynucleotide for mRNA of glial fibrillary acidic protein (GFAP) was labeled with the positron emitter 11C and administered i.v. to rats bearing glioma, which were expected to exhibit active expression of GFAP. Antisense oligodeoxynucleotide was retained in tumor cells, yielding clear images of tumors, while the control 20% mismatch oligodeoxynucleotide and sense-strand oligodeoxynucleotide were not retained in tumor cells. Findings revealed sequence-specific binding of the antisense oligodeoxynucleotide to the GFAP mRNA. Our methods can be used directly for non-invasive imaging of human gene expression using PET, a frequently used method of clinical examination.

Experimental brain injury induces expression of amyloid precursor protein, which may be related to neuronal loss in the hippocampus

Previous reports have demonstrated that some focal brain injuries increase amyloid precursor protein (APP) immunoreactivity in the region surrounding the injury where it was localized, in damaged axons and in pre-alpha 2 cells of the entorhinal cortex. However, to date, APP expression in the hippocampus remote from the impact site has not been comprehensively studied. Therefore, we have evaluated APP expression not only in the locally injured cerebral cortex but also in the hippocampus remote from the impact site. In the present paper, diffuse axonal injury was induced in rats in midline fluid percussion injury. APP expression was examined post injury using Western blot analysis and immunohistochemistry. Western blot analysis demonstrated that the expression of 100-kd APP was increased in both the cerebral cortex and hippocampus 24 h after injury. It then decreased in the hippocampus, but did not change in the cerebral cortex, 7 days after injury. Immunohistochemical studies showed increased immunoreactivity of APP in the neuronal perikarya and reactive astrocytes near the region of injury in the cerebral cortex 24 h to 7 days after injury. In the hippocampus, APP accumulated in the CA3 neurons 24 h and 3 days after injury, although no hemorrhagic lesions were seen at that site. The APP positive neurons in CA3 showed shrunken cell bodies and pyknotic nuclei 3 days after injury, and some of the neurons in CA3 had disappeared by 7 days postinjury. The results of present study suggest that traumatic brain injury induces overexpression and accumulation of APP in neuronal perikarya and that these events are followed by degeneration of CA3 neurons. Further, the decline in APP expression in the hippocampus is thought to be due to neuronal loss in CA3 subsector.

Cognitive dysfunction and histological findings in rats with chronic-stage contusion and diffuse axonal injury

The Morris water maze (MWM) technique is well known as a prominent method of evaluating learning acquisition and memory retention impairments in rats. We previously reported on a modified fluid percussion device that is able to consistently produce experimental cortical contusion (CC) and diffuse axonal injury (DAI) in separate groups of rats. The purpose of the present protocol is to evaluate the differences in learning acquisition and memory retention impairments between these two types of injured rats in the chronic stage using the MWM technique. CC and DAI rats are respectively induced by lateral and midline fluid percussion. We also compare the histological differences between these two different types of traumatic brain injury. The results show statistically significant differences in learning acquisition impairment between the sham and CC rats and between the sham and DAI rats. However, a difference in memory retention impairment was expected to be seen only between the sham and DAI rats. Histologically, the loss of CA3 pyramidal cells in the hippocampus was observed ipsilaterally in the CC and bilaterally in DAI. Neuronal cell loss was observed in bilaterally in layer II of the entorhinal cortex in DAI, but not in CC.

Evaluation of learning and memory dysfunction and histological findings in rats with chronic stage contusion and diffuse axonal injury

We previously reported a modified fluid percussion device capable of consistently producing experimental cortical contusion (CC) and diffuse axonal injury (DAI) in separate groups of rats by lateral and midline fluid percussion, respectively. The purpose of the present study was to compare the differences in learning acquisition and memory retention impairments between these two types of injured rats in the chronic stage using the Morris water maze technique. We also compared the histological differences between these two different types of traumatic brain injury. The results showed a statistically significant difference in learning acquisition impairment between the sham and CC rats and also between the sham and DAI rats. However, a significant difference in memory retention impairment was observed only between the sham and DAI rats. Histologically, the neuronal cell loss of CA3 pyramidal cells in the hippocampus was observed on the ipsilateral side in the CC and bilaterally in DAI. The neuronal cell loss was seen in bilateral entorhinal cortex layer II in DAI, but it was not seen in CC. From these results, we speculate that the marked cell loss in the hippocampus CA3 region in both CC and DAI rats was related to the impairment of spatial learning acquisition. The marked cell loss in entorhinal cortex layer II in DAI rats may be one of the important factors in the impairment of spatial memory retention.

Retrograde labelling in vivo of vagus nerve nucleus in rat by carbocyanine dye

To elucidate the patterns of visceral innervation of the vagus nerve in rats, we labelled the severed efferent path at the level of the neck in vivo by applying a solution of 0.1% carbocyanine dye DiI/100% ethanol. Two weeks after dye application, horizontal sections of the brain stem were analysed quantitatively under an epifluorescence microscope. Particles of DiI were present in neuronal cell bodies and the cellular processes in the dorsal motor nucleus (DmoX) of the vagal nerve and nucleus ambiguus (Nam). Approximately 80% of DiI-labelled cells were located in the DmoX whereas 16% were in the Nam. The rest of the labelled cells were in the vicinity of the central canal. The DiI labelling technique appears to be a useful new technique for quantitative analysis of central neurones sending visceral efferents.

Impairment of CO2 reactivity in severe head injury patients: an investigation using thermal diffusion method

For measurement of the cerebral blood flow (CBF) the thermal diffusion method is quite convenient and allows the chronological measurement of CBF and CO2 reactivity of cerebral vessels. We investigated the CO2 reactivity of fifteen head injury patients. The results showed that in head injury cases, the disturbance of the CO2 reactivity correlates well to poor outcome. Using thermal diffusion method, investigations of CO2 reactivity are useful for further understanding of the physiological state of head injury patients.

Magnetic resonance imaging of brain contusion

In this study we investigated the time course of brain contusions using magnetic resonance imaging and compared the findings with those of a computed tomography scan. The lesions, which were demonstrated as homogeneous density areas on the computed tomography scan were demonstrated as different intensity areas in the magnetic resonance image. The intensity of the images varied according to the time at which the images were obtained. The findings indicated changes in the nature of the contusions including hematoma hemoglobin, perifocal edema extension, and so on. In conclusion, magnetic resonance imaging is important in the follow-up of chronological change as well as in original diagnosis of brain contusions.

Antitumor effect of 24R,25-dihydroxyvitamin D3

24R,25(OH)2D3, one of the endogenous active metabolites of vitamin D3, showed suppressive effects on the proliferation of various tumor cells in vitro and a prolonging effect on the survival of P-388 bearing mice in vivo. Lewis lung carcinoma was found to cause hypercalcemia in tumor bearing mice. K-DR (24R,25(OH)2D3 (prepared by Kureha Chemical Ind.) significantly prolonged the survival of mice with Lewis lung carcinoma. K-DR also showed a suppressive effect on the growth of human osteosarcoma transplanted in nude mice.

Animal pharmacological effects of 24R,25-dihydroxyvitamin D3 one of the endogenous substances regulating calcium metabolism

Lewis lung carcinoma was found to cause hypercalcaemia in tumour-bearing mice. 24R,25-Dihydroxyvitamin D3, a naturally occurring steric epimer, significantly prolonged the survival time of mice with Lewis lung carcinoma. It also had an analgesic effect in mice with Lewis lung carcinoma and increased the strength of bone weakened by the carcinoma which causes abnormal calcium metabolism and results in hypercalcaemia.

Cytotoxic effects of 24R,25-dihydroxycholecalciferol on the proliferation of various tumor cell lines in vitro and its antitumor effects in vivo

24R,25(OH)2D3, one of the endogenous active metabolites of vitamin D3, showed suppressive effects on the proliferation of various tumor cells in vitro, and showed a suppressive effect on the growth of human osteosarcoma transplanted in nude mice. 24R,25(OH)2D3 increased bone strength lowered by the tumor burden which causes abnormal calcium metabolism and results in hypercalcemia.

Antitumor and other effects of 24R,25-dihydroxycholecalciferol in Lewis lung carcinoma causing abnormal calcium metabolism in tumor-bearing mice

Lewis lung carcinoma was found to cause hypercalcemia in tumor-bearing mice. 24R,25(OH)2D3 (K-DR, prepared by Kureha Chemical Ind.) significantly prolonged the survival time of mice with Lewis lung carcinoma. K-DR exhibited an antimetastatic effect on Lewis lung carcinoma, and also had an analgesic effect in mice with Lewis lung carcinoma.