Bone marrow stromal cell transplantation preserves gammaaminobutyric acid receptor function in the injured spinal cord

A surprising shortage of information surrounds the mechanisms by which bone marrow stromal cells (BMSC) restore lost neurologic functions when transplanted into the damaged central nervous system. In the present study, we sought to elucidate whether BMSCs express the neuron-specific gamma-aminobutyric acid (GABA) receptor when transplanted into injured spinal cord. To examine this, we harvested and cultured rat femoral BMSCs. We then subjected Sprague-Dawley rats to thoracic spinal cord injury (SCI) with a pneumatic impact device. Fluorescence-labeled BMSCs (n = 7) were transplanted stereotactically or the vehicle in which these cells were cultured (n = 4) was introduced stereotactically into the rostral site of SCI at 7 days after injury. We evaluated GABA receptor function by measuring the binding potential for 125I-iomazenil (125I-IMZ) through in vitro autoradiography at 4 weeks after BMSC transplantation and simultaneously examined the fate of the transplanted BMSCs by immunocytochemistry. We found that the transplanted BMSC migrated toward the core of the injury and were densely distributed in the marginal region at 4 weeks after transplantation. BMSC transplantation significantly increased the binding potential for 125I-IMZ (p = 0.0376) and increased the number of GABA receptor-positive cells (p = 0.0077) in the marginal region of the injury site. Some of the transplanted BMSCs were positive for microtubule-associated protein-2 and the alpha1 subunit of GABA(A) receptor in the region of injury. These findings suggest that BMSCs have the potential to support the survival of neurons in the marginal region of SCI and can partly differentiate into neurons, regenerating spinal cord tissue at the site of injury.

Improved expression of gamma-aminobutyric acid receptor in mice with cerebral infarct and transplanted bone marrow stromal cells: an autoradiographic and histologic analysis

Recent studies have indicated that bone marrow stromal cells (BMSC) have the potential to improve neurologic function when transplanted into animal models of central nervous system disorders. However, how the transplanted BMSC restore the lost neurologic function is not clear. In the present study, therefore, we aimed to elucidate whether BMSC express the neuron-specific gamma-aminobutyric acid (GABA) receptor when transplanted into brain that has been subjected to cerebral infarction.

METHODS

The BMSC were harvested from green fluorescent protein-transgenic mice and were cultured. The mice were subjected to permanent middle cerebral artery occlusion. The BMSC or vehicle was transplanted into the ipsilateral striatum 7 d after the insult. Using autoradiography and fluorescence immunohistochemistry, we evaluated the binding of 125I-iomazenil and the expression of GABA receptor protein in and around the cerebral infarct 4 wk after transplantation.

RESULTS

Binding of 125I-iomazenil was significantly higher in the periinfarct neocortex in the BMSC-transplanted animals than in the vehicle-transplanted animals. Likewise, the number of the GABAA receptor-positive cells was significantly higher in the periinfarct neocortex in the BMSC-transplanted animals than in the vehicle-transplanted animals. A certain subpopulation of the transplanted BMSC expressed a neuron-specific marker, microtubule-associated protein 2, and the marker protein specific for GABAA receptor in the periinfarct area.

CONCLUSION

These findings suggest that BMSC may contribute to neural tissue regeneration through migrating toward the periinfarct area and acquiring the neuron-specific receptor function.

Central-type Benzodiazepine Receptors and Epileptogenesis: Basic Mechanisms and Clinical Validity

PURPOSE

Gamma-aminobutyric acid (GABA)-A/benzodiazepine receptors (BZRs) play an important inhibitory role in epileptogenesis. [123I]Iomazenil (123I-IMZ) is a specific ligand for central-type (or neuronal-type) BNRs and is available for single-photon emission computed tomography (SPECT) in brain disorders. We demonstrated alterations of central-type BZRs in human focal epilepsies and their experimental models.

METHODS

We examined interictal 123I-IMZ SPECT in patients with mesial temporal lobe epilepsy (MTLE; n = 19) with hippocampal sclerosis and neocortical epilepsy with focal cortical dysplasia (NE-CD; n = 18), and compared those with magnetic resonance imaging (MRI) and 123I-IMP SPECT (for regional cerebral blood flow). We also investigated in vitro autoradiography with (123)I-IMZ at various time courses in the intraamygdala kainate, amygdala kindling, and in-utero irradiation models.

RESULTS

In MTLE patients, the epileptogenic hippocampus often showed decreases in both 123I-IMZ and 123I-IMP SPECT. Consistent with those, marked reduction of 125I-IMZ binding was observed in hippocampal CA1-3 regions of the kainate model, which clearly paralleled pyramidal neuronal loss. In contrast, 125I-IMZ binding was increased in the dentate gyrus at 1 month but returned to the normal level at 3-6 months, when frequent spontaneous seizures appeared. The amygdala-kindling model demonstrated similar increases in 125I-IMZ binding in the dentate gyrus without any changes in other brain regions. In NE-CD patients, the epileptogenic foci showed decreased 123I-IMZ binding with relatively normal 123I-IMP SPECT. 125I-IMZ binding also was decreased in the cerebral cortex, hippocampus (areas CA1, 2, and 4), and caudate/putamen of the in-utero irradiation model.

CONCLUSIONS

These results indicate that central-type BZRs neuroimaging is useful for detection of epileptogenic foci, but their alterations differ between epilepsy subtypes and time-courses.

Quantitative evaluation of central-type benzodiazepine receptors with [(125)I] Iomazenil in experimental epileptogenesis. I. The rat kainate model of temporal lobe epilepsy

This study aimed at quantitatively evaluating hippocampal central-type benzodiazepine receptors (BZRs) in the kainate model of temporal lobe epilepsy (TLE) by in vitro autoradiography (ARG) using [(125)I] Iomazenil (IMZ) specific ligand for central-type BZRs. Kainate (1 microg/0.5 microl) was injected into the left amygdala to induce limbic status epilepticus. One, three, or six months after injection, in vitro ARG with [(125)I] IMZ and cell counts were performed in the hippocampal CA1-4 regions and dentate gyrus ipsilateral to the kainate injection site, and were compared with the vehicle-injected control group. In all kainate-treated rats, clear pyramidal neuron loss was observed in left hippocampal areas CA1-4. Compared with the control group, progressive reduction of [(125)I] IMZ binding was also observed. This resulted in a marked binding decrease paralleling pyramidal neuron loss in hippocampal areas CA1 (down to 83% of control), CA2 (76%), CA3 (75%), and CA4 (90%) at 6 months after kainate administration. Conversely, [(125)I] IMZ binding significantly increased in the dentate gyrus (up to 106% of control) at 1 month, but returned to nearly normal at 3-6 months. These results suggest that central-type BZR neuroimaging is useful in detecting hippocampal sclerosis in the mesial TLE, though central BZR alterations differ depending on hippocampal subfields and post-seizure time-courses.

Quantitative evaluation of central-type benzodiazepine receptors with [125I]Iomazenil in experimental epileptogenesis: II. The rat cortical dysplasia model

[(123)I]Iomazenil (IMZ) is a specific ligand for central-type benzodiazepine receptors (BZRs) and is available for single photon emission computed tomography (SPECT) to detect epileptogenic foci. We have recently demonstrated time-dependent alterations of [(125)I]IMZ binding in the rat kainate model of temporal lobe epilepsy. Quantitative evaluation of central-type benzodiazepine receptors with [(125)I]Iomazenil in experimental epileptogenesis. I. The rat kainate model of temporal lobe epilepsy. In the present study, we investigated regional changes in central-type BZRs in the cortical dysplasia (CD) model of epilepsy in rats. Pregnant rats were irradiated at day 17 of gestation with 1.2 Gy to produce CD in their pups, and in vitro autoradiography with [(125)I]IMZ was performed at 8 weeks after birth. Intact rats at the same age were used as controls. [(125)I]IMZ binding was significantly decreased in various cortical regions of the in utero irradiated rats, including the bilateral frontal cortex (down to 92-93% of control), cingulate cortex (91-92%), hippocampal areas CA1 (95%), CA2 (94-95%) and CA4 (95-96%), and caudate/putamen (90-94%). In addition, amygdala-kindling was significantly facilitated in the CD model, especially during the late phase of kindling, suggesting seizure susceptibility of this model. These results may replicate the clinical usefulness of central-type BZRs neuroimaging for detection of human epileptogenic CD and indicate dysfunction of GABA-A/BZR-mediated inhibition responsible for the seizure susceptibility.

[Metabolism of 123I-FP-CIT in humans]

The metabolism of N-(3-fluoropropyl)-2 beta-carbomethoxy-3 beta-(4-iodophenyl)nortropane (123I) (123I-FP-CIT) in healthy humans was studied. Plasma and urine samples, obtained after i.v. administration of 123I-FP-CIT, were analyzed using the two-dimensional thin-layer chromatography technique. Eleven radiochemical components were detected in both plasma and urine, and four of them were the parent 123I-FP-CIT and its metabolites, N-(3-fluoropropyl)-2 beta-carboxy-3 beta-(4-iodophenyl)nortropane (123I) (123I-acid), 2 beta-carboxy-3 beta-(4-iodophenyl)nortropane (123I) (123I-nor-acid) and 2 beta-carbomethoxy-3 beta-(4-iodophenyl)nortropane (123I) (123I-nor-CIT). These four identified radiochemical components occupied about 80% or more in ratio of the radiochemical components in the plasma and urine. In the metabolites of 123I-FP-CIT, the high polar metabolites--123I-acid and 123I-nor-acid--were found to be the major components, while lipophilic 123I-nor-CIT was a minor component. Free iodide (123I-) was not found in the plasma or urine. Thus, the main metabolic reactions which 123I-FP-CIT undergoes in humans seem to be hydrolysis of the ester bond and N-dealkylation. In vivo deiodination of 123I-FP-CIT was found to be minimum. Current results suggest that the metabolites of 123I-FP-CIT hardly influence evaluation of the dopamine transporter in the human brain.

Brain acetylcholinesterase activity: validation of a PET tracer in a rat model of Alzheimer's disease

We developed three radioactive acetylcholine analogs--N[14C]methyl-4-piperidyl acetate ([14C]MP4A), propionate ([14C]MP4P) and isobutyrate ([14C]MP4IB)--as radiotracers for measuring brain acetylcholinesterase (AchE) activity in vivo. The principle of our method is that the lipophilic analog diffuses into the brain where it is metabolized by AchE to produce a hydrophilic metabolite, which is trapped at the site of its production. The purpose of this study was to examine whether the tracers would have the sensitivity needed for early diagnosis of Alzheimer' disease using rats with a unilateral lesion in the nucleus basalis magnocellularis (NBM), an animal model of the cholinergic deficit in Alzheimer's disease.

METHODS

Rats with a unilateral NBM lesion were prepared, and the N[14C]methyl-4-piperidyl esters and N-Isopropyl-p-[123I]iodoamphetamine([123I]IMP were injected intravenously 30 and 2 min, respectively, before the rats were killed. Uptake of 14C and 123I and AchE activity in the lesioned and unlesioned (control) sides of the cortex were measured simultaneously.

RESULTS

The NBM lesion showed reduced cortical AchE activity by 30%-50%, with no side-to-side differences in [123I]MP uptake. Autoradiographic studies showed that uptake of 14C from [14C]MP4A and [14C]MP4P was significantly lower in the lesioned than unlesioned side of the cortex, which agreed well with the AchE histochemical staining patterns. Tissue dissection studies showed different uptake changes for the three compounds when AchE activity in the lesioned side of the cortex was reduced by 50%: 14C uptake from [14C]MP4P, [14C]MP4A and [14C]MP4IB was reduced by 27%, 21% and 7.3%, respectively. Theoretical analysis of the observed sensitivities of the tracers in relation to their in vitro enzymatic properties indicated that tracer sensitivity was highly dependent on the enzymatic hydrolysis rate of the tracer.

CONCLUSION

The [14C]MP4A and [14C]MP4P esters had sufficient sensitivity to enable AchE activity changes in the rat cortex of less than 50% to be detected, indicating that the present method is applicable to PET diagnosis of Alzheimer's disease.

Design and evaluation of radioactive acetylcholine analogs for mapping brain acetylcholinesterase (AchE) in vivo

For mapping brain acetylcholinesterase (AchE) in vivo, seven radioactive acetylcholine analogs, N-[14C]methylpiperidyl-3- and 4-acetates, propionates, isobutyrates, and 3-butyrate were newly synthesized and evaluated in mice. The esters readily entered the brain and were hydrolyzed into the hydrophilic metabolite, which was trapped. In brain homogenates, the esters showed a wide range of enzymatic reactivity (about 40-fold), and high specificity for AchE (more than 82%) except the butyrate. Intra-brain distribution of the esters reflected a pattern of AchE activity.