Monitoring Drug-Induced Neurodegeneration by Imaging of Peripheral Benzodiazepine Receptors

Sarin-induced brain damage in rats is attenuated by delayed administration of midazolam

Sarin poisoned rats display a hyper-cholinergic activity including hypersalivation, tremors, seizures and death. Here we studied the time and dose effects of midazolam treatment following nerve agent exposure. Rats were exposed to sarin (1.2 LD50, 108 μg/kg, im), and treated 1 min later with TMB4 and atropine (TA 7.5 and 5 mg/kg, im, respectively). Midazolam was injected either at 1 min (1 mg/kg, im), or 1 h later (1 or 5 mg/kg i.m.). Cortical seizures were monitored by electrocorticogram (ECoG). At 5 weeks, rats were assessed in a water maze task, and then their brains were extracted for biochemical analysis and histological evaluation. Results revealed a time and dose dependent effects of midazolam treatment. Rats treated with TA only displayed acute signs of sarin intoxication, 29% died within 24h and the ECoG showed seizures for several hours. Animals that received midazolam within 1 min survived with only minor clinical signs but with no biochemical, behavioral, or histological sequel. Animals that lived to receive midazolam at 1h (87%) survived and the effects of the delayed administration were dose dependent. Midazolam 5 mg/kg significantly counteracted the acute signs of intoxication and the impaired behavioral performance, attenuated some of the inflammatory response with no effect on morphological damage. Midazolam 1mg/kg showed only a slight tendency to modulate the cognitive function. In addition, the delayed administration of both midazolam doses significantly attenuated ECoG compared to TA treatment only. These results suggest that following prolonged seizure, high dose midazolam is beneficial in counteracting adverse effects of sarin poisoning.

Blood glutamate scavenging as a novel neuroprotective treatment for paraoxon intoxication

Organophosphate-induced brain damage is an irreversible neuronal injury, likely because there is no pharmacological treatment to prevent or block secondary damage processes. The presence of free glutamate (Glu) in the brain has a substantial role in the propagation and maintenance of organophosphate-induced seizures, thus contributing to the secondary brain damage. This report describes for the first time the ability of blood glutamate scavengers (BGS) oxaloacetic acid in combination with glutamate oxaloacetate transaminase to reduce the neuronal damage in an animal model of paraoxon (PO) intoxication. Our method causes a rapid decrease of blood Glu levels and creates a gradient that leads to the efflux of the excess brain Glu into the blood, thus reducing neurotoxicity. We demonstrated that BGS treatment significantly prevented the peripheral benzodiazepine receptor (PBR) density elevation, after PO exposure. Furthermore, we showed that BGS was able to rescue neurons in the piriform cortex of the treated rats. In conclusion, these results suggest that treatment with BGS has a neuroprotective effect in the PO intoxication. This is the first time that this approach is used in PO intoxication and it may be of high clinical significance for the future treatment of the secondary neurologic damage post organophosphates exposure.

Impact of ethanol on the developing GABAergic system

Alcohol intake during pregnancy has a tremendous impact on the developing brain. Embryonic and early postnatal alcohol exposures have been investigated experimentally to elucidate the fetal alcohol spectrum disorders' (FASD) milieu, and new data have emerged to support a devastating effect on the GABAergic system in the adult and developing nervous system. GABA is a predominantly inhibitory neurotransmitter that during development excites neurons and orchestrates several developmental processes such as proliferation, migration, differentiation, and synaptogenesis. This review summarizes and brings new data on neurodevelopmental aspects of the GABAergic system with FASD in experimental telencephalic models.

Distinct cell proliferation events during abstinence after alcohol dependence: microglia proliferation precedes neurogenesis

Excessive alcohol intake characteristic of Alcohol Use Disorders (AUDs) produces neurodegeneration that may recover with abstinence. The mechanism of regeneration is unclear, however neurogenesis from neural stem/progenitor cells is a feasible mechanism of structural plasticity. Therefore, a timecourse of cell proliferation was examined in a rat model of an AUD and showed a striking burst in cell proliferation at 2 days of abstinence preceding the previously reported neurogenic proliferation at 7 days. New cells at 2 days, assessed by bromo-deoxy-uridine incorporation and endogenous markers, were observed throughout hippocampus and cortex. Although the majority of these new cells did not become neurons, neurogenesis was not altered at this specific time point. These new cells expressed a microglia-specific marker, Iba-1, and survived at least 2 months. This first report of microglia proliferation in a model of an AUD suggests that microgliosis could contribute to volume recovery in non-neurogenic regions during abstinence.

Methamphetamine induces long-term changes in GABAA receptor alpha2 subunit and GAD67 expression

The present study investigated whether GABA(A) receptor alpha2 subunit and GAD(67) are involved in chronic high dose methamphetamine (METH)-induced sensitization and neurotoxicity. The METH sensitization was established in rats by 7-day pump infusion plus daily injection (25mg/kg/day) and a subsequent 28-day withdrawal period. Behavioral sensitization was assessed by behavioral ratings after challenge with METH (0.5mg/kg). The neurotoxicity was evaluated by the expression of glial fibrillary acidic protein (GFAP). Western blot assay showed that METH sensitization decreases GABA(A) alpha2 subunit and GAD(67) protein levels in the nucleus accumbens (NAc) core and shell, and conversely, these proteins were increased in the caudate. An upregulation of GFAP expression was observed in the caudate, but not in the NAc core and shell. These data suggest that inhibition of GABA transmission in the NAc is related to METH behavioral sensitization, whereas activation of GABA transmission in the caudate is associated with METH-induced neurotoxicity.

Immunohistochemical expression of peripheral benzodiazepine receptors in human astrocytomas and its correlation with grade of malignancy, proliferation, apoptosis and survival

Peripheral benzodiazepine receptors (PBR) are widely distributed in peripheral tissues, astrocytes, and microglia of the brain. They are involved in apoptosis, proliferation, and many other processes, such as steroidogenesis in adrenal glands, male and female gonads, biological adaptation to stress, etc. It has been established that the expression of PBR in astrocytomas is higher than in the normal brain. The goal of this study was to explore the correlation of the immunohistochemical expression of PBR in astrocytomas with the grade of malignancy and rates of apoptosis, proliferation and survival. In 130 cases of astrocytomas (25 grade I, 25 grade II, 20 grade III, 60 grade IV), paraffin sections were stained immunohistochemically for PBR and MIB-1(Ki-67). TUNEL assay was used for evaluation of apoptosis. It was found that the intensity and extent of staining for PBR had a strong direct correlation with the grade of malignancy of the tumor, along with proliferative and apoptotic indices. The highest expression of PBR was in glioblastomas grade IV, especially around areas of necrosis. There was a strong negative correlation between PBR expression and survival. The results of this study may be applied in the pathological diagnosis of astrocytomas as an additional clue in establishing tumor grade; they may be used in the imaging of astrocytomas, both for diagnosis and follow-up, by the application of positron emission tomography scanning with PBR specific ligands. Targeting of PBR in high-grade gliomas may be a promising approach, achieving more specific anti-tumor effect.

Peripheral-type benzodiazepine receptor in neurosteroid biosynthesis, neuropathology and neurological disorders

The peripheral-type benzodiazepine receptor is a mitochondrial protein expressed at high levels in steroid synthesizing tissues, including the glial cells of the brain. Peripheral-type benzodiazepine receptor binds cholesterol with high affinity and is a key element of the cholesterol mitochondrial import machinery responsible for supplying the substrate cholesterol to the first steroidogenic enzyme, thus initiating and maintaining neurosteroid biosynthesis. Neurosteroid formation and metabolism of steroid intermediates are critical components of normal brain function. Peripheral-type benzodiazepine receptor also binds with high affinity various classes of compounds. Upon ligand activation peripheral-type benzodiazepine receptor-dependent cholesterol transport into mitochondria is accelerated leading in increased formation of neuroactive steroids. These steroids, such as allopregnanolone, have been shown to be involved in various neurological disorders, such as anxiety and mood disorders. Thus, peripheral-type benzodiazepine receptor drug ligand-induced neuroactive steroid formation offers a means to regulate brain dysfunction. Peripheral-type benzodiazepine receptor basal expression is upregulated in a number of neuropathologies, including gliomas and neurodegenerative disorders, as well as in various forms of brain injury and inflammation. In Alzheimer's disease pathology neurosteroid biosynthesis is altered and a decrease in the intermediate 22R-hydroxycholesterol levels is observed. This steroid was found to exert neuroprotective properties against beta-amyloid neurotoxicity. Based on this observation, a stable spirostenol derivative showing to display neuroprotective properties was identified, suggesting that compounds developed based on critical intermediates of neurosteroid biosynthesis could offer novel means for neuroprotection. In conclusion, changes in peripheral-type benzodiazepine receptor and neurosteroid levels are part of the phenotype seen in neuropathology and neurological disorders and offer potential targets for new therapies.

Methamphetamine-induced neuronal apoptosis involves the activation of multiple death pathways. Review

The abuse of the illicit drug methamphetamine (METH) is a major concern because it can cause terminal degeneration and neuronal cell death in the brain. METH-induced cell death occurs via processes that resemble apoptosis. In the present review, we discuss the role of various apoptotic events in the causation of METH-induced neuronal apoptosis in vitro and in vivo. Studies using comprehensive approaches to gene expression profiling have allowed for the identification of several genes that are up-regulated or down-regulated after an apoptosis-inducing dose of the drug. Further experiments have also documented the fact that the drug can cause demise of striatal enkephalinergic neurons by cross-talks between mitochondria-, endoplasmic reticulum- and receptor-mediated apoptotic events. These neuropathological observations have also been reported in models of drug-induced neuroplastic alterations used to mimic drug addiction (Nestler, 2001).