Diazepam protects against rat hippocampal neuronal cell death induced by antisense oligodeoxynucleotide to GABA(A) receptor gamma2 subunit

Effects of transcranial focal electrical stimulation alone and associated with a sub-effective dose of diazepam on pilocarpine-induced status epilepticus and subsequent neuronal damage in rats

Experiments were conducted to evaluate the effects of transcranial focal electrical stimulation (TFS) applied via tripolar concentric ring electrodes, alone and associated with a sub-effective dose of diazepam (DZP) on the expression of status epilepticus (SE) induced by lithium-pilocarpine (LP) and subsequent neuronal damage in the hippocampus. Immediately before pilocarpine injection, male Wistar rats received TFS (300Hz, 200-μs biphasic square charge-balanced 50-mA constant current pulses for 2min) alone or combined with a sub-effective dose of DZP (0.41mg/kg, i.p.). In contrast with DZP or TFS alone, DZP plus TFS reduced the incidence of, and enhanced the latency to, mild and severe generalized seizures and SE induced by LP. These effects were associated with a significant reduction in the number of degenerated neurons in the hippocampus. The present study supports the notion that TFS combined with sub-effective doses of DZP may represent a therapeutic tool to induce anticonvulsant effects and reduce the SE-induced neuronal damage.

Effect of diazepam treatment and its withdrawal on pro/antioxidative processes in rat brain

Exploratory studies were undertaken to ascertain the role of pro/antioxidative processes during a 3 weeks administration of low sub-toxic dose of diazepam and its withdrawal. Rats were administered 3 mg/kg diazepam for 21 consecutive days and the changes observed in different regions of rat brain at the sub-cellular level. Mitochondria from cerebrum showed a 27% lowering of TBARS whereas those from cerebellum and brain stem showed 48 and 24% enhanced MDA levels respectively. No significant alteration in the SOD isozymes was observed after the dose schedule. The mitochondrial glutathione reductase (GR) activity showed a decrease in all the regions with maximum decrease (36%) recorded in brain stem while post mitochondrial fraction showed significant lowering in cerebrum (37%). Total -SH content increased in all the three regions with maximum enhancement recorded in cerebellum while the free thiol content also showed significant changes (p < 0.001) in cerebellum and brain stem. One week after the withdrawal of the drug MDA levels decreased by 38% in cerebrum and 53% each in mitochondrial fractions of cerebellum and brain stem. Regional heterogeneity in response was also observed in the post mitochondrial fractions. Mn-SOD showed lowered activity in cerebellum (22%) and in brain stem (15%). The mitochondrial GR activity decreased in all the regions being highest in cerebrum with no significant change in post mitochondrial fractions. The total and free -SH content in the withdrawn animals increased by 46% in cerebellum with no change in the other two regions. The results indicate towards lower oxidative phenomenon during 3 weeks treatment with diazepam while abrupt withdrawal causes lowering of antioxidant defenses which showed regional heterogeneity. A decrease in peroxidative decomposition of polyunsaturated fatty acids of membranes was observed on withdrawal, which could be due to stabilisation of membranes after long-term binding of diazepam.

Heterogeneity of hippocampal GABA(A) receptors: regulation by corticosterone

Chronic stressors produce changes in hippocampal neurochemistry, neuronal morphology, and hippocampal-dependent learning and memory processes. In rats, stress-induced changes in CA3 apical dendritic structure are mediated by corticosterone (CORT) acting, in part, on excitatory amino acid neurotransmission. CORT also alters GABA-mediated inhibitory neurotransmission, so the GABA(A) receptor system may also contribute to dendritic remodeling and other stress-related changes in hippocampal function. A previous study indicated that chronic CORT treatment produces complex changes in GABA(A) receptor subunit mRNA levels, so we hypothesized that CORT alters the pharmacological properties of hippocampal GABA(A) receptors. To test this, adult male rats were treated with CORT or vehicle pellets for 10 d, after which we quantified [(35)S]t-butylbicyclophosphorothionate ([(35)S]TBPS) and [(3)H]flunitrazepam binding to GABA(A) receptors using in vitro receptor autoradiography. Pharmacological properties of receptors were assessed by examining the allosteric regulation of binding at both sites by GABA and 5alpha-pregnane-3alpha,21-diol-20-one (THDOC), an endogenous anxiolytic steroid. We found striking regional differences in the modulation of [(35)S]TBPS binding, particularly between strata radiatum and strata oriens, suggesting a functional heterogeneity among hippocampal GABA(A) receptors even within the apical versus basal dendrites of pyramidal neurons. Furthermore, we found that CORT treatment decreased the negative modulation of hippocampal [(35)S]TBPS binding by both GABA and THDOC and increased the enhancement of [(3)H]flunitrazepam binding by GABA and THDOC in the dentate gyrus. Together, these data suggest that prolonged exposure to stress levels of corticosteroids may alter hippocampal inhibitory tone by regulating the pharmacological properties of GABA(A) receptors in discrete dendritic subfields.

Intrahippocampal infusion of antisense oligodeoxynucleotide to the GABA(A) receptor gamma2 subunit enhances neuropeptide Y gene expression

The effects of hippocampal treatment with a phosphorothioate oligodeoxynucleotide (ODN) antisense to the gamma-aminobutyric acid (GABA)A receptor gamma2 subunit on neuropeptide Y (NPY) were studied. Adult male Wistar rats were treated with unilateral intrahippocampal infusion of gamma2 subunit antisense ODN for 5 days. Rats infused with mismatch ODN and naïve rats served as controls. Brain sections were analysed for levels of NPY mRNA by in situ hybridisation, NPY-immunoreactivity (NPY-ir) by means of immunocytochemistry, and specific NPY binding sites by in vitro receptor autoradiography. Following infusion of antisense ODN, a marked increase in cytoplasmic NPY-ir was observed in hilar neurones of the fascia dentata. Further, intense NPY-ir was visualised in the mossy fibres and in cell bodies of the entorhinal cortex and throughout the neocortex. High levels of NPY mRNA were detected in the same cortical areas of antisense treated rats. A very large increase was observed in the piriform and parietal areas. NPY gene expression also occurred in the granular cell layer, in which no NPY mRNA could be detected in normal animals. The level and distribution of cells displaying high levels of NPY mRNA differed among animals, perhaps as a result of the distinct anatomical location of ODN infusion. Finally, hippocampal levels of NPY specific binding increased, suggesting that NPY neurotransmission is markedly increased. These findings are reminiscent of reported changes in the expression of NPY mRNA and immunoreactivity in conditions of increased neuronal excitation and support the usefulness of the present animal model for the study of epileptic phenomena.

GABAA receptor antisense epilepsy: histological changes following infusion of antisense oligodeoxynucleotide to GABAA receptor gamma 2 subunit into rat hippocampus

A deficiency of neuronal inhibition mediated by gamma-aminobutyric acid (GABA) via the GABAA receptor complex has been hypothesised to be a central factor in epileptogenesis. Intrahippocampal infusion of antisense oligodeoxynucleotide (ODN) to the GABAA receptor gamma 2 subunit in rats leads to electrographic limbic status epilepticus. In this model, epileptic phenomena are accompanied by loss of hippocampal neurones. The purpose of the present study was to investigate the time-course of morphological changes following hippocampal antisense 'knockdown' of the GABAA receptor gamma 2 subunit. gamma 2 subunit antisense ODN was infused continuously into the right hippocampus for periods between 1 and 5 days. After about 4 days of infusion, pronounced neurodegenerative changes were consistently observed within the ipsilateral hippocampus. In general, marked loss of CA3 pyramidal cells was found. The notion that the histological changes induced by the antisense ODN were specific to the applied ODN sequence was supported by the finding that a mismatch control ODN did not induce neurodegenerative changes, except for a small lesion in the immediate vicinity of the infusion site. Extensive ipsilateral hippocampal infiltration with monocytes and macrophages was a feature of antisense ODN infusion, but was considerably less pronounced after the infusion of control ODN. Immunocytochemistry using an antibody labeling glial fibrillary acidic protein (GFAP), revealed marked astroglial hypertrophy/proliferation after 4 days of antisense treatment, i.e., coincident with the development of neurodegeneration, in the ipsilateral hippocampus. At this time GFAP-immunoreactivity was also evident in the contralateral hippocampus, indicating contralateral spread of seizure activity.

Transcriptional regulation of GABAA receptor gamma2 subunit gene

We have cloned the promoter regions of the genes for the mouse and human gamma2 subunits of the type A receptors for gamma-aminobutyric acid (GABA). For the mouse, the two major transcription start sites were at +1 (by definition) and +43, as established by rapid amplification of cDNA ends (RACE) and primer extension. This numbering places the start methionine at +297. There was no TATA or CCAAT box. Both mouse and human sequences have a candidate neuron-restrictive silencer element (NRSE) site in the first intron (+956 in mouse). We made assorted mouse-based promoter/reporter (luciferase) constructs starting from a core extending from -331 to +136, varying sizes at both ends, and including and excluding the putative NRSE and more proximal sequences. These were tested by transient transfection in several neuron-like and non-neuronal cell lines. Both proximal and distal downstream elements appeared to help direct expression to neuron-like cells, the NRSE in the intron, by repression in non-neurons, and a 24-bp portion of the 5' untranslated region starting at +113 (named GPE1) by preferentially promoting expression in neuron-like cells. Cotransfected human NRSF (transcription factor for NRSE) reduced reporter expression in neuron-like cells for constructs containing the NRSE in two locations. In gel mobility shift assays, the mouse gamma2 NRSE and a consensus NRSE both bound in vitro translated NRSF very similarly, and the NRSF gave the same major shifted band with the mouse gamma2 NRSE as was observed with nuclear extracts.

Differential changes in induced seizures after hippocampal treatment of rats with an antisense oligodeoxynucleotide to the GABA(A) receptor gamma2 subunit

Gamma-aminobutyric acid (GABA) is the principal inhibitory neurotransmitter in the brain. Impairment of GABAergic neurotransmission may be involved in the pathogenesis of epileptic phenomena. We have previously characterized biochemical and histological changes following unilateral intrahippocampal infusion of a phosphorothioate antisense oligodeoxynucleotide to the GABA(A) receptor gamma2 subunit in rats in vivo. The aim of the present study was to investigate the behavioral changes of rats following unilateral hippocampal antisense 'knockdown' of the GABA(A) receptor gamma2 subunit. Antisense, but not mismatch control oligodeoxynucleotide treated rats had a significant weight loss (10%) during 6 d of treatment. Antisense treated rats exhibited no changes in spontaneous behavior, including anxiety-like behavior as measured in the social interaction test, compared to mismatch oligodeoxynucleotide treated rats. However, antisense treated rats developed pronounced changes in induced seizure activity. Seizures induced by subcutaneously injected pentylenetetrazol were markedly accentuated in antisense treated rats compared to treatment naive rats, whereas mismatch treated rats showed a lower seizure score than that of naive rats. Antisense treated rats had a significantly elevated threshold for seizures induced by electrical stimulation in the maximal electroshock seizure threshold test. The results suggest that intrahippocampal infusion of antisense oligodeoxynucleotide to the GABA(A) receptor gamma2 subunit leads to specific alterations in the sensitivity to induced seizures. The results are viewed as consequences of selective down-regulation of GABA(A) receptors and diminished inhibitory neurotransmission in the hippocampus.