Luigia Grazia Fresu

Autoradiographic localization of α5 subunit-containing GABAA receptors in rat brain

Abstract Multiple subtypes of GABAA receptors are expressed in the rat central nervous system (CNS). To determine the distribution and proportion of α5 subunit containing receptors, quantitative autoradiographic analyses were performed with both [ 3 H ] L-655,708 and [ 3 H ] Ro15-1788, an α5 selective and a non selective benzodiazepine binding site ligand, respectively. High densities of [ 3 H ] L-655,708 binding sites were observed in hippocampus and olfactory bulb, where α5 receptors accounted for 20–35% of total [ 3 H ] Ro15-1788 binding sites. Low levels of [ 3 H ] L-655,708 sites were associated with the cortex as well as amygdala, thalamic, hypothalamic and midbrain nuclei. These observations indicate that although [ 3 H ] L-655,708 binding sites have an overall low expression in rat CNS, they may contribute significantly to GABAergic inhibition in specific brain regions.

Cellular defence mechanisms in the striatum of young and aged rats subchronically exposed to manganese

A deficiency of striatal dopamine (DA) is generally accepted as an expression of manganese (Mn) toxicity in experimental animals. Since compromised cellular defence mechanisms may be involved in Mn neurotoxicity, we investigated the response of the neuronal antioxidant system [ascorbic acid (AA) oxidation, glutathione (GSH) and uric acid levels] and neurochemical changes in the striatum in aged rats exposed to Mn. Levels of dopamine (DA), dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), 5-hydroxytryptamine (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), AA, dehydroascorbic acid (DHAA), GSH and uric acid were determined after subchronic oral exposure to MnCl2 200 mg/kg (3-month-old rats) and 30-100-200 mg/kg (20-month-old-rats). Aged rats had basal levels of striatal DA, DOPAC, HVA, 5-HT, 5-HIAA, GSH and AA lower than those of young rats. In the striatum of aged rats, Mn induced biphasic changes in the levels of DA, DOPAC, HVA (an increase at the lower dose and a decrease at the higher dose) and DHAA (opposite changes). Mn decreased GSH levels and increased uric acid levels both in the striatum and in synaptosomes in all groups of aged rats. All of these parameters were affected to a lesser extent in young rats. In conclusion, the response of cellular defence mechanisms in aged rats is consistent with a Mn-induced increase in the formation of reactive oxygen species. An age-related impairment of the neuronal antioxidant system may play an enabling role in Mn neurotoxicity.

Correlation between 1-methyl-4-phenylpyridinium ion (MPP+) levels, ascorbic acid oxidation and glutathione levels in the striatal synaptosomes of the 1-methyl-4-phenyl-1,2,3-6-tetrahydropyridine (MPTP)-treated rat

In 6-month-old male Wistar rats, levels of dopamine (DA), dihydroxyphenylacetic acid (DOPAC), ascorbic acid (AA), dehydroascorbic acid (DHAA), uric acid, glutathione (GSH) and 1-methyl-4-phenylpyridinium ion (MPP+) were determined by HPLC in the crude striatal synaptosomal fraction after single injections of MPTP 35 mg/kg i.p. 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) induced a 32.5% death rate within 15 min to 10 h. Groups of surviving rats were sacrificed 1, 3, 8 and 24 h after MPTP. MPTP significantly increased levels of DHAA and uric acid and decreased levels of DOPAC and GSH. Individual synaptosomal levels of MPP+ were correlated inversely with DOPAC (r = -0.601, P < 0.002) and GSH levels (r = -0.496, P < 0.02) and directly with levels of uric acid (r = +0.627, P < 0.001); these latter, in turn, were correlated with DHAA (r = +0.418, P < 0.05) and GSH levels (r = -0.357, P = 0.07). In conclusion, the response of the endogenous antioxidant system (increase in AA oxidation, decrease in GSH levels) correlates well with the MPTP-induced increase in uric acid levels and provides further evidence for a mechanism of MPTP neurotoxicity involving oxidative stress produced by xanthine oxidase.

Dopaminergic system activity and cellular defense mechanisms in the striatum and striatal synaptosomes of the rat subchronically exposed to manganese

In 6-month-old male Wistar rats, levels of dopamine (DA), dihydroxyphenylacetic acid (DOPAC), ascorbic acid (AA), dehydroascorbic acid (DHAA), uric acid and glutathione (GSH) were determined by HPLC in the striatum and striatal synaptosomes after subchronic oral exposure to MnCl2 50–100–150 mg/kg. Mn significantly decreased levels of DA and GSH and increased levels of DHAA and uric acid both in the striatum and synaptosomes. In synaptosomes, individual total Mn doses/rat were directly correlated with individual DOPAC/DA ratio values (r=+0.647), uric acid (r=+0.532) and DHAA levels (r=+0.889) and inversely correlated with DA (r=−0.757) and GSH levels (r=−0.608). In turn, GSH levels were inversely correlated with uric acid (r=−0.451) and DHAA levels (r=−0.460). In conclusion, the response of striatal cellular defense mechanisms (increase in AA oxidation, decrease in GSH levels) correlated well with changes in markers of dopaminergic system activity and increase in uric acid levels. The latter provides evidence of an Mn-induced oxidative stress mediated by xanthine oxidase.

Effect of morphine on striatal dopamine metabolism and ascorbic and uric acid release in freely moving rats

Recent ex vivo findings have shown that morphine increases dopamine (DA) and xanthine oxidative metabolism and ascorbic acid (AA) oxidation in the rat striatum. In the present study, we evaluated the effects of subcutaneous daily morphine (20 mg/kg) administration on DA, dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), AA and uric acid in the striatum of freely moving rats using microdialysis. Dialysates were assayed by high performance liquid chromatography with electrochemical detection. On the first day, morphine administration caused a significant increase in extracellular DA, DOPAC, HVA, AA and uric acid concentrations over a 3 h period after morphine. In all treated rats (n = 7), individual concentrations of DOPAC + HVA were directly correlated with individual AA and uric acid concentrations. Last morphine administration on the 4th day increased DOPAC, HVA, AA and uric acid concentrations but failed to increase those of DA. Individual DOPAC + HVA concentrations were still directly correlated with individual AA and uric acid concentrations. These results suggest that systemic morphine increases both striatal DA release and DA and xanthine oxidative metabolism. Only the former effect undergoes tolerance. The increase in DA oxidative metabolism is highly correlated with that of xanthine. The subsequent enhancement in reactive oxygen species production may account for the increase in extracellular AA.

Effects of morphine treatment and withdrawal on striatal and limbic monoaminergic activity and ascorbic acid oxidation in the rat.

Since ascorbic acid (AA) reportedly suppresses tolerance to and dependence on morphine in humans and rodents, levels of dopamine (DA), dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), 3-methoxytyramine (3-MT), 5-hydroxytryptamine (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), AA, dehydroascorbic acid (DHAA), uric acid, xanthine, hypoxanthine, glutamate and gamma-aminobutyric acid (GABA) were determined by high-pressure liquid chromatography (HPLC) in the striatum and in the limbic forebrain of the rat following morphine treatment (single or repeated) and withdrawal. Single morphine administration (20 mg/kg s.c.) increased DOPAC + HVA/DA, 5-HIAA/5-HT and DHAA/AA ratios, uric acid levels, and decreased xanthine, hypoxanthine, glutamate and GABA levels in both regions. 3-MT levels were decreased in the striatum and increased in the limbic forebrain. After 7 days of morphine treatment, striatal DOPAC + HVA/DA and DHAA/AA ratios and uric acid levels were still higher and striatal and limbic xanthine levels still lower than in controls, while all other parameters were in the range of control values in both regions. Morphine treatment also increased the glutamate/GABA ratio in the striatum. In all morphine-treated rats, individual striatal DOPAC + HVA/DA and DHAA/AA ratio values were directly correlated. After a 48 h withdrawal period, both striatal AA oxidation and glutamate/GABA ratio further increased; limbic 3-MT levels further decreased, while all other parameters did not differ from control values. We conclude that: (i) tolerance to morphine-induced increase in hypoxanthine, xanthine and AA oxidation develops in the limbic forebrain faster than in the striatum; (ii) the morphine-induced increase in striatal and limbic AA oxidation may be considered a consequence of increased formation of reactive oxygen species due to increased DA, hypoxanthine and xanthine oxidative metabolism; (iii) a striatal excitotoxic imbalance characterizes the withdrawal state and may be taken into account to explain the further increase in striatal AA oxidation.

Plasma membrane calcium ATPase isoforms in astrocytes.

The plasma membrane Ca2+‐ATPase (PMCA) is an essential component of the machinery responsible for cellular Ca2+ homeostasis. Together with the Na+/Ca2+ exchanger, the plasma membrane Ca2+‐ATPase (PMCA) is responsible for the extrusion of Ca2+ from the cytosol. Although both PMCAs and Na+/Ca2+ exchangers are present in high amounts in the brain, it is thought that only the latter localize to glia. This study investigates whether PMCAs are also present in astrocytes and thus are components of Ca2+ signalling in this cell type.

Calcineurin controls the expression of numerous genes in cerebellar granule cells

The Ca(2+)/calmodulin-dependent phosphatase calcineurin plays a crucial role in gene expression in different cell types such as T-lymphocytes, cardiac myocytes, and smooth muscle cells. A possible role for calcineurin in gene expression was recently found in neurons, where calcineurin regulates the expression of several genes involved in Ca(2+) homeostasis. To detect additional genes regulated in a calcineurin-dependent way in neurons we analysed gene expression profiles of cerebellar granule cells cultured in depolarising conditions in the presence or absence of the calcineurin inhibitory agents FK506 and CsA. Using oligonucleotide arrays we identified 34 genes that are differentially expressed between the samples and confirmed the calcineurin-dependent regulation of some of these genes by RT-PCR. Therefore, our results, which are likely not to be comprehensive, suggest that calcineurin plays a fundamental role in neuronal gene expression by either activating or repressing the expression of genes such as receptors, transcription factors, and signalling molecules.

Effects of ageing on 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) neurotoxic effects on striatum and brainstem in the rat

In 3- and 18-month-old male Wistar rats, levels of dopamine (DA), dihydroxyphenylacetic acid (DOPAC), ascorbic acid (AA), dehydroascorbic acid (DHAA), noradrenaline (NA), uric acid, glutathione (GSH) and 1-methyl-4-phenylpyridinium ion (MPP+) were determined by HPLC in the striatum and/or in the brainstem 24 h after single injections of MPTP (12-35 mg/kg i.p.). Aged rats had lower baseline levels of AA and GSH, compared to young rats. In aged rats, MPTP 35 mg/kg induced a 70% death rate and a decrease in striatal DOPAC/DA ratio which was significantly correlated to MPP+ concentrations (r = -0.840, P < 0.005); in addition, MPTP did not increase AA oxidation. In the brainstem, the MPTP-induced decrease in NA levels and increase in uric acid levels were significantly correlated to the MPP+ concentrations (r = -0.709, P < 0.05, and r = +0.888, P < 0.001, respectively). In conclusion, evidence is given of a mechanism of toxicity of MPTP involving oxidative stress produced by xanthine oxidase; in addition, in aged rats the neuronal antioxidant system (levels of AA and GSH) is considerably lower than in young rats and may play an enabling role in the MPTP age-related neurotoxic effects on striatum and brainstem.

Enhanced Peroxisome Proliferator-Activated Receptor-γ Expression in Monocyte/Macrophages from Coronary Artery Disease Patients and Possible Gender Differences

Peroxisome proliferator-activated receptor (PPAR) activation reduces inflammation and atherosclerosis, but recent evidence raised concerns about its beneficial clinical effects. However, the effects of gender on PPAR expression and basal cytokine release have not been investigated. In the present study, we evaluated PPAR-γ and -α expression, as well as cytokine release, in monocyte/macrophages from 15 male and 15 female patients with coronary artery disease (CAD) in comparison with healthy controls. Both expression and activation of PPAR-α and PPAR-γ proteins were evaluated by Western blot and electrophoretic mobility shift assay. Gene expression was evaluated by real-time polymerase chain reaction; cytokine release was measured by enzyme-linked immunosorbent assay. Monocyte/macrophages of CAD patients yielded a constitutively enhanced (approximately 10-fold; p < 0.001) protein expression of PPAR-γ, but not PPAR-α, compared with healthy controls. Evaluation of PPAR-γ gene expression showed a 60-fold increase in monocytes from CAD patients, compared with healthy donors. Moreover, monocytes spontaneously released higher amounts of proinflammatory cytokines than macrophages. It is interesting that monocytes from CAD females expressed significantly higher levels of PPAR-γ protein compared with male patients (p < 0.05) and showed the lowest basal release of tumor necrosis factor-α. These results indicate that the expression of PPAR-γ is significantly higher in CAD patients than in healthy donors and that, together with cytokine release, it seems to be gender-related. In fact, CAD women demonstrated the highest PPAR-γ expression and the lowest cytokine release. Such differences may, in part, modulate the response to PPAR-γ activators.