Walaiporn Tongjaroenbuangam

Neuroprotective effects of quercetin, rutin and okra (Abelmoschus esculentus Linn.) in dexamethasone-treated mice

The administration of dexamethasone, a synthetic glucocorticoid receptor agonist, causes neuronal death in the CA3 layer of the hippocampus, which has been associated with learning and memory impairments. This study aimed to examine the ability of okra (Abelmoschus esculentus Linn.) extract and its derivatives (quercetin and rutin) to protect neuronal function and improve learning and memory deficits in mice subjected to dexamethasone treatment. Learning and memory functions in mice were examined using the Morris water maze test. The results showed that the mice treated with dexamethasone had prolonged water maze performance latencies and shorter time spent in the target quadrant while mice pretreated with quercetin, rutin or okra extract prior to dexamethasone treatment showed shorter latencies and longer time spent in target quadrant. Morphological changes in pyramidal neurons were observed in the dexamethasone treated group. The number of CA3 hippocampal neurons was significantly lower while pretreated with quercetin, rutin or okra attenuated this change. Prolonged treatment with dexamethasone altered NMDA receptor expression in the hippocampus. Pretreatment with quercetin, rutin or okra extract prevented the reduction in NMDA receptor expression. Dentate gyrus (DG) cell proliferation was examined using the 5-bromo-2-deoxyuridine (BrdU) immunohistochemistry technique. The number of BrdU-immunopositive cells was significantly reduced in dexamethasone-treated mice compared to control mice. Pretreatment with okra extract, either quercetin or rutin was found to restore BrdU-immunoreactivity in the dentate gyrus. These findings suggest that quercetin, rutin and okra extract treatments reversed cognitive deficits, including impaired dentate gyrus (DG) cell proliferation, and protected against morphological changes in the CA3 region in dexamethasone-treated mice. The precise mechanism of the neuroprotective effect of these plant extracts should be further investigated.

Melatonin attenuates dexamethasone-induced spatial memory impairment and dexamethasone-induced reduction of synaptic protein expressions in the mouse brain

Chronic stress or prolonged exposure to high levels of glucocorticoid induces neuropathological alterations, such as dendritic atrophy of hippocampal or cortical neurons. The chronic administration of high doses of dexamethasone (DEX), a synthetic glucocorticoid receptor agonist, impairs long-term memory and motor coordination, reduces body weight and induces mortality in mice. DEX is typically administered clinically for a prolonged period. Therefore, we are interested in studying the mechanism by which chronic DEX administration affects cognitive function. In this study, we attempted to explore whether chronic DEX administration alters the process of memory formation and to determine the mechanism underlying the detrimental effect of DEX. The results showed that mice treated with DEX for 21 consecutive days had significantly impaired spatial memory in the Morris Water Maze task. Mice treated with DEX had prolonged water maze performance latencies and spent less time in the target quadrant compared to the control group. Furthermore, DEX reduced brain-derived neurotrophic factor (BDNF), N-methyl-d-aspartate (NMDA) receptor subunit (NR2A/B), calcium/calmodulin-dependent protein kinase II (CaMKII) in both the prefrontal cortex and hippocampus and synaptophysin in the prefrontal cortex. We also investigated whether melatonin, a hormone synthesized in the pineal gland, could protect against DEX-induced changes in spatial memory and synaptic plasticity. The results showed that mice pretreated with melatonin prior to the DEX treatment had shorter escape latencies and remained in the target quadrant longer compared to the group only treated with DEX. Melatonin significantly prevented a DEX-induced reduction in the expression of NR2A/B, BDNF, CaMKII and synaptophysin. The results from the present study demonstrate that melatonin pretreatment prevents cognitive impairment caused by DEX. However, the precise mechanism by which melatonin affects cognitive function requires further investigation.

Drug discrimination analysis of pseudoephedrine in rats

Rats were trained to discriminate amphetamine, 1 mg/kg given intraperitoneally, from saline injection in a two-lever operant drug discrimination task. Pseudoephedrine (a sympathomimetic drug with central and peripheral actions) at doses of 10 mg/kg failed to substitute for amphetamine, at 20 mg/kg partial substitution occurred, while at a 40 mg/kg full substitution was seen. The specificity of the amphetamine cue at the training dose used (1 mg/kg) was shown by the finding that a peripherally acting sympathomimetic drug phenylephrine at doses from 0.2 to 0.8 mg/kg failed to substitute for amphetamine. The potential for abuse of pseudoephedrine administered at high doses is discussed.

Melatonin pretreatment prevented the effect of dexamethasone negative alterations on behavior and hippocampal neurogenesis in the mouse brain.

Glucocorticoids play various physiological functions via the glucocorticoid receptor (GR). Glucocorticoid is associated with the pathophysiology of depression. Dexamethasone (DEX), a synthetic GR agonist, has a greater affinity for GR than the mineralocorticoid receptor (MR) in the hippocampus of pigs and may mimic the effects of GR possession. DEX decreases neurogenesis and induces damage to hippocampal neurons that is associated with depressive-like behavior. Melatonin, a hormone mainly synthesized in the pineal gland, is a potent free radical scavenger and antioxidant. Melatonin alters noradrenergic transmission in depressed patients. It may be interesting to further explore the mechanism of melatonin that is associated with the role of stress as a key factor to precipitate depression and as a factor altering neurogenesis. In this study, we assessed the capability of melatonin to protect the hippocampus of mouse brains to counteract the effects of chronic DEX treatment for 21 days on depressive-like behavior and neurogenesis. Our results revealed that chronic administration of DEX induced depressive-like behavior and that this could be reversed by pretreatment with melatonin. Moreover, the number of 5-bromo-2-deoxyuridine (BrdU)-immunopositive cells and doublecortin (DCX; the neuronal-specific marker) protein levels were significantly reduced in the DEX-treated mice. Pretreatment with melatonin was found to renew BrdU and DCX expression in the dentate gyrus. Furthermore, pretreatment with melatonin prevented DEX-induced reductions in GR and an extracellular-signal-regulated kinase (ERK1/2) in the hippocampal area. Melatonin may protect hippocampal neurons from damage and reverse neurogenesis after chronic DEX by activating brain-derived neurotrophic (BDNF) and ERK1/2 cascades. These results revealed that melatonin pretreatment prevented the reduction of cell proliferation, immature neuron precursor cells, and GR and ERK1/2 expression. This finding indicates that melatonin attenuates the DEX-induced depressive-like behavior, supporting the notion that melatonin possesses anti-stress and neurogenic actions.

The opioid receptors in inner ear of different stages of postnatal rats

There is increasing evidence that the opioid system has a role in hearing. To provide further evidence for such a role, the expression of opioid receptor mRNAs and proteins in the inner ear of rats was studied during development from birth (P0) to postnatal day 16 (P16). A semi-quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) was employed to detect changes in the expression of delta- (DOR) kappa- (KOR) and mu- (MOR) opioid receptor mRNAs in rat cochleae at P0, P4, P8 and P16. Expression of DOR mRNA levels steadily increased from P0 to P8 with no further increases by P16. KOR mRNA was expressed at a relatively high level at P0 and P4 followed by a decrease while MOR mRNA was expressed at a low level at P0 and P4 followed by an increase by P8 and P16. Immunocytochemical labelling of inner ear sections revealed unique developmental and distribution patterns of opioid receptors. In the organ of Corti DOR immunoreactivity (DOR-IR) was detected in hair cells from P4. In contrast MOR-IR was present only in supporting cells at P0-P16. In the spiral ganglion all three receptor subtypes were expressed from P0 on nerve cell soma and qualitatively appeared to increase with age. Also DOR-IR and MOR-IR were detected at P8 and P16 in nerve fibers within the spiral ganglion. In the limbus DOR-IR was detected at P8 and P16 on cells proximal to the tectorial membrane while MOR-IR was detected more distally. In general these findings demonstrate that within the inner ear each receptor subtype follows specific temporal and spatial developmental patterns, some of which may be associated to the onset of hearing. The data provide further evidence that the opioid system may play a role in the development and functioning of the inner ear.

Relationship of opioid receptors with GABAergic neurons in the rat inferior colliculus

The inferior colliculus is a critical structure for processing auditory information and receives ascending and descending synaptic auditory projections. In addition to GABAergic and glutamatergic innervations, other neurotransmitter systems are also reported in the inferior colliculus, including opioid peptides. In the present study, the relative distribution of each type of opioid receptor, mu (MOR), delta (DOR) and kappa (KOR) within GABAergic neurons in the inferior colliculus was examined. GABA immunoreactivity was expressed by small, medium and large neurons and distributed in the central nucleus and the pericentral nucleus of the inferior colliculus. Immunostaining for MOR, DOR and KOR receptors was found in both disc‐shaped cells and stellate cells. Punctiform β‐endorphin immunolabelling was observed in the proximity of GABA‐positive neurons. Co‐localization of GABA and MOR receptors was observed in neurons and nerve terminals in the central nucleus, dorsal cortex and external cortex of the inferior colliculus. Quantification of the co‐localization patterns determined that a higher proportion of GABA neurons was associated with MOR receptors compared with KOR or DOR receptors.

The effects of okra (Abelmoschus esculentus Linn.) on the cellular events associated with Alzheimer's disease in a stably expressed HFE neuroblastoma SH-SY5Y cell line.

It has been reported that persons carrying the H63D variant in their hemochromatosis (HFE) gene are at increased risk of Alzheimers disease (AD). We investigated the possibility that okra (Abelmoschus esculentus) and quercetin could mitigate this risk factor by examining its effect on AD-associated cellular events in HFE stably expressing SH-SY5Y cells. Treatment of H63D HFE cells either with okra or quercetin significantly decreased reactive oxygen species (ROS), hydrogen peroxide (H2O2), and protein oxidation compared to untreated cells. The levels of tau phosphorylation at serine-199, serine-202, and serine-396 sites were also significantly decreased when cells were treated with okra. Exposure of the H63D and wild type (WT) cells to iron increased tau phosphorylation, but this response was decreased significantly when cells were treated with okra. The mechanism responsible for these changes appears to be related to decreased glycogen synthase kinase (GSK)-3β activity, an upstream signaling kinase of tau phosphorylation. We also established that okra treatment dramatically decreases intracellular iron levels in H63D cells compared to untreated cells. Our results provide important in vitro data on the effects of okra on various AD-associated cellular processes in H63D variant HFE cells. These results suggest okra may be beneficial in people expressing the H63D variant to reduce the risk of AD and other neurodegenerative diseases related to oxidative stress. Further in vivo studies would help confirm this.

Amphetamine and pseudoephedrine cross-tolerance measured by c-Fos protein expression in brains of chronically treated rats

BackgroundPseudoephedrine is a drug commonly prescribed as a nasal decongestant and bronchodilator and is also freely available in cold remedies and medications. The structural and pharmacological similarity of pseudoephedrine to amphetamine has led to evaluation of its psychomotor stimulant properties within the central nervous system. Previous investigations have shown that the acute responses to pseudoephedrine were similar to those of amphetamine and other psychostimulants.ResultsThis study examined the effect of chronic administration of pseudoephedrine in rat nucleus accumbens and striatum and identified three further similarities to amphetamine. (i) Chronic exposure to pseudoephedrine reduced the c-Fos response to acute pseudoephedrine treatment suggesting that pseudoephedrine induced tolerance in the animals. (ii) In animals chronically treated with amphetamine or pseudoephedrine the acute c-Fos response to pseudoephedrine and amphetamine was reduced respectively as compared to naïve animals indicating cross-tolerance for the two drugs. (iii)The known involvement of the dopamine system in the response to amphetamine and pseudoephedrine was further confirmed in this study by demonstrating that pseudoephedrine similarly to amphetamine, but with lower potency, inhibited [3H]dopamine uptake in synaptosomal preparations.ConclusionThis work has demonstrated further similarities of the effect of pseudoephedrine to those of amphetamine in brain areas known to be associated with drug addiction. The most significant result presented here is the cross tolerance effect of amphetamine and psudoephedrine. This suggests that both drugs induce similar mechanisms of action in the brain. Further studies are required to establish whether despite its considerable lower potency, pseudoephedrine could pose health and addiction risks in humans similar to that of known psychostimulants.