T.R. Anju

NMDA and AMPA receptor mediated excitotoxicity in cerebral cortex of streptozotocin induced diabetic rat: ameliorating effects of curcumin.

Functional activity of neurotransmitter receptor and their sensitivity to regulation are altered in DM. We evaluated the neuroprotective effect of curcumin in glutamate mediated excitotoxicity in cerebral cortex of streptozotocin induced diabetic rats. Gene expression studies in diabetic rats showed a down regulation of glutamate decarboxylase mRNA leading to accumulation of glutamate. Radioreceptor binding assays showed a significant increase in α-amino-3-hydroxy-5-methyl-4-isoxazole propionate and N-methyl-D-aspartate receptors density which was confirmed by immunohistochemical studies. Decreased glutathione peroxidases gene expression indicates enhanced oxidative stress in diabetic rats. This leads to decreased expression of glutamate aspartate transporter, which in turn reduces glutamate transport. All these events lead to excitotoxic neuronal death in the cerebral cortex, which was confirmed by the increased expression of caspase 3, caspase 8 and BCL2-associated X protein. Curcumin and insulin treatment reversed these altered parameters to near control. We establish, a novel therapeutic role of curcumin by reducing the glutamate mediated excitotoxicity in cerebral cortex of diabetes through modulating the altered neurochemical parameters.

Hypoglycemia induced changes in cholinergic receptor expression in the cerebellum of diabetic rats.

Glucose homeostasis in humans is an important factor for the functioning of nervous system. Hypoglycemia and hyperglycemia is found to be associated with central and peripheral nerve system dysfunction. Changes in acetylcholine receptors have been implicated in the pathophysiology of many major diseases of the central nervous system (CNS). In the present study we showed the effects of insulin induced hypoglycemia and streptozotocin induced diabetes on the cerebellar cholinergic receptors, GLUT3 and muscle cholinergic activity. Results showed enhanced binding parameters and gene expression of Muscarinic M1, M3 receptor subtypes in cerebellum of diabetic (D) and hypoglycemic group (D + IIH and C + IIH). α7nAchR gene expression showed a significant upregulation in diabetic group and showed further upregulated expression in both D + IIH and C + IIH group. AchE expression significantly upregulated in hypoglycemic and diabetic group. ChAT showed downregulation and GLUT3 expression showed a significant upregulation in D + IIH and C + IIH and diabetic group. AchE activity enhanced in the muscle of hypoglycemic and diabetic rats. Our studies demonstrated a functional disturbance in the neuronal glucose transporter GLUT3 in the cerebellum during insulin induced hypoglycemia in diabetic rats. Altered expression of muscarinic M1, M3 and α7nAchR and increased muscle AchE activity in hypoglycemic rats in cerebellum is suggested to cause cognitive and motor dysfunction. Hypoglycemia induced changes in ChAT and AchE gene expression is suggested to cause impaired acetycholine metabolism in the cerebellum. Cerebellar dysfunction is associated with seizure generation, motor deficits and memory impairment. The results shows that cerebellar cholinergic neurotransmission is impaired during hyperglycemia and hypoglycemia and the hypoglycemia is causing more prominent imbalance in cholinergic neurotransmission which is suggested to be a cause of cerebellar dysfunction associated with hypoglycemia.

Alterations in cortical GABAB receptors in neonatal rats exposed to hypoxic stress: role of glucose, oxygen, and epinephrine resuscitation

Hypoxia in neonates can cause permanent brain damage by gene and receptor level alterations mediated through changes in neurotransmitters. The present study evaluated GABAB receptor alterations, gene expression changes in glutamate decarboxylase and hypoxia-inducible factor 1A in the cerebral cortex of hypoxic neonatal rats and the resuscitation groups with glucose, oxygen, and epinephrine. Under hypoxic stress, a significant decrease in total GABA and GABAB receptors, GABAB and GAD gene expression was observed in the cerebral cortex, which accounts for the respiratory inhibition. Hypoxia-inducible factor 1A was upregulated under hypoxia to maintain body homeostasis. Hypoxic rats supplemented with glucose alone and with oxygen showed a reversal of the receptor alterations and changes in GAD and HIF-1A to near control. Being a source of immediate energy, glucose can reduce the ATP-depletion-induced changes in GABA and oxygenation, which helps in encountering hypoxia. Resuscitation with oxygen alone and epinephrine was less effective in reversing the receptor alterations. Thus, our study suggests that reduction in the GABAB receptors functional regulation during hypoxia plays an important role in cortical damage. Resuscitation with glucose alone and glucose and oxygen to hypoxic neonatal rats helps in protecting the brain from severe hypoxic damage.

Impaired motor learning attributed to altered AMPA receptor function in the cerebellum of rats with temporal lobe epilepsy: Ameliorating effects of Withania somnifera and withanolide A

The aim of this study was to investigate the effect of Withania somnifera (WS) extract, withanolide A (WA), and carbamazepine (CBZ) on cerebellar AMPA receptor function in pilocarpine-induced temporal lobe epilepsy (TLE). In the present study, motor learning deficit was studied by rotarod test, grid walk test, and narrow beam test. Motor learning was significantly impaired in rats with epilepsy. The treatment with WS and WA significantly reversed the motor learning deficit in rats with epilepsy when compared with control rats. There was an increase in glutamate content and IP3 content observed in rats with epilepsy which was reversed in WS- and WA-treated rats with epilepsy. alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor dysfunction was analyzed using radiolabeled AMPA receptor binding assay, AMPA receptor mRNA expression, and immunohistochemistry using anti-AMPA receptor antibody. Our results suggest that there was a decrease in Bmax, mRNA expression, and AMPA receptor expression indicating AMPA receptor dysfunction, which is suggested to have contributed to the motor learning deficit observed in rats with epilepsy. Moreover, treatment with WS and WA resulted in physiological expression of AMPA receptors. There was also alteration in GAD and GLAST expression which supplemented the increase in extracellular glutamate. The treatment with WS and WA reversed the GAD and GLAST expression. These findings suggest that WS and WA regulate AMPA receptor function in the cerebellum of rats with TLE, which has therapeutic application in epilepsy.

Enhanced brain stem 5HT2A receptor function under neonatal hypoxic insult: role of glucose, oxygen, and epinephrine resuscitation

Molecular processes regulating brain stem serotonergic receptors play an important role in the control of respiration. We evaluated 5-HT2A receptor alterations in the brain stem of neonatal rats exposed to hypoxic insult and the effect of glucose, oxygen, and epinephrine resuscitation in ameliorating these alterations. Hypoxic stress increased the total 5-HT and 5-HT2A receptor number along with an up regulation of 5-HT Transporter and 5-HT2A receptor gene in the brain stem of neonates. These serotonergic alterations were reversed by glucose supplementation alone and along with oxygen to hypoxic neonates. The enhanced brain stem 5-HT2A receptors act as a modulator of ventilatory response to hypoxia, which can in turn result in pulmonary vasoconstriction and cognitive dysfunction. The adverse effects of 100% oxygenation and epinephrine administration to hypoxic neonates were also reported. This has immense clinical significance in neonatal care.

Decreased GABAB receptor function in the cerebellum and brain stem of hypoxic neonatal rats: Role of glucose, oxygen and epinephrine resuscitation

Background-Hypoxia during the first week of life can induce neuronal death in vulnerable brain regions usually associated with an impairment of cognitive function that can be detected later in life. The neurobiological changes mediated through neurotransmitters and other signaling molecules associated with neonatal hypoxia are an important aspect in establishing a proper neonatal care.Methods-The present study evaluated total GABA, GABAB receptor alterations, gene expression changes in GABAB receptor and glutamate decarboxylase in the cerebellum and brain stem of hypoxic neonatal rats and the resuscitation groups with glucose, oxygen and epinephrine. Radiolabelled GABA and baclofen were used for receptor studies of GABA and GABAB receptors respectively and Real Time PCR analysis using specific probes for GABAB receptor and GAD mRNA was done for gene expression studies.Results-The adaptive response of the body to hypoxic stress resulted in a reduction in total GABA and GABAB receptors along with decreased GABAB receptor and GAD gene expression in the cerebellum and brain stem. Hypoxic rats supplemented with glucose alone and with oxygen showed a reversal of the receptor alterations and changes in GAD. Resuscitation with oxygen alone and epinephrine was less effective in reversing the receptor alterations.Conclusions-Being a source of immediate energy, glucose can reduce the ATP-depletion-induced changes in GABA and oxygenation, which helps in encountering hypoxia. The present study suggests that reduction in the GABAB receptors functional regulation during hypoxia plays an important role in central nervous system damage. Resuscitation with glucose alone and glucose and oxygen to hypoxic neonatal rats helps in protecting the brain from severe hypoxic damage.

Vitamin D3 supplementation increases insulin level by regulating altered IP3 and AMPA receptor expression in the pancreatic islets of streptozotocin-induced diabetic rat.

Pancreatic islets, particularly insulin-secreting β cells, share common characteristics with neurons. Glutamate is one of the major excitatory neurotransmitter in the brain and pancreas, and its action is mediated through glutamate receptors. In the present work, we analysed the role of vitamin D3 in the modulation of AMPA receptor subunit and their functional role in insulin release. Radio receptor binding study in diabetic rats showed a significant increase in AMPA receptor density. Insulin AMPA colabelling study showed an altered AMPA GluR2 and GluR4 subunit expression in the pancreatic beta cells. We also found lowered IP3 content and decreased IP3 receptor in pancreas of diabetic rats. The alterations in AMPA and IP3 receptor resulted in reduced cytosolic calcium level concentration, which further blocks Ca(2+)-mediated insulin release. Vitamin D3 supplementation restored the alteration in vitamin D receptor expression, AMPA receptor density and AMPA and IP3 receptor expression in the pancreatic islets that helps to restore the calcium-mediated insulin secretion. Our study reveals the antidiabetic property of vitamin D3 that is suggested to have therapeutic role through regulating glutamatergic function in diabetic rats.

Cortical 5HT2A Receptor Function under Hypoxia in Neonatal Rats: Role of Glucose, Oxygen, and Epinephrine Resuscitation

Neonatal hypoxia induces brain injury through alterations in neurotransmitters and its receptors. Molecular processes regulating serotonergic receptors play an important role in the control of respiration under hypoxia. The present study evaluates the serotonergic regulation of neonatal hypoxia and its resuscitation methods. Receptor binding assays and gene expression studies were done to evaluate the changes in 5HT2A receptors and its transporter in the cerebral cortex of hypoxic neonatal rats and hypoxic rats resuscitated with glucose, oxygen, and epinephrine. Hypoxic stress increased total 5HT and 5HT2A receptor number along with an upregulation of 5HT2A receptor and 5HT transporter gene in the cortex. The enhanced cortical 5HT2A receptors may act as a modulator of ventilatory response to hypoxia. These alterations were reversed to near control by glucose supplementation. Glucose supplementation helped in managing the serotonergic functional alterations. Hypoxia-induced adenosine triphosphate depletion causes a reduction in blood glucose levels which can be encountered by glucose administration, and oxygenation helps in overcoming the anaerobic condition. The adverse effect of immediate oxygenation and epinephrine supplementation was also reported. This has immense clinical significance in establishing a proper resuscitation for the management of neonatal hypoxia.

Serotonergic receptor upregulation in cerebral cortex and down regulation in brainstem of streptozotocin induced diabetic rats: Antagonism by pyridoxine and insulin

Insulin secretion and glucose homeostasis is implicated through serotonergic function. Pyridoxine is involved in decarboxylation step in synthesis of serotonin. The present study was carried out to find the role of insulin in combination with pyridoxine on the concentrations of 5-HT and 5-HIAA, 5-HT receptor binding, 5-HTT gene expression and immunohistochemistry studies in the cerebral cortex and brainstem of streptozotocin induced diabetic rats. 5-HT content showed a significant decrease with a significant increase in 5-HIAA in cerebral cortex (p<0.01) and brain stem (p<0.001) in diabetic rats. 5-HT receptor binding parameters, B(max) and K(d), showed a significant decrease (p<0.001) in diabetic rats in cerebral cortex whereas in brainstem it showed a significant increase (p<0.001) compared to control. Gene expression studies of 5-HTT in cerebral cortex showed a significant down regulation (p<0.001) and in brainstem an upregulation (p<0.001) in diabetic rats compared to control. Insulin and pyridoxine treatment to diabetic rats reversed the 5-HT content, B(max), K(d) and gene expression of 5-HTT confirmed by immunohistochemistry studies in cerebral cortex and brainstem to near control. Thus our results suggest that pyridoxine along with insulin has a role in the regulation of insulin synthesis and release through serotonergic function which has clinical significance in the management of diabetes.

Cerebellar 5HT2A receptor function under hypoxia in neonatal rats: role of glucose, oxygen, and epinephrine resuscitation.

Molecular processes regulating the cerebellar serotonergic receptors play an important role in the control of respiration and cognitive functions under hypoxia. The present study examined cerebellar 5HT receptor alterations and neuroprotective effect of glucose supplementation prior to current sequence of resuscitation-oxygen and epinephrine supplementation in hypoxic neonatal rats. Hypoxic stress increased the number of total 5HT and 5HT(2A) receptors along with an up-regulation of 5HT transporter and 5HT(2A) receptor gene in cerebellum. These serotonergic alterations were reversed to near control by glucose supplementation. Immunohistochemical studies confirmed the data. Behavioral studies revealed the cognitive impairment due to neonatal hypoxia in the later stages of life and the role of timely glucose supplementation in preventing these behavioral deficits. The enhanced cerebellar 5HT(2A) receptors may act as a modulator of ventilatory response to hypoxia, which can in turn result in cognitive dysfunction. Glucose supplementation helped in managing the serotonergic functional alterations. This has immense clinical significance in neonatal care.