Dopamine Receptor Gene Expression In Streptozotocin Induced Diabetic Rats And Its Role In Insulin Secretion

Diabetes Mellitus is a metabolic disorder associated with insulin deficiency, which not.only affects the carbohydrate metabolism but also is associated with various central and peripheral complications. Chronic hyperglycemia during diabetes mellitus is a major initiator of diabetic microvascular complications like retinopathy, neuropathy, The central nervous system (CNS) neurotransmitters play an important role in the regulation of glucose homeostasis. These neurotransmitters mediate rapid intracellular communications not only within the central nervous system but also in the peripheral tissues. They exert their function through receptors present in both neuronal and non neuronal cell surface that trigger second messenger signaling pathways. Dopamine is a neurotransmitter that has been implicated in various central neuronal degenerative disorders like Parkinson's disease and behavioral diseases like Schizophrenia. Dopamine is synthesised from tyrosine, stored in vesicles in axon terminals and released when the neuron is depolarised. Dopamine interacts with specific membrane receptors to produce its effect. Dopamine plays an important role both centrally and peripherally. The recent identification of five dopamine receptor subtypes provides a basis for understanding dopamine's central and peripheral actions . Dopamine receptors are classified into two major groups : DA D1 like and DA D2 like. Dopamine D1 like receptors consists of DA D1 and DA D5 receptors . Dopamine D2 like receptors consists of DA D2, DA D3 and DA D4 receptors. Stimulation of the DA D1 receptor gives rise to increased production of cAMP. Dopamine D2 receptors inhibit cAMP production, but activate the inositol phosphate second messenger system . Impairment of central dopamine neurotransmission causes muscle rigidity, hormonal regulation , thought disorder and cocaine addiction. Peripheral dopamine receptors mediate changes in blood flow, glomerular filtration rate, sodium excretion and catecholamine release. The dopamine D2 receptors increased in the corpus striatum and cerebral cortex but decreased in the hypothalamus and brain stem indicating their involvement in regulating insulin secretion. Dopamine D2 receptor which has a stimulatory effecton insulin secretion decreased in the pancreatic islets during diabetes. Our in vitro studies confirmed the stimulatory role of dopamine D2 receptors in stimulation of glucose induced insulin secretion. A detailed study at the molecular level on the mechanisms involved in the role of dopamine in insulin secretion, its functional modification could lead to therapeutic interventions that will have immense clinical importance.

Studies om the Antiulcerogenic and Antihepatotoxic Potential of Chitosan and Glucosamine in Eeperimental Rats

The present study examined the antiulcer effect of glucosamine on mucosal antioxidant defense system in ibuprofen-induced peptic ulcer in male albino rats. The results of the present study indicate that the pre-oral administration of chitosan and glucosamine maintain near to the normal status the activities of the mucosal antioxidant enzymes and the level of GSH (Glutathione), which protect mucosa against oxidative damage by decreasing the lipid peroxidation and strengthening the mucosal barrier, and which are the first line of defense against exogenous ulcerogenic agents. In this study indicate that the oral pre-treatment of chitosan and glucosamine can prevent ibuprofen-induced peptic ulcer in rats.This study can be concluded that co-administration of chitsosan and glucosamine can effectively prevent the isonized and rifampicin induced hepatotoxicity in rats.Comparatively, chitosan was found to have better results than glucosamine in alleviating the hepatic disorders

Enhanced dopamine D2 receptor function in hypothalamus and corpus striatum: their role in liver, plasma and in vitro hepatocyte ALDH regulation in ethahol treated rats

Dopamine D2 receptors are involved in ethanol self- administration behavior and also suggested to mediate the onset and offset of ethanol drinking. In the present study, we investigated dopamine (DA) content and Dopamine D2 (DA D2) receptors in the hypothalamus and corpus striatum of ethanol treated rats and aldehyde dehydrogenase (ALDH) activity in the liver and plasma of ethanol treated rats and in vitro hepatocyte cultures. Hypothalamic and corpus striatal DA content decreased significantly (P\0.05, P\0.001 respectively) and homovanillic acid/ dopamine (HVA/DA) ratio increased significantly (P\0.001) in ethanol treated rats when compared to control. Scatchard analysis of [3H] YM-09151-2 binding to DA D2 receptors in hypothalamus showed a significant increase (P\0.001) in Bmax without any change in Kd in ethanol treated rats compared to control. The Kd of DA D2 receptors significantly decreased (P\0.05) in the corpus striatum of ethanol treated rats when compared to control. DA D2 receptor affinity in the hypothalamus and corpus striatum of control and ethanol treated rats fitted to a single site model with unity as Hill slope value. The in vitro studies on hepatocyte cultures showed that 10-5 M and 10-7 M DA can reverse the increased ALDH activity in 10% ethanol treated cells to near control level. Sulpiride, an antagonist of DA D2, reversed the effect of dopamine on 10% ethanol induced ALDH activity in hepatocytes. Our results showed a decreased dopamine concentration with enhanced DA D2 receptors in the hypothalamus and corpus striatum of ethanol treated rats. Also, increased ALDH was observed in the plasma and liver of ethanol treated rats and in vitro hepatocyte cultures with 10% ethanol as a compensatory mechanism for increased aldehyde production due to increased dopamine metabolism. A decrease in dopamine concentration in major brain regions is coupled with an increase in ALDH activity in liver and plasma, which contributes to the tendency for alcoholism. Since the administration of 10-5 M and 10-7 M DA can reverse the increased ALDH activity in ethanol treated cells to near control level, this has therapeutic application to correct ethanol addicts from addiction due to allergic reaction observed in aldehyde accumulation.

Down-regulation of cerebellar 5-HT2C receptors in pilocarpine-induced epilepsy in rats: Therapeutic role of Bacopa monnieri extract

Epilepsy is a syndrome of episodic brain dysfunction characterized by recurrent unpredictable, spontaneous seizures. Cerebellar dysfunction is a recognized complication of temporal lobe epilepsy and it is associated with seizure generation, motor deficits and memory impairment. Serotonin is known to exert a modulatory action on cerebellar function through 5HT2C receptors. 5-HT2C receptors are novel targets for developing anticonvulsant drugs. In the present study, we investigated the changes in the 5-HT2C receptors binding and gene expression in the cerebellum of control, epileptic and Bacopa monnieri treated epileptic rats. There was a significant down regulation of the 5-HT content (pb0.001), 5-HT2C gene expression (pb0.001) and 5-HT2C receptor binding (pb0.001) with an increased affinity (pb0.001). Carbamazepine and B. monnieri treatments to epileptic rats reversed the down regulated 5-HT content (pb0.01), 5-HT2C receptor binding (pb0.001) and gene expression (pb0.01) to near control level. Also, the Rotarod test confirms the motor dysfunction and recovery by B. monnieri treatment. These data suggest the neuroprotective role of B. monnieri through the upregulation of 5-HT2C receptor in epileptic rats. This has clinical significance in the management of epilepsy

Decreased GABAA Receptors Functional Regulation 3 in the Cerebral Cortex and Brainstem of Hypoxic Neonatal Rats: 4 Effect of Glucose and Oxygen Supplementation

Hypoxia in neonates can lead to biochemical and molecular alterations mediated through changes in neurotransmitters resulting in permanent damage to brain. In this study, we evaluated the changes in the receptor status of GABAA in the cerebral cortex and brainstem of hypoxic neonatal rats and hypoxic rats supplemented with glucose and oxygen using binding assays and gene expression of GABAAa1 and GABAAc5. In the cerebral cortex and brainstem of hypoxic neonatal rats, a significant decrease in GABAA receptors was observed, which accounts for the respiratory inhibition. Hypoxic rats sup- plemented with glucose alone and with glucose and oxygen showed, respectively, a reversal of the GABAA receptors, andGABAAa1 and GABAAc5 gene expression to control. Glucose acts as an immediate energy source thereby reducing the ATP-depletion-induced increase in GABA and oxygenation, which helps in encountering anoxia. Resuscitation with oxygen alone was less effective in reversing the receptor alterations. Thus, the results of this study suggest that reduction in the GABAA receptors functional regulation during hypoxia plays an important role in mediating the brain damage. Glucose alone and glucose and oxygen supplementation to hypoxic neonatal rats helps in protecting the brain from severe hypoxic damage.

Dopamine D1 and D2 Receptor Gene Expression and cGMP, IP3 and Ca2+ Regulation in the Brain Regions of Hypoxic Neonatal Rats: Role of Glucose, Oxygen and Epinephrine Supplementation

Department of Biotechnology, Cochin University of Science and Technology

Glutamate Receptor Gene Expression: IP3, cAMP, cGMP Functional Regulation in Hypoglycaemic and Diabetic Rats

Department of Biotechnology, Cochin University of Science and Technology

5-HT2C and NMDA Receptors, IP3, cGMP and cAMP Functional Regulation in Pilocarpine Induced Temporal Lobe Epilepsy in Rats: Neuroprotective Role of Bacopa monnieri

Department of Biotechnology, Cochin University of Science and Technology

Brain Cholinergic and Dopaminergic Functions in Streptozotocin Induced Diabetic Rats: Effects of Curcumin and Vitamin D3 Supplementation

Department of Biotechnology, Cochin University of Science and Technology

GABA, serotonin, muscarinic receptors - their second messengers and transcription factors functional regulation in the brain regions of hypoxic neonatal rats: Resuscitation with glucose, oxygen and epinephrine

The present study was designed to investigate the protective effect of glucose, oxygen and epinephrine resuscitation on impairment in the functional role of GABAergic, serotonergic, muscarinic receptors, PLC, BAX, SOD, CAT and GPx expression in the brain regions of hypoxia induced neonatal rats. Also, the role of hormones - Triiodothyronine (T3) and insulin, second messengers – cAMP, cGMP and IP3 and transcription factors – HIF and CREB in the regulation of neonatal hypoxia and its resuscitation methods were studied. Behavioural studies were conducted to evaluate the motor function and cognitive deficit in one month old control and experimental rats. The efficient and timely supplementation of glucose plays a crucial role in correcting the molecular changes due to hypoxia, oxygen and epinephrine. The sequence of glucose, epinephrine and oxygen administration at the molecular level is an important aspect of the study. The additive neuronal damage effect due to oxygen and epinephrine treatment is another important observation. The corrective measures by initial supply of glucose to hypoxic neonatal rats showed from the molecular study when brought to practice will lead to healthy intellectual capacity during the later developmental stages, which has immense clinical significance in neonatal care.

Brain Adrenergic and Serotonergic Receptor Function in Streptozotocin-Diabetic Rats

Department of Biotechnology, Cochin University of Science and Technology

GABAA and GABAB Receptor Gene Expression and Functional Regulation During Pancreatic Regeneration and Insulin Secretion in Rats

The present study demonstrate the functional alterations of the GABAA and GABAB receptors and the gene expression during the regeneration of pancreas following partial pancreatectomy. The role of these receptors in insulin secretion and pancreatic DNA synthesis using the specific agonists and antagonists also are studied in vitro. The alterations of GABAA and GABAR receptor function and gene expression in the brain stem, crebellum and hypothalamus play an important role in the sympathetic regulation of insulin secretion during pancreatic regeneration. Previous studies have given much information linking functional interaction between GABA and the peripheral nervous system. The involvement of specific receptor subtypes functional regulation during pancreatic regeneration has not given emphasis and research in this area seems to be scarce. We have observed a decreased GABA content, down regulation of GABAA receptors and an up regulation of GABAB receptors in the cerebral cortex, brain stem and hypothalamus. Real Time-PCR analysis confirmed the receptor data in the brain regions. These alterations in the GABAA and GABAB receptors of the brain are suggested to govern the regenerative response and growth regulation of the pancreas through sympathetic innervation. In addition, receptor binding studies and Real Time-PCR analysis revealed that during pancreatic regeneration GABAA receptors were down regulated and GABAB receptors were up regulated in pancreatic islets. This suggests an inhibitory role for GABAA receptors in islet cell proliferation i.e., the down regulation of this receptor facilitates proliferation. Insulin secretion study during 1 hour showed GABA has inhibited the insulin secretion in a dose dependent manner in normal and hyperglycaemic conditions. Bicuculline did not antagonize this effect. GABAA agonist, muscimol inhibited glucose stimulated insulin secretion from pancreatic islets except in the lowest concentration of 1O-9M in presence of 4mM glucose.Musclmol enhanced insulin secretion at 10-7 and 10-4M muscimol in presence of 20mM glucose- 4mM glucose represents normal and 20mM represent hyperglycaemic conditions. GABAB agonist, baclofen also inhibited glucose induced insulin secretion and enhanced at the concentration of 1O-5M at 4mM glucose and at 10-9M baclofen in presence of 20mM glucose. This shows a differential control of the GABAA and GABAB receptors over insulin release from the pancreatic islets. During 24 hours in vitro insulin secretion study it showed that low concentration of GABA has inhibited glucose stimulated insulin secretion from pancreatic islets. Muscimol, the GABAA agonist, inhibited the insulin secretion but, gave an enhanced secretion of insulin in presence of 4mM glucose at 10-7 , 10-5 and 1O-4M muscimol. But in presence of 20mM glucose muscimol significantly inhibited the insulin secretion. GABAB agonist, baclofen also inhibited glucose induced insulin secretion in presence of both 4mM and 20mM glucose. This shows the inhibitory role of GABA and its specific receptor subtypes over insulin synthesis from pancreatic bete-islets. In vitro DNA synthesis studies showed that activation of GABAA receptor by adding muscimol, a specific agonist, inhibited islet DNA synthesis. Also, the addition of baclofen, a specific agonist of GABAB receptor resulted in the stimulation of DNA synthesis.Thus the brain and pancreatic GABAA and GABAB receptor gene expression differentially regulates pancreatic insulin secretion and islet cell proliferation during pancreatic regeneration. This will have immense clinical significance in therapeutic applications in the management of Diabetes mellitus.

5-HT1A and -HT2c Receptor Gene Expression: Their Functional Role in Pancreatic Regeneration and Insulin Secretion in Rats

Department of Biotechnology, Cochin University of Science and Technology

Muscarinic M1 Receptor Gene Expression in Streptozotocin Induced Diabetic Rats: Regulation of Insulin Secretion By Aegle marmelose And Costus pictus Leaf Extracts

The present work is to understand the alterations of total Muscarinic and Muscarinic MI receptors in brain and pancreatic islets of Streptozotocin induced diabetic rats. The work focuses on the evaluation of the antihyperglycemic activity of aqueous extracts of Aegle marmelose and Costus pictus leaves in vivo and the changes in the total Muscarinic and Muscarinic MI receptors during diabetes and after the treatment with insulin. The insulin secretory activity of Aegle marmelose and Costus pictus leaf extracts and the effect of cholinergic receptor agonist were investigated in vitro using rat primary pancreatic islet culture. Muscarinic MI receptor kinetics and gene expression during diabetes and regulation of insulin secretion by Aegle marmelose and Costus pie/us leaf extracts will help us to elucidate the role of Muscarinic and Muscarinic MI receptors in hyperglycemia and the regulatory activity of these plant extracts on insulin secretion through Muscarinic receptors.

Serotonin- 5-HT2A and Glutamate Receptors Gene Expression in Streptozotocin induced diabetic rats:Effects of pyridoxine and Aegle marmelose leaf extract

Department of Biotechnology, Cochin University of Science and Technology