Alterations in the muscarinic M1 and M3 receptor gene expression in the brain stem during pancreatic regeneration and insulin secretion in weanling rats

Cevimeline co-treatment attenuates olanzapine-induced metabolic disorders via modulating hepatic M3 muscarinic receptor: AMPKα signalling pathway in female rats

BACKGROUND

Olanzapine is one of the most commonly used antipsychotic drugs; however, its metabolic disorders are the main obstacle in the clinic. Olanzapine is a potent antagonist of the M3 acetylcholine muscarinic receptor (M3R), while the downregulated hepatic M3R-AMPKα signalling pathway is involved in metabolic disorders.

AIM

This study investigated the effects of chronic co-treatment with cevimeline (an agonist of M3Rs) in attenuating olanzapine-induced metabolic disorders and the underlying mechanisms.

METHODS

Forty-eight adult female Sprague-Dawley rats were treated orally with olanzapine (2 mg/kg, 3 times/day (t.i.d.)) and/or cevimeline (9 mg/kg, t.i.d.), or control (vehicle) for 9 weeks.

RESULTS

Cevimeline co-treatment significantly attenuated olanzapine-induced body weight gain and glucolipid metabolic disorders. Importantly, cevimeline co-treatment attenuated olanzapine-induced upregulation of M3Rs, while the co-treatment improved olanzapine-induced downregulation of AMPKα in the liver. Cevimeline co-treatment attenuated olanzapine-induced dyslipidaemia by modulating the hepatic M3R-AMPKα downstream pathways. Cevimeline co-treatment also improved lower activated AKT-GSK3β signalling to reverse impairment of glucose metabolism and insulin resistance caused by chronic olanzapine treatment.

CONCLUSION

These results not only support the important role of M3R antagonism and its related AMPKα and downstream pathways in antipsychotic-induced metabolic disorders but also indicate that these pathways might be promising targets for pharmacological intervention to control these side effects caused by antipsychotic therapy.

Metabolome-Genome-Wide Association Study (mGWAS) Reveals Novel Metabolites Associated with Future Type 2 Diabetes Risk and Susceptibility Loci in a Case-Control Study in a Chinese Prospective Cohort

In a Chinese prospective cohort, 500 patients with new-onset type 2 diabetes (T2D) within 4.61 years and 500 matched healthy participants are selected as case and control groups, and randomized into discovery and validation sets to discover the metabolite changes before T2D onset and the related diabetogenic loci. A serum metabolomics analysis reveals that 81 metabolites changed significantly before T2D onset. Based on binary logistic regression, eight metabolites are defined as a biomarker panel for T2D prediction. Pipecolinic acid, carnitine C14:0, epinephrine and phosphatidylethanolamine 34:2 are first found associated with future T2D. The addition of the biomarker panel to the clinical markers (BMI, triglycerides, and fasting glucose) significantly improves the predictive ability in the discovery and validation sets, respectively. By associating metabolomics with genomics, a significant correlation (p < 5.0 × 10-8) between eicosatetraenoic acid and the FADS1 (rs174559) gene is observed, and suggestive correlations (p < 5.0 × 10-6) between pipecolinic acid and CHRM3 (rs535514), and leucine/isoleucine and WWOX (rs72487966) are discovered. Elevated leucine/isoleucine levels increased the risk of T2D. In conclusion, multiple metabolic dysregulations are observed to occur before T2D onset, and the new biomarker panel can help to predict T2D risk.

Second generation antipsychotic-induced type 2 diabetes: a role for the muscarinic M3 receptor

Second generation antipsychotics (SGAs) are widely prescribed to treat various disorders, most notably schizophrenia and bipolar disorder; however, SGAs can cause abnormal glucose metabolism that can lead to insulin-resistance and type 2 diabetes mellitus side-effects by largely unknown mechanisms. This review explores the potential candidature of the acetylcholine (ACh) muscarinic M3 receptor (M3R) as a prime mechanistic and possible therapeutic target of interest in SGA-induced insulin dysregulation. Studies have identified that SGA binding affinity to the M3R is a predictor of diabetes risk; indeed, olanzapine and clozapine, SGAs with the highest clinical incidence of diabetes side-effects, are potent M3R antagonists. Pancreatic M3Rs regulate the glucose-stimulated cholinergic pathway of insulin secretion; their activation on β-cells stimulates insulin secretion, while M3R blockade decreases insulin secretion. Genetic modification of M3Rs causes robust alterations in insulin levels and glucose tolerance in mice. Olanzapine alters M3R density in discrete nuclei of the hypothalamus and caudal brainstem, regions that regulate glucose homeostasis and insulin secretion through vagal innervation of the pancreas. Furthermore, studies have demonstrated a dynamic sensitivity of hypothalamic and brainstem M3Rs to altered glucometabolic status of the body. Therefore, the M3R is in a prime position to influence glucose homeostasis through direct effects on pancreatic β-cells and by potentially altering signalling in the hypothalamus and brainstem. SGA-induced insulin dysregulation may be partly due to blockade of central and peripheral M3Rs, causing an initial disruption to insulin secretion and glucose homeostasis that can progressively lead to insulin resistance and diabetes during chronic treatment.

Effects of antipsychotic medications on appetite, weight, and insulin resistance

Although clozapine, olanzapine, and other atypical antipsychotic drugs (APDs) have fewer extrapyramidal side effects, they have serious metabolic side effects such as substantial weight gain, intra-abdominal obesity, and type 2 diabetes mellitus. Given that most patients with mental disorders face chronic, even life-long, treatment with APDs, the risks of weight gain/obesity and other metabolic symptoms are major considerations for APD maintenance treatment. This review focuses on the effects of APDs on weight gain, appetite, insulin resistance, and glucose dysregulation, and the relevant underlying mechanisms that may be help to prevent and treat metabolic side effects caused by APD therapy.

Involvement of the parasympathetic nervous system in the initiation of regeneration of pancreatic β-cells

The mechanism that initiates regeneration of pancreatic β-cells is not clear at present. The vagal nerve is implicated in the regulation of gastrointestinal functions, glucose metabolism and proliferation of pancreatic β-cells under physiological conditions. To elucidate the triggering mechanism of the regeneration of pancreatic β-cells, we examined the involvement of the vagal nerve. To this end, we employed a rat pancreatic duct ligation (DL) model, in which profound β-cell neogenesis and β-cell proliferation were observed within a week. We administered atropine to block the vagal nerve. Administration of atropine inhibited proliferation of β-cells in both islets and islet-like cell clusters (ICC), without affecting ductal cell proliferation in the ligated pancreas. The numbers of PDX-1 and MafB-positive cells in or attaching to the ducts were significantly reduced by atropine. MafB/glucagon and MafB/insulin double-positive cells were also decreased by atropine. Finally, atropine reduced the number of MafA-positive ductal cells, all of which were positive for insulin, by 50% on day 5. These results strongly suggest that the vagal nerve is involved in β-cell proliferation, induction of endocrine progenitors and neogenesis of α- and β-cells.

Effects of olanzapine on muscarinic M3 receptor binding density in the brain relates to weight gain, plasma insulin and metabolic hormone levels

The second generation antipsychotic drug (SGA) olanzapine has an efficacy to treat schizophrenia, but can cause obesity and type II diabetes mellitus. Cholinergic muscarinic M3 receptors (M3R) are expressed on pancreatic β-cells and in the brain where they influence insulin secretion and may regulate other metabolic hormones via vagal innervation of the gastrointestinal tract. Olanzapine's M3R antagonism is an important risk factor for its diabetogenic liability. However, the effects of olanzapine on central M3Rs are unknown. Rats were treated with 0.25, 0.5, 1.0 or 2.0 mg olanzapine/kg or vehicle (3×/day, 14-days). M3R binding densities in the hypothalamic arcuate (Arc) and ventromedial nuclei (VMH), and dorsal vagal complex (DVC) of the brainstem were investigated using [3H]4-DAMP plus pirenzepine and AF-DX116. M3R binding correlations to body weight, food intake, insulin, ghrelin and cholecystokinin (CCK) were analyzed. Olanzapine increased M3R binding density in the Arc, VMH and DVC, body weight, food intake, circulating plasma ghrelin and CCK levels, and decreased plasma insulin and glucose. M3R negatively correlated to insulin, and positively correlated to ghrelin, CCK, food intake and body weight. Increased M3R density is a compensatory up-regulation in response to olanzapine's M3R antagonism. Olanzapine acts on M3R in regions of the brain that control food intake and insulin secretion. Olanzapine's M3R blockade in the brain may inhibit the acetylcholine pathway for insulin secretion. These findings support a role for M3Rs in the modulation of insulin, ghrelin and CCK via the vagus nerve and provide a mechanism for olanzapine's diabetogenic and weight gain liability.

Olanzapine treatment and metabolic dysfunction: a dose response study in female Sprague Dawley rats

Second generation antipsychotics are commonly prescribed for the treatment of schizophrenia, however some can induce metabolic dysfunction side-effects such as weight gain, obesity and diabetes. Clinical reports suggest olanzapine alters satiety signals, although findings appear conflicting. Previous animal model studies have utilised a range of olanzapine dosages, however the dosage that better mimics the human scenario of olanzapine-induced weight gain is unclear. Female Sprague-Dawley rats were treated orally, three times daily with olanzapine (0.25mg/kg, 0.5mg/kg, 1.0mg/kg, 2.0mg/kg), self-administered in a sweet cookie dough pellet at eight-hourly intervals) or vehicle (n=12/group) for 14-days. Olanzapine orally self-administered in multiple doses (eight-hourly intervals) may circumvent a drop in plasma drug concentration and ensure the maintenance of a consistently high olanzapine level in the rat. Olanzapine increased body weight (0.5mg/kg, 1.0mg/kg, 2.0mg/kg), food intake (2.0mg/kg) and feeding efficiency (0.5-2.0mg/kg), with no effect on water intake. Subcutaneous inguinal (1.0mg/kg, 2.0mg/kg) and intra-abdominal perirenal fat were increased (2.0mg/kg), but not interscapula brown adipose tissue. Olanzapine increased circulating ghrelin and cholecystokinin, but had no effect on peptide YY((3-36)). Olanzapine decreased insulin (0.25-2.0mg/kg) and locomotor activity in the open field arena (0.5-2.0mg/kg). A low dosage of 0.25mg/kg olanzapine had no effect on most parameters measured. Olanzapine-induced weight gain is associated with hyperphagia, enhanced feeding efficiency and adiposity, decreased locomotor activity and altered satiety signaling. The animal model used in the present study of self-administered oral olanzapine treatment (t.i.d.) at a dosage range of 0.5-2.0mg/kg (but not 0.25mg/kg) mimics aspects of the clinic.

Gain of new exons and promoters by lineage-specific transposable elements-integration and conservation event on CHRM3 gene

The CHRM3 gene is a member of the muscarinic acetylcholine receptor family that plays important roles in the regulation of fundamental physiological functions. The evolutionary mechanism of exon-acquisition and alternative splicing of the CHRM3 gene in relation to transposable elements (TEs) were analyzed using experimental approaches and in silico analysis. Five different transcript variants (T1, T2, T3, T3-1, and T4) derived from three distinct promoter regions (T1: L1HS, T2, T4: original, T3, T3-1: THE1C) were identified. A placenta (T1) and testis (T3 and T3-1)-dominated expression pattern appeared to be controlled by different TEs (L1HS and THE1C) that were integrated into the common ancestor genome during primate evolution. Remarkably, the T1 transcript was formed by the integration event of the human specific L1HS element. Among the 12 different brain regions, the brain stem, olfactory region, and cerebellum showed decreased expression patterns. Evolutionary analysis of splicing sites and alternative splicing suggested that the exon-acquisition event was determined by a selection and conservation mechanism. Furthermore, continuous integration events of transposable elements could produce lineage specific alternative transcripts by providing novel promoters and splicing sites. Taken together, exon-acquisition and alternative splicing events of CHRM3 genes were shown to have occurred through the continuous integration of transposable elements following conservation.

Muscarinic M(1), M(3) receptors function in the brainstem of streptozotocin induced diabetic rats: their role in insulin secretion from the pancreatic islets as a function of age

In the present study, we have investigated acetylcholine esterase (AChE) activity and muscarinic M(1), M(3) receptors kinetics in the brainstem of both young and old streptozotocin induced and insulin treated diabetic rats (D + I). Also, the functional role of acetylcholine and muscarinic receptors in insulin secretion from the pancreatic islets was studied in vitro. 90 week old control rats showed decreased V(max) (P < 0.001) for AChE compared to 7 week old control rats. V(max) was decreased (P < 0.001) in 7 week diabetic groups whereas 90 week old diabetic groups showed increased (P < 0.001) V(max) when compared to their respective controls. Binding studies using [(3)H]QNB and [(3)H]DAMP of 90 week old control showed significant increase in the B(max) (P < 0.001) and K(d) (P < 0.01) of muscarinic M(1) receptors whereas M(3) receptor number was decreased significantly (P < 0.001) with no change in affinity when compared to 7 week old control respectively. M(1) receptor number was decreased significantly (P < 0.001) whereas M(3) receptor number was increased significantly (P < 0.001) in both 7 week and 90 week old diabetic rat groups compared to their respective controls. The competition curve for [(3)H]QNB fitted for two sited model in 7 week old groups whereas fitted for one sited model in 90 week old groups. [(3)H]DAMP was fitted for two sited model in both 7 week and 90 week old groups. Insulin treatment significantly reversed (P < 0.001) the binding parameters to near control level. In vitro studies showed that acetylcholine through muscarinic M(1) and M(3) receptors stimulated insulin secretion from the pancreatic islets. Thus our studies suggest that both brainstem and pancreatic muscarinic M(1), M(3) receptors differentially regulate the cholinergic activity and insulin secretion which will have clinical significance in the management of diabetes and insulin treatment as a function of age.

Enhanced muscarinic M1 receptor gene expression in the corpus striatum of streptozotocin-induced diabetic rats

Acetylcholine (ACh), the first neurotransmitter to be identified, regulate the activities of central and peripheral functions through interactions with muscarinic receptors. Changes in muscarinic acetylcholine receptor (mAChR) have been implicated in the pathophysiology of many major diseases of the central nervous system (CNS). Previous reports from our laboratory on streptozotocin (STZ) induced diabetic rats showed down regulation of muscarinic M1 receptors in the brainstem, hypothalamus, cerebral cortex and pancreatic islets. In this study, we have investigated the changes of acetylcholine esterase (AChE) enzyme activity, total muscarinic and muscarinic M1 receptor binding and gene expression in the corpus striatum of STZ--diabetic rats and the insulin treated diabetic rats. The striatum, a neuronal nucleus intimately involved in motor behaviour, is one of the brain regions with the highest acetylcholine content. ACh has complex and clinically important actions in the striatum that are mediated predominantly by muscarinic receptors. We observed that insulin treatment brought back the decreased maximal velocity (Vmax) of acetylcholine esterase in the corpus striatum during diabetes to near control state. In diabetic rats there was a decrease in maximal number (Bmax) and affinity (Kd) of total muscarinic receptors whereas muscarinic M1 receptors were increased with decrease in affinity in diabetic rats. We observed that, in all cases, the binding parameters were reversed to near control by the treatment of diabetic rats with insulin. Real-time PCR experiment confirmed the increase in muscarinic M1 receptor gene expression and a similar reversal with insulin treatment. These results suggest the diabetes-induced changes of the cholinergic activity in the corpus striatum and the regulatory role of insulin on binding parameters and gene expression of total and muscarinic M1 receptors.

Gamma-aminobutyric acid A receptor functional decrease in the hypothalamus during pancreatic regeneration in rats

OBJECTIVE

In the present study, we investigated the alteration of gamma-aminobutyric acid A (GABAA) receptors in the hypothalamus of rats during pancreatic regeneration.

METHODS

Three groups of rats were used for the study: sham operated, 72 hours partially pancreatectomized, and 7 days partially pancreatectomized. The GABA receptor assay was performed by using the [H]GABA as ligand to the Triton X-100-treated membranes, and displacement with unlabeled GABA and [H]bicuculline binding to the GABAA receptors was assayed in Triton X-100-treated synaptic membranes and displacement with unlabeled bicuculline.

RESULTS

The GABA content in the brain regions and pancreas of the sham and experimental rat groups was quantified by displacement method. In the hypothalamus, the high-affinity GABAA receptor binding showed a significant decrease in maximal binding (P < 0.01) and equilibrium dissociation constant (P < 0.05) in 72 hours and 7 days partially pancreatectomized rats. The content of GABA has significantly decreased in the hypothalamus during the regeneration of pancreas.

CONCLUSIONS

This effect of GABAA receptors in hypothalamus suggests a regulatory role during active regeneration of pancreas that will have significance in insulin secretion.

Decreased muscarinic M1 receptor gene expression in the cerebral cortex of streptozotocin-induced diabetic rats and Aegle marmelose leaf extract's therapeutic function

AIM

In the present study we have investigated the changes in the total muscarinic and muscarinic M1 receptor ([(3)H]QNB) binding and gene expression in the cerebral cortex of streptozotocin (STZ) induced diabetic, insulin and aqueous extract of Aegle marmelose leaf treated diabetic rats.

MATERIALS AND METHODS

Diabetes was induced in rats by intrafemoral injection of streptozotocin. Aegle marmelose leaves was given orally to one group of rats at a dosage of 1g/kg body weight per day for fourteen days. Blood glucose and plasma insulin level were measured. Muscarinic and Muscarinic M1 receptor binding studies were done in the cerebral cortex of experimental rats. Muscarinic M1 receptor gene expression was studied using real-time PCR.

RESULTS

Scatchard analysis for total muscarinic receptors in cerebral cortex showed that the B(max) was decreased significantly (p<0.001) in diabetic rats with a significant decrease (p<0.01) in the K(d) when compared to control group. Binding analysis of Muscarinic M1 receptors showed that B(max) was decreased significantly (p<0.001) in diabetic group when compared to control group. The K(d) also decreased significantly (p<0.01) when compared to control group. The binding parameters were reversed to near control by the treatment of diabetic rats with Aegle marmelose. Real-Time PCR analysis also showed a similar change in the mRNA levels of muscarinic M1 receptors.

CONCLUSION

The results showed that there is decrease in total muscarinic and muscarinic M1 receptors during diabetes which is up regulated by insulin and Aegle marmelose leaf extract treatment. This has clinical significance in therapeutic management of diabetes.

CHRM3 gene variation is associated with decreased acute insulin secretion and increased risk for early-onset type 2 diabetes in Pima Indians

The muscarinic acetylcholine receptor subtype M3 (CHRM3) gene is expressed in islet beta-cells and has a role in stimulating insulin secretion; therefore, CHRM3 was analyzed as a candidate gene for type 2 diabetes in Pima Indians. Ten variants were genotyped in a family-based sample (n = 1,037), and 1 variant (rs3738435) located in the 5' untranslated region of an alternative transcript was found to be modestly associated with both early-onset type 2 diabetes and the acute insulin response in a small subset of these subjects. To better assess whether this variant has a role in acute insulin secretion, which could affect risk for early-onset type 2 diabetes, rs3738435 was genotyped in a larger group of normal glucose-tolerant Pima Indians who had measures of acute insulin secretion (n = 282) and a larger case-control group of Pima Indians selected for early-onset type 2 diabetes (n = 348 case subjects with age of onset <25 years; n = 392 nondiabetic control subjects aged >45 years). Genotyping in these larger sets of subjects confirmed that the C allele of rs3738435 was associated with a reduced acute insulin response (adjusted P = 0.00006) and was also modestly associated with increased risk of early-onset type 2 diabetes (adjusted P = 0.02).

Decreased [3H] YM-09151-2 binding to dopamine D2 receptors in the hypothalamus, brainstem and pancreatic islets of streptozotocin-induced diabetic rats

In the present study dopamine was measured in the hypothalamus, brainstem, pancreatic islets and plasma, using HPLC. Dopamine D2 receptor changes in the hypothalamus, brainstem and pancreatic islets were studied using [3H] YM-09151-2 in streptozotocin-induced diabetic and insulin-treated diabetic rats. There was a significant decrease in dopamine content in the hypothalamus (P<0.001), brainstem (P<0.001), pancreatic islets (P<0.001) and plasma (P<0.001) in diabetic rats when compared to control. Scatchard analysis of [3H] YM-09151-2 in the hypothalamus of diabetic rats showed a significant decrease in Bmax (P<0.001) and Kd, showing an increased affinity of D2 receptors when compared to control. Insulin treatment did not completely reverse the changes that occurred during diabetes. There was a significant decrease in Bmax (P<0.01) with decreased affinity in the brainstem of diabetic rats. The islet membrane preparation of diabetic rats showed a significant decrease (P<0.001) in the binding of [3H] YM-09151-2 with decreased Kd (P<0.001) compared to control. The increase in affinity of D2 receptors in hypothalamus and pancreatic islets and the decreased affinity in brainstem were confirmed by competition analysis. Thus our results suggest that the decreased dopamine D2 receptor function in the hypothalamus, brainstem and pancreas affects insulin secretion in diabetic rats, which has immense clinical relevance to the management of diabetes.

Decreased alpha1-adrenergic receptor binding in the cerebral cortex and brain stem during pancreatic regeneration in rats

The purpose of this study was to investigate the role of brain alpha1-adrenergic receptor binding in the rat model of pancreatic regeneration using 60-70% pancreatectomy. The alpha1-adrenergic receptors kinetics was studied in the cerebral cortex and brain stem of sham operated, 72 h pancreatectomised and 7 days pancreatectomised rats. Scatchard analysis with [3H]prazosin in cerebral cortex and brain stem showed a significant decrease (P < 0.01), (P < 0.05) in maximal binding (Bmax) with a significant decrease (P < 0.001), (P < 0.01) in the Kd in 72 h pancreatectomised rats compared with sham respectively. Competition analysis in cerebral cortex and brain stem showed a shift in affinity during pancreatic regeneration. The sympathetic activity was decreased as indicated by the significantly decreased norepinephrine level in the plasma (P < 0.001), cerebral cortex (P < 0.01) and brain stem (P < 0.001) of 72 h pancreatectomised rats compared to sham. Thus, from our results it is suggested that the central alpha1-adrenergic receptors have a functional role in the pancreatic regeneration mediated through the sympathetic pathway.

Decreased alpha2-adrenergic receptor in the brain stem and pancreatic islets during pancreatic regeneration in weanling rats

Sympathetic stimulation inhibits insulin secretion. alpha(2)-Adrenergic receptor is known to have a regulatory role in the sympathetic function. We investigated the changes in the alpha(2)-adrenergic receptors in the brain stem and pancreatic islets using [(3)H]Yohimbine during pancreatic regeneration in weanling rats. Brain stem and pancreatic islets of experimental rats showed a significant decrease (p<0.001) in norepinephrine (NE) content at 72 h after partial pancreatectomy. The epinephrine (EPI) content showed a significant decrease (p<0.001) in pancreatic islets while it was not detected in brain stem at 72 h after partial pancreatectomy. Scatchard analysis of [(3)H]Yohimbine showed a significant decrease (p<0.05) in B(max) and K(d) at 72 h after partial pancreatectomy in the brain stem. In the pancreatic islets, Scatchard analysis of [(3)H]Yohimbine showed a significant decrease (p<0.001) in B(max) and K(d) (p<0.05) at 72 h after partial pancreatectomy. The binding parameters reversed to near sham by 7 days after pancreatectomy both in brain stem and pancreatic islets. This shows that pancreatic insulin secretion is influenced by central nervous system inputs from the brain stem. In vitro studies with yohimbine showed that the alpha(2)-adrenergic receptors are inhibitory to islet DNA synthesis and insulin secretion. Thus our results suggest that decreased alpha(2)-adrenergic receptors during pancreatic regeneration functionally regulate insulin secretion and pancreatic beta-cell proliferation in weanling rats.

Increased insulin secretion by muscarinic M1 and M3 receptor function from rat pancreatic islets in vitro

Parasympathetic system plays an important role in insulin secretion from the pancreas. Cholinergic effect on pancreatic beta cells exerts primarily through muscarinic receptors. In the present study we investigated the specific role of muscarinic M1 and M3 receptors in glucose induced insulin secretion from rat pancreatic islets in vitro. The involvement of muscarinic receptors was studied using the antagonist atropine. The role of muscarinic M1 and M3 receptor subtypes was studied using subtype specific antagonists. Acetylcholine agonist, carbachol, stimulated glucose induced insulin secretion at low concentrations (10(-8)-10(-5) M) with a maximum stimulation at 10(-7) M concentration. Carbachol-stimulated insulin secretion was inhibited by atropine confirming the role of muscarinic receptors in cholinergic induced insulin secretion. Both M1 and M3 receptor antagonists blocked insulin secretion induced by carbachol. The results show that M3 receptors are functionally more prominent at 20 mM glucose concentration when compared to M1 receptors. Our studies suggest that muscarinic M1 and M3 receptors function differentially regulate glucose induced insulin secretion, which has clinical significance in glucose homeostasis.

Enhanced β-adrenergic receptors in the brain and pancreas during pancreatic regeneration in weanling rats

Adrenergic stimulation has an important role in the pancreatic beta-cell proliferation and insulin secretion. In the present study, we have investigated how sympathetic system regulates the pancreatic regeneration by analyzing Epinephrine (EPI), Norepinephrine (NE) and beta-adrenergic receptor changes in the brain as well as in the pancreas. EPI and NE showed a significant decrease in the brain regions, pancreas and plasma at 72 hrs after partial pancreatectomy. We observed an increase in the circulating insulin levels at 72 hrs. Scatchard analysis using [(3)H] propranolol showed a significant increase in the number of both the low affinity and high affinity beta-adrenergic receptors in cerebral cortex and hypothalamus of partially pancreatectomised rats during peak DNA synthesis. The affinity of the receptors decreased significantly in the low and high affinity receptors of cerebral cortex and the high affinity hypothalamic receptors. In the brain stem, low affinity receptors were increased significantly during regeneration whereas there was no change in the high affinity receptors. The pancreatic beta-adrenergic receptors were also up regulated at 72 hrs after partial pancreatectomy. In vitro studies showed that beta-adrenergic receptors are positive regulators of islet cell proliferation and insulin secretion. Thus our results suggest that the beta-adrenergic receptors are functionally enhanced during pancreatic regeneration, which in turn increases pancreatic beta-cell proliferation and insulin secretion in weanling rats.

Hypothalamic 5-HT functional regulation through 5-HT1A and 5-HT2C receptors during pancreatic regeneration

5-HT receptors are predominantly located in the brain and are involved in pancreatic function and cell proliferation through sympathetic nervous system. The objective of this study was to investigate the role of hypothalamic 5-HT, 5-HT1A and 5-HT2C receptor binding and gene expression in rat model of pancreatic regeneration using 60% pancreatectomy. The pancreatic regeneration was evaluated by 5-HT content, 5-HT1A and 5-HT2C receptor gene expression in the hypothalamus of sham operated, 72 h and 7 days pancreatectomised rats. 5-HT content was quantified by HPLC. 5-HT1A receptor assay was done by using specific agonist [3H]8-OH DPAT. 5-HT2C receptor assay was done by using specific antagonist [3H]mesulergine. The expression of 5-HT1A and 5-HT2C receptor gene was analyzed by RT-PCR. 5-HT content was higher in the hypothalamus of 72 h pancreatectomised rats. 5-HT1A and 5-HT2C receptors were down-regulated in the hypothalamus. RT-PCR analysis revealed decreased 5-HT1A and 5-HT2C receptor mRNA expression. The 5-HT1A and 5-HT2C receptors gene expression in the 7 days pancreatectomised rats reversed to near sham level. This study is the first to identify 5-HT1A and 5-HT2C receptor gene expression in the hypothalamus during pancreatic regeneration in rats. Our results suggest the hypothalamic serotonergic receptor functional regulation during pancreatic regeneration.

Decreased 5-HT2C receptor binding in the cerebral cortex and brain stem during pancreatic regeneration in rats

The purpose of this study was to investigate the role of central 5-HT2C receptor binding in rat model of pancreatic regeneration using 60-70% pancreatectomy. The 5-HT and 5-HT2C receptor kinetics were studied in cerebral cortex and brain stem of sham operated, 72 h pancreatectomised and 7 days pancreatectomised rats. Scatchard analysis with [3H] mesulergine in cerebral cortex showed a significant decrease (p < 0.05) in maximal binding (Bmax) without any change in Kd in 72 h pancreatectomised rats compared with sham. The decreased Bmax reversed to sham level by 7 days after pancreatectomy. In brain stem, Scatchard analysis showed a significant decrease (p < 0.01) in Bmax with a significant increase (p < 0.01) in Kd. Competition analysis in brain stem showed a shift in affinity towards a low affinity. These parameters were reversed to sham level by 7 days after pancreatectomy. Thus the results suggest that 5-HT through the 5-HT2C receptor in the brain has a functional regulatory role in the pancreatic regeneration.

Muscarinic M1 and M3 receptor binding alterations in pancreas during pancreatic regeneration of young rats

The importance of muscarinic receptors in proliferation of different cell types and in insulin secretion from pancreatic beta cells has been extensively studied. However, the role of pancreatic muscarinic receptors during pancreatic regeneration has not yet been studied. For the first time, the functional status of the muscarinic M1 and M3 receptors in regeneration of the pancreas is investigated here. It is observed that the number and affinity of high-affinity muscarinic M3 receptors increased at the time of regeneration. The low-affinity M3 receptors also showed a similar trend. In the case of muscarinic M1 receptors, the receptor number increased with a decrease in affinity. We also observed an increase in the circulating insulin levels at the time of active regeneration. The in vitro studies confirmed that muscarinic receptors are stimulatory to insulin secretion. Our results suggest that the increased muscarinic M1 and M3 receptor subtypes stimulate insulin secretion and islet cell proliferation during the regeneration of pancreas.