Decreased muscarinic M1 receptor gene expression in the hypothalamus, brainstem, and pancreatic islets of streptozotocin-induced diabetic rats

Hippocampal acetylcholine receptor activation-dependent long-term depression in streptozotocin-induced diabetic rats

Cholinergic innervation of the hippocampus correlates with memory formation. In a well-established animal model of type 1 diabetes mellitus, obtained by injecting young adult rats with streptozotocin (STZ), reductions have been reported in the expression of acetylcholine receptors and choline acetyltransferase. In this study, we showed that long-term synaptic depression (LTD) induced by carbachol (CCh), a nonselective cholinergic receptor agonist, at Schaffer collateral-CA1 synapses in hippocampal slices was significantly weaker in streptozotocin-induced diabetic rats (STZ rats) than in age-matched control rats. No significant change was observed in the paired-pulse ratio between before and 80 min after the application of CCh in control and STZ rats. Moreover, CCh-induced LTD in control and STZ rats was not affected by an NMDA receptor antagonist. Although the application of CCh down-regulated the surface expression of GluA2 in the hippocampus of control rats, but not STZ rats. Therefore, the present results suggest that acetylcholine receptor-mediated LTD in STZ rats requires the internalization of AMPA receptors on the postsynaptic surface and their intracellular effects in the hippocampus.

The distribution pattern of M2 and Adrenergicα2 receptors on inferior colliculi in male newborns of diabetic rats

AIMS

Despite the high prevalence of diabetes in the world, its possible effects throughut pregnancy on neonatal auditory nervous system development are still unknown. In the present research, maternal diabetes' impact on the M2 and Adrenergic_α2 receptors expression in the inferior colliculus (IC) of male newborn rats was investigated. Main methods Female rats were grouped into three: sham, insulin-treated diabetic, and diabetic. Diabetes was induced through streptozotocin (STZ) injection as one dose intraperitoneally (65 mg/kg). After mating and delivery, male rats were euthanized on P0, P7, and P14. Immunohistochemistry (IHC) was used to study the distribution pattern of receptors. Key findings The present study indicated that the expression of M2 receptors in the diabetic group was significantly increased in pairwise comparisons in the sham and diabetic treated with insulin groups (P<0.001, each). The highest M2 expression was for the diabetic group on P14 and the lowest one was for the sham group on P0. The Adrenergic_α2a receptors expression in the diabetic group was significantly reduced in pairwise comparisons in the sham and diabetic treated with insulin groups (P <0.001, each). The highest Adrenergic_α2a expression was for the sham group on P14 and the lowest one was for the diabetic group on P0. There was no significant difference between the sham and insulin groups regarding all receptors expression.

SIGNIFICANCE

This study demonstrated a time-dependent significant decrease in Adrenergic_α2a but a time-dependent significant increase in M2 receptors expression.

Cholinergic Signals from the CNS Regulate G-CSF-Mediated HSC Mobilization from Bone Marrow via a Glucocorticoid Signaling Relay

Hematopoietic stem cells (HSCs) are mobilized from niches in the bone marrow (BM) to the blood circulation by the cytokine granulocyte colony-stimulating factor (G-CSF) through complex mechanisms. Among these, signals from the sympathetic nervous system regulate HSC egress via its niche, but how the brain communicates with the BM remains largely unknown. Here we show that muscarinic receptor type-1 (Chrm1) signaling in the hypothalamus promotes G-CSF-elicited HSC mobilization via hormonal priming of the hypothalamic-pituitary-adrenal (HPA) axis. Blockade of Chrm1 in the CNS, but not the periphery, reduces HSC mobilization. Mobilization is impaired in Chrm1-∕- mice and rescued by parabiosis with wild-type mice, suggesting a relay by a blood-borne factor. We have identified the glucocorticoid (GC) hormones as critical for optimal mobilization. Physiological levels of corticosterone promote HSC migration via the GC receptor Nr3c1-dependent signaling and upregulation of actin-organizing molecules. These results uncover long-range regulation of HSC migration emerging from the brain.

The functional state of hormone-sensitive adenylyl cyclase signaling system in diabetes mellitus

Diabetes mellitus (DM) induces a large number of diseases of the nervous, cardiovascular, and some other systems of the organism. One of the main causes of the diseases is the changes in the functional activity of hormonal signaling systems which lead to the alterations and abnormalities of the cellular processes and contribute to triggering and developing many DM complications. The key role in the control of physiological and biochemical processes belongs to the adenylyl cyclase (AC) signaling system, sensitive to biogenic amines and polypeptide hormones. The review is devoted to the changes in the GPCR-G protein-AC system in the brain, heart, skeletal muscles, liver, and the adipose tissue in experimental and human DM of the types 1 and 2 and also to the role of the changes in AC signaling in the pathogenesis and etiology of DM and its complications. It is shown that the changes of the functional state of hormone-sensitive AC system are dependent to a large extent on the type and duration of DM and in experimental DM on the model of the disease. The degree of alterations and abnormalities of AC signaling pathways correlates very well with the severity of DM and its complications.

Muscarinic M₁, M₃ receptor modulation in the corpus striatum of streptozotocin induced diabetic rats as a function of age

OBJECTIVES

In this study we have investigated muscarinic M₁, M₃ receptor kinetics and the functional role of IP3 and cGMP in the corpus striatum of both young and old diabetic and insulin-treated diabetic rats.

METHODS

Radioreceptor binding assays was done in the corpus striatum using specific antagonists QNB and DAMP. IP3 and cGMP assay using [3H]IP3 and [3H]cGMP Biotrak assay system kits.

KEY FINDINGS

M₁ receptor increased and M₃ receptor decreased in control old rats when compared with young control rats. In young diabetic groups M₁ receptor increased and M₃ receptor decreased. Old diabetic groups showed reversed M₁ and M₃ receptors compared with their controls. IP3 and cGMP content increased in old control rats compared with young control rats. IP3 content increased in young diabetic rats and decreased in old diabetic rats. cGMP content was increased significantly in both young and old diabetic groups. Insulin treatment reversed these altered parameters near to control.

CONCLUSIONS

Our studies showed that M₁ and M₃ receptors, IP3 and cGMP were functionally regulated during diabetes as function of age, which will have immense clinical significance.

Curcumin modulates dopaminergic receptor, CREB and phospholipase C gene expression in the cerebral cortex and cerebellum of streptozotocin induced diabetic rats

Curcumin, an active principle component in rhizome of Curcuma longa, has proved its merit for diabetes through its anti-oxidative and anti-inflammatory properties. This study aims at evaluating the effect of curcumin in modulating the altered dopaminergic receptors, CREB and phospholipase C in the cerebral cortex and cerebellum of STZ induced diabetic rats. Radioreceptor binding assays and gene expression was done in the cerebral cortex and cerebellum of male Wistar rats using specific ligands and probes. Total dopaminergic receptor binding parameter, B_max showed an increase in cerebral cortex and decrease in the cerebellum of diabetic rats. Gene expression studies using real time PCR showed an increased expression of dopamine D1 and D2 receptor in the cerebral cortex of diabetic rats. In cerebellum dopamine D1 receptor was down regulated and D2 receptor showed an up regulation. Transcription factor CREB and phospholipase C showed a significant down regulation in cerebral cortex and cerebellum of diabetic rats. We report that curcumin supplementation reduces diabetes induced alteration of dopamine D1, D2 receptors, transcription factor CREB and phospholipase C to near control. Our results indicate that curcumin has a potential to regulate diabetes induced malfunctions of dopaminergic signalling, CREB and Phospholipase C expression in cerebral cortex and cerebellum and thereby improving the cognitive and emotional functions associated with these regions. Furthermore, in line with these studies an interaction between curcumin and dopaminergic receptors, CREB and phospholipase C is suggested, which attenuates the cortical and cerebellar dysfunction in diabetes. These results suggest that curcumin holds promise as an agent to prevent or treat CNS complications in diabetes.

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.

Neuroprotective role of curcumin in the cerebellum of streptozotocin-induced diabetic rats

AIMS

Chronic hyperglycaemia in diabetes involves a direct neuronal damage caused by intracellular glucose which leads to altered neurotransmitter functions and reduced motor activity. The present study investigated the effect of curcumin in the functional regulation of muscarinic and alpha7 nicotinic acetylcholine receptors, insulin receptors, acetylcholine esterase and Glut3 in the cerebellum of streptozotocin (STZ)-induced diabetic rats.

MAIN METHODS

All studies were done in the cerebellum of male Wistar rats. Radioreceptor binding assays were done for total muscarinic, M(1) and M(3) receptors using specific ligands, and the gene expression was also studied using specific probes.

KEY FINDINGS

Our results showed an increased gene expression of acetylcholine esterase, Glut3, muscarinic M1, M3, alpha7 nicotinic acetylcholine and insulin receptors in the cerebellum of diabetic rats in comparison to control. Scatchard analysis of total muscarinic, M1 and M3 receptors showed an increased binding parameter, B(max) in diabetic rats compared to control. Curcumin and insulin inhibited diabetes-induced elevation in the gene expression of acetylcholine esterase, Glut3, insulin and cholinergic receptors in the cerebellum of diabetic rats.

SIGNIFICANCE

Our studies suggest that curcumin plays a vital role in regulating the activity of cholinergic and insulin receptors and mechanism of glucose transportation through Glut3, which results in normalizing the diabetes-mediated cerebellar disorders. Thus, curcumin has a significant role in a therapeutic application for the prevention or progression of diabetic complications in the cerebellum.

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.

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.