Intranasal Administration of Insulin and Gangliosides Improves Spatial Memory in Rats with Neonatal Type 2 Diabetes Mellitus.

We analyzed the effects of intranasal administration of insulin (0.48 U/rat) and gangliosides (6 mg/kg) on spatial memory in rats with the neonatal model of the type 2 diabetes mellitus. The development of diabetes was verified by the glucose tolerance test. Insulin and gangliosides improved training and reversal training in diabetic rats in a modified version of Morris water maze test and reduced the time of finding the hidden platform. High effectiveness of intranasal administration of gangliosides to animals for the normalization of cognitive functions was shown for the first time. The effects of insulin and gangliosides were similar during training, but during reversal training, gangliosides were more effective. At the same time, intranasally administered insulin, unlike gangliosides, partially normalized glucose tolerance in rats with type 2 diabetes mellitus.

[The effect of Metformin on metabolic parameters and hypothalamic signaling systems in rats with obesity induced by a high-carbohydrate/high-fat diet.]

Metformin (MF), a first-line drug in the treatment of diabetes mellitus, has been used in the recent years to treat obesity. Its therapeutic effect is due not only to the influence on the peripheral tissues, but also on the hypothalamus, which controls food behavior and energy metabolism. The aim was to study the effect of MF therapy (200 mg/kg/day, 8 weeks) in rats with obesity caused by a high-carbohydrate/high-fat diet on the metabolic and hormonal parameters and functional state of the hypothalamic signaling systems. The MF treatment of obese rats (the group ObM) normalized the food behavior, reduced the body and fat weight and the glucose, insulin and leptin levels, increased the sensitivity to glucose and insulin, improved the lipid metabolism, and restored the Ser473-phosphorylation of Akt-kinase in the liver. In the hypothalamus, the stimulating adenylyl cyclase (AC) effects of the agonists of type 4 melanocortin receptor and type 1 dopamine receptor were partially restored, the inhibitory AC effect of the agonists of subtype 1B serotonin receptor (5-HT1BR) was increased, which was associated with an increase in Htr1b gene expression, and the stimulating effect of the 5-HT6R-agonist EMD-386088 was normalized. At the same time, the differences in the activity of the leptin and insulin systems and the ratio of anorexigenic and orexigenic factors in the hypothalamus of the rat groups Ob and ObM were insignificant. Thus, MF treatment changes functional activity of the hypothalamic melanocortin, dopamine and serotonin systems in obese rats, which is one of the reasons to decrease their food intake and to restore the metabolic indicators and insulin sensitivity.

Intranasal Insulin Restores Metabolic Parameters and Insulin Sensitivity in Rats with Metabolic Syndrome.

We studied the effect of 10-week treatment with intranasal insulin (0.5 IU/day) on glucose tolerance, glucose utilization, lipid metabolism, functions of pancreatic ß cells, and insulin system in the liver of rats with cafeteria diet-induced metabolic syndrome. The therapy reduced body weight and blood levels of insulin, triglycerides, and atherogenic cholesterol that are typically increased in metabolic syndrome, normalized glucose tolerance and its utilization, and increased activity of insulin signaling system in the liver, thus reducing insulin resistance. The therapy did not affect the number of pancreatic islets and ß cells. The study demonstrates prospects of using intranasal insulin for correction of metabolic parameters and reduction of insulin resistance in metabolic syndrome.

THE RESTORATION OF HYPOTHALAMIC SIGNALING SYSTEMS AS ONE OF THE CAUSES TO IMPROVE THE METABOLIC PARAMETERS IN BROMOCRYPTINE-TREATED RATS WITH NEONATAL MODEL OF DIABETES MELLITUS.

One of the approaches to correct type 2 diabetes mellitus (T2DM) and its complications is the use of drug bromocryptine mesylate (BCM), a selective agonist of type 2 dopamine receptors (DA2R). At the same time, the efficiency and the mechanisms of action of BCM in treatment of severe forms of T2DM are not currently understood. The objective was to study the effect of four-week treatment of male rats with neonatal T2DM model using BCM (300 mg/kg/day) on their metabolic parameters and activity of the adenylyl cyclase signaling system (ACSS) in the hypothalamus. The BCM treatment restored glucose tolerance and its utilization by exogenous insulin, and normalized lipid metabolism by lowering the levels of triglycerides and atherogenic cholesterol increased in T2DM. In the hypothalamus of BCM-treated diabetic rats, the regulation of ACSS by agonists of type 4 melanocortin receptor (MC4R), DA2R and 1B-subtype serotonin receptor, and the expression of Mc4r gene encoding MC4R were restored. Meanwhile, the BCM treatment had no effect on plasma insulin level and insulin production by pancreatic b-cells. The obtained data indicate the significant prospects of BCM to treat severe forms of experimental T2DM, and show that the therapeutic potential of this drug includes its ability to restore the hypothalamic signaling systems sensitive to monoamines and peptide of the melanocortin family, which are responsible for the control of energy metabolism and insulin sensitivity.

The functional activity of hypothalamic signaling systems in rats with neonatal diabetes mellitus treated with metformin.

The effect of the two-month metformin treatment (200 mg/kg/day) of rats with the neonatal model of type 2 diabetes mellitus on the functional activity of hypothalamic signaling systems was studied. It was shown that metformin treatment restored the sensitivity of hypothalamic adenylyl cyclase signaling system to agonists of the type 4 melanocortin receptor and the type 2 dopamine receptor but did not influence significantly the functions of the insulin signaling system. These data suggest new targets and mechanisms of metformin action in the CNS, which may mediate its restoring effect on energy homeostasis impaired in diabetic pathology.

[FUNCTIONAL STATE OF THE HYPOTHALAMIC SIGNALING SYSTEMS IN RATS WITH TYPE 2 DIABETES MELLITUS TREATED WITH INTRANASAL INSULIN].

In the last years intranasally administered insulin (II) is widely used to treat Alzheimer's disease and other cognitive disorders. Meanwhile, it is little used to treat the type 2 diabetes mellitus (DM2); which is due to insufficient knowledge of molecular mechanisms of its action on hormonal and metabolic status of an organism. The effect of II on the activity of hypothalamic signaling systems, which plays a key role in the central regulation of energy metabolism, is still poorly understood. The aim of the present work was to study the effect of five-week treatment of male rats with neonatal model of DM2 using 11 (0.48 IU/rat) on metabolic parameters and on functional activity of the hypothalamic signaling systems. It was shown that treatment of diabetic rats with II'(Group DI) normalized plasma glucose level, restored glucose tolerance and its utilization. In the hypothalamus of rats of the Group DI the-regulatory effects of agonists of type 4 melanocortin receptors (MC4R), type 2 dopamine receptor (D2-DAR) and subtype 1B serotonin receptor (5-HTIBR) on adenylyl cyclase (AC) activity, which were reduced in DM2, restored. Moreover, the inhibitory effect of 5-HTIR agonists even was increased as compared to control. In the Group DI, the res- toration of AC regulation by hormones was accompanied by a significant increase in the expression of genes encoding 5-HTIBR and MC4R. Along with this, the attenuation of the AC stimulating effect of D1-DAR agonists and the decreased expression of Drdl gene were found, promoting the enhancement of the negative dopamine effect on AC activity. The II treatment did not significantly affect the expression of genes encoding insulin receptor and insulin receptor substrate 2, which was reduced, though to a small extent, in the hypothalamus of diabetic rats. Thus, the II treatment of rats with the neonatal model of DM2 partially restores the hypothalamic AC signaling pathways regulated by melanocortins, serotonin and do- pamine, which is one of the mechanisms of positive influence of II on energy metabolism and insulin sensitivity in the peripheral tissues.

[Spatial memory and regulation of brain adenylyl cyclase by serotonin and dopamine in rat with streptozotocin diabetes].

The most common complication of diabetes mellitus of the type 1 (DM1) is a cognitive deficiency, which develops as a result of neurodegenerative changes in the brain. The aim of this work was to study the learning and spatial memory in rats with streptozotocin DM1 with different duration (1.5 and 6 months), as well as the activity of adenylyl cyclase signaling system (ACSS) sensitive to agonists of the serotonin and the dopamine receptors in the brain of diabetic rats. Our experiments demonstrated that rats with 1.5-months DM1 has no changes in spatial memory which were evaluated in a Morris water maze whereas in rats with 6-months DM1 the spatial memory and learning ability were decreased. The alterations of the regulation of adenylyl cyclase by agonists of types 1 and 6 serotonin receptors and type 2 dopamine receptors were found in both the 1.5- and 6-months DM1 which indicates their importance in the development of cognitive deficiency. Abnormalities in the. brain ACSS can be considered as key factors in the etiology and pathogenesis of cognitive dysfunctions in DM1. Hypothesized that cognitive deficiency occurs only in the later stages of DM1 due to alterations in the serotonin and dopamine signaling systems of the brain.

[Effects of intranasal insulin and serotonin on functional activity of the adenylyl cyclase system in the myocardium, ovaries, and uterus of rats with prolonged neonatal model of diabetes mellitus].

Disturbances in hormonal signaling systems, in the adenylyl cyclase system (ACS) in particular, occur at early stages of diabetes mellitus (DM) and are one of the key causes of its complications. Since there is a correlation between the severity of DM and of disturbances in the ACS, the study of the ACS activity can be used to monitor DM and its complications and to evaluate effectiveness of their treatment. Comparatively recently, for treatment of the type 2 DM, there began to be used the intranasal insulin (I-I) and drugs increasing brain serotonin level, which effectively restore CNS functions. However, mechanisms of their action on peripheral tissues and organs with DM remain to be not understood. The goal of this work was to study effects. of I-I and intranasal serotonin (I-S) on the ACS functional activity in myocardium, ovary, and uterus of rats with a neonatal model of the type 2 DM. In tissues of diabetic rats there were revealed changes in regulation of adenylyl cyclase (AC) by guanine nucleotides and hormones that both stimulated and inhibited this enzyme, such changes being characterized by the receptor and tissue specificity. In diabetic rats, I-I restored the AC stimulating effects of isoproterenol in the myocardium, guanine nucleotides and gonadotropin in ovaries and relaxin in uterus, as well as the AC inhibitory effects of somatostatin in all tissues, and of noradrenaline in myocardium. Treatment with IS led to a partial restoration of the AC-inhibitory effect of noradrenalin in the diabetic myocardium, but did not affect regulation of AC by other hormones. These data indicate that I-I normalizes the ACS functional activity in myocardium and in tissues of the reproductive system of female rats with neonatal DM, whereas the effect of I-S on in the studied tissues is less pronounced. These results are necessary to be taken into account at development and optimization of strategy of use of I-I and I-S for treatment of DM and of its complications.

Initial stages of the insulin signaling system in the brain of rats with experimental diabetes mellitus.

We studied reactivity of insulin signal pathway elements, insulin receptor and insulin receptor substrate protein-2 (IRS2 protein), in rat brain in response to insulin insufficiency and insulin resistance during the development of experimental type 1 or type 2 diabetes mellitus. In type 1 diabetes mellitus characterized by acute insulin insufficiency, specific binding of insulin in rat brain increased 2-fold in comparison with the control and IRS2-gene expression in rat hypothalamus and cortex 2-4 fold surpassed the normal values. In type 2 diabetes mellitus (110 and 190 days of development), changes in the test parameters in rat brain were less pronounced. These findings attest to involvement of the brain insulin signal pathway into the response to systemic insulin deficiency in type 1 diabetes mellitus.