Functional state of hypothalamic signaling systems in rats with type 2 diabetes mellitus treated with intranasal insulin

Intranasal insulin (II) administration is widely used in the last years to treat Alzheimer’s disease and other cognitive disorders. Meanwhile, it is almost not used to treat type 2 diabetes mellitus (DM2), mainly due to insufficiently studied molecular mechanisms of its effect on the hormonal and metabolic status of the organism. The effect of II on activity of the hypothalamic signaling systems playing a key role in central regulation of energy metabolism is also poorly studied. The aim of this work was to study the effect of 5-week II treatment of male rats with the neonatal model of DM2 (0.48 ME/rat) both on the metabolic parameters and functional activity of the hypothalamic signaling systems. II treatment of diabetic rats (DI group) was shown to normalize the blood glucose level and restore glucose tolerance and utilization. In the hypothalamus of the DI group, the regulatory effects of agonists of the type 4 melanocortin receptor (MC4R), type 2 dopamine receptor (D2-DAR) and serotonin 1B receptor (S1BR) on adenylyl cyclase (AC) activity, reduced under DM2, were found to be restored; moreover, the inhibitory effect of S1BR agonists became even stronger as compared to control. In the DI group, the restoration of AC hormonal regulation was associated with a considerable increase in expression of the genes encoding S1BR and MC4R. Besides, the attenuation of the AC-stimulating effect of D2-DAR agonists against the background of decreasing expression of the Drd1 gene was found to promote the enhancement of the negative effect of dopamine on AC activity. II treatment did not have a considerable effect on expression of the genes encoding the insulin receptor and insulin receptor substrate-2, which was slightly reduced in the hypothalamus of diabetic rats. Thus, II treatment of rats with the neonatal model of DM2 partially restores the hypothalamic AC signaling pathways regulated by melanocortin, serotonin and dopamine, demonstrating thereby one of the mechanisms of the positive influence of II on energy metabolism and insulin sensitivity in peripheral tissues.     

Mechanisms of tubocurarine action on nicotinic cholinoreceptors of rat sympathetic ganglia neurons

The effects of tubocurarine (TC) on current induced by acetylcholine (ACh) in neurons of rat upper cervical ganglia were investigated using techniques for voltage-clamping at the membrane. Reinforcement of TC-induced blockade was achieved by paired application of ACh following prior activation of nicotinic cholinoreceptors, indicating that TC blocked the channels opened by ACh. On average, the TC-open channel complex persisted for 9.8±0.5 sec (n=7) at –50 mV and 20–24°C. It was found that increases exponentially with hyperpolarization at the membrane (a shift in membrane potential of 61 mV corresponds to an e-fold change). Suppression of ACh-induced current (ACh current) was eliminated completely under the effects of 3–30 M with depolarization of up to 80–100 mV at the membrane. Suppression of ACh current produced by membrane potential at negative levels is intensified with increasing doses of ACh. Findings would indicate that blockade of ionic channels opened by ACh is the only mechanism of TC action on nicotinic cholinoreceptors in rat sympathetic ganglia.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 20, No. 5, pp. 672–680, September–October, 1988.     

Phosphorylation of Thr695 and Thr850 on the myosin phosphatase target subunit: inhibitory effects and occurrence in A7r5 cells

Major sites for Rho-kinase on the myosin phosphatase target subunit (MYPT1) are Thr695 and Thr850. Phosphorylation of Thr695 inhibits phosphatase activity but the role of phosphorylation at Thr850 is not clear and is evaluated here. Phosphorylation of both Thr695 and Thr850 by Rho-kinase inhibited activity of the type 1 phosphatase catalytic subunit. Rates of phosphorylation of the two sites were similar and efficacy of inhibition following phosphorylation was equivalent for each site. Phosphorylation of each site on MYPT1 was detected in A7r5 cells, but Thr850 was preferred by Rho-kinase and Thr695 was phosphorylated by an unidentified kinase(s).     

Intranasal insulin affects adenyl cyclase system in rat tissues in neonatal diabetes

The changes in hormone-regulated adenylyl cyclase (AC) signaling system implicated in control of the nervous, cardiovascular and reproductive systems may contribute to complications of diabetes mellitus (DM). We investigated the functional state of AC system in the brain, myocardium, ovary and uterus of rats with neonatal DM and examined the influence of intranasally administered insulin on the sensitivity of this system to biogenic amines and polypeptide hormones. The regulatory effects of somatostatin and 5-HT_1BR-agonist 5-nonyloxytryptamine acting via G_i protein-coupled receptors were significantly decreased in DM and partially restored in insulin-treated rats. The effects of hormones, activators of AC, are changed in tissue- and receptorspecific manner, and intranasal insulin restored the effects rather close to the level in control. In insulin-treated non-diabetic rats, AC stimulating effects of isoproterenol and relaxin in the myocardium and of human chorionic gonadotropin in the ovaries were decreased, while the effects of hormones, inhibitors of AC, were increased. These data indicate that with intranasal insulin, Gi protein-mediated signaling pathways continue to gain strength. The obtained data on the influence of hormones on AC system in the brain, myocardium, ovary and uterus allow looking anew into the mechanisms of therapeutic effects of intranasal insulin.     

Silence analysis of AMPA receptor mutated at the CaM-kinase II phosphorylation site

Direct phosphorylation of the GluR1 subunit of postsynaptic AMPA receptors by Ca(2+)/calmodulin-dependent protein kinase II (CaM-KII) is believed to be one of the major contributors to the enhanced strength of glutamatergic synapses in CA1 area of hippocampus during long-term potentiation. The molecular mechanism of AMPA receptor regulation by CaM-KII is examined here by a novel approach, silence analysis, which is independent of previously used variance analysis. I show that three fundamental channel properties-single-channel conductance, channel open probability, and the number of functional channels-can be measured in an alternative way, by analyzing the probability of channels to be simultaneously closed (silent). Validity of the approach was confirmed by modeling, and silence analysis was applied then to the GluR1 AMPA receptor mutated at S831, the site phosphorylated by CaM-KII during long-term potentiation. Silence analysis indicates that a negative charge at S831 is a critical determinant for the enhanced channel function as a charge carrier. Silence and variance analyses, when applied to the same sets of data, were in agreement on the receptor regulation upon mutations. These results provide independent evidences for the mechanism of AMPA receptor regulation by CaM-KII and further strengthens the idea how calcium-dependent phosphorylation of AMPA receptors can contribute to the plasticity at central glutamatergic synapses.     

The results of a 5-year study of listeriosis in Ukraine

Data on the isolation of Listeria spp. cultures on the territory of Ukraine, the frequency of Listeria contamination of alimentary raw materials and foodstuffs, the level of listeriosis morbidity, the clinical forms of the manifestation of this disease, as well as the occurrence of asymptomatic carriership among clinically healthy persons of epidemiologically significant professions, are given. The results of the study of the biological properties of 73 strains of Listeria spp., their sensitivity to antibiotics and Chlorophyllipt are presented.     

A Comparative Study of the Steroidogenic Effect of 5-Amino-N-tert-butyl-2-(methylthio)-4-(3-(nicotinamido)phenyl)thieno[2,3-d]-pyrimidine-6-carboxamide and Chorionic Gonadotropin with Different Methods of Administration to Male Rats

Journal of Evolutionary Biochemistry and Physiology - To correct androgen deficiency, it is necessary to develop new luteinizing hormone receptor (LHR) agonists and evaluate their steroidogenic...     

The Effect of Metformin Therapy on Luteinizing Hormone Receptor Agonist-Mediated Stimulation of Testosterone Production and Spermatogenesis in Diabetic Rats

Journal of Evolutionary Biochemistry and Physiology - The functional restoration of the male reproductive system in type 2 diabetes mellitus (DM2) is one of the urgent global challenges in modern...