Significant Increases In Extracellular Concentrations Research Articles

Selective Blockade of 5-Hydroxytryptamine (5-HT)7Receptors Enhances 5-HT Transmission, Antidepressant-Like Behavior, and Rapid Eye Movement Sleep Suppression Induced by Citalopram in Rodents

Evidence has accumulated supporting a role for 5-hydroxytryptamine (5-HT)7 receptors in circadian rhythms, sleep, and mood disorders, presumably as a consequence of the modulation of 5-HT-mediated neuronal activity. We hypothesized that a selective 5-HT7 receptor antagonist, (2R)-1-[(3-hydroxyphenyl)sulfonyl]-2-[2-(4-methyl-1-piperidinyl)ethyl]-pyrrolidine (SB-269970), should increase activity of 5-HT neurons and potentiate the effect of selective serotonin reuptake inhibitors (citalopram). In rats, administration of 3 mg/kg s.c. citalopram alone increased the extracellular concentration of 5-HT. This effect of citalopram on extracellular 5-HT concentration was significantly enhanced by an ineffective dose of SB-269970. Combining this dose of SB-269970 with a low dose of citalopram also resulted in a significant increase in extracellular concentration of 5-HT, suggesting a potentiation of neurochemical effects. In mice, citalopram and SB-269970 dose-dependently decreased immobility time in the tail suspension test. The dose-effect curve of citalopram was shifted leftward by coadministration of an effective dose of SB-269970. Furthermore, combining ineffective doses of citalopram and SB-269970 also resulted in a significant decrease of immobility time in the tail suspension test, suggesting potentiation of antidepressant-like effects. In rats, SB-269970 potentiated the increase of rapid eye movement (REM) latency and the REM sleep decrease induced by citalopram. SB-269970 also reversed the increase in sleep fragmentation induced by citalopram. Rat plasma and brain concentrations of citalopram were not affected by coadministration of SB-269970, arguing for a pharmacodynamic rather than a pharmacokinetic mechanism. Overall, these results indicate that selective blockade of 5-HT7 receptors may enhance the antidepressant efficacy of citalopram and may provide a novel therapy to alleviate sleep disturbances associated with depression.

Identifying the Components in Eggshell Membrane Responsible for Reducing the Heat Resistance of Bacterial Pathogens

The biological activity (D-value determination) of eggshell membrane (ESM) was examined to determine the membrane components and mechanisms responsible for antibacterial activity. Biological and enzymatic activities (i.e., β-N-acetylglucosaminidase [β-NAGase], lysozyme, and ovotransferrin) of ESM denatured with trypsin, lipases, or heat were compared with those of untreated ESM. Trypsin-treated ESM lost all biological activity (D-values at 54°C were 5.12 and 5.38 min for immobilized and solubilized trypsin, respectively) but showed no significant loss of enzymatic activities. Treatments with porcine lipase and a lipase cocktail did not impact biological or enzymatic activities. Heat denaturation of ESM (at 80 and 100°C for 15 min) resulted in significant decreases in biological activity (D-values of 3.99 and 4.43 min, respectively) and loss of β-NAGase activity. Lysozyme and ovotransferrin activities remained but were significantly reduced. Purified ESM and hen egg white components (i.e., β-NAGase, lysozyme, and ovotransferrin) were added to Salmonella Typhimurium suspensions (in 0.1% peptone water) at varying concentrations to evaluate their biological activity. D-values at 54°C were 4.50 and 3.68 min for treatment with lysozyme or β-NAGase alone, respectively, and 2.44 min for ovotransferrin but 1.47 min for a combination of all three components (similar to values for ESM). Exposure of Salmonella Typhimurium cells to a mixture of ovotransferrin, lysozyme, and β-NAGase or ESM resulted in significant increases in extracellular concentrations of Ca2+, Mg2+, and K+. Transmission electron microscopic examination of Salmonella Typhimurium cells treated with a combination of ovotransferrin, lysozyme, and β-NAGase revealed membrane disruption and cell lysis. The findings of this study demonstrate that ovotransferrin, lysozyme, and β-NAGase are the primary components responsible for ESM antibacterial activity. The combination of these proteins and perhaps other ESM components interferes with interactions between bacterial lipopolysaccharides, sensitizing the outer bacterial membrane to the lethal affects of heat and possibly pressure and osmotic stressors.

ATP-sensitive K + channel openers block sulpiride-induced dopamine release in the rat striatum

In vivo brain microdialysis was used to investigate the role of ATP-sensitive K + (K ATP) channel openers in dopamine release regulated by dopamine autoreceptors in the rat striatum. Local infusion of two K ATP channel openers, nicorandil (10 −5–10 −3 M) and cromakalim (10 −5–10 −3 M), into the striatum thorough the dialysis membrane produced dose-dependent decreases in extracellular concentrations of dopamine. Local application of the dopamine D 2 receptor antagonist, (−)-sulpiride (10 −5 M), produced significant increases in extracellular concentrations of dopamine. Both nicrorandil (10 −5 M) and cromakalim (10 −4 M) blocked significantly (−)-sulpiride (10 −5 M)-induced increases in dopamine levels in the striatum. These results suggest that activation of K ATP channels in the striatum causes decreases in endogenous dopamine release in vivo. Furthermore, the sulpiride-induced increases in dopamine levels caused by blocking the tonic activation of dopamine autoreceptors were inhibited by activation of K ATP channel. These data indicate that K ATP channels may be present in nigrostriatal dopaminergic terminals and that striatal dopamine autoreceptors inhibit dopamine release tonically by activation of K ATP channels.

The role of ATP-sensitive potassium channels in striatal dopamine release: An in vivo microdialysis study

We used in vivo brain microdialysis to investigate the role of adenosine triphosphate (ATP)-sensitive potassium (K ATP) channels in dopamine (DA) release regulated by DA autoreceptors in the rat striatum. Local infusions of the K ATP channel opener nicorandil (10 − 5 – 10 − 3 M) into the striatum through the dialysis membrane produced dose-dependent decreases in extracellular concentrations of DA. Local application of the D 2 receptor antagonist (−)-sulpiride (SLP, 10 − 5 M) or the K ATP channel blocker quinine (QIN, 10 − 3 M) produced significant increases in extracellular concentrations of DA. Nicorandil (10 − 3 M) significantly blocked SLP (10 − 5 M)- or QIN (10 −3 M)-induced increases in DA levels in the striatum. These results suggest that activation or inhibition of the K ATP channel in the striatum causes decreases or increases, respectively, in endogenous DA release in vivo. Furthermore, SLP-induced increases in DA levels caused by blocking the tonic activation of DA autoreceptors are inhibited by the activation of K ATP channels. These data suggest that striatal DA autoreceptors may inhibit DA release tonically by activating the K ATP channel.

Selective Alterations of Extracellular Brain Amino Acids in Relation to Function in Experimental Portal‐Systemic Encephalopathy: Results of an In Vivo Microdialysis Study

Portal-systemic encephalopathy (PSE) is characterized by neuropsychiatric symptoms progressing through stupor and coma. Previous studies in human autopsy tissue and in experimental animal models of PSE suggest that alterations in levels of brain amino acids may play a role in the pathogenesis of PSE. To assess this possibility, levels of amino acids were measured using in vivo cerebral microdialysis in frontal cortex of portacaval-shunted rats administered ammonium acetate (3.85 mmol/kg, i.p.) to precipitate severe PSE. Sham-operated rats served as controls. Portacaval shunting resulted in significant increases of levels of extracellular glutamine (threefold, p < 0.001), alanine (38%, p < 0.01), aspartate (44%, p < 0.05), phenylalanine (170%, p < 0.001), tyrosine (140%, p < 0.001), tryptophan (63%, p < 0.001), leucine (75%, p < 0.001), and serine (60%, p < 0.001). Administration of ammonium acetate to sham-operated animals led to a significant increase in extracellular glutamine and taurine content, but this response was absent in shunted rats. The lack of taurine release into extracellular fluid following ammonium acetate administration in portacaval-shunted rats could relate to the phenomenon of brain edema in these animals. Ammonium acetate administration resulted in significant increases in the extracellular concentrations of phenylalanine and tyrosine in both sham-operated and portacaval-shunted rats. Severe PSE was not accompanied by significant increases in extracellular fluid concentrations of glutamate, aspartate, GABA, tryptophan, leucine, or serine, suggesting that increased spontaneous release of these amino acids in cerebral cortex is not implicated in the pathogenesis of hepatic coma.

Electrical stimulation of reward sites in the ventral tegmental area increases dopamine transmission in the nucleus accumbens of the rat

Abstract In vivo microdialysis with HPLC-ED was used to measure dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA) in the nucleus accumbens of the rat, prior, during, and after 15-min periods of electrical brain stimulation at sites in the ventral tegmental area (VTA) that supported intracranial self-stimulation (ICSS). In the first experiment, both ICSS and yoked stimulation of the VTA evoked significant increases in extracellular concentrations of DA, its metabolites, and 5-HIAA. Comparable results from ICSS and yoked groups were interpreted as evidence that the rewarding properties of VTA stimulation were a causal factor in the elevated DA transmission in the nucleus accumbens, rather than intense operant behavior. Further evidence for this hypothesis came from a second set of data in which changes in extracellular DA levels during the measurement of rate/intensity functions for ICSS were positively correlated. 5-HIAA concentrations also increased during ICSS but these changes were not correlated with either ICSS rate or current intensity, suggesting that changes in serotonin metabolism were unlikely to subserve brain stimulation reward in the VTA. These results add to the growing body of evidence linking changes in extracellular DA in the mesolimbic DA system with both brain stimulation reward and the conditioned and unconditioned rewarding effects of biologically relevant stimuli.