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Notes: Abstract: We examined the effects of the benzodiazepine inverse agonist FG 7142 on dopamine metabolism in the core and shell subdivisions of the nucleus accumbens. FG 7142 (15 mg/kg i.p.) or vehicle was administered to adult male rats 30 min before they were killed. Selected brain regions, including samples from the whole nucleus accumbens as well as core and shell subdivisions, were collected and assayed for tissue concentrations of dopamine and its major metabolite, 3,4-dihydroxyphenylacetic acid. Consistent with previous reports, FG 7142 administration increased dopamine utilization in the medial prefrontal cortex but not the whole nucleus accumbens. Examination of subdivisions revealed that FG 7142 produced increased dopamine utilization in the shell subdivision of the nucleus accumbens. No effect of FG 7142 on dopamine utilization in the core region of the nucleus accumbens was observed. These data are discussed in terms of in vivo microdialysis studies reporting increased dopamine release in the nucleus accumbens after FG 7142 administration.

Notes: Abstract: The effect of the anxiogenic β-carboline methyl-β-carboline-3-carboxyamide (FG 7142) on dopamine release in prefrontal cortex and striatum in the awake freely moving rat was determined using the technique of microdialysis. FG 7142 (25 mg/kg, i.p.) caused a time-dependent increase in dopamine release in prefrontal cortex which was statistically significantly greater than the response to vehicle administration. Dopamine release in striatum was unaltered by FG 7142. Pretreatment of animals with the benzodiazepine antagonist Ro 15-1788 (30 mg/kg, i.p., 15 min prior to FG 7142 administration) completely abolished the increase in dopamine release caused by FG 7142 in prefrontal cortex. These data indicate that the anxiogenic benzodiazepine inverse agonist FG 7142 can selectively increase dopamine release in prefrontal cortex, and that this effect appears to be mediated via the γ-aminobutyric acid/benzodiazepine receptor complex.

Notes: Abstract: Extracellular fluid levels of dopamine and neurotensin in the rat prefrontal cortex were measured using in vivo microdialysis. Electrical stimulation of the median forebrain bundle resulted in increased release of both dopamine and neurotensin from the prefrontal cortex. Thus, stimulation of neurons in which dopamine and neurotensin are colocalized can evoke the in vivo release of both substances.

Notes: : Dopamine or agonists with D1 receptor potency stimulated cyclic AMP (cAMP) accumulation in whole cell preparations of NS20Y neuroblastoma cells. The accumulation of cAMP after D1 stimulation was rapid and linear for 3 min. Both dopamine and the novel D1 receptor agonist dihydrexidine stimulated cAMP accumulation two-to threefold over baseline. The pseudo-Km for dopamine was ⋍2 μM, whereas for dihydrexidine it was ⋍30 nM. The effects of both drugs were blocked by either the D1-selective antagonist SCH23390 (Ki, 0.3 nM) or the nonselective antagonist (+)-butaclamol (Ki, 5 nM). Both (−)-butaclamol and the D2-selective antagonist (−)-sulpiride were ineffective (Ki 〉 3 μM). Forskolin (10 μM), prostaglandin E1 (1 μM), and adenosine (10 μM) also stimulated cAMP accumulation, but none were antagonized by SCH23390 (1 μM). Finally, muscarinic receptor stimulation (100 μM carbachol) inhibited both D1-and forskolin-stimulated increases in cAMP accumulation by 80%. The present results indicate that NS20Y neuroblastoma cells have D1 receptors that are coupled to adenylate cyclase, and that these receptors have a pharmacological profile similar to that of the D1 receptor(s) found in rat striatum.

Notes: Abstract: Systemic administration of the anxiogenic benzodiazepine inverse agonist FG 7142 has been shown to increase selectively dopamine utilization in the medial prefrontal cortex and the shell, but not core, subregion of the nucleus accumbens. In the present study, we examined the functional interaction between benzodiazepine and N-methyl-d-aspartate receptor influences on dopamine utilization in these areas. Male Sprague-Dawley rats were pretreated with the glycine receptor antagonist (+)-HA 966 (15 mg/kg, i.p.) or saline 15 min before FG 7142 (20 mg/kg, i.p.) or vehicle administration. Subjects were killed 30 min later and assayed for tissue concentrations of dopamine and its major metabolite 3,4-dihydroxyphenylacetic acid in the core and shell subdivisions of the nucleus accumbens and the medial prefrontal cortex. (+)-HA 966 administration blocked FG 7142-induced increased dopamine utilization in both the medial prefrontal cortex and the shell subdivision of the nucleus accumbens. Results are discussed in terms of N-methyl-d-aspartate receptor influences on the response of mesoaccumbal dopamine neurons to stress.

Notes: Abstract: Methylxanthines can produce behavior resembling opiate withdrawal in rats. Since previous studies have demonstrated the involvement of central noradrenergic systems during naloxone-precipitated withdrawal, the effects of 3-isobutyl-l-methylxanthine (IBMX) on norepinephrine metabolism in rat brain were studied. It was found that administration of IBMX elevated levels of the major norepinephrine metabolite 3-methoxy-4-hydroxyphenyl-glycol (MHPG) in areas innervated by the locus coeruleus. The increase in MHPG was noted 1 h after administration and was maximal (270% of control) after 3 h. Levels of another norepinephrine metabolite, 3,4-di-hydroxyphenylglycol, followed a similar pattern and time course. Coad-ministration of naloxone with IBMX did not affect the IBMX-induced elevation in MHPG. Administration of the a-agonist clonidine, however, antagonized the effects of IBMX on MHPG levels. The effects of IBMX and clonidine were dose dependent; the lowest dose of IBMX needed to elevate MHPG was 30μmol/kg (i.p.), and clonidine (180 nmol/kg) reduced the effect of IBMX (100 μmol/kg) by 50%. The data, discussed in terms of a methylxanthine-noradrenergic interaction, suggest that withdrawal behaviors in general may be subserved by hyperactive noradrenergic neurons.

Notes: Abstract: In an attempt to determine if alterations in intraneuronal Ca2+ may regulate tyrosine hydroxylase activity, brain slices were subjected to experimental manipulations known to increase the intraneuronal concentration of free Ca2+ ions. Incubation of either striatal or olfactory tubercle slices in a Na+-free medium for 15 min at 37° resulted in a marked increase in the activity of tyrosine hydroxylase present in the 20,000 g supernatant fraction of homog-enates prepared from the slices. Tyrosine hydroxylase isolated from slices previously incubated in a Na+-free, choline-enriched medium or in a Na+-free, sucrose-enriched medium exhibited maximal activities when assayed at pH 6.0 and 7.0, respectively. However, the percentage stimulation of enzyme activity induced by incubation of the slices in a Na+-free medium was maximal when the enzyme assays were performed at pH 7.0. The observed increase in enzyme activity seems to be mediated by a decrease in the apparent Km of the enzyme for pteridine cofactor, regardless of whether the kinetic enzyme analyses were conducted at pH 6.0 or 7.0, and by an increase in the K1 of the enzyme for end-product inhibitor dopamine. The apparent kinetic changes in the enzyme do not seem to result from alterations in the endogenous dopamine content of the slices, and they are independent of any increase in dopamine release that might have occurred as a response to the augmented intraneuronal Ca2+ concentration. Furthermore, the activation of tyrosine hydroxylase produced by incubating slices in a Na+-free medium is observed even in slices depleted of dopamine by pretreatment of rats with reserpine 90 min before preparation of brain slices. The activation of tyrosine hydroxylase observed under these experimental conditions does not seem to be mediated by cAMP or by a cAMP-dependent phosphorylation process. It is suggested that the changes in tyrosine hydroxylase reported are mediated primarily by a rise in the free Ca2+ concentration within the nerve tissue. These observations are consistent with the hypothesis that the kinetic activation of tyrosine hydroxylase produced after depolarization of central dopaminergic neurons may occur through a Ca2+-dependent event other than transmitter release.

Notes: Abstract: [3H]Choline can be transported across cell membranes by high-affinity (KT 5 μM) and low-affinity (KT≫ 5 μM) systems. High-affinity choline accumulation (HACA) has been demonstrated in synaptosomes made from cholinergic brain regions such as the hippocampus and caudate-putamen. In cell culture. HACA has been demonstrated in glia and avian telencephalon, dissociated spinal cord, and muscle fibroblasts. We examined [3H]choline accumulation in a single normal human fibroblast line cultured from skin biopsy. [3H]Choline accumulation was temperature-dependent and linear with incubation time up to 6 min at 0.125 μM-choline. The apparent KT for [3H]choline was 5 μM which is similar to that observed in avian fibroblasts. Isoosmotic replacement of Na+ with either Li+ (144 MM) or sucrose (288 mM) severely reduced [3H]choline accumulation (by 70–90%). Pre-incubation with ouabain (100 μM), sodium orthovanadate (100 μM), or 2,4-dinitrophenol (100 μM), or replacement of Ca2+ by Mg2+ had little or no effect on subsequent [3H]choline accumulation. [3H]Choline accumulation was inhibited by hemicholinium-3 (HC-3); after pre-incubation in HC-3 at 37°C for 10 min, the IC50 (at 0.125 μM-chohne) was 5.6 μM. The HC-3 sensitivity, Na+ dependence, and low KT suggest that human skin fibroblasts have a high-affinity transport system for choline.

Notes: Abstract— The activity of glutamate decarboxylase in rat striatal slices was estimated following preincubation in either a non-depolarizing medium or in a depolarizing medium. GAD activity was significantly increased following preincubation in normal Krebs-Ringer-phosphate medium as compared to activity in slices which were not preincubated. GAD activity in slices which were depolarized in high potassium Krebs-Ringer-phosphate medium was further increased when compared to activity in slices which were preincubated in normal medium. The depolarization-induced increase in GAD activity was graded in response to the time of depolarization, and both the increase following preincubation in normal medium and the increase following preincubation in high potassium displayed a relative requirement for calcium. In addition, net GABA formation from endogenous glutamate was increased in slices preincubated in high potassium medium as compared to net GABA formation from endogenous glutamate in slices preincubated in non-depolarizing medium. In support of the use of [14C]CO2 trapping as an estimate of GAD activity in slices, preincubation of slices in the presence of the GAD inhibitor glutamic acid γ-hydrazide caused a concentration-related inhibition of [14C]CO2 evolution.

Notes: Abstract— Rat liver and brain slices were incubated in vitro with [3H]melatonin. Liver slices synthesized small amounts of [3H]5-methoxyindoleacetic acid ([3H]5-MIAA) along with other melatonin metabolites including 6-hydroxymelatonin. Pretreatment of animals prior to killing with the irreversible monoamine oxidase inhibitor pargyline allowed [3H]5-methoxytryptamine ([3H]5-MT) to be recovered from the incubation. No [3H]5-MIAA or [3H]5-MT could be detected in incubations with hypothalamic slices or following intraventrieular injection of [3H]melatonin. The possibility that the deacetylase aryl acylamidase was in part responsible for the deacetylation occurring in liver slices was examined. Liver aryl acylamidase was able to utilize [3H]melatonin as substrate to produce [3H]5-MT. Furthermore, the liver enzyme was inhibited by melatonin (Ki. 1 mm) when tested with the alternate substrate o-nitroacetanalide. Brain aryl acylamidase did not generate any detectable [3H]5-MT nor was it inhibited by melatonin. These results suggest that 5-MT is not formed in brain from melatonin although trace amounts of 5-MT in the periphery could be derived from this precursor.