Presynaptic events involved in neurotransmission

Acidity and Acid-Sensing Ion Channels in the Normal and Alzheimer's Disease Brain

Alzheimer's disease prevalence has reached epidemic proportion with very few treatment options, which are associated with a multitude of side effects. A potential avenue of research for new therapies are protons, and their associated receptor: acid-sensing ion channels (ASIC). Protons are often overlooked neurotransmitters, and proton-gated currents have been identified in the brain. Furthermore, ASICs have been determined to be crucial for proper brain function. While there is more work to be done, this review is intended to highlight protons as neurotransmitters and their role along with the role of ASICs within physiological functioning of the brain. We will also cover the pathophysiological associations between ASICs and modulators of ASICs. Finally, this review will sum up how the studies of protons, ASICs and their modulators may generate new therapeutic molecules for Alzheimer's disease and other neurodegenerative diseases.

Rational identification of enoxacin as a novel V-ATPase-directed osteoclast inhibitor

Binding between vacuolar H⁺-ATPases (V-ATPases) and microfilaments is mediated by an actin binding domain in the B-subunit. Both isoforms of mammalian B-subunit bind microfilaments with high affinity. A similar actin-binding activity has been demonstrated in the B-subunit of yeast. A conserved “profilin-like” domain in the B-subunit mediates this actin-binding activity, named due to its sequence and structural similarity to an actin-binding surface of the canonical actin binding protein profilin. Subtle mutations in the “profilin-like” domain eliminate actin binding activity without disrupting the ability of the altered protein to associate with the other subunits of V-ATPase to form a functional proton pump. Analysis of these mutated B-subunits suggests that the actin-binding activity is not required for the “housekeeping” functions of V-ATPases, but is important for certain specialized roles. In osteoclasts, the actin-binding activity is required for transport of V-ATPases to the plasma membrane, a prerequisite for bone resorption. A virtual screen led to the identification of enoxacin as a small molecule that bound to the actin-binding surface of the B2-subunit and competitively inhibited B2-subunit and actin interaction. Enoxacin disrupted osteoclastic bone resorption in vitro, but did not affect osteoblast formation or mineralization. Recently, enoxacin was identified as an inhibitor of the virulence of Candidaalbicans and more importantly of cancer growth and metastasis. Efforts are underway to determine the mechanisms by which enoxacin and other small molecule inhibitors of B2 and microfilament binding interaction selectively block bone resorption, the virulence of Candida, cancer growth, and metastasis.

5-HT2A receptor antagonist M100907 reduces serotonin synthesis: an autoradiographic study

The effects of the administration of the serotonin (5-HT)(2A) antagonist, M100907, on 5-HT synthesis rates, were evaluated using the α-[(14)C]methyl-l-tryptophan (α-MTrp) autoradiographic method. In the treatment study, M100907 (10mg/kg) was injected intraperitoneally 30 min before the α-MTrp injection (30 μCi over 2 min). A single dose of M100907 caused a significant decrease in the synthesis in the anterior olfactory nucleus, accumbens nucleus, frontal cortex, sensory-motor cortex, cingulate cortex, medial caudate-putamen, dorsal thalamus, substantia nigra, inferior collicus, raphe magnus nucleus, superior olive, and raphe pallidus nucleus. These data suggest that the terminal 5-HT(2A) receptors are involved in the regulation of 5-HT synthesis in the entire brain. Further, 5-HT synthesis is likely regulated by the 5-HT(2A) antagonistic property of M100907 in the cortices, anterior olfactory nucleus, caudate putamen, and nucleus accumbens.

The lumped constant of α-methyl-l-tryptophan is not influenced by drugs acting through serotonergic system

Lumped constant (LC) is a constant used to convert brain trapping constant of α-methyl-l-tryptophan (using α-(14)C-methyl-l-tryptophan) into the constant for conversion of tryptophan into serotonin (5-hydroxytryptamine, 5-HT), which can be then used with certain assumptions in the calculation of the brain regional 5-HT synthesis rate. The aim of the present study was to investigate the acute effects of two drugs on the regional stability of the LC and possible effect on its value. Drugs used were a selective 5-HT reuptake inhibitor, fluoxetine, and a drug that releases 5-HT and inhibits 5-HT uptake, d,l-fenfluramine. The values of the LC from those experiments were compared with the value of LC obtained in the saline treated rats. KT is the constant for tryptophan conversion into 5-HT, which was measured by an autoradiographic method in more than twenty brain regions, using labelled tryptophan ((14)C-Trp) as tracer, after the fraction incorporated into proteins was removed. The trapping constant K(α) for α-methyl-l-tryptophan was also measured autoradiographically in a separate group of rats. All measurements were done in drug and saline (control) treated rats. The regional LC constants were calculated as the ratios between KT and K(α). Statistical evaluation showed that the regional values in each of these three sets were normally distributed, and that the three sets of LC values calculated as the mean of logarithmic differences (saline 0.450 ± 0.055; fluoxetine 0.429 ± 0.091; d,l-fenfluramine 0.48 ± 0.09) did not differ significantly. The overall weighted mean value of the LC from all three sets of measurements was 0.452 ± 0.041, and this value was not significantly different from the LC value of 0.42 ± 0.07, i.e. value obtained in our previous studies. These results showed the unaltered LC value in discrete rat brain regions after treatment with fluoxetine or d,l-fenfluramine, and confirmed that the numerical value of the LC used in our previous studies was not altered by treatment with drugs affecting 5-HT transmission and 5-HT synthesis rate.

Gender differences in alpha-[(11)C]MTrp brain trapping, an index of serotonin synthesis, in medication-free individuals with major depressive disorder: a positron emission tomography study

Women are at higher risk than men for developing major depressive disorder (MDD), but the mechanisms underlying this higher risk are unknown. Here, we report proportionally normalized alpha-[(11)C]methyl-L-tryptophan brain trapping constant (alpha-[(11)C]MTrp K*(N)), an index of serotonin synthesis, in 25 medication-free individuals with MDD and in 25 gender- and age-matched healthy subjects who were studied using positron emission tomography (PET). Comparisons of alpha-[(11)C]MTrp K*(N) values between the men and women were conducted at the voxel and cluster levels using Statistical Parametric Mapping 2 (SPM2) analysis. In addition, the alpha-[(11)C]MTrp K*(N) values on both sides of the brain were extracted and compared to identify the left to right differences, as well as the gender differences. Women with MDD displayed higher alpha-[(11)C]MTrp K*(N) than men in the inferior frontal gyrus, anterior cingulate cortex (ACC), parahippocampal gyrus, precuneus, superior parietal lobule, and occipital lingual gyrus. In a matched group of normal subjects the gender differences were opposite from those found in MDD patients. Significant hemispheric differences in fronto-limbic structures between men and women with MDD were also observed. The K*(N) extracted from the volumes identified in MDD patients and in male and female normal subjects suggested no significant differences between males and females. In conclusion, depressed women have higher serotonin synthesis in multiple regions of the prefrontal cortex and limbic system involved with mood regulation, as compared with depressed men. Gender differences in brain serotonin synthesis may be related to higher risk for MDD in women.

Chronic citalopram treatment elevates serotonin synthesis in flinders sensitive and flinders resistant lines of rats, with no significant effect on Sprague-Dawley rats

The influence of citalopram on regional 5-hydroxytryptamine (serotonin, 5-HT) synthesis, one of the most important presynaptic parameters of serotonergic neurotransmission, was studied. Sprague-Dawley (SPD) rats were used as the controls, and Flinders Resistant Line (FRL) rats were used as auxiliary controls, to hopefully obtain a better understanding of the effects of citalopramon Flinders Sensitive Line (FSL; "depressed") rats. Regional 5-HT synthesis was evaluated using a radiographic method with a labelled tryptophan analog tracer. In each strain of rats, the animals were treated with citalopram (10 mg/(kg day)) or saline for 14 days. The groups consisted of between fourteen and twenty rats. There were six groups of rats with citalopram (CIT) and saline (SAL) groups in each of the strains (SPD-AL, SPD-IT, FRL-AL, FRL-IT, FSL-AL and FSL-IT). A two-factor analysis of variance was used to evaluate the effect of the treatment c., SPD-SAL relative to SPD-CIT) followed by planned comparisons to evaluate the effect in each brain region. In addition, the planned comparison with appropriate contrast was used to evaluate a relative effects in SPD relative to FSL and FRL, and FSL relative to FRL groups. A statistical analysis was first performed in the a priori selected regions, because we had learned, from previous work, that it was possible to select the brain regions in which neurochemical variables had been altered by the disorder and subsequent antidepressant treatments. The results clearly show that citalopram treatment does not have an overall effect on synthesis in the control SPD rats; there was no significant (p > 0.05) difference between the SPD-SAL and SPD-CIT rats. In "depressed" FSL rats, citalopram produced a significant (p < 0.05) elevation of synthesis in seventeen out of thirty-four regions, with a significant (p < 0.05) reduction in the dorsal and median raphe. In the FRL rats, there was a significant (p < 0.05) elevation in the synthesis in twenty-two out of thirty-four brain regions, with a reduction in the dorsal raphe. In addition to these regions magnus raphe was different in the SPD and FSL groups, but it was on the statistical grounds identified as an outlier. There were significant changes produced in the FSL and FRL rats in thirteen out of seventeen a priori selected brain regions, while in the SPD rats, citalopram produced significant changes in only four out of seventeen a priori selected regions. The statistical evaluation also revealed that changes produced by citalopram in the FSL and FRL rats were significantly greater than those in the SPD rats and that there was no significant difference between the effect produced in the FSL and FRL rats. The presented results suggest that in "depressed" FSL rats, the antidepressant citalopram elevates 5-HT synthesis, which probably in part relates to the reported improved in behaviour with citalopram.

AGN-2979, an inhibitor of tryptophan hydroxylase activation, does not affect serotonin synthesis in Flinders Sensitive Line rats, a rat model of depression, but produces a significant effect in Flinders Resistant Line rats

The neurotransmitter, serotonin, is involved in several brain functions, including both normal, physiological functions, and pathophysiological functions. Alterations in any of the normal parameters of serotonergic neurotransmission can produce several different psychiatric disorders, including major depression. In many instances, brain neurochemical variables are not able to be studied properly in humans, thus making the use of good animal models extremely valuable. One of these animal models is the Flinders Sensitive Line (FSL) of rats, which has face, predictive and constructive validities in relation to human depression. The objective of this study was to quantify the effect of the tryptophan hydroxylase (TPH) activation inhibitor, AGN-2979, on the FSL rats (rats with depression-like behaviour), and compare it to the effect on the Flinders Resistant Line (FRL) of rats used as the control rats. The effect was evaluated by measuring changes in regional serotonin synthesis in the vehicle treated rats (FSL-VEH and FRL-VEH) relative to those measured in the AGN-2979 treated rats (FSL-AGN and FRL-AGN). Regional serotonin synthesis was measured autoradiographically in more than 30 brain regions. The measurements were performed using alpha-[(14)C]methyl-l-tryptophan as the tracer. The results indicate that AGN-2979 did not produce a significant reduction of TPH activity in the AGN-2979 group relative to the vehicle group (a reduction would have been observed if there had been an activation of TPH by the experimental setup) in the FSL rats. On the other hand, there was a highly significant reduction of synthesis in the FRL rats treated by AGN-2979, relative to the vehicle group. Together, the results demonstrate that in the FSL rats, AGN-2979 does not affect serotonin synthesis. This suggests that there was no activation of TPH in the FSL rats during the experimental procedure, but such activation did occur in the FRL rats. Because of this finding, it could be hypothesized that TPH in the FSL rats cannot be easily activated. This may contribute to the development of depressive-like symptoms in the FSL rats ("depressed" rats), as they cannot easily modulate their need for elevated amounts of this neurotransmitter, and possibly other neurotransmitters. Further, because these rats represent a very good model of human depression, one can hypothesize that humans who do not have readily activated TPH may be more prone to develop depression.

Both acute and chronic buspirone treatments have different effects on regional 5-HT synthesis in Flinders Sensitive Line rats (a rat model of depression) than in control rats

The main objective of this investigation was to evaluate the effects of buspirone, a 5-HT(1A) agonist with some partial agonist properties and also an antidepressant, on regional 5-HT synthesis in Flinders Sensitive Line (FSL) rats ("depressed"), and to compare the effects to the Flinders Resistant Line (FRL) control rats (not "depressed"). In addition results were compared to those previously reported in normal Sprague-Dawley (SPD) rats (normal control). Serotonin synthesis in both FSL and FRL rats was measured following acute and chronic treatments with buspirone. Both of these strains were derived from the SPD rats. No direct comparison was done between the FSL saline and FRL saline groups, or the FSL buspirone and FRL buspirone groups, because the objective of the studies was to evaluate effects of buspirone in these two strains. The results show that acute treatment with buspirone elevates 5-HT synthesis throughout the brain in the FRL rats. In the FSL rats, there were reductions in some brain regions (e.g., dorsal and median raphe, amygdala, anterior olfactory nucleus, substantia nigra reticulate), while in other regions, there were increases in the synthesis observed (e.g., frontal, parietal, visual and somatosensory cortices, ventral hippocampus). In 20 out of the 30 brain regions investigated in the FSL rats, there was no significant change in the synthesis following acute buspirone treatment. During the chronic treatment, buspirone produced a significant reduction of 5-HT synthesis in 15 out of 30 brain regions in the FRL rats. In the FSL rats, buspirone produced a significant elevation of the synthesis in 10 out of 30 brain regions. In both the FSL and FRL rats, buspirone produced rather different effects than those reported previously for SPD (normal) rats. The acute effect in the FSL rats was somewhat similar to the effect reported previously for the SPD rats, while in the FRL rats, the acute buspirone treatment produced an effect observed previously in treatments with 5-HT(1A) antagonists suggesting an action of buspirone as partial agonist in FRL rats. The data suggest that with respect to 5-HT synthesis, FRL rats differ from SPD rats (a natural control; normal rats) and, as such, indicate that when the effects related to the serotonergic system (e.g., influence of serotonergic drugs) are studied in the FSL rats and compared to those in the FRL rats, any conclusions drawn may not reflect differences relative to a normal rat.

A genetic rat model of depression, Flinders sensitive line, has a lower density of 5-HT(1A) receptors, but a higher density of 5-HT(1B) receptors, compared to control rats

Deficiencies in brain serotonergic neurotransmission, which is in part associated with the alteration of brain serotonin (5-HT) receptors, have been proposed as part of a neurochemical imbalance in affective disorders, including depression. The drugs used for the treatment of these disorders generally act through and/or on the serotonergic system. Different animal models of depression have provided researchers with tools to obtain a better understanding of drug actions and possibilities to obtain insight into the neurochemical bases of these disorders. The measurements of the 5-HT(1A) and 5-HT(1B) receptor densities in a rat model of depression, Flinders sensitive line (FSL) rats, and comparisons with Sprague-Dawley (SPD) and Flinders resistant line (FRL) rats, are reported here. The receptor sites were quantified by autoradiography in more than 25 distinct brain regions known to have relatively large densities of respective sites. Some brain regions (e.g., dental gyrus, septal nucleus) were divided into several parts, according to previously known subdivisions, because of a substantial heterogeneity of these receptors. The densities in the FSL rats ("depressed" rats) were compared statistically to those in the SPD rats. In addition, comparisons were made to the densities in the FRL rats (rats not showing depressive symptoms). Comparisons were performed with the SPD and FRL rats because both of these strains have been used as control animals in studies of FSL rats. The results show that the densities of 5-HT(1A) receptors are not significantly different between the FSL and SPD rats, but they are significantly different from the FRL rats. 5-HT(1A) receptor density is significantly higher in the FRL rats than the SPD rats. The 5-HT(1B) receptors were significantly greater in the FSL rats than in either the SPD or FRL rats. In addition, the FRL rats have 5-HT(1B) receptor densities significantly lower in many brain regions than the SPD rats. The data presented here, in addition to previously reported differences in regional synthesis between these strains and the effect of acute citalopram on synthesis, suggest that SPD rats are likely a more appropriate control than FRL rats, when studies of FSL rats are performed with drugs acting directly or indirectly on, or through, the brain serotonergic system. However, comparisons, particularly of neurochemical and/or biological parameters in FRL rats, may reveal new insight into the alterations of 5-HT neurotransmission in this animal model of depression and possibly human depression, as well as the elevation of symptoms with treatments. The data also suggest that there could be a different fraction of 5-HT(1A) receptors in high and low affinity states in these strains, as well as the possibility of different intracellular signalling.

Acute citalopram has different effects on regional 5-HT synthesis in FSL, FRL, and SDP rats: an autoradiographic evaluation

In this study, we measured the effect of an acute treatment of citalopram on 5-hydroxytryptamine (5-HT) synthesis in a genetic rat model of depression, the Flinders Sensitive Line (FSL) rats, their counterparts, the Flinders Resistant Line (FRL) rats, and outbred Sprague-Dawley (SPD) rats, using the alpha-[(14)C]methyl-l-tryptophan (alpha-MTrp) autoradiographic method. A comparison of 5-HT synthesis in the FSL rats treated with citalopram (FSL-CTP) and those treated with saline (FSL-SAL) indicate that citalopram reduces global 5-HT synthesis in the FSL rats, as well as in all the brain areas investigated. The reduced synthesis was also observed in the dorsal raphe (DR) nucleus and the median raphe (MR) nucleus. The comparison of the synthesis between the citalopram-treated SPD rats (SPD-CTP) and the saline-treated SPD rats (SPD-SAL) revealed a global increase of 5-HT synthesis in the SPD-CTP group, as well as an increase in some terminal areas, but a reduction in the DR and the MR. In contrast to the reduction throughout the brain in the FSL rats, the FRL rats treated with citalopram (FRL-CTP), when compared to the saline group (FRL-SAL), showed a global increase of 5-HT synthesis, as well as in most of the terminal areas and in the DR and the MR. The reduction of 5-HT synthesis throughout the brain in the FSL rats is likely, in part, a result of reported supersensitivity of the 5-HT(1A) receptors. Comparing changes in the SPD, FRL, and FSL rats treated with citalopram to their respective controls (saline-treated rats), the FSL rats treated acutely with citalopram were the only rats that exhibited lower 5-HT synthesis rates in all of the limbic areas, the basal ganglia, and the neocortices. This may be related to the pathophysiological basis of depressive characteristics in FSL rats. The citalopram treatment produced unexpected results in the FRL rats: 5-HT synthesis was elevated not only in most of the terminal areas, but also in the cell body areas, the DR and MR. The increase of 5-HT synthesis throughout the brain in the FRL rats is likely, in part, a result of the reported subsensitivity of the 5-HT(1A) receptors, and possibly other sites through which 5-HT synthesis could be controlled (e.g., 5-HT(1B)). In addition differences in intracellular signaling could be at least in part responsible for these differences.

The a3 isoform of V-ATPase regulates insulin secretion from pancreatic beta-cells

Vacuolar-type H(+)-ATPase (V-ATPase) is a multi-subunit enzyme that has important roles in the acidification of a variety of intracellular compartments and some extracellular milieus. Four isoforms for the membrane-intrinsic subunit (subunit a) of the V-ATPase have been identified in mammals, and they confer distinct cellular localizations and activities on the proton pump. We found that V-ATPase with the a3 isoform is highly expressed in pancreatic islets, and is localized to membranes of insulin-containing secretory granules in beta-cells. oc/oc mice, which have a null mutation at the a3 locus, exhibited a reduced level of insulin in the blood, even with high glucose administration. However, islet lysates contained mature insulin, and the ratio of the amount of insulin to proinsulin in oc/oc islets was similar to that of wild-type islets, indicating that processing of insulin was normal even in the absence of the a3 function. The insulin contents of oc/oc islets were reduced slightly, but this was not significant enough to explain the reduced levels of the blood insulin. The secretion of insulin from isolated islets in response to glucose or depolarizing stimulation was impaired. These results suggest that the a3 isoform of V-ATPase has a regulatory function in the exocytosis of insulin secretion.

Acute effects of moclobemide and deprenyl on 5-HT synthesis rates in the rat brain: An autoradiographic study

Serotonin (5-HT), norepinephrine (NE) and dopamine (DA) released from nerve terminals in the brain are primarily removed from the synaptic cleft by a reuptake mechanism. In part, the homeostasis is maintained by monoamine oxidase (MAO) deamination achieved primarily intracellularly. The present study's aim was to examine the effect of the acute administration of the MAO inhibitors, moclobemide (a MAO-A inhibitor) and deprenyl (a MAO-B inhibitor), on 5-HT synthesis rates, measured in discrete regions of the rat brain by an autoradiographic method, using alpha-[14C]methyl-l-tryptophan as a tracer. MAO inhibitors have different effects on 5-HT synthesis rates in the cell bodies and areas of the nerve terminals. Moclobemide (10 mg/kg, i.p. 30 min before the tracer injection) and deprenyl (3 mg/kg, i.p. 2 h before the tracer injection) decreased the 5-HT synthesis rates in the dorsal (-18% and -22%) and median (-22% and -33%) raphe, respectively. Moclobemide also significantly decreased 5-HT synthesis in the entire nerve terminal areas investigated. The reductions were between 23% (cingulate cortex) and 50% (locus coeruleus). Deprenyl did not significantly affect 5-HT synthesis in the nerve terminals. The present results suggest that MAO-A, and to a lesser extent, MAO-B, are involved in the regulation of 5-HT synthesis in the rat brain. The mechanism(s) of MAO inhibitors' action on 5-HT synthesis in the raphe nuclei are probably related to an increase in the extraneuronal 5-HT concentration and also to the interaction between the serotonergic and catecholaminergic neurons. The reduction of 5-HT synthesis in the raphe nuclei likely occurs by an action of extracellular 5-HT via the dendritic autoreceptors with a possible contribution from the action of extracellular DA and NE. In the terminal regions, the most likely mechanism is via the presynaptic autoreceptors through which elevated extraneuronal 5-HT acts on synthesis control. However, there is also a possibility that the elevation in intraneuronal 5-HT directly inhibits its synthesis, especially following deprenyl treatment. A great influence of moclobemide on 5-HT synthesis could be related to its antidepressant action.

Brain 5-HT synthesis in the Flinders Sensitive Line rat model of depression: An autoradiographic study

Alterations of serotonin (5-HT) levels and serotonergic transmission have been associated with depression. 5-HT synthesis is an important factor of serotonergic neurotransmission that may also be altered in depression. Many studies of the relationships between brain serotonergic functions and affective disorders have been performed in different animal models. In this study, brain regional 5-HT synthesis was examined using the alpha-[(14)C]methyl-L-tryptophan (alpha-MTrp) autoradiographic method in a genetic rat model of depression, Flinders Sensitive Line (FSL) rats, and was compared to both the Flinders Resistant Line (FRL) rats and the control Sprague-Dawley (SD) rats. The plasma concentration of free tryptophan in the FSL rats was not significantly different (p > 0.05; ANOVA and post-hoc Bonferroni correction) when compared to that of the FRL and SD rats. The FSL rats had significantly lower 5-HT synthesis (one sample two-tailed t-test on the ratio) than both the FRL and SD rats (the mean ratios were 0.78 +/- 0.12 and 0.73 +/- 0.15, respectively). Overall, the 5-HT synthesis in the FRL rats was not significantly different (p > 0.05) from that in the SD rats (one sample two-tailed t-test on the ratio and the mean ratio was 0.93 +/- 0.13). Studies of individual brain structures, such as the raphe nuclei and their many terminal areas, including the nucleus accumbens, cingulate and frontal cortex, hippocampus, amygdala, and thalamus revealed significant reductions (typically 25-50%) in 5-HT synthesis in the FSL rats compared to the non-depressive FRL and SD rats. These results suggest that significantly reduced 5-HT synthesis in the raphe nuclei and limbic areas in FSL rats may contribute to their depressive features.

Effects of anpirtoline on regional serotonin synthesis in the rat brain: an autoradiographic study

Anpirtoline has been described as an agonist at 5-HT1B receptors with a relatively high potency. It also acts as an agonist at 5-HT1A receptors, but has a lower potency than at the 5-HT1B sites. There is very little known about the mechanism by which anpirtoline influences regional 5-HT synthesis. The aim of the present study was to investigate the effects of acutely and chronically administered anpirtoline on 5-HT synthesis in the rat brain using the autoradiographic alpha-[14C]methyl-L-tryptophan method. In the acute study, anpirtoline (2.0 mg/kg) was administered intraperitoneally 30 min before the tracer injection. The control rats were injected with the same volume of saline. In the chronic study, anpirtoline (2 mg/kg per day) was injected subcutaneously in saline once a day for 10 days. There were no significant differences between the plasma-free and total tryptophan concentrations between the anpirtoline treatment and the respective control groups. In the acute experiment, 5-HT synthesis rates in all of the brain areas investigated were significantly decreased by anpirtoline when compared to the saline-treated group. In the chronic anpirtoline experiment, 5-HT synthesis rates of almost all of the projection areas, as well as the raphe nuclei, were normalized or had a tendency to be normalized. These results suggest that it is likely that the terminal 5-HT1B receptors are involved in the regulation of 5-HT synthesis in the projection areas and that 5-HT synthesis, in the raphe, is likely influenced by anpirtoline's 5-HT1A and/or 5-HT1B agonistic properties.

Mitochondrial clustering at the vertebrate neuromuscular junction during presynaptic differentiation

During vertebrate neuromuscular junction (NMJ) development, presynaptic motor axons differentiate into nerve termini enriched in synaptic vesicles (SVs). At the nerve terminal, mitochondria are also concentrated, but how mitochondria become localized at these specialized domains is poorly understood. This process was studied in cultured Xenopus spinal neurons with mitochondrion-specific probe MitoTracker and SV markers. In nerve-muscle cocultures, mitochondria were concentrated stably at sites where neurites and muscle cells formed NMJs, and mitochondria coclustered with SVs where neurites were focally stimulated by beads coated with growth factors. Labeling with a mitochondrial membrane potential-dependent probe JC-1 revealed that these synaptic mitochondria were with higher membrane potential than the extrasynaptic ones. At early stages of bead-stimulation, actin-based protrusions and microtubule fragmentation were observed in neurites at bead contact sites, suggesting the involvement of cytoskeletal dynamics and rearrangement during presynaptic differentiation. Treating the cultures with an actin polymerization blocker, latrunculin A (Ltn A), almost completely abolished the formation of actin-based protrusions and partially inhibited bead-induced mitochondrial and SV clustering, whereas the microtubule disrupting agent nocodazole was ineffective in inhibiting the clustering of mitochondria and SVs. Lastly, in contrast to Ltn A, which blocked bead-induced clustering of both mitochondria and SVs, the ser/thr phosphatase inhibitor okadaic acid inhibited SV clustering but not mitochondrial clustering. These results suggest that at developing NMJs, synaptogenic stimuli induce the clustering of mitochondria together with SVs at presynaptic terminals in an actin cytoskeleton-dependent manner and involving different intracellular signaling molecules.

Creatine and creatinine metabolism

The goal of this review is to present a comprehensive survey of the many intriguing facets of creatine (Cr) and creatinine metabolism, encompassing the pathways and regulation of Cr biosynthesis and degradation, species and tissue distribution of the enzymes and metabolites involved, and of the inherent implications for physiology and human pathology. Very recently, a series of new discoveries have been made that are bound to have distinguished implications for bioenergetics, physiology, human pathology, and clinical diagnosis and that suggest that deregulation of the creatine kinase (CK) system is associated with a variety of diseases. Disturbances of the CK system have been observed in muscle, brain, cardiac, and renal diseases as well as in cancer. On the other hand, Cr and Cr analogs such as cyclocreatine were found to have antitumor, antiviral, and antidiabetic effects and to protect tissues from hypoxic, ischemic, neurodegenerative, or muscle damage. Oral Cr ingestion is used in sports as an ergogenic aid, and some data suggest that Cr and creatinine may be precursors of food mutagens and uremic toxins. These findings are discussed in depth, the interrelationships are outlined, and all is put into a broader context to provide a more detailed understanding of the biological functions of Cr and of the CK system.

Effect of benzodiazepines on the epithelial and neuronal high-affinity glutamate transporter EAAC1

EAAC1-mediated glutamate transport concentrates glutamate across plasma membranes of brain neurons and epithelia. In brain, EAAC1 provides a presynaptic uptake mechanism to terminate the excitatory action of released glutamate and to keep its extracellular concentration below toxic levels. Here we report the effect of well known anxiolytic compounds, benzodiazepines, on glutamate transport in EAAC1-stably transfected Chinese hamster ovary (CHO) cells and in EAAC1-expressing Xenopus laevis oocytes. Functional properties of EAAC1 agreed well with already reported characteristics of the neuronal high-affinity glutamate transporter (Km D-Asp,CHO cells: 2.23+/-0.15 microM; Km D-Asp,oocytes: 17.01+/-3.42 microM). In both expression systems, low drug concentrations (10-100 microM) activated substrate uptake (up to 200% of control), whereas concentrations in the millimolar range inhibited (up to 50%). Furthermore, the activation was more pronounced at low substrate concentrations (1 microM), and the inhibition was attenuated. The activity of other sodium cotransporters such as the sodium/D-glucose cotransporter SGLT1, stably transfected in CHO cells, was not affected by benzodiazepines. In electrophysiological studies, these drugs also failed to change the membrane potential of EAAC1-expressing Xenopus laevis oocytes. These results suggest a direct action on the glutamate transporter itself without modifying the general driving forces. Thus, in vivo low concentrations of benzodiazepines may reduce synaptic glutamate concentrations by increased uptake, providing an additional mechanism to modulate neuronal excitability.

Genes expressed in the ring gland, the major endocrine organ of Drosophila melanogaster

We have used an enhancer-trap approach to begin characterizing the function of the Drosophila endocrine system during larval development. Five hundred and ten different lethal PZ element insertions were screened to identify those in which a reporter gene within the P element showed strong expression in part or all of the ring gland, the major site of production and release of developmental hormones, and which had a mutant phenotype consistent with an endocrine defect. Nine strong candidate genes were identified in this screen, and eight of these are expressed in the lateral cells of the ring gland that produce ecdysteroid molting hormone (EC). We have confirmed that the genes detected by these enhancer traps are expressed in patterns similar to those detected by the reporter gene. Two of the genes encode proteins, protein kinase A and calmodulin, that have previously been implicated in the signaling pathway leading to EC synthesis and release in other insects. A third gene product, the translational elongation factor EF-1alpha F1, could play a role in the translational regulation of EC production. The screen also identified the genes couch potato and tramtrack, previously known from their roles in peripheral nervous system development, as being expressed in the ring gland. One enhancer trap revealed expression of the gene encoding the C subunit of vacuolar ATPase (V-ATPase) in the medial cells of the ring gland, which produce the juvenile hormone that controls progression through developmental stages. This could reveal a function of V-ATPase in the response of this part of the ring gland to adenotropic neuropeptides. However, the gene identified by this enhancer trap is ubiquitously expressed, suggesting that the enhancer trap is detecting only a subset of its control elements. The results show that the enhancer trap approach can be a productive way of exploring tissue-specific genetic functions in Drosophila.

Drosophila rosA gene, which when mutant causes aberrant photoreceptor oscillation, encodes a novel neurotransmitter transporter homologue

The Drosophila receptor oscillation A (rosA) mutations, which cause electroretinogram (ERG) defects, including oscillations, were localized to the 24F4-25A2 region of chromosome 2L. Genomic fragments from this region, isolated from bacteriophage P1 clones, included those that detect transcriptional defects in rosA mutants in RNA blot experiments. One of these genomic fragments was used to screen a head cDNA library. The largest cDNA clone (3.6 kb) isolated was shown to rescue a rosA mutant in P element-germline transformation experiments. The ROSA protein deduced from the open reading frame in the 3.6 kb rosA cDNA is 943 amino acids long and is 36-41% identical to members of the superfamily of Na+/Cl(-)-dependent neurotransmitter transporters, with no indication of higher sequence identity to any one subgroup within the superfamily. RNA blot experiments revealed multiple transcripts in various developmental stages, the most abundant one being a 3.7 kb transcript, particularly in the adult head. Tissue in situ experiments identified the rosA transcript to be localized to many tissues, with higher levels of hybridization in the nervous system and digestive tract. The results demonstrate that the rosA gene encodes a novel Na+/Cl(-)-dependent transporter important for normal response properties of the photoreceptor.

The V0 sector of the V-ATPase, synaptobrevin, and synaptophysin are associated on synaptic vesicles in a Triton X-100-resistant, freeze-thawing sensitive, complex

Anti-synaptobrevin 2 immunoprecipitates obtained from freshly prepared Triton X-100 extracts of rat synaptosomes contained, in addition to synaptophysin, a 10-kDa band, which we identified by peptide sequencing and Western blotting as the c subunit of the vacuolar proton pump (V-ATPase) also called ductin or mediatophore. Ac39 and Ac116, two other transmembrane subunits of the V0 sector of the V-ATPase, were also found by Western blotting to be enriched in the immunoprecipitates. None of these V-ATPase subunits, or synaptophysin, was present in anti-synaptobrevin 2 immunoprecipitates obtained from frozen-thawed Triton X-100 extracts, which were greatly enriched, instead, in SNAP-25 and syntaxin 1. Accordingly, V-ATPase subunit c was found in anti-synaptophysin immunoprecipitates. Thus, the two complexes appear to be mutually exclusive. Subcellular fractionation of rat brain demonstrated that V-ATPase subunit c is localized with synaptobrevin 2 and synaptophysin in synaptic vesicles. The coprecipitation of V-ATPase subunit c with the synaptobrevin-synaptophysin complex suggests that this interaction may play a role in recruiting the proton pump into synaptic vesicles. Freeze-thawing, which involves a mild denaturing step, may produce a conformational change which dissociates the complex and mimics a change which occurs in vivo as a prerequisite to SNARE complex formation.

Effect of hyperosmolarity on extracellular acidification associated with catecholamine secretion evoked by barium in perfused bovine adrenal medulla

1. The effects of the increase of osmotic strength on extracellular pH modifications produced during buffer-free, 5 mM Ba2+ stimulation was studied in decorticated perfused bovine adrenal glands. 2. A pronounced and reversible attenuation of the extracellular pH drop as well as of the release of catecholamines induced by Ba2+ was detected in glands exposed to a hyperosmotic (750 mOsm) perfusion fluid made up by the addition of NaCl. 3. Similar results were observed using sucrose as osmoticant instead of NaCl. 4. A progressive decline in both external acidification and secretory response to Ba2+ was found on gradually increasing the osmotic strength of the perfusion fluid. 5. These results provide additional evidence in favour of the existence of a close association between extracellular acidification and adrenomedullary secretion induced by buffer-free Ba2+.