Specification of neurotransmitter identity by Phox2 proteins in neural crest stem cells.
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We have investigated the specification of noradrenergic neurotransmitter identity in neural crest stem cells (NCSCs). Retroviral expression of both wild-type and dominant-negative forms of the paired homeodomain transcription factor Phox2a indicates a crucial and direct role for this protein (and/or the closely related Phox2b) in the regulation of endogenous tyrosine hydroxylase (TH) and dopamine-beta hydroxylase (DBH) gene expression in these cells. In collaboration with cAMP, Phox2a can induce expression of TH but not of DBH or of panneuronal genes. Phox2 proteins are, moreover, necessary for the induction of both TH and DBH by bone morphogenetic protein 2 (BMP2) (which induces Phox2a/b) and forskolin. They are also necessary for neuronal differentiation. These data suggest that Phox2a/b coordinates the specification of neurotransmitter identity and neuronal fate by cooperating environmental signals in sympathetic neuroblasts. (+info)
Muscarinic control of cytoskeleton in perisynaptic glia.
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Similar to astrocytes at CNS synapses, perisynaptic Schwann cells (PSCs) surround nerve terminals at the neuromuscular junction (NMJ). These special teloglial cells are sensitive to neurotransmitters and upregulate glial fibrillary acidic protein (GFAP) when deprived of synaptic activity. We found that activation of muscarinic acetylcholine receptors (mAChRs) at PSCs, but not purinergic (ATP and adenosine) or peptidergic [substance P (SP) and calcitonin gene-related peptide (CGRP)] receptors, prevented this upregulation. When applied onto single PSCs, muscarine evoked Ca2+ responses that fatigued but prevented upregulation of this glial cytoskeletal protein. Application of ATP onto single PSCs evoked Ca2+ signals that showed little fatigue, and GFAP upregulation occurred. Thus, Ca2+ signals alone cannot prevent GFAP upregulation in the PSCs. After blockade of cholinergic receptors by gallamine, neuronal activity was not effective in maintaining low GFAP levels in the perisynaptic glia. Last, immunohistochemistry disclosed mAChRs on PSCs and nearby fibroblasts. Thus, acetylcholine secreted by the nerve terminal acts on the PSCs via mAChRs to regulate GFAP. Cytoskeletal changes may influence perisynaptic glial functions, including growth, remodeling, and modulation of the synapse. (+info)
Secretion of old versus new exportable protein in rat parotid slics. Control by neurotransmitters.
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The possibility that old and new secretory granules do not mix and that older exportable protein can be secreted preferentially was tested on parotid gland in vitro. Slices from fasted animals were pulse labeled for 3 min with L-[3H]leucine. Subcellular fractionstion showed that after 1 90-min chase period, the formation of new labeled secretory granules was mostly completed. The ratio of label in secretory granules to label in microsomes increased 250-fold during the period 5--90 min postpulse. After the 90-min chase, a submaximal rate of secretion was initiated by adding a low concentration of isoproterenol to the slices. Preferential secretion of old unlabeled exportable protein was evident from the finding that the percent of total amylase secreted was 3.5-fold greater than the percent of labeled protein secreted. Preferential secretion of old unlabeled exportable amylase was undiminished even when the chase period before addition of isoproterenol was extended to 240 min. Such long chase incubations were still meaningful due to the fact that the spontaneous rat of amylase release and radioactive protein release from the slices was negligibly low. A high isoproterenol concentration added to the slices after a 90-min chase produced the following results. An initial phase of preferential secretion of old unlabeled protein was soon replaced by secretion of a random mixture of new and old exportable protein. Electron micrographs indicated that high rates of secretion involved sequential fusion of secretory granules so that the lumen extended deep into the cell where the new labeled granules were presumably located. At low rates of secretion, the lumen showed no such deep extensions. Experiments were also conducted on slices from glands which had been largely depleted of old granules by prior injection of isoproterenol into the animals. Secretion of labeled protein from such slices stopped with the export of 80% of the labeled protein. This finding indicates that about 20% of the radioactive protein is cellular nonexportable protein and that the slices are capable of exporting the entire amount of secretory protein which was symthesized in vitrol. In addition to the beta-adrenergic receptor which mediates protein secretion, the parotid acinar cell also possesses an alpha-adrenergic and a cholinergic receptor both of which cause K+ release, vacuole formation, and water secretion. Activation of either of the latter two receptors in conjunction with the beta-adrenergic receptor increased randomization of the protein secreted. It is concluded that in the rat parotid acinar cell there is little spontaneous mixing between old granules near the luminal cell membrane and new granules coming up behind from the Golgi complex. The neurotransmitters which induce secretion produce the observed randomization. (+info)
Maternal hypothyroxinemia disrupts neurotransmitter metabolic enzymes in developing brain.
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Maternal thyroid status influences early brain development and, consequently, cognitive and motor function in humans and rats. The biochemical targets of maternal thyroid hormone (TH) action in fetal brain remain poorly defined. A partially thyroidectomized rat dam model was therefore used to investigate the influence of maternal hypothyroxinemia on the specific activities of cholinergic and monoaminergic neurotransmitter metabolic enzymes in the developing brain. Maternal hypothyroxinemia was associated with reduced monoamine oxidase (MAO) activity in fetal whole brain at 16 and 19 days gestation (dg). A similar trend was observed for choline acetyltransferase (ChAT) activity. In contrast, DOPA decarboxylase (DDC) activity was markedly elevated at 21 dg. Further study of these enzymes at 14 dg showed no differences between normal and experimental progeny - suggesting they become TH sensitive after this age. Tyrosine hydroxylase (TyrH) and acetylcholinesterase (AChE) activities were unaffected prenatally. During postnatal development, the activities of TyrH, MAO, DDC and, to a lesser extent, AChE were increased in a brain region- and age-specific manner in experimental progeny. The prenatal disturbances noted in this study may have wide-ranging consequences since they occur when neurotransmitters have putative neurotropic roles in brain development. Furthermore, the chronic disturbances in enzyme activity observed during postnatal life may affect neurotransmission, thereby contributing to the behavioural dysfunction seen in adult progeny of hypothyroxinemic dams. (+info)
Regulation of basal expression of catecholamine-synthesizing enzyme genes by PACAP.
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We have previously reported that the cAMP/protein kinase A (PKA) pathway is important in the gene regulation of both induction and basal expressions of the catecholamine synthesizing enzymes tyrosine hydroxylase (TH) and dopamine beta-hydroxylase (DBH). The neuropeptide pituitary adenylate cyclase activating polypeptide (PACAP) has been shown to activate the intracellular cAMP/PKA pathway. In the present study, using primary cultured bovine adrenal medullary cells, we determined whether the basal activity of the PACAP receptor might play a role in the maintenance of the basal expression of these enzyme genes via the cAMP/PKA pathway. The potent PACAP receptor antagonist PACAP (6-38) caused a reduction of TH and DBH mRNA levels in a dose dependent manner as well as their enzyme activities and TH protein level. The effects of PACAP (6-38) and the PKA inhibitor H-89 exhibited generally similar trends, and were not additive in the reduction of TH and DBH gene expression and activities, suggesting that they take a common intracellular signaling pathway. The antagonist also caused decreases in the intracellular norepinephrine and epinephrine levels similar to the effect of H-89. Taken together, the data suggests that PACAP is involved in the regulation of maintenance of the catecholamine synthesizing enzymes TH and DBH by utilizing the cAMP/PKA pathway. (+info)
A three-pathway psychobiological model of craving for alcohol.
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In this article, by reviewing the psychological, psychophysiological, neurobiological, and psychopharmacological literature on craving for alcohol, it is argued that converging evidence from several disciplines suggests a three-pathway psychobiological model of craving. Essential to this model is the appreciation of the role of individual differences in affect regulation strategies or personality styles, conditionability, sensitivity to alcohol's effects, and related dysregulations in distinct neural circuitries or neurotransmitter systems. These factors are of crucial importance to a proper understanding of the nature of craving, its underlying mechanisms and different manifestations. As a first pathway, it is suggested that reward craving or desire for the rewarding, stimulating and/or enhancing effects of alcohol might result from either dopaminergic/opioidergic dysregulation or a personality style characterized by reward seeking or a combination of both. As a second pathway, it is suggested that relief craving or desire for the reduction of tension or arousal might result from either gamma-aminobutyric acid (GABA)ergic/glutamatergic dysregulation or a personality style characterized by stress reactivity or a combination of both. Obsessive craving, the result of the third pathway, can be defined as lack of control over intrusive thoughts about drinking resulting in impaired functioning. This type of craving might result either from a serotonin deficiency or a personality style characterized by low constraint or disinhibition or a combination of both. The putative implications of this three-pathway model for the assessment of alcohol craving, diagnosis and treatment of alcoholism, and future research on craving, are discussed. (+info)
Differential effects of saturated and monounsaturated fatty acids on postprandial lipemia and incretin responses in healthy subjects.
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BACKGROUND: Elevations of postprandial triacylglycerol-rich plasma lipoproteins and suppressions of HDL-cholesterol concentrations are considered potentially atherogenic. Long-term studies have shown beneficial effects of monounsaturated fatty acids (eg, oleic acid) on fasting lipid and lipoprotein concentrations in humans. A direct stimulatory effect of oleic acid on the secretion of glucagon-like peptide 1 (GLP-1) was shown in animal studies. OBJECTIVE: We compared the postprandial responses of glucose, insulin, fatty acids, triacylglycerol, gastric inhibitory polypeptide (GIP), and GLP-1 to test meals rich in saturated and monounsaturated fatty acids. DESIGN: Ten young, lean, healthy persons ingested 3 meals: an energy-free soup consumed with 50 g carbohydrate (control meal), the control meal plus 100 g butter, and the control meal plus 80 g olive oil. Triacylglycerol and retinyl palmitate responses were measured in total plasma, in a chylomicron-rich fraction, and in a chylomicron-poor fraction. RESULTS: No significant differences in glucose, insulin, or fatty acid responses to the 2 fat-rich meals were seen. Plasma triacylglycerol responses were highest after the butter meal, with chylomicron triacylglycerol rising 2.5-5-fold. Retinyl palmitate responses were higher and more prolonged after the butter meal than after the control and olive oil meals, whereas both postprandial HDL-cholesterol concentrations and GLP-1 and GIP responses were higher after the olive oil meal than after the butter meal. CONCLUSIONS: Olive oil induced lower triacylglycerol concentrations and higher HDL-cholesterol concentrations than butter, without eliciting differences in concentrations of glucose, insulin, or fatty acids. Furthermore, olive oil induced higher concentrations of GLP-1 and GIP than did butter, which may point to a relation between fatty acid composition, incretin responses, and triacylglycerol metabolism in the postprandial phase. (+info)
Impairments in high-frequency transmission, synaptic vesicle docking, and synaptic protein distribution in the hippocampus of BDNF knockout mice.
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Brain-derived neurotrophic factor (BDNF) promotes long-term potentiation (LTP) at hippocampal CA1 synapses by a presynaptic enhancement of synaptic transmission during high-frequency stimulation (HFS). Here we have investigated the mechanisms of BDNF action using two lines of BDNF knockout mice. Among other presynaptic impairments, the mutant mice exhibited more pronounced synaptic fatigue at CA1 synapses during high-frequency stimulation, compared with wild-type animals. Quantitative analysis of CA1 synapses revealed a significant reduction in the number of vesicles docked at presynaptic active zones in the mutant mice. Synaptosomes prepared from the mutant hippocampus exhibited a marked decrease in the levels of synaptophysin as well as synaptobrevin [vesicle-associated membrane protein (VAMP-2)], a protein known to be involved in vesicle docking and fusion. Treatment of the mutant slices with BDNF reversed the electrophysiological and biochemical deficits in the hippocampal synapses. Taken together, these results suggest a novel role for BDNF in the mobilization and/or docking of synaptic vesicles to presynaptic active zones. (+info)