Transmitter Metabolism Research Articles

Decoding the contributions of gut microbiota and cerebral metabolism in acute liver injury mice with and without cognitive dysfunction.

Patients with acute liver injury (ALI) can develop cognitive dysfunction (CD). The study investigated the role of gut microbiota and cerebral metabolism in ALI mice with and without CD. Male C57BL/6 mice that received thioacetamide were classified into ALI mice with (susceptible) or without (unsusceptible) CD-like phenotypes by hierarchical cluster analysis of behavior. The role of gut microbiota was investigated by 16S ribosomal RNA gene sequencing and feces microbiota transplantation (FMT). 1 H-[13 C] NMR and electrophysiology were used to detect the changes in cerebral neurotransmitter metabolic and synaptic transition in neurons or astrocytes. Apromixlay 55% (11/20) of mice developed CD and FMT from the susceptible group transmitted CD to gut microbiota-depleted mice. Alloprevotella was enriched in the susceptible group. GABA production was decreased in the frontal cortex, while hippocampal glutamine was increased in the susceptible group. Altered Escherichia. Shigella and Alloprevotella were correlated with behaviors and cerebral metabolic kinetics and identified as good predictors of ALI-induced CD. The frequencies of both miniature inhibitory and excitatory postsynaptic currents in hippocampal CA1 and prefrontal cortex were decreased in the susceptible group. Altered transmitter metabolism and synaptic transmission in the hippocampus and prefrontal cortex and gut microbiota disturbance may lead to ALI-induced CD.

Persistent increase in ventral hippocampal long‐term potentiation by juvenile stress: A role for astrocytic glutamine synthetase

A traumatic childhood is among the most important risk factors for developing stress-related psychopathologies such as posttraumatic stress disorder or depression later in life. However, despite the proven role of astrocytes in regulating transmitter release and synaptic plasticity, the contribution of astrocytic transmitter metabolism to such stress-induced psychopathologies is currently not understood. In rodents, childhood adversity can be modeled by juvenile stress exposure, resulting in increased anxiety, and impaired coping with stress in adulthood. We describe that such juvenile stress in rats, regardless of additional stress in adulthood, leads to reduced synaptic efficacy in the ventral CA1 (vCA1) Schaffer collaterals, but increased long-term potentiation (LTP) of synaptic transmission after high-frequency stimulation. We tested whether the glutamate-glutamine-cycle guides the lasting changes on plasticity observed after juvenile stress by blocking the astrocytic glutamate-degrading enzyme, glutamine synthetase (GS). Indeed, the pharmacological inhibition of GS by methionine sulfoximine in slices from naïve rats mimics the effect of juvenile stress on vCA1-LTP, while supplying glutamine is sufficient to normalize the LTP. Assessing steady-state mRNA levels in the vCA1 stratum radiatum reveals distinct shifts in the expression of GS, astrocytic glutamate, and glutamine transporters after stress in juvenility, adulthood, or combined juvenile/adult stress. While GS mRNA expression levels are lastingly reduced after juvenile stress, GS protein levels are maintained stable. Together our results suggest a critical role for astrocytes and the glutamate-glutamine cycle in mediating long-term effects of juvenile stress on plasticity in the vCA1, a region associated with anxiety and emotional memory processing.

Study on dose-dependent, frequency-dependent, and accumulative effects of 1.5\u2009GHz and 2.856\u2009GHz microwave on cognitive functions in Wistar rats

Many studies have revealed the cognitive decline induced by microwave radiation. However, the systematic study on dose-dependent, frequency-dependent and accumulative effects of microwave exposure at different frequencies was lacking. Here, we studied the relationship between the effects and the power and frequency of microwave and analyzed the accumulative effects of two different frequency microwaves with the same average power density. After microwave radiation, declines in spatial learning and memory and fluctuations of brain electric activities were found in the 10 mW/cm2 single frequency exposure groups and accumulative exposure groups. Meanwhile, morphological evidences in hippocampus also supported the cognitive dysfunction. Moreover, the decrease of Nissl contents in neurons indicated protein-based metabolic disorders in neurons. By detecting the key functional proteins of cholinergic transmitter metabolism, cytokines, energy metabolism and oxidative stress in the hippocampus, we found that microwave could lead to multiple metabolic disorders. Our results showed that microwave-induced cognitive decline was largely determined by its power rather than frequency. Injury effects were also found in accumulative exposure groups. We particularly concerned about the safety dose, injury effects and accumulative effects of microwaves, which might be very valuable in the future.

Microglia and Drug-Induced Plasticity in Reward-Related Neuronal Circuits

Drugs of abuse result in complex changes in neurocircuit of reward and stress. Whilst most of these changes affect neurons, the role of additional cell types, such as glia, in the development of tolerance and related neuroplastic changes during drug taking, addiction, and withdrawal is also emerging. For instance, astrocytes, which play an essential role in glutamatergic neurotransmission, as well as in energetic and growth factor support of neurons, are significantly affected by drugs of abuse (Miguel-Hidalgo, 2009). Furthermore, the role of microglia in tailoring neuronal connectivity, transmitter metabolism, and drug-induced neuroinflammation might also be important in physiology of neurons at the addiction-related brain circuitries. Microglia belong to monocyte/macrophage linage and are resident cells of the innate immune system in the brain. Microglia have at least three, functionally and morphologically distinct forms (Papaleo et al., 2008; Olah et al., 2011). Under normal conditions (1) resting microglia, through their highly mobile filopodia continuously survey the brain parenchyma (Nimmerjahn et al., 2005). Microglia became activated (2) in response to various danger signals posed by neurons and/or astrocytes (Davalos et al., 2005). At this stage, microglia are recruited and have local protective effects via regulated release of cytokines and phagocytosis of cellular debris. At certain point however, microglia gain reactive phenotype (3) characterized by uncontrolled release of inflammatory mediators. These cells furiously attack neurons, became neurotoxic and extend the damage (Banati and Graeber, 1994). It is noteworthy that different insults may converge upon microglial cell population and potentiate each other to worsen the outcome of the response (Zou et al., 2011). However, like macrophages, microglial cells are functionally polarized into different phenotypic activation states, referred as classical (M1) and alternative (M2). Alternatively activated microglia express anti-inflammatory cytokines and involved in tissue protection and repair. Activated microglia may contribute to addiction-related neuroplastic changes by several ways, such as release of proinflammatory cytokines, synaptic remodeling, neurochemical interaction with excitatory transmission and phagocytosis of newborn neurons and cellular debris.

Stochastic aspects of transmitter release and bioenergetic dysfunction in isolated nerve terminals

Synaptosomes (isolated nerve terminals) have been studied for more than 40 years. The preparation allows aspects of transmitter metabolism and release to be studied ex vivo from specific brain regions of animals of any age. Conditions can be devised to enable the terminals to fire spontaneous action potentials, allowing the presynaptic control of glutamate exocytosis to be studied. Recent developments have greatly increased the sensitivity with which the bioenergetics of the intra-synaptosomal mitochondria can be investigated.

Drosophila Ebony Activity Is Required in Glia for the Circadian Regulation of Locomotor Activity

Previous studies suggest that glia may be required for normal circadian behavior, but glial factors required for rhythmicity have not been identified in any system. We show here that a circadian rhythm in Drosophila Ebony (N-beta-alanyl-biogenic amine synthetase) abundance can be visualized in adult glia and that glial expression of Ebony rescues the altered circadian behavior of ebony mutants. We demonstrate that molecular oscillator function and clock neuron output are normal in ebony mutants, verifying a role for Ebony downstream of the clock. Surprisingly, the ebony oscillation persists in flies lacking PDF neuropeptide, indicating it is regulated by an autonomous glial oscillator or another neuronal factor. The proximity of Ebony-containing glia to aminergic neurons and genetic interaction results suggest a function in dopaminergic signaling. We thus suggest a model for ebony function wherein Ebony glia participate in the clock control of dopaminergic function and the orchestration of circadian activity rhythms.

Dopamine may be ‘hyper’ with respect to noradrenaline metabolism, but ‘hypo’ with respect to serotonin metabolism in children with attention-deficit hyperactivity disorder

Noradrenaline: Hechtman (J Psychiat Neurosci 1994;19:193) argued for a role for frontal dopamine (DA) and noradrenaline (NA) in ADHD, where Oades (Prog Neurobiol 1987;29:365) has described lateralised functional impairments. Mechanisms (e.g. via alpha-2 sites) for stimulating low NA activity in ADHD children (J Am Acad Child Adolesc Psychiatry 1997;36:1688) in order to promote interactions with mesocortical DA have been discussed (J Psychopharmacology 1997;11:151; Psychiatr Res 1994;52:305). We described with indicators of overall transmitter metabolism (monoamines, metabolites in 24 h urine samples (Behav Brain Res 1997;88:95)) significantly lower utilisation ratios (MHPG/NA) in ADHD children with respect to healthy controls. Interestingly, a comparison of between catecholamine levels (DA/NA) showed a correlation with the conditioned blocking measure of selective attention recorded at the time of collection. This measure was negatively associated with blocking in controls. These results are consistent with reports of lower DOPEG and increased DOPAC in ADHD urine (J Child Adolesc Psychopharmacol 1996;6:63) and indicate that the relatively hyperactive DA versus NA systems may have functional consequences. Serotonin: the relevance for ADHD of an association of impulsivity with low serotonin (5-HT) metabolism (Behav Brain Sci 1986;9:319) has long been played down. Yet, some symptoms have been related to CSF measures of the metabolite 5-HIAA, and in particular the HVA/5-HIAA ratio has been reported to correlate with ratings of activity (Psychiatr Res 1994;52:305). We find that while urinary measures of 5-HIAA are somewhat higher, the ratio HVA/5-HIAA is markedly lower in ADHD children versus controls. In these ADHD children 5-HIAA levels were negatively related to d-prime measures in a continuous performance task (CPTax), and the HVA/5-HIAA was negatively associated with conditioned blocking. These results suggest a relatively low DA versus 5-HT activity may have functional consequences, albeit in a subgroup of ADHD. This is consistent with drug-induced prolactin changes reported by Verbaten et al. (Eur Child Adolesc Psychiatry 1999;8:30).

Neurotransmission in the vestibular endorgans--glutamatergic transmission in the afferent synapses of hair cells.

In the sensory pathways the first synapse is that between hair cells and primary afferent neurons and its most likely neurotransmitter candidate has long been thought to be glutamate. A number of pharmacological and electrophysiological studies have lent credence to this theory (reviewed by Bledsoe et al. 1988, Bobbin 1979, Ehrenberger and Felix 1991, Puel et al. 1991; Puel 1995) as has recent neurochemical and immunocytochemical work (reviewed by Ottersen et al. 1998; Usami et al. 2000). These recent studies reveal that the afferent hair cell synapse resembles the central glutamate synapses in many ways. Of the proteins confirmed to be involved in signal transduction and transmitter metabolism at most central synapses, many are also seen in the afferent hair cell synapse, and have an analogous compartmentation. On the other hand, there are also important differences, especially those related to the molecular mechanisms that underlie transmitter release.

Open field locomotion and neurotransmission in mice evaluated by principal component factor analysis-effects of housing condition, individual activity disposition and psychotropic drugs

1. 1. Effects of housing condition and individual disposition on dopaminergically and GABAergically influenced open field locomotion and neurochemistry were studied in mice. 2. 2. Mice characterized as high active (HAM) and low active (LAM) by a running-wheel test were housed in groups or isolated for 1 day, 1 week, 3, 6, 12 or 18 weeks before an open field test was performed with saline, apomorphine (0.75 mg/kg) or diazepam (1.00 mg/kg) administration. Immediately afterwards animals were decapitated and brain sections were frozen for subsequent HPLC-analysis of dopaminergic and scrotonergic transmitter metabolism. 3. 3. Principal component factor analysis (PCA) of locomotion variables provided three factors explaining 78.5% of total variance. Variables related to the amount of locomotion loaded highly on Factor 1 (F1-Activity), variables related to place utilization loaded highly on Factor 2 (F2-Exploration) and variables related to immobility and place preference loaded highly on Factor 3 (F3-Irritation). 4. 4. Apomorphine decreased F1-Activity with smaller effects in HAM and without changes in F2-Exploration and F3-Irritation independent on housing conditions. Diazepam exerted a decrease in F2-Exploration with a small increase in F1-Activity and no effects in F3-Irritation. Diazepam induced changes depended on housing conditions and were especially pronounced in isolated HAM. 5. 5. PCA of considerable locomotion and neurochemical data revealed interrelationships between striatal dopamine metabolism and F1-Activity, between cortical dopamine and scrotonin metabolism and F2-Exploration as well as between cerebcllar, hippocampal and striatal scrotonin metabolism and F3-Irritation. 6. 6. The authors concluded that the application of PCA is a useful method to provide functionally relevant characteristics of behaviors and functionally relevant descriptions of interrrelationships between behavior and appropriate central nervous mechanisms. Furthermore the received behavioral characteristics (Fl, F2, F3) of open field locomotion were sensitive to reveal housing and drug effects.

Fibroblast growth factor and its implications for developing and regenerating neurons.

FGF is a multifunctional heparin-binding protein which was characterized by its mitogenic and angiogenic action outside the nervous system. Recent data confirm this multifunctionality also with regard to the nervous system. The distribution of FGF and its receptors seems not to be in agreement with the idea of a single function for one population but argues for a more complex action, which might be dependent on the development stage and cell type. FGF and its receptors are widely distributed in the nervous system. In brainstem and spinal cord motoneurons and in sensory ganglia the FGF-2 staining pattern is developmentally regulated suggesting a functional change during embryonic and postnatal development. In addition, after nerve lesion the FGF-2 expression is altered in sensory and motoneurons. Administration of FGF-2 reveals trophic effects on survival and transmitter metabolism in vivo and in vitro. According to a more general neurotrophic factor concept, a physiological role of FGF for distinct neuron populations during development is likely. In the motor system, for example, FGF could act synergistically with certain neurotrophins, CNTF, or other non-identified co-factors. In the sensory system, a possible non-neurotrophic role for at least postnatal and adult sensory neurons has to be further addressed in the future. In order to further define and characterize the actions of the FGFs a mapping of the different family members and their respective receptor molecules during development and in the adult has to be done.

Effect of Cell Swelling, NH4CI and Glutamate on Acridine Orange Fluorescence in Retinal Ganglion Cells

Acridine orange has been utilized to test for an effect of cell swelling and glutamate on pH in acidic intracellular compartments of retinal ganglion cells. Alkalinization of these compartments is reflected by an increase in acridine orange fluorescence intensity at > 530 nm. NH₄C1 (500 µM) and chloroquine (100 µM), weak bases known to alkalinize acidic compartments, expectedly increased acridine orange fluorescence. A similar effect was elicited by a decrease in extracellular osmolarity. An increase in extracellular K⁺ concentration, leading to isotonic cell swelling, also increased acridine orange fluorescence. Addition of 100 µ<i>M </i>glutamate increased acridine orange fluorescence, although it did not appear to affect cell volume. The glutamate-induced alkalinization was blocked by the N-methyl-<i>D</i>-aspartate (NMDA) receptor antagonist, MK-801, and mimicked by NMDA (50 µ<i>M). </i>The effect of NMDA was blocked by the removal of extracellular Ca²⁺. Similarly, NMDA-induced increases in intracellular Ca²⁺ were blocked under Ca²⁺-free conditions. Cytosolic pH measurements in the same cells demonstrated an acidification in response to reduced extracellular osmolarity. In contrast, a high K⁺ solution and 100 µ<i>M </i>glutamate both increased cytosolic pH. In conclusion, alkalinization of acidic cellular compartments of retinal ganglion cells is induced not only by NH4CI, chloroquine and maneuvers which induce cell swelling, but also by the neurotransmitter glutamate. The mechanism by which glutamate induces its effect appears to be primarily via increases in intracellular Ca²⁺. The alkalinization of acidic intracellular compartments, as such, may modify transmitter metabolism and trafficking of cell membrane proteins.

Growth properties of larval and adult locust neurons in primary cell culture.

We developed a cell culture system for thoracic neurons of fifth instar or adult locusts (Locusta migratoria) in order to obtain maximum visualization of cellular morphology and direct access to the neurons for electrophysiological analysis. The dissociated neurons regenerated new neurites in a serum-free defined culture medium, in which they remained viable for up to 3 weeks. Viability of the cells was confirmed by intracellular recordings demonstrating active membrane properties and action potentials. While the morphology of the cultured neurons is distinct from their in vivo counterparts, they retained some cellular surface properties and markers related to transmitter metabolism. Two factors influencing cellular morphology in vitro were identified in Locusta: 1) the presence of a primary neurite stump, and 2) membrane contacts between cells. Dissociated neurons of the locust species Schistocerca gregaria grown in a hemolymph-enriched medium showed a marked reduction in branching patterns and a tenfold increase in neurite length compared to neurons growing in a medium without hemolymph. This culture system could prove useful for identifying the action of hemolymph-derived growth factors.

Pentylenetetrazol kindling and factors of glutamate transmitter metabolism in rat hippocampus

Male Wistar rats administered repetitively with pentylenetetrazol developed a dose-dependent enhancement of seizure behaviour referred to as pentylenetetrazol kindling. After a daily dose of 40 mg pentylenetetrazol/kg or physiological saline (control rats) injected intraperitoneally for a period of two weeks, hippocampal tissue was studied autoradiographically for high-affinity uptake of [ 3H]glutamate and, by activity staining, for aspartate aminotransferase and glutamate dehydrogenase. Most prominent changes were found in neuropil areas known to be endowed with glutamatergic structures. The uptake capacity of glutamate decreased by 48% (maximum rate), whilst activities of aspartate aminotransferase and glutamate dehydrogenase elevated to 140 and 130%, respectively. Cytochrome c oxidase activity was found to be unaffected. The findings indicate an important role of factors of the glutamate metabolism in the kindling process with respect to the production, utilization, and availability of transmitter glutamate.

Dissociation of autoreceptor activation and behavioral consequences of low-dose apomorphine treatment

Lynch, Minda R.: Dissociation of autoreceptor activation and behavioral consequences of low-dose apomorphine treatment. Prog. Neuro-Psychopharmacol. & Biol. Psychiat. 1991, 15 (5) : 689–698. 1. 1. Low dose dopaminergic agonist effects have been used as a behavioral screen for identifying compounds with selective autoreceptor activity. 2. 2. However, results from several recent investigations suggest that these behaviors may not be generated from an autoreceptor substrate but rather from a subpopulation of postsynaptic dopamine receptors with a high affinity for the agonist. 3. 3. In support of this hypothesis, the present investigation reports that both hypomotility and yawning, induced in the rat with 0.07 mg/kg apomorphine, were not paralleled by autoreceptor-induced reductions in transmitter metabolism from either mesolimbic or neostriatal dopamine regions.

覚醒剤後遺症の慢性化に関する神経化学的検討

覚醒剤後遺症の慢性化に関する神経化学的検討

Enzymes of transmitter and energy metabolism in rat middle ear and extraocular muscles

To further investigate the peculiar characteristics of the middle ear and extraocular muscles, compared to the extensively studied skeletal muscles of the limbs, activities of enzymes of transmitter and energy metabolism were measured in homogenates of these muscles from albino and pigmented rats. These activities were compared to those for a masticatory muscle and for three hindlimb muscles chosen for their preponderance of either slow oxidative, fast glycolytic, or fast oxidative glycolytic fibers. Activities of the neuromuscular transmitter enzymes choline acetyltransferase and acetylcholinesterase were relatively very high in the extraocular and middle ear muscles. The activity of malate dehydrogenase, an enzyme of oxidative energy metabolism, was as high in the extraocular, masticatory and stapedius muscles as in the oxidative hindlimb muscles, but was lower in tensor tympani. The activity of lactate dehydrogenase, an enzyme of glycolytic energy metabolism, was remarkably low in both middle ear muscles. The results are consistent with high innervation density in the extraocular and middle ear muscles, and highly oxidative metabolism in the extraocular and stapedius muscles. Metabolic differences between the stapedius and tensor tympani suggest a relatively more active role for the former in the function of the rat middle ear.

Quantitative Distributions of Aspartate Aminotransferase and Glutaminase Activities in the Guinea Pig Cochlea

Distributions of aspartate aminotransferase and glutaminase activities in the guinea pig cochlea have been examined with use of quantitative microchemical techniques to evaluate their roles in cochlear energy metabolism and neurotransmission. Other enzyme activities analyzed were those of choline acetyltransferase and malate dehydrogenase. It is concluded that aspartate aminotransferase activity appears to be especially concerned with cochlear energy metabolism, while glutaminase activity may function in transmitter metabolism in the guinea pig cochlea. Neither enzyme shows a clear association with the olivocochlear bundle.

Changes in glutamate-related enzyme activities in the striatum of the rat following lesion of corticostriatal fibres

The behaviour of enzymes putatively involved in glutamate/aspartate transmitter metabolism (glutamate dehydrogenase, aspartate amino-transferase, alanine aminotransferase, gamma-glutamyl-transpeptidase) was studied in the striatum 3, 7, 14 days and 7 weeks after mechanical destruction of corticostriatal fibres. For a period of up to seven days after unilateral lesion, enzyme activities were significantly diminished (by up to 13% based on protein) in the ipsilateral striatum as compared to the striatum of the intact side. Later, the enzyme activities in the ipsilateral striatum recovered. After seven weeks, an increase was observed for glutamate dehydrogenase activity, whereas the activity of alanine aminotransferase showed a transient rise enzyme levels is interpreted as being attributable to the destruction of nerve endings which are considered to be glutamatergic, interfering with various compensating processes (e.g. glial cell proliferation) which occur with advancing times after lesion.

Early expression of acetylcholinesterase activity in functionally distinct neurons of the zebrafish.

The first expression and distribution of acetylcholinesterase (AChE) activity was studied among a distinct population of early neurons in embryonic zebrafish by using histochemical and retrograde labeling techniques. AChE first appeared in the nervous system in the primary motoneurons of the rostral spinal cord when the embryo had nine somites, approximately 14 hours postfertilization. Subsequent expression of AChE activity in the spinal cord proceeded in a rostral-to-caudal sequence. Cranial neurons expressed AChE activity shortly after it appeared in the rostral spinal cord. Several hours later, near the end of the first day, primary neurons in the hind-brain and spinal cord all contained AChE, including sensory neurons, reticulospinal interneurons, and primary motoneurons. AChE activity was also detected in the nucleus of the medial longitudinal fasciculus. Presumptive cranial ganglia transiently expressed AChE activity between 14 and 24 hours of development. These results, combined with previous observations that examined the time of origin and axogenesis of primary neurons, suggest that primary neurons in the embryonic zebrafish contain AChE before they sprout axons. The primary neurons appear to follow a common sequence of development consisting of a withdrawal from the cell division cycle, the expression of AChE, and axogenesis. Although this sequence is followed by all primary neurons, lack of a rostral-to-caudal sequence in the time of birth and variability in the time of axon outgrowth demonstrate that the relative timing of these three events is not rigidly programmed in individual neurons. Moreover, the very early expression of AChE in such diverse cell types suggests that it may have a developmental role in addition to its function in transmitter metabolism.

Secretin and vasoactive intestinal peptide activate tyrosine hydroxylase in sympathetic nerve endings

Secretin and vasoactive intestinal peptide (VIP) are known to stimulate tyrosine hydroxylase (TH) activity acutely in the rat superior cervical ganglion (SCG). Because TH-containing neurons in the SCG innervate the iris, submaxillary gland, and pineal gland, we examined the effects of secretin and VIP in these 3 autonomic end organs in vitro. Both peptides stimulated TH activity in each tissue. These stimulations resembled those in the SCG in that (1) secretin displayed a higher potency than VIP in all 3 end organs, (2) the peptide effects were unchanged when calcium was excluded from the incubation medium, and (3) they were mimicked by activators of the cyclic adenosine monophosphate (cAMP) pathway. These findings indicate that secretin and VIP can regulate transmitter metabolism in both the cell bodies and axon terminals of neurons originating in the SCG. Furthermore, the data raise the possibility that catecholamine synthesis in sympathetic nerve terminals is modulated by peptides released by other, nearby nerve endings.