Lactic acid-induced increase of extracellular dopamine measured by microdialysis in rat striatum: evidence for glutamatergic and oxidative mechanisms

Propionic acid induced behavioural effects of relevance to autism spectrum disorder evaluated in the hole board test with rats

Autism spectrum disorders (ASD) are a set of neurodevelopmental disorders characterized by abnormal social interactions, impaired language, and stereotypic and repetitive behaviours. Among genetically susceptible subpopulations, gut and dietary influences may play a role in etiology. Propionic acid (PPA), produced by enteric gut bacteria, crosses both the gut-blood and the blood-brain barrier. Previous research has demonstrated that repeated intracerebroventricular (ICV) infusions of PPA in adult rats produce behavioural and neuropathological changes similar to those seen in ASD patients, including hyperactivity, stereotypy, and repetitive movements. The current study examined dose and time related changes of exploratory and repetitive behaviours with the use of the hole-board task. Adult male Long-Evans rats received ICV infusions twice a day, 4 h apart, of either buffered PPA (low dose 0.052 M or high dose 0.26 M, pH 7.5, 4 μL/infusion) or phosphate buffered saline (PBS, 0.1 M) for 7 consecutive days. Locomotor activity and hole-poke behaviour were recorded daily in an automated open field apparatus (Versamax), equipped with 16 open wells, for 30 min immediately after the second infusion. In a dose dependent manner PPA infused rats displayed significantly more locomotor activity, stereotypic behaviour and nose-pokes than PBS infused rats. Low-dose PPA animals showed locomotor activity levels similar to those of PBS animals at the start of the infusion schedule, but gradually increased to levels comparable to those of high-dose PPA animals by the end of the infusion schedule, demonstrating a dose and time dependent effect of the PPA treatments.

Correlation of 3-mercaptopropionic acid induced seizures and changes in striatal neurotransmitters monitored by microdialysis

OBJECTIVES

The goal of this study was to use a status epilepticus steady-state chemical model in rats using the convulsant, 3-mercaptopropionic acid (3-MPA), and to compare the changes in striatal neurotransmission on a slow (5min) and fast (60s) timescale. In vivo microdialysis was combined with electrophysiological methods in order to provide a complete evaluation of the dynamics of the results obtained.

OBJECTIVE

To compare the effects of a steady-state chemical model pof status epilepticus on striatal amino-acid and amine neurotransmitters contents, as measured via in vivo microdialysis combined with electrophysiological methods. Measurements were performed on samples collected every 60s and every 5min. "Fast" (60s) and "slow" (5min) sampling timescales were selected, to gain more insight into the dynamics of GABA synthesis inhibition and of its effects on other neurotransmitters and on cortical electrical activity.

METHODS

3-MPA was administered in the form of an intra-venous load (60mg/kg) followed by a constant infusion (50mg/kg/min) for min. Microdialysis samples were collected from the striatum at intervals of 5min and 60s and analyzed for biogenic amine and amino acid neurotransmitters. ECoG activity was monitored via screws placed over the cortex.

RESULTS

In the 5min samples, glutamate (Glu) increased and γ-aminobutyric acid (GABA) decreased monotonically while changes in dopamine (DA) concentration were bimodal. In the sixty second samples, Glu changes were bimodal, a feature that was not apparent with the 5min samples. ECoG activity was indicative of status epilepticus.

CONCLUSIONS

This study describes the combination of in vivo microdialysis with electrophysiology to monitor the effect of 3-MPA on neurotransmission in the brain. This led to a better understanding of the chemical changes in the striatum due to the applied 3-MPA chemical model of status epilepticus.

The enteric bacterial metabolite propionic acid alters brain and plasma phospholipid molecular species: further development of a rodent model of autism spectrum disorders

Gastrointestinal symptoms and altered blood phospholipid profiles have been reported in patients with autism spectrum disorders (ASD). Most of the phospholipid analyses have been conducted on the fatty acid composition of isolated phospholipid classes following hydrolysis. A paucity of information exists on how the intact phospholipid molecular species are altered in ASD. We applied ESI/MS to determine how brain and blood intact phospholipid species were altered during the induction of ASD-like behaviors in rats following intraventricular infusions with the enteric bacterial metabolite propionic acid. Animals were infused daily for 8 days, locomotor activity assessed, and animals killed during the induced behaviors. Propionic acid infusions increased locomotor activity. Lipid analysis revealed treatment altered 21 brain and 30 blood phospholipid molecular species. Notable alterations were observed in the composition of brain SM, diacyl mono and polyunsaturated PC, PI, PS, PE, and plasmalogen PC and PE molecular species. These alterations suggest that the propionic acid rat model is a useful tool to study aberrations in lipid metabolism known to affect membrane fluidity, peroxisomal function, gap junction coupling capacity, signaling, and neuroinflammation, all of which may be associated with the pathogenesis of ASD.

Novel δ1-receptor agonist KNT-127 increases the release of dopamine and L-glutamate in the striatum, nucleus accumbens and median pre-frontal cortex

The effects of systemic δ1-agonist on neurotransmission remains obscure, since no selective δ1-agonist exists that can penetrate the blood-brain barrier. Recently, we succeeded in synthesizing a putative δ1-receptor agonist, KNT-127, which has been demonstrated the effectiveness of systemic administration against anxiety and depressive-like behavior. To clarify the functional selectivity of KNT-127 and neurotransmission regulating system of δ1-receptor, the present study investigated the interaction between KNT-127 and δ-receptor antagonists on the release of dopamine, L-glutamate and GABA in nucleus accumbens (NAc), striatum and median pre-frontal cortex (mPFC) using multi-probe microdialysis. Intraperitoneal administration of KNT-127 increased the release of dopamine and L-glutamate in three regions, but decreased and increased GABA releases in respective NAc and mPFC without affecting that in striatum. The effects of KNT-127 in the three regions were abrogated by δ1-antagonist but not by δ2-antagonist. MK801 inhibited KNT-127-induced dopamine release in striatum and NAc, but enhanced that in mPFC, inhibited KNT-127-induced mPFC GABA release without affecting KNT-127-induced GABA reduction in NAc. Muscimol enhanced KNT-127-induced dopamine release in mPFC. Sulpiride inhibited KNT-127-induced reduction of GABA release in NAc. The results indicated that KNT-127 is a selective δ1-agonist, and suggested that δ1-receptor directly activates the release of dopamine and L-glutamate in the striatum, NAc and mPFC, but not that of GABA in the three regions. δ1-receptor indirectly inhibited GABA release in NAc via activated dopaminergic transmission, while δ1-receptor indirectly enhanced GABA release in mPFC via activated glutamatergic transmission.

Altered brain phospholipid and acylcarnitine profiles in propionic acid infused rodents: further development of a potential model of autism spectrum disorders

Recent studies have demonstrated intraventricular infusions of propionic acid (PPA) a dietary and enteric short-chain fatty acid can produce brain and behavioral changes similar to those observed in autism spectrum disorder (ASD). The effects of PPA were further evaluated to determine if there are any alterations in brain lipids associated with the ASD-like behavioral changes observed following intermittent intraventricular infusions of PPA, the related enteric metabolite butyric acid (BUT) or phosphate-buffered saline vehicle. Both PPA and BUT produced significant increases (p < 0.001) in locomotor activity (total distance travelled and stereotypy). PPA and to a lesser extent BUT infusions decreased the levels of total monounsaturates, total omega6 fatty acids, total phosphatidylethanolamine plasmalogens, the ratio of omega6 : omega3 and elevated the levels of total saturates in separated phospholipid species. In addition, total acylcarnitines, total longchain (C12-C24) acylcarnitines, total short-chain (C2 to C9) acylcarnitines, and the ratio of bound to free carnitine were increased following infusions with PPA and BUT. These results provide evidence of a relationship between changes in brain lipid profiles and the occurrence of ASD-like behaviors using the autism rodent model. We propose that altered brain fatty acid metabolism may contribute to ASD.

Zonisamide enhances delta receptor-associated neurotransmitter release in striato-pallidal pathway

A recent randomized control study demonstrated that zonisamide (ZNS), an antiepileptic drug, is effective in Parkinson's disease at the lower than the therapeutic doses against epilepsy (25-50 mg/day); however, the detailed mechanism of antiparkinsonian effects of ZNS remains to be clarified. To determine the mechanism of antiparkinsonian effect of ZNS, we investigated the effects of ZNS on extracellular levels of dopamine in the striatum (STR), glutamate in substantia nigra pars reticulata (SNr), GABA in globus pallidus (GP), subthalamic nucleus (STN) and SNr, using multiple microdialysis probes. Striatal perfusion of 1000 microM ZNS (within therapeutic-relevant concentration against epilepsy) increased extracellular levels of dopamine in STR, whereas 100 microM ZNS (lower than the therapeutic-relevant concentration against epilepsy but within the therapeutic rage against Parkinson's disease) did not affect it. Striatal perfusion of ZNS (100 and 1000 microM) decreased the extracellular levels of GABA in STN and glutamate in SNr, but decreased extracellular GABA level in GP without affecting GABA level in SNr. These concentration-dependent effects of ZNS on extracellular neurotransmitter levels were independent of dopamine and delta(2) receptors; however, blockade of delta(1) receptor inhibited the effects of ZNS. Furthermore, activation of delta(1) receptor enhanced the effects of ZNS on neurotransmitter level. These results suggest that ZNS does not affect the direct pathway but inhibits the indirect pathway, which is mediated by delta(1) receptor. Therefore, the antiparkinsonian effects of ZNS seem to be mediated through the interaction between lower than therapeutically-relevant concentration against epilepsy of ZNS (100 microM) and delta(1) receptor.

Isoflurane anesthesia induces biphasic effect on dopamine release in the rat striatum

The effect of isoflurane anesthesia on changes in the extracellular concentrations of dopamine (DA) and its metabolites (3-methoxytyramine (3-MT), 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA)) modulated by pargyline, monoamine oxidase inhibitor, was studied using in vivo microdialysis techniques. A microdialysis probe was implanted into the right striatum of male SD rats. Each rat (n=5-6) was given saline or the same volume of 30 or 75 mg kg(-1) pargyline intraperitoneally with or without 1 h isoflurane anesthesia (1 or 3%). Isoflurane anesthesia increased the extracellular concentration of DA in high dose (3%) and increased the metabolite concentrations in a dose-dependent manner. Pargyline administration increased the extracellular concentration of DA and 3-MT, and decreased that of other metabolites. After 30 mg kg(-1) pargyline treatment, 1% isoflurane-induced DA release and increasing of 3-MT were preserved, whereas high dose isoflurane (3%) decreased the concentration of metabolites (DOPAC and HVA), despite of the increase by low dose isoflurane (DOPAC). When 75 mg kg(-1) pargyline was administered, isoflurane anesthesia decreased the concentration of DA and DOPAC. The isoflurane-induced 3-MT increase was preserved in all experiments. Our results suggest that isoflurane anesthesia induced biphasic effect on DA regulation probably by the potentiation of DA release and the inhibition of DA synthesis. Isoflurane might modulate DA homeostasis presynaptically.

Adenosine and ATP-sensitive potassium channels modulate dopamine release in the anoxic turtle (Trachemys scripta) striatum

Excessive dopamine (DA) is known to cause hypoxic/ischemic damage to mammalian brain. The freshwater turtle Trachemys scripta, however, maintains basal striatal DA levels in anoxia. We investigated DA balance during early anoxia when energy status in the turtle brain is compromised. The roles of ATP-sensitive potassium (K(ATP)) channels and adenosine (AD) receptors were investigated as these factors affect DA balance in mammalian neurons. Striatal extracellular DA was determined by microdialysis with HPLC in the presence or absence of the specific DA transport blocker GBR-12909, the K(ATP) blocker 2,3-butanedione monoxime, or the nonspecific AD receptor blocker theophylline. We found that in contrast to long-term anoxia, blocking DA reuptake did not significantly increase extracellular levels in 1-h anoxic turtles. Low DA levels in early anoxia were maintained instead by activation of K(ATP) channels and AD receptors. Blocking K(ATP) resulted in a 227% increase in extracellular DA in 1-h anoxic turtles but had no effect after 4 h of anoxia. Similarly, blocking AD receptors increased DA during the first hour of anoxia but did not change DA levels at 4-h anoxia. Support for the role of K(ATP) channels in DA balance comes from normoxic animals treated with K(ATP) opener; infusing diazoxide but not adenosine into the normoxic turtle striatum resulted in an immediate DA decrease to 14% of basal values within 1.5 h. Alternative strategies to maintain low extracellular levels may prevent catastrophic DA increases when intracellular energy is compromised while permitting the turtle to maintain a functional neuronal network during long-term anoxia.

The non-peptidic delta opioid receptor agonist TAN-67 enhances dopamine efflux in the nucleus accumbens of freely moving rats via a mechanism that involves both glutamate and free radicals

The activation of the delta-opioid receptors in the nucleus accumbens is known to induce a large and rapid increase of accumbal dopamine efflux. (+/-)-TAN-67 (2-methyl-4a(alpha)-(3-hydroxyphenyl)-1,2,3,4,4a,5,12,12a(alpha)-octahydro-quinolino[2,3,3,-g]isoquinoline) is a centrally acting non-peptidic delta opioid receptor agent which has recently become available. Interestingly, the (+) enantiomer of TAN-67 induces hyperalgesia in contrast to the (-) enantiomer of TAN-67 that produces profound antinociceptive effects in mice; the latter effects are mediated through delta-1 receptor stimulation. Using the microdialysis technique, the ability of the enantiomers of TAN-67 to alter the release of accumbal dopamine in vivo was analyzed. Like the 25-min infusion of the selective delta-1 opioid receptor agonist (D-[Pen2,5]-enkephalin) DPDPE (50 nM) and the delta-2 opioid receptor agonist deltorphin II (50 nM), the 25-min infusion of both (-)-TAN-67 (25 and 50 nM) and (+)-TAN-67 (25 and 50 nM) into the nucleus accumbens produced a similar transient dose-dependent increase in the accumbal extracellular dopamine level. Naloxone (1 mg/kg i.p., given 25 min prior to the drugs), namely a treatment that is known to inhibit the increase of dopamine induced by DPDPE and deltorphin II, did not affect the transient increase in the accumbal dopamine level produced by infusion of the enantiomers of TAN-67. The DPDPE and deltorphin II-induced increase in accumbal dopamine level, but not that of (-)-TAN-67 and (+)-TAN-67, was eliminated by subsequently perfused tetrodotoxin (2 microM) into the nucleus accumbens. The increase in accumbal dopamine level produced by an infusion of (-)-TAN-67 and (+)-TAN-67 was not altered by a Ca2+-free Ringer's solution. The (-)-TAN-67 and (+)-TAN-67-induced accumbal dopamine efflux was strongly prevented by reserpine (5 mg/kg i.p., given 24 h earlier) or alpha-methyl-para-tyrosine (250 mg/kg i.p., given 2 h earlier). The effects of the enantiomers of TAN-67 on the accumbal dopamine were nullified by combined treatment with reserpine and alpha-methyl-para-tyrosine. The (-)-TAN-induced dopamine efflux was significantly reduced by the N-methyl-D-aspartate (NMDA) receptor antagonists ifenprodil (20 mg/kg i.p., 20 min before) and MK-801 (0.5 mg/kg i.p., 20 min before), respectively. The effects of (-)-TAN-67 on the dopamine efflux were also inhibited by the free radical scavenger N-2-mercaptopropionyl glycine (100 mg/kg i.p., 20 min before). These results show that both enantiomers of TAN-67 enhance the release of reserpine sensitive, vesicular dopamine and alpha-methyl-p-tyrosine sensitive, cytosolic dopamine from dopaminergic nerve terminals in the nucleus accumbens in a way that is independent of neural activity; activation of delta opioid receptors plays no role in these events. All together, the results suggest that (-)-TAN-67 can generate a burst of free radicals that in turn trigger a release of glutamate that ultimately via activation of NMDA receptors enhances the release of dopamine from dopaminergic nerve terminals in the nucleus accumbens.

Effect of ischemia on TBARS and lactate production in several cerebral regions of anaesthetised and awake rats

The premise of neuroprotective therapy for acute ischemic stroke is based upon the possibility to interfere with the cellular ischemic cascade, so the understanding of the mechanisms and consequences of cerebral ischemia is necessary. The relationship between lipid peroxidation and acidosis was investigated in several regions of rat brain following ischemia without reperfusion. Male Wistar rats (280-300 g) were anaesthetised (Ketalar 33 mg/kg and Rompun 6.66 mg/kg) or not and underwent a four-vessel occlusion for 5 minutes. Then, thiobarbituric acid-reactive substances (TBARS) and lactate levels were measured in different brain regions (cerebellum, bulb, striatum, hippocampus, cortex). Induction of ischemia by ligation of two common carotid arteries and two vertebral arteries resulted in a production of TBARS (40-120%, p < 0.05) and lactate (20-60%, p < 0.05) in all cerebral regions of awake rats, especially in striatum, suggesting a potential link between lipid peroxidation and acidosis. When ischemia was realised on anaesthetised animals, an increase of lactate levels (30-50%, p < 0.05) was shown in all brain regions but TBARS were produced only in striatum (82%, p < 0.05). These data showed the particular vulnerability of striatum to ischemia and the possible opposite effects of an anaesthesia.

Slow death in the leopard frogRana pipiens: neurotransmitters and anoxia tolerance

While frogs such as Rana temporaria are known to withstand 4-5 h anoxia at room temperature, little is known about the neurological adaptations that permit this. Previous research has shown that changes in neuroactive compounds such as glutamate and dopamine in anoxia-sensitive (mammalian)brains follow a strikingly different pattern than is observed in truly anoxia-tolerant vertebrates such as the freshwater turtle. The present study measured changes in the levels of whole brain and extracellular amino acids,and extracellular dopamine, in the normoxic and 3-4 h anoxic frog Rana pipiens, in order to determine whether their neurotransmitter responses resemble the anoxia-vulnerable or anoxia-tolerant response. Increases in whole brain serine, glycine, alanine and GABA levels were similar to those seen in anoxia-tolerant species, although the levels of glutamine, taurine and glutamate did not increase as occurs in true facultative anaerobes. Extracellular levels of aspartate, taurine and GABA also increased significantly, while glutamate levels decreased. The maintenance of low extracellular glutamate was the most significant difference between the frog and the anoxic/ischemic mammalian brain, although aspartate did increase 215%over a 4 h period of anoxia. A 12-fold increase in extracellular dopamine levels during anoxia was the biggest contrast between anoxia-tolerant vertebrates and R. pipiens. The frog could thus be an interesting model in which to examine the mechanisms of dopamine failure in early anoxia,which occurs rapidly in the mammal but over a period of hours in the `slow death' of the anoxic frog brain.

Increased hydroxyl radicals in the hippocampus of stroke-prone spontaneously hypertensive rats during transient ischemia and recirculation

It has been suggested that stroke-prone spontaneously hypertensive rats (SHRSP) show vulnerability to neuronal damage following transient ischemia. To observe the effect of hydroxyl radicals on neuronal damage in the hippocampus of SHRSP during ischemia and recirculation, we measured the levels of 2,3-dihydroxybenzoic acid (2,3-DHBA), as a biological marker of hydroxyl radicals in the hippocampus of SHRSP, by high pressure liquid chromatography-electrochemical detection. The production of hydroxyl radicals in the hippocampus during the first 20 min of recirculation was a peak in all intervals. The changes in 2,3-DHBA levels during ischemia and recirculation in SHRSP were significantly higher than in Wistar-Kyoto rats. These results suggest that neuronal damage following ischemia and recirculation is, in part, caused by the increase in hydroxyl radicals during ischemia and recirculation.

The reverse transport of DA, what physiological significance?

It is well established that midbrain dopamine neurons innervating the striatum, release their neurotransmitter through an exocytotic process triggered by the neural firing and involving a transient calcium entry in the terminals. Long ago, it had been proposed, however, that another mechanism of release could co-exist with classical exocytosis, involving the reverse-transport of the cytosolic amine by the carrier, ordinarily responsible for uptake function. This atypical mode of release could be evoked directly at the preterminal level by multiple environmental endogenous factors involving transient alterations of the sodium gradient. It cannot be excluded that this mode of release participates in the firing-induced release. In contrast with the classical exocytosis of a preformed DA pool, the reverse-transport of DA requires simultaneous alterations of intraterminal amine metabolism including synthesis and displacement from storage compartment. The concept of a reverse-transport of dopamine is coming from the observations that releasing substances, such as amphetamine-related molecules, actually induce this type of transport. A large set of arguments advocates that reverse-transport plays a role in the maintenance of basal extracellular DA concentration in striatum. It was also often evoked in physiopathological situations including ischemia, neurodegenerative processes, etc. The most recent studies suggest that this release could occur mainly outside the synapses, and thus could constitute a major feature in the paracrine transmission, sometimes evoked for DA.