Simultaneous determination of cholecystokinin, dopamine, glutamate and aspartate in cortex and striatum of the rat using in vivo microdialysis

Cerebrolysin restores balance between excitatory and inhibitory amino acids in brain following concussive head injury. Superior neuroprotective effects of TiO2 nanowired drug delivery

Concussive head injury (CHI) often associated with military personnel, soccer players and related sports personnel leads to serious clinical situation causing lifetime disabilities. About 3-4k head injury per 100k populations are recorded in the United States since 2000-2014. The annual incidence of concussion has now reached to 1.2% of population in recent years. Thus, CHI inflicts a huge financial burden on the society for rehabilitation. Thus, new efforts are needed to explore novel therapeutic strategies to treat CHI cases to enhance quality of life of the victims. CHI is well known to alter endogenous balance of excitatory and inhibitory amino acid neurotransmitters in the central nervous system (CNS) leading to brain pathology. Thus, a possibility exists that restoring the balance of amino acids in the CNS following CHI using therapeutic measures may benefit the victims in improving their quality of life. In this investigation, we used a multimodal drug Cerebrolysin (Ever NeuroPharma, Austria) that is a well-balanced composition of several neurotrophic factors and active peptide fragments in exploring its effects on CHI induced alterations in key excitatory (Glutamate, Aspartate) and inhibitory (GABA, Glycine) amino acids in the CNS in relation brain pathology in dose and time-dependent manner. CHI was produced in anesthetized rats by dropping a weight of 114.6g over the right exposed parietal skull from a distance of 20cm height (0.224N impact) and blood-brain barrier (BBB), brain edema, neuronal injuries and behavioral dysfunctions were measured 8, 24, 48 and 72h after injury. Cerebrolysin (CBL) was administered (2.5, 5 or 10mL/kg, i.v.) after 4-72h following injury. Our observations show that repeated CBL induced a dose-dependent neuroprotection in CHI (5-10mL/kg) and also improved behavioral functions. Interestingly when CBL is delivered through TiO₂ nanowires superior neuroprotective effects were observed in CHI even at a lower doses (2.5-5mL/kg). These observations are the first to demonstrate that CBL is effectively capable to attenuate CHI induced brain pathology and behavioral disturbances in a dose dependent manner, not reported earlier.

Measurement of cholecystokinin release in vivo in the rat spinal dorsal horn

The microdialysis technique, used to monitor extracellular levels of transmitter substances in the central nervous system of laboratory animals as a reflection of transmitter release, is based on the ability of neurotransmitters to diffuse in the extracellular fluid from the site of release and to cross a semipermeable dialysis membrane. Even though the surgical procedure is not very complicated, the detection of released substances in the recovered dialysate may be difficult. Especially, the measurement of neuropeptide release is limited by the low extracellular concentration and of low recovery as compared to, for example, monoamines. Thus, for example, cholecystokinin (CCK), which is the most abundant neuropeptide in the central nervous system, is found at concentrations that are several orders of magnitude lower than those of classical transmitters. Therefore a highly sensitive detection method is of utmost importance. In the dorsal horn of the spinal cord CCK is found mainly in interneurons and in terminals of descending fibers. CCK seems to be involved in nociceptive transmission and CCK attenuates morphine-induced antinociception. We here describe in vivo microdialysis in the lumbar dorsal horn of the rat with subsequent quantification of the level of CCK-like immunoreactivity (-LI) by a highly sensitive radioimmunoassay.

Extracellular cholecystokinin levels in the rat spinal cord following chronic morphine exposure: an in vivo microdialysis study

Conflicting results concerning the issue of whether or not chronic morphine exposure induces an increase in CCK biosynthesis have been found in many CNS sites, including the spinal cord, where CCK activity may contribute to the facilitation of the development of opiate tolerance. The present study was undertaken in order to monitor the extracellular level of CCK under spontaneous and stimulus-evoked release in the spinal cord dorsal horn of drug naive and morphine tolerant rats. Tolerance was induced by implantation of two morphine pellets (2x75 mg) which induced a stable morphine plasma concentration after 48 h post-implantation. The tail-flick test and naloxone precipitated withdrawal were used as indexes of tolerance and dependence to morphine. The effect of morphine-pellet implantation on basal and K+-induced release of CCK-like immunoreactivity (CCK-LI) in the rat dorsal horn were monitored with in vivo microdialysis 96 h after implantation of morphine or placebo pellets, when rats showed tolerance and dependence. Basal CCK levels were below the detection limit of the assay (0.6 pM) in both tolerant and normal animals. K+ (100 mM) in the perfusion medium induced a more than 3-fold increase of the extracellular level of CCK-LI in control animals, and a more than 4-fold increase on CCK-LI in morphine-pellet implanted animals. However, this difference was not significant. In addition, naloxone (2 mg/kg; i.v.), did not induce any change in the extracellular level of CCK in either group. The present study suggests that the modulatory interaction between CCK and opioids in the development of tolerance in the spinal cord may occur without necessarily increasing the extracellular level of CCK. Another possible explanation of the finding is that the microdialysis technique is not sensitive enough to detect differences in unstimulated CCK levels in normal and tolerant animals.

Modulation of motor behaviour by NMDA- and cholecystokinin-antagonism

Motor behaviour relies on complex neurochemical interactions in the basal ganglia, in particular the striatum. Antagonistic influences in this region are exerted by afferent projections from, on the one hand, the ventral mesencephalon, utilizing dopamine as a transmitter, and, on the other hand, from the cerebral cortex, signalling by the excitatory amino acid glutamate. The activity in both these neuronal populations appears to be regulated by the neuropeptide cholecystokinin. This article concentrates on interactions between cholecystokinin and glutamate, summarizing some recent morphological, biochemical and behavioural findings. It is suggested that cholecystokinin, acting via the cholecystokininB receptor, potentiates the glutamatergic excitatory input to the striatum.

Electrical stimulation of the prefrontal cortex increases cholecystokinin, glutamate, and dopamine release in the nucleus accumbens: an in vivo microdialysis study in freely moving rats

In vivo microdialysis, radioimmunoassay, and HPLC with electrochemical or fluorometric detection were used to investigate the release of cholecystokinin (CCK), glutamate (Glu), and dopamine (DA) in nucleus accumbens septi (NAS) as a function of ipsilateral electrical stimulation of medial prefrontal cortex (mPFC). CCK was progressively elevated by mPFC stimulation at 50-200 Hz. Stimulation-induced CCK release was intensity-dependent at 250-700 microA. NAS Glu and DA levels were each elevated by stimulation at 25-400 Hz; the dopamine metabolites DOPAC and homovanillic acid were increased by stimulation at 100-400 Hz. When rats were trained to lever press for mPFC stimulation, the stimulation induced similar elevations of each of the three transmitters to those seen with experimenter-administered stimulation. Perfusion of 1 mM kynurenic acid (Kyn) into either the ventral tegmental area (VTA) or NAS blocked lever pressing for mPFC stimulation. VTA, but not NAS, perfusion of Kyn significantly attenuated the increases in NAS DA levels induced by mPFC stimulation. Kyn did not affect NAS CCK or Glu levels when perfused into either the VTA or NAS. The present results are consistent with histochemical evidence and provide the first in vivo evidence for the existence of a releasable pool of CCK in the NAS originating from the mPFC. Although dopamine is the transmitter most closely linked to reward function, it was CCK that showed frequency-dependent differences in release corresponding most closely to rewarding efficacy of the stimulation. Although not essential for the reward signal itself, coreleased CCK may modulate the impact of the glutamatergic action in this behavior.

Peripheral axotomy influences the in vivo release of cholecystokinin in the spinal cord dorsal horn-possible involvement of cholecystokinin-B receptors

An increased expression of cholecystokinin (CCK) messenger RNA (mRNA) as well as CCK-B receptor mRNA in dorsal root ganglion (DRG) cells following peripheral axotomy has previously been demonstrated. In the present in vivo microdialysis study, the effect of unilateral sciatic nerve section on basal and potassium-induced release of CCK-like (CCK-LI) immunoreactivity in the rat dorsal horn was investigated. We also compared the effects of the CCK-B receptor antagonist CI988 on basal and potassium-stimulated CCK-LI release in intact animals and in chronically axotomized rats. Perfusion of the microdialysis probe with KCl (100 mM) induced a more than 6-fold increase of the extracellular level of CCK-LI in control animals. In contrast, following unilateral sciatic nerve section the same KCl stimulation failed to evoke a release of CCK-LI ipsilaterally. However, after systemic administration of CI988 (1 mg kg-1, i.v.), 100 mM KCl induced a significant increase of the extracellular CCK-LI level in axotomized rats, similar to that observed in control animals. In control animals no effect of CI988 on KCl-stimulated CCK-LI release could be detected. CI988 by itself had no influence on the extracellular CCK-LI level in either nerve injured or control animals. The present data suggest that axotomy reduces the release of CCK-like immunoreactivity in the spinal cord by a mechanism involving the CCK-B receptor binding site.

Preferential blockade of cholecystokinin-8S-induced increases in aspartate and glutamate levels by the CCK(B) receptor antagonist, L-365,260, in rat brain

In the present studies, the ability of a locally delivered cholecystokinin (CCK) receptor agonist and systemically delivered antagonists to modulate extracellular levels of aspartate and glutamate in the frontal cortex of anaesthetised rats and frontal cortex and caudate-putamen of freely moving rats was investigated using an in vivo microdialysis technique. In the anaesthetised rats, local application of sulphated CCK octapeptide (CCK-8S, 10 microM) into the frontal cortex enhanced extracellular aspartate levels to a maximum of 265+/-16% of the basal levels, whereas glutamate levels were increased to a maximum of 168+/-7% of the basal levels. Given 40 min prior to the cortical perfusion of 10 microM of CCK-8S, the CCK(B) receptor antagonist, L-365,260 (20 mg/kg, s.c.), limited the rise in cortical aspartate by over half to 170+/-10% of the basal levels. However, this same dose of L-365,260 still allowed CCK-8S to increase glutamate by 44+/-15% above the basal levels. Whereas the enhanced glutamate levels were totally unaffected by systemic administration of the CCK(A) receptor antagonist, L-364,718 (20 mg/kg, -40 min, s.c.), this treatment was able to limit the elevation in aspartate to 220+/-4% of the basal levels. In the freely moving rats, local perfusion of CCK-8S (10 microM) increased aspartate and glutamate levels to maxima of 275+/-12% and 225+/-14% of the basal levels, respectively, in the frontal cortex. In the caudate-putamen, aspartate and glutamate levels were also elevated by CCK-8S (10 microM) to 248+/-15% and 185+/-12% of the basal levels, respectively. The respective increase in aspartate and glutamate induced by CCK-8S (10 microM) were limited to 140+/-10% and 124+/-6% (frontal cortex), of the basal levels, and 162+/-15% and 143+/-8% (caudate-putamen), by 40 min pretreatment with L-365,260 (20 mg/kg, s.c.). In conclusion, CCK-8S was able to enhance both aspartate and glutamate overflow in the frontal cortex of anaesthetised rats, and frontal cortex and caudate-putamen of freely moving rats. These increases were preferentially offset by the selective CCK(B) receptor antagonist, L-365,260, since no influence could be discerned using the selective CCK(A) receptor antagonist, L-364,718.

On the release of glutamate and aspartate in the basal ganglia of the rat: interactions with monoamines and neuropeptides

Using highly sensitive analytical procedures, glutamate (Glu), aspartate (Asp) and several putative neurotransmitters and metabolites can be monitored simultaneously in the extracellular space of neostriatum, substantia nigra and cerebral cortex of the rat by in vivo microdialysis. Glu and Asp are found at sub-micromolar concentrations in all investigated brain regions. In order to ascertain their neuronal origin, we have extensively studied the sensitivity of extracellular Glu and Asp levels to: (i) K(+)-depolarization, (ii) Na(+)-channel blockade, (iii) removal of extracellular Ca2+, (iv) depletion of presynaptic vesicles, and (v) integrity of neuronal pathways. The relevance of these criteria for several neurotransmitters monitored simultaneously or in parallel experiments has also been examined. The functional interactions among different neuronal pathways in the basal ganglia are studied by using selective pharmacological treatments, administered systemically, or locally via intracerebral injections or the microdialysis perfusion medium. Immunohistochemical evidence for the existence of Glu and/or Asp neuronal pathways in the basal ganglia of the rat is presented, discussing especially new findings indicating the existence of a Glu-independent Asp system, intrinsic to the neostriatum of the rat. The clinical relevance of these interactions is discussed, focusing on the implications for the treatment of neurodegenerative disorders affecting the basal ganglia.

Glutamate release correlates with brain-derived neurotrophic factor and trkB mRNA expression in the CA1 region of rat hippocampus

Synthesis of the neurotrophic factor brain-derived neurotrophic factor (BDNF) and its receptor TrkB in the hippocampus have been proposed to be influenced by endogenous glutamate. To test this hypothesis we have investigated if increases in BDNF and trkB mRNAs are associated with changes in the synaptic release of glutamate in the dorsal hippocampus in the conscious rat by combining the technique of in vivo microdialysis with in situ hybridization histochemistry. A 35% and 66% increase in extracellular levels of glutamate in the dorsal CA1 region was detected following injection into the lateral entorhinal cortex of 2.4 and 9.6 microg of the non-NMDA glutamate receptor agonist quisqualate, respectively. The increase in glutamate was attenuated by local administration of tetrodotoxin (TTX) indicating neuronal origin. Levels of BDNF and trkB mRNAs were increased in the hippocampus in a dose-dependent fashion following the stimulations. The extracellular levels of glutamate in individual animals correlated to the levels of BDNF and trkB mRNAs in the dorsal CA1 region of the hippocampus. This study provides for the first time evidence of an entorhinal cortex influenced concentration-dependent relationship between the release of endogenous glutamate in vivo and neuronal expression of mRNAs for BDNF and its receptor trkB in the hippocampus.

Modulation of neurotransmitter release by cholecystokinin in the neostriatum and substantia nigra of the rat: regional and receptor specificity

The effect of cholecystokinin peptides on the release of dynorphin B, aspartate, glutamate, dopamine and GABA in the neostriatum and substantia nigra of the rat was investigated using in vivo microdialysis. Sulphated cholecystokinin-8S in the dialysis perfusate (1-100 microM) induced a concentration-dependent increase in extracellular dynorphin B and aspartate levels, both in the neostriatum and substantia nigra. Striatal dopamine levels were only increased by 100 microM of cholecystokinin-8S, while in the substantia nigra they were increased by 10-100 microM of cholecystokinin-8S. Extracellular GABA and glutamate levels were increased following 100 microM of cholecystokinin-8S only. Striatal cholecystokinin-8S administration also produced a significant increase in nigral dynorphin B levels. Local cholecystokinin-4 (100 microM) produced a moderate, but significant, increase of extracellular dynorphin B and aspartate levels in the neostriatum and substantia nigra. No effect was observed on the other neurotransmitters investigated. A 6-hydroxydopamine lesion of the nigrostriatal dopamine pathway did not affect the increases in dynorphin B and aspartate levels produced by local administration of cholecystokinin-8S. Basal extracellular GABA levels were increased significantly in both the neostriatum and substantia nigra ipsilateral to the lesion. Nigral glutamate and aspartate levels were also increased in the lesioned substantia nigra, but in the lesioned neostriatum aspartate levels were decreased. The cholecystokinin-B antagonist L-365,260 (20 mg/kg, s.c.), but not the cholecystokinin-A antagonist L-364,718 (devazepide; 20 mg/kg, s.c.), significantly inhibited the effect of cholecystokinin-8S on striatal dynorphin B and aspartate levels. In the substantia nigra, however, the effect of cholecystokinin-8S on dynorphin B and aspartate levels was inhibited to a similar extent by both L-365,260 and L-364,718. Pretreatment with L-364,718, but not with L-365.260, prevented the increase in nigral dopamine levels produced by nigral cholecystokinin-8S administration. Taken together, these results suggest that cholecystokinin-8S modulates dynorphin B and aspartate release in the neostriatum and substantia nigra of the rat via different receptor mechanisms. In the neostriatum, the effect of cholecystokinin-8S on dynorphin B and aspartate release is mediated via the cholecystokinin-B receptor subtype, while in the substantia nigra, cholecystokinin-8S modulates dynorphin B and aspartate release via both cholecystokinin-A and cholecystokinin-B receptor subtypes. Cholecystokinin-8S modulates dopamine release mainly in the substantia nigra, via the cholecystokinin-A receptor subtype.

Capillary electrophoresis with laser-induced fluorescence detection: a sensitive method for monitoring extracellular concentrations of amino acids in the periaqueductal grey matter

The use of capillary electrophoresis with laser-induced fluorescence detection (CE-LIF) for the analysis of microdialysate samples from the periaqueductal grey matter (PAG) of freely moving rats is described. By employing 3-(4-carboxybenzoyl)-2-quinoline-carboxaldehyde (CBQCA) as a derivatization agent, we simultaneously monitored the concentrations of 8 amino acids (arginine, glutamine, valine, gamma-amino-n-butyric acid (GABA), alanine, glycine, glutamate, and aspartate), with nanomolar and subnanomolar detection limits. Two of the amino acids (GABA and glutamate) were analysed in parallel by conventional high-performance liquid chromatography (HPLC) in order to directly compare the two analytical methods. Other CE methods for analysis of microdialysate have been previously described, and this improved method offers greater sensitivity, ease of use, and the possibility to monitor several amino acids simultaneously. By using this technique together with an optimised form of microdialysis technique, the tiny sample consumption and the improved detection limits permit the detection of fast and transient transmitter changes.

Repeated spinal cord stimulation decreases the extracellular level of gamma-aminobutyric acid in the periaqueductal gray matter of freely moving rats

Most of the previous experimental studies on the antinociceptive effects of electrical spinal cord stimulation (SCS) have focused on short-lasting effects mainly depending on spinal mechanisms. However, patients treated with SCS for chronic pain often report pain relief exceeding the period of stimulation for several hours. The long lasting effect of SCS might not only involve spinal, but also supraspinal mechanisms. A supraspinal region of major importance for the coordination of descending pain inhibition is the periaqueductal grey matter (PAG). The aim of the present microdialysis study, performed in awake freely moving rats, was to investigate if repeated SCS (two 30 min periods separated by a 90 min resting period) alters the extracellular neurotransmitter concentrations in the ventrolateral PAG. In a first series of experiments significantly decreased (-30%; P < 0.05; n = 7) gamma-aminobutyric acid (GABA) levels were detected immediately after the second SCS session. Neither the concentration of serotonin nor that of substance P-like immunoreactivity (SP-LI) was affected by SCS. The decrease of GABA after two SCS sessions was confirmed in a second series of experiments (-30%; P < 0.05; n = 7). No spontaneous decline of GABA was observed in sham-stimulated animals (n = 6). The glutamate concentration was also determined in this latter series of experiments and a significant decrease (-23%; P < 0.05; n = 5) was observed after the second SCS session. As GABA-neurons in the PAG exert a tonic depressive effect on the activity in descending pain inhibitory pathways, a decreased extracellular GABA level in this region, as detected following repeated SCS, might indicate an increased pain inhibition.

Effect of local cholecystokinin-8 administration on extracellular levels of amino acids and glycolytic products monitored by in vivo microdialysis in the fronto-parietal cortex of the rat

The effects of local cholecystokinin-8 (CCK-8) administration on cortical extracellular levels of amino acids, catecholamines and metabolism products were studied in the halothane anaesthetized rat by in vivo microdialysis. CCK-8 (10 microM), administrated via a microdialysis probe, produced a significant increase in the levels of aspartate, glutamate and gamma-aminobutyric acid (GABA), but not of 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), lactate and pyruvate, which were simultaneously monitored. The increase in aspartate and glutamate levels produced by CCK-8 was about 3-4-fold. The effect of CCK-8 on aspartate levels was significantly inhibited by the CCKB antagonist, L-365,260 (20 mg kg-1, s.c.), but not by the CCKA antagonist, L-364,718 (20 mg kg-1, s.c.). In contrast, the increase in glutamate levels was inhibited by both L-365,260 and L-364,718. GABA was slightly, but significantly increased (approximately 30%), by local CCK-8 and was inhibited by both CCK antagonists. The present results show that CCK-8 exerts a strong modulatory action on both aspartate and glutamate release in rat cortex. While the effect of CCK-8 on aspartate is selectively mediated via CCKB receptor subtype, the effect of CCK-8 on glutamate appears to be mediated via both CCKA and CCKB receptor subtypes.

Neurocircuitry of the basal ganglia studied by monitoring neurotransmitter release. Effects of intracerebral and perinatal asphyctic lesions

The neurocircuitries of the basal ganglia are studied with in vivo microdialysis, with special consideration to dopamine transmission and its interaction with other neurotransmitter systems. The aim is to develop experimental models to study the pathophysiology and therapy of neurodegenerative disorders of the basal ganglia, as well as to develop models to study the short- and long-term consequences of perinatal asphyctic lesions. A main goal of these studies is to find and to characterize new treatments for these disorders.

On the origin of striatal cholecystokinin release: studies with in vivo microdialysis

In the present study, extracellular levels of the neuropeptide cholecystokinin (CCK), of the monoamine dopamine and its metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), and of the excitatory amino acids glutamate and aspartate were simultaneously monitored by microdialysis in the neostriatum of halothane-anesthetized rats under basal and K(+)-depolarizing conditions. Extracellular CCK and dopamine levels, but not glutamate and aspartate levels, were decreased by perfusion with a Ca(2+)-free medium, under both basal and K(+)-depolarizing conditions. HPLC revealed that the majority of the CCK-like immunoreactivity in the perfusates coeluted with CCK octapeptide. Striatal extracellular CCK levels were decreased by decortication plus callosotomy, with a parallel decrease in glutamate levels. Striatal extracellular levels of dopamine, DOPAC, and HVA were significantly decreased in animals treated previously with a unilateral 6-hydroxydopamine injection into the medial forebrain bundle. In these animals, however, the effect of decortication plus callosotomy on CCK and glutamate levels was not further augmented. Thus, this study supports the hypothesis of a neuronal origin of extracellular CCK and dopamine monitored with microdialysis in the striatum of the rat, and also supports the idea of a partly contralateral origin of corticostriatal CCK and glutamate inputs.