Microdialysis Study Research Articles

Effect of JWH-250, JWH-073 and their interaction on “tetrad”, sensorimotor, neurological and neurochemical responses in mice

JWH-250 and JWH-073 are two synthetic cannabinoid agonists with nanomolar affinity at CB1 and CB2 receptors. They are illegally marketed within “herbal blend” for theirs psychoactive effects greater than those produced by Cannabis. Recently, we analyzed an “herbal” preparation containing a mixture of both JWH-250 and JWH-073. The present study was aimed at investigating the in vitro and in vivo pharmacological activity of JWH-250 and JWH-073 in male CD-1 mice. In vitro competition binding experiments performed on mouse and human CB1 and CB2 receptors revealed a nanomolar affinity and potency of the JWH-250 and JWH-073. In vivo studies showed that JWH-250 and JWH-073, administered separately, induced a marked hypothermia, increased pain threshold to both noxious mechanical and thermal stimuli, caused catalepsy, reduced motor activity, impaired sensorimotor responses (visual, acoustic and tactile), caused seizures, myoclonia, hyperreflexia and promote aggressiveness in mice. Moreover, microdialysis study in freely moving mice showed that systemic administration of JWH-250 and JWH-073 stimulated dopamine release in the nucleus accumbens in a dose-dependent manner. Behavioral, neurological and neurochemical effects were fully prevented by the selective CB1 receptor antagonist/inverse agonist AM 251. Co-administration of ineffective doses of JWH-250 and JWH-073 impaired visual sensorimotor responses, improved mechanical pain threshold and stimulated mesolimbic DA transmission in mice, living unchanged all other behavioral and physiological parameters. For the first time the present study demonstrates the overall pharmacological effects induced by the administration of JWH-250 and JWH-073 in mice and it reveals their potentially synergistic action suggesting that co-administration of different synthetic cannabinoids may potentiate the detrimental effects of individual compounds increasing their dangerousness and abuse potential.

Behavioural and Neurochemical Assessment of Heantos 4 on Preclinical Models of Morphine-Dependence

Objective: Opiate addiction is characterized by compulsive drug use and severe withdrawal symptoms during abstinence. Heantos 4, an herbal pharmacotherapy recently approved for opiate withdrawal treatment in Vietnam, has shown anti-craving properties. The present study is the first preclinical assessment of the effects of Heantos 4 on opiate withdrawal and the rewarding properties of morphine, along with its action on a critical neural substrate of addiction, the mesolimbic dopamine (DA) system. Methods: Rats received morphine treatments (10 mg/kg, i.p.) for seven days. On Day 8, Heantos 4 (100, 250 or 500 mg/kg, p.o.) was administered prior to naloxone (1 or 10 mg/kg, i.p.). Affective withdrawal symptoms were measured using conditioned place aversion (CPA) and somatic withdrawal symptoms were scored separately. The effect of Heantos 4 on morphine-induced (5 mg/kg, i.p.) conditioned place preference (CPP) was assessed by administering it prior to conditioning, expression or morphine-induced reinstatement. Additionally, the effect of Heantos 4 on the long-term maintenance of morphine-induced CPP was assessed bi-weekly for 6 weeks. Microdialysis studies assessed DA efflux in the nucleus accumbens of rats receiving one or seven repeated treatments of Heantos 4 (500 mg/kg, p.o.) and morphine, or receiving Heantos 4 and naloxone (10 mg/kg, i.p.). Results: Heantos 4 reduced somatic but not affective components of naloxone-precipitated opiate withdrawal. It attenuated acquisition but not expression or reinstatement of morphine-induced CPP. Long-term maintenance of morphine-induced CPP was also reduced. Heantos 4 by itself enhanced DA efflux but blunted morphine-evoked DA release on Day 1 and 7. Heantos 4 attenuated naloxone-induced decrease in DA in morphine-dependent rats. Conclusion: These findings demonstrate that Heantos 4 alleviates symptoms of somatic opiate withdrawal and indicate potential effects on incentive motivation. Moreover, Heantos 4 may modulate DA transmission that limits or antagonizes non-physiological fluctuations in mesolimbic DA activity induced by morphine and naloxone.

Intracerebral hypoglycemia and its clinical relevance as a prognostic indicator in severe traumatic brain injury: A cerebral microdialysis study from India.

Traumatic brain injury (TBI) remains a major cause of morbidity and mortality worldwide. Largely, the prognosis is dependent on the nonmodifiable factors such as severity of the initial injury, Glasgow coma scale score, pupillary response, age, and presence of additional physiological derangements such as hypoxia or hypotension. However, secondary insults continue to take place after the initial injury and resuscitation. The study hypothesis in the present research article was that hypoglycemia is an independent outcome prognosticator in severe traumatic brain injury. The study aimed to assess the role of glucose monitoring in the brain parenchyma as an independent outcome prognosticator and also to study its association with plasma glucose levels. The aim of the study was to analyze the relationship of intracerebral glucose measured by intraparenchymal cerebral microdialysis (CMD), and also to study its relationship with blood glucose levels. We also evaluated the relationship of these values to the outcome of patients. Prospective nonrandomized study conducted at a tertiary care trauma center in India. Twenty-five patients with severe TBI, who underwent decompressive craniectomy, were prospectively monitored with CMD catheters. Twenty cases had unilateral catheters placed intraparenchymally (20 mm inside the brain parenchyma to accommodate 10 mm of the semipermeable catheter tip and another 10 mm of extra catheter length). Frontotemporal contusions were noted in 21 cases and an acute subdural hematoma (with/without associated contusions) were noted in 15 cases in the present series. Bilateral CMD catheters were placed during bifrontal decompressive craniectomies in five patients (two patients had peri-contusional catheters placement; these patients had bilateral frontal contusions); while, the remaining 3 patients had a contralateral catheter placement in the normal brain parenchyma [Table 1]. The position of the catheters was confirmed on postoperative computerized tomographic scan carried out in these subjects. However, bilateral catheter placement to compare the difference in cerebral biochemical values of glucose in the penumbric zone as well as the normal brain could not be done in all cases due to cost restraints. The relation between plasma glucose and CMD-measured interstitial brain glucose concentrations, as well as the temporal pattern of CMD glucose was studied for 3-5 days following a decompressive craniectomy using a CMD analyzer at the patient's bedside at 1 hourly intervals. All data were tabulated in Microsoft Excel 2011 and analyzed using SPSS version 21. To calculate the correlation between plasma and CMD glucose, Pearson's correlation was used with a two-tailed test of significance. Student's t-test was used to calculate the difference in means between the two groups. Significance was assumed at P ≤ 0.05. Fifteen patients (60%) had a good outcome in terms of the Glasgow Outcome Scale (GOS) at 3 months while the rest (10 patients) had a poor GOS at 3 months. There was a significant difference in the incidence of hyperglycemia (random blood sugar >10 mmol/L) between the two groups (P < 0.0001). The difference between the two groups while comparing episodes of hypoglycemia was also significant (P = 0.0026). The good outcome group had fewer episodes of brain hypoglycemia during the presence of systemic hypoglycemia (P = 0.0026). Neither the mean blood glucose values nor the mean cerebral glucose values predicted the outcome at 3 months. After decompressive craniectomy in severe TBI, there was a poor correlation between the plasma and CMD glucose concentration. A higher degree of variation was seen in the correlations for individual patients. Neither the mean blood glucose values nor the mean cerebral glucose values predicted the outcome at 3 months. The good outcome group had fewer episodes of both hyperglycemia and hypoglycemia.

Ethanol and acetaldehyde differentially alter extracellular dopamine and serotonin in Aldh2-knockout mouse dorsal striatum: A reverse microdialysis study

Dopamine (DA) and serotonin (5-HT) seem to be involved in several of the effects of ethanol (EtOH). Acetaldehyde (AcH), especially in the brain, induces effects that mimic those of EtOH. The purpose of this study was to investigate the effects of local perfusion of EtOH and AcH on extracellular DA and 5-HT in the dorsal striatum of Aldh2-knockout (Aldh2-KO) and wild-type (WT) mice. Aldh2-KO mice were used as a model of aldehyde dehydrogenase 2 deficiency in humans to examine the effects of AcH. Mice were perfused with Ringer’s solution (control), EtOH (100, 200, or 500mM) and AcH (100, 200, or 500μM) into the dorsal striatum. Dialysate samples were collected every 5min, and then analyzed with HPLC coupled to an ECD. We found that local perfusion with 500mM EtOH increased extracellular levels of DA (p<0.05) in both Aldh2-KO and WT mice, while 5-HT levels remain unchanged. EtOH at a dose of 200mM also increased DA in WT mice, but this was limited to a 30–40-min time-point. In contrast, perfusion with 200 and 500μM AcH decreased both DA and 5-HT (p<0.05) in Aldh2-KO mice, but this decrease was not found in WT mice at any AcH dose, indicating an effect of AcH on DA and 5-HT levels. There were no genotype effects on the basal levels of DA and 5-HT. These results indicate that high EtOH can stimulate DA, whereas high AcH can depress both DA and 5-HT in the dorsal striatum of mice.

Melanin-concentrating hormone projections to the dorsal raphe nucleus: An immunofluorescence and in vivo microdialysis study

Melanin-concentrating hormone (MCH)-containing neurons are localized in the lateral hypothalamus and incerto-hypothalamic areas, and project to several brain regions including the dorsal raphe nucleus (DRN). The MCHergic system has been involved in the regulation of emotional states and we have demonstrated that MCH microinjections into the rat DRN promote a depressive-like state. To understand the MCHergic transmission into the DRN, in the present study we characterized the distribution and density of the MCHergic fibers along the rostro-caudal axis of the rat DRN and their anatomical relationship with the 5-HT- and GABA-containing neurons. Additionally, a functional in vivo microdialysis study was carried out in order to evaluate the MCH effects on the 5-HT extracellular levels.Immunolabeling studies showed that MCHergic fibers were widely distributed throughout the rostro-caudal DRN extent and a reduced density at the most caudal level was observed. Interestingly, MCHergic fibers appeared in close apposition to 5-HT and GABA-containing neurons. Microdialysis studies evidenced an opposite effect of two concentrations of MCH on 5-HT levels: the lower concentration (30μM) produced a significant and long-lasting (up to 120min) decrease while the higher (100μM) induced a slight and brief (20min) increase.Morphological and functional results strongly suggest that both 5-HT- and GABA-containing neurons of the DRN are modulated by MCH. A different sensitivity of these neurons to MCH may explain the dose-response effect on 5-HT release. The decrease in extracellular 5-HT levels may account for the depressive-like effect induced by MCH reported in our previous studies.

In vivo measurements of limbic glutamate and GABA concentrations in epileptic patients during affective and cognitive tasks: A microdialysis study

Limbic system structures such as the amygdala (AMG) and the hippocampus (HIPP) are involved in affective and cognitive processing. However, because of the limitations in noninvasive technology, absolute concentrations of the neurotransmitters underlying limbic system engagement are not known. Here, we report changes in the concentrations of the neurotransmitters glutamate (Glu) and gamma-aminobutyric acid (GABA) in the HIPP and the AMG of patients with nonlesional temporal lobe epilepsy undergoing surgery for intracranial subdural and depth electrode implantation. We utilized an in-vivo microdialysis technique while subjects were engaged in cognitive tasks with or without emotional content. The performance of an emotion learning task (EmoLearn) was associated with a significant increase in the concentration of glutamate in the HIPP when images with high valence content were processed, as compared to its concentration while processing images with low valence. In addition, significantly decreased levels of glutamate were found in the AMG when images with predominantly low valence content were processed, as compared to its concentration at baseline. The processing of face stimuli with anger/fear content (FaceMatch task) was accompanied with significantly decreased concentrations of GABA in the AMG and HIPP compared to its levels at the baseline. The processing of shapes on the other hand was accompanied with a significantly decreased concentration of the glutamate in the AMG as well as in the HIPP compared to the baseline. Finally, the performance of a nondeclarative memory task (weather prediction task-WPT) was associated with relatively large and opposite changes in the GABA levels compared to the baseline in the AMG (decrease) and the HIPP (increase). These data are relevant for showing an involvement of the amygdala and the hippocampus in emotional processing and provide additional neurochemical clues towards a more refined model of the functional circuitry of the human limbic system.

7-Chloro-5-(furan-3-yl)-3-methyl-4H-benzo[e][1,2,4]thiadiazine 1,1-Dioxide as Positive Allosteric Modulator of α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid (AMPA) Receptor. The End of the Unsaturated-Inactive Paradigm?

5-Arylbenzothiadiazine type compounds acting as positive allosteric modulators of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPA-PAMs) have received particular attention in the past decade for their nootropic activity and lack of the excitotoxic side effects of direct agonists. Recently, our research group has published the synthesis and biological activity of 7-chloro-5-(3-furanyl)-3-methyl-3,4-dihydro-2H-1,2,4-benzothiadiazine 1,1-dioxide (1), one of the most active benzothiadiazine-derived AMPA-PAMs in vitro to date. However, 1 exists as two stereolabile enantiomers, which rapidly racemize in physiological conditions, and only one isomer is responsible for the pharmacological activity. In the present work, experiments carried out with rat liver microsomes show that 1 is converted by hepatic cytochrome P450 to the corresponding unsaturated derivative 2 and to the corresponding pharmacologically inactive benzenesulfonamide 3. Surprisingly, patch-clamp experiments reveal that 2 displays an activity comparable to that of the parent compound. Molecular modeling studies were performed to rationalize these results. Furthermore, mice cerebral microdialysis studies suggest that 2 is able to cross the blood-brain barrier and increases acetylcholine and serotonin levels in the hippocampus. The experimental data disclose that the achiral hepatic metabolite 2 possesses the same pharmacological activity of its parent compound 1 but with an enhanced chemical and stereochemical stability, as well as an improved pharmacokinetic profile compared with 1.

Treatment of Cancer Pain and Medical Narcotics

The World Health Organization has reported that when morphine is used to control pain in cancer patients, psychological dependence is not a major concern. Our studies were undertaken to ascertain the modulation of psychological dependence on morphine under a chronic pain-like state in rats. Morphine induced a dose-dependent place preference. We found that inflammatory and neuropathic pain-like states significantly suppressed the morphine-induced rewarding effect. In an inflammatory pain-like state, the suppressive effect was significantly recovered by treatment with a κ-opioid receptor antagonist. In addition, in vivo microdialysis studies clearly showed that the morphine-induced increase in the extracellular levels of dopamine (DA) in the nucleus accumbens (N.Acc.) was significantly decreased in rats pretreated with formalin. This effect was in turn reversed by the microinjection of a specific dynorphin A antibody into the N.Acc. These findings suggest that the inflammatory pain-like state may have caused the sustained activation of the κ-opioidergic system within the N.Acc., resulting in suppression of the morphine-induced rewarding effect in rats. On the other hand, we found that attenuation of the morphine-induced place preference under neuropathic pain may result from a decrease in the morphine-induced DA release in the N.Acc with a reduction in the μ-opioid receptor-mediated G-protein activation in the ventral tegmental area (VTA). Moreover, nerve injury results in the continuous release of endogenous β-endorphin to cause the dysfunction of μ-opioid receptors in the VTA. This paper also provides a review to clarify misunderstandings of opioid analgesic use to control pain in cancer patients.

In Vitro Pharmacodynamics of Vancomycin against Methicillin-Susceptible and -Resistant Staphylococcus aureus: Considering the Variability in Observed Tissue Exposure.

Vancomycin is considered a first-line antibiotic for complicated skin and skin structure infections (cSSSI) because of the risk of methicillin-resistant Staphylococcus aureus (MRSA). The vancomycin exposure of tissue can vary widely in patients with cSSSI, yet most models test only the average exposure. The in vitro pharmacodynamic model was used to simulate three tissue exposure levels attained by administering vancomycin at 1 g every 12 h (q12h), based on the median (50th), 25th, and 10th percentile tissue area under the concentration-time curve (AUC) values observed during an in vivo microdialysis study of diabetic patients. Four clinical isolates (two of MRSA [vancomycin MIC, 1 and 2 μg/ml] and two of methicillin-susceptible S. aureus [MSSA] [MIC, 1 and 2 μg/ml]) were evaluated. Experiments were performed over 72 h in duplicate. Time-kill curves were constructed, and the area under the bacterial killing and regrowth curve (AUBC) during the final 24-h dosing interval (48 to 72 h) (AUBC48-72) was calculated. Reductions in the 72-h number of CFU/ml and AUBC48-72 at the different exposure levels were compared. Target tissue vancomycin exposure levels for the 50th (AUC0-12, 102.0 ± 9.1 μg · h/ml), 25th (AUC0-12, 44.3 ± 1.8 μg · h/ml), and 10th (AUC0-12, 25.3 ± 3.1 μg · h/ml) percentiles were obtained in all studies. No differences in the 72-h number of CFU or AUBC were observed between exposure levels when all of the isolates were analyzed together. However, for the two MRSA isolates, the 10th percentile exposure level achieved a lower 72-h number of CFU/ml (-1.4 ± 0.4 log10 CFU/ml, P = 0.007) and a greater AUBC48-72 (97.1 ± 20.0 log10 CFU · h/ml, P = 0.011) than the higher exposure levels. The majority of the tissue exposure levels achieved with a vancomycin dosing regimen of 1 g q12h resulted in substantial killing of MSSA and MRSA; however, the lowest exposure levels observed in a minority of the population may explain the poor vancomycin response.

In vivo investigation of escitalopram's allosteric site on the serotonin transporter

Escitalopram is a commonly prescribed antidepressant of the selective serotonin reuptake inhibitor class. Clinical evidence and mapping of the serotonin transporter (SERT) identified that escitalopram, in addition to its binding to a primary uptake-blocking site, is capable of binding to the SERT via an allosteric site that is hypothesized to alter escitalopram's kinetics at the SERT. The studies reported here examined the in vivo role of the SERT allosteric site in escitalopram action. A knockin mouse model that possesses an allosteric-null SERT was developed. Autoradiographic studies indicated that the knockin protein was expressed at a lower density than endogenous mouse SERT (approximately 10–30% of endogenous mouse SERT), but the knockin mice are a viable tool to study the allosteric site. Microdialysis studies in the ventral hippocampus found no measurable decrease in extracellular serotonin response after local escitalopram challenge in mice without the allosteric site compared to mice with the site (p=0.297). In marble burying assays there was a modest effect of the absence of the allosteric site, with a larger systemic dose of escitalopram (10-fold) necessary for the same effect as in mice with intact SERT (p=0.023). However, there was no effect of the allosteric site in the tail suspension test. Together these data suggest that there may be a regional specificity in the role of the allosteric site. The lack of a robust effect overall suggests that the role of the allosteric site for escitalopram on the SERT may not produce meaningful in vivo effects.

Cerebral and Peripheral Metabolism to Predict Successful Reperfusion After Cardiac Arrest in Rats: A Microdialysis Study.

In clinical practice, monitoring of the efficacy of resuscitation can be challenging. The prediction of cerebral and overall outcome in particular is an unmet medical need. Microdialysis is a minimally invasive technique for the continuous determination of metabolic parameters in vivo. Using this technique, we set out to establish a model allowing for concomitant determination of cerebral and peripheral metabolism in a cardiac arrest setting in rodents. Microdialysis settings were optimized in vitro and then used in male Sprague-Dawley rats. Probes were implanted into the CA1 region of the right hippocampus and the right femoral vein. With a time interval of 8min, glucose, lactate, pyruvate, and glutamate levels were determined during baseline conditions, untreated ventricular fibrillation cardiac arrest, cardiopulmonary resuscitation (CPR), reperfusion, and death. In 16 rodents, restoration of spontaneous circulation was achieved in seven animals. Characteristic metabolic changes were evident during cardiac arrest and reperfusion with both probes. Ischemic patterns in peripheral compartments were delayed and more variable compared to the changes in cerebral metabolism highlighting the importance of cerebral metabolic monitoring. Microdialysis allowed distinguishing between survivors and non-survivors 8min after termination of CPR. Cerebral glutamate showed a trend toward higher levels in non-survivors during CPR. We established a new rodent model for research in hypoxic ischemic encephalopathy. This setting allows to investigate the impact of resuscitation methods on cerebral and peripheral metabolism simultaneously. The present model may be used to evaluate different resuscitation strategies in order to optimize brain survival in future studies.

Reward related neurotransmitter changes in a model of depression: An in vivo microdialysis study

Objectives: The self-medication hypothesis assumes that symptoms related to potential monoaminergic deficits in depression may be relieved by drug abuse. The aim of this study was to elucidate the neurotransmitter changes in a rat model of depression by measuring their levels in the nucleus accumbens shell, which is typically involved in the drug of abuse acquisition mechanism. Methods: Depression was modelled by the olfactory bulbectomy (OBX) in Wistar male rats. In vivo microdialysis was performed, starting from the baseline and following after a single methamphetamine injection and behaviour was monitored. The determination of neurotransmitters and their metabolites was performed by high-performance liquid chromatography combined with mass spectrometry. Results: OBX animals had lower basal levels of dopamine and serotonin and their metabolites. However, γ-aminobutyric acid (GABA) and glutamate levels were increased. The methamphetamine injection induced stronger dopamine and serotonin release in the OBX rats and lower release of glutamate in comparison with sham-operated rats; GABA levels did not differ significantly. Conclusions: This study provides an evidence of mesolimbic neurotransmitter changes in the rat model of depression which may elucidate mechanisms underlying intravenous self-administration studies in which OBX rats were demonstrated to have higher drug intake in comparison to intact controls.

Regional brain extracellular markers of cerebral ischaemia after aneurysmal subarachnoid haemorrhage: a combined cerebral microdialysis and perfusion CT study

Detection of cerebral ischemia after aneurysmal subarachnoid hemorrhage (SAH) remains challenging, particularly in comatose patients. The aim of this study was to examine the value of cerebral microdialysis (CMD) to predict cerebral ischemia, diagnosed by perfusion CT (PCT) imaging.

Inflammation-related alterations in corticostriatal connectivity in depression: Reversal with levodopa?

Neuroimaging studies indicate that inflammatory cytokines decrease activation of the ventral striatum in association with increased symptoms of anhedonia. Our in vivo microdialysis studies in non-human primates suggest that these effects are mediated by decreased striatal dopamine synthesis and release, which can be reversed by administration of the dopamine precursor, levodopa (L-DOPA). Herein, we examined inflammation-related alterations in functional connectivity with the ventral striatum in medically healthy, medication free patients with major depression (n = 48) in relation to symptoms of anhedonia. Pilot data was also collected from a subset of patients with high inflammation (as defined by plasma C-reactive protein [CRP]) who were administered L-DOPA before and after resting state fMRI. Increased inflammation (as determined by plasma CRP) was associated with decreased functional connectivity between the ventral striatum and ventromedial prefrontal cortex (vmPFC) in patients with major depression. These changes in functional connectivity were also associated with increased anhedonia (r = −0.48, df = 46, p = 0.001). Furthermore, preliminary data indicate that L-DOPA can reverse inflammation-associated decreases in corticostriatal connectivity. These data support the hypothesis that inflammation effects on dopamine synthesis and release may play a role in corticostriatal dysfunction that underlies symptoms of anhedonia in major depression. Ongoing work with L-DOPA will provide a foundation for future studies investigating therapeutic strategies that facilitate availability of dopamine precursors to improve symptoms of anhedonia in patients with major depression and increased inflammation.

Retrograde Cerebral Perfusion Results in Better Perfusion to the Striatum Than the Cerebral Cortex During Deep Hypothermic Circulatory Arrest: A Microdialysis Study.

It remains controversial whether contemporary cerebral perfusion techniques, utilized during deep hypothermic circulatory arrest (DHCA), establish adequate perfusion to deep structures in the brain. This study aimed to investigate whether selective antegrade cerebral perfusion (SACP) or retrograde cerebral perfusion (RCP) can provide perfusion equally to various anatomical positions in the brain using metabolic evidence obtained from microdialysis. Eighteen piglets were randomly assigned to 40 min of circulatory arrest (CA) at 18°C without cerebral perfusion (DHCA group, n = 6) or with SACP (SACP group, n = 6) or RCP (RCP group, n = 6). Microdialysis parameters (glucose, lactate, pyruvate, and glutamate) were measured every 30 min in cortex and striatum. After 3 h of reperfusion, brain tissue was harvested for Western blot measurement of α-spectrin. After 40 min of CA, the DHCA group showed marked elevations of lactate and glycerol and a reduction in glucose in the microdialysis perfusate (all P < 0.05). The changes in glucose, lactate, and glycerol in the perfusate and α-spectrin expression in brain tissue were similar between cortex and striatum in the SACP group (all P > 0.05). In the RCP group, the cortex exhibited lower glucose, higher lactate, and higher glycerol in the perfusate and higher α-spectrin expression in brain tissue compared with the striatum (all P < 0.05). Glutamate showed no difference between cortex and striatum in all groups (all P > 0.05). In summary, SACP provided uniform and continuous cerebral perfusion to most anatomical sites in the brain, whereas RCP resulted in less sufficient perfusion to the cortex but better perfusion to the striatum.

Dopamine and glutamate release in the anterior default system during rest: A monkey microdialysis study

Human neuroimaging studies have demonstrated the presence of a default system in the brain, which shows a default mode of brain activity, i.e., greater activity during rest than during an attention-demanding cognitive task. Our previous study on monkeys has revealed a default mode of brain activity in medial cortical areas. We have observed an increase in dopamine (DA) release during a working memory (WM) task compared with that during rest in the monkey lateral prefrontal cortex (LPFC). However, no previous study has examined DA release related to the default mode of brain activity. We used a microdialysis technique to investigate changes in DA release in the medial prefrontal cortex (MPFC), which constitutes the anterior default system, during the WM task and rest. Because DA and glutamate (Glu) release in the LPFC is interrelated, we also examined Glu release in the MPFC. We observed a significant increase in DA release, but no significant change in Glu release during rest compared with that during the WM task. We also observed an inhibitory relationship between the two transmitters in the MPFC. Considering that human default brain activity is related to internal thought processes and increased DA release in the LPFC plays an important role in executive control, increase in DA release during rest in the monkey anterior default system may be related to some form of internal thought process.

The role of serotonergic mechanism in the rat prefrontal cortex for controlling the micturition reflex: An in vivo microdialysis study.

To investigate the role of the PFC in the micturition reflex using an in vivo microdialysis study in rats. Adult female Sprague-Dawley rats were used and microdyalysis in the PFC and cystometrography (CMG) were performed under consciousness and free movement in the present study. Experiment 1: Samples including extracellular neurotransmitters were collected by microdyalysis and analyzed by high performance liquid chromatography. At the same time, CMG were performed to measure intercontraction interval (ICI) and maximum voiding pressure (MVP). Experiment 2: SSRI (citalopram, 1 µM) was administered into the PFC, and microdyalysis and cystometrography (CMG) were performed simultaneously. Experiment 3: Following SSRI administration, 5-HT1A agonist (8-OH-DPAT, 300 µM), which has the effect of decreasing the level of serotonin (5-HT) in the PFC, was administered into the PFC, and microdyalysis and CMG were performed simultaneously. Experiment 1: Extracellular level of 5-HT in the PFC significantly increased during micturition reflex (P < 0.05), whereas levels of glutamate or dopamine were not significantly changed. Experiment 2: Local administration of SSRI in the PFC increased the 5-HT level up to approximate 600% of the basal level. It also significantly increased ICI (P < 0.05), whereas no significant change was found in MVP. Experiment 3: The extracellular level of 5-HT gradually decreased after local administration of 5-HT1A agonist, thereby ICI significantly decreased (P < 0.05). The results of the present study suggest that the PFC has a suppressive effect on neural control of the micturition reflex via serotonin. Neurourol. Urodynam. 35:902-907, 2016. © 2015 Wiley Periodicals, Inc.

Histamine H3 receptor antagonist decreases cue-induced alcohol reinstatement in mice

We have earlier found that the histamine H3 receptor (H3R) antagonism diminishes motivational aspects of alcohol reinforcement in mice. Here we studied the role of H3Rs in cue-induced reinstatement of alcohol seeking in C57BL/6J mice using two different H3R antagonists. Systemic administration of H3R antagonists attenuated cue-induced alcohol seeking suggesting that H3R antagonists may reduce alcohol craving. To understand how alcohol affects dopamine and histamine release, a microdialysis study was performed on C57BL/6J mice and the levels of histamine, dopamine and dopamine metabolites were measured in the nucleus accumbens. Alcohol administration was combined with an H3R antagonist pretreatment to reveal whether modulation of H3R affects the effects of alcohol on neurotransmitter release. Alcohol significantly increased the release of dopamine in the nucleus accumbens but did not affect histamine release. Pretreatment with H3R antagonist ciproxifan did not modify the effect of alcohol on dopamine release. However, histamine release was markedly increased with ciproxifan. In conclusion, our findings demonstrate that H3R antagonism attenuates cue-induced reinstatement of alcohol seeking in mice. Alcohol alone does not affect histamine release in the nucleus accumbens but H3R antagonist instead increases histamine release significantly suggesting that the mechanism by which H3R antagonist inhibits alcohol seeking found in the present study and the decreased alcohol reinforcement, reward and consumption found earlier might include alterations in the histaminergic neurotransmission in the nucleus accumbens. These findings imply that selective antagonists of H3Rs could be a therapeutic strategy to prevent relapse and possibly diminish craving to alcohol use.This article is part of the Special Issue entitled ‘Histamine Receptors’.

Glutamatergic regulation of brain histamine neurons: In vivo microdialysis and electrophysiology studies in the rat

The interactions between the glutamatergic and the histaminergic systems in the brain are not fully understood. Here we studied histamine release in the medial prefrontal cortex and the posterior hypothalamus-tuberomamillary nucleus (PH-TMN) using in vivo microdialysis and electrophysiological recordings of histaminergc neurons in the PH-TMN in vivo to further address the mechanistic details of these interactions. We demonstrated that histaminergic activity was regulated by group II metabotropic glutamate receptors (mGluR 2 and 3) using systemic dosing with mGluR 2/3 agonist and antagonists and an mGluR 2 positive allosteric modulator. These interactions likely occur via direct modulation of glutamate release in the PH-TMN. The importance of circadian rhythm for histamine release was also shown using microdialysis studies with mGluR 2/3 compounds under light and dark conditions. Based on histamine release studies with NMDA and ketamine, we propose the existence of two sub-populations of NMDA receptors where one subtype is located on histaminergic cell bodies in the PH-TMN and the second on GABA-ergic neurons projecting to the PH-TMN. These subpopulations could be distinguished based on function, notably opposing actions were seen on histamine release in the medial prefrontal cortex of the rat.In summary, this paper provides evidence that the histaminergic system is closely regulated by glutamate neurons in multiple ways. In addition, this interaction depends to a great extent on the activity state of the subject.

Dopamine in the nucleus accumbens core, but not shell, increases during signaled food reward and decreases during delayed extinction

Microdialysis studies in rat have generally shown that appetitive stimuli release dopamine (DA) in the nucleus accumbens (NAc) shell and core. Here we examined the release of DA in the NAc during delivery of reward (food) and during extinction of food reward in the freely moving animal by use of in vivo microdialysis and HPLC. Fifty-two male Wistar rats were trained to receive food reward associated with appearance of cue-lights in a Skinner-box during in vivo microdialysis. Different behavioral protocols were used to assess the effects of extinction on DA and its metabolites.Results Exp. 1: (a) During a 20-min period of cued reward delivery, DA increased significantly in the NAc core, but not shell subregion; (b) for the next 60min period half of the rats underwent immediate extinction (with the CS light presented during non-reward) and the other half did not undergo extinction to the cue lights (CS was not presented during non-reward). DA remained significantly increased in both groups, providing no evidence for a decrease in DA during extinction in either NAc core or shell regions. (c) In half of the animals of the group that was not subjected to extinction, the cue lights were turned on for 30min, thus, initiating extinction to cue CS at a 1h delay from the period of reward. In this group DA in the NAc core, but not shell, significantly decreased. Behavioral analysis showed that while grooming is an indicator of extinction-induced behavior, glances toward the cue-lights (sign tracking) are an index of resistance to extinction.Results Exp. 2: (a) As in Exp. 1, during a 30-min period of cued reward delivery, DA levels again increased significantly in the NAc core but not in the NAc shell. (b) When extinction (the absence of reward with the cue lights presented) was administered 24h after the last reward session, DA again significantly decreased in the NAc core, but not in the NAc shell.Conclusions: (a) These results confirm the importance of DA release in the NAc for reward-related states, with DA increasing in the core, but not shell subregion. (b) They provide first evidence that during the withholding of expected reward, DA decreases in the NAc core, but not shell region. (c) This decrease in DA appears only after a delay between delivery of reward and extinction likely due to it being masked by persisting DA release. We hypothesize the decrease in extinction-induced release of DA in the NAc core to be a marker for the despair/depression that is known to accompany the failure to obtain expected rewards/reinforcers.