Jouni Ihalainen

Age-related decrease in stimulated glutamate release and vesicular glutamate transporters in APP/PS1 transgenic and wild-type mice

We assessed baseline and KCl‐stimulated glutamate release by using microdialysis in freely moving young adult (7 months) and middle‐aged (17 months) transgenic mice carrying mutated human amyloid precursor protein and presenilin genes (APdE9 mice) and their wild‐type littermates. In addition, we assessed the age‐related development of amyloid pathology and spatial memory impaired in the water maze and changes in glutamate transporters. APdE9 mice showed gradual spatial memory impairment between 6 and 15 months of age. The stimulated glutamate release declined very robustly in 17‐month‐old APdE9 mice as compared to 7‐month‐old APdE9 mice. This age‐dependent decrease in stimulated glutamate release was also evident in wild‐type mice, although it was not as robust as in APdE9 mice. When compared to individual baselines, all aged wild‐type mice showed 25% or greater increase in glutamate release upon KCl stimulation, but none of the aged APdE9 mice. There was an age‐dependent decline in VGLUT1 levels, but not in the levels of VGLUT2, GLT‐1 or synaptophysin. Astrocyte activation as measured by glial acidic fibrillary protein was increased in middle‐aged APdE9 mice. Blunted pre‐synaptic glutamate response may contribute to memory deficit in middle‐aged APdE9 mice.

Cortical glutamate–dopamine interaction and ketamine-induced psychotic symptoms in man

RationaleThe noncompetitive glutamate N-methyl-d-aspartate receptor antagonist ketamine induces transient psychotic symptoms in man. Involvement of dopaminergic mechanisms in these effects has been suggested.ObjectivesThe purpose of this article is to study the effects of ketamine on extrastriatal dopamine receptor availability in healthy subjects and extracellular dopamine levels in rat cortex.Materials and methodsThe effect of computer-driven subanesthetic ketamine infusion on cortical dopamine release was studied in healthy male subjects using a controlled study design. Dopamine D2/D3 receptor availability was quantified using positron emission tomography (PET) and [11C]FLB 457. A conventional region of interest-based analysis and voxel-based analysis was applied to the PET data. The ketamine-induced cortical dopamine release in rats was studied using in vivo microdialysis.ResultsKetamine infusion reduced significantly the [11C]FLB 457 binding potential (BP) in the posterior cingulate/retrosplenial cortices, suggestive of increased dopamine release. This brain imaging finding was further supported by a microdialysis experiment in rats showing that ketamine increased the extracellular dopamine concentration by up to 200% in the retrosplenial cortex. Ketamine-induced psychotic symptoms were associated with changes in the [11C]FLB 457 BP in the dorsolateral prefrontal and anterior cingulate cortices.ConclusionsOur results suggest that cortical dopaminergic mechanisms have a role in the emergence of ketamine-induced psychosis-like symptoms in man. The glutamate–dopamine interaction in the posterior cingulate during ketamine infusion is well in line with the recent functional and structural imaging studies suggesting involvement of this cortical area in the development of schizophrenic psychosis.

In vivo regulation of dopamine and noradrenaline release by α2A-adrenoceptors in the mouse prefrontal cortex

The present study investigated the role of α2A‐adrenoceptor subtype in the regulation of noradrenaline and dopamine release in the medial prefrontal cortex. The effect of local introduction of the α2‐adrenoceptor agonist dexmedetomidine (10−9−10−8 m) on noradrenaline and dopamine release was investigated in α2A‐adrenoceptor knockout and control mice by using in vivo microdialysis. Furthermore, to reveal a possible distinction between regulation of baseline and peak release, we sampled the dialysate during both rest and handling‐induced mild stress. Baseline noradrenaline and dopamine concentrations did not differ between α2A‐adrenoceptor knockout and control mice. Dexmedetomidine decreased, in a concentration‐dependent manner, noradrenaline and dopamine levels in both genotypes. However, the effect of dexmedetomidine on noradrenaline release was attenuated in the α2A‐adrenoceptor knockout mice, whereas the effect on dopamine release did not differ between the genotypes. The first handling episode increased noradrenaline and dopamine levels to the same extent in both genotypes. However, in α2A‐adrenoceptor knockout mice the noradrenaline and dopamine levels remained elevated in the samples following the first handling whilst, in the control mice, transmitter levels returned to baseline levels. In control mice the handling‐induced peak noradrenaline and dopamine levels were lower after the administration of dexmedetomidine than during the first handling episode, but in α2A‐adrenoceptor knockout mice no drug effect on handling‐induced peak noradrenaline and dopamine levels was found. Our results suggest that the release of noradrenaline in the medial prefrontal cortex is mainly regulated via α2A‐adrenoceptors, whilst other α‐adrenoceptor subtypes play a significant role in the regulation of dopamine release.

In vivo regulation of dopamine and noradrenaline release by alpha2A-adrenoceptors in the mouse nucleus accumbens

The present study investigated the role of alpha2A‐adrenoceptor (α2A‐AR) subtype in the regulation of noradrenaline (NA) and dopamine (DA) release in the nucleus accumbens (NAc). The effect of locally infused and systemically injected α2‐AR agonist, dexmedetomidine (DMT), and α2‐AR antagonist, atipamezole, on NA and DA release was investigated in α2A‐AR knockout and control mice by using in vivo microdialysis. In addition, we compared the drug effects on DA and NA release in the NAc to their effect on locomotor activity. Baseline NA and DA concentrations did not differ between genotypes. Local infusion of DMT decreased, in a concentration‐dependent manner, NA, but not DA, levels in the control mice. However, systemic injection of DMT decreased both NA and DA levels in the control mice. In both cases DMT had no effects on transmitter release in α2A‐AR knockout mice. Our results suggest that α2‐ARs regulate the release of NA, but not DA, at the terminal level in the NAc. However, α2‐ARs regulate DA release in the NAc indirectly by their effect on DA neurones in the ventral tegmental area via an unknown mechanism. In both cases the regulation is mediated by α2A‐adrenoceptor subtype. Also the modulation of locomotor activity by α2‐AR agonist and antagonist seems to be mediated via α2A‐adrenoceptors.

Effects of NMDA-Receptor Antagonist Treatment on c-fos Expression in Rat Brain Areas Implicated in Schizophrenia

Abstract1. The noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonists produce behavioral responses that closely resemble both positive and negative symptoms of schizophrenia. These drugs also induce excitatory and neurotoxic effects in limbic cortical areas.2. We have here mapped the brain areas which show increased activity in response to noncompetitive NMDA-receptor antagonist administration concentrating especially to those brain areas that have been suggested to be relevant in the pathophysiology of schizophrenia.3. Rats were treated intraperitoneally with a NMDA-receptor antagonist MK801 and activation of brain areas was detected by monitoring the expression of c-fos mRNA by using in situ hybridization.4. MK801 induced c-fos mRNA expression of in the retrosplenial, entorhinal, and prefrontal cortices. Lower c-fos expression was observed in the layer IV of the parietal and frontal cortex. In the thalamus, c-fos mRNA expression was detected in the midline nuclei and in the reticular nucleus but not in the dorsomedial nucleus. In addition, c-fos mRNA was expressed in the anterior olfactory nucleus, the ventral tegmental area, and in cerebellar granule neurons.5. NMDA-receptor antagonist ketamine increased dopamine release in the parietal cortex, in the region where NMDA-receptor antagonist increased c-fos mRNA expression.6. Thus, the psychotropic NMDA-receptor antagonist induced c-fos mRNA expression in most, but not all, brain areas implicated in the pathophysiology of schizophrenia. The high spatial resolution of in situ hybridization may help to define regions of interest for human imaging studies.

Decreased reuptake of dopamine in the dorsal striatum in the absence of alpha-synuclein

The presynaptic protein alpha-synuclein (α-syn) plays a role in dopaminergic neurotransmission in the nigrostriatal dopaminergic system. Mutations in this protein have been linked to pathogenesis of Parkinsons disease. However, the details of regulation of dopamine homeostasis by α-syn and its molecular targets are generally unknown. We investigated the effect of α-syn deletion on striatal dopaminergic homeostasis. Two α-syn deficient mouse lines, one carrying a spontaneous deletion of α-syn locus and the other a transgenic α-syn knockout, were used in the study. Stimulated and basal extracellular dopamine levels were determined in the dorsal striatum by in vivo voltammetry and in vivo microdialysis, respectively. Dopamine transporter expression was studied by immunohistochemistry. Stimulated dopamine overflow and basal extracellular dopamine levels were higher in mice lacking α-syn with a concomitant decrease in dopamine transporter expression and reuptake in the dorsal striatum. We show that α-syn deletion produces significant adaptive changes in the striatal dopaminergic system via modulation of reuptake.

Effects of memantine and donepezil on cortical and hippocampal acetylcholine levels and object recognition memory in rats

This preclinical study investigated the ability of memantine (MEM) to stimulate brain acetylcholine (ACh) release, potentially acting synergistically with donepezil (DON, an acetylcholinesterase inhibitor). Acute systemic administration of either MEM or DON to anesthetized rats caused dose-dependent increases of ACh levels in neocortex and hippocampus, and the combination of MEM (5 mg/kg) and DON (0.5 mg/kg) produced significantly greater increases than either drug alone. To determine whether ACh release correlated with cognitive improvement, rats with partial fimbria-fornix (FF) lesions were treated with acute or chronic MEM or DON. Acute MEM treatment significantly elevated baseline hippocampal ACh release but did not significantly improve task performance on a delayed non-match-to-sample (DNMS) task, whereas chronic MEM treatment significantly improved DNMS performance but only marginally elevated baseline ACh levels. Acute or chronic treatment with DON (in the presence of neostigmine to allow ACh collection) did not significantly improve DNMS performance or alter ACh release. In order to investigate the effect of adding MEM to ongoing DON therapy, lesioned rats pretreated with DON for 3 weeks were given a single intraperitoneal dose of MEM. MEM significantly elevated baseline hippocampal ACh levels, but did not significantly improve DNMS task scores compared to chronic DON-treated animals. These data indicate that MEM, in addition to acting as an NMDA receptor antagonist, can also augment ACh release; however, in this preclinical model, increased ACh levels did not directly correlate with improved cognitive performance.

Amyloid-β and Tau Dynamics in Human Brain Interstitial Fluid in Patients with Suspected Normal Pressure Hydrocephalus

BACKGROUND Amyloid-β (Aβ1 - 42), total tau (T-tau), and phosphorylated tau (P-tau181) in the cerebrospinal fluid (CSF) are the most promising biomarkers of Alzheimers disease (AD). Still, little is known about the dynamics of these molecules in the living brain. In a transgenic mouse brain, soluble Aβ decreases with increasing age and advanced Aβ pathology as seen similarly in CSF. OBJECTIVE To assess the relationship between AD-related pathological changes in human brain tissue, ventricular and lumbar CSF, and brain interstitial fluid (ISF). METHODS Altogether 11 patients with suspected idiopathic normal pressure hydrocephalus underwent frontal cortical brain biopsy, 24-h intraventricular pressure monitoring, and a microdialysis procedure. AD-related biomarkers were analyzed from brain tissue, CSF, and ISF. RESULTS ISF T-tau levels decreased strongly within the first 12 h, then plateauing until the end of the experiment. Aβ1 - 42 and P-tau181 remained stable during the experiment (n = 3). T-tau and P-tau were higher in the ISF than in ventricular or lumbar CSF, while Aβ1 - 42 levels were within similar range in both CSF and ISF samples. ISF P-tau correlated with the ventricular CSF T-tau (r = 0.70, p = 0.017) and P-tau181 (r = 0.64, p = 0.034). Five patients with amyloid pathology in the brain biopsy tended to reveal lower ISF Aβ1 - 42 levels than those six without amyloid pathology. CONCLUSIONS This is the first study to report ISF Aβ and tau levels in the human brain without significant brain injury. The set-up used enables sampling from the brain ISF for at least 24 h without causing adverse effects due to the microdialysis procedure to follow the dynamics of the key molecules in AD pathogenesis in the living brain at various stages of the disease.

Methylphenidate Modifies Overflow and Presynaptic Compartmentalization of Dopamine via an α-Synuclein-Dependent Mechanism

Methylphenidate (MPD) modulates dopamine (DA) overflow in part by redistributing vesicle pools, a function shared by the presynaptic protein α-synuclein (α-syn). We suggest that α-syn modifies the effect of MPD on DA neurotransmission. The effect was studied in the dorsal striatum in wild-type mice and two mouse lines lacking α-syn by using in vivo voltammetry and microdialysis. MPD (1 mg/kg) attenuated evoked DA overflow only in mice lacking α-syn but produced a similar increase in the extracellular DA levels in all three lines. A kinetic analysis showed that MPD decreased DA release per stimulus pulse in α-syn-deficient mice but increased in wild-type mice. MPD blocked DA reuptake and produced a similar increase in the apparent affinity (Km) for DA reuptake in all three lines. Repeated-burst stimulation redistributes vesicular storage pools and facilitates DA overflow, and this form of facilitation is significantly enhanced in α-syn knockout mice. The DA reuptake inhibitor 1-[2-[bis(4-fluorophenyl)methoxy]ethyl]-4-(3-phenylpropyl)piperazine (GBR12909) (10 mg/kg) completely blocked the facilitation of DA overflow in all three lines, whereas MPD (1 mg/kg) selectively decreased it only in mice lacking α-syn. MPD (5 mg/kg) and GBR12909 (10 mg/kg) produced equipotent inhibition of DA reuptake (in terms of Km), indicating that reuptake inhibition does not explain the MPD selectivity. Our data indicate that MPD decreases DA release probability in the absence of α-syn and increases it in control animals, whereas the effect of MPD on DA reuptake is independent of α-syn. We suggest that this selectivity is based on α-syn-dependent compartmentalization of presynaptic DA.

Alpha2C-adrenoceptor mediated regulation of cortical EEG arousal

Alpha2-adrenergic drugs modulate cortical arousal and EEG. However, the role of individual alpha2-adrenoceptor (alpha(2)-AR) subtypes in these functions is not clear. We investigated the role of alpha(2C)-ARs in the modulation of baseline cortical EEG activity and EEG responses to the alpha(2)-AR selective agonist, dexmedetomidine (3-300 microg/kg, s.c.), and antagonist, atipamezole (3-1000 microg/kg, s.c.), by using alpha(2C)-AR knockout (KO) and wildtype (WT) mice. The overall amplitude (1-30 Hz) was not significantly altered in KO mice although the activity of theta band (4-8 Hz) was increased in these mice. The main finding was that dexmedetomidine (30-300 microg/kg) more effectively slowed and atipamezole (30-1000 microg/kg) less effectively increased cortical EEG arousal in KO mice compared to WT controls. Importantly, autoradiographical results showed no compensatory increase in other alpha(2)-AR subtypes in cortical, thalamic or other brain structures of KO mice. Furthermore, there were no differences between the genotypes in the levels of hippocampal choline acetyltransferase, monoamines or their metabolites. Altered baseline cortical EEG activity and EEG responses to alpha(2)-AR selective drugs in KO mice indicate that alpha(2C)-ARs are involved in regulation of cortical arousal. These results suggest that alpha(2C)-ARs may antagonize the sedative effect of alpha(2)-AR agonists mediated by activation of alpha(2A)-ARs.