Ceftriaxone regulates glutamate production and vesicular assembly in presynaptic terminals through GLT-1 in APP/PS1 mice.

Perturbations in the glutamate-glutamine cycle and glutamate release from presynaptic terminals have been involved in the development of cognitive deficits in Alzheimer's disease (AD) patients and mouse models. Glutamate transporter-1 (GLT-1) removes glutamate from the synaptic cleft and transports it into astrocytes, where it is used as substrate for the glutamate-glutamine cycle. Ceftriaxone has been reported to improve cognitive deficits in AD mice by increasing GLT-1 expression, glutamate transformation to glutamine, and glutamine efflux from astrocytes. However, the impact of ceftriaxone on glutamine metabolism in neurons is unknown. The present study aimed to investigate whether ceftriaxone regulated the production and vesicular assembly of glutamate in the presynaptic terminals of neurons and to determine GLT-1 involvement in this process. We used the amyloid precursor protein (APP)/presenilin-1 (PS1) AD mouse model and GLT-1 knockdown APP/PS1 (GLT-1+/-/APP/PS1) mice. The expression levels of sodium-coupled neutral amino-acid transporter 1 (SNAT1) and vesicular glutamate transporters 1 and 2 (VGLUT1/2) were analyzed by immunofluorescence and immunohistochemistry staining as well as by Western blotting. Glutaminase activity was assayed by fluorometry. Ceftriaxone treatment significantly increased SNAT1 expression and glutaminase activity in neurons in APP/PS1 mice. Similarly, VGLUT1/2 levels were increased in the presynaptic terminals of APP/PS1 mice treated with ceftriaxone. The deletion of one GLT-1 allele in APP/PS1 mice prevented the ceftriaxone-induced upregulation of SNAT1 and VGLUT1/2 expression, indicating that GLT-1 played an important role in ceftriaxone effect. Based on the role of SNAT1, glutaminase, and VGLUT1/2 in the glutamate-glutamine cycle in neurons, the present results suggested that ceftriaxone improved the production and vesicular assembly of glutamate as a neurotransmitter in presynaptic terminals by acting on GLT-1 in APP/PS1 mice.

Methamphetamine promotes habitual action and alters the density of striatal glutamate receptor and vesicular proteins in dorsal striatum.

Goal-directed actions are controlled by the value of the consequences they produce and so increase when what they produce is valuable and decrease when it is not. With continued invariant practice, however, goal-directed actions can become habits, controlled not by their consequences but by antecedent, reward-related states and stimuli. Here, we show that pre-exposure to methamphetamine (METH) caused abnormally rapid development of habitual control. Furthermore, these drug-induced habits differed strikingly from conventional habits; we found that they were insensitive both to changes in reward value and to the effects of negative feedback. In addition to these behavioral changes, METH exposure produced bidirectional changes to synaptic proteins in the dorsal striatum. In the dorsomedial striatum, a structure critical for goal-directed action, METH exposure was associated with a reduction in glutamate receptor and glutamate vesicular proteins, whereas in the dorsolateral striatum, a region that has previously been implicated in habit learning, there was an increase in these proteins. Together, these results indicate that METH exposure promotes habitual control of action that appears to be the result of bidirectional changes in glutamatergic transmission in the circuits underlying goal-directed and habit-based learning.

Ethanol affects limbic and striatal presynaptic glutamatergic and DNA methylation gene expression in outbred rats exposed to early-life stress.

Alcohol use disorder is the outcome of both genetic and environmental influences and their interaction via epigenetic mechanisms. The neurotransmitter glutamate is an important regulator of reward circuits and implicated in adaptive changes induced by ethanol intake. The present study aimed at investigating corticolimbic and corticostriatal genetic signatures focusing on the glutamatergic phenotype in relation to early-life stress (ELS) and consequent adult ethanol consumption. A rodent maternal separation model was employed to mimic ELS, and a free-choice paradigm was used to assess ethanol intake in adulthood. Gene expression levels of the Vesicular Glutamate Transporters (Vglut) 1, 2 and 3, as well as two key regulators of DNA methylation, DNA (cytosine-5)-methyltransferase 1 (Dnmt1) and methyl-CpG-binding protein 2 (Mecp2), were analyzed. Brain regions of interest were the ventral tegmental area (VTA), nucleus accumbens (Acb), medial prefrontal cortex (mPFC) and dorsal striatum (dStr), all involved in mediating aspects of ethanol reward. Region-specific Vglut, Dnmt1 and Mecp2 expression patterns were observed. ELS was associated with down-regulated expression of Vglut2 in the VTA and mPFC. Rats exposed to ELS were more sensitive to ethanol-induced changes in Vglut expression in the VTA, Acb, and dStr and in Dnmt1 and Mecp2 expression in the striatal regions. These findings suggest long-term glutamatergic and DNA methylation neuroadaptations as a consequence of ELS, and show an association between voluntary drinking in non-preferring, non-dependent, rodents and different Vglut, Dnmt1 and Mecp2 expression depending on early-life history.

Bacopa monnieri (Brahmi) Enhanced Cognitive Function and Prevented Cognitive Impairment by Increasing VGLUT2 Immunodensity in Prefrontal Cortex of Sub-Chronic Phencyclidine Rat Model of Schizophrenia.

BACKGROUND: Glutamatergic hypofunction is affected in schizophrenia. The decrement ofpresynaptic glutamatergic marker remarkably vesicular glutamate transporter type 1 (VGLUT1) indicates the deficit ofglutamatergic and cognitive function in schizophrenic brain. However there have been afew studies in VGLUT2. Brahmi, a traditional herbal medicine, might be a new frontier of cognitive deficit treatment and prevention in schizophrenia by changing cerebral VGLUT2 density. OBJECTIVE: To study cognitive enhancement- and neuroprotective-effects of Brahmi on novel object recognition task and cerebral VGLUT2 immunodensity in sub-chronic phencyclidine (PCP) rat model of schizophrenia. MATERIAL AND METHOD: Cognitive enhancement effect study; rats were assigned to three groups; Group-1: Control, Group-2: PCP administration and Group-3: PCP + Brahmi. Neuroprotective effect study; rats were assigned to three groups; Group-1: Control, Group-2: PCP administration and Group-3: Brahmi + PCP Discrimination ratio (DR) representing cognitive ability was obtained from novel object recognition task. VGLUT2 immunodensity was measured in prefrontal cortex, striatum, cornu ammonis fields 1 (CA1) and 2/3 (CA2/3) of hippocampus using immunohistochemistry. RESULTS: DR was significantly reduced in PCP group compared with control. This occurred alongside VGLUT2 reduction in prefrontal cortex, but not in striatum, CA1 or CA2/3. Both PCP + Brahmi and Brahmi + PCP groups showed an increased DR score up to normal, which occurred alongside a significantly increased VGLUT2 immunodensity in the prefrontal cortex, compared with PCP group. CONCLUSION: The decrement of VGLUT2 density in prefrontal cortex resulted in cognitive deficit in rats receiving PCP. Interestingly, receiving Brahmi after PCP administration can restore this cognitive deficit by increasing VGLUT2 density in prefrontal cortex. This investigation is defined as Brahmi's cognitive enhancement effect. Additionally, receiving Brahmi before PCP administration can also prevent cognitive impairment by elevating VGLUT2 density in prefrontal cortex. This observation indicates neuroprotective effect of Brahmi. Therefore, Brahmi could be a new frontier of restoration and prevention of cognitive deficit in schizophrenia.

Ethanol and nicotine interaction within the posterior ventral tegmental area in male and female alcohol-preferring rats: evidence of synergy and differential gene activation in the nucleus accumbens shell.

RATIONALE: Ethanol and nicotine are frequently co-abused. The biological basis for the high co-morbidity rate is not known. Alcohol-preferring (P) rats will self-administer EtOH or nicotine directly into the posterior ventral tegmental area (pVTA). OBJECTIVE: The current experiments examined whether sub-threshold concentrations of EtOH and nicotine would support the development of self-administration behaviors if the drugs were combined. METHODS: Rats were implanted with a guide cannula aimed at the pVTA. Rats were randomly assigned to groups that self-administered sub-threshold concentrations of EtOH (50 mg%) or nicotine (1 µM) or combinations of ethanol (25 or 50 mg%) and nicotine (0.5 or 1.0 µM). Alterations in gene expression downstream projections areas (nucleus accumbens shell, AcbSh) were assessed following a single, acute exposure to EtOH (50 mg%), nicotine (1 µM), or ethanol and nicotine (50 mg% + 1 µM) directly into the pVTA. RESULTS: The results indicated that P rats would co-administer EtOH and nicotine directly into the pVTA at concentrations that did not support individual self-administration. EtOH and nicotine directly administered into the pVTA resulted in alterations in gene expression in the AcbSh (50.8-fold increase in brain-derived neurotrophic factor (BDNF), 2.4-fold decrease in glial cell line-derived neurotrophic factor (GDNF), 10.3-fold increase in vesicular glutamate transporter 1 (Vglut1)) that were not observed following microinjections of equivalent concentrations/doses of ethanol or nicotine. CONCLUSION: The data indicate that ethanol and nicotine act synergistically to produce reinforcement and alter gene expression within the mesolimbic dopamine system. The high rate of co-morbidity of alcoholism and nicotine dependence could be the result of the interactions of EtOH and nicotine within the mesolimbic dopamine system.

Down-regulation of BK channel expression in the pilocarpine model of temporal lobe epilepsy.

In the hippocampus, BK channels are preferentially localized in presynaptic glutamatergic terminals including mossy fibers where they are thought to play an important role regulating excessive glutamate release during hyperactive states. Large conductance calcium-activated potassium channels (BK, MaxiK, Slo) have recently been implicated in the pathogenesis of genetic epilepsy. However, the role of BK channels in acquired mesial temporal lobe epilepsy (MTLE) remains unknown. Here we used immunohistochemistry, laser scanning confocal microscopy (LSCM), Western immunoblotting and RT-PCR to investigate the expression pattern of the alpha-pore-forming subunit of BK channels in the hippocampus and cortex of chronically epileptic rats obtained by the pilocarpine model of MTLE. All epileptic rats experiencing recurrent spontaneous seizures exhibited a significant down-regulation of BK channel immunostaining in the mossy fibers at the hilus and stratum lucidum of the CA3 area. Quantitative analysis of immunofluorescence signals by LSCM revealed a significant 47% reduction in BK channel immunofluorescent signals in epileptic rats when compared to age-matched non-epileptic control rats. These data correlate with a similar reduction in BK channel protein levels and transcripts in the cortex and hippocampus. Our data indicate a seizure-related down-regulation of BK channels in chronically epileptic rats. Further functional assays are necessary to determine whether altered BK channel expression is an acquired channelopathy or a compensatory mechanism affecting the network excitability in MTLE. Moreover, seizure-mediated BK down-regulation may disturb neuronal excitability and presynaptic control at glutamatergic terminals triggering exaggerated glutamate release and seizures.

Anti-glutamatergic effect of riluzole: comparison with valproic acid.

Riluzole, an anti-amyotrophic lateral sclerosis drug, known to decrease presynaptic glutamate release, is viewed as a candidate supplementary medication for epilepsy. In the present study, we compared the effects of riluzole and valproate (VPA) in the pilocarpine-induced limbic seizure model and in the gamma-hydroxybutyrate lactone (GBL)-induced absence seizure model. We applied immunohistochemical study for vesicular transporter 1 (VGLUT1) and extracellular recording in the rat dentate gyrus of both pilocarpine- and GBL-induced seizure models to measure effects of riluzole and VPA. Both VPA and riluzole treatments reduced VGLUT1 immunoreactivity. Riluzole treatment completely inhibited pre-ictal spikes and spike-wave discharges in the pilocarpine- and GBL-induced epilepsy models, whereas VPA partially inhibited these phenomena. In both seizure models, the anti-epileptic effects of VPA and riluzole are basically related to anti-glutamatergic (reducing field excitatory postsynaptic potential slope and excitability ratio), not GABAergic (paired-pulse inhibition) effect. Riluzole was more effective at reducing seizure activity in both epilepsy models than VPA. These results suggest that riluzole is a potential antiepileptic drug with activity against limbic seizure and absence seizure.