Long-Lasting Enhancement of Corticostriatal Transmission by Taurine: Role of Dopamine and Acetylcholine

Histamine-induced plasticity and gene expression in corticostriatal pathway under hyperammonemia

Aims

Histamine H3 receptor (H3R) antagonists/inverse agonists increase vigilance. We studied brain histaminergic pathways under hyperammonemia and the transcriptome of receptors and their signaling cascades to provide a rationale for wake‐promoting therapies.

Methods

We analyzed histamine‐induced long‐lasting depression of corticostriatal synaptic transmission (LLDhist). As the expression of dopamine 1 receptors (D1R) is upregulated in LGS‐KO striatum where D1R‐H3R dimers may exist, we investigated actions of H3R and D1R agonists and antagonists. We analyzed transcription of selected genes in cortex and dorsal striatum in a mouse model of inborn hyperammonemia (liver‐specific glutamine synthetase knockout: LGS‐KO) and compared it with human hepatic encephalopathy.

Results

LGS‐KO mice showed significant reduction of the direct depression (DD) but not the long‐lasting depression (LLD) by histamine. Neither pharmacological activation nor inhibition of D1R significantly affected DDhist and LLDhist in WT striatum, while in LGS‐KO mice D1R activation suppressed LLDhist. Histaminergic signaling was found unchanged at the transcriptional level except for the H2R. A study of cAMP‐regulated genes indicated a significant reduction in the molecular signature of wakefulness in the diseased cortex.

Conclusions

Our findings provide a rationale for the development of aminergic wake‐promoting therapeutics in hyperammonemic disorders.

Behavioral effects of the combined use of alcohol and energy drinks on alcohol hangover in an experimental mice model

In last few years it has been a significant increase in the consumption of alcohol combined with energy drink. The aim of this work was to study the effect of this mixture in motor and affective behaviors during an alcohol hangover episode. Male Swiss mice received one of the following treatments: saline + sucrose; saline + energy drink; ethanol + sucrose; ethanol + energy drink. Ethanol dose was 3.8 g/kg BW (i.p.) and energy drink dose was 18 ml/kg BW (gavage) at ZT1 (8 am) (ZT: Zeitgeber time; ZT0: 7 am; lights on). The behavioral tests used were tight rope test to determine motor coordination; hanging wire test to study muscular strength; elevated plus maze and open field tests to evaluate anxiety like-behavior and locomotor activity. Tests were carried out at basal point that matched with lights onset and every 6 h up to 18 h after treatments. Hangover onset was established at ZT7 when blood alcohol concentration (BAC) was almost zero. Our results showed that the mixture of alcohol and energy drink altered significantly motor skills. Specifically, a significant decrease was observed in the performance of the animals in the tightrope and hanging wire tests in groups treated with the mixture of alcohol and energy drink. A significant impairment in the anxiety-like behavior was observed mainly at the beginning of alcohol hangover. These findings suggest that energy drink added to alcohol extends motor disabilities observed during an alcohol hangover episode in comparison with animals that received alcohol alone.

Effects of Electroacupuncture on Metabolic Changes in Motor Cortex and Striatum of 6-Hydroxydopamine-Induced Parkinsonian Rats

OBJECTIVE

To explore the possible underlying mechanism by investigating the effect of electroacupuncture (EA) treatment on the primary motor cortex and striatum in a unilateral 6-hydroxydopamine (6-OHDA) induced rat Parkinson's disease (PD) model.

METHODS

Male Sprague-Dawley rats were randomly divided into sham group (n=16), model group (n=14), and EA group (n=14). EA stimulation at Dazhui (GV 14) and Baihui (GV20) was applied to PD rats in the EA group for 4 weeks. Behavioral tests were conducted to evaluate the effectiveness of EA treatment. Metabolites were detected by 7.0 T proton nuclear magnetic resonance.

RESULTS

Following 4 weeks of EA treatment in PD model rats, the abnormal behavioral impairment induced by 6-OHDA was alleviated. In monitoring changes in metabolic activity, ratios of myoinositol/creatine (Cr) and N-acetyl aspartate (NAA)/Cr in the primary motor cortex were significantly lower at the injected side than the non-injected side in PD rats (P=0.024 and 0.020). The ratios of glutamate + glutamine (Glx)/Cr and NAA/Cr in the striatum were higher and lower, respectively, at the injected side than the non-injected side (P=0.046 and 0.008). EA treatment restored the balance of metabolic activity in the primary motor cortex and striatum. In addition, the taurine/Cr ratio and Glx/Cr ratio were elevated in the striatum of PD model rats compared to sham-lesioned rats (P=0.026 and 0.000). EA treatment alleviated the excessive glutamatergic transmission by down-regulating the striatal Glx/Cr ratio (P=0.001). The Glx/Cr ratio was negatively correlated with floor plane spontaneous locomotion in PD rats (P=0.027 and P=0.0007).

CONCLUSIONS

EA treatment is able to normalize the metabolic balance in the primary motor cortex and striatum of PD rats, which may contribute to its therapeutic effect on motor deficits. The striatal Glx/Cr ratio may serve as a potential indicator of PD and a therapeutic target of EA treatment.

Protective effect of taurine on the decreased biogenic amine neurotransmitter levels in the brain of mice exposed to arsenic

Arsenic (As) exposure has a toxic effect on the central nervous system, especially on learning and memory. Norepinephrine (NE), dopamine (DA), and serotonin (5-HT) play an important role in learning and memory function of the brain. In the present study, the protective effect of taurine on the disturbed biogenic amine neurotransmitter levels in the mouse brain induced by arsenic was examined. Sixty SPF mice were divided into three groups. The As exposure group was administered with 4 ppm As(2)O(3) through drinking water for 60 days. The protective group was treated with both 4 ppm As(2)O(3) and 150 mg/kg taurine. The control group was given drinking water alone. The levels of NE, DA, and 5-HT were determined by HPLC in the cerebrum and cerebellum of mice. Ultrastructure of synapses in brain tissue of mice was observed in these groups by transmission electron microscopy. The mRNA expressions of dopamine beta hydroxylase (DBH), tyrosine hydroxylase (TH), and tryptophan hydroxylase (TPH) as NE, DA, and 5-HT synzymes were also analyzed by real-time RT-PCR. The results showed that the concentrations of NE, DA, and 5-HT; the number of synaptic vesicles; and the expressions of TH, TPH, and DBH genes in the brains of mice exposed to As alone were significantly decreased. However, administration of taurine significantly alleviated the toxic effect on biochemicals detected in the experiment, compared with that in the brain of mice exposed to As alone. These results indicated that taurine was effective in counteracting the decreased biogenic amine neurotransmitter level and the mRNA expressions of their synzymes induced by arsenic.

Ethanol-induced modulation of synaptic output from the dorsolateral striatum in rat is regulated by cholinergic interneurons

The striatum is the largest input nucleus to the basal ganglia and associated with reward-based behavior. We assessed whether acute ethanol (EtOH) exposure could modulate synaptic efficacy in the dorsolateral striatum of juvenile Wistar rats. Since acute EtOH administration can both increase and decrease the probability of release of different neurotransmitters from synaptic terminals, we used field potential recordings to evaluate the net effect of EtOH on striatal output. We showed that 50mM EtOH but not 20, 80 or 100mM, depresses population spike (PS) amplitude in the dorsolateral striatum. This depression of synaptic output is insensitive to the N-methyl-d-aspartic acid (NMDA) receptor inhibitor DL-2-amino-5-phosphonopentanoic acid (AP-5, 50μM), but is blocked in slices treated with glycine receptor antagonists (strychnine, 1μM; PMBA, 50μM), nicotinic acetylcholine receptor antagonists (mecamylamine, 10μM; methyllycaconitine citrate (MLA), 40nM), or GABA(A) receptor inhibitors (picrotoxin, 100μM; bicuculline, 2μM, 20μM). A long-term facilitation of synaptic output, which is more pronounced in slices from adult Wistar rats, is detected following EtOH washout (50, 80, 100mM). This long-term enhancement of PS amplitude is regulated by cholinergic interneurons and completely blocked by mecamylamine, MLA or the non-selective muscarinic antagonist scopolamine (10μM). Administration of 100mM EtOH significantly depresses PS amplitude in scopolamine-treated slices, suggesting that EtOH exerts dual actions on striatal output that are initiated instantly upon drug wash-on. In conclusion, EtOH modulates striatal microcircuitry and neurotransmission in a way that could be of importance for understanding the intoxicating properties as well as the acute reward sensation of EtOH.

Taurine interaction with neurotransmitter receptors in the CNS: an update

Taurine appears to have multiple functions in the brain participating both in volume regulation and neurotransmission. In the latter context it may exert its actions by serving as an agonist at receptors of the GABAergic and glycinergic neurotransmitter systems. Its interaction with GABAA and GABAB receptors as well as with glycine receptors is reviewed and the physiological relevance of such interactions is evaluated. The question as to whether local extracellular concentrations of taurine are likely to reach the threshold level for the pertinent receptor populations cannot presently be answered satisfactorily. Hence more sophisticated analytical methods are warranted in order to obtain a definite answer to this important question.