Regulation of gene expression by neurotransmitters in the central nervous system

Transcranial direct current stimulation of the prefrontal cortex improves depression-like behaviors in rats with Parkinson's disease

Depression associated with Parkinson's disease (PD) seriously affects patients, and there is a lack of effective treatments. Transcranial direct current stimulation (tDCS) is increasingly used as a new non-invasive neuromodulation technique in the treatment of neuropsychiatric diseases. However, there is a paucity of research on tDCS for PD-related depression. Our study used PD model rats established with unilateral destruction of the medial forebrain bundle (MFB) to observe the modulatory effects of tDCS acting on the mPFC on depression-like behaviors. We found that tDCS acting on the mPFC improved depression-like behaviors in PD model rats by increasing sucrose intake in sucrose preference test (n = 7-10 rats/group) and shortening immobility time in forced swimming test (n = 7-8 rats/group). Meanwhile, tDCS decreased the expression of c-Fos protein (n = 8-11 rats/group) and the excitation of glutamatergic neurons (n = 6-8 rats/group) in the PrL and LHb of PD model rats. Western blots showed that tDCS decreased the overexpression of serine 845 phosphorylation site of AMPA receptor GluR1 (p-GluR1-S845) in the PrL and LHb of PD model rats (n = 8-11 rats/group), and the overexpression of p-GluR1-S831 in the LHb (n = 8-11 rats/group). The results of this study show that tDCS acting on the mPFC helps to improve PD-related depression, which involves the modulation of excitability and AMPA receptor phosphorylation on the PrL and LHb neurons.

The antidepressant-like effect of tDCS in mice: A behavioral and neurobiological characterization

BACKGROUND

Transcranial direct current stimulation (tDCS) is a non-invasive method increasingly popular for the treatment of several brain disorders, such as major depression. Despite great enthusiasm and promising results, some studies report discrepant findings and no consensus exists for the clinical use of tDCS.

OBJECTIVE

The present study aims to (i) determine the most effective stimulation parameters to optimize antidepressant-like effect of tDCS in the forced-swim test in mice and (ii) identify brain regions recruited by tDCS and possibly involved in its behavioral effect using Fos immunohistochemistry.

RESULTS

We reported that tDCS induced long-lasting antidepressant-like effect, which varied as a function of stimulation settings including number, duration, intensity and polarity of stimulation. Interestingly, the present study also demonstrated that tDCS reduced depressive-like behaviors induced by chronic corticosterone exposure. Furthermore, behavioral outcomes induced by a single stimulation were associated with neuronal activation in the prefrontal cortex, dorsal hippocampus, ventral tegmental area and nucleus accumbens, whereas no overexpression of c-fos was associated with 10 stimulations.

CONCLUSION

The strongest behavioral response was observed with an anodal stimulation of 200 μA during 20min. The repetition of this stimulation was necessary to induce long-lasting behavioral effects that are probably associated with plastic changes in the neuronal response.

Ropinirole regulates emotionality and neuronal activity markers in the limbic forebrain

Restless legs syndrome (RLS) and Parkinson's disease (PD) are movement disorders usually accompanied by emotional and cognitive deficits. Although D3/D2 receptor agonists are effective against motor and non-motor deficits in RLS and PD, the exact behavioral and neurochemical effects of these drugs are not clearly defined. This study aimed to evaluate the effects of acute ropinirole (0, 0.1, 1 or 10 mg/kg, i.p.), a preferential D3/D2 receptor agonist, on intracranial self-stimulation (ICSS), spontaneous motor activity, anxiety- and depression-like behaviors, spatial reference and working memory in rats as well as on certain markers of neuronal activity, i.e. induction of immediate early genes, such as c-fos and arc, and crucial phosphorylations on GluA1 subunit of α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors and NA1, NA2A and NA2B subunits of N-methyl-D-aspartate (NMDA) receptors. Ropinirole decreased ICSS thresholds and induced anxiolytic- and antidepressive-like effects without affecting motor activity or spatial memory. The effects on emotionality were associated with a decrease in p-Ser897-NA1 and an increase in p-Tyr1472-NA2B in the ventral striatum as well as an increased induction of c-fos messenger RNA (mRNA) in the prefrontal cortex (PFC) and decreased expression of arc mRNA in the striatum and the shell of the nucleus accumbens. Our data indicate that ropinirole significantly affects emotionality at doses (1-10 mg/kg, i.p.) that exert no robust effects on locomotion or cognition. The data reinforce the use of D3/D2 receptor agonists in the treatment of RLS and PD patients characterized by emotional deficits and suggest that altered NMDA-mediated neurotransmission in the limbic forebrain may underlie some of ropinirole's therapeutic actions.

Canine distemper virus infection of primary hippocampal cells induces increase in extracellular glutamate and neurodegeneration

The canine distemper virus (CDV) belongs to the Morbillivirus genus which includes important human pathogens like the closely related measles virus. CDV infection can reach the nervous system where it causes serious malfunctions. Although this pathology is well described, the molecular events in brain infection are still poorly understood. Here we studied infection in vitro by CDV using a model of dissociated cell cultures from newborn rat hippocampus. We used a recombinant CDV closely related to the neurovirulent A75/17 which also expresses the enhanced green fluorescent protein. We found that infected neurons and astrocytes could be clearly detected, and that infection spreads only slowly to neighboring cells. Interestingly, this infection causes a massive cell death of neurons, which includes also non-infected neurons. Antagonists of NMDA-type or alpha-amino-3-hydroxy-5-methylisoxazole-4-propinate (AMPA)-type glutamate receptors could slow down this neuron loss, indicating an involvement of the glutamatergic system in the induction of cell death in infected and non-infected cells. Finally, we show that, following CDV infection, there is a steady increase in extracellular glutamate in infected cultures. These results indicate that CDV infection induces excitotoxic insults on neurons via glutamatergic signaling.

Spatio-temporal expression of immediate early genes in the central nervous system of SJL/J mice

Gene products of immediate early genes (IEGs) interact with specific binding sites in promoter regions of inducible and constitutively expressed genes. Thereby, they control transcription of down-stream targets, like pro- and anti-apoptotic genes and matrix-metalloproteinases (MMPs), known to play an important role in development, plasticity, response to injury and repair of the central nervous system (CNS). A real-time quantitative RT-PCR and immunohistochemical investigation was performed to study mRNA expression levels and protein distribution patterns of IEGs in cerebrum, cerebellum, and spinal cord of SJL/J mice between postnatal weeks 1 and 40. A down-regulation of c-jun, NF-kappaB1, Max, Ets-1, and p53 mRNA, and an up-regulation of c-fos mRNA was noticed. Down-regulations of Ets-1 and p53 were most prominent between week 1 and 3. The prominent role in CNS development for c-jun, Ets-1 and Max was supported by immunohistochemistry. One-week-old mice were strongly positive for all three proteins in cerebral cortex, medulla oblongata, and gray matter of the spinal cord. A high staining intensity was detected in the developing granule cell layer of the cerebellum for c-jun and Ets-1, and in the Purkinje cell layer of the cerebellum for Max. In addition to the general down-regulation of most mRNAs, minor up-regulations of all IEG proteins could be detected in restricted parts of the CNS indicating regional variations and differential expression and translation during development. Apoptosis was demonstrated using immunohistochemistry for active caspase-3. The expression patterns of IEGs might represent the key to understand the balance of proteolytic activities by MMPs, myelination, and the induction of apoptosis during the development of the CNS.

The effects of RB101, a mixed inhibitor of enkephalin-catabolizing enzymes, on carrageenin-induced spinal c-Fos expression are completely blocked by beta-funaltrexamine, a selective mu-opioid receptor antagonist

We have demonstrated that pre-administered RB101 (40 mg/kg, i.v.), a mixed inhibitor of enkephalin-catabolizing enzymes, decreased spinal c-Fos expression induced 1 h and 30 min after intraplantar (i.pl.) carrageenin (41% reduction, p<0.01). These effects were completely blocked by pre-administered beta-funaltrexamine (10 mg/kg, i.v., 24 h prior to stimulation), a selective long-lasting mu-opioid receptor antagonist. In conclusion, these results clearly demonstrate that the effects of endogenous enkephalins on noxiously evoked spinal c-Fos expression are essentially mediated via mu-opioid receptors.

Effects of NMDA receptor antagonists on morphine tolerance: a c-Fos study in the lumbar spinal cord of the rat

This study investigated the contribution of NMDA receptors to the development of tolerance to the antinociceptive properties of morphine at the level of the spinal cord dorsal horn. The expression of c-Fos protein following intraplantar (i.pl.) injection of carrageenin (6 mg/150 microl of saline) was used. In naive rats, acute intravenous (i.v.) administration of morphine (3 mg/kg) decreased the total number per section of Fos-Like-Immunoreactive (Fos-LI) neurons by 51%, observed at 2 h after injection of carrageenin. In tolerant rats, acute morphine did not significantly modify the total number of Fos-like immunoreactive neurons/section. In rats receiving chronic morphine and chronic injections of the non-competitive ((+)-MK 801 maleate: (5R,10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,1 0-imine) or the competitive (LY 235959: [3S-(3alpha,4a alpha,6beta,8a alpha)]-Decahydro-6-(phosphonomethyl)-3-isoquinolinecarboxylic+ ++ acid) NMDA receptor antagonists, only partial tolerance to the acute effects of morphine were observed (decrease of 42% and 38%, respectively). Administration of an antagonist at the strychnine-insensitive glycine site of the NMDA receptor ((+)-HA-966: R(+)-3-Amino-1-hydroxypyrrolidin-2-one) did not affect the development of morphine tolerance. These findings suggest that compounds attenuating the actions of the NMDA receptor via blockade of the glycine modulatory site may be substantially different from those acting at the ion channel of the NMDA receptor complex. This in vivo experiment in freely moving animals demonstrates for the first time an attenuation of tolerance at the cellular level.

PET supports the hypothesized existence of a male sexual brain algorithm that may respond to treatment combining psychotherapy with virtual reality

Could a brain circuit exist, verifiable using positron emission tomography (PET), that links coitus and its dysfunctions, such as impotence? Could re-establishing normal sexual functioning be linked with the normalization of some sort of altered brain metabolism utilizing a therapeutic project that uses psychodynamic psychotherapy integrating virtual reality (VR)? A Brain PET Scan and a self-administered sexual activity questionnaire were given to 11 heterosexual patients affected by impotence due to psychological causes, both before and approximately 6 months after a cycle of psychodynamic psychotherapy. Seven randomly-selected patients received psychotherapy with VR technology using the Optale Method. PET data, used to indicate glucose consumption in various brain areas, were compared with data from normal patients, and a statistical analysis was run. Alterations in cerebral metabolic functioning were displayed in the following areas: frontal cortex, nucleus caudatus, and thalamus. The seven patients who received psychotherapy with VR technology "normalized" in these same areas and attained satisfactory sexual performance. The existence of a male sex algorithm may be hypothesized that links the frontal cortex, nucleus caudatus, and thalamus, and explains its action on cortical motor areas and/or on the medial preoptic area of the hypothalamus, which may respond to treatment combining psychotherapy with VR.