Influence of nootropic and antidepressive drugs on open field and running wheel behavior in spontaneously high and low active mice

Suppression of neuropathic pain and comorbidities by recurrent cycles of repetitive transcranial direct current motor cortex stimulation in mice

Transcranial, minimally-invasive stimulation of the primary motor cortex (M1) has recently emerged to show promise in treating clinically refractory neuropathic pain. However, there is a major need for improving efficacy, reducing variability and understanding mechanisms. Rodent models hold promise in helping to overcome these obstacles. However, there still remains a major divide between clinical and preclinical studies with respect to stimulation programs, analysis of pain as a multidimensional sensory-affective-motivational state and lack of focus on chronic phases of established pain. Here, we employed direct transcranial M1 stimulation (M1 tDCS) either as a single 5-day block or recurring blocks of repetitive stimulation over early or chronic phases of peripherally-induced neuropathic pain in mice. We report that repeated blocks of stimulation reverse established neuropathic mechanical allodynia more strongly than a single 5-day regime and also suppress cold allodynia, aversive behavior and anxiety without adversely affecting motor function over a long period. Activity mapping revealed highly selective alterations in the posterior insula, periaqueductal gray subdivisions and superficial spinal laminae in reversal of mechanical allodynia. Our preclinical data reveal multimodal analgesia and improvement in quality of life by multiple blocks of M1 tDCS and uncover underlying brain networks, thus helping promote clinical translation.

Running wheel activity is sensitive to acute treatment with selective inhibitors for either serotonin or norepinephrine reuptake

RATIONALE

Most antidepressants (AD) directly or indirectly enhance the serotonergic tone in the CNS. Since the serotonin system is involved in both, the modulation of mood and motor behavior, it was reasoned that these drugs might also interfere with running wheel activity (RWA), a form of positively motivated motor behavior, which might be linked to pathological states like obsessive-compulsive disorder (OCD).

OBJECTIVES

We used RWA to characterize ADs from all major classes. Effects on RWA were compared to effects on general locomotor activity (LOC) to control for unspecific effects on general locomotion.

METHODS

Two hours before lights-off, mice were treated with either vehicle or one of the following AD: the selective serotonin reuptake inhibitors (SSRIs) citalopram (3-10 mg/kg), paroxetine (1-10 mg/kg) and fluoxetine (2-6.6 mg/kg), the selective norepinephrine reuptake inhibitor (SNRI) reboxetine (1-10 mg/kg), the monoamine oxidase (MAO) inhibitors tranylcypromine (1-3 mg/kg) and moclobemide (3-10 mg/kg), and the tricyclic ADs desipramine and imipramine (10-30 mg/kg, each). LOC and RWA were measured after lights-off.

RESULTS

At the highest dose tested, all ADs, with the exception of the MAO inhibitors, significantly reduced RWA. Both tricyclics inhibited RWA only at doses that similarly affected LOC. In contrast, all SSRI and reboxetine inhibited RWA at doses that left LOC unaffected.

CONCLUSIONS

SSRI and the SNRI reboxetine inhibit RWA at doses not suppressing LOC. RWA may represent a simple behavioral readout of positively motivated behavior that merits further attention for psychopharmacology.

Lithium and cognitive enhancement: leave it or take it?

RATIONALE

Lithium is established as an effective treatment of acute mania, bipolar and unipolar depression and as prophylaxis against bipolar disorder. Accumulating evidence is also delineating a neuroprotective and neurotrophic role for lithium. However, its primary effects on cognitive functioning remain ambiguous.

OBJECTIVES

The aim of this paper is to review and combine the relevant translational studies, focusing on the putative cognitive enhancement properties of lithium, specifically on learning, memory, and attention.

DISCUSSION

These properties are also discussed in reference to research demonstrating a protective action of lithium against cognitive deficits induced by various challenges to the nervous system, such as stress, trauma, neurodegenerative disorders, and psychiatric disorders.

CONCLUSIONS

It is suggested on the basis of the evidence that the cognitive effects of lithium are best expressed and should, therefore, be sought under conditions of functional or biological challenge to the nervous system.

Long-term voluntary exercise and the mouse hypothalamic-pituitary-adrenocortical axis: impact of concurrent treatment with the antidepressant drug tianeptine

We investigated whether voluntary exercise and concurrent antidepressant treatment (tianeptine; 20 mg/kg/day; 4 weeks) exert synergistic effects on the mouse hypothalamic-pituitary-adrenocortical (HPA) axis. Animals had access to a running wheel, were treated with the antidepressant, or received both conditions combined. Control mice received no running wheel and no drug treatment. Exercise resulted in asymmetric changes in the adrenal glands. Whereas sedentary mice had larger left adrenals than right ones, this situation was abolished in exercising animals, mainly due to enlargement of the right adrenal cortex. However, antidepressant treatment alone was ineffective whereas the combination of antidepressant treatment and exercise resulted in an enlargement of both adrenal cortices. In these respective conditions, the levels of tyrosine hydroxylase (TH) mRNA expression in the left and right adrenal medullas varied greatly in parallel to the changes observed in the adrenal cortex sizes. TH mRNA expression in the locus coeruleus of exercising mice was significantly increased irrespective of concomitant tianeptine treatment. Corticotrophin-releasing factor mRNA levels in the hypothalamic paraventricular nucleus were decreased after voluntary exercise but were unaffected by tianeptine. Exercise, particularly in combination with tianeptine treatment, resulted in decreased early morning baseline plasma levels of corticosterone. If animals were exposed to novelty (i.e. a mild psychological stressor), a decreased response in plasma corticosterone levels was observed in the exercising mice. By contrast, after restraint, a mixed physical and psychological stressor, exercising mice showed an enhanced response in plasma corticosterone compared to the controls; a response which was even further boosted in exercising mice concomitantly treated with tianeptine. Under either condition, plasma adrenocorticotrophic hormone levels were not different between groups. Thus, voluntary exercise impacts substantially on HPA axis regulation. Concurrent tianeptine treatment results in synergistic actions, mainly at the adrenal level, affecting both its structure and function.

Effect of chronic stress on spatial memory in rats is attenuated by lithium treatment

Stress is known to alter cognitive functions, such as memory, and it has been linked to the pathophysiology of mood and anxiety disorders. Chronic lithium treatment is used in some psychiatric disorders and has been suggested to act upon mechanisms which can enhance neuronal viability. The purpose of this work is to investigate a possible effect of lithium treatment in a chronic stress model. Adult male Wistar rats were divided in two groups, control and chronically stressed, treated either with normal chow or with chow containing LiCl for 40 days. Stress treatment was a chronic variable stress model, consisting of different stressors which were applied in a random fashion, once a day, every day. Memory was assessed by using the water maze task. The results demonstrated a marked decrease in reference memory in the water maze task in chronically stressed rats. This effect was attenuated by lithium treatment in all the parameters considered. No effect was observed in the working memory. These results indicate that lithium treatment may counteract some effects of chronic stress situations, particularly concerning spatial memory.

The open field as a paradigm to measure the effects of drugs on anxiety-like behaviors: a review

The open field is a very popular animal model of anxiety-like behavior. An overview of the literature on the action elicited by effective or putative anxiolytics in animal subjected to this procedure indicates that classical treatments such as benzodiazepine receptor full agonists or 5-HT(1A) receptor full or partial agonists elicit an anxiolytic-like effect in this procedure in most cases (approximately 2/3). However, compounds (triazolobenzodiazepines such as adinazolam and alprazolam, selective serotonin reuptake inhibitors) that have a different spectrum of therapeutic efficacy in anxiety disorders such as panic attacks, generalized anxiety disorder or obsessive-compulsive disorder were poorly effective as anxiolytics in the open field test, suggesting that this paradigm may not model features of anxiety disorders. The procedure is also relevant for the study of compounds endowed with anxiogenic effects, as such effects were detected after treatments with benzodiazepine receptor inverse agonists or with corticotropin releasing factor (CRF) receptor agonists.

Open field locomotion and neurotransmission in mice evaluated by principal component factor analysis-effects of housing condition, individual activity disposition and psychotropic drugs

Effects of housing condition and individual disposition on dopaminergically and GABAergically influenced open field locomotion and neurochemistry were studied in mice. Mice characterized as high active (HAM) and low active (LAM) by a running-wheel test were housed in groups or isolated for 1 day, 1 week, 3, 6, 12 or 18 weeks before an open field test was performed with saline, apomorphine (0.75 mg/kg) or diazepam (1.00 mg/kg) administration. Immediately afterwards animals were decapitated and brain sections were frozen for subsequent HPLC-analysis of dopaminergic and serotonergic transmitter metabolism. Principal component factor analysis (PCA) of locomotion variables provided three factors explaining 78.5% of total variance. Variables related to the amount of locomotion loaded highly on Factor 1 (F1-Activity), variables related to place utilization loaded highly on Factor 2 (F2-Exploration) and variables related to immobility and place preference loaded highly on Factor 3 (F3-Irritation). Apomorphine decreased F1-Activity with smaller effects in HAM and without changes in F2-Exploration and F3-Irritation independent on housing conditions. Diazepam exerted a decrease in F2-Exploration with a small increase in FI-Activity and no effects in F3-Irritation. Diazepam induced changes depended on housing conditions and were especially pronounced in isolated HAM. PCA of considerable locomotion and neurochemical data revealed interrelationships between striatal dopamine metabolism and F1-Activity, between cortical dopamine and serotonin metabolism and F2-Exploration as well as between cerebellar, hippocampal and striatal serotonin metabolism and F3-Irritation. The authors concluded that the application of PCA is a useful method to provide functionally relevant characteristics of behaviors and functionally relevant descriptions of interrrelationships between behavior and appropriate central nervous mechanisms. Furthermore the received behavioral characteristics (F1, F2, F3) of open field locomotion were sensitive to reveal housing and drug effects.

Cyclic GTP imitates the potentiating effect of the nootrope vinpocetine on the high-threshold A-current in mollusk neurons

Isolated common snail neurons were studied using two-microelectrode potential clamping to record high-threshold (threshold = 10 mV) rapidly-inactivating potassium current (I(Aht)); the effects of the nootrope vinpocetine on this current were studied and were compared with the effects of cyclic nucleotides. Intracellular application of dibutyryl derivatives of cyclic adenosine monophosphate (dcAMP) and guanosine monophosphate (dcGMP) was used. The results showed that vinpocetine potentiates or fails to alter I(Aht) in different cells, while dcGMP imitates the effect of vinpocetine. Simultaneous application of vinpocetine and dcGMP did not result in additive effects. Unlike dcGMP, dcAMP did not imitate the effects of vinpocetine, and decreased I(Aht) in most cells. These data suggest that cGMP mediates the potentiating effect of vinpocetine on I(Aht).

Dynamic alterations of serotonergic metabolism and receptors during social isolation of low- and high-active mice

Alterations induced by social isolation (1 day to 18 weeks) in low- and high-active mice (LAM and HAM) were studied in respect to serotonin metabolism, [3H]-8-OH-DPAT binding of presynaptic (midbrain), postsynaptic (hippocampus) 5-HT1A receptors and [3H]-ketanserin binding of cortical 5-HT2A receptors. Individual housing of mice was associated with reduction of serotonin metabolism, depending on isolation time and brain structure. Whereas a transient decrease in the striatum and cortex was detected between 1 week and 6 weeks, reduction of cerebellar and hippocampal serotonin metabolism was found later (12-18 weeks). Serotonergic systems of HAM were found to be more reactive to environmental disturbances, and their serotonin metabolism was more affected by social isolation. Isolation-induced upregulation of cortical 5-HT2A receptors was measured only in HAM. Densities of postsynaptic 5-HT1A receptors in the hippocampus did differ either in grouped or isolated mice. However, there were significant differences in hippocampal 5-HT1A receptor affinity, especially between 1 day and 3 weeks. Transient downregulation of presynaptic 5-HT1A receptors in the midbrain was found in isolated mice between 3 and 6 weeks. These results are discussed in terms of interactions between serotonergic alterations and isolation-induced aggression.