Diverse Efficacy of Dimethyl Fumarate in Alleviating the Late Streptozotocin-Induced Cognitive Impairment and Neuropathological Features in Rat.

Our previous study showed that dimethyl fumarate (DMF) treatment performed within three weeks after intracerebroventricular (ICV) injection of streptozotocin (STZ) attenuated spatial memory impairment, hippocampal neurodegeneration, and neuroinflammation in rats. The present study is aimed at verifying the hypothesis that DMF alleviates late effects of STZ (6 months after ICV injection) which reflects advanced stage of the Alzheimer's disease (AD) in human patients. Spatial memory was assessed with Morris water maze (MWM), general brain level of amyloid ß (Aß) and p-tau was measured by western blot, immunofluorescent labelling of active microglia (IBA1), Aß and p-tau and histological assay of neurodegeneration (Fluoro-Jade C) were performed in hippocampus and cortex. Two-week oral therapy with DMF normalized spatial memory disrupted by STZ but had no influence on general brain level of Aß and p-tau. However, immunofluorescence showed local reduction of Aß aggregates number in parietal cortex and p-tau+ cells in CA2 hippocampal area. Microgliosis was alleviated by DMF in CA1 area and parietal cortex. DMF-treated STZ injected rats showed higher number of Aß containing microglia than untreated group in CA2 and frontal cortex, which may be the result of increased phagocytic activity in these areas after DMF treatment. STZ-induced neurodegeneration was alleviated by DMF in dentate gyrus and frontal cortex. In conclusion DMF treatment exerts beneficial effect on spatial memory in the rat model of late stage of AD, but weakly influences neuropathological features, as only local reduction in number of Aß aggregates, p-tau containing cells, neurodegeneration, and microgliosis was found.

Deep-Brain Subthalamic Nucleus Stimulation Enhances Food-Related Motivation by Influencing Neuroinflammation and Anxiety Levels in a Rat Model of Early-Stage Parkinson's Disease.

Deep-brain subthalamic nucleus stimulation (DBS-STN) has become a well-established therapeutic option for advanced Parkinson's disease (PD). While the motor benefits of DBS-STN are widely acknowledged, the neuropsychiatric effects are still being investigated. Beyond its immediate effects on neuronal circuits, emerging research suggests that DBS-STN might also modulate the peripheral inflammation and neuroinflammation. In this work, we assessed the effects of DBS-STN on food-related motivation, food intake pattern, and the level of anxiety and compared them with markers of cellular and immune activation in nigrostriatal and mesolimbic areas in rats with the 6-OHDA model of early PD. To evaluate the potential mechanism of observed effects, we also measured corticosterone concentration in plasma and leukocyte distribution in peripheral blood. We found that DBS-STN applied during neurodegeneration has beneficial effects on food intake pattern and motivation and reduces anxiety. These behavioral effects occur with reduced percentages of IL-6-labeled cells in the ventral tegmental area and substantia nigra pars compacta in the stimulated brain hemisphere. At the same brain structures, the cFos cell activations were confirmed. Simultaneously, the corticosterone plasma concentration was elevated, and the peripheral blood lymphocytes were reduced after DBS-STN. We believe that comprehending the relationship between the effects of DBS-STN on inflammation and its therapeutic results is essential for optimizing DBS therapy in PD.

Dimethyl Fumarate Alleviates Adult Neurogenesis Disruption in Hippocampus and Olfactory Bulb and Spatial Cognitive Deficits Induced by Intracerebroventricular Streptozotocin Injection in Young and Aged Rats.

The disorder of adult neurogenesis is considered an important mechanism underlying the learning and memory impairment observed in Alzheimer's disease (AD). The sporadic nonhereditary form of AD (sAD) affects over 95% of AD patients and is related to interactions between genetic and environmental factors. An intracerebroventricular injection of streptozotocin (STZ-ICV) is a representative and well-established method to induce sAD-like pathology. Dimethyl fumarate (DMF) has antioxidant and anti-inflammatory properties and is used for multiple sclerosis treatment. The present study determines whether a 26-day DMF therapy ameliorates the disruption of adult neurogenesis and BDNF-related neuroprotection in the hippocampus and olfactory bulb (OB) in an STZ-ICV rat model of sAD. Considering age as an important risk factor for developing AD, this study was performed using 3-month-old (the young group) and 22-month-old (the aged group) male Wistar rats. Spatial cognitive functions were evaluated with the Morris water maze task. Immunofluorescent labelling was used to assess the parameters of adult neurogenesis and BDNF-related neuroprotection in the hippocampus and OB. Our results showed that the STZ-ICV evoked spatial learning and memory impairment and disturbances in adult neurogenesis and BDNF expression in both examined brain structures. In the aged animals, the deficits were more severe. We found that the DMF treatment significantly alleviated STZ-ICV-induced behavioural and neuronal disorders in both age groups of the rats. Our findings suggest that DMF, due to its beneficial effect on the formation of new neurons and BDNF-related neuroprotection, may be considered as a promising new therapeutic agent in human sAD.

Dimethyl fumarate: A review of preclinical efficacy in models of neurodegenerative diseases.

Dimethyl fumarate (DMF) is an antioxidative and anti-inflammatory drug approved for treatment of multiple sclerosis and psoriasis; however, beneficial effects of DMF have also been found in other inflammatory diseases and cancers. DMF is a prodrug that is immediately hydrolysed to monomethyl fumarate (MMF) in vivo. Both fumarates activate the nuclear factor (erythroid-derived 2)-like 2 (Nrf2) pathway, and Nrf2 is a key transcription factor of the antioxidant response. The immunosuppressive and anti-inflammatory actions of DMF occur through several mechanisms: via inhibition of the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) pathway and by downregulation of aerobic glycolysis and pyroptosis in activated myeloid and lymphoid cells. MMF is also an agonist of hydroxycarboxylic acid receptor 2 (HCAR2). Differences in the strength of effects and mechanisms of action of both fumarates are discussed. The aim of this review was to analyse and compare the neuroprotective, antioxidative and anti-inflammatory effects of DMF and its active metabolite, MMF, in cellular (in vitro) and animal models of neurodegenerative diseases (NDs), other than multiple sclerosis. There are more than twenty studies that currently represent this field. Most of the studies are concerned with cellular or animal models of Alzheimer's disease (AD) and Parkinson's disease (PD), one utilized a mouse model of Huntington's disease (HD) and one clinical trial was carried out with amyotrophic lateral sclerosis (ALS) patients. The discrepancies in the results of the various studies are discussed, and issues requiring further research have been identified.

Dimethyl Fumarate as the Peripheral Blood Inflammatory Mediators Inhibitor in Prevention of Streptozotocin-Induced Neuroinflammation in Aged Rats.

PURPOSE: Intracerebroventricular-(ICV)-streptozotocin-(STZ)-induced neuroinflammation is a model of Alzheimer's disease (AD) compatible with the inflammation hypothesis of ageing ("inflammaging" state). Previously, we observed age-dependent (young vs aged) dimethyl fumarate (DMF)-induced anti-inflammatory and neuroprotective effects in the brain along with improvement in cognitive functions in rats with the ICV-STZ-induced model of AD. To evaluate whether DMF reduces neuroinflammation based on the peripheral inflammatory response inhibition, we determined peripheral inflammatory mediators in young and aged rats with the ICV-STZ-induced AD pathology following DMF therapy. MATERIALS AND METHODS: Young (4-month-old) and aged (22-month-old) rats were fed with 0.4% DMF rat chow for 21 consecutive days after ICV-STZ (3 mg/ventricle) injections. After behavioral testing, blood and spleens were collected to determine the numbers of leukocytes (WBC), lymphocytes and their subpopulations, haematological parameters, the concanavalin (Con)-A-induced production and plasma concentration of interferon (IFN)-γ, interleukin (IL)-6, IL-10 and corticosterone (COR). RESULTS: Age-dependent anti-inflammatory effect of the DMF treatment in rats with ICV-STZ injections manifested as decreased peripheral WBC and lymphocyte numbers, including TCD3+CD4+CD8-, TCD3+CD4-CD8+, B (CD45RA+) and NK (161a+), in aged rats. Furthermore, DMF lowered the blood and spleen lymphocyte production of pro-inflammatory IFN-γ and IL-6 in young and aged rats, whereas it enhanced the plasma level of anti-inflammatory IL-10 and lymphocyte's ability to produce it in aged rats only. In parallel to changes in peripheral WBC numbers in the model of AD, DMF decreased the red blood cell number, haemoglobin concentration, haematocrit and mean platelet volume in aged, but not young, rats. In contrast to controls, DMF did not influence the COR response in STZ groups. CONCLUSION: Besides preventing neuroinflammation, DMF acts on the pro-/anti-inflammatory balance in the periphery and causes an anti-inflammatory shift in T lymphocytes which could contribute to DMF's therapeutic effects in the ICV-STZ-induced model of AD, in particular, in aged rats.

Prolonged Peripheral Immunosuppressive Responses as Consequences of Random Amphetamine Treatment, Amphetamine Withdrawal and Subsequent Amphetamine Challenges in Rats.

Drug-induced immunosuppression may underline increased hypothalamic-pituitary-adrenal axis response to stress observed following chronic psychostimulant treatment. However, the consequences of random amphetamine (AMPH) treatment, withdrawal and AMPH challenge after withdrawal on the peripheral immunity and systemic corticosterone response are unknown. In this study, the total blood and spleen leukocyte, lymphocyte, T, B, NK, TCD4+/TCD8+ cell numbers and ratio, pro-inflammatory interferon gamma (IFN-γ), and anti-inflammatory interleukin-4 (IL-4) production, and plasma corticosterone concentration in Wistar rats were investigated after: chronic, random AMPH/SAL treatment alone (20 injections in 60 days, 1 mg/kg b.w., i.p.), AMPH/SAL withdrawal (for 20 consecutive days after random AMPH/SAL exposure) or AMPH/SAL challenge after withdrawal (single injection after the AMPH/SAL withdrawal phase). The results showed blood and spleen leukopenia, lymphopenia, lower blood production of IFN-ɤ, and increased plasma corticosterone concentration after the AMPH treatment, which were more pronounced in the AMPH after withdrawal group. In contrast, an increased number of blood NK cells and production of IL-4 after chronic, random AMPH treatment alone, were found. Blood AMPH-induced leukopenia and lymphopenia were due to decreased total number of T, B lymphocytes and, at least in part, of granulocytes and monocytes. Moreover, decreases in the number of blood TCD4+ and TCD8+ lymphocytes both in the AMPH chronic alone and withdrawal phases, were found.The major findings of this study are that AMPH treatment after the long-term withdrawal from previous random AMPH exposure, accelerates the drug-induced immunosuppressive and systemic corticosterone responses, suggesting prolonged immunosuppressive effects and an increase in incidence of infectious diseases. Prolonged peripheral immunosuppressive responses as consequences of random amphetamine…The results indicate that the chronic and random AMPH exposure alone and the acute (single injection) challenge of the drug after the withdrawal phase induced long-term immunosuppressive effects, which were similar to those occurring during the stress response, and sensitized the peripheral immunosuppressive and corticosterone responses of the rat to the disinhibitory effects of this stressor.

Subthalamic Deep Brain Stimulation Affects Plasma Corticosterone Concentration and Peripheral Immunity Changes in Rat Model of Parkinson's Disease.

Deep brain stimulation of the subthalamic nucleus (DBS-STN) is an effective treatment for advanced motor symptoms of Parkinson's disease (PD). Recently, a connection between the limbic part of the STN and side effects of DBS-STN has been increasingly recognized. Animal studies have shown that DBS-STN influences behavior and provokes neurochemical changes in regions of the limbic system. Some of these regions, which are activated during DBS-STN, are involved in neuroimmunomodulation. The therapeutic effects of DBS-STN in PD treatment are clear, but the influence of DBS-STN on peripheral immunity has not been reported so far. In this study, we examined the effects of unilateral DBS-STN applied in male Wistar rats with 6-hydroxydopamine PD model (DBS-6OHDA) and rats without nigral dopamine depletion (DBS) on corticosterone (CORT) plasma concentration, blood natural killer cell cytotoxicity (NKCC), leukocyte numbers, lymphocyte population and apoptosis numbers, plasma interferon gamma (IFN-γ), interleukin 6 (IL-6), and tumor necrosis factor (TNF-α) concentration. The same peripheral immune parameters we measured also in non-stimulated rats with PD model (6OHDA). We observed peripheral immunity changes related to PD model. The NKCC and percentage of T cytotoxic lymphocytes were enhanced, while the level of lymphocyte apoptosis was down regulated in 6OHDA and DBS-6OHDA groups. After DBS-STN (DBS-6OHDA and DBS groups), the plasma CORT and TNF-α were elevated, the number of NK cells and percentage of apoptosis were increased, while the number of B lymphocytes was decreased. We also found, changes in plasma IFN-γ and IL-6 levels in all the groups. These results suggest potential peripheral immunomodulative effects of DBS-STN in the rat model of PD. However, further studies are necessary to explain these findings and their clinical implication. Graphical Abstract Influence of deep brain stimulation of the subthalamic nucleus on peripheral immunity in rat model of Parkinson's disease.

Autophagy-dependent mechanism of genistein-mediated elimination of behavioral and biochemical defects in the rat model of sporadic Alzheimer's disease.

Alzheimer's disease is one of severe neurological diseases for which no effective treatment is currently available. The use of genistein (5,7-dihydroxy-3-(4-hydroxyphenyl)-4H-1-benzopyran-4-one) has been proposed previously as one of approaches to improve the disease symptoms, as some positive effects of this compound in cellular and animal models were reported. Inhibition of apoptosis and antioxidative functions were suggested as causes of these effects. Here, we demonstrate that high genistein dose (150 mg/kg/day; the dose significantly higher than those used previously in AD studies by others) can activate autophagy in the streptozotocin-induced rat model of the sporadic form of AD. We found that this dose of genistein led to complete degradation of ß-amyloid and hyperphosphorylated tau protein in the brain, while experiments with cell cultures demonstrated that these effects require autophagy stimulation, which has never been shown before. Importantly, behavior of high dose genistein-treated AD rats was completely corrected, i.e. it was indistinguishable from that of healthy animals. This was observed in all performed behavioral tests: Morris water maze test, elevated plus-maze test, open field test, and locomotor measurements in an actometer. We conclude that autophagy-dependent mechanism is responsible for genistein-mediated correction of AD when this isoflavone is used at the high dose.

Age-dependent effects of dimethyl fumarate on cognitive and neuropathological features in the streptozotocin-induced rat model of Alzheimer's disease.

We previously demonstrated that dimethyl fumarate (DMF), an anti-oxidative and immunosuppresive compound, prevents intracerebroventricular (ICV) streptozotocin-induced disruption of spatial memory and neurodegeneration in 4-month-old rats. The present study evaluated the influence of age on DMF's therapeutic effect. Aged rats (22-months-old, n = 40) were provided rodent chow containing DMF (0.4%) and given ICV injections of streptozotocin (STZ) or vehicle (Sham) on days 2 and 4. Spatial memory was evaluated using the Morris water maze (MWM) on days 14-21. Hippocampal samples from young (4-month-old, n = 36, collected previously) and aged rats were assessed for presence of activated (CD68-positive) microglia, IL-10 and oxidative/nitrative stress marker nitrotyrosine. Aged rat samples were also stained with Fluoro-JadeB marker for neurodegeneration. Previously obtained MWM and Fluoro-JadeB data from young rats served as a reference for assessing impact of age. Aged Sham DMF-fed rats exhibited better spatial memory and less neurodegeneration in the CA3 region of the hippocampus compared to corresponding young rats. Aged STZ rats displayed greater memory impairment and increased CA2 neurodegeneration, CA1 nitrotyrosine immunoreactivity, and microglial activation in the dentate gyrus (DG), compared to young STZ rats. Notably, within aged STZ-injected rats, DMF treatment was associated with improved performance in MWM, reduced neurodegeneration in all hippocampal areas, reduced DG microglia activation, and reduced CA1 nitrotyrosine labeling compared to age-matched rats without DMF treatment. This beneficial age-related effect of DMF treatment after STZ ICV injections may result from reduced microglial activation in the hippocampus that leads to an alleviation of oxidative stress, neurodegeneration, and memory impairments.

Dimethyl fumarate attenuates intracerebroventricular streptozotocin-induced spatial memory impairment and hippocampal neurodegeneration in rats.

Intracerebroventricular (ICV) injection of streptozotocin (STZ) is a widely-accepted animal model of sporadic Alzheimer's disease (sAD). The present study evaluated the ability of dimethyl fumarate (DMF), an agent with antioxidant and anti-inflammatory properties, to prevent spatial memory impairments and hippocampal neurodegeneration mediated by ICV injection of STZ in 4-month-old rats. Rodent chow containing DMF (0.4%) or standard rodent chow was made available on day 0. Rat body weight and food intake were measured daily for whole the experiment (21days). STZ or vehicle (SHAM) ICV injections were performed on days 2 and 4. Spatial reference and working memory were evaluated using the Morris water maze on days 14-21. Cells containing Fluoro-Jade B (neurodegeneration marker), IL-6, IL-10 were quantified in the hippocampus and choline acetyltransferase (ChAT) in the basal forebrain. The disruption of spatial memory and a high density of hippocampal CA1-3 cells labeled with Fluoro-Jade B or containing IL-6 or IL-10 were observed in the STZ group but not in the STZ+DMF group, as compared to the SHAM or SHAM+DMF groups. STZ vs. STZ+DMF differences were found: worse reference memory acquisition, fewer ChAT-positive neurons in the medial septum (Ch1), more Fluoro-Jade-positive CA1 hippocampal cells in STZ rats. DMF therapy in a rodent model of sAD prevented the disruption of spatial reference and working memory, loss of Ch1 cholinergic cells and hippocampal neurodegeneration as well as the induction of IL-6 and IL-10 in CA1. These beneficial cognitive and molecular effects validate the anti-inflammatory and neuroprotective properties of DMF in the hippocampus.

Medial Septal NMDA Glutamate Receptors are Involved in Modulation of Blood Natural Killer Cell Activity in Rats.

The purpose of the present study was to determine the specific role of the medial septal (MS) NMDA glutamate receptors on peripheral blood natural killer cell cytotoxicity (NKCC) and their (large granular lymphocyte, LGL) number, as well as the plasma concentration of tumor necrosis factor α (TNF-α) and corticosterone in male Wistar rats exposed to elevated plus maze (EPM) stress or non-stress conditions. The NMDA groups were injected with NMDA glutamate receptor agonist (N-methyl-D-aspartate; 0.25 µg/rat), the D-AP7 group was injected with DL-2-amino-7-phosphoheptanoate (0.1 µg/rat), an antagonist of NMDA glutamate receptors, and the control Sal group with saline (0.5 µl/rat) via previously implanted cannulae into the MS. There was an increase in the NKCC, NK/LGL number and plasma TNF-α concentration after the NMDA injections, being much stronger within the rats under non-stress conditions rather than the rats exposed to EPM stress. These parameters were decreased in the D-AP7 rats, suggesting receptor/ion channel specificity. Moreover, a lower plasma corticosterone concentration within the NMDA rather than the Sal and D-AP7 groups was found. The obtained results suggest that activation of the NMDA glutamate receptors in the MS, accompanied by changes in the corticosterone and cytokine responses, may be involved in modulation of the blood natural anti-tumor response, under EPM stress and non-stress conditions.

[The interleukin-10 in the central nervous system]. / Interleukina 10 w osrodkowym ukladzie nerwowym.

Cytokines, including interleukin-10 (IL-10), are cell signaling molecules taking part in cell­to­cell communication, cell proliferation, differentiation, migration and apoptosis. Cytokines also have the ability to induce, regulate, and inhibit inflammation. Cytokines are produced mainly by activated peripheral immune cells, but due to dissemination of the concept of the central nervous system as an immunologically specialized zone, it is considered that cytokine signaling is one of the components of the immune system which can modulate brain functioning. IL-10 shows immunosuppressive properties, and since expression of this cytokine has been shown in the central nervous system, researchers have started to investigate the therapeutic possibilities of IL-10 action in the context of neurodegenerative diseases, which may involve neuroinflammation in their pathogenesis. Recent studies using cell cultures or animal models of neurodegenerative disorders have shown that the importance of IL-10 in the central nervous system goes beyond the anti-inflammatory activity of this cytokine. Involvement of IL-10 in neuroprotection, neurogenesis, regulation of the stress response and hippocampal synaptic plasticity connected with learning and memory is suggested.

Effects of chronic desipramine pretreatment on open field-induced suppression of blood natural killer cell activity and cytokine response depend on the rat's behavioral characteristics.

Effects of 14 consecutive day exposure to desipramine (10mg/kg i.p.), by itself or following chronic open field (OF) exposure, on subsequent neuroimmunological effects of acute (30 min) OF stress and the involvement of individual differences in response to novelty or social position in the anti-depressive responsiveness were investigated. Chronic desipramine pretreatment did not protect against OF stress-induced suppression of blood anti-tumor natural killer cell activity but increased plasma interleukin-10 and decreased interferon-γ and corticosterone concentration. These effects were particularly dangerous for the animals with increased responsivity to stress (desipramine alone) or with low behavioral activity (desipramine after chronic stress).

Chronic antidepressant desipramine treatment increases open field-induced brain expression and spleen production of interleukin 10 in rats.

In the present study, we established a role of individual differences in locomotor response to novelty or social position in modulatory effect of chronic (14 consecutive days) antidepressant drug desipramine pretreatment (10mg/kg i.p.) on acute (30 min), white and illuminated open field (OF)-induced changes in spleen anti-tumor activity of natural killer (NK) cells (chromium release assay) in parallel to the brain anti-inflammatory interleukin 10 (IL-10) and Fos expression (immunohistochemistry), splenocytic pro-inflammatory interferon γ (IFN-γ) and IL-10 production (ELISA), and plasma corticosterone concentration (RIA) in rats. The involvement of individual differences (high (HR) and low (LR) responders to novelty or dominants (D) and subordinates (S)) in the anti-depressive responsiveness, was investigated in the desipramine treated by itself (DES) or following 7 consecutive days of OF exposure (ChS-DES) group. In the desipramine pretreated groups, OF stress decreased spleen NKCC, behavioral activity, the Con A-stimulated splenocyte IFN-γ response and plasma corticosterone concentration whereas it increased the brain and splenocyte IL-10 response. The percentage of OF-induced IL-10/Fos(+) cells was increased in the CA1 and dentate gyrus of the hippocampus and amygdaloid nucleus, particularly in the LR-D (DES) and LR-S (ChS-DES) rats. Moreover, a decreased splenocytic ability to produce IFN-γ and IL-10, particularly in the HR-S (DES) and LR-S (ChS-DES) rats, was noted. There were no significant differences in the OF-induced NKCC suppression between the behavioral groups. These studies emphasize that chronic desipramine pretreatment had anti-inflammatory but not immunoprotective properties against OF stress-induced neuroimmunological effects which depend on the animal's behavioral characteristics and treatment.

Behavioral response elicited by stimulation of the mesolimbic system after procaine and bicuculline injection into the pedunculopontine tegmental nucleus in rats.

The pedunculopontine tegmental nucleus (PPN) is anatomically connected with dopaminergic cells in the ventral tegmental area (VTA). In the present study, VTA-stimulation induced feeding or locomotor response was tested after temporary inactivation (procaine injection) or activation (bicuculline injection) of the PPN in the ipsi- or contralateral hemisphere. Motor and motivation aspects of appetitive behavior were analyzed on the basis of the latency/stimulation frequency curve shift paradigm, in male Wistar rats (n=48). Procaine injections into the PPN had more significant effects on both types of behavioral response during VTA stimulation than bicuculline. On the day of injection (day 0) procaine increased reaction threshold of the observed responses: a rise by 22% after contra- and 17% after ipsilateral injection in the case of feeding, and an inverse result side-wise for locomotor response, i.e. around 12% and 20% respectively. Bicuculline injected into the PPN did not cause significant effects on day 0 and the values of reaction threshold oscillated around ±10% for both behaviors, except in rats with locomotor reaction after contralateral injection. The observed reactions stabilized within on consecutive days (days 1-3) after procaine/bicuculline injection in both behavioral groups. The results indicate that the PPN and VTA belong to the same central circuitry involved in the regulation of psychomotor activation. However, the influence of PPN-VTA inter-hemispheric connections on reward and addiction function of the VTA is still unexplained.

Stress-induced differences in the limbic system Fos expression are more pronounced in rats differing in responsiveness to novelty than social position.

We determined the interaction between such individual behavioural profiles as locomotor response to novelty or social position and the activation (Fos expression) of the brain's limbic regions following chronic laboratory and social interaction stress. Male Wistar rats (n=45), housed separately and handled for 2 weeks, were divided into high (HR) and low (LR) responders to novelty. Seven days later, 12 HRs and 12 LRs were subjected to a chronic 23 consecutive day social interaction test (Nov/SocI group), 5 HRs and 5 LRs were subjected to chronic laboratory stress: carrying from the vivarium to the laboratory for 23 consecutive days (Nov/Carr group) while the remaining rats stayed in the vivarium in their home cages (Nov/Home group). The highest limbic system activation was found 7 days later in the Nov/SocI rats. In comparison with the LRs, the HRs showed a higher number of Fos(+) cells in most of the limbic prosencephalic structures (24 areas) in the Nov/SocI group, and in 12 areas, especially in the amygdala and the hypothalamus, in the Nov/Carr group. There were no HR/LR differences in the limbic system's activity in the Nov/Home group. Within dominance/submission differences, a higher Fos expression was found in 6 structures, especially in the limbic cortex, in the dominant rather than the subordinate HRs. We conclude that chronic social and laboratory stress persistently activates the limbic system, with the largest effects in the brains of rats responding maximally to novelty. Social position was less predictive of Fos expression than was activity to novelty.

Induction of hippocampal theta rhythm by electrical stimulation of the ventral tegmental area and its loss after septum inactivation.

The ventral tegmental area (VTA), which may be one of the structures involved in regulation of hippocampal theta rhythm, sends direct projections to the hippocampus and also to the forebrain septum, the key centres involved in theta generation. In the present study we aimed at assessing which projections from the VTA (direct or through the septum) participate in regulation of hippocampal electric activity. Experiments were conducted on 3 groups of urethanised male Wistar rats. In the first group (n=6) electrical stimulation of the VTA was used to evoke theta rhythm episodes in hippocampus. Stimulation was repeatedly applied in control conditions and after procainic blockade of the septum. The second group (n=6), subjected to unilateral electrical stimulation of the VTA (30-s stimulation at 10-min intervals during 2h) and to subsequent detection of Fos expression, served to measure neuronal activation of the target mesolimbic structures. Activation levels of selected structures were compared to data from analogous stimulation of the zona incerta (ZI, the third group, n=6). Stimulation of the VTA immediately generated regular theta rhythm in both hippocampi. Inactivation of the septum with procaine temporarily abolished this effect. VTA stimulation increased the density of Fos in the ipsilateral nucleus accumbens. Stimulation of the ZI never generated theta but evoked significant induction of Fos expression in the hippocampus. Our data suggest that the projection through which the VTA enhances theta rhythm is not direct but is incorporated into the main route of theta generation, which involves septum as the main relay node.

Lesion and stimulation of the ventral tegmental area increases cholinergic activity in the rat brain.

Our previous study indicated that unilateral lesion of the ventral tegmental area (VTA) facilitates contralateral VTA stimulation-induced feeding or exploration. The present study was aimed to determine the possible role of the central cholinergic systems in this effect. Immunohistochemistry for choline acetyltransferase (ChAT) was used to measure the number of active cholinergic neurons in their major groups (Ch1-Ch6) and in striatal regions in rats subjected to unilateral electrocoagulation and contralateral VTA electrical stimulation (L/S group) in comparison to the unilaterally stimulated (S), unilaterally lesioned (L) and sham (Sh) groups. The study showed that unilateral VTA lesion increased (as compared to Sh group) the number of ChAT+ neurons in the Ch1-Ch3 and unilateral VTA stimulation increased the number in the Ch1 and the ventral pallidum only. The most sensitive to these changes in the mesolimbic system were cholinergic structures providing hippocampal afferentation. Surprisingly, there was no significant increase in the number of ChAT+ neurons in the L/S group. The obtained results did not confirm any evident influence of the cholinergic systems on the VTA lesion-induced facilitation of the behavioral response evoked by contralateral VTA stimulation.

Lesion of the ventral tegmental area amplifies stimulation-induced Fos expression in the rat brain.

Unilateral lesions of the ventral tegmental area (VTA), the key structure of the mesolimbic system, facilitate behavioral responses induced by electrical stimulation of the VTA in the contralateral hemisphere. In search of the neuronal mechanism behind this phenomenon, Fos expression was used to measure neuronal activation of the target mesolimbic structures in rats subjected to unilateral electrocoagulation and simultaneously to contralateral electrical stimulation of the VTA (L/S group). These were compared to the level of mesolimbic activation after unilateral electrocoagulation of the VTA (L group), unilateral electrical stimulation of the VTA (S group) and bilateral electrode implantation into the VTA in the sham (Sh) group. We found that unilateral stimulation of the VTA alone increased the density of Fos containing neurons in the ipsilateral mesolimbic target structures: nucleus accumbens, lateral septum and amygdala in comparison with the sham group. However, unilateral lesion of the VTA was devoid of effect in non-stimulated (L) rats and it significantly amplified the stimulation-induced Fos-immunoreactivity (L/S vs S group). Stimulation of the VTA performed after contralateral lesion (L/S) evoked strong bilateral induction of Fos expression in the mesolimbic structures involved in motivation and reward (nucleus accumbens and lateral septum) and the processing of the reinforcing properties of olfactory stimuli (anterior cortical amygdaloid nucleus) in parallel with facilitation of behavioral function measured as shortened latency of eating or exploration. Our data suggest that VTA lesion sensitizes mesolimbic system to stimuli by suppressing an inhibitory influence of brain areas afferenting the VTA.