Intracranial self stimulation upregulates the expression of synaptic plasticity related genes and Arc protein expression in rat hippocampus

CREB-Binding Protein Regulates Cocaine- and Amphetamine-Regulated Transcript Peptide Expression in the Lateral Hypothalamus: Implication in Reward and Reinforcement

Neuropeptide cocaine- and amphetamine-regulated transcript peptide (CARTp) is known to play an important role in reward processing. The rats conditioned to intra-cranial self-stimulation (ICSS) showed massive upregulation of CART protein and mRNA in the vicinity of the electrode implanted to deliver the electric current directly at the lateral hypothalamus (LH)-medial forebrain bundle (MFB) area. However, the underlying mechanisms leading to the upregulation of CART in ICSS animals remain elusive. We tested the putative role of CREB-binding protein (CBP), an epigenetic enzyme with intrinsic histone acetyltransferase (HAT) activity, in regulating CART expression during ICSS. An electrode was implanted in LH-MFB and the rats were conditioned to self-stimulation in an operant chamber. CBP siRNA was delivered ipsilaterally in the LH-MFB to knock-down CBP and the effects on lever press activity were monitored. While ICSS-conditioned rats showed distinct increase in CART, CBP and pCREB levels, enhanced CBP binding and histone acetylation (H3K9ac) were noticed on the CART promoter in chromatin immunoprecipitation assay. Direct infusion of CBP siRNA in the LH-MFB lowered lever press activity, CBP levels, histone acetylation at the CART promoter, and CART mRNA and peptide expression. Co-infusion of CARTp in LH-MFB rescued the waning effects of CBP siRNA on self-stimulation. We suggest that CBP-mediated histone acetylation may play a causal role in CART expression in LH, which in turn may drive the positive reinforcement of lever press activity.

Intracranial Self-stimulation of the Medial Forebrain Bundle Ameliorates Memory Disturbances and Pathological Hallmarks in an Alzheimer's Disease Model by Intracerebral Administration of Amyloid-β in Rats

No curative or fully effective treatments are currently available for Alzheimer's disease (AD), the most common form of dementia. Electrical stimulation of deep brain areas has been proposed as a novel neuromodulatory therapeutic approach. Previous research from our lab demonstrates that intracranial self-stimulation (ICSS) targeting medial forebrain bundle (MFB) facilitates explicit and implicit learning and memory in rats with age or lesion-related memory impairment. At a molecular level, MFB-ICSS modulates the expression of plasticity and neuroprotection-related genes in memory-related brain areas. On this basis, we suggest that MFB could be a promising stimulation target for AD treatment. In this study, we aimed to assess the effects of MFB-ICSS on both explicit memory as well as the levels of neuropathological markers ptau and drebrin (DBN) in memory-related areas, in an AD rat model obtained by Aβ icv-injection. A total of 36 male rats were trained in the Morris water maze on days 26-30 after Aβ injection and tested on day 33. Results demonstrate that this Aβ model displayed spatial memory impairment in the retention test, accompanied by changes in the levels of DBN and ptau in lateral entorhinal cortex and hippocampus, resembling pathological alterations in early AD. Administration of MFB-ICSS treatment consisting of 5 post-training sessions to AD rats managed to reverse the memory deficits as well as the alteration in ptau and DBN levels. Thus, this paper reports both cognitive and molecular effects of a post-training reinforcing deep brain stimulation procedure in a sporadic AD model for the first time.

LSD1-BDNF activity in lateral hypothalamus-medial forebrain bundle area is essential for reward seeking behavior

Reward induces activity-dependant gene expression and synaptic plasticity-related changes. Lysine-specific histone demethylase 1 (LSD1), a key enzyme driving histone modifications, regulates transcription in neural circuits of memory and emotional behavior. Herein, we focus on the role of LSD1 in modulating the expression of brain derived neurotrophic factor (BDNF), the master regulator of synaptic plasticity, in the lateral hypothalamus-medial forebrain bundle (LH-MFB) circuit during positive reinforcement. Rats, trained for intracranial self-stimulation (ICSS) via an electrode-cannula assembly in the LH-MFB area, were assayed for lever press activity, epigenetic parameters and dendritic sprouting. LSD1 expression and markers of synaptic plasticity like BDNF and dendritic arborization in the LH, showed distinct increase in conditioned animals. H3K4me2 levels at Bdnf IV and Bdnf IX promoters were increased in ICSS-conditioned rats, but H3K9me2 was decreased. While intra LH-MFB treatment with pan Lsd1 siRNA inhibited lever press activity, analyses of LH tissue showed reduction in BDNF expression and levels of H3K4me2 and H3K9me2. However, co-administration of BDNF peptide restored lever press activity mitigated by Lsd1 siRNA. BDNF expression in LH, driven by LSD1 via histone demethylation, may play an important role in reshaping the reward pathway and hold the key to decode the molecular basis of addiction.

Intracranial Self-Stimulation Modulates Levels of SIRT1 Protein and Neural Plasticity-Related microRNAs

Deep brain stimulation (DBS) of reward system brain areas, such as the medial forebrain bundle (MFB), by means of intracranial self-stimulation (ICSS), facilitates learning and memory in rodents. MFB-ICSS has been found capable of modifying different plasticity-related proteins, but its underlying molecular mechanisms require further elucidation. MicroRNAs (miRNAs) and the longevity-associated SIRT1 protein have emerged as important regulatory molecules implicated in neural plasticity. Thus, we aimed to analyze the effects of MFB-ICSS on miRNAs expression and SIRT1 protein levels in hippocampal subfields and serum. We used OpenArray to select miRNA candidates differentially expressed in the dentate gyrus (DG) of ICSS-treated (3 sessions, 45' session/day) and sham rats. We further analyzed the expression of these miRNAs, together with candidates selected after bibliographic screening (miR-132-3p, miR-134-5p, miR-146a-5p, miR-181c-5p) in DG, CA1, and CA3, as well as in serum, by qRT-PCR. We also assessed tissue and serum SIRT1 protein levels by Western Blot and ELISA, respectively. Expression of miR-132-3p, miR-181c-5p, miR-495-3p, and SIRT1 protein was upregulated in DG of ICSS rats (P < 0.05). None of the analyzed molecules was regulated in CA3, while miR-132-3p was also increased in CA1 (P = 0.011) and serum (P = 0.048). This work shows for the first time that a DBS procedure, specifically MFB-ICSS, modulates the levels of plasticity-related miRNAs and SIRT1 in specific hippocampal subfields. The mechanistic role of these molecules could be key to the improvement of memory by MFB-ICSS. Moreover, regarding the proposed clinical applicability of DBS, serum miR-132 is suggested as a potential treatment biomarker.

Orexin-1 receptor blockade differentially affects spatial and visual discrimination memory facilitation by intracranial self-stimulation

Intracranial self-stimulation (ICSS) of the medial forebrain bundle is an effective treatment to facilitate memory. Performance in both explicit and implicit memory tasks has been improved by ICSS, and this treatment has even been capable of recovering loss of memory function due to lesions or old age. Several neurochemical systems have been studied in regard to their role in ICSS effects on memory, however the possible involvement of the orexinergic system in this facilitation has yet to be explored. The present study aims to examine the relationship between the OX1R and the facilitative effects of ICSS on two different types of memory tasks, both carried out in the Morris Water Maze: spatial and visual discrimination. Results show that the OX1R blockade, by intraventricular administration of SB-334867, partially negates the facilitating effect of ICSS on spatial memory, whereas it hinders ICSS facilitation of the discrimination task. However, ICSS treatment was capable of compensating for the severe detrimental effects of OX1R blockade on both memory paradigms. These results suggest different levels of involvement of the orexinergic system in the facilitation of memory by ICSS, depending on the memory task.

Rewarding deep brain stimulation at the medial forebrain bundle favours avoidance conditioned response in a remote memory test, hinders extinction and increases neurogenesis

Intracranial Self-Stimulation (ICSS) at the medial forebrain bundle consistently facilitates learning and memory in rats when administered post-training or when administered non-concurrent to training, but its scope regarding remote memory has not yet been studied. The present work aims to test whether the combination of these two forms of ICSS administration can cause a greater persistence of the facilitating effect on remote retention and affect neurogenesis in the dentate gyrus (DG) of the hippocampus. Rats were trained in active avoidance conditioning and tested in two retention sessions (10 and 90 days) and later extinction. Subjects received an ICSS session after each of the five avoidance acquisition sessions (post-training treatment) and half of them also received ten additional ICSS sessions during the rest period between retention tests (non-concurrent treatment). All the stimulated groups showed a higher performance in acquisition and retention sessions, but only the rats receiving both ICSS treatments showed greater resistance to extinction. Remarkably, at seven months, rats receiving the non-concurrent ICSS treatment had a greater number of DCX-positive cells in the DG as well as a higher amount of new-born cells within the granular layer compared to rats that did not receive this additional ICSS treatment. Our present findings significantly extend the temporal window of the facilitating effect of ICSS on active avoidance and demonstrate a neurogenic effect of rewarding medial forebrain bundle stimulation.

Chronic brain stimulation rewarding experience ameliorates depression-induced cognitive deficits and restores aberrant plasticity in the prefrontal cortex

BACKGROUND

Major depressive disorder (MDD) is a multifactorial disease which often coexists with cognitive deficits. Depression-induced cognitive deficits are known to be associated with aberrant reward processing, neurochemical and structural alterations. Recent studies have shown that chronic electrical stimulation of brain reward areas induces a robust antidepressant effect. However, the effects of repeated electrical self-stimulation of lateral hypothalamus - medial forebrain bundle (LH-MFB) on depression-induced cognitive deficits and associated neurochemical and structural alterations in the prefrontal cortex (PFC) are unknown.

OBJECTIVES

We investigated the effect of chronic rewarding self-stimulation of LH-MFB in neonatal clomipramine (CLI) model of depression. During adulthood, neonatal CLI and saline administered rats were implanted with bilateral electrodes stereotaxically in the LH-MFB and trained to receive intracranial self-stimulation (ICSS) for 14 days. The rats were tested for depressive-like behaviors, learning and memory followed by estimation of PFC volumes, levels of monoamines and its metabolites in the PFC.

RESULTS

We found that chronic ICSS of LH-MFB reverses CLI-induced behavioral despair and anhedonia. Interestingly, self-stimulation normalizes the impaired novel object and location recognition memory in CLI rats. The amelioration of learning impairments in CLI rats was associated with the reversal of volume loss and restoration of monoamine metabolism in the PFC.

CONCLUSION

We demonstrated that repeated intracranial self-stimulation of LH-MFB ameliorates CLI-induced learning deficits, reverses altered monoamine metabolism and the atrophy of PFC. Our results support the hypothesis that chronic brain stimulation rewarding experience might be evolved as a potential treatment strategy for reversal of learning deficits in depression and associated disorders.

Sustained pain hypersensitivity in the stressed colon: Role of mast cell-derived nerve growth factor-mediated enteric synaptic plasticity

BACKGROUND

Sustained pain hypersensitivity is the hallmark of stressed colon which could be partially explained by central sensitization with synaptic plasticity, the key mechanism of memory. We previously identified that synaptic plasticity of enteric nerve system (ENS) contributed to peripheral pain maintaining in the gut. However, the mechanisms of enteric "memory" formation remain elusive.

METHODS

In this study, rats were exposed to water avoidance stress (WAS) or sham stress (SS), with cromolyn sodium or physiological saline injected intraperitoneally 30 minutes before stress every day. The abdominal withdrawal reflex scores, mesenteric afferent nerve activity, enteric neural c-fos expression, and enteric synaptic plasticity were assessed, and mast cell infiltration and degranulation. Furthermore, colonic mucosal mediators-induced enteric synaptic plasticity and the role of mast cell-derived nerve growth factor (NGF), tryptase, and histamine were investigated via ex vivo longitudinal muscle-myenteric plexus (LMMP) organotypic culture.

KEY RESULTS

It is shown that mast cell stabilizing inhibited WAS-induced visceral hypersensitivity through enhancing visceral pain threshold, decreasing spontaneous and distention-induced mesenteric afferent firing, and downregulating enteric neural activation (c-fos). Importantly, WAS led to evident enteric synaptic plasticity, but decreased by cromolyn. Water avoidance stress-derived mucosal supernatants markedly enhanced the c-fos expression and enteric synaptic plasticity in LMMP tissues, which could be eliminated by mast cell inhibition or NGF neutralization, but not tryptase or histamine blocking.

CONCLUSIONS & INFERENCES

In conclusion, mast cells/NGF pathway may be the key regulator of synaptic plasticity of ENS and participate in the formation of chronic stress-induced sustained visceral hypersensitivity.

Arc protein expression after unilateral intracranial self-stimulation of the medial forebrain bundle is upregulated in specific nuclei of memory-related areas

Background

Intracranial Self-Stimulation (ICSS) of the medial forebrain bundle (MFB) is a deep brain stimulation procedure, which has a powerful enhancement effect on explicit and implicit memory. However, the downstream synaptic plasticity events of MFB-ICSS in memory related areas have not been described thoroughly. This study complements previous work studying the effect of MFB-ICSS on the expression of the activity-regulated cytoskeleton-associated (Arc) protein, which has been widely established as a synaptic plasticity marker. We provide new integrated measurements from memory related regions and take possible regional hemispheric differences into consideration.

Results

Arc protein expression levels were analyzed 4.5 h after MFB-ICSS by immunohistochemistry in the hippocampus, habenula, and memory related amygdalar and thalamic nuclei, in both the ipsilateral and contralateral hemispheres to the stimulating electrode location. MFB-ICSS was performed using the same paradigm which has previously been shown to facilitate memory. Our findings illustrate that MFB-ICSS upregulates the expression of Arc protein in the oriens and radiatum layers of ipsilateral CA1 and contralateral CA3 hippocampal regions; the hilus bilaterally, the lateral amygdala and dorsolateral thalamic areas as well as the central medial thalamic nucleus. In contrast, the central amygdala, mediodorsal and paraventricular thalamic nuclei, and the habenular complex did not show changes in Arc expression after MFB-ICSS.

Conclusions

Our results expand our knowledge of which specific memory related areas MFB-ICSS activates and, motivates the definition of three functionally separate groups according to their Arc-related synaptic plasticity response: (1) the hippocampus and dorsolateral thalamic area, (2) the central medial thalamic area and (3) the lateral amygdala.

Electronic supplementary material

The online version of this article (10.1186/s12868-018-0449-5) contains supplementary material, which is available to authorized users.

Late Effect of Developmental Exposure to 3,3'-Iminodipropionitrile on Neurogenesis in the Hippocampal Dentate Gyrus of Mice

The effects of developmental exposure to 3,3'-iminodipropionitrile (IDPN), a neurotoxicant that causes proximal axonopathy, on mouse hippocampal neurogenesis was examined. Pregnant mice were exposed to IDPN at 0, 600, or 1200 ppm in their drinking water from gestational day 6 to postnatal day (PND) 21. On PND 21, male offspring showed increased postmitotic neuron-specific NeuN-immunoreactive⁽⁺⁾ granule cell numbers in the dentate subgranular zone (SGZ) and granule cell layer (GCL) and decreased glutamate receptor gene Grin2d levels in the dentate gyrus at 1200 ppm. On PND 77, decreased numbers were observed for TBR2⁺ progenitor cells in the SGZ at ≥600 ppm and GFAP⁺ stem cells, DCX⁺ progenitor cells and immature granule cells, NeuN⁺ immature and mature granule cells, PCNA⁺ proliferating cells in the SGZ and/or GCL, and immunoreactive cells for ARC or FOS, immediate-early gene products related to neuronal and synaptic plasticity, in the GCL at 1200 ppm. Additionally, at 1200 ppm of IDPN, downregulation of Kit, the gene encoding the stem cell factor (SCF) receptor, and upregulation of Kitl, encoding SCF, were observed in the dentate gyrus. Therefore, maternal IDPN exposure in mice affects neurogenesis involving glutamatergic signals at the end of developmental exposure, with late effects suppressing SGZ cell proliferation, reducing the broad range of granule cell lineage population, which may be responsible for SCF receptor downregulation. The upregulated SCF was likely a feedback response to the decreased receptor level. These results suggest that reduced SCF signaling may cause suppressed neuronal and synaptic plasticity.

Neonatal Irradiation Leads to Persistent Proteome Alterations Involved in Synaptic Plasticity in the Mouse Hippocampus and Cortex

Recent epidemiological data indicate that radiation doses as low as those used in computer tomography may result in long-term neurocognitive side effects. The aim of this study was to elucidate long-term molecular alterations related to memory formation in the brain after low and moderate doses of γ radiation. Female C57BL/6J mice were irradiated on postnatal day 10 with total body doses of 0.1, 0.5, or 2.0 Gy; the control group was sham-irradiated. The proteome analysis of hippocampus, cortex, and synaptosomes isolated from these brain regions indicated changes in ephrin-related, RhoGDI, and axonal guidance signaling. Immunoblotting and miRNA-quantification demonstrated an imbalance in the synapse morphology-related Rac1-Cofilin pathway and long-term potentiation-related cAMP response element-binding protein (CREB) signaling. Proteome profiling also showed impaired oxidative phosphorylation, especially in the synaptic mitochondria. This was accompanied by an early (4 weeks) reduction of mitochondrial respiration capacity in the hippocampus. Although the respiratory capacity was restored by 24 weeks, the number of deregulated mitochondrial complex proteins was increased at this time. All observed changes were significant at doses of 0.5 and 2.0 Gy but not at 0.1 Gy. This study strongly suggests that ionizing radiation at the neonatal state triggers persistent proteomic alterations associated with synaptic impairment.

Low-dose ionizing radiation rapidly affects mitochondrial and synaptic signaling pathways in murine hippocampus and cortex

The increased use of radiation-based medical imaging methods such as computer tomography is a matter of concern due to potential radiation-induced adverse effects. Efficient protection against such detrimental effects has not been possible due to inadequate understanding of radiation-induced alterations in signaling pathways. The aim of this study was to elucidate the molecular mechanisms behind learning and memory deficits after acute low and moderate doses of ionizing radiation. Female C57BL/6J mice were irradiated on postnatal day 10 (PND10) with gamma doses of 0.1 or 0.5 Gy. This was followed by evaluation of the cellular proteome, pathway-focused transcriptome, and neurological development/disease-focused miRNAome of hippocampus and cortex 24 h postirradiation. Our analysis showed that signaling pathways related to mitochondrial and synaptic functions were changed by acute irradiation. This may lead to reduced mitochondrial function paralleled by enhanced number of dendritic spines and neurite outgrowth due to elevated long-term potentiation, triggered by increased phosphorylated CREB. This was predominately observed in the cortex at 0.1 and 0.5 Gy and in the hippocampus only at 0.5 Gy. Moreover, a radiation-induced increase in the expression of several neural miRNAs associated with synaptic plasticity was found. The early changes in signaling pathways related to memory formation may be associated with the acute neurocognitive side effects in patients after brain radiotherapy but might also contribute to late radiation-induced cognitive injury.

Sign-tracking to an appetitive cue predicts incubation of conditioned fear in rats

Although post-traumatic stress disorder (PTSD) and addiction are very different disorders, both are characterized by hyperreactivity to trauma- or drug-related cues, respectively. We investigated whether an appetitive conditioning task, Pavlovian conditioned approach, which predicts vulnerability to reinstatement of cocaine-seeking, also predicts fear incubation, which may be a marker for vulnerability to PTSD. We classified rats based on whether they learned to approach and interact with a food predictive cue (sign-trackers), or, whether upon cue presentation they went to the location of impending food delivery (goal-trackers). Rats were then exposed to extensive Pavlovian tone-shock pairings, which causes the fear response to increase or "incubate" over time. We found that the fear incubation effect was only present in sign-trackers. The behavior of goal-trackers was more consistent with a normal fear response-it was most robust immediately after training and decayed slowly over time. Sign-trackers also had lower levels of brain-derived neurotrophic factor (BDNF) protein in the prefrontal cortex than goal-trackers. These results indicate that, while many factors likely contribute to the disproportionate co-occurrence of PTSD and substance abuse, one such factor may be a core psychological trait that biases some individuals to attribute excessive motivational significance to predictive cues, regardless of the emotional valence of those cues. High levels of BDNF in the prefrontal cortex may be protective against developing excessive emotional and motivational responses to salient cues.

The cognitive defects of neonatally irradiated mice are accompanied by changed synaptic plasticity, adult neurogenesis and neuroinflammation

Background/purpose of the study

Epidemiological evidence suggests that low doses of ionising radiation (≤1.0 Gy) produce persistent alterations in cognition if the exposure occurs at a young age. The mechanisms underlying such alterations are unknown. We investigated the long-term effects of low doses of total body gamma radiation on neonatally exposed NMRI mice on the molecular and cellular level to elucidate neurodegeneration.

Results

Significant alterations in spontaneous behaviour were observed at 2 and 4 months following a single 0.5 or 1.0 Gy exposure. Alterations in the brain proteome, transcriptome, and several miRNAs were analysed 6–7 months post-irradiation in the hippocampus, dentate gyrus (DG) and cortex. Signalling pathways related to synaptic actin remodelling such as the Rac1-Cofilin pathway were altered in the cortex and hippocampus. Further, synaptic proteins MAP-2 and PSD-95 were increased in the DG and hippocampus (1.0 Gy). The expression of synaptic plasticity genes Arc, c-Fos and CREB was persistently reduced at 1.0 Gy in the hippocampus and cortex. These changes were coupled to epigenetic modulation via increased levels of microRNAs (miR-132/miR-212, miR-134). Astrogliosis, activation of insulin-growth factor/insulin signalling and increased level of microglial cytokine TNFα indicated radiation-induced neuroinflammation. In addition, adult neurogenesis within the DG was persistently negatively affected after irradiation, particularly at 1.0 Gy.

Conclusion

These data suggest that neurocognitive disorders may be induced in adults when exposed at a young age to low and moderate cranial doses of radiation. This raises concerns about radiation safety standards and regulatory practices.

Electronic supplementary material

The online version of this article (doi:10.1186/1750-1326-9-57) contains supplementary material, which is available to authorized users.

Self administration of oxycodone alters synaptic plasticity gene expression in the hippocampus differentially in male adolescent and adult mice

Abuse and addiction to prescription opioids such as oxycodone (a short-acting Mu opioid receptor (MOP-r) agonist) in adolescence is a pressing public health issue. We have previously shown differences in oxycodone self-administration behaviors between adolescent and adult C57BL/6J mice and expression of striatal neurotransmitter receptor genes, in areas involved in reward. In this study, we aimed to determine whether oxycodone self-administration differentially affects genes regulating synaptic plasticity in the hippocampus of adolescent compared to adult mice, since the hippocampus may be involved in learning aspects associated with chronic drug self administration. Hippocampus was isolated for mRNA analysis from mice that had self administered oxycodone (0.25 mg/kg/infusion) 2h/day for 14 consecutive days or from yoked saline controls. Gene expression was analyzed with real-time polymerase chain reaction (PCR) using a commercially available "synaptic plasticity" PCR array containing 84 genes. We found that adolescent and adult control mice significantly differed in the expression of several genes in the absence of oxycodone exposure, including those coding for mitogen-activated protein kinase, calcium/calmodulin-dependent protein kinase II gamma subunit, glutamate receptor, ionotropic AMPA2 and metabotropic 5. Chronic oxycodone self administration increased proviral integration site 1 (Pim1) and thymoma viral proto-oncogene 1 mRNA levels compared to controls in both age groups. Both Pim1 and cadherin 2 mRNAs showed a significant combined effect of Drug Condition and Age × Drug Condition. Furthermore, the mRNA levels of both cadherin 2 and cAMP response element modulators showed an experiment-wise significant difference between oxycodone and saline control in adult but not in adolescent mice. Overall, this study demonstrates for the first time that chronic oxycodone self-administration differentially alters synaptic plasticity gene expression in the hippocampus of adolescent and adult mice.