Effects of cocaine on c-fos and NGFI-B mRNA expression in transgenic mice underexpressing glucocorticoid receptors

Striatal miR-183-5p inhibits methamphetamine-induced locomotion by regulating glucocorticoid receptor signaling

MicroRNA (miRNA)-mediated striatal gene regulation may play an important role in methamphetamine (METH) addiction. This study aimed to identify changes in novel miRNAs and their target genes during METH self-administration and investigate their roles in METH-induced locomotion. RNA sequencing analysis revealed that mir-183-5p was upregulated in the striatum of METH self-administered rats, and target gene prediction revealed that the glucocorticoid receptor (GR) gene, Nr3c1, was a potential target gene for mir-183-5p. We confirmed that single and repeated METH administrations increased METH-induced locomotion and plasma corticosterone levels in rats. Additionally, increased miR-185-5p expression and decreased GR gene expression were observed only in the repeated-METH-injection group but not in the single-injection group. We then investigated the effects of miR-183-5p on METH-induced locomotion using a miR-183-5p mimic and inhibitor. Injection of a mir-183-5p mimic in the striatum of rats attenuated METH-induced locomotion, whereas injection of a miR-183-5p inhibitor enhanced the locomotor activity in METH-administered rats. Furthermore, the miR-183-5p mimic reduced the phosphorylation of tyrosine hydroxylase (TH) whereas the inhibitor increased it. Taken together, these results indicate that repeated METH injections increase striatal miR-183-5p expression and regulate METH-induced locomotion by regulating GR expression in rats, thereby suggesting a potential role of miR-183-5p as a novel regulator of METH-induced locomotion.

Nuclear Receptor Nr4a1 Regulates Striatal Striosome Development and Dopamine D1 Receptor Signaling

The GABAergic medium-size spiny neuron (MSN), the striatal output neuron, may be classified into striosome, also known as patch, and matrix, based on neurochemical differences between the two compartments. At this time, little is known regarding the regulation of the development of the two compartments. Nr4a1, primarily described as a nuclear receptor/immediate early gene involved in the homeostasis of the dopaminergic system, is a striosomal marker. Using Nr4a1-overexpressing and Nr4a1-null mice, we sought to determine whether Nr4a1 is necessary and/or sufficient for striosome development. We report that in vivo and in vitro, Nr4a1 and Oprm1 mRNA levels are correlated. In the absence of Nr4a, there is a decrease in the percentage of striatal surface area occupied by striosomes. Alterations in Nr4a1 expression leads to dysregulation of multiple mRNAs of members of the dopamine receptor D₁ signal transduction system. Constitutive overexpression of Nr4a1 decreases both the induction of phosphorylation of ERK after a single cocaine exposure and locomotor sensitization following chronic cocaine exposure. Nr4a1 overexpression increases MSN excitability but reduces MSN long-term potentiation. In the resting state, type 5 adenylyl cyclase (AC5) activity is normal, but the ability of AC5 to be activated by Drd1 G-protein-coupled receptor inputs is decreased. Our results support a role for Nr4a1 in determination of striatal patch/matrix structure and in regulation of dopaminoceptive neuronal function.

Altered regulation of Nur77 nuclear receptor gene expression in the mesocorticolimbic regions of rat brain by amphetamine sensitization

The mechanisms underlying psychostimulant drug-induced sensitization include long-term cellular and molecular adaptations in dopaminergic circuits. Nur77, a member of the Nur family of transcription factors, is expressed in brain regions receiving dopamine inputs and plays a role in activity-induced synaptic modification. Here we evaluated changes in Nur77 mRNA levels in the medial prefrontal cortex (mPFC), dorsal striatum (Str) and nucleus accumbens (NAc) of rats receiving a repeated, sensitizing regimen of amphetamine (AMPH). Results were compared to two groups of controls - animals receiving repeated injections of saline (Rp-SAL) or with no treatment (CON). Two weeks after the last injection, the effect of an acute challenge dose of AMPH on Nur77 expression was evaluated using in-situ hybridization. Repeated AMPH treatment (Rp-AMPH) increased the levels of Nur77 mRNA in the mPFC, NAc core and shell regions. However, the effects of an acute injection of AMPH in each of the three groups of animals was distinct. Whereas an acute AMPH led to a significant increase of Nur77 in all brain regions of the CON animals, it had no significant effect in Rp-SAL animals. Interestingly, in acute AMPH-injected Rp-AMPH animals, Nur77 mRNA levels in the mPFC, Str and NAc regions were significantly lower compared to CON and Rp-SAL animals treated with acute AMPH. There was a positive correlation between AMPH -induced locomotor activity and Nur77 mRNA expression in CON animals; however, this relationship was absent in Rp-SAL and Rp-AMPH animals. The data suggest that Nur77 is a part of neuroadaptive changes caused by either mild stress of repeated injections as well as AMPH-sensitization and may play a role in abnormal behaviors induced by the drug.

Nur transcription factors in stress and addiction

The Nur transcription factors Nur77 (NGFI-B, NR4A1), Nurr1 (NR4A2), and Nor-1 (NR4A3) are a sub-family of orphan members of the nuclear receptor superfamily. These transcription factors are products of immediate early genes, whose expression is rapidly and transiently induced in the central nervous system by several types of stimuli. Nur factors are present throughout the hypothalamus-pituitary-adrenal (HPA) axis where are prominently induced in response to stress. Drugs of abuse and stress also induce the expression of Nur factors in nuclei of the motivation/reward circuit of the brain, indicating their participation in the process of drug addiction and in non-hypothalamic responses to stress. Repeated use of addictive drugs and chronic stress induce long-lasting dysregulation of the brain motivation/reward circuit due to reprogramming of gene expression and enduring alterations in neuronal function. Here, we review the data supporting that Nur transcription factors are key players in the molecular basis of the dysregulation of neuronal circuits involved in chronic stress and addiction.

The transcription factors Nur77 and retinoid X receptors participate in amphetamine-induced locomotor activities

INTRODUCTION

The major substrate underlying amphetamine (AMPH)-induced locomotor activity is associated with dopamine forebrain circuits. Brain regions associated with AMPH-induced locomotor activity express high levels of retinoid receptors. However, the role of these transcription factors in dopamine-mediated effects remains poorly understood. Two nuclear receptor families, the retinoic acid receptors (RAR) and the retinoid X receptors (RXR), transduce retinoic acid signal. RARs are specifically involved in retinoid signaling, whereas RXRs also participate in other signaling pathways as partners for other nuclear receptors such as Nur77, an orphan member of the nuclear receptor family expresses in dopamine system.

MATERIALS AND METHODS

To explore the role of retinoid receptors and Nur77 in AMPH-induced locomotor activity, we administered selective retinoid receptor drugs in combination with AMPH in adult wild-type and Nur77-deficient mice. At a low dose, AMPH similarly increased ambulatory activity in wild-type and Nur77-deficient mice, while it did not alter non-ambulatory activity.

RESULTS AND DISCUSSION

At a high dose, AMPH did not alter ambulatory activity anymore, while non-ambulatory activity strongly increased in wild-type mice. Nur77-deficient mice still displayed a higher ambulatory activity with no change in non-ambulatory activity. HX531, a synthetic RXR antagonist, blocks AMPH-induced ambulatory activity, whereas RAR drugs tested remained without effect. Interestingly, the effect of HX531 was abolished in Nur77-deficient mice, suggesting that this orphan nuclear receptor is essential for the action of the RXR drug.

CONCLUSION

This study shows that RXR and Nur77 participate in AMPH-induced locomotor activity and prompts for further investigations on the role of Nur77 and RXR in addiction and reward-related behaviors.

Stress, alcohol and drug interaction: an update of human research

A challenging question that continues unanswered in the field of addiction is why some individuals are more vulnerable to substance use disorders than others. Numerous risk factors for alcohol and other drugs of abuse, including exposure to various forms of stress, have been identified in clinical studies. However, the neurobiological mechanisms that underlie this relationship remain unclear. Critical neurotransmitters, hormones and neurobiological sites have been recognized, which may provide the substrates that convey individual differences in vulnerability to addiction. With the advent of more sophisticated measures of brain function in humans, such as functional imaging technology, the mechanisms and neural pathways involved in the interactions between drugs of abuse, the mesocorticolimbic dopamine system and stress systems are beginning to be characterized. This review provides a neuroadaptive perspective regarding the role of the hormonal and brain stress systems in drug addiction with a focus on the changes that occur during the transition from occasional drug use to drug dependence. We also review factors that contribute to different levels of hormonal/brain stress activation, which has implications for understanding individual vulnerability to drug dependence. Ultimately, these efforts may improve our chances of designing treatment strategies that target addiction at the core of the disorder.

Extracellular signal-regulated kinases (ERK) and protein kinase C (PKC) activities are involved in the modulation of Nur77 and Nor-1 expression by dopaminergic drugs

The dopamine system is the main target of antipsychotic and psychostimulant drugs. These drugs induce intracellular events that culminate in the transcription of immediate early genes, such as c-fos. Another class of transcription factors, namely, the nuclear receptor subgroup called Nurs (Nur77, Nurr1 and Nor-1), has recently been associated with behavioral and biochemical effects mediated by dopamine. However, the signaling cascade leading to modulation of Nur mRNA levels in the brain has never been investigated. In the present study, we explore in vivo using specific kinase inhibitors the role of mitogen-associated and extracellular signal-regulated kinases (MEK) and protein kinase C (PKC) in the modulation of Nur expression induced by dopamine receptor drugs. Modulation of Nur77 expression by a dopamine D(2) receptor antagonist is associated with MEK and PKC activities, whereas only the PKC activity participates in the modulation of Nor-1 expression. Both MEK and PKC activities also participate in the modulation of Nur77 mRNA levels induced by dopamine receptor agonists, whereas a selective MEK activity is associated with the modulation of Nor-1 mRNA levels. Interestingly, modulation of dopamine drug-induced locomotor activities by kinase inhibitors is in accordance with the effects on Nur77, but not Nor-1, expression. Taken together, the results indicate that signaling events leading to modulation of Nur77 and Nor-1 expression following dopamine receptor interacting drugs are distinct. Considering that orphan nuclear receptors of the Nur subgroup display an important ligand-independent constitutive activity, characterization of the signaling cascades involved in the regulation of their expression represents an important step for understanding their role in dopamine system physiology and pathophysiology.

Acute stress and nicotine cues interact to unveil locomotor arousal and activity-dependent gene expression in the prefrontal cortex

BACKGROUND

This study examines the interactive effects of acute stress and nicotine-associated contextual cues on locomotor activity and activity-dependent gene expression in subregions of the prefrontal cortex.

METHODS

Locomotor activity of rats was measured in a context associated with either low-dose nicotine or saline administration with or without 5 minutes of pre-exposure to ferrets, a nonphysical stressor. After 45 minutes in the test environment, plasma corticosterone levels and mRNA levels of the immediate-early genes Arc, NGFI-B, and c-Fos in prefrontal and primary motor cortical subregions were measured.

RESULTS

Stress alone increased plasma corticosterone and prefrontal cortex gene expression. Low-dose nicotine cues had no effect on corticosterone levels nor did they elicit conditioned motor activation, and they caused minor elevations in gene expression. Stress and low-dose nicotine cues, however, interacted to elicit conditioned motor activation and further increases in early response gene expression in prefrontal but not in the primary motor cortical subregions.

CONCLUSIONS

Stress interacts with nicotine-associated cues to uncover locomotor arousal, a state associated with prefrontal neuronal activation and immediate early gene expression. Thus, in nicotine-experienced individuals, stress may be an important determinant of subjective reactivity and prefrontal cortex activation that occurs in response to nicotine-associated cues.

Nur77 and retinoid X receptors: crucial factors in dopamine-related neuroadaptation

Dopaminergic systems in the brain adapt in response to various stimuli from the internal and external world, but the mechanisms underlying this process are incompletely understood. Here, we review recent evidence that certain types of transcription factor of the nuclear receptor family, specifically Nur77 and retinoid X receptors, have important roles in adaptation and homeostatic regulation of dopaminergic systems. These findings call for a reassessment of our fundamental understanding of the molecular and cellular basis of dopamine-mediated transmission. Given that diseases such as Parkinson's disease and schizophrenia are thought to involve adaptation of dopamine signalling, these findings might provide new insight into these pathologies and offer new avenues for drug development.

Nur77 gene knockout alters dopamine neuron biochemical activity and dopamine turnover

BACKGROUND

Transcription factors of the Nur family (Nurr1, Nur77, and Nor-1) are orphan nuclear receptors closely associated with dopamine neurotransmission in the central nervous system. Nur77 expression is strongly modulated by antipsychotic and ant-parkinsonian drugs in dopaminoceptive brain areas. However, the role of Nur77 in dopamine neuron activity and turnover remains elusive.

METHODS

We compared various behavioral and biochemical parameters between Nur77 knockout -/- and wild-type +/+ mice in basal and haloperidol-challenged conditions.

RESULTS

We report here that Nur77-deficient mice display enhanced spontaneous locomotor activity, greater sensitivity to a small dose of the dopamine D2 receptor agonist quinpirole acting mainly at autoreceptor sites, and higher levels of the dopamine metabolite DOPAC relative to wild-type mice. Dopamine turnover disturbances are also found after acute challenge with haloperidol, a dopamine D2 receptor antagonist. These alterations are associated with increased tyrosine hydroxylase expression and activity, and reduced catechol-O-methyltransferase expression.

CONCLUSION

Taken together, these results are consistent with the involvement of Nur77 in dopamine neuron biochemical activity and dopamine turnover.

Expression of spinal NMDA receptor and PKCgamma after chronic morphine is regulated by spinal glucocorticoid receptor

Spinal NMDA receptor (NMDAR), protein kinase C (PKC), and glucocorticoid receptor (GR) have all been implicated in the mechanisms of morphine tolerance; however, how these cellular elements interact after chronic morphine exposure remains unclear. Here we show that the expression of spinal NMDAR and PKCgamma after chronic morphine is regulated by spinal GR through a cAMP response element-binding protein (CREB)-dependent pathway. Chronic morphine (10 microg, i.t.; twice daily for 6 d) induced a time-dependent upregulation of GR, the NR1 subunit of NMDAR, and PKCgamma within the rat's spinal cord dorsal horn. This NR1 and PKCgamma upregulation was significantly diminished by intrathecal coadministration of morphine with the GR antagonist RU38486 or a GR antisense oligodeoxynucleotide. Intrathecal coadministration of morphine with an adenylyl cyclase inhibitor (2',5'-dideoxyadenosine) or a protein kinase A inhibitor (H89) also significantly attenuated morphine-induced NR1 and PKCgamma expression, whereas intrathecal treatment with an adenylyl cyclase activator (forskolin) alone mimicked morphine-induced expression of GR, NR1, and PKCgamma. Moreover, the expression of phosphorylated CREB was upregulated within the spinal cord dorsal horn after chronic morphine, and a CREB antisense oligodeoxynucleotide coadministered intrathecally with morphine prevented the upregulation of GR, NR1, and PKCgamma. These results indicate that spinal GR through the cAMP-CREB pathway played a significant role in NMDAR and PKCgamma expression after chronic morphine exposure. The data suggest that genomic interaction among spinal GR, NMDAR, and PKCgamma may be an important mechanism that contributes to the development of morphine tolerance.

Striatal neuroadaptation and rescue of locomotor deficit by l-dopa in aphakia mice, a model of Parkinson's disease

Preferential neurodegeneration of dopaminergic neurons in the ventral substantia nigra of the midbrain is a hallmark of Parkinson's disease. The homeobox transcription factor Pitx3 is similarly and selectively expressed in the same neurons. Pitx3 deficiency in a natural mouse mutant, the aphakia mouse, was correlated with the loss of these neurons and with a deficit in locomotor activity. We now report that the locomotor deficit of aphakia mice is established by 40 days of age and that it can be rescued by injection of l-dopa. We further show that downstream striatal correlates of the midbrain neuronal losses in aphakia mice, as assessed by dopamine transporter binding and expression of dopamine receptors, enkephalin, dynorphin and neurotensin, are highly similar to neuroadaptive responses observed following rapid neurodegeneration induced by neurotoxin administration in adult animals or following the progressive neurodegenerative processes as seen in Parkinson patients. Taken collectively, these data support the idea that the aphakia mice represent a selective model of dopaminergic deficiency that closely resembles the midbrain and striatal neuropathology associated with Parkinson's disease, and this suggests that these mice are a good model to assess therapies for Parkinson's disease as well as to understand the susceptibility of these neurons to neurodegeneration.

Central glucocorticoid receptors modulate the expression and function of spinal NMDA receptors after peripheral nerve injury

Central glucocorticoid receptors (GRs) and NMDA receptors (NMDARs) have been shown to play a significant role in the mechanisms of neuropathic pain after peripheral nerve injury; however, how central GRs and NMDARs interact in this process remains unknown. Here we show that the expression and function of spinal NMDARs after peripheral nerve injury were modulated by central GRs. Chronic constriction nerve injury (CCI) in rats induced a time-dependent upregulation of NR1 and NR2 subunits of the NMDAR within the spinal cord dorsal horn ipsilateral to CCI. The upregulation of NMDARs was significantly diminished by intrathecal administration (twice daily for postoperative days 1-6) of either the GR antagonist RU38486 or an antisense oligonucleotide against GRs. Moreover, this CCI-induced expression of NMDARs was significantly attenuated in rats receiving intrathecal treatment with an interleukin-6 (IL-6) antiserum and in mice with protein kinase Cgamma (PKCgamma) knock-out. Because IL-6 and PKCgamma mediated the upregulation of central GRs after CCI as demonstrated previously, the results suggest that IL-6 and PKCgamma served as cellular mediators contributing to the GR-mediated expression of NMDARs after CCI. Functionally, nociceptive behaviors induced by NMDAR activation and CCI were reversed by a single intrathecal administration of the GR antagonist RU38486. Conversely, a single intrathecal injection with the noncompetitive NMDAR antagonist MK-801 reversed neuropathic pain behaviors exacerbated by the GR agonist dexamethasone in CCI rats. These data suggest that interactions between central GRs and NMDARs through genomic and nongenomic regulation may be an important mechanism critical to neuropathic pain behaviors in rats.

Expression of central glucocorticoid receptors after peripheral nerve injury contributes to neuropathic pain behaviors in rats

Peripheral glucocorticoid receptors (GRs) play a significant role in the anti-inflammatory effects of glucocorticoids; however, the role of central GRs in nociceptive behaviors after peripheral nerve injury (neuropathic pain behaviors) remains unknown. Here we show that the development of neuropathic pain behaviors (thermal hyperalgesia and mechanical allodynia) induced by chronic constriction nerve injury (CCI) in rats was attenuated by either the GR antagonist RU38486 (4 = 2 > 1 = 0.5 microg) or a GR antisense oligonucleotide administered intrathecally twice daily for postoperative days 1-6. The development of thermal hyperalgesia and mechanical allodynia after CCI also was prevented in adrenalectomized rats, whereas the GR agonist dexamethasone (100 microg/kg) given subcutaneously twice daily for postoperative day 1-6 restored CCI-induced neuropathic pain behaviors in the adrenalectomized rats. Mechanistically, CCI induced a time-dependent and region-specific expression of neuronal GRs primarily within the spinal cord dorsal horn ipsilateral to nerve injury, which showed a time course parallel to that of the development of neuropathic pain behaviors. Moreover, the expression of neuronal GR after CCI was mediated in part through an elevated spinal level of interleukin-6 (IL-6) and protein kinase Cgamma (PKCgamma), because intrathecal treatment with an IL-6 antiserum, a PKC inhibitor (cheryrithrine), or PKCgamma knock-out substantially reduced the expression of neuronal GRs as well as neuropathic pain behaviors after CCI. These findings indicate a central role of neuronal GRs in the mechanisms of neuropathic pain behaviors in rats and suggest a potential role for GR antagonists in clinical management of neuropathic pain.

Evidence for a long-term influence on morphine tolerance after previous morphine exposure: role of neuronal glucocorticoid receptors

Opioid analgesic tolerance is a pharmacological phenomenon that overtime diminishes the opioid analgesic effect. However, it remains unknown as to whether a previous opioid exposure would have a long-term influence on opioid tolerance upon subsequent opioid administration. Here, we show that the onset and degree of antinociceptive tolerance to a subsequent cycle of morphine exposure were substantially exacerbated in rats made tolerant to and then recovered from previous morphine administration, indicating a long-term influence from a previous morphine exposure on the development of morphine tolerance. Mechanistically, morphine exposure induced a cyclic AMP and protein kinase A-dependent upregulation of neuronal glucocorticoid receptors (GR) within the spinal cord dorsal horn, which was maintained after discontinuation of morphine administration and significantly enhanced upon a second cycle of morphine exposure. Prevention of the GR upregulation with GR antisense oligonucleotides as well as inhibition of GR activation with the GR antagonist RU38486 effectively prevented the exacerbated morphine tolerance after subsequent cycles of morphine exposure. The results indicate that a previous morphine exposure could induce lasting cellular changes mediated through neuronal GR and influence morphine analgesia upon a subsequent exposure. These findings may have significant implications in clinical opioid therapy and substance abuse.

Glucocorticoids and vulnerability to psychostimulant drugs: toward substrate and mechanism

Glucocorticoid hormones can modulate the propensity of individuals to develop addictive behavior and, by doing so, contribute to the existence of individual differences in vulnerability to drugs. This article summarizes recent findings that increase our knowledge about drug-induced neuronal adaptations in the brain reward system and the role glucocorticoids may play in this process. Evidence exists that drugs and stress can induce similar changes in excitatory synaptic strength within the mesolimbic dopamine system, suggesting a coordinate mechanism for drugs of abuse and glucocorticoids. The glucocorticoid receptor (GR) plays an essential role in the stress-induced synaptic alterations, and studies using transgenic mice suggest that the GR is a key modulator of the motivation to take drugs and of the behavioral effects of repeated drug intake. The current state of research into the interplay between glucocorticoid hormones and addiction has reached a new phase in which detailed cellular and molecular analyses of the actual mechanisms will become possible. An important role is assigned to the GR, although many issues remain to be addressed, such as the actual site of glucocorticoid action in the brain, the molecular mechanisms and targets of GR-mediated glucocorticoid effects, and their interaction with genetic background.

Neonatal ventral hippocampus lesion leads to reductions in nerve growth factor inducible-B mRNA in the prefrontal cortex and increased amphetamine response in the nucleus accumbens and dorsal striatum

Converging evidence in schizophrenia suggests prefrontal cortical neuronal deficits that correlate with exaggerated subcortical dopamine (DA) functions: Excitotoxic lesion of the ventral hippocampus (VH) in neonatal rats is widely considered a putative animal model of schizophrenia as they lead to characteristic post-pubertal emergence of behavioral and cognitive abnormalities suggesting a developmental change in the neural circuits comprising the prefrontal cortex (PFC) and subcortical DA. Nerve growth factor inducible-B (NGFI-B, also known as Nur77), an orphan nuclear receptor and transcriptional regulator, is constitutively expressed in the target structures of DA pathways. It acts as an immediate early gene with rapid modulation of its mRNA expression by stress, DA and antipsychotic drugs. The present study assessed the effects of neonatal VH (nVH) lesion and amphetamine treatment on the expression of NGFI-B mRNA in pre- and post-pubertal rats. Sprague-Dawley rat pups received bilateral injection of ibotenic acid or phosphate buffered saline in VH at postnatal (PD) 7. At PD35 and PD56, groups of sham and lesioned animals were administered with D-amphetamine (1.5 mg/kg) or saline and killed 20 min later. In situ hybridization analyses showed that the basal level of NGFI-B mRNA in saline-treated lesioned rats was significantly reduced in the medial PFC (mPFC) and cingulate cortex (CC) only at post-pubertal (PD56) age. No significant difference in NGFI-B mRNA levels was seen in the dorsal striatum or nucleus accumbens (NAcc). Amphetamine treatment increased the expression of NGFI-B mRNA in the mPFC, CC, striatum and NAcc in both control and lesioned animals of both ages. Interestingly, however, striatal and NAcc regions of lesioned rats showed a significantly greater effect of amphetamine at PD56. The data suggest that nVH lesions lead to delayed changes in PFC gene expression along with functional DAergic hyperactivity in subcortical regions.

Amyloid suppresses induction of genes critical for memory consolidation in APP + PS1 transgenic mice

Mice transgenic for mutated forms of the amyloid precursor protein (APP) plus presenilin-1 (PS1) genes (APP + PS1 mice) gradually develop memory deficits which correlate with the extent of amyloid deposition. The expression of several immediate-early genes (IEGs: Arc, Nur77 and Zif268) and several other plasticity-related genes (GluR1, CaMKIIalpha and Na-K- ATPase alphaIII) critical for learning and memory was normal in young APP + PS1 mice preceding amyloid deposition, but declined as mice grew older and amyloid deposits accumulated. Gene repression was less in APP + PS1 mouse brain regions that contain less Abeta and in APP mice compared with APP + PS1 mice, further linking the extent of amyloid deposition and the extent of gene repression. Critically, we demonstrated that amyloid deposition led specifically to impaired induction of the IEGs with no effects on basal expression using exposure to a novel environment 30 min prior to being killed to induce IEGs. These data imply that Abeta deposition can selectively reduce expression of multiple genes linked to synaptic plasticity, and provide a molecular basis for memory deficiencies found in transgenic APP mice and, most likely, in early stage Alzheimer's disease (AD). Presumably, pharmacological agents blocking the Abeta-related inhibition of gene expression will have benefit in AD.