Single-Prolonged Stress: A Review of Two Decades of Progress in a Rodent Model of Post-traumatic Stress Disorder

Post-traumatic stress disorder (PTSD) is a common, costly, and often debilitating psychiatric condition. However, the biological mechanisms underlying this disease are still largely unknown or poorly understood. Considerable evidence indicates that PTSD results from dysfunction in highly-conserved brain systems involved in stress, anxiety, fear, and reward. Pre-clinical models of traumatic stress exposure are critical in defining the neurobiological mechanisms of PTSD, which will ultimately aid in the development of new treatments for PTSD. Single prolonged stress (SPS) is a pre-clinical model that displays behavioral, molecular, and physiological alterations that recapitulate many of the same alterations observed in PTSD, illustrating its validity and giving it utility as a model for investigating post-traumatic adaptations and pre-trauma risk and protective factors. In this manuscript, we review the present state of research using the SPS model, with the goals of (1) describing the utility of the SPS model as a tool for investigating post-trauma adaptations, (2) relating findings using the SPS model to findings in patients with PTSD, and (3) indicating research gaps and strategies to address them in order to improve our understanding of the pathophysiology of PTSD.

Mild traumatic brain injury induces apoptotic cell death in the cortex that is preceded by decreases in cellular Bcl-2 immunoreactivity

Although mild traumatic brain injury is associated with behavioral dysfunction and histopathological alterations, few studies have assessed the temporal pattern of regional apoptosis following mild brain injury. Anesthetized rats were subjected to mild lateral fluid-percussion brain injury (1.1-1.3 atm), and brains were evaluated for the presence of in situ DNA fragmentation (terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end-labeling, TUNEL) and morphologic characteristics of apoptotic cell death (nuclear and cytoplasmic condensation, presence of apoptotic bodies). Significant numbers of apoptotic TUNEL(+) cells were observed in the injured parietal cortex and underlying white matter up to 72 h post-injury (P<0.05 compared to sham-injured-injured), with maximal numbers present at 24 h. Apoptosis was confirmed by the presence of 180-200 bp nuclear DNA fragments in tissue homogenates. The appearance of apoptotic TUNEL(+) cells in the injured cortex was preceded by a marked decrease in immunoreactivity for the anti-cell death protein, Bcl-2, as early as 2 h post-injury. This decrease in cellular Bcl-2 staining was not accompanied by a concomitant loss of staining for the pro-cell death Bax protein, suggesting that post-traumatic neuronal death in the cortex may be dependent on altered cellular ratios of Bcl-2:Bax. In the hippocampus, no significant increase in apoptotic TUNEL(+) cells was observed compared to sham-injured-injured animals. However, selective neuronal loss was evident in the CA3 region at 24 h post-injury, that was preceded by an overt loss of neuronal Bcl-2 immunoreactivity at 6 h. No changes in either cellular Bcl-2 or Bax expression were observed in the thalamus or white matter at any time post-injury. Taken together from these data, we suggest that apoptosis contributes to cell death in both gray and white matter, and that decreases in cellular Bcl-2 may, in part, be associated with both apoptotic and non-apoptotic cell death following mild brain trauma.

cAMP response element-binding protein deficiency allows for increased neurogenesis and a rapid onset of antidepressant response

cAMP response element-binding protein (CREB) has been implicated in the molecular and cellular mechanisms of chronic antidepressant (AD) treatment, although its role in the behavioral response is unclear. CREB-deficient (CREB(alpha delta) mutant) mice demonstrate an antidepressant phenotype in the tail suspension test (TST) and forced-swim test. Here, we show that, at baseline, CREB(alpha delta) mutant mice exhibited increased hippocampal cell proliferation and neurogenesis compared with wild-type (WT) controls, effects similar to those observed in WT mice after chronic desipramine (DMI) administration. Neurogenesis was not further augmented by chronic DMI treatment in CREB(alpha delta) mutant mice. Serotonin depletion decreased neurogenesis in CREB(alpha delta) mutant mice to WT levels, which correlated with a reversal of the antidepressant phenotype in the TST. This effect was specific for the reversal of the antidepressant phenotype in these mice, because serotonin depletion did not alter a baseline anxiety-like behavior in CREB(alpha delta) mutant mice. The response to chronic AD treatment in the novelty-induced hypophagia (NIH) test may rely on neurogenesis. Therefore, we used this paradigm to evaluate chronic AD treatment in CREB(alpha delta) mutant mice to determine whether the increased neurogenesis in these mice alters their response in the NIH paradigm. Whereas both WT and CREB(alpha delta) mutant mice responded to chronic AD treatment in the NIH paradigm, only CREB(alpha delta) mutant mice responded to acute AD treatment. However, in the elevated zero maze, DMI did not reverse anxiety behavior in mutant mice. Together, these data show that increased hippocampal neurogenesis allows for an antidepressant phenotype as well as a rapid onset of behavioral responses to AD treatment.

Severe, multimodal stress exposure induces PTSD-like characteristics in a mouse model of single prolonged stress

Appropriate animal models of posttraumatic stress disorder (PTSD) are needed because human studies remain limited in their ability to probe the underlying neurobiology of PTSD. Although the single prolonged stress (SPS) model is an established rat model of PTSD, the development of a similarly-validated mouse model emphasizes the benefits and cross-species utility of rodent PTSD models and offers unique methodological advantages to that of the rat. Therefore, the aims of this study were to develop and describe a SPS model for mice and to provide data that support current mechanisms relevant to PTSD. The mouse single prolonged stress (mSPS) paradigm, involves exposing C57Bl/6 mice to a series of severe, multimodal stressors, including 2h restraint, 10 min group forced swim, exposure to soiled rat bedding scent, and exposure to ether until unconsciousness. Following a 7-day undisturbed period, mice were tested for cue-induced fear behavior, effects of paroxetine on cue-induced fear behavior, extinction retention of a previously extinguished fear memory, dexamethasone suppression of corticosterone (CORT) response, dorsal hippocampal glucocorticoid receptor protein and mRNA expression, and prefrontal cortex glutamate levels. Exposure to mSPS enhanced cue-induced fear, which was attenuated by oral paroxetine treatment. mSPS also disrupted extinction retention, enhanced suppression of stress-induced CORT response, increased mRNA expression of dorsal hippocampal glucocorticoid receptors and decreased prefrontal cortex glutamate levels. These data suggest that the mSPS model is a translationally-relevant model for future PTSD research with strong face, construct, and predictive validity. In summary, mSPS models characteristics relevant to PTSD and this severe, multimodal stress modifies fear learning in mice that coincides with changes in the hypothalamo-pituitary-adrenal (HPA) axis, brain glucocorticoid systems, and glutamatergic signaling in the prefrontal cortex.

Distinct regional and subcellular localization of adenylyl cyclases type 1 and 8 in mouse brain

Adenylyl cyclases (ACs) convert ATP to cAMP and therefore, subserve multiple regulatory functions in the nervous system. AC1 and AC8 are the only cyclases stimulated by calcium and calmodulin, making them uniquely poised to regulate neuronal development and neuronal processes such as learning and memory. Here, we detail the production and application of a novel antibody against mouse AC1. Along with AC8 immunohistochemistry, these data reveal distinct and partially overlapping patterns of protein expression in brain during murine development and adulthood. AC1 protein increased in abundance in the neonatal hippocampus from postnatal days 7-14. By adulthood, abundant AC1 protein expression was observed in the mossy fiber tract in the hippocampus and the molecular layer in the cerebellum, with diffuse expression in the cortex and thalamus. AC8 protein levels were abundant during development, with diffuse and increasing expression in the hippocampus that intensified in the CA1/CA2 region by adulthood. AC8 expression was weak in the cerebellum at postnatal day 7 and decreased further by postnatal day 14. Analysis of synaptosome fractions from the adult brain demonstrated robust expression of AC1 in the postsynaptic density and extrasynaptic regions, while expression of AC8 was observed in the presynaptic active zone and extrasynaptic fractions. These findings were confirmed with localization of AC1 and/or AC8 with PSD-95, tau, synaptophysin and microtubule-associated protein-2 (MAP-2) expression throughout the brain. Together, these data provide insight into the functional roles of AC1 and AC8 in mice as reflected by their distinct localization in cellular and subcellular compartments.

Hyperglycemia in stroke and possible treatments

Hyperglycemia affects approximately one-third of acute ischemic stroke patients and is associated with poor clinical outcomes. In experimental and clinical stroke studies, hyperglycemia has been shown to be detrimental to the penumbral tissue for several reasons. First, hyperglycemia exacerbates both calcium imbalance and the accumulation of reactive oxygen species (ROS) in neurons, leading to increased apoptosis. Second, hyperglycemia fuels anaerobic energy production, causing lactic acidosis, which further stresses neurons in the penumbral regions. Third, hyperglycemia decreases blood perfusion after ischemic stroke by lowering the availability of nitric oxide (NO), which is a crucial mediator of vasodilation. Lastly, hyperglycemia intensifies the inflammatory response after stroke, causing edema, and hemorrhage through disruption of the blood brain barrier and degradation of white matter, which leads to a worsening of functional outcomes. Many neuroprotective treatments addressing hyperglycemia in stroke have been implemented in the past decade. Early clinical use of insulin provided mixed results due to insufficiently controlled glucose levels and heterogeneity of patient population. Recently, however, the latest Stroke Hyperglycemia Insulin Network Effort trial has addressed the shortcomings of insulin therapy. While glucagon-like protein-1 administration, hyperbaric oxygen preconditioning, and ethanol therapy appear promising, these treatments remain in their infancy and more research is needed to better understand the mechanisms underlying hyperglycemia-induced injuries. Elucidation of these mechanistic pathways could lead to the development of rational treatments that reduce hyperglycemia-associated injuries and improve functional outcomes for ischemic stroke patients.

Experimental traumatic brain injury alters ethanol consumption and sensitivity

Altered alcohol consumption patterns after traumatic brain injury (TBI) can lead to significant impairments in TBI recovery. Few preclinical models have been used to examine alcohol use across distinct phases of the post-injury period, leaving mechanistic questions unanswered. To address this, the aim of this study was to describe the histological and behavioral outcomes of a noncontusive closed-head TBI in the mouse, after which sensitivity to and consumption of alcohol were quantified, in addition to dopaminergic signaling markers. We hypothesized that TBI would alter alcohol consumption patterns and related signal transduction pathways that were congruent to clinical observations. After midline impact to the skull, latency to right after injury, motor deficits, traumatic axonal injury, and reactive astrogliosis were evaluated in C57BL/6J mice. Amyloid precursor protein (APP) accumulation was observed in white matter tracts at 6, 24, and 72 h post-TBI. Increased intensity of glial fibrillary acidic protein (GFAP) immunoreactivity was observed by 24 h, primarily under the impact site and in the nucleus accumbens, a striatal subregion, as early as 72 h, persisting to 7 days, after TBI. At 14 days post-TBI, when mice were tested for ethanol sensitivity after acute high-dose ethanol (4 g/kg, intraperitoneally), brain-injured mice exhibited increased sedation time compared with uninjured mice, which was accompanied by deficits in striatal dopamine- and cAMP-regulated neuronal phosphoprotein, 32 kDa (DARPP-32) phosphorylation. At 17 days post-TBI, ethanol intake was assessed using the Drinking-in-the-Dark paradigm. Intake across 7 days of consumption was significantly reduced in TBI mice compared with sham controls, paralleling the reduction in alcohol consumption observed clinically in the initial post-injury period. These data demonstrate that TBI increases sensitivity to ethanol-induced sedation and affects downstream signaling mediators of striatal dopaminergic neurotransmission while altering ethanol consumption. Examining TBI effects on ethanol responsitivity will improve our understanding of alcohol use post-TBI in humans.

Inducible cAMP early repressor regulates corticosterone suppression after tricyclic antidepressant treatment

The cAMP-response element binding protein (CREB) is involved in antidepressant action, but the role of related CRE-binding transcription factors in the behavioral and endocrine responses to antidepressants is unclear. Alternative transcription of the cAMP response element-modulator (CREM) gene yields activator and repressor isoforms, including the strong repressor inducible cAMP early repressor (ICER). ICER is highly expressed in hypothalamic tissues and upregulated after electroconvulsive seizure. Thus, ICER may be a novel mediator of antidepressant action at endocrine and/or behavioral levels. Here we establish that both subchronic and chronic desipramine (DMI) treatments upregulate hypothalamic ICER expression in wild-type mice. Behavioral responses to DMI in the forced swim and tail suspension tests are unchanged in mice lacking ICER. However, the ability of DMI to suppress an acute corticosterone response after swim stress is compromised in ICER-deficient mice, suggesting that increased hypothalamic ICER mRNA after DMI treatment may be required for suppression of corticosterone release. To investigate the mechanism underlying this response, we measured corticotropin releasing factor (CRF), an upstream modulator of corticosterone release. Using real-time quantitative PCR, we establish that hypothalamic CRF expression is significantly reduced after swim exposure in DMI-treated wild-type mice, however DMI is unable to blunt hypothalamic CRF expression in ICER-deficient mice. Furthermore, we demonstrate that ICER is enriched in CRF-expressing neurons in the paraventricular nucleus of the hypothalamus. These data indicate that ICER is required for DMI to reduce stress-induced corticosterone release through regulation of hypothalamic CRF expression, revealing a novel role for ICER in antidepressant regulation of the hypothalamic-pituitary adrenal axis.

Single-Prolonged Stress Impairs Prefrontal Cortex Control of Amygdala and Striatum in Rats

Medial prefrontal cortex (mPFC), amygdala, and striatum neurocircuitry has been shown to play an important role in post-traumatic stress disorder (PTSD) pathology in humans. Clinical studies show hypoactivity in the mPFC and hyperactivity in the amygdala and striatum of PTSD patients, which has been associated with decreased mPFC glutamate levels. The ability to refine neurobiological characteristics of PTSD in an animal model is critical in furthering our mechanistic understanding of the disease. To this end, we exposed male rats to single-prolonged stress (SPS), a validated model of PTSD, and hypothesized that traumatic stress would differentially activate mPFC subregions [prelimbic (PL) and infralimbic (IL) cortices] and increase striatal and amygdalar activity, which would be associated with decreased mPFC glutamate levels. in vivo, neural activity in the subregions of the mPFC, amygdala, and striatum was measured using manganese-enhanced magnetic resonance imaging (MEMRI), and glutamate and N-acetylaspartate (NAA) levels in the mPFC and the dorsal striatum (dSTR) were measured using proton magnetic resonance spectroscopy (1H-MRS) longitudinally, in rats exposed to SPS or control conditions. As hypothesized, SPS decreased MEMRI-based neural activity in the IL, but not PL, cortex concomitantly increasing activity within the basolateral amygdala (BLA) and dorsomedial striatum (dmSTR). 1H-MRS studies in a separate cohort revealed SPS decreased glutamate levels in the mPFC and increased NAA levels in the dSTR. These results confirm previous findings that suggest SPS causes mPFC hypoactivation as well as identifies concurrent hyperactivation in dmSTR and BLA, effects which parallel the clinical neuropathology of PTSD.

Adenylyl cyclases 1 and 8 initiate a presynaptic homeostatic response to ethanol treatment

BACKGROUND

Although ethanol exerts widespread action in the brain, only recently has progress been made in understanding the specific events occurring at the synapse during ethanol exposure. Mice deficient in the calcium-stimulated adenylyl cyclases, AC1 and AC8 (DKO), demonstrate increased sedation duration and impaired phosphorylation by protein kinase A (PKA) following acute ethanol treatment. While not direct targets for ethanol, we hypothesize that these cyclases initiate a homeostatic presynaptic response by PKA to reactivate neurons from ethanol-mediated inhibition.

METHODOLOGY/PRINCIPAL FINDINGS

Here, we have used phosphoproteomic techniques and identified several presynaptic proteins that are phosphorylated in the brains of wild type mice (WT) after ethanol exposure, including synapsin, a known PKA target. Phosphorylation of synapsins I and II, as well as phosphorylation of non-PKA targets, such as, eukaryotic elongation factor-2 (eEF-2) and dynamin is significantly impaired in the brains of DKO mice. This deficit is primarily driven by AC1, as AC1-deficient, but not AC8-deficient mice also demonstrate significant reductions in phosphorylation of synapsin and eEF-2 in cortical and hippocampal tissues. DKO mice have a reduced pool of functional recycling vesicles and fewer active terminals as measured by FM1-43 uptake compared to WT controls, which may be a contributing factor to the impaired presynaptic response to ethanol treatment.

CONCLUSIONS/SIGNIFICANCE

These data demonstrate that calcium-stimulated AC-dependent PKA activation in the presynaptic terminal, primarily driven by AC1, is a critical event in the reactivation of neurons following ethanol-induced activity blockade.

Regulation of Antidepressant Activity by cAMP Response Element Binding Proteins

Depression is a clinically and biologically heterogeneous disease that is one of the most prevalent and costly psychiatric disorders. It is the leading cause of disability regarding job performance and burden on family members in the United States and worldwide. Although the therapeutic efficacy of antidepressant drugs has been recognized for years, the exact molecular mechanisms of action remain elusive, making the systematic approach to the development of new drugs difficult. The acute increases in levels of monoamines brought about by various classes of antidepressants cannot account for the requirement of repeated, chronic administration for up to 2-6 wk before treatment benefits become evident. Furthermore, despite their efficacy, current antidepressant drugs improve symptoms in only 60% of patients treated. The development of new and better therapies depends on a thorough understanding of the neurobiology of depression and the molecular mechanisms underlying antidepressant drug action. Early studies focusing on alterations in the levels of receptors and second messengers helped define the important signaling pathways initiated by these drugs, whereas recent molecular studies suggested that long-term adaptations in cellular signaling mechanisms may be required for the onset and/or maintenance of antidepressant effects. Attention has now focused on downstream targets of Ca++ and cyclic adenosine monophosphate (cAMP) in the cell, such as the activation of transcription factors. This article discusses the transcription factor cAMP response element binding protein and a related protein, cyclic AMP response element modulator, and their roles as molecular mediators of antidepressant action.

Cocaine-induced locomotor sensitization in rats correlates with nucleus accumbens activity on manganese-enhanced MRI

A long-standing goal of substance abuse research has been to link drug-induced behavioral outcomes with the activity of specific brain regions to understand the neurobiology of addiction behaviors and to search for drug-able targets. Here, we tested the hypothesis that cocaine produces locomotor (behavioral) sensitization that correlates with increased calcium channel-mediated neuroactivity in brain regions linked with drug addiction, such as the nucleus accumbens (NAC), anterior striatum (AST) and hippocampus, as measured using manganese-enhanced MRI (MEMRI). Rats were treated with cocaine for 5 days, followed by a 2-day drug-free period. The following day, locomotor sensitization was quantified as a metric of cocaine-induced neuroplasticity in the presence of manganese. Immediately following behavioral testing, rats were examined for changes in calcium channel-mediated neuronal activity in the NAC, AST, hippocampus and temporalis muscle, which was associated with behavioral sensitization using MEMRI. Cocaine significantly increased locomotor activity and produced behavioral sensitization compared with saline treatment of control rats. A significant increase in MEMRI signal intensity was determined in the NAC, but not AST or hippocampus, of cocaine-treated rats compared with saline-treated control rats. Cocaine did not increase signal intensity in the temporalis muscle. Notably, in support of our hypothesis, behavior was significantly and positively correlated with MEMRI signal intensity in the NAC. As neuronal uptake of manganese is regulated by calcium channels, these results indicate that MEMRI is a powerful research tool to study neuronal activity in freely behaving animals and to guide new calcium channel-based therapies for the treatment of cocaine abuse and dependence.

The mouse nac1 gene, encoding a cocaine-regulated bric-a-brac tramtrac broad complex/pox virus and zinc finger protein, is regulated by ap1

NAC1 cDNA was identified as a novel transcript induced in the nucleus accumbens from rats chronically treated with cocaine. NAC1 is a member of the Bric-a-brac Tramtrac Broad complex/Pox virus and Zinc finger family of transcription factors and has been shown by overexpression studies to prevent the development of behavioral sensitization resulting from repeated cocaine treatment. This paper reports the cloning and characterization of the corresponding gene. The mouse Nac1 gene consist of six exons, with exon 2 containing an alternative splice donor, providing a molecular explanation of the splice variants observed in mouse and rat. Transcripts of Nac1 were ubiquitously detected in different mouse tissues with prominent expression in the brain. The mouse Nac1 gene was localized to chromosome 8, suggesting a highly plausible candidate gene to explain differences in cocaine-induced behaviors between C57BL6/J and DBA/2J mice that had previously been mapped to the area. In addition, a functional AP1 binding site has been identified in an intron 1 enhancer of the Nac1 gene that plays an essential role in the activation of the gene in differentiation of neuroblastoma cells. Co-transfection with c-jun and c-fos expression plasmids, which encode the two subunits of AP1, activated the wild type Nac1 intron 1 enhancer two-fold over basal, nearly at the level of NAC1 enhancer activity seen in differentiated N2A cells. Mutation of the AP1 site completely abrogated all activation of the NAC1 enhancer in differentiated N2A cells. Activation of immediate early genes such as c-fos and c-jun following chronic drug treatments has been well characterized. The present data describe one potential regulatory cascade involving these transcription factors and activation of NAC1. Identification of drug induced alterations in gene expression is key to understanding the types of molecular adaptations underlying addiction.

Deficits in behavioral sensitization and dopaminergic responses to methamphetamine in adenylyl cyclase 1/8-deficient mice

The cAMP/protein kinase A pathway regulates methamphetamine (METH)-induced neuroplasticity underlying behavioral sensitization. We hypothesize that adenylyl cyclases (AC) 1/8 mediate these neuroplastic events and associated striatal dopamine regulation. Locomotor responses to METH (1 and 5 mg/kg) and striatal dopamine function were evaluated in mice lacking AC 1/8 (DKO) and wild-type (WT) mice. Only 5 mg/kg METH induced an acute locomotor response in DKO mice, which was significantly attenuated versus WT controls. DKO mice showed a marked attenuation in the development and expression of METH-induced behavioral sensitization across doses relative to WT controls. While basal and acute METH (5 mg/kg)-evoked accumbal dialysate dopamine levels were similar between genotypes, saline-treated DKO mice showed elevated tissue content of dopamine and homovanillic acid in the dorsal striatum (DS), reflecting dysregulated dopamine homeostasis and/or metabolism. Significant reductions in DS dopamine levels were observed in METH-sensitized DKO mice compared to saline-treated controls, an effect not observed in WT mice. Notably, saline-treated DKO mice had significantly increased phosphorylated Dopamine- and cAMP-regulated phosphoprotein levels, which were not further augmented following METH sensitization, as observed in WT mice. These data indicate that AC 1/8 are critical to mechanisms subserving drug-induced behavioral sensitization and mediate nigrostriatal pathway METH sensitivity. Calcium/calmodulin-stimulated adenylyl cyclase (AC) isoforms 1 and 8 were studied for their involvement in the adaptive neurobehavioral responses to methamphetamine. AC 1/8 double knockout (DKO) mice showed heightened basal locomotor activity and dorsal striatal dopamine responsivity. Conversely, methamphetamine-induced locomotor activity was attenuated in DKO mice, accompanied by reductions in dopamine and HVA content and impaired DARPP-32 activation. These findings indicate AC 1/8 signaling regulates the sensitivity of the nigrostriatal pathway subserving stimulant and neuroadaptive sensitizing effects of methamphetamine. 3-MT, 3-methoxytyramine; Ca(2+), calcium; CaM, calmodulin; cdk5; cyclin-dependent kinase 5; DA, dopamine; DARPP-32, dopamine- and cAMP-regulated phosphoprotein; D1R, dopamine D1 receptor; HVA, homovanillic acid; PKA, protein kinase A.

Postnatal ethanol exposure simplifies the dendritic morphology of medium spiny neurons independently of adenylyl cyclase 1 and 8 activity in mice

BACKGROUND

Fetal exposure to alcohol can have multiple deleterious effects, including learning disorders and behavioral and executive functioning abnormalities, collectively termed fetal alcohol spectrum disorders. Neonatal mice lacking both calcium-/calmodulin-stimulated adenylyl cyclases (ACs) 1 and 8 demonstrate increased vulnerability to ethanol (EtOH)-induced neurotoxicity in the striatum compared with wild-type (WT) controls. However, the developmental impact on surviving neurons is still unclear.

METHODS

WT and AC1/8 double knockout (DKO) mice were administered 1 dose of EtOH (2.5 g/kg) between postnatal days 5 to 7 (P5-7). At P30, brains were removed and processed for Golgi-Cox staining. Medium spiny neurons (MSNs) from the caudate putamen were analyzed for changes in dendritic complexity; number of branches, branch points and terminals, total and average dendritic length; spine density and soma size.

RESULTS

EtOH significantly reduced the dendritic complexity and soma size in surviving MSNs regardless of genotype without affecting spine density. In the absence of EtOH, genetic deletion of AC1/8 reduced the dendritic complexity, number of branch points, spine density, and soma size of MSNs compared with WT controls.

CONCLUSIONS

These data indicate that neonatal exposure to a single dose of EtOH is sufficient to cause long-term alterations in the dendritic complexity of MSNs and that this outcome is not altered by the functional status of AC1 and AC8. Therefore, although deletion of AC1/8 demonstrates a role for the ACs in normal morphologic development and EtOH-induced neurodegeneration, loss of AC1/8 activity does not exacerbate the effects of EtOH on dendritic morphology or spine density.

Investigation of calcium-stimulated adenylyl cyclases 1 and 8 on toluene and ethanol neurobehavioral actions

The abused inhalant toluene has potent behavioral effects, but only recently has progress been made in understanding the molecular pathways that mediate the action of toluene in the brain. Toluene and ethanol induce similar behavioral effects and share some targets including NMDA and GABA receptors. In studies examining neuronal actions of ethanol, mice lacking the calcium-stimulated adenylyl cyclases (ACs), AC1 and AC8 (DKO), show increased sedation durations and impaired protein kinase A (PKA) phosphorylation following acute ethanol treatment. Therefore, using DKO mice, we compared the neurobehavioral responses following toluene exposure to that of ethanol exposure to determine if these abused substances share molecular mechanisms of action. In the present study, acute sensitivity to toluene- or ethanol-induced changes in locomotor activity was evaluated in DKO and wild type (WT) mice. Mice were exposed to toluene vapor (0, 500, 1000, 2000, 6000, or 8000ppm) for 30min in static exposure chambers equipped with activity monitors. Both WT and DKO mice demonstrated increased ambulatory distance during exposure to a 2000-ppm concentration of toluene compared to respective air-exposed (0ppm) controls. Significant increases in locomotor activity were also observed during an air-only recovery period following toluene exposure in WT and DKO mice that had been exposed to 2000ppm of toluene compared to respective air controls. Sedative effects of toluene were equivalent in WT and DKO mice, both during exposure and afterwards during recovery. Although no significant differences in locomotor activity were detected in DKO compared to WT mice at individual doses tested, a significant main effect of toluene was achieved, with DKO mice demonstrating a generalized reduction in locomotor activity during the post-toluene recovery period compared to WT mice (when analyzing all doses collectively). For comparison to toluene, additional WT and DKO mice were treated with 1.0 or 2.0g/kg ethanol (i.p.) and monitored for locomotor activation. In WT mice, both doses of ethanol increased distance traveled compared to saline controls. Conversely, DKO mice demonstrated no increase in locomotor activation at 1.0g/kg, with significantly reduced distances traveled at both doses compared to ethanol-treated WT mice. These behavioral activity results suggest that acute effects of ethanol and toluene are distinct in the mechanisms by which they induce acute sedating effects with respect to AC1 and AC8 activity, but may be similar in the mechanisms subserving locomotor stimulation.

Repeated stress exposure in mid-adolescence attenuates behavioral, noradrenergic, and epigenetic effects of trauma-like stress in early adult male rats

Stress in adolescence can regulate vulnerability to traumatic stress in adulthood through region-specific epigenetic activity and catecholamine levels. We hypothesized that stress in adolescence would increase adult trauma vulnerability by impairing extinction-retention, a deficit in PTSD, by (1) altering class IIa histone deacetylases (HDACs), which integrate effects of stress on gene expression, and (2) enhancing norepinephrine in brain regions regulating cognitive effects of trauma. We investigated the effects of adolescent-stress on adult vulnerability to severe stress using the single-prolonged stress (SPS) model in male rats. Rats were exposed to either (1) adolescent-stress (33-35 postnatal days) then SPS (58-60 postnatal days; n = 14), or (2) no adolescent-stress and SPS (58-60 postnatal days; n = 14), or (3) unstressed conditions (n = 8). We then measured extinction-retention, norepinephrine, HDAC4, and HDAC5. As expected, SPS exposure induced an extinction-retention deficit. Adolescent-stress prior to SPS eliminated this deficit, suggesting adolescent-stress conferred resiliency to adult severe stress. Adolescent-stress also conferred region-specific resilience to norepinephrine changes. HDAC4 and HDAC5 were down-regulated following SPS, and these changes were also modulated by adolescent-stress. Regulation of HDAC levels was consistent with the pattern of cognitive effects of SPS; only animals exposed to SPS without adolescent-stress exhibited reduced HDAC4 and HDAC5 in the prelimbic cortex, hippocampus, and striatum. Thus, HDAC regulation caused by severe stress in adulthood interacts with stress history such that seemingly conflicting reports describing effects of adolescent stress on adult PTSD vulnerability may stem in part from dynamic HDAC changes following trauma that are shaped by adolescent stress history.

Impaired Ethanol-Induced Sensitization and Decreased Cannabinoid Receptor-1 in a Model of Posttraumatic Stress Disorder

BACKGROUND AND PURPOSE

Impaired striatal neuroplasticity may underlie increased alcoholism documented in those with posttraumatic stress disorder (PTSD). Cannabinoid receptor-1 (CB1) is sensitive to the effects of ethanol (EtOH) and traumatic stress, and is a critical regulator of striatal plasticity. To investigate CB1 involvement in the PTSD-alcohol interaction, this study measured the effects of traumatic stress using a model of PTSD, mouse single-prolonged stress (mSPS), on EtOH-induced locomotor sensitization and striatal CB1 levels.

METHODS

Mice were exposed to mSPS, which includes: 2-h restraint, 10-min group forced swim, 15-min exposure to rat bedding odor, and diethyl ether exposure until unconsciousness or control conditions. Seven days following mSPS exposure, the locomotor sensitizing effects of EtOH were assessed. CB1, post-synaptic density-95 (PSD95), and dopamine-2 receptor (D2) protein levels were then quantified in the dorsal striatum using standard immunoblotting techniques.

RESULTS

Mice exposed to mSPS-EtOH demonstrated impaired EtOH-induced locomotor sensitization compared to Control-EtOH mice, which was accompanied by reduced striatal CB1 levels. EtOH increased striatal PSD95 in control and mSPS-exposed mice. Additionally, mSPS-Saline exposure increased striatal PSD95 and decreased D2 protein expression, with mSPS-EtOH exposure alleviating these changes.

CONCLUSIONS

These data indicate that the mSPS model of PTSD blunts the behavioral sensitizing effects of EtOH, a response that suggests impaired striatal neuroplasticity. Additionally, this study demonstrates that mice exposed to mSPS and repeated EtOH exposure decreases CB1 in the striatum, providing a mechanism of interest for understanding the effects of EtOH following severe, multimodal stress exposure.

Adenylyl cylases 1 and 8 mediate select striatal-dependent behaviors and sensitivity to ethanol stimulation in the adolescent period following acute neonatal ethanol exposure

Neonatal alcohol exposure in rodents causes dramatic neurodegenerative effects throughout the developing nervous system, particularly in the striatum, acutely after exposure. These acute neurodegenerative effects are augmented in mice lacking adenylyl cyclases 1 and 8 (AC1/8) as neonatal mice with a genetic deletion of both AC isoforms (DKO) have increased vulnerability to ethanol-induced striatal neurotoxicity compared to wild type (WT) controls. While neonatal ethanol exposure is known to negatively impact cognitive behaviors, such as executive functioning and working memory in adolescent and adult animals, the threshold of ethanol exposure required to impinge upon developmental behaviors in mice has not been extensively examined. Therefore, the purpose of this study was to determine the behavioral effects of neonatal ethanol exposure using various striatal-dependent developmental benchmarks and to assess the impact of AC1/8 deletion on this developmental progression. WT and DKO mice were treated with 2.5 g/kg ethanol or saline on postnatal day (P)6 and later subjected to the wire suspension, negative geotaxis, postural reflex, grid hang, tail suspension and accelerating rotarod tests at various time points. At P30, mice were evaluated for their hypnotic responses to 4.0 g/kg ethanol by using the loss of righting reflex assay and ethanol-induced stimulation of locomotor activity after 2.0 g/kg ethanol. Ethanol exposure significantly impaired DKO performance in the negative geotaxis test while genetic deletion of AC1/8 alone increased grid hang time and decreased immobility time in the tail suspension test with a concomitant increase in hindlimb clasping behavior. Locomotor stimulation was significantly increased in animals that received ethanol as neonates, peaking significantly in ethanol-treated DKO mice compared to ethanol-treated WT controls, while sedation duration following high-dose ethanol challenge was unaffected. These data indicate that the maturational parameters examined in the current study may not be sensitive enough to detect effects of a single ethanol exposure during the brain growth spurt period. Genetic deletion of AC1/8 reveals a role for these cylases in attenuating ethanol-induced behavioral effects in the neonatally-exposed adolescent.

Age-related murine hippocampal CA1 laminae oxidative stress measured in vivo by QUEnch-assiSTed (QUEST) MRI: impact of isoflurane anesthesia

Age-related impairments in spatial learning and memory often precede non-familial neurodegenerative disease. Ex vivo studies suggest that physiologic age-related oxidative stress in hippocampus area CA1 may contribute to prodromal spatial disorientation and to morbidity. Yet, conventional blood or cerebrospinal fluid assays appear insufficient for early detection or management of oxidative stress within CA1 sub-regions in vivo. Here, we address this biomarker problem using a non-invasive MRI index of CA1 laminae oxidative stress based on reduction in R1 (= 1/T1) after anti-oxidant administration. An R1 reduction reflects quenching of continuous and excessive production of endogenous paramagnetic free radicals. Careful motion-correction image acquisition, and avoiding repeated exposure to isoflurane, facilitates detection of hippocampus CA1 laminae oxidative stress with QUEnch-assiSTed (QUEST) MRI. Intriguingly, age- and isoflurane-related oxidative stress is localized to the stratum lacunosum of the CA1 region. Our data raise the possibility of using QUEST MRI and FDA-approved anti-oxidants to remediate spatial disorientation and later neurodegeneration with age in animals and humans.

Divergent effects of repeated cocaine and novel environment exposure on locus coeruleus c-fos expression and brain catecholamine concentrations in rats

INTRODUCTION

Chronic administration of cocaine causes a disinhibited, hyperexploratory response to novel environments. As the norepinephrine (NE) system regulates exploration and is dysregulated following cocaine exposure, we hypothesized that this cocaine-mediated hyperexploratory response is associated with increased locus coeruleus (LC) reactivity.

METHODS

To test this hypothesis, we used dual fluorescent in situ hybridization immunofluorescence to analyze novelty-induced c-fos and tyrosine hydroxylase expression in the LC and high-pressure liquid chromatography to measure dopamine (DA) and NE concentrations in key catecholamine projection regions following exposure to cocaine.

RESULTS

Repeated cocaine exposure followed by a 14-day drug-free period increased exploration of novel environments, replicating previous findings. Novelty exposure increased LC c-fos expression, increased anterior cingulate NE, and decreased ventral tegmental area DA. Cocaine exposure decreased amygdala (AMY) DA, but had no effect on LC c-fos expression or NE in any tested brain region. No interactions between cocaine and novelty were found. Open arm exploration was positively correlated with LC c-fos expression and NE concentrations in both the anterior cingulate and nucleus accumbens, and negatively correlated with AMY DA concentration.

CONCLUSIONS

Our findings confirm that exposure to novel environments increases LC activity and NE in the anterior cingulate cortex, that long-term exposure to cocaine dysregulates AMY DA, and that disinhibited exploration in novel environments correlates with NE and DA in regions that modulate risk-taking and avoidance behavior. Further studies investigating the effects of cocaine on brain catecholamine systems are important in understanding the long-lasting effects of cocaine on brain function.

Calcium/calmodulin-stimulated adenylyl cyclases 1 and 8 regulate reward-related brain activity and ethanol consumption

Evidence suggests a predictive link between elevated basal activity within reward-related networks (e.g., cortico-basal ganglia-thalamic networks) and vulnerability for alcoholism. Both calcium channel function and cyclic adenosine monophosphate (cAMP)/protein kinase A-mediated signaling are critical modulators of reward neurocircuitry and reward-related behaviors. Calcium/calmodulin-stimulated adenylyl cyclases (AC) 1 and 8 are sensitive to activity-dependent increases in intracellular calcium and catalyze cAMP production. Therefore, we hypothesized AC1 and 8 regulate brain activity in reward regions of the cortico-basal ganglia-thalamic circuit and that this regulatory influence predicts voluntary ethanol drinking responses. This hypothesis was evaluated by manganese-enhanced magnetic resonance imaging and chronic, intermittent ethanol access procedures. Ethanol-naïve mice with genetic deletion of both AC1 and 8 (DKO mice) exhibited bilateral reductions in baseline activity within cortico-basal ganglia-thalamic regions associated with reward processing compared to wild-type controls (WT, C57BL/6 mice). Significant activity changes were not evident in regions either outside of the cortico-basal ganglia-thalamic network or within the network that are not associated with reward processing. Parallel studies demonstrated that reward network hypoactivity in DKO mice predicted a significant attenuation in consumption and preference levels to escalating ethanol concentrations (12, 20 and 30%) compared to WT mice, an effect that was maintained over extended access (14 sessions) to 20% ethanol. Summarizing, these data support a contribution of AC1 and 8 in cortico-basal ganglia-thalamic activity and the predictive value of this regulatory influence on ethanol drinking behavior, which merits the future evaluation of calcium-stimulated ACs in the neural processes that engender vulnerability to maladaptive alcohol drinking.

Requirement for the POZ/BTB protein NAC1 in acute but not chronic psychomotor stimulant response

NAC1 is a novel member of the POZ/BTB (Pox virus and Zinc finger/Bric-a-bracTramtrack Broad complex) but varies from other proteins of this class in that it lacks the characteristic DNA-binding motif, suggesting a novel role. We have employed constitutive gene deletion to elucidate the role of NAC1 in vivo. Nac1 mutant mice are viable with no obvious developmental or physiological impairments. Previous studies suggest a role for NAC1 in cocaine-mediated behaviors. Therefore, we evaluated a variety of behaviors associated with psychomotor stimulant effects in Nac1 mutant mice. Acute locomotor activating effects of cocaine or amphetamine are absent in Nac1 mutant mice, however longer exposure to these psychomotor stimulants result in the development of behavioral sensitization. Acute rewarding properties of cocaine and amphetamine are also blunted in mutant mice, yet repeated exposure resulted in conditioned place preference similar to that observed in wild-type mice. Lastly, increases in extracellular dopamine in the nucleus accumbens, which accompany acute cocaine administration, are blunted in mutant mice, but following chronic cocaine extracellular dopamine levels are increased to the same extent as in wild-type mice. Together these data indicate involvement of NAC1 in the acute behavioral and neurochemical responses to psychomotor stimulants.

Adenylyl Cyclase 1 Is Required for Ethanol-Induced Locomotor Sensitization and Associated Increases in NMDA Receptor Phosphorylation and Function in the Dorsal Medial Striatum

Neuroadaptive responses to chronic ethanol, such as behavioral sensitization, are associated with N-methyl-D-aspartate receptor (NMDAR) recruitment. Ethanol enhances GluN2B-containing NMDAR function and phosphorylation (Tyr-1472) of the GluN2B-NMDAR subunit in the dorsal medial striatum (DMS) through a protein kinase A (PKA)-dependent pathway. Ethanol-induced phosphorylation of PKA substrates is partially mediated by calcium-stimulated adenylyl cyclase 1 (AC1), which is enriched in the dorsal striatum. As such, AC1 is poised as an upstream modulator of ethanol-induced DMS neuroadaptations that promote drug responding, and thus represents a therapeutic target. Our hypothesis is that loss of AC1 activity will prevent ethanol-induced locomotor sensitization and associated DMS GluN2B-NMDAR adaptations. We evaluated AC1's contribution to ethanol-evoked locomotor responses and DMS GluN2B-NMDAR phosphorylation and function using AC1 knockout (AC1KO) mice. Results were mechanistically validated with the AC1 inhibitor, NB001. Acute ethanol (2.0 g/kg) locomotor responses in AC1KO and wild-type (WT) mice pretreated with NB001 (10 mg/kg) were comparable to WT ethanol controls. However, repeated ethanol treatment (10 days, 2.5 g/kg) failed to produce sensitization in AC1KO or NB001 pretreated mice, as observed in WT ethanol controls, following challenge exposure (2.0 g/kg). Repeated exposure to ethanol in the sensitization procedure significantly increased pTyr-1472 GluN2B levels and GluN2B-containing NMDAR transmission in the DMS of WT mice. Loss of AC1 signaling impaired ethanol-induced increases in DMS pGluN2B levels and NMDAR-mediated transmission. Together, these data support a critical and specific role for AC1 in striatal signaling that mediates ethanol-induced behavioral sensitization, and identify GluN2B-containing NMDARs as an important AC1 target.