Inhibition of p75 neurotrophin receptor does not rescue cognitive impairment in adulthood after isoflurane exposure in neonatal mice.

BACKGROUND: Isoflurane is widely used for anaesthesia in humans. Isoflurane exposure of rodents prior to post-natal day 7 (PND7) leads to widespread neurodegeneration in laboratory animals. Previous data from our laboratory suggest an attenuation of apoptosis with the p75 neurotrophin receptor (p75NTR) inhibitor TAT-Pep5. We hypothesized that isoflurane toxicity leads to behavioural and cognitive abnormalities and can be rescued with pre-anaesthesia administration of TAT-Pep5. METHODS: Neonatal mouse pups were pretreated with either TAT-Pep5 (25 µl, 10 µM i.p.) or a scrambled control peptide (TAT-ctrl; 25 µl, 10 µM i.p.) prior to isoflurane exposure (1.4%; 4 h) or control ( n = 15-26/group). Three to 5 months after exposure, behavioural testing and endpoint assays [brain volume (stereology) and immunoblotting] were performed. RESULTS: No significant difference was observed in open field, T-maze, balance beam or wire-hanging testing. The Barnes maze revealed a significant effect of isoflurane ( P = 0.019) in errors to find the escape tunnel during the day 5 probe trial, a finding indicative of impaired short-term spatial memory. No difference was found for brain volumes or protein expression. TAT-Pep5 treatment did not reverse the effects of isoflurane on neurocognitive behaviour. CONCLUSION: A single isoflurane exposure to early post-natal mice caused a hippocampal-dependent memory deficit that was not prevented by pre-administration of TAT-Pep5, although TAT-Pep5, an inhibitor of p75NTR, has been shown to reduce isoflurane-induced apoptosis. These findings suggest that neuronal apoptosis is not requisite for the development of cognitive deficits in the adults attendant with neonatal anaesthetic exposure.

Gene networks specific for innate immunity define post-traumatic stress disorder.

The molecular factors involved in the development of Post-Traumatic Stress Disorder (PTSD) remain poorly understood. Previous transcriptomic studies investigating the mechanisms of PTSD apply targeted approaches to identify individual genes under a cross-sectional framework lack a holistic view of the behaviours and properties of these genes at the system-level. Here we sought to apply an unsupervised gene-network based approach to a prospective experimental design using whole-transcriptome RNA-Seq gene expression from peripheral blood leukocytes of U.S. Marines (N=188), obtained both pre- and post-deployment to conflict zones. We identified discrete groups of co-regulated genes (i.e., co-expression modules) and tested them for association to PTSD. We identified one module at both pre- and post-deployment containing putative causal signatures for PTSD development displaying an over-expression of genes enriched for functions of innate-immune response and interferon signalling (Type-I and Type-II). Importantly, these results were replicated in a second non-overlapping independent dataset of U.S. Marines (N=96), further outlining the role of innate immune and interferon signalling genes within co-expression modules to explain at least part of the causal pathophysiology for PTSD development. A second module, consequential of trauma exposure, contained PTSD resiliency signatures and an over-expression of genes involved in hemostasis and wound responsiveness suggesting that chronic levels of stress impair proper wound healing during/after exposure to the battlefield while highlighting the role of the hemostatic system as a clinical indicator of chronic-based stress. These findings provide novel insights for early preventative measures and advanced PTSD detection, which may lead to interventions that delay or perhaps abrogate the development of PTSD.

Selection for contextual fear conditioning affects anxiety-like behaviors and gene expression.

Conditioned fear and anxiety-like behaviors have many similarities at the neuroanatomical and pharmacological levels, but their genetic relationship is less well defined. We used short-term selection for contextual fear conditioning (FC) to produce outbred mouse lines with robust genetic differences in FC. The high and low selected lines showed differences in fear learning that were stable across various training parameters and were not secondary to differences in sensitivity to the unconditioned stimulus (foot shock). They also showed a divergence in fear potentiated startle, indicating that differences induced by selection generalized to another measure of fear learning. However, there were no differences in performance in a Pavlovian approach conditioning task or the Morris water maze, indicating no change in general learning ability. The high fear learning line showed greater anxiety-like behavior in the open field and zero maze, confirming a genetic relationship between FC and anxiety-like behavior. Gene expression analysis of the amygdala and hippocampus identified genes that were differentially expressed between the two lines. Quantitative trait locus (QTL) analysis identified several chromosomal regions that may underlie the behavioral response to selection; cis-acting expression QTL were identified in some of these regions, possibly identifying genes that underlie these behavioral QTL. These studies support the validity of a broad genetic construct that includes both learned fear and anxiety and provides a basis for further studies aimed at gene identification.

Conditioned fear and extinction learning performance and its association with psychiatric symptoms in active duty Marines.

BACKGROUND: Posttraumatic Stress Disorder (PTSD) is a major public health concern, especially given the recent wars in Iraq and Afghanistan. Nevertheless, despite a sharp increase in the incidence of psychiatric disorders in returning veterans, empirically based prevention strategies are still lacking. To develop effective prevention and treatment strategies, it is necessary to understand the underlying biological mechanisms contributing to PTSD and other trauma related symptoms. METHODS: The "Marine Resiliency Study II" (MRS-II; October 2011-October 2013) Neurocognition project is an investigation of neurocognitive performance in Marines about to be deployed to Afghanistan. As part of this investigation, 1195 Marines and Navy corpsmen underwent a fear conditioning and extinction paradigm and psychiatric symptom assessment prior to deployment. The current study assesses (1) the effectiveness of the fear potentiated startle paradigm in producing fear learning and extinction and (2) the association of performance in the paradigm with baseline psychiatric symptom classes (healthy: n=923, PTSD symptoms: n=42, anxiety symptoms: n=37, and depression symptoms: n=12). RESULTS: Results suggest that the task was effective in producing differential fear learning and fear extinction in this cohort. Further, distinct patterns emerged differentiating the PTSD and anxiety symptom classes from both healthy and depression classes. During fear acquisition, the PTSD symptom group was the only group to show deficient discrimination between the conditioned stimulus (CS+) and safety cue (CS-), exhibiting larger startle responses during the safety cue compared to the healthy group. During extinction learning, the PTSD symptom group showed significantly less reduction in their CS+ responding over time compared to the healthy group, as well as reduced extinction of self-reported anxiety to the CS+ by the end of the extinction session. Conversely, the anxiety symptom group showed normal safety signal discrimination and extinction of conditioned fear, but exhibited increased baseline startle reactivity and potentiated startle to CS+, as well as higher self-reported anxiety to both cues. The depression symptom group showed similar physiological and self-report measures as the healthy group. DISCUSSION: These data are consistent with the idea that safety signal discrimination is a relatively specific marker of PTSD symptoms compared to general anxiety and depression symptoms. Further research is needed to determine if deficits in fear inhibition vs. exaggerated fear responding are separate biological "domains" across anxiety disorders that may predict differential biological mechanisms and possibly treatment needs. Future longitudinal analyses will examine whether poor learning of safety signals provides a marker of vulnerability to develop PTSD or is specific to symptom state.

Clonidine blocks acquisition but not expression of conditioned opiate withdrawal in rats.

Previous studies in rodents have reported that clonidine, an alpha 2-adrenergic receptor agonist, attenuated conditioned aversions to naloxone-precipitated opiate withdrawal when administered prior to each withdrawal conditioning episode. The current study was designed to determine whether clonidine could modify the expression of previously established conditioned place aversions and conditioned suppression of operant responding. Dose- and time-dependent effects of clonidine on activity and suppression of operant responding for food identified appropriate treatment parameters for subsequent studies in which rats rendered dependent on opiates through implantation of morphine pellets were tested for: (1) conditioned place aversion; and (2) conditioned suppression of operant responding for food (fixed ratio-15 schedule), in a paradigm wherein rats received four pairings of naloxone with a distinct tone and odor stimulus. Clonidine dose-dependently blocked the acquisition of both conditioned behaviors when administered prior to naloxone on each conditioning trial, but was ineffective in blocking the expression of these conditioned withdrawal signs when administered prior to the test session.

Psychophysiology in the study of psychological trauma: where are we now and where do we need to be?

Posttraumatic stress disorder (PTSD) is a major public health concern, which has been seeing increased recent attention partly due to the wars in Iraq and Afghanistan. Historically, research attempting to understand the etiology and treatment of PTSD has made frequent use of psychophysiological measures of arousal as they provide a number of advantages in providing objective, non-self-report outcomes that are closely related to proposed neurobiological mechanisms and provide opportunity for cross-species translation. Further, the ongoing shift in classification of psychiatric illness based on symptom clusters to specific biological, physiological, and behavioral constructs, as outlined in the US National Institute of Mental Health (NIMH) Research Domain Criteria project (RDoC), promises that psychophysiological research will continue to play a prominent role in research on trauma-related illnesses. This review focuses on the current state of the knowledge regarding psychophysiological measures and PTSD with a focus on physiological markers associated with current PTSD symptoms, as well as markers of constructs thought to be relevant to PTSD symptomatology (safety signal learning, fear extinction), and psychophysiological markers of risk for developing PTSD following trauma. Future directions and issues for the psychophysiological study of trauma including traumatic brain injury (TBI), treatment outcome studies, and new wearable physiological monitoring technologies are also discussed.

Reversal of autism-like behaviors and metabolism in adult mice with single-dose antipurinergic therapy.

Autism spectrum disorders (ASDs) now affect 1-2% of the children born in the United States. Hundreds of genetic, metabolic and environmental factors are known to increase the risk of ASD. Similar factors are known to influence the risk of schizophrenia and bipolar disorder; however, a unifying mechanistic explanation has remained elusive. Here we used the maternal immune activation (MIA) mouse model of neurodevelopmental and neuropsychiatric disorders to study the effects of a single dose of the antipurinergic drug suramin on the behavior and metabolism of adult animals. We found that disturbances in social behavior, novelty preference and metabolism are not permanent but are treatable with antipurinergic therapy (APT) in this model of ASD and schizophrenia. A single dose of suramin (20 mg kg(-1) intraperitoneally (i.p.)) given to 6-month-old adults restored normal social behavior, novelty preference and metabolism. Comprehensive metabolomic analysis identified purine metabolism as the key regulatory pathway. Correction of purine metabolism normalized 17 of 18 metabolic pathways that were disturbed in the MIA model. Two days after treatment, the suramin concentration in the plasma and brainstem was 7.64 µM pmol µl(-1) (±0.50) and 5.15 pmol mg(-1) (±0.49), respectively. These data show good uptake of suramin into the central nervous system at the level of the brainstem. Most of the improvements associated with APT were lost after 5 weeks of drug washout, consistent with the 1-week plasma half-life of suramin in mice. Our results show that purine metabolism is a master regulator of behavior and metabolism in the MIA model, and that single-dose APT with suramin acutely reverses these abnormalities, even in adults.

The role of PKC signaling in CRF-induced modulation of startle.

RATIONALE: Hypersignaling of corticotropin releasing factor (CRF) has been implicated in stress disorders; however, many of its downstream mechanisms of action remain unclear. In vitro, CRF1 receptor activation initiates multiple cell signaling cascades, including protein kinase A (PKA), protein kinase C (PKC), and mitogen-activated protein kinase kinase MEK1/2 signaling. It is unclear, however, which of these signaling cascades mediate CRF-induced behaviors during stress. OBJECTIVES: We examined the role of PKA, PKC, and MEK1/2 signaling pathways in CRF-induced anxiety as measured by startle hyperreactivity. METHODS: Mice treated with intracerbroventricular (ICV) ovine CRF (oCRF) were pretreated with the PKA inhibitor Rp-cAMPS, PKC inhibitor bisindolylmaleimide (BIM), or MEK1/2 inhibitor PD98059 (ICV) and assessed for acoustic startle reactivity. RESULTS: The PKC inhibitor BIM significantly attenuated CRF-induced increases in startle. BIM was also able to block startle increases induced by oCRF when both compounds were infused directly into the bed nucleus of stria terminalis (BNST). PKA and MEK1/2 inhibition had no significant effects on CRF-induced changes in startle at the dose ranges tested. CRF-induced disruption of prepulse inhibition was not significantly reversed by any of the three pretreatments at the dose ranges tested. CONCLUSIONS: PKC signaling is required for CRF-induced increases in startle, and this effect is mediated at least in part at the BNST. These findings suggest that PKC signaling cascades (1) may be important for the acute effects of CRF to induce startle hyperreactivity and (2) support further research of the role of PKC signaling in startle abnormalities relevant to disorders such as posttraumatic stress disorder.

Effects of a novel cholinergic ion channel agonist SIB-1765F on locomotor activity in rats.

SIB-1765F ([+/-]-5-ethynyl-3-(1-methyl-2-pyrrolidinyl)pyridine fumarate) is a novel nicotinic acetylcholine receptor (NAChR) agonist displaying a different in vitro pharmacological profile than nicotine and epibatidine, suggestive of NAChR subtype selectivity. Our study describes the effects of SIB-1765F on locomotor activity in rats, which were compared to those observed for nicotine and epibatidine. The three NAChR agonists decreased or increased locomotor activity in rats naive or habituated to the test apparatus, respectively. The transient reduction in locomotor activity induced by SIB-1765F was quantitatively similar to those induced by nicotine and epibatidine but, unlike the effects of nicotine and epibatidine, was not blocked by the NAChR antagonists mecamylamine and dihydro-beta-erythroidine, suggesting different mechanisms of action. Furthermore, SIB-1765F produced a larger and longer-lasting increase in locomotor activity when administered to rats familiar with the test apparatus. Mecamylamine and dihydro-beta-erythroidine but not hexamethonium blocked the increase in locomotor activity induced by SIB-1765F, suggesting that SIB-1765F elicits this effect predominantly through the activation of central NAChR. The SIB-1765F-induced increase in locomotor activity was also attenuated by selective D1 and D2 dopamine receptor antagonists, implying that this increase in locomotor activity is mediated through the activation of dopamine receptors subsequent to the release of dopamine. Based on these results, SIB-1765F appears to have a different locomotor activity profile than nicotine and epibatidine.

Interactions between a novel cholinergic ion channel agonist, SIB-1765F and L-DOPA in the reserpine model of Parkinson's disease in rats.

SIB-1765F, a novel nicotinic acetylcholine receptor agonist, was tested for its efficacy in attenuating reserpine-induced hypolocomotion in rats. SIB-1765F was administered alone or in combination with L-DOPA and its effects were compared to those of nicotine, d-amphetamine and amantadine in the same conditions. Consistent with previous reports, reserpine-induced hypolocomotion was reversed by L-DOPA (plus benserazide), d-amphetamine and amantadine in a dose-dependent manner and the effect of L-DOPA in reserpine-treated rats was potentiated by amantadine. SIB-1765F also increased the locomotor activity of reserpine-treated rats and potentiated the effect of L-DOPA on reserpine-induced hypolocomotion. The onset of potentiation of L-DOPA by SIB-1765F was rapid (< 5 min) compared to the onset of potentiation by amantadine (> 105 min). Interestingly, nicotine did not attenuate reserpine-induced hypolocomotion nor did it affect the action of L-DOPA on reserpine-treated rats. Biochemical analysis of levels of dopamine and its metabolites, dihydroxyphenylacetic and homovanillic acid, indicated that, in contrast to amphetamine, SIB-1765F did not inhibit dopamine reuptake. The effect of SIB-1765F in reserpine-treated rats was attenuated by alpha-methyl-p-tyrosine, implying that SIB-1765F acts by releasing dopamine from both reserpine-insensitive and reserpine-sensitive pools. Our findings demonstrate that nicotinic acetylcholine receptor agonists may offer a new therapeutic approach to the symptomatic treatment of the motor deficits in patients with Parkinson's disease.

Effects of (+/-)-4-[[2-(1-methyl-2-pyrrolidinyl)ethyl]thio]phenol hydrochloride (SIB-1553A), a selective ligand for nicotinic acetylcholine receptors, in tests of visual attention and distractibility in rats and monkeys.

Nicotine, a nonselective ligand for nicotinic acetylcholine receptors (nAChRs), has been shown to improve attention and reduce distractibility in humans. Although the numerous side effects induced by nicotine prevent its use as a therapeutic agent, it is hypothesized that subtype-selective nAChR ligands may offer a potential therapeutic benefit to humans with attention deficits. In this study, we evaluated the attention-enhancing properties of (+/-)-4-[[2-(1-methyl-2-pyrrolidinyl)ethyl]thio]phenol hydrochloride (SIB-1553A), a ligand selective for neuronal nAChRs with predominant activity at the human beta 4 subtype. SIB-1553A was evaluated in a test of attention (i.e., five-choice serial reaction time task or SRTT) and distractibility (i.e., delayed matching to sample task with distractor or DMTS-D) in adult rats and monkeys, respectively. SIB-1553A did not improve SRTT performance in normal rats, but reversed deficits induced by the N-methyl-D-aspartate (NMDA) antagonist dizocilpine. In the DMTS-D, SIB-1553A improved accuracy across several doses at the short delay intervals, which were affected most by distracting stimuli in adult monkeys. Subsequent testing with optimal doses for each monkey was also associated with significant improvements in DMTS-D accuracy at short delays, indicating the reproducibility of the drug effect. In both species, SIB-1553A had no significant effects on latencies for sample or choice selection and was not associated with adverse effects at efficacious doses. Although it remains to be further demonstrated, SIB-1553A may act through combined nicotinic and non-nicotinic mechanisms. Collectively, the present data suggest that in specific conditions SIB-1553A may improve certain aspects of attentional function in young adult rats and nonhuman primates without adverse side effects.

SIB-1553A, (+/-)-4-[[2-(1-methyl-2-pyrrolidinyl)ethyl]thio]phenol hydrochloride, a subtype-selective ligand for nicotinic acetylcholine receptors with putative cognitive-enhancing properties: effects on working and reference memory performances in aged rodents and nonhuman primates.

Preclinical and clinical data have suggested the potential use of nicotinic acetylcholine receptor (nAChR) ligands for treating cognitive dysfunction associated with neurodegenerative diseases, such as Alzheimer's disease. SIB-1553A, (+/-)-4-[[2-(1-methyl-2-pyrrolidinyl)ethyl]thio]phenol hydrochloride, a novel nAChR ligand with predominant agonist subtype selectivity for beta4 subunit-containing human neuronal nAChRs, was tested in a variety of cognitive paradigms in aged rodents and nonhuman primates after acute and repeated administration. Subcutaneous administration of SIB-1553A improved delayed nonmatching to place performance in aged mice. In aged rhesus monkeys, intramuscular and oral administration of SIB-1553A improved choice accuracy in a delayed matching to sample task. SIB-1553A improved performances in these spatial and nonspatial working memory tasks but was less effective at improving performances in spatial reference memory tasks (i.e., aged rodents exposed to a discrimination task in a T-maze or trained to locate a hidden platform in a water maze). These data suggest that SIB-1553A has a predominant effect on attention/working memory processes. SIB-1553A also induced the release of acetylcholine in the hippocampus of aged rats and was equally effective whether administered acutely or repeatedly (6 weeks of daily subcutaneous administration). Thus, rats repeatedly treated with SIB-1553A exhibit neither tolerance nor sensitization to the effects of the compound. The SIB-1553A-induced cognitive improvement may be in part related to an increase in cholinergic function. The present study provides additional support for the use of subtype-selective nAChR ligands as a potential therapy for the symptomatic treatment of specific cognitive deficits (such as attention/working memory deficits) associated with aging and neurological diseases.