Thrombin generation using the calibrated automated thrombinoscope to assess reversibility of dabigatran and rivaroxaban

The new direct-acting anticoagulants such as dabigatran and rivaroxaban are usually not monitored but may be associated with haemorrhage, particularly where renal impairment occurs. They have no effective "antidotes". We studied 17 patients receiving dabigatran 150 mg twice daily for non-valvular atrial fibrillation and 15 patients receiving rivaroxaban 10 mg daily for the prevention of deep venous thrombosis after hip or knee replacement surgery. We assessed the effect of these drugs on commonly used laboratory tests and Calibrated Automated Thrombogram (CAT) using plasma samples. We also assessed effects in fresh whole blood citrated patient samples using thromboelastography on the TEG and the ROTEM. The efficacy of nonspecific haemostatic agents prothrombin complex concentrate (PCC), Factor VIII Inhibitor By-passing Activity (FEIBA) and recombinant activated factor VII (rVIIa) were tested by reversal of abnormal thrombin generation using the CAT. Concentrations added ex vivo were chosen to reflect doses normally given in vivo. Dabigatran significantly increased the dynamic parameters of the TEG and ROTEM and the lag time of the CAT. It significantly reduced the endogenous thrombin potential (ETP) and reduced the peak height of the CAT. Rivaroxaban did not affect the TEG and ROTEM parameters but did increase the lag time and reduce ETP and peak height of the CAT. For both drugs, these parameters were significantly and meaningfully corrected by PCC and FEIBA and to a lesser but still significant extent by rFVIIa. These results may be useful in devising a reversal strategy in patients but clinical experience will be needed to verify them.

Reversal strategy in antagonizing the P2Y12 -inhibitor ticagrelor

BACKGROUND

Patients on antiplatelet therapy have a higher incidence of bleeding complications. Reversal of antiplatelet drug effects is an important issue at trauma or emergency departments. For old and conventional anticoagulants, reversal strategies are established. While the effects of ticagrelor are reversible, developing a method to restore platelet function in patients is of importance due to its longer half-life (approximately 8 h), compared with other P2Y12 -inhibitors.

MATERIALS AND METHODS

We report an ex vivo model to reverse the effects of the novel and highly effective P2Y12 -inhibitor ticagrelor in 20 healthy volunteers. To normalize platelet reactivity, we added increasing amounts of autologous platelet-rich plasma (PRP) to whole blood which was obtained 3 h after the intake of 180 mg of ticagrelor. Platelet aggregation was assessed by whole blood multiple electrode aggregometry (MEA), which is based on impedance aggregometry.

RESULTS

The basal ADP-induced platelet aggregation averaged 71 ± 16 U (Units). Ticagrelor decreased ADP-induced platelet aggregation to 16 ± 8 U. A clear dose-response was obtained after spiking whole blood with increasing amounts of PRP. It is estimated that ≥2 units of apheresis platelet concentrates will be necessary to completely restore baseline platelet aggregation in the majority of patients after ticagrelor.

CONCLUSIONS

Platelets dose dependently improve ex vivo platelet aggregation of subjects after a loading dose of 180 mg of ticagrelor, making transfusion of platelet concentrates potentially useful in bleeding patients and those who need to undergo emergency surgery.

Corolla morphology influences diversification rates in bifid toadflaxes (Linaria sect. Versicolores)

BACKGROUND AND AIMS

The role of flower specialization in plant speciation and evolution remains controversial. In this study the evolution of flower traits restricting access to pollinators was analysed in the bifid toadflaxes (Linaria sect. Versicolores), a monophyletic group of ~30 species and subspecies with highly specialized corollas.

METHODS

A time-calibrated phylogeny based on both nuclear and plastid DNA sequences was obtained using a coalescent-based method, and flower morphology was characterized by means of morphometric analyses. Directional trends in flower shape evolution and trait-dependent diversification rates were jointly analysed using recently developed methods, and morphological shifts were reconstructed along the phylogeny. Pollinator surveys were conducted for a representative sample of species.

KEY RESULTS

A restrictive character state (narrow corolla tube) was reconstructed in the most recent common ancestor of Linaria sect. Versicolores. After its early loss in the most species-rich clade, this character state has been convergently reacquired in multiple lineages of this clade in recent times, yet it seems to have exerted a negative influence on diversification rates. Comparative analyses and pollinator surveys suggest that the narrow- and broad-tubed flowers are evolutionary optima representing divergent strategies of pollen placement on nectar-feeding insects.

CONCLUSIONS

The results confirm that different forms of floral specialization can lead to dissimilar evolutionary success in terms of diversification. It is additionally suggested that opposing individual-level and species-level selection pressures may have driven the evolution of pollinator-restrictive traits in bifid toadflaxes.

Activated prothrombin complex concentrates for the reversal of anticoagulant-associated coagulopathy

OBJECTIVE

Prothrombin complex concentrate (PCC) products are emerging as alternative strategies for reversing anticoagulant pharmacotherapy. Factor eight inhibitor bypassing activity (FEIBA, or anti-inhibitor coagulant complex) is an activated PCC (aPCC). Although FEIBA is approved by the FDA to control spontaneous bleeding episodes and to prevent bleeding with surgical interventions in hemophilia A and hemophilia B patients with inhibitors to factor VIII, recent data have suggested that the product may be used off-label as an anticoagulant-reversal agent. To evaluate the safety and efficacy of aPCC products in reversing anticoagulant pharmacotherapy, we searched online databases for English-language publications that discussed this topic.

DATA SOURCES

The EMBASE, MEDLINE, and International Pharmaceutical Abstracts databases were used. We evaluated all articles published in the English language identified from the data sources. We included studies conducted in human subjects and in in vitro and in vivo models in our review.

RESULTS

Current published evidence suggests that the use of an aPCC, compared with fresh-frozen plasma, is associated with a significantly faster correction of supratherapeutic International Normalized Ratios (INRs) secondary to warfarin therapy. Conflicting evidence exists regarding the ability of aPCCs to reverse the prolonged bleeding times caused by the anticoagulant agents dabigatran etexilate (Pradaxa), rivaroxaban (Xarelto), apixaban (Eliquis), and fondaparinux (Arixtra).

CONCLUSION

The theoretical risks of thrombosis associated with PCC products must be carefully considered before they are administered to patients who require coagulation therapy. The use of aPCCs to reverse the anticoagulant effects of warfarin, dabigatran, or rivaroxaban should be limited because of the lack of efficacy and safety data in humans. Moreover, the safety of aPCCs in off-label indications has not been adequately assessed.

Laparoscopic reversal of Hartmann's procedure: safety and feasibility

Aims: The present study aimed to compare the surgical outcomes of patients receiving laparoscopic reversal of Hartmann’s procedure (RHP) with those receiving open surgery.

Methods: Records of all patients with RHP performed in our unit (including laparoscopic and open surgery) between 2000 and 2012 were retrieved. Data were retrospectively reviewed and compared.

Results: Eighty-two RHPs were performed between 2000 and 2012. Thirty-five were performed with an open approach and 47 with a laparoscopic approach. Conversion rate was 28% in the laparoscopic group. There was no difference, between the two groups, in operation time or blood loss. The median length of stay was significantly shorter in the laparoscopic group (12 vs 14 days, P = 0.002) and fewer patients in the laparoscopic group had complications with post-operative paralytic ileus (2 vs 17%, P = 0.038). None of the patients in the laparoscopic group developed incisional hernia at the conclusion of follow-up, as opposed to five in the open group (0 vs 14%, P = 0.012).

Conclusion: Laparoscopic RHP is safe and feasible, with more favorable surgical outcomes, when compared with open surgery. Conversion rate is acceptable. It should be the technique of choice for patients undergoing RHP.

Reversal of multidrug resistance by cisplatin-loaded magnetic Fe3O4 nanoparticles in A549/DDP lung cancer cells in vitro and in vivo

The purpose of this study was to explore whether magnetic Fe(3)O(4) nanoparticles (Fe(3)O(4)-MNP) loaded with cisplatin (Fe(3)O(4)-MNP-DDP) can reverse DDP resistance in lung cancer cells and to investigate mechanisms of multidrug resistance in vitro and in vivo. MTT assay showed that DDP inhibited both A549 cells and DDP-resistant A549 cells in a time-dependent and dose-dependent manner, and that this inhibition was enhanced by Fe(3)O(4)-MNP. An increased rate of apoptosis was detected in the Fe(3)O(4)-MNP-DDP group compared with a control group and the Fe(3)O(4)-MNP group by flow cytometry, and typical morphologic features of apoptosis were confirmed by confocal microscopy. Accumulation of intracellular DDP in the Fe(3)O(4)-MNP-DDP group was greater than that in the DDP group by inductively coupled plasma mass spectrometry. Further, lower levels of multidrug resistance-associated protein-1, lung resistance-related protein, Akt, and Bad, and higher levels of caspase-3 genes and proteins, were demonstrated by reverse transcriptase polymerase chain reaction and Western blotting in the presence of Fe(3)O(4)-MNP-DDP. We also demonstrated that Fe(3)O(4)-MNP enhanced the effect of DDP on tumor growth in BALB/c nude mice bearing DDP-resistant human A549 xenografts by decreasing localization of lung resistance-related protein and Ki-67 immunoreactivity in cells. There were no apparent signs of toxicity in the animals. Overall, these findings suggest potential clinical application of Fe(3)O(4)-MNP-DDP to increase cytotoxicity in lung tumor xenografts.

Effect of curcumin on human colon cancer multidrug resistance in vitro and in vivo

OBJECTIVE

To determine whether curcumin reverses the multidrug resistance of human colon cancer cells in vitro and in vivo.

METHODS

In a vincristine-resistant cell line of human colon cancer, the cell viability of curcumin-treated cells was determined using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Rhodamine123 efflux was evaluated to detect P-glycoprotein transporter activity, and expression of the multidrug resistance protein 1 and survivin genes was analyzed by reverse transcription polymerase chain reaction and western blotting. In addition, xenograft mouse tumors were grown and treated with curcumin. The morphology of the xenografts was investigated by hematoxylin-eosin staining. The in vivo expression of the multidrug resistance gene and P-glycoprotein and survivin genes and proteins was observed using reverse transcription-polymerase chain reaction and western blotting, respectively.

RESULTS

Curcumin was not obviously toxic to the vincristine-resistant human colon cancer cells at concentrations less than 25 μM, but the growth of cells was significantly inhibited. At concentrations greater than 25 μM, curcumin was toxic in a concentration-dependent manner. The sensitivity of cells to vincristine, cisplatin, fluorouracil, and hydroxycamptothecin was enhanced, intracellular Rhodamine123 accumulation was increased (p<0.05), and the expression of the multidrug resistance gene and P-glycoprotein were significantly suppressed (p<0.05). The combination of curcumin and vincristine significantly inhibited xenograft growth. The expression of the multidrug resistance protein 1 and survivin genes was significantly reduced in xenografts of curcumin-treated mice and mice treated with both curcumin and vincristine relative to control mice.

CONCLUSION

Curcumin has strong reversal effects on the multidrug resistance of human colon carcinoma in vitro and in vivo.

Pharmacologic reversal of warfarin-associated coagulopathy in geriatric patients with hip fractures: a retrospective study of thromboembolic events, postoperative complications, and time to surgery

PURPOSE

Patients with acute hip fractures who are on maintenance warfarin for anticoagulation present a significant challenge and their management remains controversial. The purpose of this study was to assess thromboembolic and systemic complications associated with pharmacological reversal of warfarin-associated coagulopathy in a population of geriatric patients with hip fractures.

METHODS

This retrospective cohort study identified patients with operative hip fractures on oral warfarin therapy who had an international normalized ratio (INR) >1.50 on admission (N = 93) approximately over a 13-year span. The control group consisted of patients whose warfarin was held upon admission without further intervention preoperatively (n = 23). The treatment group consisted of patients who underwent pharmacologic reversal of elevated INR with vitamin K and/or fresh frozen plasma (FFP) in addition to holding warfarin (n = 70). Primary outcomes included thromboembolic and other complications as well as mortality within 3 months of presentation. Time to surgery was a secondary outcome.

RESULTS

The 3-month mortality rate was 4% in the pharmacological intervention group and 17% in the watch-and-wait group; this difference trended toward statistical significance (P = .06). There were no significant differences in the likelihoods of other thromboembolic or nonthromboembolic complications between groups. While the difference in mean time to surgery was not significantly different overall between groups, this difference was significant in a subgroup of patients with higher baseline INRs (n = 46, INR >2.17), with a mean difference of 4.0 fewer days until surgery in the pharmacological intervention group (P < .01).

CONCLUSIONS

Pharmacological reversal of warfarin-associated coagulopathy with a combination of vitamin K and FFP appears to be a safe way to optimize patients for operative fixation of hip fractures and is associated with a shorter delay to surgery in patients with more elevated INRs preoperatively.

LEVEL OF EVIDENCE

retrospective cohort study (level III).

Reduction in arterial stiffness and vascular age by naltrexone-induced interruption of opiate agonism: a cohort study

OBJECTIVE

To prospectively assess if opiate antagonist treatment or the opiate-free status could reverse opiate-related vasculopathy.

DESIGN

Longitudinal Open Observational, Serial 'N of One', over 6.5 years under various treatment conditions: opiate dependence, naltrexone and opiate-free.

SETTING

Primary care, Australia.

PARTICIPANTS

20 opiate-dependent patients (16 males: 16 cases of buprenorphine 4.11±1.17 mg, two of methadone 57.5±12.5 mg and two of heroin 0.75±0.25 g).

INTERVENTION

Studies of central arterial stiffness and vascular reference age (RA) were performed longitudinally by SphygmoCor Pulse Wave Analysis (AtCor, Sydney).

PRIMARY OUTCOMES

Primary outcome was vascular age and arterial stiffness accrual under different treatment conditions.

RESULTS

The mean chronological age (CA) was 33.62±2.03 years. The opiate-free condition was associated with a lower apparent vascular age both in itself (males: p=0.0402 and females: p=0.0360) and in interaction with time (males: p=0.0001 and females: p=0.0004), and confirmed with other measures of arterial stiffness. The mean modelled RA was 38.82, 37.73 and 35.05 years in the opiate, naltrexone and opiate-free conditions, respectively. The opiate-free condition was superior to opiate agonism after full multivariate adjustment (p=0.0131), with modelled RA/CA of 1.0173, 0.9563 and 0.8985 (reductions of 6.1% and 11.9%, respectively).

CONCLUSIONS

Data demonstrate that opiate-free status improves vascular age and arterial stiffness in previous chronic opiate users. The role of opiate antagonist treatment in achieving these outcomes requires future clarification and offers hope of novel therapeutic remediation.

Latent vulnerability in cognitive performance following chronic cocaine self-administration in rhesus monkeys

RATIONALE

Cocaine use is associated with cognitive impairment which impacts treatment outcome. A clearer understanding of those deficits, and whether particular environments exacerbate them, is needed.

OBJECTIVES

This study evaluated whether previously observed domain-specific cognitive deficits persisted following a 3-month cessation from chronic cocaine self-administration, as well as the impact of novel and cocaine-associated attentional distractors.

METHODS

Control and experimental groups of monkeys performed stimulus discrimination, stimulus reversal, and delayed match-to-sample (DMS) tasks. After establishing post-cocaine baseline performance, we examined general distractibility in both groups, using brief novel distractors counterbalanced across each task. After testing the novel distractor, an identical approach was used for exposure to an appetitive distractor previously associated with cocaine in the experimental group or water in the control group.

RESULTS

Post-administration baseline performance was equivalent between groups on all tasks. In the cocaine group, stimulus discrimination was unaffected by either distractor, whereas reversal performance was disrupted by both the novel and appetitive distractors. DMS performance was impaired in the cocaine group in the presence of the novel distractor. The control group's performance was not affected by the presentation of either distractor on any task.

CONCLUSION

Our results reveal that despite normalized performance between groups, there exists in the cocaine group a domain-specific latent vulnerability of cognitive performance to impairment by environmental distractors. The pattern of vulnerability recapitulates the frank impairments seen in drug-free animals during an active self-administration phase. A greater impact of the cocaine-associated distractor over the novel one was not observed.

In vivo and in vitro models for the therapeutic targeting of Wnt signaling using a Tet-OΔN89β-catenin system

Although significant progress has been made in understanding the importance of Wnt signaling in the initiation of colorectal cancer, less is known about responses that accompany the reversal of oncogenic Wnt signaling. The aim of this study was to analyze in vivo and in vitro responses to an 'ideal' Wnt pathway inhibitor as a model for the therapeutic targeting of the pathway. A tetracycline-inducible transgenic mouse model expressing truncated β-catenin (ΔN89β-catenin) that exhibited a strong intestinal hyperplasia was analyzed during the removal of oncogenic β-catenin expression both in 3D 'crypt culture' and in vivo. Oncogenic Wnt signaling was rapidly and completely reversed. The strongest inhibition of Wnt target gene expression occurred within 24 h of doxycycline removal at which time the target genes Ascl2, Axin2 and C-myc were downregulated to levels below that in the control intestine. In vitro, the small molecule Wnt inhibitor CCT036477 induced a response within 4 h of treatment. By 7 days following doxycycline withdrawal, gene expression, cell proliferation and tissue morphology were undistinguishable from control animals.In conclusion, these results demonstrate that the reversal of Wnt signaling by inhibitors should ideally be studied within hours of treatment. The reversible system described, involving medium throughput in vitro approaches and rapid in vivo responses, should allow the rapid advance of early stage compounds into efficacy models that are more usually considered later in the drug discovery pipeline.

The prevention and regression of atherosclerotic plaques: emerging treatments

Occlusive vascular diseases, such as sudden coronary syndromes, stroke, and peripheral arterial disease, are a huge burden on the health care systems of developed and developing countries. Tremendous advances have been made over the last few decades in the diagnosis and treatment of atherosclerotic diseases. Intravascular ultrasound has been able to provide detailed information of plaque anatomy and has been used in several studies to assess outcomes. The presence of atherosclerosis disrupts the normal protective mechanism provided by the endothelium and this mechanism has been implicated in the pathophysiology of coronary artery disease and stroke. Efforts are being put into the prevention of atherosclerosis, which has been shown to begin in childhood. This paper reviews the pathophysiology of atherosclerosis and discusses the current options available for the prevention and reversal of plaque formation.

Non-cardiogenic pulmonary oedema after neostigmine given for reversal: A report of two cases

Non-cardiogenic pulmonary oedema (NCPE) is a clinical syndrome characterized by simultaneous presence of severe hypoxemia, bilateral alveolar infiltrates on chest radiograph, and no evidence of left atrial hypertension/congestive heart failure/fluid overload. The diagnosis of drug-related NCPE relies upon documented exclusion of other causes of NCPE like gastric aspiration, sepsis, trauma, negative pressure pulmonary oedema, etc. We describe two cases (45-year male and 6-year male), who had undergone elective surgery under general anaesthesia. They developed NCPE within 3-5 minutes after administration of ‘neostigmine-glycopyrrolate’ used to reverse residual neuromuscular blockade. Both patients were treated successfully with mechanical ventilatory support, and adjuvant therapy, viz., frusemide, dopamine, steroids. This report emphasizes that this fatal complication may be seen with neostigmine, the pathogenic mechanism remains unknown, and it probably is a drug-related NCPE.

Localization of dysfunction in major depressive disorder: prefrontal cortex and amygdala

Despite considerable effort, the localization of dysfunction in major depressive disorder (MDD) remains poorly understood. We present a hypothesis about its localization that builds on recent findings from primate neuropsychology. The hypothesis has four key components: a deficit in the valuation of "self" underlies the core disorder in MDD; the medial frontal cortex represents "self"; interactions between the amygdala and cortical representations update their valuation; and inefficiency in using positive feedback by orbital prefrontal cortex contributes to MDD.

Similarities Among the Shapes of Writing and Their Effects on Learning

Writing systems are usually studied in terms of the level of language that they represent, with little attention to the shapes that are used to do so. Those shapes are not random or accidental, however. They tend to be similar to one another within a script. Many of the Latin letters have a roughly vertical stem or hasta with an appendage or coda to the right. This arrangement is more common than one with the coda on the left of the hasta. We present data to show that young children are generally better at copying and writing from memory shapes such as <b> and <F>, which have the typical arrangement with the coda on the right, than those such as <d> and <J>, which do not. The results suggest that children start to learn about the statistics of the letter shapes before they know how or that these shapes represent language.

Correction of coagulopathy for percutaneous interventions

Due to medical illness or pharmacotherapy, patients undergoing percutaneous interventions often have abnormal hemostasis. Its etiology may include alterations in the protein-based coagulation system, thrombocytopenia, deficient platelet function, or mixed deficits such as disseminated intravascular coagulation. In this article, the authors review the basic science of each of these etiologies, as well as their available methods of correction. They also review the evidence and guidelines regarding the assessment and treatment of coagulopathy in image-guided procedures. The periprocedural bleeding risk and the urgency of a given procedure guide the management of abnormal hemostasis in this patient population.

Conventional and laparoscopic reversal of the Hartmann procedure: a review of literature

PURPOSE

The aim of this study was to provide a systematic overview on both laparoscopic and conventional Hartmann reversal. Furthermore, the Hartmann procedure is reevaluated in the light of new emerging alternatives.

METHODS

Medline, Ovid, EMBASE, and Cochrane database were searched for studies reporting on outcomes after Hartmann reversal.

RESULTS

Thirty-five studies were included in this review of which 30 were retrospective. A total of 6,249 patients with a mean age of 60 years underwent Hartmann reversal. Two thirds of patients were classified as American Society of Anesthesiologists (ASA) I-II. The mean reversal rate after a Hartmann procedure was 44%, and mean time interval between Hartmann procedure and Hartmann reversal was 7.5 months. The most frequent reported reasons for renouncing Hartmann reversal were high ASA classification and patients' refusal. The overall morbidity rate ranged from 3% to 50% (mean 16.3%) and mortality rate from 0% to 7.1% (mean 1%). Patients treated laparoscopically had a shorter hospital stay (6.9 vs. 10.7 days) and appeared to have lower mean morbidity rates compared to conventional surgery (12.2% vs. 20.3%).

CONCLUSION

Hartmann reversal carries a high risk on perioperative morbidity and mortality. The mean reversal rate is considerably low (44%). Laparoscopic reversal compares favorably to conventional; however, high level evidence is needed to determine whether it is superior.

Silent trace eliminates differential eyeblink learning in abstinent alcoholics

Chronic alcoholism has profound effects on the brain, including volume reductions in regions critical for eyeblink classical conditioning (EBCC). The current study challenged abstinent alcoholics using delay (n = 20) and trace (n = 17) discrimination/reversal EBCC. Comparisons revealed a significant difference between delay and trace conditioning performance during reversal (t (35) = 2.08, p < 0.05). The difference between the two tasks for discrimination was not significant (p = 0.44). These data support the notion that alcoholics are increasingly impaired in the complex task of reversing a previously learned discrimination when a silent trace interval is introduced. Alcoholics' impairment in flexibly altering learned associations may be central to their continued addiction.

Neural substrates of cognitive inflexibility after chronic cocaine exposure

Cognitive changes in addicts and animals exposed to addictive drugs have been extensively investigated over the past decades. One advantage of studying addiction using cognitive paradigms is that neural processing in addicts or drug-exposed animals can be compared to that in normal subjects. Tests of cognitive flexibility that measure the ability to change responding to a previously rewarded or punished stimulus are of potential interest in the study of addiction, because addiction can itself be viewed as an inability to change responding to stimuli previously associated with drug reward. One such test is reversal learning, which is impaired in cocaine addicts and animals that have chronically self-administered or been exposed to cocaine. A circuit including orbitofrontal cortex, basolateral amygdala and striatum subserves reversal learning. In rats that have been previously exposed to cocaine, neurons in these regions show selective and distinct changes in how they encode information during reversal learning. These changes suggest that in these rats, orbitofrontal cortex loses the ability to signal expected outcomes, and basolateral amygdala becomes inflexible in its encoding of cue significance. These changes could explain cocaine-induced impairments to cognitive flexibility and may have theoretical importance in addiction.

Liver cirrhosis

Cirrhosis is defined as the histological development of regenerative nodules surrounded by fibrous bands in response to chronic liver injury, which leads to portal hypertension and end-stage liver disease. Recent advances in the understanding of the natural history and pathophysiology of cirrhosis, and in treatment of its complications, have resulted in improved management, quality of life, and life expectancy of patients. Liver transplantation remains the only curative option for a selected group of patients, but pharmacological treatments that can halt progression to decompensated cirrhosis or even reverse cirrhosis are currently being developed. This Seminar focuses on the diagnosis, complications, and management of cirrhosis, and new clinical and scientific developments.

Associative encoding in anterior piriform cortex versus orbitofrontal cortex during odor discrimination and reversal learning

Recent proposals have conceptualized piriform cortex as an association cortex, capable of integrating incoming olfactory information with descending input from higher order associative regions such as orbitofrontal cortex (OFC). If true, encoding in piriform cortex should reflect associative features prominent in these areas during associative learning involving olfactory cues. To test this hypothesis, we recorded from neurons in OFC and anatomically related parts of the anterior piriform cortex (APC) in rats, learning and reversing novel odor discriminations. Findings in OFC were similar to what we have reported previously, with nearly all the cue-selective neurons exhibiting substantial plasticity during learning and reversal. Also, many of the cue-selective neurons were originally responsive in anticipation of the outcomes early in learning, thereby providing a single-unit representation of the cue-outcome associations. Some of these features were also evident in firing activity in APC, including some plasticity across learning and reversal. However, APC neurons failed to reverse cue selectivity when the associated outcome was changed, and the cue-selective population did not include neurons that were active prior to outcome delivery. Thus, although representations in APC are substantially more associative than expected in a purely sensory region, they do appear to be somewhat more constrained by the sensory features of the odor cues than representations in downstream areas of OFC.

Abnormal associative encoding in orbitofrontal neurons in cocaine-experienced rats during decision-making

Recent evidence has linked exposure to addictive drugs to an inability to employ information about adverse consequences, or outcomes, to control behavior. For instance, addicts and drug-experienced animals fail to adapt their behavior to avoid adverse outcomes in gambling and reversal tasks or after changes in the value of expected rewards. These deficits are similar to those caused by damage to the orbitofrontal cortex, suggesting that addictive drugs may cause long-lasting changes in the representation of outcome associations in a circuit that includes the orbitofrontal cortex. Here we test this hypothesis by recording from orbitofrontal neurons in a discrimination task in rats previously exposed to cocaine (30 mg/kg i.p. for 14 days). We found that orbitofrontal neurons recorded in cocaine-experienced rats failed to signal the adverse outcome at the time a decision was made in the task. The loss of this signal was associated with abnormal changes in response latencies on aversive trials. Furthermore, upon reversal of the cue-outcome associations, orbitofrontal neurons in cocaine-treated rats with enduring reversal impairments failed to reverse their cue-selectivity, while orbitofrontal neurons in cocaine-treated rats with normal performance showed an increase in the plasticity of cue-selective firing after reversal. These results provide direct neurophysiological evidence that exposure to cocaine can cause behaviorally relevant changes in the processing of associative information in a circuit that includes the orbitofrontal cortex.

Long-term potentiation is impaired in middle-aged rats: regional specificity and reversal by adenosine receptor antagonists

Memory loss in humans begins early in adult life and progresses thereafter. It is not known whether these losses reflect the failure of cellular processes that encode memory or disturbances in events that retrieve it. Here, we report that impairments in hippocampal long-term potentiation (LTP), a form of synaptic plasticity associated with memory, are present by middle age in rats but only in select portions of pyramidal cell dendritic trees. Specifically, LTP induced with theta-burst stimulation in basal dendrites of hippocampal field CA1 decayed rapidly in slices prepared from 7- to 10-month-old rats but not in slices from young adults. There were no evident age-related differences in LTP in the apical dendrites. Both the adenosine A1 receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine and a positive AMPA receptor modulator (ampakine) offset age-related LTP deficits. Adenosine produced greater depression of synaptic responses in middle-aged versus young adult slices and in basal versus apical dendrites. These results were not associated with variations in A1 receptor densities and may instead reflect regional and age-related differences in adenosine clearance. Pertinent to this, brief applications of A1 receptor antagonists immediately after theta stimulation fully restored LTP in middle-aged rats. We hypothesize that the build-up of extracellular adenosine during theta activity persists into the postinduction period in the basal dendrites of middle-aged slices and thereby activates the A1 receptor-dependent LTP reversal effect. Regardless of the underlying mechanism, the present results provide a candidate explanation for memory losses during normal aging and indicate that, with regard to plasticity, different segments of pyramidal neurons age at different rates.

Lesions of nucleus accumbens disrupt learning about aversive outcomes

Nucleus accumbens (NAcc) is critical for encoding and using information regarding the learned significance of cues predictive of reward. However, its role in processing information about cues predictive of aversive outcomes is less well studied. Here, we examined the effects of NAcc lesions in an odor-guided discrimination task in which rats use odor cues predictive of either appetitive or aversive outcomes to guide responding. Rats with sham or neurotoxic lesions of NAcc were trained on a series of two-odor discrimination problems. Performance on each problem was assessed by monitoring accuracy of choice behavior and by measuring latency to respond for fluid reinforcement after odor sampling. After acquisition of four problems, rats were trained on serial reversals of the final problem. Rats with NAcc lesions exhibited normal choice performance relative to controls on both acquisition and reversal of the discrimination problems (indeed, lesioned rats exhibited a mild facilitation on the first discrimination problem). Despite normal choice performance, however, lesioned rats failed to show normal changes in response latency during discrimination learning, particularly on trials involving the aversive outcome. These findings are consistent with a deficit in processing cue-outcome associations. These results are compared with those obtained from studies of basolateral amygdala and orbitofrontal cortex lesions in this task and suggest that NAcc integrates the motivational value of both appetitive and aversive cues to bias or modulate the vigor of subsequent responding.