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Results for “augmented feedback”

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PubMed2006

Distinct Wnt signaling pathways have opposing roles in appendage regeneration.

In contrast to mammals, lower vertebrates have a remarkable capacity to regenerate complex structures damaged by injury or disease. This process, termed epimorphic regeneration, involves progenitor cells created through the reprogramming of differentiated cells or through the activation of resident stem cells. Wnt/beta-catenin signaling regulates progenitor cell fate and proliferation during embryonic development and stem cell function in adults, but its functional involvement in epimorphic regeneration has not been addressed. Using transgenic fish lines, we show that Wnt/beta-catenin signaling is activated in the regenerating zebrafish tail fin and is required for formation and subsequent proliferation of the progenitor cells of the blastema. Wnt/beta-catenin signaling appears to act upstream of FGF signaling, which has recently been found to be essential for fin regeneration. Intriguingly, increased Wnt/beta-catenin signaling is sufficient to augment regeneration, as tail fins regenerate faster in fish heterozygous for a loss-of-function mutation in axin1, a negative regulator of the pathway. Likewise, activation of Wnt/beta-catenin signaling by overexpression of wnt8 increases proliferation of progenitor cells in the regenerating fin. By contrast, overexpression of wnt5b (pipetail) reduces expression of Wnt/beta-catenin target genes, impairs proliferation of progenitors and inhibits fin regeneration. Importantly, fin regeneration is accelerated in wnt5b mutant fish. These data suggest that Wnt/beta-catenin signaling promotes regeneration, whereas a distinct pathway activated by wnt5b acts in a negative-feedback loop to limit regeneration.

Adult Stem Cells↗

PubMed1996

The frontal cortex-basal ganglia system in primates.

The primate basal ganglia receives information from most of the cerebrum, including the frontal cortex, but projects (via the dorsal thalamus) primarily to the frontal lobe, perhaps in its entirety. As such, the frontal cortex and basal ganglia constitute an integrated, distributed neuronal architecture. We review evidence that the frontal lobe and basal ganglia specialize in different, but related, aspects of response learning. Frontal cortex acts when new rules need to be learned and older ones rejected, whereas the basal ganglia potentiate previously learned rules based on environmental context and reinforcement history. Such potentiation increases the probability that the central nervous system will select a particular rule to guide behavior. We outline a possible mechanism for the basal ganglia's proposed role in rule potentiation, one that involves both the direct and indirect striatal output pathways and their dopaminergic input. It has previously been proposed that direct-pathway neurons recognize a pattern of corticostriatal inputs, which promotes activity in recurrent, positive-feedback modules (or loops) of which they are an integral part. We propose that this recurrent activity potentiates a rule associated with those modules. If so, then the dopaminergic system is well situated and organized to modulate rule potentiation in both the short and long term. Dopaminergic neurons of the midbrain increase activity during learning and other periods of relatively unpredictable reinforcement. Dopamine enhances gene expression and other forms of activity in striatal neurons of the direct pathway, while suppressing neurons of the indirect pathway. In the short term, then, dopamine may augment the activity of modules triggered by a recognized context, whereas in the long term it may promote context-dependent activation of the same modules. Together, these modulatory influences could support both rule potentiation and learning the context for potentiating that rule.

Animals↗

PubMedDate not supplied

Affecting residents' literature reading attitudes, behaviors, and knowledge through a journal club intervention.

OBJECTIVE: To investigate whether a limited teaching intervention, based on principles of adult education, could change residents' literature reading attitudes, behaviors, and knowledge. DESIGN: The educational intervention supplemented an ongoing bimonthly journal club. The effects on residents were studied prospectively before and four months following the intervention. SETTING: A community hospital internal medicine training program. PARTICIPANTS: All 14 residents: six in the first year, and four each in the second and third years of training. INTERVENTION: A one-hour seminar incorporating principles of adult education, including the use of multiple teaching modalities. The content was based on the critical literature reading guidelines published by the McMaster group. Reinforcement of learning objectives was achieved by learner participation, written assignments, active feedback, and follow-up in subsequent journal clubs. RESULTS: Residents improved their performances on objective testing of critical appraisal knowledge by 60% (p = 0.02). They reported improved ability to appraise original research articles critically (p = 0.01) and reported spending more useful time reading. Unaffected were the total time spent reading journals, the reasons for reading them, and the perceived value of journals in "keeping up" with advances in medical knowledge. CONCLUSION: Journal clubs are important to residents, and their effectiveness in teaching critical appraisal and promoting reading of the literature may be augmented by applying principles of adult education.

Adult↗

PubMed1997

Nitric oxide increased interleukin-4 expression in T lymphocytes.

Nitric oxide (NO) is a regulator of many biological functions including T helper 1 (Th1)/T helper 2 cells balance. It has been demonstrated that NO inhibits the secretion of interleukin-2 (IL-2) and interferon-gamma on Th1 cells. Here we showed that, in addition to the suppression of IL-2 production, NO-generating agents sodium nitroprusside (SNP) and S-nitroso-N-acetylpenicillamine (SNAP) increased the secretion of IL-4 both in Th2 clones and EL4 T cells. The additive effect was dependent on the dose of SNP and SNAP. Augmentation of IL-4 production was detected with 1 microM SNP, and up to threefold increase in IL-4 secretion could be observed with higher concentrations of SNP/SNAP. NO also weakly increased the activation of IL-4 promoter. In contrast, NO markedly inhibited the induction of IL-2 promoter, which could account for most of the reduction in IL-2 production. Analysis of the transcriptional elements on IL-2 and IL-4 promoters revealed a selective inactivation of NF-kappa B and NF-AT. It is suggested that despite the complex feedback network regulating NO production, the enhanced IL-4 expression would lead to the expansion of Th2 cells once NO is generated.

Cell Culture Techniques↗

PubMed2004

Estrogen Induces Neuropeptide Y (NPY) Y1 receptor gene expression and responsiveness to NPY in gonadotrope-enriched pituitary cell cultures.

We showed previously that neuropeptide Y1 receptor (Y1R) expression is increased in the hypothalamus on proestrus afternoon and that this up-regulation of Y1R mRNA may permit neuropeptide Y (NPY) to facilitate release of the preovulatory GnRH surge. Because NPY also modulates LH release directly, we examined steroid regulation of Y1R expression in the female rat anterior pituitary. Treatment of female rats with estrogen in vivo decreased the levels of Y1R mRNA in the whole pituitary gland. In lactotrope/somatotrope-enriched pituitary cells separated by unit gravity sedimentation, 17beta-estradiol (E(2)) treatment likewise suppressed Y1R expression. In contrast, E(2) elevated Y1R mRNA in gonadotrope-enriched cell populations, indicating that estrogen regulates Y1R mRNA expression differently in gonadotropes vs. other pituitary cell types. After exposure to E(2), NPY augmented GnRH-induced LH release from gonadotrope-enriched cells in a manner requiring Y1R activation. Without steroid exposure, this augmentation disappeared, and with progesterone alone, NPY reduced GnRH-induced LH release. In addition, NPY inhibited prolactin secretion from primary pituitary cells in a steroid-free environment, but not in the presence of estrogen. These findings demonstrate that E(2) can directly up-regulate gonadotrope responsiveness to NPY and suggest that this action is mediated at least in part by E(2)'s ability to stimulate Y1R gene expression in gonadotropes. Our observations are consistent with the idea that this regulatory mechanism represents a component of E(2)'s positive feedback actions in pituitary gonadotropes. The biological importance of E(2)'s opposite effects on Y1R expression in other pituitary cell types remains to be determined.

Animals↗

PubMed2004

Gonadotrophin treatment in patients with polycystic ovary syndrome.

Gonadotrophin treatment in clomiphene citrate resistant polycystic ovarian syndrome (PCOS) patients, using either low-dose step-up or low-dose step-down protocols, is highly effective to achieve singleton live births. Concomitant use of gonadotrophin releasing hormone analogues (GnRHa), which will block the endogenous feedback for monofollicular development during the low-dose step-up protocol, should not be employed. It is more difficult to induce ovulation in patients with more 'severe' PCOS, characterized by obesity and insulin resistance. There is need for optimization of starting doses for both the low-dose step-up and step-down protocols. Such optimization will prevent hyperstimulation due to a starting dose far above the FSH threshold, as well as minimize the time-consuming low-dose increments by starting with a higher dose in women with augmented FSH threshold. External validation of reported models for prediction of FSH response is warranted for tailoring and optimizing treatment for everyday clinical practice. Although preliminary, the partial cessation of follicular development, along with regression leading to atresia, lends support to the LH ceiling theory, emphasizing the delicate balance and need for both FSH and LH in normal follicular development. Future well-designed randomized controlled trials will reveal whether IVF with or without in-vitro maturation of the oocytes will improve safety and efficacy compared with classical ovulation induction strategies.

Adult↗

PubMed1999

The calcium/calmodulin-dependent phosphodiesterase PDE1C down-regulates glucose-induced insulin secretion.

To understand the role cAMP phosphodiesterases (PDEs) play in the regulation of insulin secretion, we analyzed cyclic nucleotide PDEs of a pancreatic beta-cell line and used family and isozyme-specific PDE inhibitors to identify the PDEs that counteract glucose-stimulated insulin secretion. We demonstrate the presence of soluble PDE1C, PDE4A and 4D, a cGMP-specific PDE, and of particulate PDE3, activities in betaTC3 insulinoma cells. Selective inhibition of PDE1C, but not of PDE4, augmented glucose-stimulated insulin secretion in a dose-dependent fashion thus demonstrating that PDE1C is the major PDE counteracting glucose-dependent insulin secretion from betaTC3 cells. In pancreatic islets, inhibition of both PDE1C and PDE3 augmented glucose-dependent insulin secretion. The PDE1C of betaTC3 cells is a novel isozyme possessing a K(m) of 0.47 microM for cAMP and 0.25 microM for cGMP. The PDE1C isozyme of betaTC3 cells is sensitive to 8-methoxymethyl isobutylmethylxanthine and zaprinast (IC(50) = 7.5 and 4.5 microM, respectively) and resistant to vinpocetine (IC(50) > 100 microM). Increased responsiveness of PDE1C activity to calcium/calmodulin is evident upon exposure of cells to glucose. Enhanced cAMP degradation by PDE1C, due to increases in its responsiveness to calcium/calmodulin and in intracellular calcium, constitutes a glucose-dependent feedback mechanism for the control of insulin secretion.

3',5'-Cyclic-AMP Phosphodiesterases↗

PubMed2002

Optimal enhancement of immune response.

MOTIVATION: Therapeutic enhancement of innate immune response to microbial attack is addressed as the optimal control of a dynamic system. Interactions between an invading pathogen and the innate immune system are characterized by four non-linear, ordinary differential equations that describe rates of change of pathogen, plasma cell, and antibody concentrations, and of an indicator of organic health. Without therapy, the dynamic model evidences sub-clinical or clinical decay, chronic stabilization, or unrestrained lethal growth of the pathogen; the response pattern depends on the initial concentration of pathogens in the simulated attack. In the model, immune response can be augmented by therapeutic agents that kill the pathogen directly, that stimulate the production of plasma cells or antibodies, or that enhance organ health. A previous paper demonstrated open-loop optimal control solutions that defeat the pathogen and preserve organ health, given initial conditions that otherwise would be lethal (Stengel et al. (2002)). Therapies based on separate and combined application of the agents were derived by minimizing a quadratic cost function that weighted both system response and control usage, providing implicit control over harmful side effects. RESULTS: We demonstrate the ability of neighboring-optimal feedback control to account for a range of unknown initial conditions and persistent input of pathogens by adjusting the therapy to account for perturbations from the nominal-optimal response history. We examine therapies that combine open-loop control of one agent with closed-loop control of another. We show that optimal control theory points the way toward new protocols for treatment and cure of human diseases. CONTACT: stengel@princeton.edu; rghiglia@princeton.edu; nkulkarn@princeton.edu

Antibodies↗

PubMed2005

Vertebral position alters paraspinal muscle spindle responsiveness in the feline spine: effect of positioning duration.

Proprioceptive information from paraspinal tissues including muscle contributes to neuromuscular control of the vertebral column. We investigated whether the history of a vertebra's position can affect signalling from paraspinal muscle spindles. Single unit recordings were obtained from muscle spindle afferents in the L6 dorsal roots of 30 Nembutal-anaesthetized cats. Each afferent's receptive field was in the intact muscles of the low back. The L6 vertebra was controlled using a displacement-controlled feedback motor and was held in each of three different conditioning positions for durations of 0, 2, 4, 6 and 8 s. Conditioning positions (1.0-2.2 mm dorsal and ventral relative to an intermediate position) were based upon the displacement that loaded the L6 vertebra to 50-60% of the cat's body weight. Following conditioning positions that stretched (hold-long) and shortened (hold-short) the spindle, the vertebra was repositioned identically and muscle spindle discharge at rest and to movement was compared with conditioning at the intermediate position. Hold-short conditioning augmented mean resting spindle discharge by +4.1 to +6.2 impulses s(-1); however, the duration of hold-short did not significantly affect this increase (F(4,145) = 0.49, P = 0.74). The increase was maintained at the beginning of vertebral movement but quickly returned to baseline. Conversely, hold-long conditioning significantly diminished mean resting spindle discharge by -2.0 to -16.1 impulses s(-1) (F(4,145) = 11.23, P < 0.001). The relationship between conditioning duration and the diminished resting discharge could be described by a quadratic (F(1,145) = 9.28, P = 0.003) revealing that the effects of positioning history were fully developed within 2 s of conditioning. In addition, 2 s or greater of hold-long conditioning significantly diminished spindle discharge to vertebral movement by -5.7 to -10.0 impulses s(-1) (F(4,145) = 11.0, P < 0.001). These effects of vertebral positioning history may be a mechanism whereby spinal biomechanics interacts with the spine's proprioceptive system to produce acute effects on neuromuscular control of the vertebral column.

Action Potentials↗

PubMed2026

The use of 3-dimensional (3D) printing in teaching musculoskeletal oncology for medical undergraduates.

INTRODUCTION: The approach to integrating relevant anatomy in the medical curriculum has been debated for many years. Current literature has explored the broad impact of 3D printing in medical education. However, there is little evidence on 3D printing for the teaching of musculoskeletal oncology (MSO). This is a self-controlled case series (SCCS) study that aims to analyse the effectiveness of 3D printed models in MSO in enhancing the learning experience, engagement and understanding of clinical and surgical anatomy for medical students. METHOD: A cross-sectional cohort study involving 75 clinical year medical students across 3 years from 2 medical schools that rotated through a single teaching hospital's orthopaedic department. Participants first viewed a set of computed-tomography (CT) images of a large pelvic osteosarcoma from a free open-source database, the Cancer Genome Atlas Sarcoma Collection (TCGA-SARC). A standardised 10-minute pre-intervention questionnaire which comprised 15 questions categorised by: 4 questions in 'anatomical knowledge', 7 questions in 'spatial awareness', 4 questions in 'surgical planning and complications', was administered to assess the baseline knowledge in their interpretation of the pathology via CT images only. Next, a 3D-printed model of the pelvic osteosarcoma, which included colour-coded adjacent structures, was provided as an adjunct to answer the same questionnaire. This concluded with a 5-point Likert scale feedback survey to gauge their perspectives and experience. RESULTS: The mean scores comparing their pre- and post-intervention assessment questionnaire increased by +1.34 from 8.15 (SD = 1.85) to 9.49 (SD = 1.7) (p < 0.001). The final year students had the greatest improvement of +1.54 from 8.00 (SD = 1.89) to 9.54 (SD = 1.59) (p = 0.004). There was no significant difference between the scores amongst the 2 medical schools. 91% of students agreed that the 3D model had helped them further their understanding of the anatomy of the sarcoma and 87% would want 3D printing models to augment their learning in anatomy. Baseline weaker students demonstrated significantly greater improvement in scores compared with baseline stronger students (mean difference +2.04 vs +0.30, p < 0.001). CONCLUSION: 3D printing is an effective teaching adjunct for musculoskeletal oncology surgical anatomy for medical undergraduates and could be used to enhance their understanding and learning experience. 3D models could be integrated in the teaching curriculum of surgical anatomy for undergraduate students.

Humans↗

PubMed1992

Recombinant tumor necrosis factor-alpha potentiates neutrophil degranulation in response to host defense cytokines neutrophil-activating peptide 2 and IL-8 by modulating intracellular cyclic AMP levels.

The neutrophil-activating peptide 2 (NAP-2) and IL-8 are closely related in structure and function. In order to further determine their potential biologic roles in inflammation, we studied their interaction with TNF-alpha-primed human polymorphonuclear neutrophil granulocytes at the levels of effector functions and signal transduction. After short term priming (5 min) by TNF-alpha, suspended cytochalasin B-treated PMN responded to NAP-2 or rIL-8 by substantial augmentation of the degranulation response. After priming with 3 ng/ml TNF-alpha marker release from both azurophilic and specific granules was near maximum. NAP-2 and rIL-8 cooperated with TNF-alpha in very similar ways, as indicated by the almost identical increases in release rates that were induced by equipotent doses of either secondary stimulus. At the signal transduction level, pharmacologic elevation of intracellular cAMP led to the inhibition of NAP-2- or rIL-8-induced degranulation in primed and unprimed PMN, indicating a role for this second messenger as a negative feedback signal. Direct measurement of intracellular cAMP revealed that TNF-alpha by itself did not affect its levels. Instead, TNF-alpha reduced both the scale as well as the duration of the cAMP burst generated in response to secondary stimuli NAP-2 or rIL-8. Thus, there is evidence that TNF-alpha priming of neutrophils for enhanced NAP-2- or rIL-8-promoted degranulation involves the antagonistic down-modulation of stimulus-induced rises in cAMP.

Cell Degranulation↗

PubMed2003

Impact of maternal deprivation on brain corticotropin-releasing hormone circuits: prevention of CRH receptor-2 mRNA changes by desipramine treatment.

Corticotropin-releasing hormone (CRH) acts within the brain and pituitary to coordinate the overall endocrinological and behavioral stress response. From postnatal day (PND) 4 to 14, the infant rat displays minimal adrenal response to mild stress. However, maternal deprivation alters the pituitary-adrenal system such that the infants become responsive to specific stimuli. We hypothesized that maternal deprivation would also affect CRH brain circuits. Since tricyclic antidepressants have been shown to decrease the adrenal response to stress in adult rats, we hypothesized that CRH-related changes induced by maternal deprivation would be prevented by this treatment. Thus, we investigated CRH-related molecules on animals that were maternally deprived on PND 13 compared with nondeprived animals. We found that maternal deprivation caused alterations in the gene expression of both CRH receptors (CRHr) 1 and 2 in specific brain regions, and that some of these effects were augmented by chronic isotonic saline injections. There was a significant increase in CRH, CRHr1, and r2 mRNA in the cortex. In amygdala, CRHr1 and r2 mRNAs were decreased. CRHr2 mRNA was also decreased in the ventromedial nucleus of the hypothalamus, whereas an increase was detected in the hippocampal pyramidal cells. One week of desipramine (DES) administration preceding the maternal deprivation event prevented all the deprivation-induced changes in CRHr2 mRNA, regardless of the direction of the original change. We also found that chronic injection treatments enhanced the adrenocortical response and improved the efficiency of negative feedback in maternal deprivation animals. These results demonstrate that maternal deprivation elicits modifications of CRH brain circuits in a site-specific manner, and that the regulation of CRHr2 gene expression is mediated by mechanisms different from those involved with the modulation of CRHr1 in the infant rat.

Animals↗

PubMed2001

Influences of age and ovarian follicular reserve on estrous cycle patterns, ovulation, and hormone secretion in the Long-Evans rat.

This study examined the influences of aging and reduced ovarian follicular reserve on estrous cyclicity, estradiol (E(2)) production, and gonadotropin secretion. Young virgin and middle-aged (MA) retired breeder female rats were unilaterally ovariectomized (ULO) or sham operated (control). Unilateral ovariectomy of young rats reduced the ovarian follicular reserve by one-half, to a level similar to that found in MA controls. Unilateral ovariectomy of MA females reduced the follicular pool further, to one half of MA controls. The incidence of regular cyclicity was significantly lower in MA ULO females than in young controls, with intermediate cycle frequency in young ULO and MA controls. Among cyclic rats, the magnitude of the proestrous LH surge was highest in young controls, intermediate in young ULO rats and MA controls, and lowest in MA ULO females. Similarly, ovulation rates were highest in young controls, intermediate in young ULO rats and MA controls, and lowest in MA ULO females. While young ULO rats exhibited augmented secondary FSH surges on estrous morning, middle-aged ULO females displayed secondary FSH levels comparable to young controls. The effects of age and reduced follicle number on estrous cyclicity and gonadotropin secretion were not due to altered E(2) secretion, as preovulatory E(2) levels were similar among all groups. Thus, experimental reduction in the follicular reserve exerts acute effects on the preovulatory LH surge, ovulation rate, and estrous cyclicity in both young and MA rats. However, decreased follicle number increases FSH levels only in young rats, indicating aging-related alterations in the feedback regulation of FSH.

Aging↗

PubMed1989

Norepinephrine induces lung vascular prostacyclin synthesis via alpha 1-adrenergic receptors.

Sympathetic nerve stimulation can cause pulmonary vasoconstriction related to norepinephrine (NE) release. Because of recent reports that NE caused prostacyclin (PGI2) release from systemic arteries, we wondered whether NE caused pulmonary vascular PGI2 release and whether a feedback mechanism existed whereby PGI2 modulated NE-induced vasoconstriction. NE-induced PGI2 synthesis in rat main pulmonary artery rings was larger than that induced by KCl, passive stretch, or a thromboxane analogue, was alpha-adrenergic receptor dependent, and was enhanced by endothelium removal. The NE-induced PGI2 synthesis was not tightly coupled to the magnitude of the pulmonary artery ring contractile response, and inhibition of NE-induced PGI2 production by cyclooxygenase blockade in either the pulmonary artery ring preparation or in isolated rat lungs perfused with a physiological solution did not augment the magnitude of the contractile response. We concluded that NE is a potent stimulus for PGI2 synthesis in the rat main pulmonary artery ring and in the rat lung, yet PGI2 is not important as a modulator of NE-induced vasoconstriction in the rat lung.

6-Ketoprostaglandin F1 alpha↗

PubMed1995

Amplification of nitric oxide synthase expression by nitric oxide in interleukin 1 beta-stimulated rat mesangial cells.

Nitric oxide (NO) plays an important role in immunological reactions as a host defense mechanism against tumor cells and invasive microorganisms, but it may also damage healthy tissue. The excessive formation of NO in IL-1 beta-stimulated renal mesangial cells not only alters glomerular filtration, but it may also cause tissue injury and thus contribute to the pathogenesis of certain forms of glomerulonephritis. We report here that, although NO alone has no evident effect on NO synthase expression, it potently augments IL-1 beta-stimulated NO synthase expression in mesangial cells. NO donors such as sodium nitroprusside and S-nitroso-N-acetyl-D,L-penicillamine markedly increase IL-1 beta-induced NO synthase mRNA and protein levels as well as enzyme activity. Nuclear run-on experiments suggest that NO acts to increase IL-1 beta-induced NO synthase gene expression at the transcriptional level. Furthermore, inhibition of NO synthesis by different pharmacological approaches reduces IL-1 beta-induced NO synthase expression, thus suggesting that NO functions in a positive feedback loop that speeds up and strengthens its own biosynthesis. We suggest that this potent amplification mechanism forms the basis for the excessive formation of NO in acute and chronic inflammatory diseases.

Amino Acid Oxidoreductases↗

PubMed1982

Augmentative and inhibitory effects of chronic steroid injections on LH release and their dependency on time.

The effect of daily s. c. injections of 50 micrograms ethinyl estradiol, 1 mg norethindrone and of 1 mg megestrol acetate upon basal and LH-RH-stimulated LH release was investigated in intact female rats. Basal serum LH was rapidly depressed by ethinyl estradiol and norethindrone, while megestrol acetate was less effective. the pituitary response to 30 or 150 ng LH-RH was initially augmented by the treatment with norethindrone reaching a maximum after 5 days, by ethinyl estradiol with a maximum after 10 days, and megestrol acetate after 20 days. In every case, the positive effect was followed by inhibition of H-RH mediated LH release when treatment with the respective steroid was continued. Two weeks after discontinuing of the daily injections, the blockade of the pituitary was abolished. It is concluded that a rapid decrease of endogenous LH-RH release is responsible for the suppression of basal serum LH, while a concomitant direct action on the pituitary augments the response to exogenous LH-RH during the first days of steroid application. When the treatment with steroids is continued for a prolonged period of time, the pulsatile pattern of LH-RH release from the hypothalamus becomes impaired, and this results in dependency on the type of steroid in inhibiting of pituitary response.

Animals↗

PubMed2006

Anatomy of a decision: striato-orbitofrontal interactions in reinforcement learning, decision making, and reversal.

The authors explore the division of labor between the basal ganglia-dopamine (BG-DA) system and the orbitofrontal cortex (OFC) in decision making. They show that a primitive neural network model of the BG-DA system slowly learns to make decisions on the basis of the relative probability of rewards but is not as sensitive to (a) recency or (b) the value of specific rewards. An augmented model that explores BG-OFC interactions is more successful at estimating the true expected value of decisions and is faster at switching behavior when reinforcement contingencies change. In the augmented model, OFC areas exert top-down control on the BG and premotor areas by representing reinforcement magnitudes in working memory. The model successfully captures patterns of behavior resulting from OFC damage in decision making, reversal learning, and devaluation paradigms and makes additional predictions for the underlying source of these deficits.

Animals↗

PubMed2006

Augmentation of exposure therapy with D-cycloserine for social anxiety disorder.

CONTEXT: Social anxiety disorder (SAD) is common and debilitating. Although exposure therapy is one of the most effective forms of psychotherapy for this disorder, many patients remain symptomatic. Fear reduction in exposure therapy is similar to extinction learning, and early clinical data with specific phobias suggest that the treatment effects of exposure therapy for SAD may be enhanced with d-cycloserine, an agonist at the glutamatergic N-methyl-d-aspartate receptor. OBJECTIVE: To determine whether short-term treatment with 50 mg of d-cycloserine enhances the efficacy of exposure therapy for SAD. DESIGN: Randomized, double-blind, placebo-controlled augmentation trial examining the combination of d-cycloserine or pill placebo with exposure therapy for SAD. SETTING: Patients were self-referred from the general community to 1 of 3 research clinics. PARTICIPANTS: Twenty-seven participants meeting DSM-IV criteria for SAD with significant public speaking anxiety. INTERVENTIONS: Following a diagnostic interview and pretreatment assessment, participants received 5 therapy sessions delivered in either an individual or group therapy format. The first session provided an introduction to the treatment model and was followed by 4 sessions emphasizing exposure to increasingly challenging public speech situations with videotaped feedback of performances. One hour prior to each session, participants received single doses of d-cycloserine or placebo. MAIN OUTCOME MEASURES: Symptoms were assessed by patient self-report and by clinicians blind to the randomization condition before treatment, after treatment, and 1 month after the last session. RESULTS: Participants receiving d-cycloserine in addition to exposure therapy reported significantly less social anxiety compared with patients receiving exposure therapy plus placebo. Controlled effect sizes were in the medium to large range. CONCLUSION: The pilot data provide preliminary support for the use of short-term dosing of d-cycloserine as an adjunctive intervention to exposure therapy for SAD.

Adult↗