Mechanisms of G protein activation via the D-2 dopamine receptor: evidence for persistent receptor/G protein interaction after agonist stimulation

Background and purpose: The aim of this report is to study mechanisms of G protein activation by agonists. Experimental approach: The association and dissociation of guanosine 5'-O-(3-[S-35] thio) triphosphate ([S-35] GTP gamma S) binding at G proteins in membranes of CHO cells stably transfected with the human dopamine D-2short receptor was studied in the presence of a range of agonists. Key results: Binding of [S-35] GTPgS was dissociable in the absence of agonist and dissociation was accelerated both in rate and extent by dopamine, an effect which was blocked by the dopamine D-2 receptor antagonist raclopride and by suramin, which inhibits receptor/G protein interaction. A range of agonists of varying efficacy increased the rate of dissociation of [S-35] GTPgS binding, with the more efficacious agonists resulting in faster dissociation. Agonists were able to dissociate about 70% of the pre-bound [S-35] GTPgS, leaving a component which may not be accessible to the agonist-bound receptor. The dissociable component of the [S-35] GTPgS binding was reduced with longer association times and increased [S-35] GTPgS concentrations. Conclusions and implications: These data are consistent with [S-35] GTPgS binding being initially to receptor-linked G proteins and then to G proteins which have separated from the agonist bound receptor. Under the conditions used typically for [S-35] GTPgS binding assays, therefore, much of the agonist-receptor complex remains in proximity to G proteins after they have been activated by agonist.

Agonist-selective, receptor-specific interaction of human P-2Y receptors with beta-arrestin-1 and-2

Interaction of G-protein-coupled receptors with beta-arrestins is an important step in receptor desensitization and in triggering "alternative" signals. By means of confocal microscopy and fluorescence resonance energy transfer, we have investigated the internalization of the human P2Y receptors 1, 2, 4, 6, 11, and 12 and their interaction with beta-arrestin-1 and -2. Co-transfection of each individual P2Y receptor with beta-arrestin-1-GFP or beta-arrestin-2-YFP into HEK-293 cells and stimulation with the corresponding agonists resulted in a receptor-specific interaction pattern. The P2Y(1) receptor stimulated with ADP strongly translocated beta-arrestin-2-YFP, whereas only a slight translocation was observed for beta-arrestin-1-GFP. The P2Y(4) receptor exhibited equally strong translocation for beta-arrestin-1-GFP and beta-arrestin-2YFP when stimulated with UTP. The P2Y(6), P2Y(11), and P2Y(12) receptor internalized only when GRK2 was additionally cotransfected, but beta-arrestin translocation was only visible for the P2Y(6) and P2Y(11) receptor. The P2Y(2) receptor showed a beta-arrestin translocation pattern that was dependent on the agonist used for stimulation. UTP translocated beta-arrestin-1-GFP and beta-arrestin-2-YFP equally well, whereas ATP translocated beta-arrestin-1-GFP to a much lower extent than beta-arrestin2- YFP. The same agonist-dependent pattern was seen in fluorescence resonance energy transfer experiments between the fluorescently labeled P2Y(2) receptor and beta-arrestins. Thus, the P2Y(2) receptor would be classified as a class A receptor when stimulated with ATP or as a class B receptor when stimulated with UTP. The ligand-specific recruitment of beta-arrestins by ATP and UTP stimulation of P2Y(2) receptors was further found to result in differential stimulation of ERK phosphorylation. This suggests that the two different agonists induce distinct active states of this receptor that show differential interactions with beta-arrestins.

Drug interaction and location in liposomes: correlation with polar surface areas

An important step in liposome characterization is to determine the location of a drug within the liposome. This work thus investigated the interaction of dipalmitoylphosphatidylcholine liposomes with drugs of varied water solubility, polar surface area (PSA) and partition coefficient using high sensitivity differential scanning calorimetry. Lipophilic estradiol (ES) interacted strongest with the acyl chains of the lipid membrane, followed by the somewhat polar 5-fluorouracil (5-FU). Strongly hydrophilic mannitol (MAN) showed no evidence of interaction but water soluble polymers inulin (IN) and an antisense oligonucleotide (OLG), which have very high PSAs, interacted with the lipid head groups. Accordingly, the drugs could be classified as: hydrophilic ones situated in the aqueous core and which may interact with the head groups; those located at the water-bilayer interface with some degree of penetration into the lipid bilayer; those lipophilic drugs constrained within the bilayer. (c) 2004 Elsevier B.V. All rights reserved.

The effect of the functional attributes of objects within the caged environment on interaction time in laboratory rats

Determining rat preferences for, and behaviour towards, environmental enrichment objects allows us to provide evidence-based information about how the caged environment may be enriched. In recent years there have been many studies investigating the preferences of laboratory rodents for a wide variety of environmental enrichment objects and materials. While these have provided important information regarding the animals' perception of the items, very few studies have attempted to systematically investigate the precise attributes that constitute a preferred object and the behaviour that these objects afford. We have designed a research program to systematically study rats' motivation to interact with enrichment objects. Here we present the results from two experiments which examined the time rats spent with objects that only differed in size. This showed that rats spent longer with large objects rather than small ones, even though objects were presented individually. We also investigated the rats' behaviour with the objects in an open field and found that rats spent longer climbing on top of the large object. This behaviour continued when the large objects were laid on their sides instead of placed upright in the arena, suggesting that the rats were not simply climbing on the objects to investigate the top of the arena and thus an escape route, but instead were genuinely motivated to climb. This suggests that rat welfare could be enhanced by the addition to their cages of objects that permit climbing. (C) 2009 Elsevier B.V. All rights reserved.

Social interaction deficits and conversational inadequacy in Williams syndrome

Research on social communication skills in individuals with Williams syndrome has been inconclusive, with some arguing that these skills are a relative strength and others that they are a weakness. The aim of the present study was to investigate social interaction abilities in a group of children with WS, and to compare them to a group of children with specific language impairment and a group of typically developing children. Semi-structured conversations were conducted and 100-150 utterances were selected for analysis in terms of exchange structure, turn taking, information transfer and conversational inadequacy. The statistical analyses showed that the children with WS had difficulties with exchange structure and responding appropriately to the interlocutor's requests for information and clarification. They also had significant difficulties with interpreting meaning and providing enough information for the conversational partner. Despite similar language abilities with a group of children with specific language impairment, the children with WS had different social interaction skills, which suggests that they follow an atypical trajectory of development and their neurolinguistic profile does not directly support innate modularity. (c) 2005 Elsevier Ltd. All rights reserved.

The effect of postnatal depression on mother-infant interaction, infant response to the still-face perturbation, and performance on an instrumental learning task

A representative community sample of primiparous depressed women and a nondepressed control group were assessed while in interaction with their infants at 2 months postpartum. At 3 months, infants were assessed on the Still-face perturbation of face to face interaction, and a subsample completed an Instrumental Learning paradigm. Compared to nondepressed women, depressed mothers' interactions were both less contingent and less affectively attuned to infant behavior. Postnatal depression did not adversely affect the infant's performance in either the Still-face perturbation or the Instrumental Learning assessment. Maternal responsiveness in interactions at 2 months predicted the infant's performance in the Instrumental Learning assessment but not in the Still-face perturbation. The implications of these findings for theories of infant cognitive and emotional development are discussed.

The effect of colored lenses on the visual evoked response in children with visual stress

Purpose. Some children with visual stress and/or headaches have fewer symptoms when wearing colored lenses. Although subjective reports of improved perception exist, few objective correlates of these effects have been established. Methods. In a pilot study, 10 children who wore Intuitive Colorimeter lenses, and claimed benefit, and two asymptomatic children were tested. Steady-state potentials were measured in response to low contrast patterns modulating at a frequency of 12 Hz. Four viewing conditions were compared: 1) no lens; 2) Colorimeter lens; 3) lens of complementary color; and 4) spectrally neutral lens with similar photopic transmission. Results. The asymptomatic children showed little or no difference between the lens and no lens conditions. When all the symptomatic children were tested together, a similar result was found. However, when the symptomatic children were divided into two groups depending on their symptoms, an interaction emerged. Children with visual stress but no headaches showed the largest amplitude visual evoked potential response in the no lens condition, whereas those children whose symptoms included severe headaches or migraine showed the largest amplitude visual evoked potential response when wearing their prescribed lens. Conclusions. The results suggest that it is possible to measure objective correlates of the beneficial subjective perceptual effects of colored lenses, at least in some children who have a history of migraine or severe headaches.

Developing social interaction and understanding in individuals with autism spectrum disorder: a groupwork intervention

Background: Difficulties with social interaction and understanding lie at the heart of the communication disorder that characterises the autism spectrum. This study sought to improve social communication for individuals with autism spectrum disorder (ASD) by means of a groupwork intervention focusing on social and emotional perspective-taking, conversation skills, and friendship skills. It also aimed to address some of the limitations of previous interventions, including a lack of generalisation to other settings, so as to maximise inclusion in the community. Method A group of 46 high functioning children and adolescents with ASD (38 boys, 8 girls, age range 6-16 years) were allocated to one of 6 intervention groups. Each group met over a period of 12-16 weeks for a minimum of one 1 1/2-hour weekly session aimed at promoting key areas of social interaction and understanding, supported by home-based practice. Results: Significant gains were achieved in comparison with a normative population, and individual parent ratings showed marked and sustained changes in the key areas targeted in the group sessions. Conclusion: Social communication in children and adolescents with ASD can be enhanced through the use of a groupwork intervention addressing social interaction and understanding.

Sibling interaction of children with autism: development over 12 months

While deficits in social interaction are central to autism, the sibling relationship has been found to provide a key medium for the development of such skills. Naturalistic observations of sibling pairs including children with autism and controls with Down syndrome were made across two time periods, twelve months apart. Consistent with the evidence on typically developing children, the amount and rate of initiations of both prosocial and agonistic interaction increased, but further analysis suggested that these interactions were stage-managed by the typically developing children. Results show social interaction and imitation in children with autism and the special role that sibling interactions can play. Longitudinal research on the acquisition of social skills in children with developmental disabilities is needed.

Living with ASD: how do children and their parents assess their difficulties with social interaction and understanding?

Social interaction and understanding in autistic spectrum disorder (ASD) are key areas of concern to practitioners and researchers alike. However, there is a relative lack of information about the skills and competencies of children and young people with ASD who access ordinary community facilities including mainstream education. In particular, contributions by parents and their children have been under-utilized. Using two structured questionnaires, 19 children with ASD reported difficulties with social skills including social engagement and temper management and also reported difficulties with social competence, affecting both friendships and peer relationships. Parents rated the children's social skill and competence as significantly worse than did the children themselves, but there was considerable agreement about the areas that were problematic. Using an informal measure to highlight their children's difficulties, parents raised issues relating to conversation skills, social emotional reciprocity and peer relationships. The implications for assessment and intervention are discussed.

The role played by the interaction between genetic factors and attachment in the stress response in infancy

Background: The importance of understanding which environmental and biological factors are involved in determining individual differences in physiological response to stress is widely recognized, given the impact that stress has on physical and mental health. Methods: The child-mother attachment relationship and some genetic polymorphisms (5-HTTLPR, COMT and GABRA6) were tested as predictors of salivary cortisol and alpha amylase concentrations, two biomarkers of hypothalamic-pituitary-adrenocortical (HPA) axis and sympathetic adrenomedullary (SAM) system activity, during the Strange Situation (SS) procedure in a sample of more than 100 healthy infants, aged 12 to 18 months. Results: Individual differences in alpha amylase response to separation were predicted by security of attachment in interaction with 5-HTTLPR and GABRA6 genetic polymorphisms, whereas alpha amylase basal levels were predicted by COMT x attachment interaction. No significant effect of attachment, genetics and their interaction on cortisol activity emerged. Conclusions: These results help to disentangle the role played by both genetic and environmental factors in determining individual differences in stress response in infancy. The results also shed light on the suggestion that HPA and SAM systems are likely to have different characteristic responses to stress.

Towards dynamical system models of language-related brain potentials

Event-related brain potentials (ERP) are important neural correlates of cognitive processes. In the domain of language processing, the N400 and P600 reflect lexical-semantic integration and syntactic processing problems, respectively. We suggest an interpretation of these markers in terms of dynamical system theory and present two nonlinear dynamical models for syntactic computations where different processing strategies correspond to functionally different regions in the system's phase space.

Adaptive control of event integration: evidence from event-related potentials

We investigated whether it is possible to control the temporal window of attention used to rapidly integrate visual information. To study the underlying neural mechanisms, we recorded ERPs in an attentional blink task, known to elicit Lag-1 sparing. Lag-1 sparing fosters joint integration of the two targets, evidenced by increased order errors. Short versus long integration windows were induced by showing participants mostly fast or slow stimuli. Participants expecting slow speed used a longer integration window, increasing joint integration. Difference waves showed an early (200 ms post-T2) negative and a late positive modulation (390 ms) in the fast group, but not in the slow group. The modulations suggest the creation of a separate event for T2, which is not needed in the slow group, where targets were often jointly integrated. This suggests that attention can be guided by global expectations of presentation speed within tens of milliseconds.

Determining feature relevance for the grouping of motor unit action potentials through generative topographic mapping

The study of motor unit action potential (MUAP) activity from electrornyographic signals is an important stage on neurological investigations that aim to understand the state of the neuromuscular system. In this context, the identification and clustering of MUAPs that exhibit common characteristics, and the assessment of which data features are most relevant for the definition of such cluster structure are central issues. In this paper, we propose the application of an unsupervised Feature Relevance Determination (FRD) method to the analysis of experimental MUAPs obtained from healthy human subjects. In contrast to approaches that require the knowledge of a priori information from the data, this FRD method is embedded on a constrained mixture model, known as Generative Topographic Mapping, which simultaneously performs clustering and visualization of MUAPs. The experimental results of the analysis of a data set consisting of MUAPs measured from the surface of the First Dorsal Interosseous, a hand muscle, indicate that the MUAP features corresponding to the hyperpolarization period in the physisiological process of generation of muscle fibre action potentials are consistently estimated as the most relevant and, therefore, as those that should be paid preferential attention for the interpretation of the MUAP groupings.