Biomedical subjects

Douglas Ramsay

Publications and source records attributed to Douglas Ramsay.

9 recordsLinked to original sources

PubMed2006

Reactivity and regulation in children prenatally exposed to cocaine.

Children prenatally exposed to cocaine may be at elevated risk for adjustment problems in early development because of greater reactivity and reduced regulation during challenging tasks. Few studies have examined whether cocaine-exposed children show such difficulties during the preschool years, a period marked by increased social and cognitive demands and by rapid changes in reactivity and regulation. The authors addressed this question by examining frustration reactivity and regulation of behavior during a problem-solving task in cocaine-exposed and -unexposed preschoolers. Participants were 174 4.5-year-olds (M age = 4.55 years, SD = 0.09). Frustration reactivity was measured as latency to show frustration and number of disruptive behaviors, whereas regulation was measured as latency to approach and attempt the problem-solving task and number of problem-solving behaviors. Results indicated that cocaine-exposed children took longer to attempt the problem-solving task but that cocaine-exposed boys showed the most difficulties: They were quicker to express frustration and were more disruptive. Effect sizes were relatively small, suggesting both resilience and vulnerabilities.

Adaptation, Psychological↗

PubMed2004

High-affinity interactions between human alpha1A-adrenoceptor C-terminal splice variants produce homo- and heterodimers but do not generate the alpha1L-adrenoceptor.

Using combinations of bioluminescence resonance energy transfer, time-resolved fluorescence resonance energy transfer and the functional complementation of pairs of inactive receptor-G protein fusion proteins, the human alpha(1A-1)-adrenoceptor was shown to form homodimeric/oligomeric complexes when expressed in human embryonic kidney (HEK) 293 cells. Saturation bioluminescence resonance energy transfer studies indicated the alpha(1A-1)-adrenoceptor homodimer interactions to be high affinity and some 75 times greater than interactions between the alpha(1A-1)-adrenoceptor and the delta opioid peptide receptor. Only a fraction of the alpha(1A-1)-adrenoceptors was at the plasma membrane of HEK293 cells at steady state. However, dimers of alpha(1A-1)-adrenoceptors were also present in intracellular membranes, and the dimer status of those delivered to the cell surface was unaffected by the presence of agonist. Splice variation can generate at least three forms of the human alpha(1A-1)-adrenoceptor with differences limited to the C-terminal tail. Each of the alpha(1A-1), alpha(1A-2a), and alpha(1A-3a)-adrenoceptor splice variants formed homodimers/oligomers, and all combinations of these splice variants were able to generate heterodimeric/oligomeric interactions. Despite the coexpression of these splice variants in human tissues that possess the pharmacologically defined alpha(1L)-adrenoceptor binding site, coexpression of any pair in HEK293 cells failed to generate ligand binding characteristic of the alpha(1L)-adrenoceptor.

Alternative Splicing↗

PubMed2003

GPCR dimerisation.

The concept that GPCRs exist and potentially function as dimers and/or higher oligomers has progressed recently from hypothesis to being widely accepted. A range of techniques has contributed to this understanding, including co-immunoprecipitation and various forms of fluorescence and bioluminescence resonance energy transfer. Although co-immunoprecipitation studies indicate the capacity of a wide range of GPCRs to form hetero-dimers as well as homo-dimers, this approach is not well suited to examine selectivity of interactions. Both bioluminescence resonance energy transfer (BRET) and fluorescence resonance energy transfer (FRET) have been applied to the detection of GPCR dimerisation in intact cells and BRET and FRET have been used to attempt to quantitate the fraction of GPCRs present as dimers. Following heterologous expression, a considerable fraction of many GPCRs is not fully processed and is trafficked to the proteasome or lysosome for destruction. A distinct limitation of both BRET and conventional FRET approaches is that both the energy donor and energy acceptor tags are inside the cell. Time-resolved FRET employing N-terminally epitope-tagged GPCRs has been used to allow detection only of dimers trafficked successfully to the cell surface. Reports indicating the appearance of distinct pharmacology and function following co-expression of two GPCRs are fascinating. Much remains to be examined, however, on the specificity and mechanisms of these interactions and to develop techniques to monitor the function only of hetero-dimers when the corresponding homo-dimers must also be present.

Animals↗

PubMed2002

Homo- and hetero-oligomeric interactions between G-protein-coupled receptors in living cells monitored by two variants of bioluminescence resonance energy transfer (BRET): hetero-oligomers between receptor subtypes form more efficiently than between less closely related sequences.

Homo- and hetero-oligomerization of G-protein-coupled receptors (GPCRs) were examined in HEK-293 cells using two variants of bioluminescence resonance energy transfer (BRET). BRET(2) (a variant of BRET) offers greatly improved separation of the emission spectra of the donor and acceptor moieties compared with traditional BRET. Previously recorded homo-oligomerization of the human delta-opioid receptor was confirmed using BRET(2). Homo-oligomerization of the kappa-opioid receptor was observed using both BRET techniques. Both homo- and hetero-oligomers, containing both delta- and kappa-opioid receptors, were unaffected by the presence of receptor ligands. BRET detection of opioid receptor homo- and hetero-oligomers required expression of 50,000-100,000 copies of the receptor energy acceptor construct per cell. The effectiveness of delta-kappa-opioid receptor hetero-oligomer formation was as great as for homomeric interactions. The capacity of the two opioid receptors to form oligomeric complexes with the beta(2)-adrenoceptor was also assessed. Although such interactions were detected, at least 250,000 copies per cell of the energy acceptor were required. Requirement for high levels of receptor expression was equally pronounced in attempts to measure hetero-oligomer formation between the kappa-opioid receptor and the thyrotropin-releasing hormone receptor-1. These studies indicate that constitutively formed homo- and hetero-oligomers of opioid receptor subtypes can be detected in living cells containing less than 100,000 copies of the receptors. However, although hetero-oligomeric interactions between certain less closely related GPCRs can be detected, they appear to be of lower affinity than homo- or hetero-oligomers containing closely related sequences. Interactions recorded between certain GPCR family members in heterologous expression systems are likely to be artefacts of extreme levels of overexpression.

Base Sequence↗

PubMedDate not supplied

Cortisol response to embarrassment and shame.

This study examined individual differences in 4-year-old children's (N = 60) expression of the self-conscious emotions of embarrassment and shame and their relation to differences in cortisol response to stress. Results indicated the presence of two different types of embarrassment--one that reflected negative evaluation of the self, and the other a nonevaluative type that reflected simply exposure of the self when the individual was the object of attention of others. Results also indicated a relation between a higher cortisol response to stress and the greater expression of the self-conscious emotions of evaluative embarrassment and shame that reflected negative self-evaluation.

Arousal↗

PubMedDate not supplied

Reactivity and regulation in cortisol and behavioral responses to stress.

This study examined relations between reactivity (i.e., peak response) and regulation (i.e., response dampening) in 6-month-old infants' cortisol and behavioral responses to inoculation (N = 62). Data showed that reactivity and regulation were unrelated for both cortisol and behavior. The independence of reactivity and regulation suggests that measures of both are needed to characterize infant cortisol or behavioral response to stress more completely. For both reactivity and regulation, cortisol and behavior were unrelated, suggesting that measures of both are needed to assess infant stress more adequately. There was considerable variation in the timing of the peak cortisol response, suggesting that obtaining only a single poststressor cortisol sample does not provide a sensitive measure of cortisol reactivity.

Female↗

PubMedDate not supplied

Development of self-recognition, personal pronoun use, and pretend play during the 2nd year.

This study examined the relation of visual self-recognition to personal pronoun use and pretend play. For a longitudinal sample (N=66) at the ages when self-recognition was emerging (15, 18, and 21 months), self-recognition was related to personal pronoun use and pretend play such that children showing self-recognition used more personal pronouns and demonstrated more advanced pretend play than did children not showing self-recognition. The finding of a relation among these measures provides additional evidence that in the middle of the 2nd year of life a metarepresentation of self emerges in the human child.

Child Language↗

PubMedDate not supplied

Infant emotional and cortisol responses to goal blockage.

This study examined the relation of infant emotional responses of anger and sadness to cortisol response in 2 goal blockage situations. One goal blockage with 4-month-old infants (N = 56) involved a contingency learning procedure where infants' learned response was no longer effective in reinstating an event. The other goal blockage with 6-month-old infants (N = 84) involved the still face procedure where infants' reactions to their mothers' lack of responsivity were not effective in reestablishing interaction. For both blockages, sadness was related to cortisol response, though anger was not--the greater the sadness, the higher the cortisol response. This differential relation is consistent with other evidence indicating the more positive role of anger as opposed to sadness in overcoming an obstacle.

Affect↗

PubMedDate not supplied

Ligand rescue of constitutively active mutant receptors.

Constitutively active mutants (CAMs) of G protein-coupled receptors are found naturally in disease states and they can be generated by point mutation. As these mutants are able to activate G proteins in the absence of a ligand, they are useful tools in the study of conformational changes leading to receptor activation and in the drug discovery process. Early studies on CAMs noted that they are often expressed at lower levels than their wild-type forms. In this review we discuss the mechanisms responsible for this reduced expression and also provide an explanation for the observation that challenging cells with receptor ligands can increase the CAM expression level. The application of these observations to the development of a high-throughput reporter assay suitable for ligand identification is also discussed.

Animals↗