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Biomedical subjects

R J Barrett

Publications and source records attributed to R J Barrett.

At least 19 recordsLinked to original sources
PubMed2005

Evidence for PTZ-like cues as a function of time following treatment with chlordiazepoxide: implications for understanding tolerance and withdrawal.

The present study used a two-lever, drug-discrimination procedure to train rats to discriminate between the cues associated with 5 mg/kg of the anxiolytic, chlordiazepoxide (CDP) and 15 mg/kg of the anxiogenic, pentylenetetrazol (PTZ), to investigate the relationship between withdrawal and acute tolerance. Training doses of the two drugs were chosen so that rats responded about equally on both levers when tested on saline (SAL). Following acquisition of the discrimination, rats were injected with 10 mg/kg CDP and tested for lever choice at various intervals from 6 h to 192 h. These tests revealed that cues associated with CDP withdrawal lasted approximately three times longer than the cues associated with the drug's primary effects. At the shortest retest interval (6 h) after treatment with 10 mg/kg CDP, rats responded primarily on the CDP lever, followed by a shift to predominant responding on the PTZ lever at the 16 h and 24 h intervals before returning to predrug, baseline levels at the longer intervals (48-192 h). In order to investigate the relationship between tolerance and withdrawal to the cue properties of CDP, CDP dose-response curves were determined 24 h following treatment with SAL or 10 mg/kg CDP. Acute tolerance, as defined by a rightward, parallel shift in the dose-response function, was observed in the rats pretreated with CDP. Furthermore, it was evident that the baseline shift associated with CDP withdrawal, rather than a weaker drug cue, accounted for acute tolerance. The results from this study are relevant to evaluating the role positive and negative reinforcement play in motivating compulsive drug use.

Animals↗
PubMed2005

Mental health nurses' and psychiatrists' views on the prognosis of schizophrenia and depression: an exploratory, qualitative investigation.

This study uses a qualitative methodology to explore mental health literacy, specifically perceptions of prognosis, which is typically investigated with a quantitative, questionnaire-based approach. Two vignettes--one of a person with schizophrenia and one with depression--were shown to three mental health nurses and three psychiatrists. During semi-structured, open-ended interviews, they were asked to discuss their thoughts about the prognosis for the patient presented in each vignette. Participants tended to use the terms 'prognosis' and 'outcome' interchangeably. Psychiatrists tended to be more guarded in determining a prognosis than nurses. Both groups emphasized the importance of clinical experience in formulating views. However, nurses also discussed the role of the multidisciplinary team, whilst psychiatrists emphasized their reliance upon the scientific literature in shaping opinions. Participants identified information relevant for incorporating into future vignettes, to allow more informed research into literacy. The results of quantitative mental health literacy research should be interpreted with caution. Simplifying responses to allow comparative analysis is necessary, but masks more complex and important interpretations. Further qualitative research is recommended, the results of which can inform more comprehensive quantitative studies in the area.

Adult↗
PubMed2001

Inconsistent reconstitution of cytomegalovirus-specific cell-mediated immunity in human immunodeficiency virus-infected patients receiving highly active antiretroviral therapy.

Cytomegalovirus (CMV)-immune recovery was characterized in human immunodeficiency virus (HIV)-infected patients receiving highly active antiretroviral therapy. CMV lymphocyte proliferation (LP), responder-cell frequency (RCF), and interferon (IFN)-gamma and interleukin (IL)-2 secretion were studied in CMV-seropositive HIV-infected patients and in CMV-seropositive HIV-uninfected control subjects. HIV-infected patients and control subjects had similar proportions of IL-2 and IFN-gamma, but levels were lower in HIV-infected patients. LP and RCF were significantly less frequent and of lower magnitude in HIV-infected patients. The measures of CMV cell-mediated immunity were correlated in HIV-uninfected but not in HIV-infected subjects. To investigate this, IL-2, IL-12, anti-CD28 plus anti-CD49d, or anti-IL-10 was added in vitro, with no effect on LP. However, CD8 cell depletion of mononuclear cells from HIV-infected patients increased LP responses to levels similar to those of uninfected control subjects; before depletion, only RCF correlated with CD4 cell counts, but after depletion, LP also correlated with CD4 cell counts.

AIDS-Related Opportunistic Infections↗
PubMed2001

Long-lasting rebound cue effects following single doses of nicotine and amphetamine: implications for understanding tolerance.

RATIONALE: Previous drug-discrimination studies have, with the exception of nicotine (NIC), demonstrated tolerance to the cue effects of a broad range of drugs of abuse. Barrett et al. have shown that tolerance to a drug's cue properties reflects drug-induced rebound shifts in the discrimination baseline and not a weakened or less salient cue. OBJECTIVES: The objective of the present study was to use a discrimination task sensitive to bidirectional cue changes to characterize the interoceptive cues associated with both the primary and rebound cues produced by nicotine in an attempt to understand why a recent study by Shoaib et al. failed to observe tolerance to the nicotine cue. METHODS: Since dopamine (DA) has been implicated in mediating the NIC cue, rats were trained to discriminate between 0.25 mg/kg amphetamine (AMPH), an indirect DA agonist, and 0.033 mg/kg haloperidol (HAL), a DA antagonist at the D2 receptor site. Training doses were chosen so that rats responded about equally on both levers when tested on saline (SAL) following acquisition. This procedure provided a behavioral baseline to assess NIC-related changes along a presumed continuum of DA-mediated cues. Following acquisition of the discrimination: (i) NIC substitution tests were conducted, (ii) rats were tested for lever choice at intervals from 2 h to 48 h following treatment with single doses of 0.25 mg/kg and 0.50 mg/kg NIC, and (iii) rats were challenged with test doses of NIC during a period of NIC rebound. RESULTS: (i) NIC substituted for AMPH in a dose- dependent manner. (ii) At short intervals after treatment with 0.25 mg/kg and 0.50 mg/kg NIC, rats responded primarily on the AMPH lever followed by a shift to predominant responding on the HAL lever 16-24 h post-treatment, before returning to predrug levels. (iii) No evidence was observed for acute tolerance to NIC. CONCLUSIONS: The robust and long-lasting rebound cues associated with training level doses of NIC suggest that maximal tolerance would likely develop to the NIC cue during the acquisition phase of the conventional NIC-saline discrimination study.

Amphetamine↗
PubMed2000

Tubal sterilization and risk of cancer of the endometrium.

OBJECTIVE: Surgical sterilization is a common method of contraception among U.S. women. Most surgical sterilizations are tubal ligations, but few studies have investigated their potential impact on endometrial cancer risk. METHODS: A case-control study included 405 women diagnosed with endometrial cancer at 5 U.S. medical centers between 1987 and 1990 and 297 age-, race-, and location-matched controls who were identified by random-digit-dialing. Questionnaires ascertained information on tubal sterilization, and logistic regression models generated odds ratios (ORs) to estimate relative risk. RESULTS: The OR and 95% confidence interval for tubal sterilization, which was reported by 47 cases and 40 controls, was 0.9 (0.6-1.4) before adjustment and 1. 4 (0.8-2.4) after adjustment for age, parity, and oral contraceptive use. Age at surgery, years since surgery, or calendar years of surgery were not associated with endometrial cancer, and associations did not vary according to parity or stage of disease at diagnosis. CONCLUSIONS: Tubal sterilization is not substantially associated with endometrial cancer.

Adult↗
PubMed2000

Concurrent chemotherapy and pelvic radiation therapy compared with pelvic radiation therapy alone as adjuvant therapy after radical surgery in high-risk early-stage cancer of the cervix.

PURPOSE: To determine whether the addition of cisplatin-based chemotherapy (CT) to pelvic radiation therapy (RT) will improve the survival of early-stage, high-risk patients with cervical carcinoma. PATIENTS AND METHODS: Patients with clinical stage IA(2), IB, and IIA carcinoma of the cervix, initially treated with radical hysterectomy and pelvic lymphadenectomy, and who had positive pelvic lymph nodes and/or positive margins and/or microscopic involvement of the parametrium were eligible for this study. Patients were randomized to receive RT or RT + CT. Patients in each group received 49.3 GY RT in 29 fractions to a standard pelvic field. Chemotherapy consisted of bolus cisplatin 70 mg/m(2) and a 96-hour infusion of fluorouracil 1,000 mg/m(2)/d every 3 weeks for four cycles, with the first and second cycles given concurrent to RT. RESULTS: Between 1991 and 1996, 268 patients were entered onto the study. Two hundred forty-three patients were assessable (127 RT + CT patients and 116 RT patients). Progression-free and overall survival are significantly improved in the patients receiving CT. The hazard ratios for progression-free survival and overall survival in the RT only arm versus the RT + CT arm are 2.01 (P =.003) and 1.96 (P =. 007), respectively. The projected progression-free survivals at 4 years is 63% with RT and 80% with RT + CT. The projected overall survival rate at 4 years is 71% with RT and 81% with RT + CT. Grades 3 and 4 hematologic and gastrointestinal toxicity were more frequent in the RT + CT group. CONCLUSION: The addition of concurrent cisplatin-based CT to RT significantly improves progression-free and overall survival for high-risk, early-stage patients who undergo radical hysterectomy and pelvic lymphadenectomy for carcinoma of the cervix.

Adult↗
PubMed1999

Characterizing withdrawal in rats following repeated drug administration using an amphetamine-vehicle-haloperidol drug discrimination.

RATIONALE: Previous research using an amphetamine (AM)-haloperidol (HA) drug- drug discrimination task has shown that predominant responding on the HA-appropriate lever occurs 24 h after a single or multiple administrations of 10 mg/kg AM. Conversely, rebound responding on the AM-appropriate lever occurs following single or multiple administrations of 1 mg/kg HA. HA-appropriate responding was also observed 24 h following a single injection of AM using a three-lever, AM-vehicle-HA discrimination task. However, a single administration of HA did not produce robust rebound responding on the AM-appropriate lever. The present studies seek to clarify the discrepancy between responding following HA in the two- and three-choice tasks. OBJECTIVE: Experiment 1 examined the extent of rebound responding that could be achieved following ten daily administrations of either 10 mg/kg AM or 1 mg/kg HA. Experiment 2 explored potential differences between the two- and three-choice tasks in characterizing the post-HA cue. METHODS: Animals were trained to discriminate 0.35 mg/kg AM, vehicle, and 0.033 mg/kg HA. In experiment 1, animals received ten daily injections of 10 mg/kg AM, vehicle, or 1 mg/kg HA, and were tested 24 h after the final injection, and again 8, 15, and 22 days post-treatment. In experiment 2, animals were retrained and then treated daily with either vehicle or 1.0 mg/kg HA for 10 days, and then tested 24 h after the final injection, and again 5 and 11 days post-treatment, with either all three levers or with only the AM- and HA-appropriate levers available. RESULTS: In experiment 1, multiple injections of AM produced robust HA lever responding, which is consistent with results from previous studies that used the two-choice, AM-HA discrimination task. However, multiple injections of HA did not produce predominant responding on the AM-appropriate lever. In experiment 2, animals treated with either vehicle or HA responded predominantly on the vehicle-appropriate lever when tested with all three levers present. When tested with the vehicle lever removed, however, animals treated with vehicle responded predominantly on the HA-appropriate lever, whereas those treated with HA responded predominantly on the AM-appropriate lever. CONCLUSIONS: These results suggest that the two-choice and three-choice task used here differ in how the post-HA withdrawal cue is characterized. This finding emphasizes the importance of knowing the relative locations of the agonist-, vehicle-, and antagonist-produced cues on the interoceptive stimulus continuum established by discrimination training.

Amphetamine↗
PubMed1999

Mechanism of tolerance development to 2,5-dimethoxy-4-iodoamphetamine in rats: down-regulation of the 5-HT2A, but not 5-HT2C, receptor.

RATIONALE: Defining the mechanism of tolerance development to hallucinogenic drugs will help to explain their mechanism of action. OBJECTIVES: The present study was conducted to determine first, if tolerance develops to the discriminative stimulus (DS) properties of the hallucinogen, 2,5 dimethoxy-4-iodo-amphetamine (DOI) and second, the mechanism mediating tolerance. METHODS: Rats were trained to discriminate 0.75 mg/kg DOI from saline on a concurrent VI-30-min schedule of reinforcement with a 15-min time-out for incorrect responses. To evaluate tolerance development, rats were assigned to one of four groups and treated with either chronic saline or chronic DOI. Prior to chronic treatment, two groups were tested for choice behavior following vehicle administration while the remaining two groups were tested following the administration of 0.375 mg/kg DOI. One group from each pre-test condition was injected with either saline or DOI (1 mg/kg) for 8 days. Twenty-four hours after the last chronic injection the pre-test treatments were replicated. Using receptor autoradiography, the density of 5-HT2A and 5-HT2C receptors was measured in independent groups of rats that had received identical treatment conditions. RESULTS: Animals receiving chronic DOI showed a 60% decrease in DOI lever responding (from 100% to 40%) when tested on 0.375 mg/kg DOI, while animals receiving chronic saline showed no change in percent choice (100%) on the DOI lever. Significant changes in binding were observed in 5-HT2A receptors but not 5-HT2C receptors. The results of tests with antagonists were consistent with the changes in binding. CONCLUSIONS: These results suggest that behavioral tolerance to DOI reflects neuroadaptive changes in 5-HT2A receptors.

Amphetamines↗
PubMed1998

Evidence for a common etiology for endometrial carcinomas and malignant mixed mullerian tumors.

OBJECTIVE: To elucidate factors linked to the development of malignant mixed mullerian tumors (MMMT) and determine whether the risk factor profile for these tumors corresponds with that for the more common endometrial carcinomas. METHODS: A multicenter case-control study of 424 women diagnosed with endometrial carcinoma, 29 women diagnosed with MMMT, and 320 community controls was conducted. Review of pathological reports and slides was performed to classify cases by histological type. All participants were asked to respond to a questionnaire which ascertained information on exposure to factors postulated to be linked to the development of uterine tumors. RESULTS: Women with endometrial carcinomas and MMMTs were similar with respect to age and educational attainment. Women diagnosed with MMMTs were more likely than those diagnosed with carcinomas to be of African-American descent (28% vs 4%; P = 0.001). Weight, exogenous estrogen use, and nulliparity were related to risk of both tumor types. Marked obesity was associated with a 4.8-fold (95% CI = 3.0,7.6) increase in risk of carcinoma and a 3.2-fold (95% CI = 1.1,9.1) increase in risk of MMMT development. Use of exogenous estrogens increased the odds of developing carcinomas by 2-fold (95% CI = 1.3,3.2) and that of developing MMMTs by 1.8-fold (95% CI = 0.57,5.5). Nulliparity was associated with a 2.9-fold (95% CI = 1.9,4.8) increase in risk of carcinomas and a 1.7-fold (95% CI = 0.53,5.6) increase in risk of MMMTs. Oral contraceptive use protected against the development of both carcinomas (OR = 0.39; 95% CI = 0.26,0.58) and MMMTs (OR = 0.76; 95% CI = 0.25,2.3). Current smokers were at a reduced risk of developing endometrial carcinomas (OR = 0.34; 95% CI = 0.21,0.55) and MMMTs (OR = 0.57; 95% CI = 0.15,2.3), while former smokers were at an increased risk of MMMT (OR = 2.7; 95% CI = 1.1,6.8) but not carcinoma development (OR = 0.81; 95% CI = 0.56,1.2). CONCLUSION: Results from this study suggest that MMMTs and carcinomas have a similar risk factor profile. This observation is compatible with the hypothesis that the pathogenesis of these two histological types of uterine tumors is similar.

Adult↗
PubMed1998

Agonist properties of N,N-dimethyltryptamine at serotonin 5-HT2A and 5-HT2C receptors.

Extensive behavioral and biochemical evidence suggests an agonist role at the 5-HT2A receptor, and perhaps the 5-HT2C receptor, in the mechanism of action of hallucinogenic drugs. However the published in vitro pharmacological properties of N,N-dimethyltryptamine (DMT), an hallucinogenic tryptamine analog, are not consistent with this hypothesis. We, therefore, undertook an extensive investigation into the properties of DMT at 5-HT2A and 5-HT2C receptors. In fibroblasts transfected with the 5-HT2A receptor or the 5-HT2C receptor, DMT activated the major intracellular signaling pathway (phosphoinositide hydrolysis) to an extent comparable to that produced by serotonin. Because drug efficacy changes with receptor density and cellular microenvironment, we also examined the properties of DMT in native preparations using a behavioral and biochemical approach. Rats were trained to discriminate an antagonist ketanserin from an agonist 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) in a two-lever choice paradigm. Pharmacological studies showed that responding on the DOI and ketanserin lever reflected agonist and antagonist activity at 5-HT2A receptors, and hence, was a suitable model for evaluating the in vivo functional properties of DMT. Like other 5-HT2A receptor agonists, DMT substituted fully for DOI. Intact choroid plexus was used to evaluate the agonist properties at endogenous 5-HT2C receptors; DMT was a partial agonist at 5-HT2C receptors in this native preparation. Thus, we conclude that DMT behaves as an agonist at both 5-HT2A and 5-HT2A receptors. One difference was evident in that the 5-HT2C, but not the 5-HT2A, receptor showed a profound desensitization to DMT over time. This difference is interesting in light of the recent report that the hallucinogenic activity of DMT does not tolerate in humans and suggests the 5-HT2C receptor plays a less prominent role in the action of DMT.

3T3 Cells↗
PubMed1998

Conceptual foundations of schizophrenia: I. Degeneration.

OBJECTIVE: This is the first of two papers that aim to identify some of the institutional processes of 19th century European psychiatry, and some prevailing cultural themes of that era that played a role in shaping the development of schizophrenia as a disease concept. METHOD: Three areas of psychiatric history are examined: the first is concerned with the key figures who coined the concept of dementia praecox; the second with the rise of the asylum; and the third is to do with the ideology of 19th century psychiatric science and its relationship to a broader intellectual milieu. These three literatures are examined for common themes. RESULTS: The theme of degeneration is evident in all three literatures, and denotes both a biological process (neuro-degeneration) and a moral state (degeneracy). CONCLUSIONS: The idea of degeneration, a pervasive cultural theme of the 19th century, dominated psychiatric thinking long before schizophrenia was developed as a diagnostic category. It contributed to the ideational form-work that gave foundation, structure and shape to the concept of schizophrenia.

Disease Progression↗
PubMed1998

Conceptual foundations of schizophrenia: II. Disintegration and division.

OBJECTIVE: This is the second of two papers that aim to identify some cultural themes and institutional processes that shaped the development of schizophrenia as a disease concept. METHOD: A number of domains within 19th century European history are explored for evidence of the concept of the divided or disintegrated person. These include German academic psychiatry, Mesmerism and hypnosis, neurology and neurophysiology, psychoanalysis and German Romantic literature, and its descendants within a wider European literature. RESULTS: Representations of division or disintegration are evident in all these domains, enjoying widespread currency and penetration throughout the 19th century. CONCLUSIONS: These culturally based ideas, combined with the idea of degeneration, were important elements in the foundation of the schizophrenia concept.

Dissociative Disorders↗
PubMed1998

Analysis of histopathological features of endometrioid uterine carcinomas and epidemiologic risk factors.

A large case-control study was performed to determine whether risk factors for endometrioid carcinoma, the most common type of endometrial cancer, vary according to the histological features of the tumor. Study subjects consisted of 328 women with newly diagnosed endometrioid adenocarcinoma and 320 population-based control subjects. Variables studied included age at menarche, menopausal estrogen use, weight, parity, cigarette smoking, and oral contraceptive use. The risk factor profile for endometrioid carcinomas with and without squamous differentiation was very similar. No striking differences in risk factors were observed between endometrioid cancers with and without adjacent endometrial hyperplasia. Finally, none of the risk factors varied substantially between early-stage and late-stage tumors or low-grade and high-grade tumors. In summary, this study indicates that risk factors for endometrioid carcinomas are not related to the morphological features of the tumor.

Adult↗
PubMed1997

Amphetamine-induced withdrawal responding: effects of repeated drug administration.

The first purpose of this research was to assess withdrawal haloperidol-appropriate lever responding 24 h after a single administration of 0.35, 0.75, and 1.00 mg/kg amphetamine. Rats were trained to discriminate among 0.35 mg/kg amphetamine (AM), distilled water (DW), and 0.033 mg/kg haloperidol (HA) in a three-lever drug discrimination task. An increase in HA-appropriate lever responding occurred following the 1.00 mg/kg dose of AM but not after either of the lower doses. The second purpose was to determine the effect of repeated administration of 0.75 mg/kg AM. Two groups of animals were given five administrations of drug, one at an interdose interval (IDI) of 24 h and the other at an IDI of 48 h. Control animals were given injections of DW. Increased HA-appropriate lever responding occurred in both of the AM-treated groups. The magnitude of this effect tended to be less in the 48-h IDI group. Thus, even though HA-lever responding was not evident 24 h after a single administration of 0.75 mg/kg AM, it was produced by repeated administration of this dose, even at 48-h intervals.

Amphetamine↗
PubMed1997

Tolerance to the anticonflict effects of diazepam: importance of methodological considerations.

The present study examines the effects of chronic diazepam treatment on conflict behavior in rats using the Geller-Seifter paradigm. A dose-response function for the effects of diazepam (DZ) on punished and unpunished responding was determined (0.0, 0.63, 1.25, 2.5, and 5.0 mg/kg DZ intraperitoneally) using five independent groups. The test doses of DZ produced an inverted U-shaped function where punished responding increased as a function of dose up to 2.5 mg/kg and then decreased at 5.0 mg/kg. All groups were then treated with 2 x 5 mg/kg DZ per day for 5 days. When the dose-response function was redetermined at 36 h post-chronic treatment, it was found that the function had shifted to the right, indicating tolerance. Because of the inverted U-shaped nature of the original function, tolerance was manifested as a decrease in responding on the ascending portion of the function and as an increase in responding on the dose (5 mg/kg) representing the descending side of the inverted U.

Animals↗