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Biomedical subjects

A Gifford

Publications and source records attributed to A Gifford.

At least 19 recordsLinked to original sources
PubMed2002

Gestational length in the koala, Phascolarctos cinereus.

We report a possible case of extended gestation in the koala, Phascolarctos cinereus. Birth of a pouch young was first observed 127 days after the removal of the male from a multi-female colony at Taronga Zoo. No other males were present at that time or had access to the facility. Head measurements and other growth data collected at the time of detection and over the period of pouch life indicates the time from removal of the male and the date of birth to be between 50 and 77 days. DNA fingerprinting using microsatellite loci unambiguously assigned paternity of the pouch young to this male. These observations suggest either an extended period of gestation of at least 50 days, or activation of a dormant blastocyst from the previous breeding season, as the female entered the period of seasonal oestrus.

Animals↗
PubMed2001

Therapeutic doses of oral methylphenidate significantly increase extracellular dopamine in the human brain.

Methylphenidate (Ritalin) is the most commonly prescribed psychoactive drug in children for the treatment of attention deficit hyperactivity disorder (ADHD), yet the mechanisms responsible for its therapeutic effects are poorly understood. Whereas methylphenidate blocks the dopamine transporter (main mechanism for removal of extracellular dopamine), it is unclear whether at doses used therapeutically it significantly changes extracellular dopamine (DA) concentration. Here we used positron emission tomography and [(11)C]raclopride (D2 receptor radioligand that competes with endogenous DA for binding to the receptor) to evaluate whether oral methylphenidate changes extracellular DA in the human brain in 11 healthy controls. We showed that oral methylphenidate (average dose 0.8 +/- 0.11 mg/kg) significantly increased extracellular DA in brain, as evidenced by a significant reduction in B(max)/K(d) (measure of D2 receptor availability) in striatum (20 +/- 12%; p < 0.0005). These results provide direct evidence that oral methylphenidate at doses within the therapeutic range significantly increases extracellular DA in human brain. This result coupled with recent findings of increased dopamine transporters in ADHD patients (which is expected to result in reductions in extracellular DA) provides a mechanistic framework for the therapeutic efficacy of methylphenidate. The increase in DA caused by the blockade of dopamine transporters by methylphenidate predominantly reflects an amplification of spontaneously released DA, which in turn is responsive to environmental stimulation. Because DA decreases background firing rates and increases signal-to-noise in target neurons, we postulate that the amplification of weak DA signals in subjects with ADHD by methylphenidate would enhance task-specific signaling, improving attention and decreasing distractibility. Alternatively methylphenidate-induced increases in DA, a neurotransmitter involved with motivation and reward, could enhance the salience of the task facilitating the "interest that it elicits" and thus improving performance.

Administration, Oral↗
PubMed2001

Low level of brain dopamine D2 receptors in methamphetamine abusers: association with metabolism in the orbitofrontal cortex.

OBJECTIVE: The role of dopamine in the addictive process (loss of control and compulsive drug intake) is poorly understood. A consistent finding in drug-addicted subjects is a lower level of dopamine D2 receptors. In cocaine abusers, low levels of D2 receptors are associated with a lower level of metabolism in the orbitofrontal cortex. Because the orbitofrontal cortex is associated with compulsive behaviors, its disruption may contribute to compulsive drug intake in addicted subjects. This study explored whether a similar association occurs in methamphetamine abusers. METHOD: Fifteen methamphetamine abusers and 20 non-drug-abusing comparison subjects were studied with positron emission tomography (PET) and [11C]raclopride to assess the availability of dopamine D2 receptors and with [18F]fluorodeoxyglucose to assess regional brain glucose metabolism, a marker of brain function. RESULTS: Methamphetamine abusers had a significantly lower level of D2 receptor availability than comparison subjects (a difference of 16% in the caudate and 10% in the putamen). D2 receptor availability was associated with metabolic rate in the orbitofrontal cortex in abusers and in comparison subjects. CONCLUSIONS: Lower levels of dopamine D2 receptor availability have been previously reported in cocaine abusers, alcoholics, and heroine abusers. This study extends this finding to methamphetamine abusers. The association between level of dopamine D2 receptors and metabolism in the orbitofrontal cortex in methamphetamine abusers, which replicates previous findings in cocaine abusers, suggests that D2 receptor-mediated dysregulation of the orbitofrontal cortex could underlie a common mechanism for loss of control and compulsive drug intake in drug-addicted subjects.

Adult↗
PubMed2000

Prevalence and predictors of highly active antiretroviral therapy use in patients with HIV infection in the united states. HCSUS Consortium. HIV Cost and Services Utilization.

BACKGROUND: Highly active antiretroviral therapy (HAART) became standard for HIV in 1996. Studies at that time showed that most people infected with HIV had initiated HAART, but that members of minority groups and poor people had lower HAART use. It is not known whether high levels of HAART use have been sustained or whether socioeconomic and racial disparities have diminished over time. OBJECTIVES: To determine the proportion of patients who had received and were receiving HAART by January 1998, and to evaluate predictors of HAART receipt. DESIGN AND PARTICIPANTS: Prospective cohort study of a national probability sample of 2267 adults receiving HIV care who completed baseline, first follow-up, and second follow-up interviews from January 1996 to January 1998. MAIN OUTCOME VARIABLES: Proportion currently using HAART at second follow-up (August 1997 to January 1998), contrasted with the cumulative proportions using HAART at any time before January 1998 and before December 1996. ANALYSES: Bivariate and multiple logistic regression analysis of population characteristics predicting current use of HAART at the time of the second follow-up interview. RESULTS: The proportion of patients ever having received HAART increased from 37% in December 1996 to 71% by January 1998, but only 53% of people were receiving HAART at the time of the second follow-up interview. Differences between sociodemographic groups in ever using HAART narrowed after 1996. In bivariate analysis, several groups remained significantly less likely to be using HAART at the time of the second follow-up interview: blacks, male and female drug users, female heterosexuals, people with less education, those uninsured and insured by Medicaid, those in the Northeast, and those with CD4 counts of >/=500 cells/microl (all p <.05). Using multiple logistic regression analysis, low CD4 count (for CD4 <50 cells/microl: odds ratio [OR], 3.20; p <.001) remained a significant predictor of current HAART use at the time of the second follow-up interview, but lack of insurance (OR, 0.71; p <.05) predicted not receiving HAART. CONCLUSIONS: The proportion of persons under HIV care in the United States who had ever received HAART increased to over 70% of the affected population by January 1998 and the disparities in use between groups narrowed but did not disappear. However, nearly half of those eligible for HAART according to the U.S. Department of Health and Human Services guidelines were not actually receiving it nearly 2 years after these medications were first introduced. Strategies to promote the initiation and continuation of HAART are needed for those without contraindications and those who can tolerate it.

Adolescent↗
PubMed2000

Access of vulnerable groups to antiretroviral therapy among persons in care for HIV disease in the United States. HCSUS Consortium. HIV Cost and Services Utilization Study.

OBJECTIVE: To employ the behavioral model of health services use in examining the extent to which predisposing, enabling, and need factors explain the treatment of the HIV-positive population in the United States with highly active antiretroviral therapy (HAART). DATA SOURCE: A national probability sample of 2,776 adults under treatment for human immunodeficiency virus (HIV) infection. STUDY DESIGN: The article uses data from the baseline and six-month follow-up surveys. The key independent variables describe vulnerable population groups including women, drug users, ethnic minorities, and the less educated. The dependent variable is whether or not a respondent received HAART by December 1996. DATA COLLECTION: All interviews were conducted using computer-assisted personal interview instruments designed for this study. Ninety-two percent of the baseline interviews were conducted in person and the remainder over the telephone. PRINCIPAL FINDINGS: A multistage logit regression shows that the predisposing factors that have previously described vulnerable groups in the general population with limited access to medical care also define HIV-positive groups who are less likely to gain early access to HAART including women, injection drug users, African Americans, and the least educated (odds ratios, controlling for need, ranged from 0.35 to 0.59). CONCLUSIONS: Those HIV-positive persons with the greatest need (defined by a low CD4 count) are most likely to have early access to HAART, which suggests equitable access. However, some predisposing and enabling variables continue to be important as well, suggesting inequitable access, especially for African Americans and lower-income groups. Policymakers and clinicians need to be sensitized to the continued problems of African Americans and other vulnerable populations in gaining access to such potentially beneficial therapies. Higher income, anonymous test sites, and same-day appointments are important enabling resources.

Adult↗
PubMed2000

Comparison between intraperitoneal and oral methylphenidate administration: A microdialysis and locomotor activity study.

The therapeutic and stimulant properties of methylphenidate (MP), a drug commonly prescribed for the treatment of attention deficit hyperactivity disorder, have been attributed to increases in synaptic dopamine (DA) concentrations resulting from the blockade of DA transporters. In addition to obvious difficulties inherent in any interspecies comparison, interpretation of preclinical studies done with MP is further complicated by different routes of administration in animals (i.v. and i.p.) compared with humans (oral). In the present study we compared the effects of i.p. and intragastric (oral) MP both on rat nucleus accumbens DA assessed by in vivo microdialysis and on locomotor activity measured in a photocell apparatus. We also compared regional brain uptake and plasma levels of [(3)H]MP after administration of 5 mg/kg via both routes. Intraperitoneal MP (5 and 10 mg/kg) was approximately twice as potent as intragastric MP in terms of increasing extracellular DA levels and in stimulating locomotion. This was consistent with the higher brain uptake of [(3)H]MP when given i.p. rather than intragastrically. The dose of 2 mg/kg produced significant increases in both measurements when administered i.p., but not intragastrically. This study shows that relatively low doses of MP (2 mg i.p. and 5 mg intragastric) significantly increase extracellular DA and locomotor activity and indicates that the differences in the neurochemical and behavioral effects of MP between the intragastric and the i.p. routes are due to central drug bioavailability.

Administration, Oral↗
PubMed1999

Comparable changes in synaptic dopamine induced by methylphenidate and by cocaine in the baboon brain.

Though the blockade of dopamine transporters (DAT) is associated with cocaine's and methylphenidate's reinforcing effects, it is the stimulation of dopamine (DA) receptors, achieved by increases in synaptic DA, that enables these effects to occur. Positron emission tomography (PET) and [11C]raclopride were used to assess the levels of occupancy of DA D2 receptors by dopamine achieved by doses of cocaine or methylphenidate previously documented to block over 70% of DAT. Studies were performed in five baboons using a paired scan protocol designed to measure DA D2 receptor availability (Bmax/Kd) at baseline conditions and after intravenous administration of either cocaine or methylphenidate. Cocaine (1-2 mg/kg) or methylphenidate (0.5 mg/kg) administered 5 min prior to [11C]raclopride decreased Bmax/Kd by 29+/-3% and 32 + 4%, respectively. Smaller reductions in Bmax/Kd (13% for cocaine given 30 min before [11C]raclopride and 25+/-10% for methylphenidate given 40 min before [11C]raclopride) were seen with longer periods between drug and radioligand. These observations are consistent with the slower striatal clearance kinetics of [11C]methylphenidate than [1C]cocaine observed in previous PET experiments and with the approximately twofold higher potency of methylphenidate than cocaine in in vitro experiments. Though the elevation of synaptic DA induced by >70% occupancy of DAT by these drugs lead to a modest increase in occupancy of D2 receptors (25-30%), further studies are required to assess if this is an underestimation because of differences in D2 receptor binding kinetics between raclopride and DA.

Animals↗
PubMed1999

Methylphenidate and cocaine have a similar in vivo potency to block dopamine transporters in the human brain.

The reinforcing effects of cocaine and methylphenidate have been linked to their ability to block dopamine transporters (DAT). Though cocaine and methylphenidate have similar in vitro affinities for DAT the abuse of methylphenidate in humans is substantially lower than of cocaine. To test if differences in in vivo potency at the DAT between these two drugs could account for the differences in their abuse liability we compared the levels of DAT occupancies that we had previously reported separately for intravenous methylphenidate in controls and for intravenous cocaine in cocaine abusers. DAT occupancies were measured with Positron Emission Tomography using [11C]cocaine, as a DAT ligand, in 8 normal controls for the methylphenidate study and in 17 active cocaine abusers for the cocaine study. The ratio of the distribution volume of [11C]cocaine in striatum to that in cerebellum, which corresponds to Bmax/Kd +1, was used as measure of DAT availability. Parallel measures were obtained to assess the cardiovascular effects of these two drugs. Methylphenidate and cocaine produced comparable dose-dependent blockade of DAT with an estimated ED50 (dose required to block 50% of the DAT) for methylphenidate of 0.07 mg/kg and for cocaine of 0.13 mg/kg. Both drugs induced similar increases in heart rate and blood pressure but the duration of the effects were significantly longer for methylphenidate than for cocaine. The similar in vivo potencies at the DAT for methylphenidate than for cocaine are in agreement with their reported relative in vitro affinities (Ki 390 nM and 640 nM respectively), which is likely to reflect the similar degree of uptake (8-10% of the injected dose) and regional distribution of these two drugs in the human brain. Thus, differences in the in vivo potency of these two drugs at the DAT cannot be responsible for the differences in their rate of abuse in humans. Other variables i.e. longer duration of methylphenidate's side effects may counterbalance its reinforcing effects.

Adult↗
PubMed1999

Prediction of reinforcing responses to psychostimulants in humans by brain dopamine D2 receptor levels.

OBJECTIVE: This study assessed whether brain dopamine D2 receptor levels, which show significant intersubject variability, predict reinforcing responses to psychostimulants in humans. METHOD: [11C]Raclopride and positron emission tomography were used to measure D2 receptor levels in 23 healthy men (mean age = 34 years, SD = 7) who had no drug abuse histories in order to assess if there were differences between the subjects who liked and those who disliked the effects of intravenous methylphenidate (0.5 mg/kg). RESULTS: Subjects who liked the effects of methylphenidate had significantly lower D2 receptor levels (mean = 2.72 Bmax/Kd, SD = 0.3) than subjects who disliked its effects (mean = 3.16, SD = 0.3). Moreover, the higher the D2 levels found, the more intense were methylphenidate's unpleasant effects. CONCLUSIONS: These results provide preliminary evidence that D2 receptor levels predict response to psychostimulants in humans and that low D2 receptors may contribute to psychostimulant abuse by favoring pleasant response.

Adult↗
PubMed1996

Regulation of cyclin E transcription by E2Fs and retinoblastoma protein.

Cyclin E is critical for the advance of cells through the G1 phase of their growth cycle. Transcription of the cyclin E gene is known to be cell cycle-dependent. We have shown previously that mRNA levels of cyclin E are regulated positively by mitogens and negatively by TGF-beta. Much circumstantial evidence implicates both E2F transcription factors and the retinoblastoma protein (pRB) in the control of cyclin E expression. However, the molecular basis of this control has remained unclear. We report here the cloning of the cyclin E promoter and the identification of several putative E2F binding sites within the promoter sequence. We have found that cell cycle regulation of cyclin E transcription is mediated by E2F binding sites present in the promoter. The activity of this promoter can be regulated negatively by pRB. Our results suggest the operation of a positive-feedback loop in late G1 that functions to ensure continued cyclin E expression and pRB inactivation.

3T3 Cells↗
PubMed1995

Pregnancy-induced alterations of neurogenic constriction and dilation of human uterine artery.

The responses to electrical field stimulation (EFS) of perivascular nerves in human uterine arteries were characterized. The arteries were removed from pregnant and nonpregnant patients undergoing hysterectomy. Tetrodotoxin, guanethidine, and phentolamine blocked EFS (2 min, 80 V, 0.1-ms duration)-induced constriction. The constrictions and the endogenous norepinephrine levels were lower (P < 0.01) in uterine arteries from pregnant than from nonpregnant patients. When arterial rings were precontracted, the response to EFS was biphasic, consisting of an initial constriction followed by a postconstriction relaxation. The EFS-induced relaxation was endothelium independent and was greater (P < 0.01) in uterine arteries from pregnant than from nonpregnant patients. The relaxation was enhanced by guanethidine and superoxide dismutase, inhibited by nitric oxide synthase inhibitors, blocked by tetrodotoxin, and unaffected by atropine, propranolol, or indomethacin. The results demonstrate that human uterine arteries respond to EFS with contraction and relaxation and that these responses may be mediated, respectively, by norepinephrine and, in part, by nitric oxide released from periarterial nerves. The decrease in neuronally mediated uterine arterial constriction and the increase in dilation could be physiological mechanisms for ensuring appropriate uteroplacental perfusion.

Adult↗
PubMed1989

Purified bovine NF-kappa B recognizes regulatory sequences in multiple genes expressed during activation of T- and B-lymphocytes.

To characterize the NF-kappa B binding factor in molecular terms and to facilitate the cloning of its gene, we have purified this protein from bovine spleen tissue. We have found it is a 42,000-dalton protein that exists in solution as a dimer. We were able to use the purified protein to show that the same polypeptide is able to recognize sites important for activation of genes in either B- or T-lymphocytes. Moreover, we were able to define a consensus sequence which allows ascertainment of a wider variety of sequences that are capable of interacting with this protein. The implication of the same protein in gene regulation in two different lineages of lymphoid cells reveals an unexpected unity in the mechanism of gene expression during B- and T-lymphocyte activation. This also suggests that other regulatory events must participate with NF-kappa B activation in determining B- or T-cell-specific expression.

Animals↗
PubMed1988

NF-kappa B protein purification from bovine spleen: nucleotide stimulation and binding site specificity.

The activity of the enhancer for the kappa immunoglobulin light chain gene critically depends on the presence in the nucleus of the NF-kappa B protein. We purified NF-kappa B over 50,000-fold and identified two protein species, 42 and 44 kDa, that could be eluted and renatured from a sodium dodecyl sulfate/polyacrylamide gel to give specific DNA-binding activity. Binding of the purified bovine NF-kappa B as well as that from human and murine B- or T-lymphoid cell extracts was dramatically stimulated by nucleoside triphosphates. This effect distinguished NF-kappa B from a related factor, H2-TF1. Purified NF-kappa B interacted efficiently with regulatory sequences that function during either B- or T-lymphocyte activation, including the human immunodeficiency virus enhancer and a NF-kappa B binding site we detected in the interleukin 2 enhancer.

Animals↗
PubMed1985

DNA elements are asymmetrically joined during the site-specific recombination of kappa immunoglobulin genes.

Immunoglobulin K genes are constructed during lymphocyte differentiation by the joining of two DNA elements, VK and JK, to form both a VKJK coding unit and a reciprocal recombination product. The two products formed in single VK-to-JK joining events can be directly isolated through the use of a retrovirally introduced recombination substrate. The structural analysis of a number of recombinants and the derivation of secondary recombination products define some of the basic features of the mechanism of immunoglobulin gene assembly.

Animals↗
PubMed1985

Cyclic AMP induces terminal deoxynucleotidyl transferase in immature B cell leukemia lines.

Terminal deoxynucleotidyl transferase (Tdt), a unique DNA polymerase found only in lymphoid cells, may be involved in the generation of immunoglobulin-combining site diversity. To study the actual metabolic function of the enzyme, we developed a system in which Tdt expression is induced under defined culture conditions. We found that pharmacologic agents that raise intracellular cyclic AMP levels, such as caffeine, induce a three- to 10-fold increase in enzyme biosynthesis rate and activity. This phenomenon is observed only in pre-B cell lines of human or murine origin.

Animals↗
PubMed1981

Lethal effect of the Abelson murine leukemia virus transforming gene product.

Infection of NIH/3T3 and Balb/c/3T3 fibroblastic cell lines by Abelson virus results in stable transformation in most cases. We have observed that certain rodent cell lines, including some Balb/c/3T3 sublines, do not maintain stable transformation following infection. Within three to four weeks of infection of these cell lines a large fraction of the cells is not recoverable upon serial passage and appear to be killed. The residual population of cells displays a flat, nontransformed phenotype. Concomitant with this reversion is the loss of the integrated provirus and loss of expression of the Abelson virus transforming protein. This loss of the integrated provirus is specific to transformation-competent viral strains. The effect of Abelson virus on these cells appears to be, in part, due to a lethal effect of the transforming protein on the cells. We have selectively isolated mutants of Abelson virus that stably transform these rodent cell lines without expressing a lethal effect. Analysis of the nucleic acid and protein structure of these mutant virus strains showed that the transforming proteins are shorter, having lost expression of the carboxy-terminal one third of the protein. We suspect that the carboxy-terminal portion of the wild-type Abelson protein may modulate the in vivo expression of the protein kinase activity and that this may cause the transforming protein to have a deleterious effect on certain cell lines.

3T3 Cells↗
PubMed1981

Phosphorylation of the Abelson murine leukemia virus transforming protein.

The Abelson murine leukemia virus transforming gene product is a phosphorylated protein encoded by both viral and cellular sequences. This gene product has an amino-terminal region derived from the gag gene of its parent virus and a carboxyl-terminal region of (abl) derived from a normal murine cellular gene. Using a combination of partial proteolytic cleavage techniques and antisera specific for gag and abl sequences, we mapped in vivo phosphorylation sites to different regions of the protein. Phosphoproteins encoded by strain variants and transformation-defective mutants of Abelson murine leukemia virus with defined deletions in the primary sequence of the abl region were compared by two dimensional limit digest peptide mapping. Specific phosphorylation pattern differences for wild-type and mutant proteins probably represented deletions of specific phosphate acceptor sites in the abl region. An in vitro autophosphorylation activity copurified with the Abelson murine leukemia virus protein from transformation-competent strains. A peptide analysis of such in vitro reactions demonstrated that these phosphorylation sites were restricted to the amino-terminal region, and the specific sites appeared to be unrelated to the sites found on proteins phosphorylated in vivo. Thus, the autophosphorylation reaction probably correlates with an activity important in transformation, but the specific end product in vitro bears little resemblance to its function in vivo.

Abelson murine leukemia virus↗