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Biomedical subjects

K Y Little

Publications and source records attributed to K Y Little.

At least 19 recordsLinked to original sources
PubMed1999

Striatal dopaminergic abnormalities in human cocaine users.

OBJECTIVE: Previous human postmortem experiments have shown an abnormally high number of dopamine uptake sites in the striatum of chronic cocaine users, which might contribute to cocaine withdrawal symptoms such as depression and suicidality. Previous inconsistencies in results were perhaps related to selective radioligand affinity changes or a coexisting loss of dopamine neurons. METHOD: In the present study, binding of the cocaine analog [3H]WIN 35428 to the dopamine transporter was assayed in postmortem striatal samples from 15 cocaine-using subjects and 15 matched comparison subjects to determine whether there were differences in number of binding sites or in affinity. Binding to the vesicular monoamine transporter, a measure of total dopaminergic terminals, was also assessed by using the radioligand (+)-[3H]dihydrotetrabenazine (DTBZ). RESULTS: Striatal [3H]WIN 35428 binding sites were significantly more numerous in the cocaine users: the mean Bmax value was 9.0 fmol bound/microg protein (SD = 2.8) for the cocaine users but only 6.0 (SD = 1.7) for the comparison subjects. Severity of chronic cocaine use was significantly related to [3H]WIN 35428 binding level. [3H]DTBZ binding was significantly lower in the cocaine users (mean = 330 nCi/mg, SD = 42) than in the comparison subjects (mean = 374, SD = 68). CONCLUSIONS: The present results confirm that cocaine users have a high number of dopamine transporter binding sites on dopaminergic neurons, despite an apparent low number of total dopamine terminals. These abnormalities may contribute to the abnormalities in subjective experience and behavior characteristic of chronic cocaine abusers.

Adolescent↗
PubMed1998

Expression and regulation of the human dopamine transporter in a neuronal cell line.

Human cocaine users exhibit increased striatal [3H]WIN35428 binding to the dopamine transporter (DAT). However, the nature of the changes induced in the DAT are complex and may not result from a simple increase in number of DAT molecules. To better understand the regulation of DAT inhibitor binding sites and their relationship to the overall process of dopamine uptake, a neuronal model system expressing the human DAT has been developed. Initial experiments were attempted with native dopaminergic neurons so as to allow examination of DAT interactions with vesicular release and storage mechanisms. Dissociated fetal rat mesencephalic neurons, of various ages and mixtures with target cells, were grown to confluence. However, [3H]WIN35428 binding was of low affinity at all levels of maturity. Following this, a simpler model was assessed, using DAT cDNA transfected into neuroblastoma-derived Neuro2A cells. Initially, no specific and little non-specific [3H]WIN35428 or [3H]paroxetine binding was found in non-transfected cells. After transfection with the human DAT inserted in the pcDNA vector, both DAT binding and dopamine uptake were significantly and stably present. Treatment with (-)cocaine, 10-6 M for 24 h, increased DAT binding and uptake, which did not occur in parallel COS-7 experiments. Other experiments with Neuro2A cells also found that dopamine uptake was down-regulated by treatment with a PKC activator. These results suggest that the transfected Neuro2A neurons should be useful for ongoing experiments examining the regulation of the DAT by assorted treatments.

Animals↗
PubMed1998

A.E. Bennett Research Award. Regulation of serotonin1A, glucocorticoid, and mineralocorticoid receptor in rat and human hippocampus: implications for the neurobiology of depression.

BACKGROUND: Disturbances of the limbic-hypothalamic-pituitary-adrenal axis and the serotonin system are commonly found in depressive illness. Studying the effect of stress on these two neurobiological systems may give us important clues into the pathophysiology of affective illness and help us understand how stress and mood disorders are related. METHODS: We studied the effect of chronic unpredictable stress and antidepressant treatment on serotonin 1A (5-HT1A), glucocorticoid (GR), anti mineralocorticoid (MR) receptor levels in rat hippocampus, using in situ hybridization and receptor autoradiography. We also used in situ hybridization to quantify hippocampal 5-HT1A, GR, and MR messenger (mRNA) levels in a small group of suicide victims with a history of depression, compared to matched controls (n = 6). RESULTS: We found that rats subjected to chronic unpredictable stress showed a significant elevation of basal plasma corticosterone compared to nonstressed rats. Chronic stress also caused a decrease in 5-HT1A mRNA and binding in the hippocampus. In addition, chronic stress produced alterations on the MR/GR mRNA ratio in this same region. The decreases in 5-HT1A mRNA and binding, as well as the MR/GR alterations, were prevented in animals that received imipramine or desipramine antidepressant treatment. Zimelidine was unable to reverse stress-induced increases in corticosterone, and was only partially successful in preventing the stress-induced receptor changes in the hippocampus. Suicide victims with a history of depression showed changes that were very similar to the changes found in chronic stress. CONCLUSIONS: Alterations in hippocampal 5-HT1A levels and in the MR/GR balance may be one of the mechanisms by which stress may trigger and/or maintain depressive episodes.

Adrenalectomy↗
PubMed1998

Brain dopamine transporter messenger RNA and binding sites in cocaine users: a postmortem study.

BACKGROUND: Results of recent radioligand binding experiments suggest that chronic cocaine exposure increases dopamine transporter (DAT) synthesis throughout the striatum of humans. However, detection of cocaine binding site increases in animals and humans has varied depending on the radioligand used. The present experiment tested the hypothesis in cocaine-using humans that synthesis of midbrain DAT messenger RNA increases parallel with increased striatal DAT binding sites. METHODS: Striatal and midbrain samples were collected during autopsy examination from human cocaine users (n = 34) and from age-, sex-, and race-matched control subjects (n = 36). Levels of DAT messenger RNA were quantified in the medial and lateral midbrain regions using in situ hybridization, and striatal DAT binding sites were assessed by quantitative autoradiography using the DAT-specific radioligand [3H]WIN 35428. RESULTS: Striatal DAT binding sites were markedly increased in cocaine users, but, paradoxically, medial DAT messenger RNA levels were decreased. CONCLUSION: Cocaine exposure has a marked effect on DAT function, but the mechanisms involved may be complex.

Adult↗
PubMed1998

Species differences in regional patterns of 3H-8-OH-DPAT and 3H-zolpidem binding in the rat and human brain.

The rat has proven to be a valuable preclinical model for characterizing effects of psychotrophic drugs and for identifying new psychotherapeutic agents in pharmacological screens. However, substantial differences have been described between the rat and human brain in regard to the neuroanatomical distribution of some drug and neurotransmitter receptor binding sites. To assess the utility of the rat as a model for the neuroanatomical topography of 5-HT1A and type 1 benzodiazepine (BDZ) receptors in humans, the distribution of binding sites for 3H-8-OH-DPAT (5-HT1A agonist) and 3H-zolpidem (type 1 BDZ agonist) was compared with autoradiography in select regions of the rat and human brain. Concordance in the binding patterns for the two ligands was observed in several brain regions for the two species. However, substantial differences were also found in the topography of binding sites for the ligands in the rat and human brain. High 3H-8-OH-DPAT binding was seen in the dorsal raphe nucleus and hippocampal formation in both the rat and human brain. However, species differences were observed in the relative distribution of ligand binding among hippocampal subregions. In the cerebral cortex, the laminar distribution of 3H-8-OH-DPAT binding sites was notably different for rats and humans. In humans, outer cortical layers were most densely labeled with 3H-8-OH-DPAT, whereas in the rat cortex, the highest binding was in the inner layers. A striking difference between rats and humans was observed for 3H-8-OH-DPAT binding in the lateral septal nucleus, which was densely labeled in the rat but weakly labeled in humans. Substantial differences between rats and humans were also observed for 3H-zolpidem binding. In the rat brain, high densities of binding sites were found in the medial septum, inferior colliculus, and substantia nigra reticulata. These regions showed very low 3H-zolpidem binding in the human brain. Intermediate binding was seen in the rat cerebral cortex, and low binding was found in the hippocampus. By contrast, in humans, cerebral cortical regions were the most densely labeled of all regions studied, and certain hippocampal subregions exhibited relatively high binding. The striking neuroanatomical differences in 3H-8-OH-DPAT and 3H-zolpidem binding observed between rats and humans suggest that different functional consequences may be produced within specific brain regions after administration of drugs that influence 5-HT1A and type 1 BZD receptors.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed1998

Striatal [125I]RTI-55 binding sites in cocaine-abusing humans.

1. Previous experiments in this laboratory found that striatal [3H]WIN 35428 binding was increased in post mortem specimens from human cocaine users (Little et al, 1993a). Although structurally similar, preliminary studies have suggested that [3H]WIN 35428 and the related cocaine congener [125I]RTI-55 differ in some respects pharmacologically. 2. The present experiments tested the hypothesis that striatal [125I]RTI-55 binding would be increased, as was [3H]WIN 35428 binding, in post mortem specimens from cocaine users compared to matched controls. 3. However, computer-generated parameters derived from saturation experiments found only trends toward increased Bmax and decreased affinity (increased KD) in the cocaine users. The magnitude of the increases were notably smaller than the statistically significant increases previously found in high affinity [3H]WIN 35428 binding in these same subjects. 4. Evidence from the present and earlier experiments suggests that cocaine exposure may induce conformational changes in the dopamine transporter.

Adult↗
PubMed1998

Cocaine, ethanol, and genotype effects on human midbrain serotonin transporter binding sites and mRNA levels.

OBJECTIVE: Earlier platelet and postmortem brain studies have found alterations in serotonin transporter function in ethanol-abusing human subjects. The present investigation tested the hypothesis that brain serotonin transporter function is altered in chronic users of ethanol and cocaine, which might be related to a common serotonin transporter promoter polymorphism. METHOD: Serotonin transporter binding sites, serotonin transporter mRNA levels, and serotonin transporter promoter variants were quantified in postmortem samples from a group of human subjects who had been ethanol users or cocaine users and then compared to those of a matched group of comparison subjects. Quantitative autoradiographic and in situ hybridization assays were performed in midbrain samples that contained the dorsal and median raphe nuclei (the location of serotonin cell bodies that innervate the forebrain). RESULTS: There was a significant overall cocaine-by-ethanol-by-genotype interaction. Dorsal raphe [125I]CIT binding to the serotonin transporter was lower in cocaine users than in comparison subjects. In addition, serotonin transporter binding and serotonin transporter mRNA levels varied significantly by genotype. It was also found that serotonin transporter binding in subjects with either the short or heterozygote genotype was significantly higher in the ethanol-user subjects. CONCLUSIONS: Serotonin transporter binding sites were regulated in a region-specific and substance-specific pattern, which was not simply a local response to functional blockade. Also, a reciprocal relationship appeared to exist between cocaine and ethanol effects in the dorsal raphe, which may have interesting clinical implications for dual-diagnosis patients. It is possible that serotonin transporter promoter genotype may play a complex role in chronic ethanol dependence.

Adult↗
PubMed1998

GABA(A) receptor alpha1, alpha4, and beta3 subunit mRNA and protein expression in the frontal cortex of human alcoholics.

Animal studies have shown that chronic ethanol consumption produces physical dependence upon ethanol and alters gamma-aminobutyric acid-A (GABA(A)) receptor subunit gene expression in brain. Although extensive investigation has been conducted in animal models, relatively little work has been performed directly on human alcoholic brain tissue to determine if there are alterations in GABA(A) receptor gene expression. In this study, GABA(A) receptor alpha1, alpha4, and beta3 subunit mRNA and peptide expression in postmortem frontal cortex from human alcoholics (n = 15) and age- and sex-matched controls (n = 13) were measured by quantitative, competitive reverse transcription polymerase chain reaction and Western blot analysis. GABA(A) receptor beta3 subunit mRNA expression was 35% greater (p < 0.05) in alcoholics, compared with nonalcoholic controls. We found no significant difference in alpha1 and alpha4 subunit mRNA levels between groups. However, there was a trend toward greater (21%) alpha1 subunit mRNA expression. There was no difference in alpha1, alpha4, or beta2/3 subunit peptide levels in frontal cortex between controls and alcoholics. Neither the age of the subjects nor the postmortem interval correlated with mRNA or peptide levels. Blood ethanol content also did not correlate with mRNA or peptide expression in alcoholic samples. These data suggest that GABA(A) receptor adaptations, resulting from prolonged alcohol consumption in human alcoholics, may differ from animal models of alcohol dependence. These differences may be related to the longevity of alcohol exposure in human alcoholics, as well as variability in the dependence/withdrawal state of the human subjects. Therefore, further studies in human postmortem brain tissue are warranted.

Adult↗
PubMed1998

Overt behavior problems and serotonergic function in middle childhood among male and female offspring of alcoholic fathers.

A large body of literature indicates that the serotonergic system is involved in behavioral regulation, as evidenced by the inverse relationship between impulsive aggression and serotonergic function found in adult alcoholics and nonalcoholics. However, studies of this relationship among child and adolescent offspring of alcoholics (COAs) have not previously been done. This study examines the potentially parallel relationship between behavioral dysregulation and low serotonergic function in young COAs. The relationship is of potential interest as a phenotypic marker of biological vulnerability to aggressiveness, which itself has been hypothesized to be a risk factor for later antisocial alcoholism. The present work is part of an ongoing prospective study of the development of risk for alcohol abuse/dependence and other problematic outcomes in a sample of families subtyped by the fathers' alcoholism classification. We examined the relationship between overt behavior problems in middle childhood (mean age = 10.5 +/- 1.7 years) and whole blood serotonin (5-HT) in a subsample of the offspring (N = 32 boys and 12 girls). Using a Child Behavior Checklist (CBCL) index of behavioral undercontrol, we obtained results indicating that high total behavior problem (TBP) children had lower levels of whole blood 5-HT than did low-TBP children (p < 0.01). These results support the hypothesis that there is an inverse relationship between whole blood serotonin levels and behavior problems in young male and female COAs. A father's alcoholism status was not significantly related to his child's 5-HT level, i.e., the child's phenotypic expression of behavioral dysregulation was more reliably connected to serotonergic function than was paternal alcoholism.

Adolescent↗
PubMed1997

Serotonin transporter binding sites and mRNA levels in depressed persons committing suicide.

The serotonin transporter (5-HTT) has been found altered in postmortem brain samples from persons committing suicide, but the results of radioligand binding studies have been inconsistent. In the present series of experiments, autoradiographic radioligand binding and in situ hybridization techniques were utilized to examine 5-HTT function in the brains of 8 depressed subjects who had committed suicide, and matched controls. It was hypothesized that depressed subjects would demonstrate decreased numbers of 5-HTT binding sites and mRNA; however, [125I]RTI-55 binding to the 5-HTT was not different in the midbrain, hippocampus, or frontal cortex of depressed subjects. Also, 5-HTT mRNA levels in dorsal and median raphe nuclei were not different between controls and depressed subjects. The current results, although limited in scope because of the small number of subjects included, offer no evidence that alterations in the 5-HTT occur in pertinent brain regions of depressed individuals.

Adult↗
PubMed1997

Lack of pineal beta-adrenergic receptor alterations in suicide victims with major depression.

Noradrenergic function may be altered in depressive illness and thereby contribute to decreased pineal production of melatonin levels, as previously described in some depressed subjects. In the present study, the hypothesis was tested that pineal beta-adrenergic binding would be increased in persons committing suicide with evidence of depressive disorders, reflecting diminished noradrenergic input. Initially, post-mortem human pineal glands were obtained at autopsy. Diagnostic and symptomatic information was then systematically collected from family members using standardized interview techniques. Seven subjects who committed suicide and suffered from major depression, and without exposure to treatment for depressive symptoms were age- and sex-matched with control subjects. Pineal beta-adrenergic binding was assessed by quantitative autoradiography employing four concentrations of [125I]pindolol. Because of possibly complex adrenergic regulation of the pineal, beta-adrenergic receptor binding were subtyped using the selective blocker ICI 89406. No differences in beta-adrenergic receptors were detected between subjects with major depression compared to the matched controls.

Adult↗
PubMed1996

Lack of dopamine receptor agonists effect on striatal dopamine transporter binding sites.

Depending on experimental conditions, chronic cocaine exposure can induce an increase in binding to the dopamine transporter (DAT). One possible mechanism for the cocaine-induced-upregulation in DAT binding sites is through stimulation of presynaptic D2 receptors by excess synaptic dopamine. To test this hypothesis, the present experiment examined in rats the effect of chronic quinpirole and apomorphine treatments on striatal DAT binding sites. Rats were chronically injected subcutaneously with either: quinpirole, 0.7 mg/kg body weight, apomorphine, 2.0 mg/kg body weight, or vehicle. Striatal DAT binding was then examined autoradiographically using the DAT-selective cocaine congeners [125I]RTI-121 and [3H]WIN 35428. Analysis of the results indicated that quinpirole and apomorphine administration did not alter DAT cocaine binding sites.

Animals↗
PubMed1996

Acute stimulant response prediction of chronic trazodone effects.

1. Depressed patients who acutely improve after taking a stimulant drug have a better eventual response to chronic antidepressant treatment than do stimulant non-responders. Unlike the stimulants and most antidepressants, trazodone (TRZ) is not a potent monoamine reuptake inhibitor. 2. The authors tested the hypothesis that acute methylphenidate (MPH) and d-amphetamine (d-AMP) response would not correlate with eventual trazodone response because its site of action was different from other antidepressants. 3. It was found that acute MPH-induced improvement correlated with eventual TRZ-induced improvement to a limited degree. 4. This correlation might reflect serotonin reuptake inhibition by trazodone and suggests that this effect is therapeutically relevant.

Adult↗
PubMed1996

Effect of cocaine on dopamine transporter receptors depends on routes of chronic cocaine administration.

Investigation of residual behavioral states produced by withdrawal from different routes of cocaine administration indicates that depending on the mode of intake, chronic cocaine produces either tolerance or sensitization to subsequent challenge doses of cocaine. We studied the effect of routes of cocaine administration on the dopamine transporter receptors (DATR), the presumed neuronal mediator of cocaine reward, using the diphenyl substituted piperazine derivative, [3H]GBR 12935 and the cocaine analogue [3H]WIN 35,428. Alzet osmotic mini-pumps filled with either cocaine (100 mg/ml) or saline were surgically implanted on rats into a subcutaneous pocket at the dorsal midline, continuously infusing cocaine at the rate of 40 mg/kg/day. The pumps were removed 14 days later, and the rats were killed 7 days after the removal of pumps. For the intermittent administration, two groups of rats were injected daily either with 40 mg/kg of cocaine or saline for 14 days. Rats were killed 7 days following the last injection. Continuous infusion of cocaine did not alter the [3H]GBR 12935 dopamine transporter (DAT) binding either in the caudate nucleus or in the prefrontal cortex, but it enhanced the density of [3H]WIN 35,428-labeled DAT receptor sites in the caudate putamen. In contrast, intermittent administration of cocaine resulted in a selective alteration of [3H]GBR 12935 binding in the prefrontal cortex but not in the caudate; the cocaine-injected rats had a 48% decrease in [3H]GBR 12935, Bmax (p < .05), without changing the KD. The contrast between the lack of effect of cocaine on [3H]GBR 12935-DATR and the increased binding of [3H]WIN 35,428-DATR highlights the differential sensitivities of the two binding sites to the continuous presence of cocaine.

Animals↗
PubMed1996

Expression of serotonin transporter mRNA in human brainstem raphe nuclei.

The distribution of the messenger RNA (mRNA) encoding the serotonin transporter was investigated in the entire extent of the ascending raphe systems of the human brainstem, using a sensitive cRNA probe. This mRNA is abundant in the neurons of the raphe nuclei, especially in the dorsal and median raphe. The subregional distribution of this mRNA closely corresponds to that described for tryptophan hydroxylase in immunocytochemical studies. It is expressed at the highest levels in ventral and ventrolateral subregions of the dorsal raphe, with lower levels of expression in the median raphe, oral pontine reticular nuclei, and the supralemniscal cell groups. These results provide a description of the distribution of this mRNA in normal subjects and will serve as the basis for future studies of the subregional distribution of this mRNA in the brains of depressed patients and those who have committed suicide.

Adult↗
PubMed1996

Dose-response studies with thyrotropin-releasing hormone: evidence for differential pituitary responses in men with major depression, alcoholism, or no psychopathology.

A reduced thyrotropin (TSH) response to thyrotropin-releasing hormone (TRH) has been reported in both alcoholic and depressed men. To discern whether the pathophysiological basis of a reduced TSH response is similar in these two disorders, the present study compares the dose-response patterns of TSH and prolactin (PRL) to TRH in depressed, alcoholic, and control men. Four doses of TRH (25, 100, 500, and 800 micrograms) were given at several day intervals to 6 men with major depression, 8 men with alcohol dependence, and 7 control men. Examination of the pattern of TRH-induced TSH and PRL response revealed differences for each paired group comparison: depressed versus control, depressed versus alcoholic, and alcoholic versus control. Compared with controls, depressed men had low TSH and low PRL responses to TRH, whereas alcoholic men had low TSH responses and normal PRL responses. Levels of neither thyroid hormones, cortisol, or sex steroids, nor age or body size, explained these differences. These findings suggest that the pathophysiological basis of a reduced TSH response to TRH is different in alcoholism, compared with depression.

Adult↗
PubMed1996

Beta-adrenergic receptor subtypes in human pineal gland.

The secretion of melatonin by the pineal has been promoted as a direct monitor of adrenergic function in depressive illness. However, discrepant findings have been reported, possibly reflecting a complex adrenergic regulation of pineal output. In order to clarify the anatomical localization and relative density of beta-adrenergic receptors and their subtypes in human pineal, quantitative autoradiographic analysis was conducted of beta-adrenergic receptors in postmortem specimens using the high affinity radioligand 125I-pindolol. Dense specific binding was found throughout the gland. beta 1 -adrenergic receptors were more numerous, but beta 2-receptors were present in an overlapping anatomical distribution with beta 1-receptors.

Adrenergic beta-Antagonists↗