Dopamine, behavior, and addiction

Addictive drugs are habit-forming. Addiction is a learned behavior; repeated exposure to addictive drugs can stamp in learning. Dopamine-depleted or dopamine-deleted animals have only unlearned reflexes; they lack learned seeking and learned avoidance. Burst-firing of dopamine neurons enables learning-long-term potentiation (LTP)-of search and avoidance responses. It sets the stage for learning that occurs between glutamatergic sensory inputs and GABAergic motor-related outputs of the striatum; this learning establishes the ability to search and avoid. Independent of burst-firing, the rate of single-spiking-or "pacemaker firing"-of dopaminergic neurons mediates motivational arousal. Motivational arousal increases during need states and its level determines the responsiveness of the animal to established predictive stimuli. Addictive drugs, while usually not serving as an external stimulus, have varying abilities to activate the dopamine system; the comparative abilities of different addictive drugs to facilitate LTP is something that might be studied in the future.

Dopamine and Addiction

Addiction is commonly identified with habitual nonmedical self-administration of drugs. It is usually defined by characteristics of intoxication or by characteristics of withdrawal symptoms. Such addictions can also be defined in terms of the brain mechanisms they activate; most addictive drugs cause elevations in extracellular levels of the neurotransmitter dopamine. Animals unable to synthesize or use dopamine lack the conditioned reflexes discussed by Pavlov or the appetitive behavior discussed by Craig; they have only unconditioned consummatory reflexes. Burst discharges (phasic firing) of dopamine-containing neurons are necessary to establish long-term memories associating predictive stimuli with rewards and punishers. Independent discharges of dopamine neurons (tonic or pacemaker firing) determine the motivation to respond to such cues. As a result of habitual intake of addictive drugs, dopamine receptors expressed in the brain are decreased, thereby reducing interest in activities not already stamped in by habitual rewards.

Prevalence and risk factors of restrictive spirometry in a cohort of Peruvian adults

INTRODUCTION

Few studies have described the prevalence of and lung function decline among those with a restrictive spirometric pattern (RSP) in low- and middle-income countries.

METHODS

We analyzed prospective data from 3055 adults recruited across four diverse settings in Peru over a 3-year period. Multivariable logistic regression was used to study the association between the presence of restriction and associated risk factors. Multivariable linear mixed models were used to determine lung function decline.

RESULTS

Among 3055 participants, the average age was 55.4 years (SD 12.4); 49% were male. Overall prevalence of RSP was 4.7%, ranging from 2.8% (Lima) to 6.9% (Tumbes). The odds of having RSP were higher among those who lived in a rural environment (OR 2.19, 95%CI 1.43-3.37), had a diagnosis of diabetes (OR 1.94, 95%CI 1.10-3.40) and among women (OR 2.09, 95%CI 1.41-3.09). When adjusting for baseline lung function, adults with RSP had accelerated decline in forced expiratory volume in 1 s (FEV1) compared with non-obstructed, non-restricted individuals.

DISCUSSION

RSP is prevalent particularly among women and in individuals living in rural settings of Peru. When adjusted for baseline lung function, participants with RSP had accelerated rates of FEV1 decline. Our findings are consistent with the notion that RSP is an insidious inflammatory condition with deleterious effects of lung function decline.

Chronic respiratory disease and high altitude are associated with depressive symptoms in four diverse settings

SETTING

Depression is a prevalent comorbidity of chronic respiratory disease (CRD), and may indicate worse clinical outcomes. The relationship between depression and living with chronic hypoxia due to CRD or residence at altitude has received little attention in resource-poor settings.

OBJECTIVE

To investigate the association between CRD conditions and depressive symptoms in four settings in Peru.

DESIGN

We collected data on CRD and depressive symptoms in adults aged ⩾35 years. Depressive symptoms were measured according to the Center for Epidemiologic Studies Depression scale. Multivariable ordinal logistic regression was used to assess the adjusted odds of being in a higher category of depressive symptoms as a function of CRD.

RESULTS

We analyzed data from 2953 participants (mean age 55.3 years, 49% male). The prevalence of major depressive symptoms was 19%, with significant variation according to setting. Participants with at least one CRD (OR 1.34, 95%CI 1.06-1.69) and those living at altitude (OR 1.64, 95%CI 1.10-2.43) had an increased adjusted odds of being in a higher category of depressive symptoms.

CONCLUSION

We found a high prevalence of depressive symptoms, and a positive association between depressive symptoms with CRD and with living at altitude, both of which cause chronic hypoxia.

Effect of obesity on sinonasal disease in asthma

OBJECTIVE

Sinonasal disease can contribute to poor asthma control. There are reports that link obesity with an increased prevalence of sinonasal disease, but no studies evaluating the severity of sinonasal disease in obese asthmatics, and how this impacts asthma control. The purpose of the current study was to determine if obesity is associated with increased severity of sinonasal disease, and/or affects response to nasal corticosteroid treatment in asthma.

METHODS

This study included 236 adults participating in a 24-week randomized, double-masked, placebo-controlled study of nasal mometasone for the treatment of poorly controlled asthma. Sinonasal disease severity was assessed using validated questionnaires, and compared in participants of differing BMIs. Eosinophilic inflammation was assessed using markers in nasal lavage, serum and exhaled nitric oxide. Response to treatment was compared in different BMI groups.

RESULTS

Obesity had no effect on the severity of sinonasal disease symptoms in asthmatics (Sino-Nasal Outcome Test 22 (SNOT 22) score [mean ± SD] 35.4 ± 18.5, 40.2 ± 22.8, and 39.1 ± 21.7, p = 0.43, in lean, overweight and obese participants), nor on nasal, bronchial or systemic markers of allergic inflammation. Nasal steroids had some limited effects on symptoms, lung function and inflammatory markers in lean participants, but no detectable effect was found in obese patients.

CONCLUSIONS

Obesity does not affect severity of sinonasal disease in patients with asthma; the association of sinonasal disease symptoms with increased asthma severity and markers of Type 2 inflammation are consistent across all BMI groups. The response of obese patients to nasal corticosteroids requires further study.

Chronic exposure to biomass fuel smoke and markers of endothelial inflammation

Indoor smoke exposure may affect cardiovascular disease (CVD) risk via lung-mediated inflammation, oxidative stress, and endothelial inflammation. We sought to explore the association between indoor smoke exposure from burning biomass fuels and a selected group of markers for endothelial inflammation. We compared serum concentrations of amyloid A protein, E-selectin, soluble intercellular adhesion molecule 1 (ICAM-1) and VCAM-1, von Willebrand factor (vWF), and high-sensitivity C-reactive protein (hs-CRP) in 228 biomass-exposed vs. 228 non-exposed participants living in Puno, Peru. Average age was 56 years (s.d. = 13), average BMI was 26.5 kg/m(2) (s.d. = 4.4), 48% were male, 59.4% completed high school, and 2% reported a physician diagnosis of CVD. In unadjusted analysis, serum levels of soluble ICAM-1 (330 vs. 302 ng/ml; P < 0.001), soluble VCAM-1 (403 vs. 362 ng/ml; P < 0.001), and E-selectin (54.2 vs. 52.7 ng/ml; P = 0.05) were increased in biomass-exposed vs. non-exposed participants, respectively, whereas serum levels of vWF (1148 vs. 1311 mU/ml; P < 0.001) and hs-CRP (2.56 vs. 3.12 mg/l; P < 0.001) were decreased, respectively. In adjusted analyses, chronic exposure to biomass fuels remained positively associated with serum levels of soluble ICAM-1 (P = 0.03) and VCAM-1 (P = 0.05) and E-selectin (P = 0.05), and remained negatively associated with serum levels of vWF (P = 0.02) and hs-CRP (P < 0.001). Daily exposure to biomass fuel smoke was associated with important differences in specific biomarkers of endothelial inflammation and may help explain accelerated atherosclerosis among those who are chronically exposed.

Can a simple test of functional capacity add to the clinical assessment of diabetes?

AIM

To identify impairment in functional capacity associated with complicated and non-complicated diabetes using the 6-min walk distance test.

METHODS

We enrolled 111 adults, aged ≥40 years, with Type 2 diabetes from a hospital facility and 150 healthy control subjects of similar age and sex from a community site in Lima, Peru. All participants completed a 6-min walk test.

RESULTS

The mean age of the 261 participants was 58.3 years, and 43.3% were male. Among those with diabetes, 67 (60%) had non-complicated diabetes and 44 (40%) had complications such as peripheral neuropathy, retinopathy or nephropathy. The mean unadjusted 6-min walk distances were 376 m and 394 m in adults with and without diabetes complications, respectively, vs 469 m in control subjects (P<0.001). In multivariable regression, the subjects with diabetes complications walked 84 m less far (95% CI -104 to -63 m) and those without complications walked 60 m less far (-77 to -42 m) than did control subjects. When using HbA1c level as a covariate in multivariable regression, participants walked 13 m less far (-16.9 to -9.9 m) for each % increase in HbA1c .

CONCLUSIONS

The subjects with diabetes had lower functional capacity compared with healthy control subjects with similar characteristics. Differences in 6-min walk distance were even apparent in the subjects without diabetes complications. Potential mechanisms that could explain this finding are early cardiovascular disease or deconditioning.

Optogenetic Activation of a Lateral Hypothalamic-Ventral Tegmental Drive-Reward Pathway

Electrical stimulation of the lateral hypothalamus can motivate feeding or can serve as a reward in its own right. It remains unclear whether the same or independent but anatomically overlapping circuitries mediate the two effects. Electrical stimulation findings implicate medial forebrain bundle (MFB) fibers of passage in both effects, and optogenetic studies confirm a contribution from fibers originating in the lateral hypothalamic area and projecting to or through the ventral tegmental area. Here we report that optogenetic activation of ventral tegmental fibers from cells of origin in more anterior or posterior portions of the MFB failed to induce either reward or feeding. The feeding and reward induced by optogenetic activation of fibers from the lateral hypothalamic cells of origin were influenced similarly by variations in stimulation pulse width and pulse frequency, consistent with the hypothesis of a common substrate for the two effects. There were, however, several cases where feeding but not self-stimulation or self-stimulation but not feeding were induced, consistent with the hypothesis that distinct but anatomically overlapping systems mediate the two effects. Thus while optogenetic stimulation provides a more selective tool for characterizing the mechanisms of stimulation-induced feeding and reward, it does not yet resolve the question of common or independent substrates.

Patterns of Growth and Decline in Lung Function in Persistent Childhood Asthma

BACKGROUND

Tracking longitudinal measurements of growth and decline in lung function in patients with persistent childhood asthma may reveal links between asthma and subsequent chronic airflow obstruction.

METHODS

We classified children with asthma according to four characteristic patterns of lung-function growth and decline on the basis of graphs showing forced expiratory volume in 1 second (FEV1), representing spirometric measurements performed from childhood into adulthood. Risk factors associated with abnormal patterns were also examined. To define normal values, we used FEV1 values from participants in the National Health and Nutrition Examination Survey who did not have asthma.

RESULTS

Of the 684 study participants, 170 (25%) had a normal pattern of lung-function growth without early decline, and 514 (75%) had abnormal patterns: 176 (26%) had reduced growth and an early decline, 160 (23%) had reduced growth only, and 178 (26%) had normal growth and an early decline. Lower baseline values for FEV1, smaller bronchodilator response, airway hyperresponsiveness at baseline, and male sex were associated with reduced growth (P<0.001 for all comparisons). At the last spirometric measurement (mean [±SD] age, 26.0±1.8 years), 73 participants (11%) met Global Initiative for Chronic Obstructive Lung Disease spirometric criteria for lung-function impairment that was consistent with chronic obstructive pulmonary disease (COPD); these participants were more likely to have a reduced pattern of growth than a normal pattern (18% vs. 3%, P<0.001).

CONCLUSIONS

Childhood impairment of lung function and male sex were the most significant predictors of abnormal longitudinal patterns of lung-function growth and decline. Children with persistent asthma and reduced growth of lung function are at increased risk for fixed airflow obstruction and possibly COPD in early adulthood. (Funded by the Parker B. Francis Foundation and others; ClinicalTrials.gov number, NCT00000575.).

Reciprocal Inhibitory Interactions Between the Reward-Related Effects of Leptin and Cocaine

Cocaine is habit-forming because of its ability to enhance dopaminergic neurotransmission in the forebrain. In addition to neuronal inputs, forebrain dopamine circuits are modulated by hormonal influences; one of these is leptin, an adipose-derived hormone that attenuates the rewarding effects of food- and hunger-associated brain stimulation reward. Here we report reciprocal inhibition between the reward-related effects of leptin and the reward-related effects of cocaine in rats. First, we report that cocaine and the expectancy of cocaine each depresses plasma leptin levels. Second, we report that exogenous leptin, given systemically or directly into the ventral tegmental area, attenuates the ability of cocaine to elevate dopamine levels in the nucleus accumbens, the ability of cocaine to establish a conditioned place preference, and the ability of cocaine-predictive stimuli to prolong responding in extinction of cocaine-seeking. Thus, whereas leptin represents an endogenous antagonist of the habit-forming and habit-sustaining effects of cocaine, this antagonism is attenuated by cocaine and comes to be attenuated by the expectancy of cocaine.

25-hydroxy vitamin D levels are associated with childhood asthma in a population-based study in Peru

BACKGROUND

Vitamin D deficiency may be associated with an increased risk of asthma.

OBJECTIVE

We studied the association between 25-hydroxy (25-OH) vitamin D deficiency and asthma prevalence in two Peruvian populations close to the equator but with disparate degrees of urbanization.

METHODS

We conducted a population-based study in 1441 children in two communities in Peru, of which 1134 (79%) provided a blood sample for 25-OH vitamin D analysis.

RESULTS

In these 1134 children, mean age was 14.8 years; 52% were boys; asthma and atopy prevalence was 12% in Lima vs. 3% in Tumbes (P < 0.001) and 59% in Lima vs. 41% in Tumbes (P < 0.001), respectively; and, mean 25-OH vitamin D level was 20.8 ng/mL in Lima vs. 30.1 ng/mL in Tumbes (P < 0.001). Prevalence of 25-OH vitamin D deficiency (< 20 ng/mL) was 47% in Lima vs. 7% in Tumbes (P < 0.001). In multi-variable logistic regression, we found that lower 25-OH vitamin D levels were associated with an increased odds of asthma (OR = 1.7 per each 10 ng/mL decrease in 25-OH vitamin D levels, 95% CI 1.2-2.6; P < 0.01). In stratified analyses, the association between lower 25-OH vitamin D levels and asthma was limited to children with atopy (OR = 2.2, 95% CI 1.3-3.6) and not in those without atopy (OR = 0.9, 95% CI 0.5-2.0). We did not find associations between 25-OH vitamin D levels and other clinical biomarkers for asthma, including exhaled nitric oxide, total serum IgE and pulmonary function.

CONCLUSION AND CLINICAL RELEVANCE

Both asthma and 25-OH vitamin D deficiency were common among children living in Lima (latitude = 12.0 °S) but not among those in Tumbes (3.6 °S). The relationship between 25-OH vitamin D deficiency and asthma was similar in both sites and was limited among children with atopy. Future supplementation trials may need to consider stratification by atopy at the time of design.

Prevalence and risk factors for allergic rhinitis in two resource-limited settings in Peru with disparate degrees of urbanization

BACKGROUND

Allergic rhinitis is a disease with a high global disease burden, but risk factors that contribute to this condition are not well understood.

OBJECTIVE

To assess the prevalence and risk factors of allergic rhinitis in two Peruvian populations with disparate degrees of urbanization.

METHODS

We conducted a population-based, cross-sectional study on 1441 children aged 13-15 years at enrollment (mean age 14.9 years, 51% boys) to investigate the prevalence of allergic disease. We used a standardized, Spanish validated questionnaire to determine the prevalence of allergic rhinitis and asked about sociodemographics and family history of allergies. Children also underwent spirometry, exhaled nitric oxide, allergy skin testing to 10 common household allergens and provided a blood sample for measurement of 25OH vitamin D and total serum IgE.

RESULTS

Overall prevalence of allergic rhinitis was 18% (95% CI 16% to 20%). When stratified by site, the prevalence of allergic rhinitis was 23% Lima vs. 13% in Tumbes (P < 0.001); however, this difference was no longer significant after controlling for subject-specific factors (P = 0.95). There was a strong association with other allergic diseases: 53% of children with asthma had allergic rhinitis vs. 15% in those without asthma (P < 0.001) and 42% of children with eczema vs. 17% of those without eczema (P < 0.001). Important risk factors for allergic rhinitis were parental rhinitis (adjusted OR = 3.0, 95% CI 1.9-4.7 for 1 parent and adjusted OR = 4.4, 95% CI 1.5-13.7 for 2 parents); allergic sensitization to common household aeroallergens (1.6, 1.1-2.3); being overweight (1.5, 1.0-2.3); exhaled nitric oxide ≥ 20 ppb (1.9, 1.3-2.7); and total serum IgE ≥ 95th percentile (2.4, 1.2-4.8). Population attributable risk of important factors for allergic rhinitis were 25% for high exhaled nitric oxide, 22% for allergic sensitization to common household aeroallergens, 22% for paternal rhinitis, 10% for being overweight and 7% for an elevated total serum IgE.

CONCLUSION AND CLINICAL RELEVANCE

Allergic rhinitis was prevalent in both settings, and important risk factors include elevated exhaled nitric oxide, allergic sensitization to common household aeroallergens, parental rhinitis, being overweight and high total serum IgE. When considering subject-specific factors, the difference in prevalence between the urban and rural settings became non-important.

Supplemental morphine infusion into the posterior ventral tegmentum extends the satiating effects of self-administered intravenous heroin

Rats learn to self-administer intravenous heroin; well-trained animals lever-press at a slow and regular pace over a wide range of intravenous doses. The pauses between successive earned infusions are proportional to the dose of the previous injection and are thought to reflect periods of drug satiety. Rats will also self-administer opiates by microinjection directly into sites in the posterior regions of the ventral tegmentum. To determine if the pauses between self-administered intravenous injections are due to opiate actions in posterior ventral tegmentum, we delivered supplemental morphine directly into this region during intravenous self-administration sessions in well-trained rats. Reverse dialysis of morphine into the posterior ventral tegmentum increased the intervals between earned injections. The inter-response intervals were greatest for infusion into the most posterior ventral tegmental sites, sites in a region variously known as the tail of the ventral tegmental area or as the rostromedial tegmental nucleus. These sites at which morphine prolongs inter-response intervals, correspond to the sites at which opiates have been found most effective in reinforcing instrumental behavior.

Increased latencies to initiate cocaine self-administration following laterodorsal tegmental nucleus lesions

Cholinergic input to the ventral tegmental area (VTA), origin of the mesocorticolimbic dopamine system that is critical for cocaine reward, is important for both cocaine seeking and cocaine taking. The laterodorsal tegmental nucleus (LDTg) provides one of the two major sources of excitatory cholinergic input to the VTA, but little is known of the role of the LDTg in cocaine reward. LDTg cholinergic cells express urotensin-II receptors and here we used local microinjections of a conjugate of the endogenous ligand for these receptors with diphtheria toxin (Dtx::UII) to lesion the cholinergic cells of the LDTg in rats previously trained to self-administer cocaine (1mg/kg/infusion, i.v.). Lesioned rats showed long latencies to initiate cocaine self-administration after treatment with the toxin, which resulted in a reduction in cocaine intake per session. Priming injections reduced latencies to initiate responding for cocaine in lesioned rats, and once they began to respond the rats regulated their moment-to-moment cocaine intake within normal limits. Thus we conclude that while LDTg cholinergic cell loss does not significantly alter the rewarding effects of cocaine, LDTg lesions can reduce the rat's responsiveness to cocaine-predictive stimuli.

Obesity and symptoms of depression contribute independently to the poor asthma control of obesity

Obesity is a major risk factor for poorly controlled asthma, but the reasons for poor asthma control in this patient population are unclear. Symptoms of depression have been associated with poor asthma control, and increase with higher body mass index (BMI). The purpose of this study was to assess whether depressive symptoms underlie poor asthma control in obesity.

METHODS

We determined the relationship between BMI, psychological morbidity and asthma control at baseline in a well-characterized patient population participating in a clinical trial conducted by the American Lung Association-Asthma Clinical Research Centers.

RESULTS

Obese asthmatic participants had increased symptoms of depression (Center for Epidemiologic Studies Depression Scale score in lean 10.1 ± 8.1, overweight 10.0 ± 8.1, obese 12.4 ± 9.9; p = 0.03), worse asthma control (Juniper Asthma Control Questionnaire score in lean 1.43 ± 0.68, overweight 1.52 ± 0.71, obese 1.76 ± 0.75; p < 0.0001), and worse asthma quality of life (scores in lean 5.21 ± 1.08, overweight 5.08 ± 1.05, obese 4.64 ± 1.09; p < 0.0001). Asthmatics with obesity and those with symptoms of depression both had a higher risk of having poorly controlled asthma (adjusted odds ratio of 1.83 CI 1.23-3.52 for obesity, and 2.08 CI 1.23-3.52 for depression), but there was no interaction between the two.

CONCLUSION

Obesity and symptoms of depression are independently associated with poor asthma control. As depression is increased in obese asthmatics it may be an important co-morbidity contributing to poor asthma control in this population, but factors other than depression also contribute to poor asthma control in obesity.

Lesions of cholinergic pedunculopontine tegmental nucleus neurons fail to affect cocaine or heroin self-administration or conditioned place preference in rats

Cholinergic input to the ventral tegmental area (VTA) is known to contribute to reward. Although it is known that the pedunculopontine tegmental nucleus (PPTg) provides an important source of excitatory input to the dopamine system, the specific role of PPTg cholinergic input to the VTA in cocaine reward has not been previously determined. We used a diphtheria toxin conjugated to urotensin-II (Dtx::UII), the endogenous ligand for urotensin-II receptors expressed by PPTg cholinergic but not glutamatergic or GABAergic cells, to lesion cholinergic PPTg neurons. Dtx::UII toxin infusion resulted in the loss of 95.78 (±0.65)% of PPTg cholinergic cells but did not significantly alter either cocaine or heroin self-administration or the development of cocaine or heroin conditioned place preferences. Thus, cholinergic cells originating in PPTg do not appear to be critical for the rewarding effects of cocaine or of heroin.

The development and maintenance of drug addiction

What is the defining property of addiction? We dust off a several-decades-long debate about the relative importance of two forms of reinforcement—positive reinforcement, subjectively linked to drug-induced euphoria, and negative reinforcement, subjectively linked to the alleviation of pain—both of which figure importantly in addiction theory; each of these forms has dominated addiction theory in its time. We agree that addiction begins with the formation of habits through positive reinforcement and that drug-opposite physiological responses often establish the conditions for negative reinforcement to come into play at a time when tolerance, in the form of increasing reward thresholds, appears to develop into positive reinforcement. Wise’s work has tended to focus on positive-reinforcement mechanisms that are important for establishing drug-seeking habits and reinstating them quickly after periods of abstinence, whereas Koob’s work has tended to focus on the negative-reinforcement mechanisms that become most obvious in the late stages of sustained addiction. While we tend to agree with each other about the early and late stages of addiction, we hold different views as to (i) the point between early and late at which the diagnosis of ‘addiction’ should be invoked, (ii) the relative importance of positive and negative reinforcement leading up to this transition, and (iii) the degree to which the specifics of negative reinforcement can be generalized across the range of addictive agents.

Ventral tegmental site of opiate reward: antagonism by a hydrophilic opiate receptor blocker

The ventral tegmental area has been suggested as a possible site of action for the rewarding effect of opiates on the basis of the fact that local morphine injections in this but not other regions are rewarding. That this is a necessary and not just a sufficient site of opiate rewarding action was suggested by the fact that diallyl-normorphinium bromide, a hydrophilic opiate blocker, caused compensatory increases in intravenous heroin self-administration when injected into the ventral tegmental area but not other brain regions.

ALOX5 polymorphism associates with increased leukotriene production and reduced lung function and asthma control in children with poorly controlled asthma

BACKGROUND

Identification of risk factors for reduced asthma control could improve the understanding and treatment of asthma. A promoter polymorphism in the 5-lipoxygenase gene affects gene expression and response to asthma therapy, but its impact on disease control remains unclear.

OBJECTIVE

We sought to determine if the ALOX5 promoter SP1 tandem repeat polymorphism was associated with changes in cysteinyl leukotriene production, lung function, airway inflammation and asthma control score.

METHODS

We analysed 270 children, 6- to 17-years old, with poorly controlled asthma enrolled in a 6-month clinical trial (NCT00604851). In secondary analysis, we associated the ALOX5 promoter SP1 tandem repeat polymorphism genotype (rs59439148) with asthma outcomes using both additive and recessive genetic models. We evaluated FEV1 percent predicted, symptom control, exhaled nitric oxide and urinary LTE4 levels.

RESULTS

Of all children, 14.8% (40/270) (and 28% (38/135) of African Americans) carried two non-5-repeat variant alleles of rs59439148. Children who were homozygous for variant alleles had significantly higher urinary LTE4 levels (38 vs. 30 nmol/mol creatinine, P = 0.0134), significantly worse FEV1% predicted (84 vs. 91, P = 0.017) and a trend towards worse asthma control. FEV1% predicted values were significantly negatively correlated with urinary LTE4 (r = -0.192, P = 0.009).

CONCLUSION AND CLINICAL RELEVANCE

Carrying two copies of a minor variant ALOX5 promoter SP1 tandem repeat allele contributes to increased cysLT exposure as determined by urinary LTE4 levels, reduced lung function and potentially worse asthma control. ALOX5 promoter SP1 tandem repeat genotype may be a risk factor for worse asthma outcomes.

Conditioned contribution of peripheral cocaine actions to cocaine reward and cocaine-seeking

Cocaine has actions in the peripheral nervous system that reliably precede--and thus predict--its soon-to-follow central rewarding effects. In cocaine-experienced animals, the peripheral cocaine signal is relayed to the central nervous system, triggering excitatory input to the ventral tegmental origin of the mesocorticolimbic dopamine system, the system that mediates the rewarding effects of the drug. We used cocaine methiodide, a cocaine analog that does not cross the blood-brain barrier, to isolate the peripheral actions of cocaine and determine their central and behavioral effects in animals first trained to lever-press for cocaine hydrochloride (the centrally acting and abused form of the drug). We first confirmed with fast-scan cyclic voltammetry that cocaine methiodide causes rapid dopamine release from dopamine terminals in cocaine hydrochloride-trained rats. We then compared the ability of cocaine hydrochloride and cocaine methiodide to establish conditioned place preferences in rats with self-administration experience. While cocaine hydrochloride established stronger place preferences, cocaine methiodide was also effective and its effectiveness increased (incubated) over weeks of cocaine abstinence. Cocaine self-administration was extinguished when cocaine methiodide or saline was substituted for cocaine hydrochloride in the intravenous self-administration paradigm, but cocaine hydrochloride and cocaine methiodide each reinstated non-rewarded lever-pressing after extinction. Rats extinguished by cocaine methiodide substitution showed weaker cocaine-induced reinstatement than rats extinguished by saline substitution. These findings suggest that the conditioned peripheral effects of cocaine can contribute significantly to cocaine-induced (but not stress-induced) cocaine craving, and also suggest the cocaine cue as an important target for cue-exposure therapies for cocaine addiction.

Dual roles of dopamine in food and drug seeking: the drive-reward paradox

The question of whether (or to what degree) obesity reflects addiction to high-energy foods often narrows to the question of whether the overeating of these foods causes the same long-term neuroadaptations as are identified with the late stages of addiction. Of equal or perhaps greater interest is the question of whether common brain mechanisms mediate the acquisition and development of eating and drug-taking habits. The earliest evidence on this question is rooted in early studies of brain stimulation reward. Lateral hypothalamic electrical stimulation can be reinforcing in some conditions and can motivate feeding in others. That stimulation of the same brain region should be both reinforcing and drive inducing is paradoxical; why should an animal work to induce a drive-like state such as hunger? This is known as the drive-reward paradox. Insights into the substrates of the drive-reward paradox suggest an answer to the controversial question of whether the dopamine system--a system downstream from the stimulated fibers of the lateral hypothalamus--is more critically involved in wanting or in liking of various rewards including food and addictive drugs. That the same brain circuitry is implicated in the motivation for and the reinforcement by both food and addictive drugs extends the argument for a common mechanism underlying compulsive overeating and compulsive drug taking.

Heroin self-administration experience establishes control of ventral tegmental glutamate release by stress and environmental stimuli

Heroin and cocaine have very different unconditioned receptor-mediated actions; however, in the brain circuitry of drug-reward and motivation, the two drugs establish common conditioned consequences. A single experience with either drug can change the sensitivity of ventral tegmental area (VTA) dopamine neurons to glutamatergic input. In the case of cocaine, repeated intravenous self-administration establishes de novo VTA glutamate release and dopaminergic activation in response to conditioned stimuli and mild footshock stress. Here we determined whether repeated self-administration of heroin would establish similar glutamate release and dopaminergic activation. Although self-administration of heroin itself did not cause VTA glutamate release, conditioned glutamate release was seen when rats expecting rewarding heroin were given nonrewarding saline in its place. Mild footshock stress also caused glutamate release in heroin-trained animals. In each case, the VTA glutamate release was accompanied by elevations in VTA dopamine levels, indicative of dopaminergic activation. In each case, infusion of the ionotropic glutamate antagonist kynurenic acid blocked the VTA dopamine release associated with VTA glutamate elevation. Although glutamate levels in the extinction and reinstatement tests were similar to those reported in cocaine studies, the effects of heroin self-administration itself were quite different from what has been seen during cocaine self-administration.

Linking context with reward: a functional circuit from hippocampal CA3 to ventral tegmental area

Reward-motivated behavior is strongly influenced by the learned significance of contextual stimuli in the environment. However, the neural pathways that mediate context-reward relations are not well understood. We have identified a circuit from area CA3 of dorsal hippocampus to ventral tegmental area (VTA) that uses lateral septum (LS) as a relay. Theta frequency stimulation of CA3 excited VTA dopamine (DA) neurons and inhibited non-DA neurons. DA neuron excitation was likely mediated by disinhibition because local antagonism of γ-aminobutyric acid receptors blocked responses to CA3 stimulation. Inactivating components of the CA3-LS-VTA pathway blocked evoked responses in VTA and also reinstatement of cocaine-seeking by contextual stimuli. This transsynaptic link between hippocampus and VTA appears to be an important substrate by which environmental context regulates goal-directed behavior.

Supplementation with vitamin A early in life and subsequent risk of asthma

Animal models suggest that vitamin A deficiency affects lung development adversely and promotes airway hyperresponsiveness, and may predispose to an increased risk of asthma. We examined the long-term effects of vitamin A supplementation early in life on later asthma risk. In 2006-2008, we revisited participants from two cohorts in rural Nepal who were enrolled in randomised trials of vitamin A supplementation. The first cohort received vitamin A or placebo for <16 months during their pre-school years (1989-1991). The second cohort was born to mothers who received vitamin A, β-carotene or placebo before, during and after pregnancy (1994-1997). At follow-up, we asked about asthma symptoms and performed spirometry. Out of 6,421 subjects eligible to participate, 5,430 (85%) responded to our respiratory survey. Wheezing prevalence during the previous year was 4.8% in participants aged 9-13 yrs and 6.6% in participants aged 14-23 yrs. We found no differences between the vitamin A supplemented and placebo groups from either trial in the prevalence of lifetime or current asthma and wheeze or in spirometric indices of obstruction (p ≥ 0.12 for all comparisons). Vitamin A supplementation early in life was not associated with a decreased risk of asthma in an area with chronic vitamin A deficiency.

Differentiating the rapid actions of cocaine

The subjective effects of intravenous cocaine are felt almost immediately, and this immediacy plays an important part in the drug's rewarding impact. The primary rewarding effect of cocaine involves blockade of dopamine reuptake; however, the onset of this action is too late to account for the drug's initial effects. Recent studies suggest that cocaine-predictive cues--including peripheral interoceptive cues generated by cocaine itself--come to cause more direct and earlier reward signalling by activating excitatory inputs to the dopamine system. The conditioned activation of the dopamine system by cocaine-predictive cues offers a new target for potential addiction therapies.

Dorsal as well as ventral striatal lesions affect levels of intravenous cocaine and morphine self-administration in rats

While the ventral striatum has long been implicated in the rewarding properties of psychomotor stimulants and opiates, little attention has been paid to the possible contribution of more dorsal regions of the striatum. We have thus examined the effects of lesions in three different striatal subregions on cocaine and morphine self-administration. Different groups of rats were trained to self-administer intravenous cocaine (1.0mg/kg/infusion) or morphine (0.5mg/kg/infusion) first under fixed ratio (FR) and then under progressive ratio (PR) schedules of reinforcement. Upon completion of the training, independent groups received bilateral electrolytic or sham lesions of the dorsal portion of the caudate-putamen (dCPu), the ventral portion of the caudate-putamen (vCPu) or the more ventral nucleus accumbens (NAS). Following recovery, they were tested for self-administration of cocaine (0.25, 0.5, 1.0 and 1.5mg/kg/infusion) or morphine (0.125, 0.25, 0.5 and 0.75mg/kg/infusion) under the PR schedule. The PR responding for each drug was significantly reduced in a dose-dependent manner following lesions of dCPu, vCPu and NAS. While the relative effectiveness of these lesions is likely to be specific to the conditions of this experiment, NAS lesions reduced self-administration of each drug to a greater extent than did dCPu or vCPu lesions.

The minimal important difference of exercise tests in severe COPD

Our aim was to determine the minimal important difference (MID) for 6-min walk distance (6MWD) and maximal cycle exercise capacity (MCEC) in patients with severe chronic obstructive pulmonary disease (COPD). 1,218 patients enrolled in the National Emphysema Treatment Trial completed exercise tests before and after 4-6 weeks of pre-trial rehabilitation, and 6 months after randomisation to surgery or medical care. The St George's Respiratory Questionnaire (domain and total scores) and University of California San Diego Shortness of Breath Questionnaire (total score) served as anchors for anchor-based MID estimates. In order to calculate distribution-based estimates, we used the standard error of measurement, Cohen's effect size and the empirical rule effect size. Anchor-based estimates for the 6MWD were 18.9 m (95% CI 18.1-20.1 m), 24.2 m (95% CI 23.4-25.4 m), 24.6 m (95% CI 23.4-25.7 m) and 26.4 m (95% CI 25.4-27.4 m), which were similar to distribution-based MID estimates of 25.7, 26.8 and 30.6 m. For MCEC, anchor-based estimates for the MID were 2.2 W (95% CI 2.0-2.4 W), 3.2 W (95% CI 3.0-3.4 W), 3.2 W (95% CI 3.0-3.4 W) and 3.3 W (95% CI 3.0-3.5 W), while distribution-based estimates were 5.3 and 5.5 W. We suggest a MID of 26 ± 2 m for 6MWD and 4 ± 1 W for MCEC for patients with severe COPD.

Extracellular fluctuations of dopamine and glutamate in the nucleus accumbens core and shell associated with lever-pressing during cocaine self-administration, extinction, and yoked cocaine administration

RATIONALE

Dopamine and glutamate in the nucleus accumbens (NAS) are differentially implicated in cocaine-directed behavior.

OBJECTIVES

We sought to compare extracellular fluctuations of dopamine and glutamate in core and shell of NAS associated with operant responding during cocaine self-administration, extinction, and yoked cocaine administration.

METHODS

Rats were trained to lever-press for cocaine or saline under FR1 before undergoing microdialysis testing during cocaine self-administration, extinction, or yoked cocaine administration. Microdialysis samples were collected every 20 min and were analyzed for dopamine and glutamate with high-performance liquid chromatography.

RESULTS

Rats actively lever-pressed during cocaine self-administration and extinction. However, lever-pressing was minimal during yoked cocaine administration in both cocaine-trained and saline-trained rats. Dopamine was elevated throughout cocaine self-administration and yoked cocaine administration. The extent of cocaine-evoked dopamine was greater in shell than in core, greater in cocaine-trained than in saline-trained rats, and greater during self-administration than during yoked administration. Dopamine was also elevated in core (first 60 min) and in shell (first 40 min) during extinction. Basal concentration of glutamate, but not dopamine, was lower in cocaine-trained than in saline-trained rats. In cocaine-trained rats, glutamate was elevated during cocaine self-administration and extinction but was depressed below baseline during yoked cocaine administration. The extent and direction of glutamate fluctuation was similar between core and shell. In saline-trained rats, glutamate was not affected by yoked cocaine.

CONCLUSION

Distinct patterns of dopamine and glutamate fluctuations in core and shell appear to underlie characteristic patterns of lever-pressing associated with cocaine self-administration, extinction, and yoked cocaine administration.

Methamphetamine acts on subpopulations of neurons regulating sexual behavior in male rats

Methamphetamine (Meth) is a highly addictive stimulant. Meth abuse is commonly associated with the practice of sexual risk behavior and increased prevalence of Human Immunodeficiency Virus and Meth users report heightened sexual desire, arousal, and sexual pleasure. The biological basis for this drug-sex nexus is unknown. The current study demonstrates that Meth administration in male rats activates neurons in brain regions of the mesolimbic system that are involved in the regulation of sexual behavior. Specifically, Meth and mating co-activate cells in the nucleus accumbens core and shell, basolateral amygdala, and anterior cingulate cortex. These findings illustrate that in contrast to current belief drugs of abuse can activate the same cells as a natural reinforcer, that is sexual behavior, and in turn may influence compulsive seeking of this natural reward.

Roles for nigrostriatal--not just mesocorticolimbic--dopamine in reward and addiction

Forebrain dopamine circuitry has traditionally been studied by two largely independent specialist groups: students of Parkinson's disease who study the nigrostriatal dopamine system that originates in the substantia nigra (SN), and students of motivation and addiction who study the role of the mesolimbic and mesocortical dopamine systems that originate in the ventral tegmental area (VTA). The anatomical evidence for independent nigrostriatal and mesolimbic dopamine systems has, however, long been obsolete. There is now compelling evidence that both nominal "systems" participate in reward function and addiction. Electrical stimulation of both SN and VTA is rewarding, blockade of glutamatergic or cholinergic input to either SN or VTA attenuates the habit-forming effects of intravenous cocaine, and dopamine in both nigrostriatal and mesocorticolimbic terminal fields participates in the defining property of rewarding events: the reinforcement of memory consolidation. Thus, the similarities between nigrostriatal and mesolimbic dopamine systems can be as important as their differences.

Control of within-binge cocaine-seeking by dopamine and glutamate in the core of nucleus accumbens

RATIONALE

Dopamine and glutamate are thought to interact in the ventral striatum and to play important roles there in the cocaine-seeking of cocaine-experienced animals.

OBJECTIVES

We sought to determine the relative roles of the two transmitters in the two major zones of the nucleus accumbens (NAS), the core and shell subregions.

METHODS

We assessed the effects of dopamine and glutamate receptor blockade in the core and shell on intravenous cocaine self-administration in rats. Trained animals were allowed to self-administer cocaine for an initial hour, and then D1-type or D2-type dopamine receptor blockers or NMDA-type or AMPA-type glutamate receptor blockers were infused by reverse microdialysis into one of the two regions for an additional 3 h of testing.

RESULTS

The D1-type antagonist SCH23390 and the D2-type antagonist raclopride each increased cocaine intake whereas the AMPA-type antagonist CNQX decreased responding when infused into the core. SCH23390 increased cocaine intake less strongly when infused into the shell, while raclopride and CNQX were each ineffective when infused into the shell. The NMDA-antagonist CPP failed to affect cocaine self-administration when infused into either site.

CONCLUSIONS

These findings implicate the core of NAS in the maintenance of established cocaine self-administration in trained animals, despite the fact that the reinforcement of responding in untrained animals appears to results from cocaine actions in the olfactory tubercle and medial shell and not the core of accumbens.

Associations of IL6 polymorphisms with lung function decline and COPD

BACKGROUND

Interleukin-6 (IL6) is a pleiotropic pro-inflammatory and immunomodulatory cytokine which probably plays an important role in the pathogenesis of chronic obstructive pulmonary disease (COPD). There is a functional single nucleotide polymorphism (SNP), -174G/C, in the promoter region of IL6. It was hypothesised that IL6 SNPs influence susceptibility for impaired lung function and COPD in smokers.

METHODS

Seven and five SNPs in IL6 were genotyped in two nested case-control samples derived from the Lung Health Study (LHS) based on phenotypes of rate of decline of forced expiratory volume in 1 s (FEV(1)) over 5 years and baseline FEV(1) at the beginning of the LHS. Serum IL6 concentrations were measured for all subjects. A partially overlapping panel of nine IL6 SNPs was genotyped in 389 cases of COPD from the National Emphysema Treatment Trial (NETT) and 420 controls from the Normative Aging Study (NAS).

RESULTS

In the LHS, three IL6 SNPs were associated with decline in FEV(1) (0.023< or =p< or =0.041 in additive models). Among them, the IL6_-174C allele was associated with a rapid decline in lung function. The association was more significant in a genotype-based analysis (p = 0.006). In the NETT-NAS study, IL6_-174G/C and four other IL6 SNPs, all of which are in linkage disequilibrium with IL6_-174G/C, were associated with susceptibility to COPD (0.01< or =p< or =0.04 in additive genetic models).

CONCLUSION

The results suggest that the IL6_-174G/C SNP is associated with a rapid decline in FEV(1) and susceptibility to COPD in smokers.

Leptin receptor polymorphisms and lung function decline in COPD

Only a fraction of all smokers develop chronic obstructive pulmonary disease (COPD), suggesting a large role for genetic susceptibility. The leptin receptor (LEPR) is present in human lung tissue and may play a role in COPD pathogenesis. The present study examined the association between genetic variants in the LEPR gene and lung function decline in COPD. In total, 429 European Americans were randomly selected from the National Heart Lung and Blood Institute Lung Health Study. 36 single nucleotide polymorphisms (SNPs) in LEPR were genotyped using the Illumina GoldenGate platform (Broad Institute, Cambridge, MA, USA). Mean annual decline in forced expiratory volume in 1 s % predicted over the 5-yr period was calculated using linear regression. Linear regression models were also used to adjust for potential confounders. In addition, in vivo expression of the receptor gene was assessed with immunohistochemistry on lungs from smoke-exposed inbred mice. We identified significant associations (p<0.05) between lung function decline and 21 SNPs. Haplotype analyses confirmed several of these associations seen with individual markers. Immunohistochemistry results in inbred mice strains support a potential role of LEPR in COPD pathogenesis. We identified genetic variants in the LEPR gene significantly associated with lung function decline in a population of smokers with COPD. Our results support a role for LEPR as a novel candidate gene for COPD.

Dopamine and reward: the anhedonia hypothesis 30 years on

The anhedonia hypothesis--that brain dopamine plays a critical role in the subjective pleasure associated with positive rewards--was intended to draw the attention of psychiatrists to the growing evidence that dopamine plays a critical role in the objective reinforcement and incentive motivation associated with food and water, brain stimulation reward, and psychomotor stimulant and opiate reward. The hypothesis called to attention the apparent paradox that neuroleptics, drugs used to treat a condition involving anhedonia (schizophrenia), attenuated in laboratory animals the positive reinforcement that we normally associate with pleasure. The hypothesis held only brief interest for psychiatrists, who pointed out that the animal studies reflected acute actions of neuroleptics whereas the treatment of schizophrenia appears to result from neuroadaptations to chronic neuroleptic administration, and that it is the positive symptoms of schizophrenia that neuroleptics alleviate, rather than the negative symptoms that include anhedonia. Perhaps for these reasons, the hypothesis has had minimal impact in the psychiatric literature. Despite its limited heuristic value for the understanding of schizophrenia, however, the anhedonia hypothesis has had major impact on biological theories of reinforcement, motivation, and addiction. Brain dopamine plays a very important role in reinforcement of response habits, conditioned preferences, and synaptic plasticity in cellular models of learning and memory. The notion that dopamine plays a dominant role in reinforcement is fundamental to the psychomotor stimulant theory of addiction, to most neuroadaptation theories of addiction, and to current theories of conditioned reinforcement and reward prediction. Properly understood, it is also fundamental to recent theories of incentive motivation.

Cocaine serves as a peripheral interoceptive conditioned stimulus for central glutamate and dopamine release

Intravenous injections of cocaine HCl are habit-forming because, among their many actions, they elevate extracellular dopamine levels in the terminal fields of the mesocorticolimbic dopamine system. This action, thought to be very important for cocaine's strong addiction liability, is believed to have very short latency and is assumed to reflect rapid brain entry and pharmacokinetics of the drug. However, while intravenous cocaine HCl has almost immediate effects on behavior and extracellular dopamine levels, recent evidence suggests that its central pharmacological effects are not evident until 10 or more seconds after IV injection. Thus the immediate effects of a given intravenous cocaine injection on extracellular dopamine concentration and behavior appear to occur before there is sufficient time for cocaine to act centrally as a dopamine uptake inhibitor. To explore the contribution of peripheral effects of cocaine to the early activation of the dopamine system, we used brain microdialysis to measure the effects of cocaine methiodide (MI)--a cocaine analogue that does not cross the blood brain barrier--on glutamate (excitatory) input to the dopamine cells. IP injections of cocaine MI were ineffective in cocaine-naïve animals but stimulated ventral tegmental glutamate release in rats previously trained to lever-press for cocaine HCl. This peripherally triggered glutamate input was sufficient to reinstate cocaine-seeking in previously trained animals that had undergone extinction of the habit. These findings offer an explanation for short-latency behavioral responses and immediate dopamine elevations seen following cocaine injections in cocaine-experienced but not cocaine-naïve animals.

Ventral tegmental glutamate: a role in stress-, cue-, and cocaine-induced reinstatement of cocaine-seeking

Ventral tegmental dopamine neurons are activated by primary rewards and, when such rewards are predictable' by reward-predicting stimuli. Glutamatergic input to the ventral tegmental area contributes to this activation: in animals trained to self-administer cocaine, cocaine-predictive cues trigger ventral tegmental glutamate release and dopaminergic activation. Mild footshock stress similarly causes glutamate release and dopaminergic activation in cocaine-trained but not cocaine-naïve animals. The ability of cocaine-predictive and stress-associated cues to activate the dopamine system and to trigger cocaine craving appears to be related to changes in the ability of glutamate to activate dopaminergic neurons, changes known to be caused by experience with stress or with drugs of abuse.

Functional implications of glutamatergic projections to the ventral tegmental area

Glutamatergic afferents of the ventral tegmental area (VTA) play an important role in the functioning of the VTA and are involved in the pathophysiology of drug addiction. It has recently been demonstrated that the VTA is densely innervated by glutamatergic axons and that glutamatergic neurons projecting to the VTA are situated in almost all structures that project there. While the projection from the prefrontal cortex is essentially entirely glutamatergic, subcortical glutamatergic neurons innervating the VTA intermingle with non-glutamatergic, most likely GABAergic and/or peptidergic VTA-projecting neurons. The first part of this review focuses on the origins and putative functional implications of various glutamatergic projections to the VTA. In the second part we consider how different neuropeptides via different mechanisms modulate glutamatergic actions in the VTA. We conclude by developing a model of how the glutamatergic afferents might together contribute to the functions of the VTA.

A role for conditioned ventral tegmental glutamate release in cocaine seeking

Initiation of cocaine self-administration in rats was associated with release of glutamate in the ventral tegmental area (VTA). The glutamate release was transient, despite continued cocaine intake. Similar glutamate release was seen in rats earning, for the first time, unexpected saline rather than expected cocaine. VTA glutamate release was not seen in similarly trained rats earning saline instead of cocaine for the 13th time. VTA glutamate release was also seen in similarly trained rats that received yoked rather than earned cocaine injections on test day. VTA glutamate release was not seen in a group of rats that had never earned cocaine but had received yoked injections during the training period. Glutamate release was also not seen in a group of rats that received yoked injections but had no previous experience with cocaine. VTA GABA levels did not fluctuate during any aspect of cocaine seeking. Blockade of VTA glutamate receptors appeared to attenuate the rewarding effects of intravenous cocaine injections and blocked almost completely the conditioned responding normally seen during extinction trials. These findings indicate that VTA glutamate release is a conditioned response dependent on an associative process and is not a simple consequence of previous cocaine exposure. The findings implicate glutamate as at least one of the sources of VTA signals from reward-associated environmental stimuli.

Stress-induced relapse to cocaine seeking: roles for the CRF(2) receptor and CRF-binding protein in the ventral tegmental area of the rat

RATIONALE

Footshock reinstates cocaine seeking in cocaine-experienced rats by inducing corticotropin-releasing factor (CRF) and glutamate release in the ventral tegmental area (VTA) and thus activating VTA dopaminergic neurons. Footshock-induced VTA glutamate release, dopamine activation and reinstatements are blocked by VTA administration of a alpha-helical CRF, a nonselective CRF receptor antagonist. The effects of selective CRF antagonists have not yet been reported.

OBJECTIVE

The present studies were designed to explore the roles of VTA CRF receptor subtypes and CRF-BP in these effects induced by footshock.

METHODS

Rats were first trained to lever-press for intravenous cocaine (1 mg/infusion/0.13 ml, FR-1 schedule), and then tested under extinction conditions until response rates returned to the pretraining baseline. Reinstatements, VTA glutamate and dopamine levels [microdialysis with high performance liquid chromatography (HPLC)] were then assessed, under various pharmacological conditions, after mild inescapable footshock.

RESULTS

Footshock-induced reinstatement of cocaine seeking and release of VTA glutamate and dopamine were blocked by selective blockade of VTA CRF(2) receptors (CRF(2)Rs) but not CRF(1)Rs. VTA perfusion of CRF or CRF(2)R agonists that have strong affinity for CRF-BP mimicked the effects induced by footshock while CRFR agonists that do not bind CRF-BP were ineffective. CRF(6-33), which competes for the CRF binding site on CRF-BP, attenuated the effects of CRF or urocortin I on VTA glutamate and dopamine release and on reinstatement of cocaine seeking.

CONCLUSIONS

The present studies revealed a role of VTA CRF-BP and suggest an involvement of CRF(2)R in the effectiveness of stress in triggering glutamate and dopamine release and cocaine seeking in drug-experienced animals.

Long-term upregulation of protein kinase A and adenylate cyclase levels in human smokers

Repeated injections of cocaine and morphine in laboratory rats cause a variety of molecular neuroadaptations in the cAMP signaling pathway in nucleus accumbens and ventral tegmental area. Here we report similar neuroadaptations in postmortem tissue from the brains of human smokers and former smokers. Activity levels of two major components of cAMP signaling, cAMP-dependent protein kinase A (PKA) and adenylate cyclase, were abnormally elevated in nucleus accumbens of smokers and in ventral midbrain dopaminergic region of both smokers and former smokers. Protein levels of the catalytic subunit of PKA were correspondingly higher in the ventral midbrain dopaminergic region of both smokers and former smokers. Protein levels of other candidate neuroadaptations, including glutamate receptor subunits, tyrosine hydroxylase, and other protein kinases, were within normal range. These findings extend our understanding of addiction-related neuroadaptations of cAMP signaling to tobacco smoking in human subjects and suggest that smoking-induced brain neuroadaptations can persist for significant periods in former smokers.

Heteromeric nicotinic acetylcholine-dopamine autoreceptor complexes modulate striatal dopamine release

In the striatum, dopamine and acetylcholine (ACh) modulate dopamine release by acting, respectively, on dopamine D(2) autoreceptors and nicotinic ACh (nACh) heteroreceptors localized on dopaminergic nerve terminals. The possibility that functional interactions exist between striatal D(2) autoreceptors and nACh receptors was studied with in vivo microdialysis in freely moving rats. Local perfusion of nicotine in the ventral striatum (shell of the nucleus accumbens) produced a marked increase in the extracellular levels of dopamine, which was completely counteracted by co-perfusion with either the non-alpha(7) nACh receptor antagonist dihydro-beta-erythroidine or the D(2-3) receptor agonist quinpirole. Local perfusion of the D(2-3) receptor antagonist raclopride produced an increase in the extracellular levels of dopamine, which was partially, but significantly, counteracted by coperfusion with dihydro-beta-erythroidine. These findings demonstrate a potent crosstalk between G protein-coupled receptors and ligand-gated ion channels in dopaminergic nerve terminals, with the D(2) autoreceptor modulating the efficacy of non-alpha(7) nACh receptor-mediated modulation of dopamine release. We further demonstrate physical interactions between beta(2) subunits of non-alpha(7) nicotinic acetylcholine receptors and D(2) autoreceptors in co-immunoprecipitation experiments with membrane preparations from co-transfected mammalian cells and rat striatum. These results reveal that striatal non-alpha(7) nicotinic acetylcholine receptors form part of heteromeric dopamine autoreceptor complexes that modulate dopamine release.

Role of brain dopamine in food reward and reinforcement

The ability of food to establish and maintain response habits and conditioned preferences depends largely on the function of brain dopamine systems. While dopaminergic transmission in the nucleus accumbens appears sufficient for some forms of reward, the role of dopamine in food reward does not appear to be restricted to this region. Dopamine plays an important role in both the ability to energize feeding and to reinforce food-seeking behaviour; the role in energizing feeding is secondary to the prerequisite role in reinforcement. Dopaminergic activation is triggered by the auditory and visual as well as the tactile, olfactory, and gustatory stimuli of foods. While dopamine plays a central role in the feeding and food-seeking of normal animals, some food rewarded learning can be seen in genetically engineered dopamine-deficient mice.

Two brain sites for cannabinoid reward

The recent findings that Delta9tetrahydrocannabinol (Delta9THC), the active agent in marijuana and hashish, (1) is self-administered intravenously, (2) potentiates the rewarding effects of electrical brain stimulation, and (3) can establish conditioned place preferences in laboratory animals, suggest that these drugs activate biologically primitive brain reward mechanisms. Here, we identify two chemical trigger zones for stimulant and rewarding actions of Delta9THC. Microinjections of Delta9THC into the posterior ventral tegmental area (VTA) or into the shell of the nucleus accumbens (NAS) increased locomotion, and rats learned to lever-press for injections of Delta9THC into each of these regions. Substitution of vehicle for drug or treatment with a cannabinoid CB1 receptor antagonist caused response cessation. Microinjections of Delta9THC into the posterior VTA and into the posterior shell of NAS established conditioned place preferences. Injections into the core of the NAS, the anterior VTA, or dorsal to the VTA were ineffective. These findings link the sites of rewarding action of Delta9THC to brain regions where such drugs as amphetamines, cocaine, heroin, and nicotine are also thought to have their sites of rewarding action.

C-reactive protein and mortality in mild to moderate chronic obstructive pulmonary disease

BACKGROUND

Although C-reactive protein (CRP) levels are increased in chronic obstructive pulmonary disease (COPD), it is not certain whether they are associated with adverse clinical outcomes.

METHODS

Serum CRP levels were measured in 4803 participants in the Lung Health Study with mild to moderate COPD. The risk of all-cause and disease specific causes of mortality was determined as well as cardiovascular event rates, adjusting for important covariates such as age, sex, cigarette smoking, and lung function. Cardiovascular events were defined as death from coronary heart disease or stroke, or non-fatal myocardial infarction or stroke requiring admission to hospital.

RESULTS

CRP levels were associated with all-cause, cardiovascular, and cancer specific causes of mortality. Individuals in the highest quintile of CRP had a relative risk (RR) for all-cause mortality of 1.79 (95% confidence interval (CI) 1.25 to 2.56) compared with those in the lowest quintile of CRP. For cardiovascular events and cancer deaths the corresponding RRs were 1.51 (95% CI 1.20 to 1.90) and 1.85 (95% CI 1.10 to 3.13), respectively. CRP levels were also associated with an accelerated decline in forced expiratory volume in 1 second (p < 0.001). The discriminative property of CRP was greatest during the first year of measurement and decayed over time. Comparing the highest and lowest CRP quintiles, the RR was 4.03 (95% CI 1.23 to 13.21) for 1 year mortality, 3.30 (95% CI 1.38 to 7.86) for 2 year mortality, and 1.82 (95% CI 1.22 to 2.68) for > or =5 year mortality.

CONCLUSIONS

CRP measurements provide incremental prognostic information beyond that achieved by traditional markers of prognosis in patients with mild to moderate COPD, and may enable more accurate detection of patients at a high risk of mortality.

A new peptide input to learning and addiction

In this issue of Neuron, Borgland et al. report that the arousal-associated peptide orexin enhances LTP-like changes in glutamatergic excitability of ventral tegmental dopamine neurons. This parallels a similar effect of corticotropin-releasing factor and suggests a form of neuroadaptation that increases the likelihood of addiction relapse.