Prolonged exposure to cocaine self-administration results in a continued progression of alterations in functional activity in a nonhuman primate model.

Background: Studies of nonhuman primates with exposures of up to 100 days of cocaine self-administration (SA) have provided evidence that the central effects of cocaine progress over time. These durations of cocaine exposure, however, may be insufficient to capture the extent of the neurobiological alterations observed in cocaine users, many of whom use the drug for years. The goal of the present study was to determine whether 1.5 years of cocaine SA would result in further progression of alterations in functional brain activity. Methods: Adult male rhesus monkeys were exposed to 300 sessions of high-dose cocaine SA over 1.5 years. Following the final session rates of local cerebral glucose utilization (LCGU) were assessed with the 2-[14C]-deoxyglucose method and compared to rates of LCGU in control monkeys who responded for food reinforcement. In addition, LCGU in these animals was compared to a previously published group of monkeys that had self-administered cocaine or food for 100 sessions over a 4-5 month period. Results: Compared to 100 days of exposure, 300 days of cocaine SA further reduced LCGU in the post-commissural striatum and produced reductions in areas unaffected by the shorter duration of exposure, such as the hypothalamus, all of the amygdala, and large expanses of cortex. Conclusions: These findings demonstrate a clear progression of the impact of cocaine on functional activity with increasing durations of drug experience and have important implications for the development of potential strategies for the treatment of cocaine use disorder.

Positron Emission Tomography-Computed Tomography Imaging of Selective Lobar Delivery of Stem Cells in Ex Vivo Lung Model of Mechanical Ventilation.

Introduction: The delivery of cell therapies may be an important frontier to treat different respiratory diseases in the near future. However, the cell size, delivery conditions, cell viability, and effect in the pulmonary function are critical factors. We performed a proof-of-concept experiment using ex vivo lungs and novel subglottic airway device that allows for selective lobar isolation and administration of drugs and biologics in liquid solution deep into the lung tissues, while simultaneously ventilating the rest of the lung lobes. Methods: We used radiolabeled cells and positron emission tomography-computed tomography (PET-CT) imaging to demonstrate the feasibility of high-yield cell delivery to a specifically targeted lobe. This study proposes an alternative delivery method of live cells labeled with radioactive isotope into the lung parenchyma and tracks the cell delivery using PET-CT imaging. The technique combines selective lobar isolation and lobar infusion to carry large particles distal to the trachea, subtending bronchial segments and reaching alveoli in targeted regions. Results: The solution with cells and carrier achieved a complete and homogeneous lobar distribution. An increase in tissue density was shown on the computed tomography (CT) scan, and the PET-CT imaging demonstrated retention of the activity at central, peripheral lung parenchyma, and pleural surface. The increase in CT density and metabolic activity of the isotope was restricted to the desired lobe only without leak to other lobes. Conclusion: The selective lobe delivery is targeted and imaging-guided by bronchoscopy and CT to a specific diseased lobe during mechanical ventilation. The feasibility of high-yield cell delivery demonstrated in this study will lead to the development of potential novel therapies that contribute to lung health.

Residual deficits in functional brain activity after chronic cocaine self-administration in rhesus monkeys.

Previous studies in humans and in animals have shown dramatic effects of cocaine on measures of brain function that persist into abstinence. The purpose of this study was to examine the neurobiological consequences of abstinence from cocaine, using a model that removes the potential confound of cocaine cues. Adult male rhesus monkeys self-administered cocaine (0.3 mg/kg/injection; N = 8) during daily sessions or served as food-reinforcement controls (N = 4). Two times per week, monkeys were placed in a neutral environment and presented with a cartoon video for ~30 min, sometimes pre- and sometimes post-operant session, but no reinforcement was presented during the video. After ~100 sessions and when the cocaine groups had self-administered 900 mg/kg cocaine, the final experimental condition was a terminal 2-[14C]-deoxyglucose procedure, which occurred in the neutral (cartoon video) environment; for half of the monkeys in each group, this occurred after 1 day of abstinence and for the others after 30 days of abstinence. Rates of local cerebral glucose metabolism were measured in 57 brain regions. Global rates of cerebral metabolism were significantly lower in animals 1 day and 30 days post-cocaine self-administration when compared to those of food-reinforced controls. Effects were larger in 30- vs. 1-day cocaine abstinence, especially in prefrontal, parietal and cingulate cortex, as well as dorsal striatum and thalamus. Because these measures were obtained from monkeys while in a neutral environment, the deficits in glucose utilization can be attributed to the consequences of cocaine exposure and not to effects of conditioned stimuli associated with cocaine.

Chronic phenmetrazine treatment promotes D2 dopaminergic and α2-adrenergic receptor desensitization and alters phosphorylation of signaling proteins and local cerebral glucose metabolism in the rat brain.

Phenmetrazine (PHEN) is a putative treatment for cocaine and psychostimulant recidivism; however, neurochemical changes underlying its activity have not been fully elucidated. We sought to characterize brain homeostatic adaptations to chronic PHEN, specifically on functional brain activity (local cerebral glucose utilization), G-Protein Coupled Receptor-stimulated G-protein activation, and phosphorylation of ERK1/2Thr202/Tyr204, GSK3ßTyr216, and DARPP-32Thr34. Male Sprague-Dawley rats were implanted with sub-cutaneous minipumps delivering either saline (vehicle), acute (2-day) or chronic (14-day) low dose (25 mg/kg/day) or high dose (50 mg/kg/day) PHEN. Acute administration of high dose PHEN increased local cerebral glucose utilization measured by 2-[14C]-deoxyglucose uptake in basal ganglia and motor-related regions of the rat brain. However, chronically treated animals developed tolerance to these effects. To identify the neurochemical changes associated with PHEN's activity, we performed [35S]GTPγS binding assays on unfixed and immunohistochemistry on fixed coronal brain sections. Chronic PHEN treatment dose-dependently attenuated D2 dopamine and α2-adrenergic, but not 5-HT1A, receptor-mediated G-protein activation. Two distinct patterns of effects on pERK1/2 and pDARPP-32 were observed: 1) chronic low dose PHEN decreased pERK1/2, and also significantly increased pDARPP-32 levels in some regions; 2) acute and chronic PHEN increased pERK1/2, but chronic high dose PHEN treatment tended to decrease pDARPP-32. Chronic low dose, but not high dose, PHEN significantly reduced pGSK3ß levels in several regions. Our study provides definitive evidence that extended length PHEN dosage schedules elicit distinct modes of neuronal acclimatization in cellular signaling. These pharmacodynamic modifications should be considered in drug development for chronic use.

Neural Correlates of Exposure to Cocaine Cues in Rhesus Monkeys: Modulation by the Dopamine Transporter.

BACKGROUND: A major goal of treatments for cocaine addiction is to reduce relapse-associated cravings, which are typically induced by environmental stimuli associated with cocaine use and related to changes in dopamine neurotransmission. METHODS: The present study used an animal model of cocaine seeking to determine functional consequences of cue exposure using fluorodeoxyglucose positron emission tomography and to relate findings to juvenile levels of dopamine transporter and D2-like receptor availabilities determined before any drug exposure. Adult male rhesus monkeys (N = 11) self-administered cocaine (0.2 mg/kg per injection) under a second-order schedule of reinforcement, in which responding was maintained by conditioned reinforcers. Positron emission tomography scans assessing glucose utilization, a marker of functional activation, were conducted during cocaine-cue responding and food-reinforced responding in a context where cocaine was never available. RESULTS: Compared with the noncocaine condition, we found significant functional activation in the medial prefrontal cortex, anterior cingulate, precuneus region of the parietal cortex, and striatum-findings similar to those reported in humans who abuse cocaine. Furthermore, these functional activations in the prefrontal, cingulate, and parietal cortex measured during cocaine-cue responding were significantly correlated with juvenile measures of dopamine transporter availability, whereas no significant relationship with prior D2-like receptor availability was observed in any brain region. CONCLUSIONS: The similarity between the present findings and findings in humans who use cocaine supports the use of this model for examination of factors that affect the development and intensity of cue-induced drug seeking and provides evidence for potential biomarkers for the evaluation of potential treatments (behavioral and pharmacologic) for cocaine abuse.

Loss of laterality in chronic cocaine users: an fMRI investigation of sensorimotor control.

Movement disturbances are often overlooked consequences of chronic cocaine abuse. The purpose of this study was to systematically investigate sensorimotor performance in chronic cocaine users and characterize changes in brain activity among movement-related regions of interest (ROIs) in these users. Functional magnetic resonance imaging data were collected from 14 chronic cocaine users and 15 age- and gender-matched controls. All participants performed a sequential finger-tapping task with their dominant, right hand interleaved with blocks of rest. For each participant, percent signal change from rest was calculated for seven movement-related ROIs in both the left and right hemisphere. Cocaine users had significantly longer reaction times and higher error rates than controls. Whereas the controls used a left-sided network of motor-related brain areas to perform the task, cocaine users activated a less lateralized pattern of brain activity. Users had significantly more activity in the ipsilateral (right) motor and premotor cortical areas, anterior cingulate cortex and the putamen than controls. These data demonstrate that, in addition to the cognitive and affective consequences of chronic cocaine abuse, there are also pronounced alterations in sensorimotor control in these individuals, which are associated with functional alterations throughout movement-related neural networks.

Metabolic mapping of the effects of cocaine during the initial phases of self-administration in the nonhuman primate.

Because most human studies of the neurobiological substrates of the effects of cocaine have been performed with drug-dependent subjects, little information is available about the effects of cocaine in the initial phases of drug use before neuroadaptations to chronic exposure have developed. The purpose of the present study, therefore, was to define the substrates that mediate the initial effects of cocaine in a nonhuman primate model of cocaine self-administration using the 2-[14C]deoxyglucose method. Rhesus monkeys were trained to self-administer 0.03 mg/kg per injection (N = 4) or 0.3 mg/kg per injection (N = 4) cocaine and compared with monkeys trained to respond under an identical schedule of food reinforcement (N = 4). Monkeys received 30 reinforcers per session, and metabolic mapping was conducted at the end of the fifth self-administration session. Cocaine self-administration reduced glucose utilization in the mesolimbic system, including the ventral tegmental area, ventral striatum, and medial prefrontal cortex. In addition, metabolic activity was increased in the dorsolateral and dorsomedial prefrontal cortex, as well as in the mediodorsal nucleus of the thalamus. These latter effects are distinctly different from those seen after the noncontingent administration of cocaine, suggesting that self-administration engages circuits beyond those engaged merely by the pharmacological actions of cocaine. The involvement of cortical areas subserving working memory suggests that strong associations between cocaine and the internal and external environment are formed from the very outset of cocaine self-administration. The assessment of the effects of cocaine at a time not readily evaluated in humans provides a baseline from which the effects of chronic cocaine exposure can be investigated.

Dose-dependent effects of Delta9-tetrahydrocannabinol on rates of local cerebral glucose utilization in rat.

Recent reports have demonstrated that Delta(9)-tetrahydrocannabinol (Delta(9)-THC) stimulates locomotor activity at low doses (<2.5 mg/kg), while higher doses (>2.5 mg/kg) produce decreases in spontaneous activity. Using quantitative 2-[(14)C]deoxyglucose (2-DG) autoradiography, we systematically studied the effects of acute Delta(9)-THC on rates of local cerebral glucose utilization. The first series of experiments was designed to determine if Delta(9)-THC-mediated changes in cerebral metabolism followed a clear dose-response relationship. Adult male Sprague-Dawley rats were treated with either vehicle or Delta(9)-THC (0.25-2.5 mg/kg) and the 2-DG procedure was initiated 15 min following exposure. Administration of 2.5 mg/kg Delta(9)-THC produced significant decreases in cerebral metabolism in most brain regions studied. In contrast, administration of 0.25 mg/kg Delta(9)-THC produced no significant alterations in any brain region studied, while 1.0 mg/kg of Delta(9)-THC produced a restricted pattern of metabolic decreases. Significant decreases in metabolism following 1.0 mg/kg were concentrated in structures subserving limbic and sensory functions. In a second series of experiments, the effects of pretreatment with the cannabinoid receptor antagonist SR141716A (1.0 mg/kg) on Delta(9)-THC-induced changes in functional activity were measured. Pretreatment with SR141716A attenuated the majority of functional changes produced by Delta(9)-THC, suggesting that these effects are primarily mediated by central cannabinoid receptors. Moreover, these findings indicate that the effects of Delta(9)-THC on cerebral metabolism are dose-dependent and that there are regional differences in the metabolic response to acute cannabinoid exposure.