Presence of pro-opiomelanocortin mRNA in the rat medial prefrontal cortex, nucleus accumbens and ventral tegmental area: studies by RT-PCR and in situ hybridization techniques

Differential Effects of Prenatal Buprenorphine and Methadone on Postnatal Growth and Gene Expression in the Nucleus Accumbens

Methadone and buprenorphine are commonly prescribed during pregnancy to maintain recovery and prevent symptoms of withdrawal in women with opioid use disorder. Infants prenatally exposed to medications for opioid use disorder (MOUD), however, commonly show signs of neonatal opioid withdrawal syndrome (NOWS), which can include feeding-related issues like hyperphagia. To investigate the effects of prenatal MOUD exposure on feeding behavior, female Sprague-Dawley rats were implanted with osmotic minipumps filled with methadone, buprenorphine, or saline and subsequently mated. On postnatal day (PND) 1, buprenorphine- and methadone-exposed offspring weighed less than saline-exposed subjects. Throughout early postnatal development (PND2, 7, and 12), this reduction in weight persisted in buprenorphine, but not methadone, offspring. RNAscope in situ hybridization was then used to measure expression of genes in the nucleus accumbens (NAc) previously associated with hyperphagia in NOWS infants, including proopiomelanocortin (Pomc), neuropeptide Y2 receptors (Npy2r), and dopamine type 2 receptors (Drd2). Distinct developmental expression patterns were noted across the postnatal period, with few effects of MOUD; however, significantly lower Pomc expression was observed in methadone-exposed but not buprenorphine-exposed offspring. These findings demonstrate differential effects of methadone and buprenorphine on offspring development and gene expression, highlighting differences in offspring outcomes associated with these two MOUDs.

Differential DNA methylation in iPSC-derived dopaminergic neurons: a step forward on the role of SNORD116 microdeletion in the pathophysiology of addictive behavior in Prader-Willi syndrome

INTRODUCTION

A microdeletion including the SNORD116 gene (SNORD116 MD) has been shown to drive the Prader-Willi syndrome (PWS) features. PWS is a neurodevelopmental disorder clinically characterized by endocrine impairment, intellectual disability and psychiatric symptoms such as a lack of emotional regulation, impulsivity, and intense temper tantrums with outbursts. In addition, this syndrome is associated with a nutritional trajectory characterized by addiction-like behavior around food in adulthood. PWS is related to the genetic loss of expression of a minimal region that plays a potential role in epigenetic regulation. Nevertheless, the role of the SNORD116 MD in DNA methylation, as well as the impact of the oxytocin (OXT) on it, have never been investigated in human neurons.

METHODS

We studied the methylation marks in induced pluripotent stem-derived dopaminergic neurons carrying a SNORD116 MD in comparison with those from an age-matched adult healthy control. We also performed identical neuron differentiation in the presence of OXT. We performed a genome-wide DNA methylation analysis from the iPSC-derived dopaminergic neurons by reduced-representation bisulfite sequencing. In addition, we performed RNA sequencing analysis in these iPSC-derived dopaminergic neurons differentiated with or without OXT.

RESULTS

The analysis revealed that 153,826 cytosines were differentially methylated between SNORD116 MD neurons and control neurons. Among the differentially methylated genes, we determined a list of genes also differentially expressed. Enrichment analysis of this list encompassed the dopaminergic system with COMT and SLC6A3. COMT displayed hypermethylation and under-expression in SNORD116 MD, and SLC6A3 displayed hypomethylation and over-expression in SNORD116 MD. RT-qPCR confirmed significant over-expression of SLC6A3 in SNORD116 MD neurons. Moreover, the expression of this gene was significantly decreased in the case of OXT adjunction during the differentiation.

CONCLUSION

SNORD116 MD dopaminergic neurons displayed differential methylation and expression in the COMT and SLC6A3 genes, which are related to dopaminergic clearance.

Turning the 'Tides on Neuropsychiatric Diseases: The Role of Peptides in the Prefrontal Cortex

Recent advancements in technology have enabled researchers to probe the brain with the greater region, cell, and receptor specificity. These developments have allowed for a more thorough understanding of how regulation of the neurophysiology within a region is essential for maintaining healthy brain function. Stress has been shown to alter the prefrontal cortex (PFC) functioning, and evidence links functional impairments in PFC brain activity with neuropsychiatric disorders. Moreover, a growing body of literature highlights the importance of neuropeptides in the PFC to modulate neural signaling and to influence behavior. The converging evidence outlined in this review indicates that neuropeptides in the PFC are specifically impacted by stress, and are found to be dysregulated in numerous stress-related neuropsychiatric disorders including substance use disorder, major depressive disorder (MDD), posttraumatic stress disorder, and schizophrenia. This review explores how neuropeptides in the PFC function to regulate the neural activity, and how genetic and environmental factors, such as stress, lead to dysregulation in neuropeptide systems, which may ultimately contribute to the pathology of neuropsychiatric diseases.

The patterns of exercise-induced β-endorphin expression in the central nervous system of rats

Exercise at different intensities is able to induce different physical and psychological statuses of the subjects. The β-endorphin (β-EP) in central nervous system is thought to play an important role in physical exercise. However, its expression patterns and physiological effects in the central nuclei under different exercise states are not well understood. Five-week old male Sprague-Dawley rats were randomly divided into two groups of 21 each: Control and Exercise. Control rats were sedentary while Exercise rats were arranged to run on a treadmill (5-week adapting or moderate exercise and 2-week high-intensity exercise). Seven rats were taken from each group at day33, day42 and day49 for examination of blood biochemical parameters (lactate, Lac; blood urea nitrogen, BUN; glucose) and for detection of nuclei β-EP level with immunohistochemistry. The results showed that Lac and BUN levels were significant increased after the high intensity exercise. The five-week exercise caused a significantly increased β-EP in caudate putamen (CPu), amygdala, paraventricular thalamic nucleus (PVT), ventromedial hypothalamus nucleus (VMH) and gigantocellular reticular nucleus (Gi). The high intensity exercise induced an elevated β-EP in CPu and nucleus of the solitary tract (Sol), but a decreased β-EP in globus pallidus (GP). Compared with Control, exercise rats showed an elevated β-EP in CPu, PVT, VMH, accumbens nucleus, Gi and Sol, and a decreased β-EP in GP at day49. The β-EP levels in acurate nucleus, periadueductal gray and parabrachial nucleus were not changed at day33, 42 and 49. In conclusion, β-EP levels in different nuclei changed under the moderate and high intensity exercises, which may contribute to modifying exercise-produced psychological and physiological effects.

Selective alterations in endogenous opioid system genes expression in rats selected for high ethanol intake during adolescence

Historically, the roots of alcoholism have been linked to either environment or heredity. However, the interaction between these factors is still largely unexplored. The evidence supports a link between alcohol consumption and the endogenous opioid system. We here studied the opioid genes expression in male and female Wistar rats derived from a short-term breeding program which selected -- at adolescence -- for high (ADHI line) or low (ADLO line) ethanol drinking. Specifically, in this work we analyzed central opioid gene expression in the rats of the second filial generation (S₂-ADLO and S₂-ADHI). Selective downregulation of pronociceptin (Pnoc) and its receptor (Oprl1) mRNA levels were observed in the prefrontal cortex of male S₂-ADHI rats when compared to S₂-ADLO, and for Oprl1 also in the nucleus accumbens. An increase in gene expression was instead observed for pro-opiomelanocortin (Pomc) in the nucleus accumbens of S₂-ADHI males when compared to S₂-ADLO, as well as for mu opioid receptor (Oprm1) but in females. The differences in mRNA levels may be due to the different alcohol consumption between the two groups of rats or may represent pre-existing differences between them. Moreover, we show a sex-specific modulation of the expression of these genes, thus pointing out the importance of sex on ethanol responses. The results might lead to more specific and effective pharmacological treatments for alcoholism.

Involvement of Activated Brain Stress Responsive Systems in Excessive and "Relapse" Alcohol Drinking in Rodent Models: Implications for Therapeutics

Addictive diseases, including addiction to alcohol, pose massive public health costs. Addiction is a chronic relapsing disease caused by both the direct effects induced by drugs and persistent neuroadaptations at the molecular, cellular, and behavioral levels. These drug-type specific neuroadaptations are brought on largely by the reinforcing effects of drugs on the central nervous system and environmental stressors. Results from animal experiments have demonstrated important interactions between alcohol and stress-responsive systems. Addiction to specific drugs such as alcohol, psychostimulants, and opioids shares some common direct or downstream effects on the brain's stress-responsive systems, including arginine vasopressin and its V1b receptors, dynorphin and the κ-opioid receptors, pro-opiomelanocortin/β-endorphin and the μ-opioid receptors, and the endocannabinoids. Further study of these systems through laboratory-based and translational research could lead to the discovery of novel treatment targets and the early optimization of interventions (for example, combination) for the pharmacologic therapy of alcoholism.

Prefrontal Cortical Opioids and Dysregulated Motivation: A Network Hypothesis

Loss of inhibitory control over appetitively motivated behavior occurs in multiple psychiatric disorders, including drug abuse, behavioral addictions, and eating disorders with binge features. In this opinion article, novel actions of μ-opioid peptides in the prefrontal cortex (PFC) that could contribute to inhibitory control deficits will be discussed. Evidence has accrued to suggest that excessive intra-PFC μ-opioid receptor (μ-OR) signaling alters the PFC response to excitatory drive, resulting in supernormal and incoherent recruitment of multiple PFC output pathways. Affected pathways include functionally opposed PFC→hypothalamus 'appetitive driver' and PFC→striatum 'appetitive limiter' projections. This network perturbation engenders disorganized, impulsive appetitive responses. Evidence supporting this hypothesis from human imaging and animal studies will be discussed, and combinatorial drug treatments targeting μ-ORs and specific PFC subcortical targets will be explored.

Mechanisms and significance of brain glucose signaling in energy balance, glucose homeostasis, and food-induced reward

The concept that hypothalamic glucose signaling plays an important role in regulating energy balance, e.g., as instantiated in the so-called "glucostat" hypothesis, is one of the oldest in the field of metabolism. However the mechanisms by which neurons in the hypothalamus sense glucose, and the function of glucose signaling in the brain, has been difficult to establish. Nevertheless recent studies probing mechanisms of glucose signaling have also strongly supported a role for glucose signaling in regulating energy balance, glucose homeostasis, and food-induced reward.

A comparison of a behavioral weight loss program to a stress management program: A pilot randomized controlled trial

OBJECTIVES

This study compared a behavioral weight loss program (BWL) with a stress management-based program, Emotional Brain Training (EBT), on weight loss, blood pressure, depression, perceived stress, diet, and physical activity.

METHODS

Subjects with a body mass index (BMI) of >28 and <45 kg/m(2) were recruited in Lexington, Kentucky in January 2014 and randomized to BWL or EBT for a 20-week intervention. Of those recruited, 49 participants were randomized to EBT or BWL. Randomization and allocation to group were performed using SPSS software. Weight, blood pressure, depression, perceived stress, dietary intake, and physical activity were measured at baseline, 10 week, and 20 week. Linear models for change over time were fit to calculate 95% confidence intervals of intervention effects.

RESULTS

BWL produced greater changes in BMI than EBT at both 10 (P = 0.02) and 20 wk (P = 0.03). At 10 wk, both EBT and BWL improved BMI, systolic blood pressure, depression and perceived stress (P < 0.05). BWL also improved diastolic blood pressure (P = 0.005). At 20 wk, EBT maintained improvements in BMI, systolic blood pressure, depression, and perceived stress while BWL maintained improvements only in BMI and depression (P < 0.05).

CONCLUSIONS

BWL produced greater weight loss than EBT; however, EBT produced sustained improvements in stress, depression, and systolic blood pressure. A combination of the two approaches should be explored.

Opioid system in the medial prefrontal cortex mediates binge-like eating

Binge eating disorder is an addiction-like disorder characterized by excessive food consumption within discrete periods of time. This study was aimed at understanding the role of the opioid system within the medial prefrontal cortex (mPFC) in the consummatory and motivational aspects of binge-like eating. For this purpose, we trained male rats to obtain either a sugary, highly palatable diet (Palatable rats) or a chow diet (Chow rats) for 1 hour/day. We then evaluated the effects of the opioid receptor antagonist, naltrexone, given either systemically or site-specifically into the nucleus accumbens (NAcc) or the mPFC on a fixed ratio 1 (FR1) and a progressive ratio schedule of reinforcement for food. Finally, we assessed the expression of the genes proopiomelanocortin (POMC), pro-dynorphin (PDyn) and pro-enkephalin (PEnk), coding for the opioids peptides in the NAcc and the mPFC in both groups. Palatable rats rapidly escalated their intake by four times. Naltrexone, when administered systemically and into the NAcc, reduced FR1 responding for food and motivation to eat under a progressive ratio in both Chow and Palatable rats; conversely, when administered into the mPFC, the effects were highly selective for binge eating rats. Furthermore, we found a twofold increase in POMC and a ∼50% reduction in PDyn gene expression in the mPFC of Palatable rats, when compared to control rats; however, no changes were observed in the NAcc. Our data suggest that neuroadaptations of the opioid system in the mPFC occur following intermittent access to highly palatable food, which may be responsible for the development of binge-like eating.

Alcohol: a stimulant activating brain stress responsive systems with persistent neuroadaptation

Addictive diseases, including addiction to alcohol, opiates or cocaine, pose massive public health costs. Addictions are chronic relapsing brain diseases, caused by drug-induced direct effects and persistent neuroadaptations at the molecular, cellular and behavioral levels. These drug-type specific neuroadapations are mainly contributed by three factors: environment, including stress, the direct reinforcing effects of the drug on the CNS, and genetics. Results from animal models and basic clinical research (including human genetic study) have shown important interactions between the stress responsive systems and alcohol abuse. In this review we will discuss the involvement of the dysregulation of the stress responsive hypothalamic-pituitary-adrenal (HPA) axis in alcohol addiction (Section I). Addictions to specific drugs such as alcohol, psychostimulants and opiates (e.g., heroin) have some common direct or downstream effects on several brain stress-responsive systems, including vasopressin and its receptor system (Section II), POMC and mu opioid receptor system (Section III) and dynorphin and kappa opioid receptor systems (Section IV). Further understanding of these systems, through laboratory-based and translational studies, have the potential to optimize early interventions and to discover new treatment targets for the therapy of alcoholism. This article is part of the Special Issue entitled 'CNS Stimulants'.

Effects of morphine on the differentiation and survival of developing pyramidal neurons during the brain growth spurt

Although morphine is frequently administered to treat procedural pain in neonates and young children, little is known about the effects of this drug on developing neural circuitry during the brain growth spurt. Here we systematically explored the impact of morphine on neuronal survival and differentiation during the peak synaptogenic period. By focusing on the rat medial prefrontal cortex, we show that single bolus ip injections of morphine, although it induces deep sedation and analgesia, do not entrain apoptosis in this cortical region either at postnatal day 7 or at postnatal day 15. Iontophoretic single cell injections of Lucifer Yellow followed by semiautomatic neuronal arbor tracing revealed that repeated daily administration of this drug between postnatal days 7 and 15 or 15 and 20 did not interfere with dendritic development of layer 5 pyramidal neurons. Confocal microscopic analysis of dendritic spines at the aforementioned distinct stages of the brain growth spurt demonstrated that neither single bolus nor repeated administration of morphine affected the density of these postsynaptic structures. Altogether, these preclinical rodent experimental observations argue against overt neurotoxic effects of morphine exposure during the brain growth spurt.

Voluntary alcohol drinking enhances proopiomelanocortin gene expression in nucleus accumbens shell and hypothalamus of Sardinian alcohol-preferring rats

BACKGROUND

Evidence obtained in humans and rodents indicates that beta-endorphin (encoded by the proopiomelanocortin [POMC] gene) is critical in the regulation of alcohol drinking behavior. However, the alcohol effect on POMC gene expression has not been studied in rodent mesolimbic regions, such as the nucleus accumbens (NAc).

METHODS

In this study, we first utilized POMC-enhanced green fluorescent protein (EGFP) transgenic mice to visualize POMC neurons and found that POMC-EGFP cells were modestly distributed throughout the NAc shell and core, in addition to the hypothalamic arcuate nucleus. POMC mRNA expression in the NAc of mice and rats was confirmed using reverse transcriptase-polymerase chain reaction and solution hybridization assays. We then investigated whether there are genetically determined differences in basal mRNA levels of POMC and mu opioid receptor (MOP-r) between selectively bred Sardinian alcohol-preferring (sP) and nonpreferring (sNP) rats, and whether these mRNA levels are altered in sP rats after alcohol drinking (10%, unlimited access) for 17 days.

RESULTS

Alcohol-naïve sP rats had higher basal POMC mRNA levels than sNP rats only in hypothalamus. Alcohol drinking increased POMC mRNA levels in both the NAc shell (by 100%) and the hypothalamus (by 50%) of sP rats. Although sP rats had lower basal levels of MOP-r mRNA and GTPγS binding in NAc shell than sNP rats, voluntary alcohol consumption had no effect on MOP-r mRNA levels in the NAc shell.

CONCLUSIONS

Our results define the distribution of POMC-expressing neurons in the NAc of mice and rats. Higher POMC expression at basal levels in sP rats (genetically determined), along with increases after drinking (alcohol-induced) in the NAc shell and hypothalamus, suggests that the POMC systems play a role in high alcohol preference and consumption.

Nicotine-induced changes of brain β-endorphin

A consensus has emerged that endogenous opioid peptides and their receptors play an important role in the psychoactive properties of nicotine. Although behavioral studies have shown that β-endorphin contributes to the rewarding and emotional effects of nicotine, whether the drug alters the function of brain endorphinergic neurons is not fully explored. These studies investigated the effect of acute, 1mg/kg, sc, and chronic, daily injection of 1mg/kg, sc, for 14 days, administration of free base nicotine on brain β-endorphin and its precursor proopiomelanocortin (POMC). Acute and chronic treatment with nicotine decreased β-endorphin content in hypothalamus, the principal site of β-endorphin producing neurons in the brain, and in the endorphinergic terminal fields in striatum and hippocampus. The acute effect of nicotine on β-endorphin was reversed by the nicotinic antagonist mecamylamine and the dopamine antagonist haloperidol, indicating pharmacological specificity and involvement of dopamine D2-like receptors. Similar observations were made in prefrontal cortex. POMC mRNA in hypothalamus and prefrontal cortex was unchanged following acute nicotine, but it decreased moderately with chronic treatment. The nicotine treatments had no effect on pituitary and plasma β-endorphin. Taken together, these results could be interpreted to indicate that nicotine alters the synthesis and release of β-endorphin in the limbic brain in vivo. Altered endorphinergic function may contribute to the behavioral effects of acute and chronic nicotine treatment and play a role in nicotine addiction.

Induction of hyperphagia and carbohydrate intake by μ-opioid receptor stimulation in circumscribed regions of frontal cortex

Frontal cortical regions are activated by food-associated stimuli, and this activation appears to be dysregulated in individuals with eating disorders. Nevertheless, frontal control of basic unconditioned feeding responses remains poorly understood. Here we show that hyperphagia can be driven by μ-opioid receptor stimulation in restricted regions of ventral medial prefrontal cortex (vmPFC) and orbitofrontal cortex. In both ad libitum-fed and food-restricted male Sprague Dawley rats, bilateral infusions of the μ-opioid agonist [d-Ala2, N-Me-Phe4, Gly5-ol]-enkephalin (DAMGO) markedly increased intake of standard rat chow. When given a choice between palatable fat-enriched versus carbohydrate-enriched test diets, intra-vmPFC DAMGO infusions selectively increased carbohydrate intake, even in rats with a baseline fat preference. Rats also exhibited motor hyperactivity characterized by rapid switching between brief bouts of investigatory and ingestive behaviors. Intra-vmPFC DAMGO affected neither water intake nor nonspecific oral behavior. Similar DAMGO infusions into neighboring areas of lateral orbital or anterior motor cortex had minimal effects on feeding. Neither stimulation of vmPFC-localized δ-opioid, κ-opioid, dopaminergic, serotonergic, or noradrenergic receptors, nor antagonism of D1, 5HT1A, or α- or β-adrenoceptors, reproduced the profile of DAMGO effects. Muscimol-mediated inactivation of the vmPFC, and intra-vmPFC stimulation of κ-opioid receptors or blockade of 5-HT2A (5-hydroxytryptamine receptor 2A) receptors, suppressed motor activity and increased feeding bout duration-a profile opposite to that seen with DAMGO. Hence, μ-opioid-induced hyperphagia and carbohydrate intake can be elicited with remarkable pharmacological and behavioral specificity from discrete subterritories of the frontal cortex. These findings may have implications for understanding affect-driven feeding and loss of restraint in eating disorders.

Ethanol exposure selectively alters beta-endorphin content but not [3H]-DAMGO binding in discrete regions of the rat brain

The dopaminergic mesocorticolimbic system plays an important role in the reinforcing effects of ethanol. Opioid peptides modulate the activity of this system and have been suggested to mediate, at least in part, the reinforcing properties of ethanol. Thus, beta-endorphin (beta-END) could participate in the development of ethanol reinforcement and addiction. The aim of this work was to investigate the acute and chronic ethanol effects on beta-END content in regions of the mesolimbic system and to examine if chronic ethanol treatment alters ligand binding to mu opioid receptor (muOR). Male Wistar rats received a single acute ethanol dose of 2.5 g/kg or water by intra-gastric administration. For chronic ethanol treatment experiments, one group of rats was given ethanol (10% v/v solution) to drink, two groups were given equivalent volumes of sucrose (14.14% isocaloric solution) or water, respectively, and a fourth group had ad libitum access to food and water. Treatment was followed for 4 weeks. Beta-endorphin content in brain regions was quantified by radioimmunoassay and ligand binding studies to muOR were performed by quantitative autoradiography using 8 nM [(3)H]-DAMGO as radioligand. Acute ethanol decreased beta-END content in the hypothalamus (26%) 1h after administration. No ethanol effects were observed in the midbrain, ventral tegmental area, substantia nigra, nucleus accumbens, nucleus accumbens-septum and prefrontal cortex. Chronic ethanol treatment neither changed beta-END levels nor [(3)H]-DAMGO binding to mu opioid receptors in any of the regions studied. However, beta-END levels in the sucrose group were significantly increased in the nucleus accumbens and substantia nigra, in comparison to all other groups. These findings suggest that different neural mechanisms and specific brain regions may be involved in the reinforcing effects of ethanol and sucrose.

Reward processing by the opioid system in the brain

The opioid system consists of three receptors, mu, delta, and kappa, which are activated by endogenous opioid peptides processed from three protein precursors, proopiomelanocortin, proenkephalin, and prodynorphin. Opioid receptors are recruited in response to natural rewarding stimuli and drugs of abuse, and both endogenous opioids and their receptors are modified as addiction develops. Mechanisms whereby aberrant activation and modifications of the opioid system contribute to drug craving and relapse remain to be clarified. This review summarizes our present knowledge on brain sites where the endogenous opioid system controls hedonic responses and is modified in response to drugs of abuse in the rodent brain. We review 1) the latest data on the anatomy of the opioid system, 2) the consequences of local intracerebral pharmacological manipulation of the opioid system on reinforced behaviors, 3) the consequences of gene knockout on reinforced behaviors and drug dependence, and 4) the consequences of chronic exposure to drugs of abuse on expression levels of opioid system genes. Future studies will establish key molecular actors of the system and neural sites where opioid peptides and receptors contribute to the onset of addictive disorders. Combined with data from human and nonhuman primate (not reviewed here), research in this extremely active field has implications both for our understanding of the biology of addiction and for therapeutic interventions to treat the disorder.

Endogenous opiates and behavior: 2007

This paper is the thirtieth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2007 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia; stress and social status; tolerance and dependence; learning and memory; eating and drinking; alcohol and drugs of abuse; sexual activity and hormones, pregnancy, development and endocrinology; mental illness and mood; seizures and neurologic disorders; electrical-related activity and neurophysiology; general activity and locomotion; gastrointestinal, renal and hepatic functions; cardiovascular responses; respiration and thermoregulation; and immunological responses.

Characterizing intercellular signaling peptides in drug addiction

Intercellular signaling peptides (SPs) coordinate the activity of cells and influence organism behavior. SPs, a chemically and structurally diverse group of compounds responsible for transferring information between neurons, are broadly involved in neural plasticity, learning and memory, as well as in drug addiction phenomena. Historically, SP discovery and characterization has tracked advances in measurement capabilities. Today, a suite of analytical technologies is available to investigate individual SPs, as well as entire intercellular signaling complements, in samples ranging from individual cells to entire organisms. Immunochemistry and in situ hybridization are commonly used for following preselected SPs. Discovery-type investigations targeting the transcriptome and proteome are accomplished using high-throughput characterization technologies such as microarrays and mass spectrometry. By integrating directed approaches with discovery approaches, multiplatform studies fill critical gaps in our knowledge of drug-induced alterations in intercellular signaling. Throughout the past 35 years, the National Institute on Drug Abuse has made significant resources available to scientists that study the mechanisms of drug addiction. The roles of SPs in the addiction process are highlighted, as are the analytical approaches used to detect and characterize them.