Cocaine-induced neuron subtype mitochondrial dynamics through Egr3 transcriptional regulation.

Mitochondrial function is required for brain energy homeostasis and neuroadaptation. Recent studies demonstrate that cocaine affects mitochondrial dynamics and morphological characteristics within the nucleus accumbens (NAc). Further, mitochondria are differentially regulated by cocaine in dopamine receptor-1 containing medium spiny neurons (D1-MSNs) vs dopamine receptor-2 (D2)-MSNs. However, there is little understanding into cocaine-induced transcriptional mechanisms and their role in regulating mitochondrial processes. Here, we demonstrate that cocaine enhances binding of the transcription factor, early growth response factor 3 (Egr3), to nuclear genes involved in mitochondrial function and dynamics. Moreover, cocaine exposure regulates mRNA of these mitochondria-associated nuclear genes in both contingent or noncontingent cocaine administration and in both rodent models and human postmortem tissue. Interestingly, several mitochondrial nuclear genes showed distinct profiles of expression in D1-MSNs vs D2-MSNs, with cocaine exposure generally increasing mitochondrial-associated nuclear gene expression in D1-MSNs vs suppression in D2-MSNs. Further, blunting Egr3 expression in D1-MSNs blocks cocaine-enhancement of the mitochondrial-associated transcriptional coactivator, peroxisome proliferator-activated receptor gamma coactivator (PGC1α), and the mitochondrial fission molecule, dynamin related protein 1 (Drp1). Finally, reduction of D1-MSN Egr3 expression attenuates cocaine-induced enhancement of small-sized mitochondria, causally demonstrating that Egr3 regulates mitochondrial morphological adaptations. Collectively, these studies demonstrate cocaine exposure impacts mitochondrial dynamics and morphology by Egr3 transcriptional regulation of mitochondria-related nuclear gene transcripts; indicating roles for these molecular mechanisms in neuronal function and plasticity occurring with cocaine exposure.

Dissecting Mechanisms of Motivation within the Nucleus Accumbens Using Optogenetics.

Studies mapping psychological functions to discrete brain regions often require manipulations that yield changes in a particular area and observing a subsequent shift in behavior. As investigators tap into neural underpinnings of behavior, it is useful to utilize technologies that permit temporally and spatially discrete shifts in neural signaling and neurobiological processes. This chapter contains protocols for creating "Fos plumes," a means of mapping alterations in neural activity induced by neural manipulations. By localizing increases or decreases in c-Fos in targeted brain regions, the relative spread of each manipulation can be mapped, and the functional roles of individual mechanisms within particular brain areas can be defined. The chapter also provides examples of behavioral testing protocols using optogenetics to localize psychological functions in the nucleus accumbens (NAc), a brain region involved in the production of motivated behaviors. Together, these methods provide avenues for researchers to localize and causally demonstrate the impact of neural manipulations in the brain.

Desire or Dread from Nucleus Accumbens Inhibitions: Reversed by Same-Site Optogenetic Excitations.

Microinjections of a glutamate AMPA antagonist (DNQX) in medial shell of nucleus accumbens (NAc) can cause either intense appetitive motivation (i.e., 'desire') or intense defensive motivation (i.e., 'dread'), depending on site along a flexible rostrocaudal gradient and on environmental ambience. DNQX, by blocking excitatory AMPA glutamate inputs, is hypothesized to produce relative inhibitions of NAc neurons. However, given potential alternative explanations, it is not known whether neuronal inhibition is in fact necessary for NAc DNQX microinjections to generate motivations. Here we provide a direct test of whether local neuronal inhibition in NAc is necessary for DNQX microinjections to produce either desire or dread. We used optogenetic channelrhodopsin (ChR2) excitations at the same local sites in NAc as DNQX microinjections to oppose relative neuronal inhibitions induced by DNQX in female and male rats. We found that same-site ChR2 excitation effectively reversed the ability of NAc DNQX microinjections to generate appetitive motivation, and similarly reversed ability of DNQX microinjections to generate defensive motivation. Same-site NAc optogenetic excitations also attenuated recruitment of Fos expression in other limbic structures throughout the brain, which was otherwise elevated by NAc DNQX microinjections that generated motivation. However, to successfully reverse motivation generation, an optic fiber tip for ChR2 illumination needed to be located within <1 mm of the corresponding DNQX microinjector tip; that is, both truly at the same NAc site. Thus, we confirm that localized NAc neuronal inhibition is required for AMPA-blocking microinjections in medial shell to induce either positively-valenced 'desire' or negatively-valenced 'dread'.SIGNIFICANCE STATEMENT A major hypothesis posits neuronal inhibitions in nucleus accumbens generate intense motivation. Microinjections in nucleus accumbens of glutamate antagonist, DNQX, which might suppress local neuronal firing, generate either appetitive or defensive motivation, depending on site and environmental factors. Is neuronal inhibition in nucleus accumbens required for such pharmacologically-induced motivations? Here we demonstrate that neuronal inhibition is necessary to generate appetitive or defensive motivations, using local optogenetic excitations to oppose putative DNQX-induced inhibitions. We show that excitation at the same site prevents DNQX microinjections from recruiting downstream limbic structures into neurobiological activation, and simultaneously prevents generation of either appetitive or defensive motivated behaviors. These results may be relevant to roles of nucleus accumbens mechanisms in pathological motivations, including addiction and paranoia.

Optogenetic self-stimulation in the nucleus accumbens: D1 reward versus D2 ambivalence.

The nucleus accumbens (NAc) contains multiple subpopulations of medium spiny neurons (MSNs). One subpopulation expresses D1-type dopamine receptors, another expresses D2-type receptors, and a third expresses both. The relative roles in NAc of D1 neurons versus D2 neurons in appetitive motivation were assessed here. Specifically, we asked whether D1-Cre mice would instrumentally seek optogenetic self-stimulation specifically targeted at D1 MSNs in NAc, and similarly if D2-Cre mice would self-stimulate D2 neurons in NAc. Mice were implanted with Cre-targeted channelrhodopsin (ChR2) virus and optic fibers in NAc. Subsequently, mice could earn brief NAc laser illuminations by actively touching a metal spout in one task, or by going to a particular location in a separate task. Results indicated that D1 neuronal excitation in NAc supported intense self-stimulation in both tasks. D1-Cre mice earned hundreds to thousands of spout-touches per half-hour session, and also sought out locations that delivered NAc laser to excite D1 MSNs. By comparison, D2 ChR2 mice showed lower but still positive levels of self-stimulation in the spout-touch task, earning dozens to hundreds of NAc laser illuminations. However, in the location task, D2 mice failed to show positive self-stimulation. If anything, a few D2 individuals gradually avoided the laser location. Brain-wide measures indicated that D1 and D2 stimulations in NAc recruited heavily overlapping patterns of Fos activation in distant limbic structures. These results confirm that excitation of D1 MSNs in NAc supports strong incentive motivation to self-stimulate. They also suggest that excitation of D2 neurons in NAc supports self-stimulation under some conditions, but fails under others and possibly may even shift to negative avoidance.

Lateral hypothalamus, nucleus accumbens, and ventral pallidum roles in eating and hunger: interactions between homeostatic and reward circuitry.

The study of the neural bases of eating behavior, hunger, and reward has consistently implicated the lateral hypothalamus (LH) and its interactions with mesocorticolimbic circuitry, such as mesolimbic dopamine projections to nucleus accumbens (NAc) and ventral pallidum (VP), in controlling motivation to eat. The NAc and VP play special roles in mediating the hedonic impact ("liking") and motivational incentive salience ("wanting") of food rewards, and their interactions with LH help permit regulatory hunger/satiety modulation of food motivation and reward. Here, we review some progress that has been made regarding this circuitry and its functions: the identification of localized anatomical hedonic hotspots within NAc and VP for enhancing hedonic impact; interactions of NAc/VP hedonic hotspots with specific LH signals such as orexin; an anterior-posterior gradient of sites in NAc shell for producing intense appetitive eating vs. intense fearful reactions; and anatomically distributed appetitive functions of dopamine and mu opioid signals in NAc shell and related structures. Such findings help improve our understanding of NAc, VP, and LH interactions in mediating affective and motivation functions, including "liking" and "wanting" for food rewards.

Social influences on morphine conditioned place preference in adolescent mice.

Social/peer influences are among the strongest predictors of adolescent drug use. However, this important subject does not get much attention in pre-clinical studies. We recently observed that exposure to different social partners modulates morphine locomotor sensitization. Sensitivity to the hyper-locomotor response of drugs of abuse is a predictor of sensitivity to other drug-induced behaviors. Thus, this study examined how exposure to different social partners affected the rewarding properties of morphine. All animals were group-housed four per cage in one of two conditions referred to as 'only' and 'cage-mates'. In the mixed treatment condition, morphine- and saline-treated mice were housed together. These groups are referred to as 'morphine cage-mates' and 'saline cage-mates', respectively. In the separated treatment conditions, all mice in the cage received morphine (i.e. 'morphine only') or saline (i.e. 'saline only'), and cages were visually separated from each other. All animals were subsequently individually tested for the acquisition of morphine conditioned place preference (CPP) following one conditioning session with 10, 20 or 40 mg/kg morphine or saline. As expected, one conditioning session established morphine CPP in the morphine only animals, but not in the saline only animals. Notably, morphine CPP was not acquired by the morphine cage-mate animals. Additionally, 40 mg/kg morphine was sufficient to establish morphine CPP in the saline cage-mate animals. These results indicate that social environment has an effect on the rewarding properties of morphine. It suggests that exposure to different peers can alter the abuse potential of opioids and potentially other illicit drugs.

Parent or caregiver, staff, and dentist perspectives on access to dental care issues for head start children in Ohio.

OBJECTIVES: We conducted 5 surveys on consumer and provider perspectives on access to dental care for Ohio Head Start children to assess the need and appropriate strategies for action. METHODS: We collected information from Head Start children (open-mouth screenings), their parents or caregivers (questionnaire and telephone interviews), Head Start staff (interviews), and dentists (questionnaire). Geocoded addresses were also analyzed. RESULTS: Twenty-eight percent of Head Start children had at least 1 decayed tooth. For the 11% of parents whose children could not get desired dental care, cost of care or lack of insurance (34%) and dental office factors (20%) were primary factors. Only 7% of general dentists and 29% of pediatric dentists reported accepting children aged 0 through 5 years of age as Medicaid recipients without limitation. Head Start staff and dentists felt that poor appointment attendance negatively affected children's receiving care, but parents/caregivers said finding accessible dentists was the major problem. CONCLUSIONS: Many Ohio Head Start children do not receive dental care. Medicaid and patient age were primary dental office limitations that are partly offset by the role Head Start plays in ensuring dental care. Dentists, Head Start staff, and parents/caregivers have different perspectives on the problem of access to dental care.