D1-family Receptors Research Articles

Amphetamine improves rat 5-choice continuous performance test (5C-CPT) irrespective of concurrent low-dose haloperidol treatment.

Cognitive dysfunction mediates functional impairment in patients with schizophrenia, necessitating the timely development of pro-cognitive therapeutics. An important initial step in this process is to establish what, if any, pro-cognitive agents and associated mechanisms can be identified using cross-species translational paradigms. For example, attentional deficits-a core feature of schizophrenia-can be measured across species using the 5-choice continuous performance test (5C-CPT). The psychostimulant, amphetamine, improves human and rodent 5C-CPT performance. Here, we tested whether amphetamine would similarly improve 5C-CPT performance in the presence of dopamine D2 receptor blockade, since pro-cognitive treatments in schizophrenia would virtually always be used in conjunction with D2 receptor antagonists. We established the dose-response effects of amphetamine (0, 0.1, 0.3, or 1.0 mg/kg) and haloperidol (0, 3.2, 10, or 32 μg/kg) on 5C-CPT performance in Long Evans rats, and then tested an amphetamine (0.3 mg/kg) × haloperidol (10 μg/kg) interaction; the low dose was chosen because higher doses exerted deleterious non-specific effects on performance. Amphetamine improved 5C-CPT performance in poorly performing rats by increasing target detection, independent of haloperidol pretreatment. The pro-attentional effects of amphetamine were most likely mediated by dopamine release at D1-family receptors, since they persisted in the presence of acute D2 blockade. Alternative explanations for these findings are also discussed, as are their potential implications for future pro-cognitive therapeutics in schizophrenia.

Catecholaminergic hippocampal activation is necessary for object recognition memory persistence induced by one-single physical exercise session

Previously we demonstrated that a single physical exercise session promotes the persistence of object recognition (OR) memory and this effect involves the activation of the noradrenergic system. Here, using adult male Wistar rats (3 months old) we confirm that an aerobic single physical exercise session (30 min of treadmill running at an intensity of 60–70 % of indirect VO2 max.) after OR learning promotes memory persistence. We also demonstrate that this effect involves the dopaminergic system, since it is blocked when a D1-family receptor antagonist (SCH-23390, 1μg/μl) is infused into the hippocampus after the physical exercise session. Additionally, through HPLC experiments we demonstrate that a physical exercise session increases the hippocampal dopamine levels. Taken together, our results demonstrate that acute post-learning physical exercise is able to promote the persistence of OR memory, inducing the release of dopamine in hippocampus, which is necessary for the modulation of memory persistence. This work brings new evidences on the benefit of a single physical exercise session to memory, as well as suggests that catecholaminergic mechanisms are behind this effect.

Dopamine Receptors Influence Internally Generated Oscillations during Rule Processing in Primate Prefrontal Cortex.

Neural oscillations in distinct frequency bands in the prefrontal cortex (pFC) are associated with specialized roles during cognitive control. How dopamine modulates oscillations to structure pFC functions remains unknown. We trained macaques to switch between two numerical rules and recorded local field potentials from pFC while applying dopamine receptor targeting drugs using microiontophoresis. We show that the D1 and D2 family receptors (D1Rs and D2Rs, respectively) specifically altered internally generated prefrontal oscillations, whereas sensory-evoked potentials remained unchanged. Blocking D1Rs or stimulating D2Rs increased low-frequency theta and alpha oscillations known to be involved in learning and memory. In contrast, only D1R inhibition enhanced high-frequency beta oscillations, whereas only D2R stimulation increased gamma oscillations linked to top-down and bottom-up attentional processing. These findings suggest that dopamine alters neural oscillations relevant for executive functioning through dissociable actions at the receptor level.

Blockade of dopamine D1-family receptors attenuates the mania-like hyperactive, risk-preferring, and high motivation behavioral profile of mice with low dopamine transporter levels.

Patients with bipolar disorder mania exhibit poor cognition, impulsivity, risk-taking, and goal-directed activity that negatively impact their quality of life. To date, existing treatments for bipolar disorder do not adequately remediate cognitive dysfunction. Reducing dopamine transporter expression recreates many bipolar disorder mania-relevant behaviors (i.e. hyperactivity and risk-taking). The current study investigated whether dopamine D1-family receptor blockade would attenuate the risk-taking, hypermotivation, and hyperactivity of dopamine transporter knockdown mice. Dopamine transporter knockdown and wild-type littermate mice were tested in mouse versions of the Iowa Gambling Task (risk-taking), Progressive Ratio Breakpoint Test (effortful motivation), and Behavioral Pattern Monitor (activity). Prior to testing, the mice were treated with the dopamine D1-family receptor antagonist SCH 23390 hydrochloride (0.03, 0.1, or 0.3 mg/kg), or vehicle. Dopamine transporter knockdown mice exhibited hyperactivity and hyperexploration, hypermotivation, and risk-taking preference compared with wild-type littermates. SCH 23390 hydrochloride treatment decreased premature responding in dopamine transporter knockdown mice and attenuated their hypermotivation. SCH 23390 hydrochloride flattened the safe/risk preference, while reducing activity and exploratory levels of both genotypes similarly. Dopamine transporter knockdown mice exhibited mania-relevant behavior compared to wild-type mice. Systemic dopamine D1-family receptor antagonism attenuated these behaviors in dopamine transporter knockdown, but not all effects were specific to only the knockdown mice. The normalization of behavior via blockade of dopamine D1-family receptors supports the hypothesis that D1 and/or D5 receptors could contribute to the mania-relevant behaviors of dopamine transporter knockdown mice.

A critical role of nucleus accumbens dopamine D1-family receptors in renewal of alcohol seeking after punishment-imposed abstinence.

In humans, places or contexts previously associated with alcohol use often provoke relapse during abstinence. This phenomenon is modeled in laboratory animals using the ABA renewal procedure, in which extinction training in context (B) suppresses alcohol seeking, and renewal of this seeking occurs when the animal returns to the original training context (A). However, extinction training does not adequately capture the motivation for abstinence in human alcoholics who typically self-initiate abstinence in response to the negative consequences of excessive use. We recently developed a procedure to study renewal in laboratory rats after abstinence imposed by negative consequences (footshock punishment). The mechanisms of renewal of punished alcohol seeking are largely unknown. Here, we used the D1-family receptor antagonist SCH 23390 to examine the role of nucleus accumbens (NAc) shell and core dopamine in renewal of alcohol seeking after punishment-imposed abstinence. We trained alcohol-preferring "P rats" to self-administer 20% alcohol in Context A and subsequently suppressed alcohol taking via response-contingent footshock punishment in Context B. We tested the effects of systemic, NAc shell, or NAc core injections of SCH 23390 on renewal of alcohol seeking after punishment-imposed abstinence. We found that both systemic and NAc shell and core injections of SCH 23390 decreased renewal of punished alcohol seeking. Our results demonstrate a critical role of NAc dopamine in renewal of alcohol seeking after punishment-imposed abstinence. We discuss these results in reference to the brain mechanisms of renewal of alcohol seeking after extinction versus punishment.

Incubation of methamphetamine craving is associated with selective increases in expression of Bdnf and trkb, glutamate receptors, and epigenetic enzymes in cue-activated fos-expressing dorsal striatal neurons.

Cue-induced methamphetamine seeking progressively increases after withdrawal (incubation of methamphetamine craving), but the underlying mechanisms are largely unknown. We determined whether this incubation is associated with alterations in candidate genes in dorsal striatum (DS), a brain area implicated in cue- and context-induced drug relapse. We first measured mRNA expression of 24 candidate genes in whole DS extracts after short (2 d) or prolonged (1 month) withdrawal in rats following extended-access methamphetamine or saline (control condition) self-administration (9 h/d, 10 d). We found minimal changes. Next, using fluorescence-activated cell sorting, we compared gene expression in Fos-positive dorsal striatal neurons, which were activated during "incubated" cue-induced drug-seeking tests after prolonged withdrawal, with nonactivated Fos-negative neurons. We found significant increases in mRNA expression of immediate early genes (Arc, Egr1), Bdnf and its receptor (Trkb), glutamate receptor subunits (Gria1, Gria3, Grm1), and epigenetic enzymes (Hdac3, Hdac4, Hdac5, GLP, Dnmt3a, Kdm1a) in the Fos-positive neurons only. Using RNAscope to determine striatal subregion and cell-type specificity of the activated neurons, we measured colabeling of Fos with Drd1 and Drd2 in three DS subregions. Fos expression was neither subregion nor cell-type specific (52.5 and 39.2% of Fos expression colabeled with Drd1 and Drd2, respectively). Finally, we found that DS injections of SCH23390 (C17H18ClNO), a D1-family receptor antagonist known to block cue-induced Fos induction, decreased incubated cue-induced methamphetamine seeking after prolonged withdrawal. Results demonstrate a critical role of DS in incubation of methamphetamine craving and that this incubation is associated with selective gene-expression alterations in cue-activated D1- and D2-expressing DS neurons.

D1 and D5 dopamine receptors participate on the consolidation of two different memories

Memory consolidation is the process by which recently acquired information becomes stable and is modulated by different neurotransmitters depending on the structure involved and the nature of the memory. Here we evaluate the participation of both D1 and D5 dopamine receptors in the CA1 region of the hippocampus in the consolidation of the memory of two different tasks, object recognition (OR) and inhibitory avoidance (IA). For this, male rats with infusion cannulae stereotaxically implanted in the CA1 region of the dorsal hippocampus were trained in an OR task involving exposure to two different objects, or in a one-trial step-down IA task. At different times after the training, some of the animals received intrahippocampal infusions of the D1-family receptor antagonist SCH-23390. In a test session carried out 24h later, the animals that received infusions immediately or 60min but not 180min after the training showed impaired long-term memory. Since D1- and D5-subtypes engage different signaling pathways involving cAMP-dependent protein kinase (PKA) and protein kinase C (PKC), respectively, we assessed whether they participate distinctively in consolidation. The animals that received intra-CA1 infusions of the PKA inhibitor, Rp-cAMP, or the PKC inhibitor, Gö6976, immediately after OR or IA training had a long-term memory impairment and the amnesic effect caused by SCH-23390 was reversed when co-infused with activators of PKA (8Br-cAMP) or PKC (PMA). These results indicate that both D1 and D5 dopamine receptors are required in the CA1 region of the hippocampus for consolidation of the two tasks. This supports the notion of a commonality of consolidation mechanisms across tasks.

Role of Projections from Ventral Medial Prefrontal Cortex to Nucleus Accumbens Shell in Context-Induced Reinstatement of Heroin Seeking

In humans, exposure to contexts previously associated with heroin use can provoke relapse. In rats, exposure to heroin-paired contexts after extinction of drug-reinforced responding in different contexts reinstates heroin seeking. This effect is attenuated by inhibition of glutamate or dopamine transmission in nucleus accumbens shell, or inactivation of ventral medial prefrontal cortex (mPFC). Here, we used an anatomical asymmetrical disconnection procedure to demonstrate that an interaction between glutamatergic projections from ventral mPFC to accumbens shell and local dopamine D(1) postsynaptic receptors contributes to context-induced reinstatement of heroin seeking. We also combined the marker of neuronal activity, Fos, with the retrograde tracer Fluoro-Gold to assess activation in this pathway during context-induced reinstatement. Rats were trained to self-administer heroin for 12 d; drug infusions were paired with a discrete tone-light cue. Lever pressing was subsequently extinguished in a nondrug-associated context in the presence of the discrete cue. Rats were then tested in the heroin- or extinction-associated contexts under extinction conditions. Injections of muscimol + baclofen into ventral mPFC in one hemisphere and D(1)-family receptor antagonist SCH 23390 into the contralateral or ipsilateral accumbens shell decreased context-induced reinstatement. Unilateral injections of muscimol + baclofen into ventral mPFC or SCH 23390 into the accumbens shell had no effect. Context-induced reinstatement was associated with increased Fos expression in ventral mPFC neurons, including those projecting to accumbens shell, with higher double-labeling in the ipsilateral projection than in the contralateral projection. Our results demonstrate that activation of glutamatergic projections from ventral mPFC to accumbens shell, previously implicated in inhibition of cocaine relapse, promotes heroin relapse.

Dopaminergic modulation of ganglion‐cell photoreceptors in rat

A novel class of photoreceptors, the intrinsically photosensitive retinal ganglion cells (ipRGCs), express the photopigment melanopsin and drive non-image-forming responses to light such as circadian photoentrainment, the pupillary light reflex and suppression of nocturnal melatonin production in the pineal. Because dendrites from one subclass of these cells - the M1-type ipRGCs - make presumptive synaptic contacts at sites of dopamine release from dopaminergic amacrine cells, they are prime targets for modulation by dopamine, a neuromodulator implicated in retinal circadian rhythms and light adaptation. In patch-clamp recordings from ipRGCs in intact rat retinas, dopamine attenuated the melanopsin-based photocurrent. We confirmed that this was the result of direct action on ipRGCs by replicating the effect in dissociated ipRGCs that were isolated from influences of other retinal neurons. In these recordings, the D1-family dopamine receptor agonist SKF38393 attenuated the photocurrent, caused a modest depolarization, and reduced the input resistance of ipRGCs. The D2-family agonist quinpirole had no effect on the photocurrent. Single-cell reverse-transcriptase polymerase chain reaction revealed that the majority of ipRGCs tested expressed drd1a, the gene coding for the D1a dopamine receptor. This finding was supported by immunohistochemical localization of D1a receptor protein in melanopsin-expressing ganglion cells. Finally, the adenylate cyclase activator forskolin, applied in combination with the phosphodiesterase inhibitor IBMX (isobutylmethylxanthine), mimicked the effects of SKF38393 on the ipRGC photocurrent, membrane potential and input resistance, consistent with a D1-receptor signaling pathway. These data suggest that dopamine, acting via D1-family receptors, alters the responses of ipRGCs and thus of non-image-forming vision.

Role of dorsal medial prefrontal cortex dopamine D1-family receptors in relapse to high-fat food seeking induced by the anxiogenic drug yohimbine.

In humans, relapse to maladaptive eating habits during dieting is often provoked by stress. In rats, the anxiogenic drug yohimbine, which causes stress-like responses in both humans and nonhumans, reinstates food seeking in a relapse model. In this study, we examined the role of medial prefrontal cortex (mPFC) dopamine D1-family receptors, previously implicated in stress-induced reinstatement of drug seeking, in yohimbine-induced reinstatement of food seeking. We trained food-restricted rats to lever press for 35% high-fat pellets every other day (9-15 sessions, 3 h each); pellet delivery was accompanied by a discrete tone-light cue. We then extinguished operant responding for 10-16 days by removing the pellets. Subsequently, we examined the effect of yohimbine (2 mg/kg, i.p.) on reinstatement of food seeking and Fos (a neuronal activity marker) induction in mPFC. We then examined the effect of systemic injections of the D1-family receptor antagonist SCH23390 (10 μg/kg, s.c.) on yohimbine-induced reinstatement and Fos induction, and that of mPFC SCH23390 (0.5 and 1.0 μg/side) injections on this reinstatement. Yohimbine-induced reinstatement was associated with strong Fos induction in the dorsal mPFC and with weaker Fos induction in the ventral mPFC. Systemic SCH23390 injections blocked both yohimbine-induced reinstatement and mPFC Fos induction. Dorsal, but not ventral, mPFC injections of SCH23390 decreased yohimbine-induced reinstatement of food seeking. In addition, dorsal mPFC SCH23390 injections decreased pellet-priming-induced reinstatement, but had no effect on ongoing high-fat pellet self-administration or discrete-cue-induced reinstatement. Results indicate a critical role of dorsal mPFC dopamine D1-family receptors in stress-induced relapse to palatable food seeking, as well as relapse induced by acute re-exposure to food taste, texture, and smell.

Localization of dopamine- and cAMP-regulated phosphoprotein-32 and inhibitor-1 in area 9 of Macaca mulatta prefrontal cortex

The actions of dopamine D1 family receptors (D1R) depend upon a signal transduction cascade that modulates the phosphorylation state of important effector proteins, such as glutamate receptors and ion channels. This is accomplished both through activation of protein kinase A (PKA) and the inhibition of protein phosphatase-1 (PP1). Inhibition of PP1 occurs through PKA-mediated phosphorylation of dopamine- and cAMP-regulated phosphoprotein 32 kDa (DARPP-32) or the related protein inhibitor-1 (I-1), and the availability of DARPP-32 is essential to the functional outcome of D1R activation in the basal ganglia. While D1R activation is critical for prefrontal cortex (PFC) function, especially working memory, the functional role played by DARPP-32 or I-1 is less clear. In order to examine this more thoroughly, we have utilized immunoelectron microscopy to quantitatively determine the localization of DARPP-32 and I-1 in the neuropil of the rhesus monkey PFC. Both were distributed widely in the different components of the neuropil, but were enriched in dendritic shafts. I-1 label was more frequently identified in axon terminals than was DARPP-32, and DARPP-32 label was more frequently identified in glia than was I-1. We also quantified the extent to which these proteins were found in dendritic spines. DARPP-32 and I-1 were present in small subpopulations of dendritic spines, (4.4% and 7.7% and respectively), which were substantially smaller than observed for D1R in our previous studies (20%). Double-label experiments did not find evidence for colocalization of D1R and DARPP-32 or I-1 in spines or terminals. Thus, at the least, not all prefrontal spines which contain D1R also contain I-1 or DARPP-32, suggesting important differences in D1R signaling in the PFC compared to the striatum.

Distribution of D1 and D5 dopamine receptors in the primate and rat basolateral amygdala

Dopamine, acting at the D1 family receptors (D1R) is critical for the functioning of the amygdala, including fear conditioning and cue-induced reinstatement of drug self administration. However, little is known about the different contributions of the two D1R subtypes, D(1) and D(5). We identified D(1)-immunoreactive patches in the primate that appear similar to the intercalated cell masses reported in the rodent; however, both receptors were present across the subdivisions of the primate amygdala including the basolateral amygdala (BLA). Using immunoelectron microscopy, we established that both receptors have widespread distributions in BLA. The D1R subtypes colocalize in dendritic spines and terminals, with D(1) predominant in spines and D(5) in terminals. Single-cell RT-PCR confirmed that individual BLA projection neurons express both D(1) and D(5) mRNA. The responses of primate BLA neurons to dopamine and D1R drugs were studied using in vitro slices. We found that responses were similar to those previously reported in rat BLA neurons and included a mixture of postsynaptic and presynaptic actions. We investigated the distribution of D1R in the rat BLA and found that there were similarities between the species, such as more prominent D(5) localization to presynaptic structures. The higher affinity of D(5) for dopamine suggests that presynaptic actions may predominate in the BLA at low levels of dopamine, while postsynaptic effects increase and dominate as dopaminergic drive increases. The results presented here suggest a complex action of dopamine on BLA circuitry that may evolve with different degrees of dopaminergic stimulation.

Role of dopamine D1-family receptors in dorsolateral striatum in context-induced reinstatement of heroin seeking in rats

In humans, exposure to environmental contexts previously associated with heroin intake can provoke relapse to drug use. In rats, exposure to heroin-associated contexts after extinction of drug-reinforced responding in different contexts reinstates heroin seeking. This effect is attenuated by blockade of D(1)-family receptors in lateral or medial accumbens shell, but not accumbens core. In this study, we further characterized the role of striatal D(1)-family receptors in context-induced reinstatement by assessing the effect of dorsolateral or dorsomedial injections of the D(1)-family receptor antagonist SCH 23390 on this reinstatement. Rats were trained to self-administer heroin (0.05-0.10 mg/kg per infusion) for 12 days; drug infusions were paired with a discrete tone-light cue. Subsequently, heroin-reinforced lever pressing was extinguished in the presence of the discrete cue in a nondrug context. During reinstatement tests under extinction conditions, the D(1)-family receptor antagonist SCH 23390 (0.3-1.0 microg per side) was injected into the dorsolateral or dorsomedial striatum prior to exposure to heroin self-administration context or the nondrug (extinction) context. We then used a disconnection procedure to examine whether D(1)-family receptors in the dorsolateral striatum and lateral accumbens shell jointly or independently support context-induced reinstatement. Dorsolateral but not dorsomedial SCH 23390 injections attenuated context-induced reinstatement of heroin seeking. SCH 23390 injections into the dorsolateral striatum of one hemisphere and lateral accumbens shell of the other hemisphere were ineffective. Results indicate that dorsolateral striatum D(1)-family dopamine receptors are critical for context-induced reinstatement of heroin seeking. Results also suggest that D(1)-receptor-mediated dopamine transmission in the dorsolateral striatum and lateral accumbens shell independently support this reinstatement.

Dopamine D1 and D5 Receptors Are Localized to Discrete Populations of Interneurons in Primate Prefrontal Cortex

Working memory (WM) is a core cognitive process that depends upon activation of D1 family receptors (D1R) and inhibitory interneurons in the prefrontal cortex (PFC). D1R are comprised of the D(1) and D(5) subtypes, and D(5) has a 10-fold higher affinity for dopamine. Parvalbumin (PV) and calretinin (CR) are 2 interneuron populations that are differentially affected by D1R stimulation and have discrete postsynaptic targets, such that PV interneurons provide strong inhibition to pyramidal cells, whereas CR interneurons inhibit other interneurons. The distinct properties of both the D1R and interneuron subtypes may contribute to the "inverted-U" relationship of D1R stimulation and WM ability. To determine the prevalence of D(1) and D(5) in PV and CR interneurons, we performed quantitative double-label immunoelectron microscopy in layer III of macaque area 9. We found that D(1) was the predominant D1R subtype in PV interneurons and was found mainly in dendrites. In contrast, D(5) was the predominant D1R subtype in CR interneurons and was found mainly in dendrites. Integrating these findings with previously published electrophysiological data, we propose a circuitry model as a framework for understanding the inverted-U relationship between dopamine stimulation of D1R and WM performance.

Quantification of D1 and D5 dopamine receptor localization in layers I, III, and V of Macaca mulatta prefrontal cortical area 9: Coexpression in dendritic spines and axon terminals

D1 family receptors (D1R) in prefrontal cortex (PFC) are critical for normal cognition and are implicated in pathological states such as schizophrenia. The two D1R subtypes, D1 and D5, cannot be pharmacologically distinguished but have important functional differences. To understand their contributions to cortical function, we quantified their localization in the neuropil of primate PFC. We identified different patterns of distribution for the two receptors that showed variation across cortical laminae. Although D1 was enriched in spines and D5 in dendrites, there was considerable overlap in their distribution within neuronal compartments. To determine whether the D1 and D5 receptors are localized to separate populations of synapses, we employed double-labeling methods. We found the two receptors colocalized and quantified the overlap of their distribution in spines and axon terminals of prefrontal cortical area 9 in the Macaca mulatta monkey. The two receptors are found in partially overlapping populations, such that the D5 receptor is found in a subpopulation of those spines and terminals that contain D1. These results indicate that dopamine activation of the two D1R subtypes does not modulate disparate populations of synapses onto dendritic spines in prefrontal cortical area 9; rather, dopamine can activate D1 and D5 receptors on the same spines, plus an additional group of spines that contains only D1. The implications of these results for the dose-dependent relationship between D1R activation and PFC function are discussed.

Contributions of Dopamine D1, D2, and D3 Receptor Subtypes to the Disruptive Effects of Cocaine on Prepulse Inhibition in Mice

Deficits in prepulse inhibition (PPI) of startle, an operational measure of sensorimotor gating, are characteristics of schizophrenia and related neuropsychiatric disorders. Previous studies in mice demonstrate a contribution of dopamine (DA) D(1)-family receptors in modulating PPI and DA D(2) receptors (D2R) in mediating the PPI-disruptive effects of amphetamine. To examine further the contributions of DA receptor subtypes in PPI, we used a combined pharmacological and genetic approach. In congenic C57BL/6 J wild-type mice, we tested whether the D1R antagonist SCH23390 or the D2/3R antagonist raclopride would attenuate the effects of the indirect DA agonist cocaine (40 mg/kg). Both the D1R and D2/3R antagonists attenuated the cocaine-induced PPI deficit. We also tested the effect of cocaine on PPI in wild-type and DA D1R, D2R, or D3R knockout mice. The cocaine-induced PPI deficit was influenced differently by the three DA receptor subtypes, being absent in D1R knockout mice, partially attenuated in D2R knockout mice, and exaggerated in D3R knockout mice. Thus, the D1R is necessary for the PPI-disruptive effects of cocaine, while the D2R partially contributes to these effects. Conversely, the D3R appears to inhibit the PPI-disruptive effects of cocaine. Uncovering neural mechanisms involved in PPI will further our understanding of substrates of sensorimotor gating and could lead to better therapeutics to treat complex cognitive disorders such as schizophrenia.

Differential Effects of Blockade of Dopamine D1-Family Receptors in Nucleus Accumbens Core or Shell on Reinstatement of Heroin Seeking Induced by Contextual and Discrete Cues

In humans, exposure to environmental contexts previously associated with heroin intake can provoke drug relapse, but the neuronal mechanisms mediating this relapse are unknown. Using a drug relapse model, we found previously that reexposing rats to heroin-associated contexts, after extinction of drug-reinforced responding in different contexts, reinstates heroin seeking. This effect is attenuated by inhibition of glutamate transmission in the ventral tegmental area and medial accumbens shell, components of the mesolimbic dopamine system. Here, we explored the role of dopamine of the accumbens in context-induced reinstatement by using the D1-family receptor antagonist SCH 23390 [R(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrochloride]. Rats were trained to self-administer heroin for 12 d; drug infusions were paired with a discrete tone-light cue. Subsequently, the heroin-reinforced lever pressing was extinguished in the presence of the discrete cue in a context that differed from the drug self-administration context in terms of visual, auditory, tactile, and circadian cues. When tested in the original drug self-administration context, systemic and medial or lateral accumbens shell SCH 23390 injections attenuated context-induced reinstatement of heroin seeking, whereas accumbens core SCH 23390 injections were ineffective. In contrast, core but not lateral or medial shell SCH 23390 injections attenuated discrete-cue-induced reinstatement in a nondrug context after extinction of lever presses without this cue. Results indicate that activation of medial and lateral accumbens shell D1-family dopamine receptors mediate context-induced reinstatement of heroin seeking and provide the first demonstration for a role of lateral shell dopamine in conditioned drug effects. Results also demonstrate novel dissociable roles of accumbens core and shell in context- versus discrete-cue-induced reinstatement of heroin seeking.

Differential Localization of Protein Phosphatase-1α, β and γ1 Isoforms in Primate Prefrontal Cortex

Prefrontal cortical functioning depends on D1 family receptors and their complex signal transduction cascade, including protein phosphatase-1 (PP1). Three PP1 isoforms are prominent in the brain: PP1alpha, PP1beta and PP1gamma1. PP1 localization by a variety of scaffolding proteins is critical for dopamine-mediated modulation of glutamatergic neurotransmission. We have quantified the subcellular distribution of each isoform in primate prefrontal cortex using immunoelectron microscopy. All three are found in spines, dendrites, axon terminals, axons and glia. However, PP1alpha and PP1gamma1 labeling is enriched in spines, whereas PP1beta label is enriched in dendrites. Using post-embedding immunogold labeling, we further examined the distribution of PP1alpha and PP1gamma1 within spines. PP1gamma1 is highly and specifically concentrated in the postsynaptic density (PSD) of these spines, while PP1alpha is enriched in the PSD but also found subjacent to the PSD in moderate amounts. Thus, PP1 isoforms are heterogeneously distributed in the cortical neuropil and within spines. These results suggest that each PP1 isoform has access to a different set of substrates and, furthermore, they demonstrate that the composition of signal transduction proteins varies in different parts of the neuron and even in different regions of a dendritic spine in the primate PFC.

Dopamine D1 rather than D2 receptor agonists disrupt prepulse inhibition of startle in mice.

Although substantial literature describes the modulation of prepulse inhibition (PPI) by dopamine (DA) in rats, few reports address the effects of dopaminergic manipulations on PPI in mice. We characterized the effects of subtype-specific DA agonists in the PPI paradigm to further delineate the specific influences of each DA receptor subtype on sensorimotor gating in mice. The mixed D1/D2 agonist apomorphine and the preferential D1-family agonists SKF82958 and dihydrexidine significantly disrupted PPI, with differing or no effects on startle. In contrast to findings in rats, the D2/D3 agonist quinpirole reduced startle but had no effect on PPI. Pergolide, which has affinity for D2/D3 and D1-like receptors, reduced both startle and PPI, but only at the higher, nonspecific doses. In addition, the D1-family receptor antagonist SCH23390 blocked the PPI-disruptive effects of apomorphine on PPI, but the D2-family receptor antagonist raclopride failed to alter the disruptive effect of apomorphine. These studies reveal potential species differences in the DA receptor modulation of PPI between rats and mice, where D1-family receptors may play a more prominent and independent role in the modulation of PPI in mice than in rats. Nevertheless, due to the limited selectivity of DA receptor agonists, further studies using specific receptor knockout mice are warranted to clarify the respective roles of specific DA receptor subtypes in modulating PPI in mice.

D1Receptor in Interneurons of Macaque Prefrontal Cortex: Distribution and Subcellular Localization

Working memory performance is influenced by dopamine activation of D1 family dopamine receptors in the prefrontal cortex; working memory performance is maximal at moderate stimulation of D1 family receptors and is reduced by either higher or lower levels of D1 stimulation. The neuronal mechanisms that underlie this complex relationship are not yet understood. Previous work from this laboratory has demonstrated that the D1 family receptors, D1 and D5, are located in different compartments of pyramidal cells. Here we use an antibody specific to the D1 receptor and double-label immunohistochemistry at the light and electron microscopic level to demonstrate that D1-like immunoreactivity (D1-LIR) is also present in interneurons. D1 receptor is prevalent in parvalbumin-containing interneurons and is less common in calretinin-containing interneurons. At the ultrastructural level, D1-LIR is found associated with the Golgi apparatus and endoplasmic reticulum in the soma, with the membranes of vesicles in proximal dendrites, and with the plasma membrane on distal dendrites, where it is often located near asymmetric synapses. In addition, D1-LIR is also seen in presynaptic axon terminals, which give rise to symmetric synapses onto dendritic shafts and soma. These results raise the possibility that the circuit basis of working memory in the prefrontal cortex involves a D1-mediated inhibitory component.