Requisite Role of Basolateral Amygdala Glucocorticoid Receptor Stimulation in Drug Context-Induced Cocaine-Seeking Behavior

Exposure to cocaine-associated stimuli triggers a robust rise in circulating glucocorticoid levels. Glucocorticoid receptors are richly expressed in the basolateral amygdala, a brain region that controls the reinstatement of cocaine-seeking behavior upon exposure to a previously cocaine-paired environmental context. In the present study, we investigated whether glucocorticoid receptor stimulation in the basolateral amygdala is integral to drug context-induced motivation to seek cocaine in a rat model of drug relapse

Changes in Sensitivity of Reward and Motor Behavior to Dopaminergic, Glutamatergic, and Cholinergic Drugs in a Mouse Model of Fragile X Syndrome

Fragile X syndrome (FXS) is a leading cause of intellectual disability. FXS is caused by loss of function of the FMR1 gene, and mice in which Fmr1 has been inactivated have been used extensively as a preclinical model for FXS. We investigated the behavioral pharmacology of drugs acting through dopaminergic, glutamatergic, and cholinergic systems in fragile X (Fmr1-/Y) mice with intracranial self-stimulation (ICSS) and locomotor activity measurements. We also measured brain expression of tyrosine hydroxylase (TH), the rate-limiting enzyme in dopamine biosynthesis. Fmr1-/Y mice were more sensitive than wild type mice to the rewarding effects of cocaine, but less sensitive to its locomotor stimulating effects. Anhedonic but not motor depressant effects of the atypical neuroleptic, aripiprazole, were reduced in Fmr1-/Y mice. The mGluR5-selective antagonist, 6-methyl-2-(phenylethynyl)pyridine (MPEP), was more rewarding and the preferential M1 antagonist, trihexyphenidyl, was less rewarding in Fmr1-/Y than wild type mice. Motor stimulation by MPEP was unchanged, but stimulation by trihexyphenidyl was markedly increased, in Fmr1-/Y mice. Numbers of midbrain TH+ neurons in the ventral tegmental area were unchanged, but were lower in the substantia nigra of Fmr1-/Y mice, although no changes in TH levels were found in their forebrain targets. The data are discussed in the context of known changes in the synaptic physiology and pharmacology of limbic motor systems in the Fmr1-/Y mouse model. Preclinical findings suggest that drugs acting through multiple neurotransmitter systems may be necessary to fully address abnormal behaviors in individuals with FXS

Acute phenylalanine/tyrosine depletion of phasic dopamine in the rat brain

Dopamine plays a critical role in striatal and cortical function, and depletion of the dopamine precursors phenylalanine and tyrosine is used in humans to temporarily reduce dopamine and probe the role of dopamine in behavior. This method has been shown to alter addiction-related behaviors and cognitive functioning presumably by reducing dopamine transmission, but it is unclear what specific aspects of dopamine transmission are altered

Orbitofrontal Participation in Sign- and Goal-Tracking Conditioned Responses: Effects of Nicotine

Pavlovian conditioned stimuli can acquire incentive motivational properties, and this phenomenon can be measured in animals using Pavlovian conditioned approach behavior. Drugs of abuse can influence the expression of this behavior, and nicotine in particular exhibits incentive amplifying effects. Both conditioned approach behavior and drug abuse rely on overlapping corticolimbic circuitry. We hypothesize that the orbitofrontal cortex (OFC) regulates conditioned approach, and that one site of nicotine action is in the OFC where it reduces cortical output. To test this, we repeatedly exposed rats to 0.4 mg/kg nicotine (s.c.) during training and then pharmacologically inactivated the lateral OFC or performed in vivo electrophysiological recordings of lateral OFC neurons in the presence or absence of nicotine. In Experiment 1, animals were trained in a Pavlovian conditioning paradigm and behavior was evaluated after inactivation of the OFC by microinfusion of the GABA agonists baclofen and muscimol. In Experiment 2, we monitored phasic firing of OFC neurons during Pavlovian conditioning sessions. Nicotine reliably enhanced conditioned responding to the conditioned cue, and inactivation of the OFC reduced conditioned responding, especially the sign-tracking response. OFC neurons exhibited phasic excitations to cue presentation and during goal tracking, and nicotine acutely blunted this phasic neuronal firing. When nicotine was withheld, both conditioned responding and phasic firing in the OFC returned to the level of controls. These results suggest that the OFC is recruited for the expression of conditioned responses, and that nicotine acutely influences this behavior by reducing phasic firing in the OFC

Requisite Role of Basolateral Amygdala Glucocorticoid Receptor Stimulation in Drug Context-Induced Cocaine-Seeking Behavior

BACKGROUND: Exposure to cocaine-associated stimuli triggers a robust rise in circulating glucocorticoid levels. Glucocorticoid receptors are richly expressed in the basolateral amygdala, a brain region that controls the reinstatement of cocaine-seeking behavior upon exposure to a previously cocaine-paired environmental context. In the present study, we investigated whether glucocorticoid receptor stimulation in the basolateral amygdala is integral to drug context-induced motivation to seek cocaine in a rat model of drug relapse. METHODS: Rats were trained to lever press for cocaine reinforcement in a distinct environmental context and were then given daily extinction training sessions in a different context. At test, the rats received bilateral glucocorticoid receptor antagonist (mifepristone; 3 or 10ng/hemisphere) or vehicle microinfusions into either the basolateral amygdala or the overlying posterior caudate-putamen (anatomical control region). Immediately thereafter, drug-seeking behavior (i.e., nonreinforced lever presses) was assessed in the previously cocaine-paired context and locomotor activity was assessed in a novel context. RESULTS: Intra-basolateral amygdala, but not intra-posterior caudate-putamen, mifepristone dose-dependently attenuated drug context-induced cocaine-seeking behavior relative to vehicle, such that responding was similar to that observed in the extinction context. In contrast, mifepristone treatment did not alter locomotor activity. CONCLUSIONS: These findings suggest that basolateral amygdala glucocorticoid receptor stimulation is necessary for drug context-induced motivation to seek cocaine

Changes in Sensitivity of Reward and Motor Behavior to Dopaminergic, Glutamatergic, and Cholinergic Drugs in a Mouse Model of Fragile X Syndrome

<div><p>Fragile X syndrome (FXS) is a leading cause of intellectual disability. FXS is caused by loss of function of the FMR1 gene, and mice in which <i>Fmr1</i> has been inactivated have been used extensively as a preclinical model for FXS. We investigated the behavioral pharmacology of drugs acting through dopaminergic, glutamatergic, and cholinergic systems in fragile X (<i>Fmr1</i>^-/Y) mice with intracranial self-stimulation (ICSS) and locomotor activity measurements. We also measured brain expression of tyrosine hydroxylase (TH), the rate-limiting enzyme in dopamine biosynthesis. <i>Fmr1</i>^-/Y mice were more sensitive than wild type mice to the rewarding effects of cocaine, but less sensitive to its locomotor stimulating effects. Anhedonic but not motor depressant effects of the atypical neuroleptic, aripiprazole, were reduced in <i>Fmr1</i>^-/Y mice. The mGluR5-selective antagonist, 6-methyl-2-(phenylethynyl)pyridine (MPEP), was more rewarding and the preferential M1 antagonist, trihexyphenidyl, was less rewarding in <i>Fmr1</i>^-/Y than wild type mice. Motor stimulation by MPEP was unchanged, but stimulation by trihexyphenidyl was markedly increased, in <i>Fmr1</i>^-/Y mice. Numbers of midbrain TH+ neurons in the ventral tegmental area were unchanged, but were lower in the substantia nigra of <i>Fmr1</i>^-/Y mice, although no changes in TH levels were found in their forebrain targets. The data are discussed in the context of known changes in the synaptic physiology and pharmacology of limbic motor systems in the <i>Fmr1</i>^-/Y mouse model. Preclinical findings suggest that drugs acting through multiple neurotransmitter systems may be necessary to fully address abnormal behaviors in individuals with FXS.</p> </div

Effects of cocaine on ICSS and locomotor behavior in wild type (WT, <i>white</i><i>circles</i>) and <i>Fmr1</i>^-/Y mice (red circles).

<p>Changes in BSR threshold (<b>A</b>) and maximum operant response rate (MAX, <b>B</b>) in the first 15 minute series after i.p. cocaine injections are shown. Values are expressed as mean percentages of pre-injection baselines ± SEM. <b>C</b>. Mean change in locomotion (± SEM) as a percentage of pre-injection baseline activity after injection of saline (V) or cocaine (1.0, 3.0, or 10.0 mg/kg i.p.) in the first 15 minutes after injection. For A-C, asterisks (*) indicate <i>p</i> < 0.05 vs. vehicle (V); daggers (†) indicate <i>p</i> < 0.05 vs. WT (dose x genotype interaction <i>post </i><i>hoc</i>). <b>D</b>. Mean distance traveled (± SEM) before and after injection of saline (VEH) or cocaine (COC, 1.0, 3.0, or 10.0 mg/kg i.p.) in 15-minute intervals. Shading indicates post-injection time points. Daggers (†) indicate <i>p</i> < 0.05 vs. WT (time x genotype interaction <i>post </i><i>hoc</i>).</p

Comparison of ICSS and locomotor behavior in wild type (WT, <i>white</i><i>circles</i>) and <i>Fmr1</i>^-/Y mice (red circles).

<p><b>A</b>. Both <i>Fmr1</i>^-/Y and WT mice responded for BSR in a frequency-dependent manner. Values are mean number of responses per 50 sec access to BSR at each stimulus frequency ± SEM. <b>B</b>. BSR sensitivity expressed as electrical charge delivery at baseline BSR threshold frequency (θ₀) did not differ between WT (white bars) and <i>Fmr1</i>^-/Y mice (red bars). Values are mean charge in Coulombs ± SEM. <b>C</b>. Baseline maximum operant response rates were lower in <i>Fmr1</i>^-/Y mice than WT mice. Values are mean maximum number of responses ± SEM. * = <i>p</i> < 0.05 vs. WT. <b>D</b>-<b>F</b>. Habituation to the novel locomotor apparatus and handling in WT and <i>Fmr1</i>^-/Y mice. On Day 1 (D) <i>Fmr1</i>^-/Y mice were less active at all time points before (15-45 min) and after handling (60-105 min), and had lower cumulative total locomotion before and after handling (inset). On Day 2 (E) <i>Fmr1</i>^-/Y mice were less active prior to (inset) and for 30 min following handling. By Day 3 (F), total locomotion remained lower in <i>Fmr1</i>^-/Y mice prior to handling but no difference in locomotion was seen after handling (inset). Dashed lines indicate handling time points. Values are mean distance traveled ± SEM. Asterisks (*) indicate <i>p</i> < 0.05 vs. WT.</p

Anatomical and biochemical correlates of dopaminergic function in wild type (WT, <i>white</i><i>bars</i>) and <i>Fmr1</i>^-/Y mice (red bars).

<p><b>A</b>. Mean numbers of tyrosine hydroxylase (TH) expressing neurons (± SEM, <i>top</i>) in the substantia nigra pars compacta (SNc) and ventral tegmental area (VTA) of WT and <i>Fmr1</i>^-/Y mice estimated with design-based stereology. Numbers of mice are indicated in each column. Ventral midbrain image (bottom left) is magnified 4x and inset showing TH staining (bottom right) 40x. Asterisks (*) indicate <i>p</i> < 0.05 vs. WT. cp = cerebral peduncle; fr = fasciculus retroflexus; ml = medial lemniscus. <b>B</b>. Mean ratio of TH to β-Actin staining intensity expressed as percentage of mean WT values (± SEM, <i>top</i>) in western blots of homogenates from dorsal striatum and nucleus accumbens (NAc) of WT and <i>Fmr1</i>^-/Y mice. Numbers of mice are indicated in each column. Representative bands (bottom) are shown for each column above.</p

Effects of the atypical neuroleptic aripiprazole on ICSS and locomotor behavior in wild type (WT, <i>white</i><i>circles</i>) and <i>Fmr1</i>^-/Y mice (red circles).

<div><p>Changes in BSR threshold (<b>A</b>) and maximum operant response rate (MAX, <b>B</b>) 46-60 minutes after i.p. aripiprazole injections are shown. Values are expressed as mean percentages of pre-injection baselines ± SEM. </p> <p>Asterisks (*) indicate <i>p</i> < 0.05 vs. vehicle (V). <b>C</b>. Mean distance traveled (± SEM) before and after injection of vehicle (VEH) or aripiprazole (ARI, 0.1 mg/kg i.p.) in 15-minute intervals. Shading indicates post-injection time points. <b>D</b>. Mean change in locomotion (± SEM) as a percentage of pre-injection baseline activity for 60 minutes after injection of vehicle (VEH) or aripiprazole (ARI, 0.1 mg/kg i.p.).</p></div