Acute withdrawal-related hypophagia elicited by amphetamine is attenuated by pretreatment with selective dopamine D1 or D2 receptor antagonists in rats

A D2 to D1 shift in dopaminergic inputs to midbrain 5-HT neurons causes anorexia in mice

Midbrain dopamine (DA) and serotonin (5-HT) neurons regulate motivated behaviors, including feeding, but less is known about how these circuits may interact. In this study, we found that DA neurons in the mouse ventral tegmental area bidirectionally regulate the activity of 5-HT neurons in the dorsal raphe nucleus (DRN), with weaker stimulation causing DRD2-dependent inhibition and overeating, while stronger stimulation causing DRD1-dependent activation and anorexia. Furthermore, in the activity-based anorexia (ABA) paradigm, which is a mouse model mimicking some clinical features of human anorexia nervosa (AN), we observed a DRD2 to DRD1 shift of DA neurotransmission on 5-HT^DRN neurons, which causes constant activation of these neurons and contributes to AN-like behaviors. Finally, we found that systemic administration of a DRD1 antagonist can prevent anorexia and weight loss in ABA. Our results revealed regulation of feeding behavior by stimulation strength-dependent interactions between DA and 5-HT neurons, which may contribute to the pathophysiology of AN.

Opioid gene expression changes and post-translational histone modifications at promoter regions in the rat nucleus accumbens after acute and repeated 3,4-methylenedioxy-methamphetamine (MDMA) exposure

The recreational drug of abuse 3,4-methylenedioxymethamphetamine (MDMA) has been shown to produce neurotoxic damage and long-lasting changes in several brain areas. In addition to the involvement of serotoninergic and dopaminergic systems, little information exists about the contribution of nociceptin/orphaninFQ (N/OFQ)-NOP and dynorphin (DYN)-KOP systems in neuronal adaptations evoked by MDMA. Here we investigated the behavioral and molecular effects induced by acute (8mg/kg) or repeated (8mg/kg twice daily for seven days) MDMA exposure. MDMA exposure affected body weight gain and induced hyperlocomotion; this latter effect progressively decreased after repeated administration. Gene expression analysis indicated a down-regulation of the N/OFQ system and an up-regulation of the DYN system in the nucleus accumbens (NAc), highlighting an opposite systems regulation in response to MDMA exposure. Since histone modifications have been strongly associated to the addiction-related maladaptive changes, we examined two permissive (acH3K9 and me3H3K4) and two repressive transcription marks (me3H3K27 and me2H3K9) at the pertinent opioid gene promoter regions. Chromatin immunoprecipitation assays revealed that acute MDMA increased me3H3K4 at the pN/OFQ, pDYN and NOP promoters. Following acute and repeated treatment a significant decrease of acH3K9 at the pN/OFQ promoter was observed, which correlated with gene expression results. Acute treatment caused an acH3K9 increase and a me2H3K9 decrease at the pDYN promoter which matched its mRNA up-regulation. Our data indicate that the activation of the DYNergic stress system together with the inactivation of the N/OFQergic anti-stress system contribute to the neuroadaptive actions of MDMA and offer novel epigenetic information associated with MDMA abuse.

Amphetamine and morphine may produce acute-withdrawal related hypoactivity by initially activating a common dopamine pathway

Rats given drugs of abuse such as amphetamine or morphine show longer-term effects, that is, signs of acute withdrawal, including hypoactivity, hypophagia, and blunted affect, sometime between 12 and 24h after treatment. This research explores the possibility that signs of acute withdrawal produced by different drugs of abuse are instigated by overlapping mechanisms. The specific objectives of the research were to see if amphetamine and morphine produced longer-term hypoactivity, and to see if any longer-term hypoactivity elicited by the drugs could be blocked by SCH23390, a dopamine D1 antagonist. Six groups of rats, with eight rats in each group, were exposed to a series of five-day tests. Near light onset of Test Day 1, each animal was given control administrations, consisting of a saline treatment (1.0ml/kg) followed 30m later by a saline posttreatment, and locomotor activity was monitored for the next 24h. On Test Day 3, each animal was given experimental administrations, and locomotor activity was again monitored for 24h. Each group received only one combination of experimental administrations across tests. Experimental administrations consisted of saline, amphetamine (2.0mg/kg), or morphine (5.0mg/kg), followed by saline or SCH23390 (0.05mg/kg). All administrations were subcutaneous. Amphetamine and morphine produced longer-term hypoactivity, having similar time courses and magnitudes. SCH23390 blocked the longer-term hypoactivity produced by both drugs. Saline and SCH23390 produced no changes in longer-term activity in their own right. The time course of amphetamine-elicited longer-term hypoactivity resembled that of amphetamine-elicited longer-term hypophagia observed in a prior study. Approximately 1/4 of the animals given amphetamine or morphine did not show longer-term hypoactivity ("low withdrawal" rats). Amphetamine and morphine may initiate the cascade of events resulting in signs of acute withdrawal by producing activation in a common pathway that uses dopamine as a neurotransmitter. Different signs of acute withdrawal (hypoactivity and hypophagia) may involve the short-term activation of the same common pathway. Low withdrawal rats may have a different vulnerability to amphetamine and may show differences in drug assessment outcomes relative to animals that manifest distinct signs of acute withdrawal.