No abstract

Cannabinoids and ethanol activate the same reward pathways, and recent advances in the understanding of the neurobiological basis of alcoholism suggest that the CB 1 receptor system may play a key role in the reinforcing effects of ethanol and in modulating ethanol intake. In the present study, male CB 1 receptors knockout mice generated on a CD1 background displayed decreased ethanol-induced conditioned place preference (CPP) compared to wild-type (CB 1 þ / þ ) mice. Ethanol (0.5, 1.0, 1.5, and 2.0 g/kg) induced significant CPP in CB 1 þ / þ mice at all doses tested, whereas it induced significant CPP only at the highest dose of ethanol (2.0 g/kg) in CB 1 À/À mice.However, there was no genotypic difference in cocaine (20 mg/kg)-induced CPP. There was also no genotypic difference, neither in cocaine (10-50 mg/kg) nor in D-amphetamine (1.2-5 mg/kg)-induced locomotor effects. In addition, mutant and wild-type mice did not differ in sensitivity to the anxiolytic effects of ethanol (1.5 g/kg) when tested using the elevated plus maze. Interestingly, this decrease in ethanol efficacy to induce CPP in CB 1 À/À mice was correlated with an increase in D2/D3 receptors, as determined by [ 3 H]raclopride binding, whereas there was no difference in D1-like receptors, as determined by [ 3 H]SCH23390 binding, measured in the striatum from drug-naïve mice. This increase in D2/D3 binding sites observed in CB 1 knockout mice was associated with an altered locomotor response to the D2/D3 agonist quinpirole (low doses 0.02-0.1 mg/kg) but not to an alteration of quinpirole (0.1-1.0 mg/kg)-induced CPP compared to wild-type mice. Altogether, the present results indicate that lifelong deletion of CB 1 receptors reduced ethanol-induced CPP and that these reduced rewarding effects of ethanol are correlated to an overexpression of striatal dopamine D2 receptors.

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Huntington's disease is characterized by death of striatal projection neurons. We used a Cre/Lox transgenic approach to generate an animal model in which D1 dopamine receptor (Drd1a)؉ cells are progressively ablated in the postnatal brain. Striatal Drd1a, substance P, and dynorphin expression is progressively lost, whereas D2 dopamine receptor (Drd2) and enkephalin expression is up-regulated. Magnetic resonance spectroscopic analysis demonstrated early elevation of the striatal choline/creatine ratio, a finding associated with extensive reactive striatal astrogliosis. Sequential MRI demonstrated a progressive reduction in striatal volume and secondary ventricular enlargement confirmed to be due to loss of striatal cells. Mutant mice had normal gait and rotarod performance but displayed hindlimb dystonia, locomotor hyperactivity, and handling-induced electrographically verified spontaneous seizures. Ethological assessment identified an increase in rearing and impairments in the oral behaviors of sifting and chewing. In line with the limbic seizure profile, cell loss, astrogliosis, microgliosis, and down-regulated dynorphin expression were seen in the hippocampal dentate gyrus. This study specifically implicates Drd1a؉ cell loss with tail suspension hindlimb dystonia, hyperactivity, and abnormal oral function. The latter may relate to the speech and swallowing disturbances and the classic sign of tongueprotrusion motor impersistence observed in Huntington's disease. In addition, the findings of this study support the notion that Drd1a and Drd2 are segregated on striatal projection neurons. striatum ͉ Cre ͉ Huntington's disease T he nigrostriatal pathway projects from the midbrain substantia nigra pars compacta to innervate the dorsal striatum. Dopamine is released from dopaminergic terminals in the striatum to regulate motor activity and eating behavior (1). Early studies suggested that dopamine D1 (Drd1a) and D2 receptors (Drd2) are segregated on striatal projection neurons; the Drd1a is expressed on substance P and dynorphin-positive striatal neurons, which project directly to the substantia nigra pars reticulata/entopeduncular complex (known as the direct pathway), whereas Drd2 is preferentially expressed on enkephalin-positive striatopallidal projecting neurons (2). Neurons within the globus pallidus then project to the subthalamic nucleus, which in turn relays to the substantia nigra pars reticulata/entopeduncular complex (known as the indirect pathway). Dopamine also modulates the activity of glutamatergic corticostriatal input on striatal projection neurons.Idiopathic Parkinson's disease is characterized by the death of dopaminergic neurons; however, rare Parkinsonian syndromes have been identified in which the defect is associated with cell death in the dopamine-responsive neurons in the striatum (3-6). Huntington's disease (HD) (7-10), a neurodegenerative condition with motor, cognitive, and psychiatric disturbances, also involves death of dopamine receptor-expressing striatal projection neurons. Several ...