Our aim was to investigate the functional state of mesolimbic dopamine (DA) system by behavioral analysis and microdialysis in N. Accumbens (NAc) core and shell of the Naples High-Excitability (NHE) rats, an animal model of Attention Deficit and Hyperactivity Disorder (ADHD).Thus, young adult male NHE rats and random-bred (NRB) controls were tested in a spatial novelty (Làt-maze) for 30 min for indices of activity, non selective attention (rearing durations) and emotionality (defecation score). Then, “in vivo” DA release was monitored in freely moving rats by microdialysis 24h after implant of vertical probes in the NAc core and shell. Samples were monitored under basal condition and after morphine challenge (1 mg/kg/sc) every 20 min for 3h.The behavioral profile showed higher activity and lower scanning time in NHE rats, vs. NRB controls. Microdialysis studies showed respectively a lower and a higher DA basal levels in the core and shell of NHE vs. NRB rats. Moreover, an association was found between DA basal level in the NAc shell and total activity by Spearman’s rank order correlation (ρs 0.545; p<0.036). In addition morphine increased extracellular DA, expressed as percent of basal values, and it was maximal 60 minutes after injection with similar extent in the two rat lines. In particular, in the NAc shell of NHE rats, after morphine DA levels increased rapidly until 60 min, then decreasing by the end of the experiment (180 min). The trend of NRB was similar to NHE, but the peak value was attained later then NHE (60 min) to decrease at a lower level then NHE rats by the end of experiment. In contrast, in the NAc core, the maximal increase was reached by NHE and NRB 60 min after injection. However in the NHE it was stable whereas in NRB it decreased by 180 min. Therefore, since only mesocortical DA branch has been shown to be hypertrophic in this ADHD model, the differential functional state of mesolimbic DA branch in NHE rats, i.e. lower in the core and higher in the shell under basal conditions but higher in the shell after morphine, may be viewed as a compensative effect to overcome defective prefronto-striatal glutamate neurotransmission.

A behavioral and microdialysis study on basal and morphine-induced dopamine release in the nucleus accumbens core and shell of the Naples High-Excitability rats

VALENTINI, VALENTINA;
2006-01-01

Abstract

Our aim was to investigate the functional state of mesolimbic dopamine (DA) system by behavioral analysis and microdialysis in N. Accumbens (NAc) core and shell of the Naples High-Excitability (NHE) rats, an animal model of Attention Deficit and Hyperactivity Disorder (ADHD).Thus, young adult male NHE rats and random-bred (NRB) controls were tested in a spatial novelty (Làt-maze) for 30 min for indices of activity, non selective attention (rearing durations) and emotionality (defecation score). Then, “in vivo” DA release was monitored in freely moving rats by microdialysis 24h after implant of vertical probes in the NAc core and shell. Samples were monitored under basal condition and after morphine challenge (1 mg/kg/sc) every 20 min for 3h.The behavioral profile showed higher activity and lower scanning time in NHE rats, vs. NRB controls. Microdialysis studies showed respectively a lower and a higher DA basal levels in the core and shell of NHE vs. NRB rats. Moreover, an association was found between DA basal level in the NAc shell and total activity by Spearman’s rank order correlation (ρs 0.545; p<0.036). In addition morphine increased extracellular DA, expressed as percent of basal values, and it was maximal 60 minutes after injection with similar extent in the two rat lines. In particular, in the NAc shell of NHE rats, after morphine DA levels increased rapidly until 60 min, then decreasing by the end of the experiment (180 min). The trend of NRB was similar to NHE, but the peak value was attained later then NHE (60 min) to decrease at a lower level then NHE rats by the end of experiment. In contrast, in the NAc core, the maximal increase was reached by NHE and NRB 60 min after injection. However in the NHE it was stable whereas in NRB it decreased by 180 min. Therefore, since only mesocortical DA branch has been shown to be hypertrophic in this ADHD model, the differential functional state of mesolimbic DA branch in NHE rats, i.e. lower in the core and higher in the shell under basal conditions but higher in the shell after morphine, may be viewed as a compensative effect to overcome defective prefronto-striatal glutamate neurotransmission.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11584/109314
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