The enhanced oral response to the 5-HT2 agonist Ro 60-0175 in parkinsonian rats involves the entopeduncular nucleus: Electrophysiological correlates

M. Lagière, S. Navailles, L. Mignon, A. Roumegous, M.-F. Chesselet, P. De Deurwaerdère
Exp Brain Res. 2013-03-28; 230(4): 513-524
DOI: 10.1007/s00221-013-3478-4

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Lesions of nigrostriatal dopaminergic neurons as seen in Parkinson’s disease (PD)
increase orofacial responses to serotonergic (5-HT) agonists in rodents. Although
this response to 5-HT agonists has been related to aberrant signalling in the
basal ganglia, a group a subcortical structures involved in the control of motor
behaviours, it deserves additional studies with respect to the specific loci
involved. Using measurements of orofacial activity, as well as single-cell
recordings in vivo, we have studied the role of the entopeduncular nucleus (EPN;
equivalent to the internal globus pallidus of primates), an output structure of
basal ganglia, in the hypersensitized responses to a 5-HT agonist in sham- or
unilaterally dopamine-depleted rats. Intra-EPN injections of Ro 60-0175 (0.3 and
1 μg/100 nl) promoted robust oral movements in 6-OHDA rats without affecting oral
activity in sham-depleted rats. Peripheral administration of Ro 60-0175 (3 mg/kg
ip) decreased EPN neuronal firing rate in 6-OHDA rats compared to sham-depleted
rats. Such an effect was also observed when the agonist (0.2 μg/20 nl) was
locally applied onto EPN neurons. These data demonstrate the contribution of EPN
to hypersensitized responses to 5-HT agonists in a rat model of PD.

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