Acute an
d chronic methylpheni
date (MPD) exposure was recor
de
d simultaneously for the rat's locomotor activity an
d the nucleus accumbens (NAc) neuronal activity. The evaluation of the neuronal events was base
d on the animal's behavior response to chronic MPD a
dministration: 1) Animals exhibiting behavioral sensitization, 2) Animals exhibiting behavioral tolerance. The experiment laste
d for 10
days with four groups of animals; saline, 0.6, 2.5, an
d 10.0 mg/kg MPD. For the main behavioral fin
dings, about half of the animals exhibite
d behavioral sensitization or behavioral tolerance to 0.6, 2.5, an
d/or 10 mg/kg MPD respectively. Three hun
dre
d an
d forty one NAc neuronal units were evaluate
d. Approximately 80% of NAc units respon
de
d to 0.6, 2.5, an
d 10.0 mg/kg MPD. When the neuronal activity was analyze
d base
d on the animals' behavioral response to chronic MPD exposure, significant
differences were seen between the neuronal population responses recor
de
d from animals that expresse
d behavioral sensitization when compare
d to the NAc neuronal responses recor
de
d from animals exhibiting behavioral tolerance. Three types of neurophysiological sensitization an
d neurophysiological tolerance can be recognize
d following chronic MPD a
dministration to the neuronal populations.
Collectively, these findings show that the same dose of chronic MPD can elicit either behavioral tolerance or behavioral sensitization. Differential statistical analyses were used to verify our hypothesis that the neuronal activity recorded from animals exhibiting behavioral sensitization will respond differently to MPD compared to those animals exhibiting behavioral tolerance, thus, suggesting that it is essential to record the animal's behavior concomitantly with neuronal recordings.