The Study and the Method:
The locomotor activity of adult male Sprague-Dawley was automatically recorded in a circular corridor - circadian changes are described as well as the response to the novel situation and its habituation over three hours.
Four groups of animals were compared, - those with sham/vehicle operations and those with 6-OHDA dopamine (DA) depleting lesions in -
the frontal cortex,
the limbic septum, and
the ventral tegmental area (VTA - A10).
Results:
1/ Lesions of the VTA resulted in increased dark-phase activity, - and a large response to an apomorphine challenge in comparison to other lesion and control groups:
2/ Septal 6-OHDA lesions did not alter locomotion:
3/ After frontal DA depletion there was a small increase of locomotion after the apomorphine challenge, that might reflect increased receptor sensitivity in cortical or sub-cortical areas:
(Table 1: HPLC measures of NA, DA and DOPAC for each group in the prefrontal cortex, septum and N. accumbens)
Figure 1 illustrates the cumulative photocell counts per hour over 24 hours for the 4 groups:.
Figure 2 illustrates the cumulative photocell counts every 10 minutes over 90 minutes post-apomorphine treatment - maximal at 20-30 minutes and habituating over 60 minutes (90 minutes for the VTA group): overall activity VTA >> Frontal > Septal > Controls.
Conclusions:
Along with correlations found for motor activity with cortical levels of DA and NA, these results are interpreted to support a role for DA, NA and the region of the frontal cortex in modulating locomotion that is primarily mediated by mesolimbic VTA - accumbens - DA activity