Single-cell activity and local field potentials in the ventral tegmental area of awake, freely moving rats

The ventral tegmental area (VTA) is known to be involved in reward analysis and detection of salience of events. It contains dopaminergic (DA), GABAergic and perhaps other neurons. Much is known about the activity of DA neurons in anaesthetized animals and brain slices. However, there is a clear lack of data on their dynamic regulation in awake animals, although their reactivity to drugs of abuse, for example, is dramatically different in these different conditions (Koulchitsky et al., 2012). Moreover, little is known about the network activity of the VTA.
<br /><br />Using a telemetric recording system and 8-microelectrode-arrays, spanning most of the extent of the VTA, we observed both single cell activity and local field potentials (LFPs), as recently described by others (Fujisawa and Buzsáki, 2011). Neurons were considered as being DA when their firing rate was decreased by more than 50% by an i.p. injection of 100 µg/kg of quinpirole.
<br /><br />The firing rate of individual DA neurons was very variable over time, as was the spectrum of LFPs. In many cases, sharp changes in the firing rate/bursting of some DA neurons correlated with an increase in the amplitude of the theta band (~5-8 Hz). They were also coherent to the locomotor activity of the animals. However, the extent to which the firing rate of individual neurons within a rat correlated with the increased theta rhythm was very variable, suggesting that the functional connectivity of different DA neurons at a given moment is quite heterogenous. We are currently attempting to use our recordings to infer a “functional topography” of the VTA.