The posterior basal diencephalon of rats enhances expression of an activated state

Various ablation studies have implicated the posterior basal diencephalon in the promotion of wakefulness. Although many studies have examined the role of this structure in promotion of cortical arousal, few investigations have attempted to examine its importance in regulation of motor activation (behavioral arousal). In the current study, recordings of freely moving decerebrate rats with and without a posterior basal diencephalon were performed. These studies allowed determination of the behavioral states expressed by the preparations and whether removal of the posterior basal diencephalon completely eliminated expression of both activated state with and activated state without limb movements.

Muscle activity was recorded from limb and neck muscles. Eye movements and heart rate were also monitored. The percentage of time spent in various behavioral states and the proportion of limb movements expressed in each of these states were determined.

Rats with an intact posterior basal diencephalon cycled between all behavioral states. However, they spent most of the recording time in an activated state. In contrast, removal of the posterior basal diencephalon produced rats that spent most of the recording period in a quiescent state. Limb movements were expressed mainly by animals with an intact posterior basal diencephalon, and only when these animals were in the activated state.

The results of this study suggest that the posterior basal diencephalon is required for expression of an activated state and specifically provide evidence for a descending projection from this region required for expression of this state and associated motor activation.