Dopaminergic neuromodulation of high gamma stimulus phase-locking in gerbil primary auditory cortex mediated by D1/D5-receptors.

Cortical release of the neurotransmitter dopamine has been implied in adapting cortical processing with respect to various functions including coding of stimulus salience, expectancy, error prediction, behavioral relevance and learning. Dopamine agonists have been shown to modulate recurrent cortico-thalamic feedback, and should therefore also affect synchronization and amplitude of thalamo-cortical oscillations. In this study, we have used multitaper spectral and time-frequency analysis of stimulus-evoked and spontaneous current source density patterns in primary auditory cortex of Mongolian gerbils to characterize dopaminergic neuromodulation of the oscillatory structure of current sources and sinks. We systemically applied D1/D5-receptor agonist SKF-38393 followed by competitive D1/D5-receptor antagonist SCH-23390. Our results reveal an increase in stimulus phase-locking in the high gamma-band (88-97 Hz) by SKF-38393, specifically in layers III/IV at the best frequency, which occurred at 20 ms after tone onset, and was reversed by SCH-23390. However, changes in induced oscillatory power after SKF-38393 treatment occurred stimulus-independently in the background activity in different layers than phase-locking effects and were not reversed by SCH-23390. These effects might either reflect longer-lasting changes in neural background noise, non-specific changes due to ketamine anesthesia, or an interaction of both. Without concomitant stimulus-induced power increase, increased stimulus phase-locking in layers III/IV indicates enhanced phase-resetting of neural oscillations by the stimulus after D1/D5-receptor activation. The frequency characteristics, together with the demonstrated stimulus specificity and layer specificity, suggest that changes in phase-resetting originate from dopaminergic neuromodulation of thalamo-cortical interactions. Enhanced phase-resetting might be a key step in the recruitment of cortical activity modes interpreting sensory input.