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Zusammenfassung:
Dopamine (DA) is thought to have a gating role in the communication between thalamus and primary sensory areas. In the primary visual pathway D2-receptors (D2Rs) are predominantly found in lateral geniculate nucleus (LGN) while D1-receptors (D1Rs) show higher density in primary visual cortex. D1Rs have a facilitating effect on neuronal processing whereas D2Rs show a dampening effect. Given their differences in anatomical distribution and functionality the two dopaminergic (DAergic) receptors may have a differential effect on thalamocortical information transfer. Here we set out to investigate DAergic impact on V1 by using combined fMRI and neurophysiological measurements in anesthetized non-human primates, during systemic application of L-DOPA (LD: 2.1 mg/kg) and Carbidopa (C: 0.5 mg/kg). Our results show that the stimulus-induced modulation of the BOLD signal decreases by 45 ± 8 for 10 ± 3 min (n=6, p < 0.05). This decrease is concomitant with an improvement in signal-to-noise ratio (SNR) in multi unit activity (MUA: 900-3200 Hz) as well as decrease in CV (p<0.05) of the theta (4-8 Hz), low-gamma (20-60 Hz) and gamma (65-120 Hz) bands of LFP. In contrast, local application of DA in V1 did not induce any changes in neuronal activity indicating that the observed effects are most probably mediated by D2Rs of LGN. DAergic neuromodulation improved SNR of the neuronal recordings in V1 which reflects a sparse and dampened firing pattern with little background interferences. These findings suggest that the visual inputs are attenuated by the local DAergic circuitry of LGN (D2Rs) generating sparse and precise neuronal firing in V1. At the same time, however, the reduced mass-activity appears to reduce the energy demands, and the stimulus-induced modulation of the BOLD signal. Our findings confirm the important role of D2Rs in gating inputs to primary visual cortex by achieving sparse and adequate neuronal firing.
