19. März, 2026, 14.00 Uhr: Anatomisches Kolloquium

Deciphering the activity of individual synapses in vivo is essential to understanding how the brain processes information. The first in vivo two-photon imaging recordings of single synaptic inputs were performed in mouse visual (Jia et al., Nature 2010) and auditory cortices (Chen et al., Nature 2011). They relied on detecting calcium entry through NMDA receptor channels in dendritic spines. While informative, a limitation of calcium imaging when recording single-synapse synaptic events is the ambiguity introduced by calcium signaling evoked by back-propagating action potentials. This problem is avoided when imaging extracellularly released glutamate. In my presentation, I will report progress on the use of two-photon glutamate imaging to characterize thalamocortical synapses onto layer 4 neurons in the mouse visual cortex in vivo. In these recordings, we identified fundamental properties of thalamocortical synapses onto layer 4 neurons, each of which represents an individual upstream lateral geniculate nucleus neuron with a characteristic receptive field. Overall, our results validate, at the single-synapse level, some of the basic aspects of Hubel and Wiesel's theory of orientation selectivity in mammalian visual cortex neurons and provide insights into unexpected and unique mechanisms of thalamocortical synapses.