VISUALLY-GUIDED IN VIVO JUXTACELLULAR RECORDING FROM CCK/CB1+ BASKET CELLS AND AXO-AXONIC CELLS IN THE MOUSE M2 PREMOTOR CORTEX
Perisomatic region-targeting inhibitory neurons (PTIs) in the brain are in a key position to control the activity of their postsynaptic partners. In cortical structures one of the main inhibitory inputs onto the soma and proximal dendrites of pyramidal cells originates from cholecystokinin and type 1 cannabinoid receptor-expressing basket cells (CCK/CB1+ BCs), while the axon initial segment (AIS) of pyramidal neurons is innervated exclusively by axo-axonic cells (AACs). In spite of the importance of the PTIs, the in vivo spiking activity of these two interneuron types is largely unknown in higher order associative cortices. Here, we aimed to reveal the firing characteristics of these interneurons in M2 premotor cortex in response to noxious stimuli. We made visually-guided in vivo juxtacellular recordings to detect the firing of CCK/CB1+ BCs and AACs and their responses to noxious stimuli in urethane-anesthetized mice and compared these results to the activity of the neighboring pyramidal cells. Our results show that the spiking of CCK/CB1+ BCs is elevated upon noxious stimuli. This increase in their firing is most likely caused by the pain-triggered overall network activity, since their spiking response followed pyramidal cell firing with a slight delay. In contrast, AACs were also modulated by noxious stimuli, but their spiking activity varied from short- and long-term suppression even to massive increase in their firing rate. These observations suggest that CCK/CB1+ BCs might inhibit pyramidal cells in a feedback manner upon noxious stimulation, whereas the activity of AACs is more diverse under these circumstances.