Postnatal Development of Pyramidal Neurons Excitability and Synaptic Inputs in Mouse Gustatory Cortical Circuits

Cortical neurons in sensory areas undergo a protracted process of postnatal maturation that includes changes in membrane properties, synaptic drive, and connectivity. The completion of this process is associated with the closure of critical periods for experience-dependent plasticity in visual, auditory, and somatosensory cortices. Whether these findings extend to the postnatal development of cortical circuits for taste is currently unknown. Taste receptor cells in the taste buds reliably fire action potentials in response to taste stimuli by the third postnatal week and show extended refinement of membrane excitability into adulthood. Taste responsive neurons in the nucleus of the solitary tract show reorganization of peripheral nerve terminals (NTS) over a timeline comparable to taste buds. However, no study to date investigated the postnatal development of neurons in the gustatory cortex (GC). Here, we focused on pyramidal neurons in the deep layers of GC in acute slices from male and female mice and compared their membrane properties from the third to the eighth postnatal week. We report changes in intrinsic excitability and a shift of the excitation/inhibition (E/I) balance toward inhibition as pyramidal neurons reach their young adult properties. The increase in inhibitory drive accompanied a protracted process of postnatal maturation of inhibitory circuits mediated by parvalbumin-expressing neurons (PV⁺ neurons) that showed an increase in their association with perineuronal nets as well as refinement of their connectivity onto pyramidal neurons. Together, our results indicate that GC neurons undergo protracted postnatal maturation that may influence taste response properties.