Specificity of inhibitory control of cortical interneurons in layer 4 of mouse somatosensory barrel cortex

Abstract

Cortical processing of sensory information relies on a diversity of inhibitory control. This thesis examines the cell type specificity in layer 4 of mouse somatosensory barrel cortex of two understudied mechanisms of GABA inhibition: (1) tonic inhibition mediated by specific GABA_A receptors, and (2) GABA_B receptor mediated inhibition. Using whole-cell patch clamp techniques, we find that tonic GABA_A inhibition is greatest in inhibitory neurons. This inhibition of inhibitory neurons produces a net excitatory effect. Within inhibitory neurons, there is additional diversity of tonic GABA_A inhibition, with consequences for information processing, seen specifically in fast spiking (FS) mediated feed forward inhibition. GABA _B receptor mediated inhibition of neurotransmitter release acts on both excitatory and inhibitory neurons, with the greatest effect seen in a non-FS interneurons. Paired recordings between synaptically coupled neurons show an approximate 50% inhibition at synapses with either excitatory or FS inhibitory interneurons presynaptic, while responses produced by non-FS cells were essentially abolished by activation of GABA_B receptors. In contrast to tonic GABA_A inhibition, in adult animals, inhibitory currents from activation of GABA_B receptors is greatest in excitatory neurons, rather than inhibitory neurons. However, in younger animals, there is equal GABA _B inhibition of non-FS inhibitory interneurons. This inhibition decreases with age, with potential implications for plasticity.