Specificity of inhibitory control of cortical interneurons in layer 4 of mouse somatosensory barrel cortex
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 GABAA receptors, and (2) GABAB receptor mediated inhibition. Using whole-cell patch clamp techniques, we find that tonic GABAA 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 GABAA 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 GABAB receptors. In contrast to tonic GABAA inhibition, in adult animals, inhibitory currents from activation of GABAB 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.