title: Deprivation-induced strengthening of presynaptic and postsynaptic inhibitory transmission in layer 4 of visual cortex during the critical period.
abstract: Inhibition from fast-spiking (FS) interneurons plays a crucial role in shaping cortical response properties and gating developmental periods of activity-dependent plasticity, yet the expression mechanisms underlying FS inhibitory plasticity remain largely unexplored. In layer 4 of visual cortex (V1), monocular deprivation (MD) induces either depression or potentiation of FS to star pyramidal neuron (FS→SP) synapses, depending on the age of onset (Maffei et al., 2004, 2006). This reversal in the sign (- to +) of plasticity occurs on the cusp of the canonical critical period (CP). To investigate the expression locus behind this switch in sign of inhibitory plasticity, mice underwent MD during the pre-CP [eye-opening to postnatal day (p)17] or CP (p22-p25), and FS→SP synaptic strength within layer 4 was assessed using confocal and immunoelectron microscopy, as well as optogenetic activation of FS cells to probe quantal amplitude at FS→SP synapses. Brief MD before p17 or p25 did not alter the density of FS→SP contacts. However, at the ultrastructural level, FS→SP synapses in deprived hemispheres during the CP, but not the pre-CP or in GAD65 knock-out mice, had larger synapses and increased docked vesicle density compared with synapses from the nondeprived control hemispheres. Moreover, FS→SP evoked miniature IPSCs increased in deprived hemispheres when MD was initiated during the CP, accompanied by an increase in the density of postsynaptic GABAA receptors at FS→SP synapses. These coordinated changes in FS→SP synaptic strength define an expression pathway modulating excitatory output during CP plasticity in visual cortex.
authors: Department of Biology and Center for Behavioral Genomics, Brandeis University, Waltham, Massachusetts 02454.
authors: Marc
authors: M
authors: Nahmani
authors: Gina G
authors: GG
authors: Turrigiano
mesh_terms: D000818:Animals; D005455:Fluorescent Antibody Technique; D007395:Interneurons / Q000502:physiology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018613:Microscopy, Confocal; D016253:Microscopy, Immunoelectron; D009473:Neuronal Plasticity / Q000502:physiology*; D018408:Patch-Clamp Techniques; D013569:Synapses / Q000648:ultrastructure*; D009435:Synaptic Transmission / Q000502:physiology*; D014793:Visual Cortex / Q000254:growth & development* / Q000502:physiology* / Q000648:ultrastructure
keywords: LTP; electron microscopy; fast-spiking; monocular deprivation; optogenetic; pyramidal