Spiny and Non-spiny Parvalbumin-Positive Hippocampal Interneurons Show Different Plastic Properties

摘要

class="head no_bottom_margin" id="sec1title">IntroductionExperience-based changes of synaptic strength and neuronal connectivity form the basis of learning and memory (, , , ). Dendritic spines, which in principal cells (PCs) receive the vast majority of excitatory inputs, are thought to be critical sites of plasticity (, ). These dendritic protrusions minimize interference between excitatory inputs by electrical isolation and by compartmentalization of post-synaptic calcium transients and molecular signaling cascades, which in turn control the strength of synaptic transmission (). In cortical PCs, structural changes of dendritic spines, including the generation of new and elimination of existing spines, underlie long-term changes of synaptic strength, connectivity, and memory formation (, ). Parvalbumin-expressing GABAergic interneurons (PVIs) comprise mainly basket and axo-axonic cells. These neurons target the perisomatic region of postsynaptic cells and are critical regulators of PC activity (). Due to their rapid action potential firing, phase locked to neuronal network oscillations, and their ion channel and receptor expression profile, they have been suggested to form a rigid interconnected network geared toward rapid signaling and oscillatory entrainment of PC ensembles (, ). In line with this concept, PVIs have been reported to be largely devoid of dendritic spines (, ), but see and href="#bib36" rid="bib36" class=" bibr popnode">Sancho and Bloodgood (2018), a property which may aid in rapid signal propagation and fast input to output conversion (href="#bib18" rid="bib18" class=" bibr popnode">Hu et al., 2014). However, recent reports have shown behavior-dependent changes in protein expression in hippocampal PVIs (href="#bib5" rid="bib5" class=" bibr popnode">Donato et al., 2015), remodeling of their axonal branches (href="#bib34" rid="bib34" class=" bibr popnode">Pieraut et al., 2014) and functional plasticity at excitatory inputs targeting PVIs (href="#bib12" rid="bib12" class=" bibr popnode">Hainmueller et al., 2014), suggesting that these neurons participate in experience-induced network plasticity. Inspired by several studies on the mostly sparse occurrence of spines on different types of cortical interneurons (href="#bib9" rid="bib9" class=" bibr popnode">Guirado et al., 2014, href="#bib21" rid="bib21" class=" bibr popnode">Kawaguchi et al., 2006, href="#bib22" rid="bib22" class=" bibr popnode">Keck et al., 2011, href="#bib30" rid="bib30" class=" bibr popnode">McBain et al., 1994, href="#bib36" rid="bib36" class=" bibr popnode">Sancho and Bloodgood, 2018, href="#bib37" rid="bib37" class=" bibr popnode">Scheuss and Bonhoeffer, 2014), we assessed the existence and organization of dendritic spines in PVIs of the hippocampal formation in adult mice. We show that a fraction of PVIs in the dentate gyrus (DG) but not the cornu ammonis (CA) areas 1 and 3 carry high densities of dendritic spines. These spines form in areas with weakly developed perineuronal nets (PNNs), display non-homogeneous input-dependent distributions, predispose for plastic changes, and show input-specific re-organization after behavioral experience.