Abstract
Psychostimulant drugs of abuse increase dendritic spine density in reward centers of the brain. However, little is known about their effects in the hippocampus, where activity-dependent changes in the density of dendritic spine are associated with learning and memory. Recent reports suggest that Cdk5 plays an important role in drug addiction, but its role in psychostimulant’s effects on dendritic spines in hippocampus remain unknown. We used in vivo and in vitro approaches to demonstrate that amphetamine increases dendritic spine density in pyramidal neurons of the hippocampus. Primary cultures and organotypic slice cultures were used for cellular, molecular, pharmacological and biochemical analyses of the role of Cdk5/p25 in amphetamine-induced dendritic spine formation. Amphetamine (two-injection protocol) increased dendritic spine density in hippocampal neurons of thy1-green fluorescent protein (GFP) mice, as well as in hippocampal cultured neurons and organotypic slice cultures. Either genetic or pharmacological inhibition of Cdk5 activity prevented the amphetamine–induced increase in dendritic spine density. Amphetamine also increased spine density in neurons overexpressing the strong Cdk5 activator p25. Finally, inhibition of calpain, the protease necessary for the conversion of p35 to p25, prevented amphetamine’s effect on dendritic spine density. We demonstrate, for the first time, that amphetamine increases the density of dendritic spine in hippocampal pyramidal neurons in vivo and in vitro. Moreover, we show that the Cdk5/p25 signaling and calpain activity are both necessary for the effect of amphetamine on dendritic spine density. The identification of molecular mechanisms underlying psychostimulant effects provides novel and promising therapeutic approaches for the treatment of drug addiction.
Highlights
Changes in behavior that occur as a function of experience, like environmental enrichment (Engmann et al, 2015), drug addition (Robinson and Kolb, 1997; Rasakham et al, 2014), injuries (Tseng and Hu, 1996; Chen et al, 2003) and throughout aging (Scheibel et al, 1975; Wang et al, 2009), have their basis in the reorganization of excitatory synaptic connections, Amphetamine via Cdk5/p25 Increases Dendritic Spines known as structural plasticity of dendritic spines
These results demonstrate that amphetamine, administrated in a two-injection protocol known to trigger locomotor sensitization, increases dendritic spine density in CA1 pyramidal neurons favoring the mature stubby type
Using thy1-green fluorescent protein (GFP) transgenic mice, we show that amphetamine administrated in a two-injection protocol increased dendritic spine density in CA1 pyramidal neurons and shifted the density of morphological types in favor of mature stubby spines
Summary
Changes in behavior that occur as a function of experience, like environmental enrichment (Engmann et al, 2015), drug addition (Robinson and Kolb, 1997; Rasakham et al, 2014), injuries (Tseng and Hu, 1996; Chen et al, 2003) and throughout aging (Scheibel et al, 1975; Wang et al, 2009), have their basis in the reorganization of excitatory synaptic connections, Amphetamine via Cdk5/p25 Increases Dendritic Spines known as structural plasticity of dendritic spines. Activity-dependent dynamic changes in spines of hippocampal pyramidal neurons are essential for learning and memory (Yuste and Bonhoeffer, 2001; Kasai et al, 2003). The Cdk5/p35 signaling complex has been involved in multiple processes during typical brain development, including neuronal migration and the formation of axons and dendrites (Nikolic et al, 1996; Chae et al, 1997; Paglini et al, 1998, 2001; Kwon et al, 1999; Smith and Tsai, 2002), as well as in associative learning and memory in adult rodents (Fischer et al, 2002, 2005; Angelo et al, 2006; Bignante et al, 2008). Transient expression of p25 increased the number of synapses and dendritic spine density, enhancing hippocampal LTP and facilitating learning and memory (Fischer et al, 2005)
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