Synapse density and dendritic complexity are reduced in the prefrontal cortex following seven days of forced abstinence from cocaine self-administration.

Chronic cocaine exposure in both human addicts and in rodent models of addiction reduces prefrontal cortical activity, which subsequently dysregulates reward processing and higher order executive function. The net effect of this impaired gating of behavior is enhanced vulnerability to relapse. Previously we have shown that cocaine-induced increases in brain-derived neurotrophic factor (BDNF) expression in the medial prefrontal cortex (PFC) is a neuroadaptive mechanism that blunts the reinforcing efficacy of cocaine. As BDNF is known to affect neuronal survival and synaptic plasticity, we tested the hypothesis that abstinence from cocaine self-administration would lead to alterations in neuronal morphology and synaptic density in the PFC. Using a novel technique, array tomography and Golgi staining, morphological changes in the rat PFC were analyzed following 14 days of cocaine self-administration and 7 days of forced abstinence. Our results indicate that overall dendritic branching and total synaptic density are significantly reduced in the rat PFC. In contrast, the density of thin dendritic spines are significantly increased on layer V pyramidal neurons of the PFC. These findings indicate that dynamic structural changes occur during cocaine abstinence that may contribute to the observed hypo-activity of the PFC in cocaine-addicted individuals

Array tomography reveals alterations in synapse density in the PFC following 7 days of abstinence from cocaine.

<p>(<b>A</b>) Ribbons of 70 nm sections were stained with postsynaptic marker PSD95 (red), presynaptic marker synaptophysin (green), and DAPI to label nuclei (blue) (<b>B</b>) Another set of ribbons were stained with synaptophysin (green) and GAD65 (magenta) to determine the percentage of inhibitory synapses. Raw images of single sections from saline (left) and cocaine treated (right) rats are shown in the top row of panels <b>A</b> and <b>B</b>. Images were aligned, processed to remove noise, and synapses detected in three-dimensional volumes as shown in the 3D rendering of 5 serial sections (bottom rows <b>A</b> and <b>B</b>) (<b>C</b>) Quantification of presynaptic terminals (<b>D</b>) Quantification of PSD95 positive postsynaptic terminals (<b>E</b>) Quantification of GAD65 positive terminals. Graphs show mean + S.E.M. * p<0.05 t-test; n = 5 animals/group; scale bar  = 10 µm top panels, and 2 µm bottom panels.</p

Single section Golgi analysis reveals alterations in dendritic branching and spine formation in the PFC following 7 days of abstinence from cocaine.

<p>(<b>A</b>) Representative photomicrograph of a Golgi stain pyramidal neuron and tracing from yoked-saline control (top left, top right) and cocaine (bottom left, bottom right) treated rats scale bar  = 50 µm (<b>B</b>) Sholl plot analysis of animals self-administering saline (open circles) and cocaine (black-filled circles) (<b>C</b>) Representative basal dendritic segment from a yoked-saline (top) and cocaine (bottom) neuron scale bar  = 10 µm (<b>D</b>) Quantitative analysis of total spine number and spine density classified by spine sub-type from 4–5 segments from 5–7 neurons from each animal, n = 4 animals/group. *, <i>p</i><0.05; ***, <i>p</i><0.001.</p