Withdrawal from cocaine self-administration alters NMDA receptor-mediated Ca2+ entry in nucleus accumbens dendritic spines - PubMed (original) (raw)

Withdrawal from cocaine self-administration alters NMDA receptor-mediated Ca2+ entry in nucleus accumbens dendritic spines

Carrie R Ferrario et al. PLoS One. 2012.

Abstract

We previously showed that the time-dependent intensification ("incubation") of cue-induced cocaine seeking after withdrawal from extended-access cocaine self-administration is accompanied by accumulation of Ca(2+)-permeable AMPA receptors (CP-AMPARs) in the rat nucleus accumbens (NAc). These results suggest an enduring change in Ca(2+) signaling in NAc dendritic spines. The purpose of the present study was to determine if Ca(2+) signaling via NMDA receptors (NMDARs) is also altered after incubation. Rats self-administered cocaine or saline for 10 days (6 h/day). After 45-47 days of withdrawal, NMDAR-mediated Ca(2+) entry elicited by glutamate uncaging was monitored in individual NAc dendritic spines. NMDAR currents were simultaneously recorded using whole cell patch clamp recordings. We also measured NMDAR subunit levels in a postsynaptic density (PSD) fraction prepared from the NAc of identically treated rats. NMDAR currents did not differ between groups, but a smaller percentage of spines in the cocaine group responded to glutamate uncaging with NMDAR-mediated Ca(2+) entry. No significant group differences in NMDAR subunit protein levels were found. The decrease in the proportion of spines showing NMDAR-mediated Ca(2+) entry suggests that NAc neurons in the cocaine group contain more spines which lack NMDARs (non-responding spines). The fact that cocaine and saline groups did not differ in NMDAR currents or NMDAR subunit levels suggests that the number of NMDARs on responding spines is not significantly altered by cocaine exposure. These findings are discussed in light of increases in dendritic spine density in the NAc observed after withdrawal from repeated cocaine exposure.

PubMed Disclaimer

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1

Figure 1. Self-administration behavior.

Mean number of infusions (± SEM) taken during each 6 hour self-administration session for saline (open squares) or cocaine (closed circles) groups.

Figure 2

Figure 2. The percentage of spines exhibiting NMDAR-mediated Ca2+ entry is decreased after 45 days of withdrawal from cocaine self-administration.

A) Left: The percent of dendritic spines showing a NMDAR-mediated Ca2+ response upon photolysis of caged glutamate is significantly reduced in the cocaine group compared to the saline group. Right: Representative 2–photon image of a fura–2 filled dendrite from a MSN in the NAc core. B) Left: In spines that did exhibit an NMDAR-mediated Ca2+ response, the relative magnitude of the Ca2+ response did not differ between saline and cocaine groups. Right: Representative NMDAR-evoked Ca2+ transient from a MSN spine from the saline group. C) Left: The peak amplitude of the NMDAR-evoked whole cell currents did not differ between saline and cocaine groups. Right: Representative traces of NMDAR currents in MSN from saline (black) and cocaine (dark gray) groups. NMDAR currents in both groups were completely blocked by addition of APV (light gray trace shows APV blockade in a saline-treated animal). A 20 ms UV flash in the absence of caged MNI-glutamate did not generate a current response (data not shown). Data are presented as mean (± SEM). *p<0.05.

Figure 3

Figure 3. Expression of NMDAR subunits in the postsynaptic density (PSD) fraction after 45 days of withdrawal from cocaine or saline self-administration.

Data are presented as mean (± SEM) expressed as percent of saline controls. NR1, NR2A and NR2B protein levels in the cocaine group were slightly decreased on WD45 compared to the saline group, though this did not reach statistical significance. Representative blots are shown below each bar.

Similar articles

Cited by

References

    1. Holtmaat A, Svoboda K (2009) Experience-dependent structural synaptic plasticity in the mammalian brain. Nat Rev Neurosci 10: 647–658. - PubMed
    1. Robinson TE, Kolb B (2004) Structural plasticity associated with exposure to drugs of abuse. Neuropharmacol 47: 33–46. - PubMed
    1. Russo SJ, Dietz DM, Dumitriu D, Morrison JH, Malenka RC, et al. (2010) The addicted synapse: mechanisms of synaptic and structural plasticity in nucleus accumbens. Trends Neurosci 33: 267–276. - PMC - PubMed
    1. Robinson TE, Kolb B (1999) Alterations in the morphology of dendrites and dendritic spines in the nucleus accumbens and prefrontal cortex following repeated treatment with amphetamine or cocaine. Eur J Neurosci 11: 1598–1604. - PubMed
    1. Robinson TE, Gorny G, Mitton E, Kolb B (2001) Cocaine self-administration alters the morphology of dendrites and dendritic spines in the nucleus accumbens and neocortex. Synapse 39: 257–266. - PubMed

Publication types

MeSH terms

Substances

Grants and funding

LinkOut - more resources