Transient viral-mediated overexpression of alpha-calcium/calmodulin-dependent protein kinase II in the nucleus accumbens shell leads to long-lasting functional upregulation of alpha-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate receptors: dopamine type-1 receptor and protein kinase A dependence

Abstract

Calcium/calmodulin-dependent protein kinase II (CaMKII) activity is necessary for the long-lasting expression of locomotor sensitization and enhanced drug-taking observed in rats previously exposed to psychostimulants. Exposure to these drugs also transiently increases alphaCaMKII levels in the nucleus accumbens (NAcc), an effect that, when mimicked by transient viral-mediated overexpression of alphaCaMKII in NAcc shell neurons, leads to long-lasting enhancement in locomotor responding to amphetamine and NAcc alpha-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate (AMPA). The present experiments characterized the dopamine (DA) dependence of the functional AMPA receptor upregulation observed long after transient overexpression of alphaCaMKII. Rats infected with herpes simplex virus-alphaCaMKII in the NAcc shell showed a transient increase in alphaCaMKII levels that peaked at 4 days post-infection and returned to baseline 8 days later. When challenged with AMPA (0.8 nmol/side) in the NAcc shell at 20 days post-infection, these rats showed enhanced locomotion compared with controls. This sensitized locomotor response was blocked when AMPA was coinfused with either the DA type-1 receptor antagonist SCH23390 (0.8 nmol/side) or the protein kinase A inhibitor Rp-cAMPS (80 nmol/side). Neither SCH23390 nor Rp-cAMPS produced locomotor effects when infused by itself into the NAcc shell. Furthermore, these antagonists did not block the acute non-sensitized locomotor response to AMPA observed in control rats. These findings show that transient viral-mediated overexpression of alphaCaMKII in neurons of the NAcc shell leads to long-lasting functional upregulation of AMPA receptors that is DA type-1 receptor and protein kinase A dependent. Thus, transient increases in levels of alphaCaMKII in the NAcc shell produce long-lasting changes in the way that DA and glutamate interact in this site to generate locomotor behavior.

Fig. 1

Viral-mediated gene transfer in the NAcc causes a transient increase in levels of the transgene. (A) Western blots of αCaMKII and β-actin (internal loading control) at 4 and 8 days after microinjection of HSV-T286D αCaMKII in the NAcc shell. αCaMKII was significantly increased at 4 days, but not 8 days, post-infection (PI). Protein levels are expressed as group mean (+SEM) % change from controls (HSV-LacZ or 10% sucrose) (n = 3–4/group; *P < 0.05, HSV-T286D αCaMKII vs. control). (B) Photomicrograph of a section of the NAcc (+1.2 mm from bregma) obtained at 4 days after infection with HSV-LacZ displaying β-galactosidase-positive neurons in close proximity to the injection cannula tip in the NAcc shell (arrow). Dashed lines delineating the NAcc core and shell subregions are superimposed from Paxinos & Watson (1997). ac, anterior commissure. (C) A green fluorescent protein (GFP)-positive neuron in the NAcc shell photographed at 4 days following infection with HSV-αCaMKII-GFP.

Fig. 2

Enhanced locomotor responding to NAcc shell AMPA at 20 days post-infection requires D1 receptor and PKA activation. Data in (A–F) are shown as group mean (±SEM) locomotor counts obtained before and after the challenge injection (arrows). (A and B) The locomotor response to NAcc shell AMPA was significantly enhanced in αCaMKII compared with control group rats. Little locomotor activity was observed in either group following NAcc shell saline. Coadministration of either SCH23390 (C and D) or Rp-cAMPS (E and F) with AMPA into the NAcc shell blocked the enhanced locomotor response in αCaMKII compared with control group rats but spared the locomotor effects of AMPA in both groups compared with NAcc shell saline. Neither SCH23390 nor Rp-cAMPS produced effects that differed significantly from saline when administered alone. (G) Summary of post-challenge injection results illustrated as group mean (+SEM) 2 h total locomotor counts. *P < 0.001, AMPA vs. saline; ^†P < 0.01, αCaMKII vs. control; revealed by post-hoc Scheffé comparisons following anova.

Fig. 3

Location of microinjection cannula tips in the NAcc shell for all rats included in the data analyses. Line drawings of coronal sections (adapted from Paxinos and Watson, 1997) show the location of the microinjection cannula tips in the NAcc shell for rats tested with no inhibitor (A), with SCH23390 (B) or with Rp-cAMPS (C). Numbers to the right indicate mm from bregma. Symbols denote group affiliation: filled circles, αCaMKII-AMPA; open circles, control-AMPA; filled squares, αCaMKII-saline; open ssquares, control-saline.