Region-specific involvement of AMPA/Kainate receptors in Fos protein expression induced by cocaine-conditioned cues

Abstract

This study investigated the effects of the AMPA/Kainate receptor antagonist, NBQX, on cue-elicited cocaine-seeking behavior and concomitant changes in Fos protein expression. After cocaine self-administration training, rats underwent 24 days of abstinence during which they were exposed daily either to the self-administration environment with response-contingent cues previously paired with cocaine infusions available (Extinction group) or to an alternate environment (No Extinction group). Subsequently, rats were tested for cocaine-seeking behavior (i.e., operant responses without cocaine reinforcement) elicited by the cocaine-associated cues after pretreatment with either vehicle or NBQX (10 mg/kg, IP). NBQX markedly attenuated cue-elicited cocaine-seeking behavior relative to vehicle pretreatment in the No Extinction group and also decreased cue-elicited Fos protein expression in a region-specific manner in the anterior cingulate and orbitofrontal cortices, basolateral amygdala, nucleus accumbens core, and dorsal caudate-putamen, suggesting involvement of AMPA glutamate systems in specific subregions of the neuronal circuitry activated by cocaine cues.

Figure 1

Effects of Vehicle (n = 11) or 10 mg/kg, IP NBQX (n = 11) pretreatment on spontaneous locomotor activity. Rats were injected with their pretreatment 20 min prior to being placed into the locomotor activity chambers.

Figure 2

Effect of extinction training on active (top) and inactive (bottom) lever presses in rats with a history of cocaine self-administration [Cocaine-Extinction (n = 20)] or saline-yoked administration [Saline-Extinction (n = 9)]. * represents a difference from the Saline-Extinction group (P<0.05).

Figure 3

Lever presses on the active and inactive levers across the 90-min test session. Rats in the Saline, Cocaine-Extinction, and Cocaine-No Extinction groups were pretreated with either Vehicle (n = 8–10) or 10 mg/kg, IP NBQX (n = 9–10) 20 min prior to being placed into the self-administration environment. ^*represents a difference from all other groups (Tukey test, P<0.05).

Figure 4

Schematic representation of coronal sections of the rat brain (+3.2, +1.6, −2.56, and −5.6 mm from Bregma) adapted from Paxinos and Watson (1998) illustrating regions analyzed for Fos protein expression. Numbers in the sections represent the regions analyzed as follows: 1) prelimbic cortex (PrL); 2) infralimbic cortex (IL); 3) orbitofrontal cortex (OF); 4) Cg2 region of the anterior cingulate cortex (ACg); 5) dorsal caudate-putamen (dCPu); 6) nucleus accumbens shell (NAcS); 7) nucleus accumbens core (NAcC); 8) motor cortex (MC); 9) central amygdala (CeA); 10) basolateral amygdala (BlA); 11) ventral tegmental area (VTA); 12) ventral subiculum (VSub). For each brain region, the location and the size of the subregion measured within the region is indicated.

Figure 5

Photomicrographs of coronal sections taken at 20× magnification demonstrating labeling in the basolateral amygdala (BlA) for Fos-immunoreactivity (black arrows) in representative rats in the Saline, Cocaine-Extinction, and Cocaine-No Extinction groups pretreated with Vehicle or NBQX. Scale bar is equal to 100 μm.

Figure 6

Number of Fos-immunoreactive labeled cells (±SEM) in cortical, striatal, and limbic regions of rats following the test for cocaine-seeking behavior (see Figure 4 caption for definition of brain region abbreviations and Figure 3 caption for explanation of group labels). For all regions the number of Fos positive cells are presented per 0.26 mm², except for the he NAcS and VSub in which the number of Fos positive cells are presented per 0.065 mm^{2. *}represents a difference from all other groups, Tukey HSD test (P<0.05). ^#represents a difference from Saline and Cocaine-Extinction groups, main effect of group and Tukey HSD test (P<0.05). ⁺represents a difference from the Cocaine-Extinction groups, main effect of group and Tukey HSD (P<0.05).

Figure 7

Number of Fos-immunoreactive labeled cells (±SEM) in the CeA (top graph) and VTA (bottom graph) of rats following systemic administration of Vehicle or NBQX (10 mg/kg, IP) pretreatment on the test day. The data are averaged across the Saline, Cocaine-Extinction, and Cocaine-No Extinction conditions. ^*represents a main effect of test drug (P<0.05).