Fos and Egr1 expression in the rat brain in response to olfactory cue after taste-potentiated odor aversion retrieval

Abstract

When an odor is paired with a delayed illness, rats acquire a relatively weak odor aversion. In contrast, rats develop a strong aversion to an olfactory cue paired with delayed illness if it is presented simultaneously with a gustatory cue. Such a conditioning effect has been referred to as taste-potentiated odor aversion learning (TPOA). TPOA is an interesting model for studying neural mechanisms of plasticity because of its robustness and rapid acquisition. However, the neural substrate involved in TPOA retrieval has not been well characterized. To address this question, we used immunocytochemical detection of inducible transcription factors encoded by the immediate-early genes Fos and Egr1. Thirsty male rats were conditioned to TPOA learning, and they were submitted to retrieval in the presence of the learned odor 3 d later. Significant increases in both Fos and Egr1 expressions were observed in basolateral amygdala, insular cortex, and hippocampus in aversive rats in comparison with the all the control groups. The pattern of neuronal activity seemed unlikely to be related to the sole LiCl injection. Lastly, opposite patterns of Fos and Egr1 were noted in the entorhinal cortex and the central nucleus of amygdala, suggesting a differential involvement of these markers in retrieval of TPOA.Odors are critical cues for rodents since odors give the rodents information about their environment. Odors allow the rodents to escape from predators, to find food, or to avoid consumption of toxic products. Memorization of such information is crucial for animal survival. Moreover, olfactory learning permits a previously neutral cue to acquire significance after having been paired with a biologically relevant reinforcement. Rats can acquire weak aversion when an odor is paired with delayed-illness (Bernstein 1991). In contrast, when an odor is simultaneously presented with a taste cue, rats can develop strong aversion to the odor cue. Such a conditioning has been referred to as tastepotentiated odor aversion (TPOA) learning (Palmerino et al. 1980). Thus, taste-mediated potentiation allows odor to gain associative strength and the animals to avoid consumption of poisonous substance on the basis of its odor only (Bernstein 1991). TPOA learning is an attractive model for studying odor memory because of its robustness, rapid acquisition, and adaptive feature (Welzl et al. 2001).Most of the data regarding the brain areas that could mediate TPOA learning are provided by either lesion or pharmalogical experiments. Various brains areas involved in olfactory, gustatory, and visceral pain processing could play a role in TPOA learning. Several studies (Bermùdez-Rattoni et al. 1986;Hatfield et al. 1992;Ferry et al. 1995) indicate that the basolateral nucleus of amygdala (BLA) could play a major role in the acquisition but not in the retrieval of TPOA. In addition, the BLA is known for its involvement in learning the biological significance of events and could modulate memory storage of emotional events (McGaugh 2002). In contrast, the l...

The Way an Odor Is Experienced during Aversive Conditioning Determines the Extent of the Network Recruited during Retrieval: A Multisite Electrophysiological Study in Rats

“…According to the alimentary status of animals, mitral cells of OB present increased activity in response to an odor associated to toxicosis (Pager and Royet, 1976). Fos immunoreactivity in PC increased during the retrieval of taste potentiated odor aversion (TPOA) (Dardou et al, 2006(Dardou et al, , 2007. Our data show that COA learning clearly modified odor-induced oscillatory activity in these structures.…”

Functional Internal Complexity of Amygdala: Focus on Gene Activity Mapping After Behavioral Training and Drugs of Abuse

“…They showed activation of the basolateral, but not central and medial, parts of the amygdala as measured by c-Fos expression and activation of none of the above-mentioned nuclei as measured with Zif268 expression. Moreover, Dardou et al (84) showed increased level of c-Fos and Zif268 expression in the basolateral amygdala following taste-potentiated odor aversion retrieval; however, in the same test in the central amygdala, they observed no changes in the c-Fos expression and the elevated level of Zif268 expression. Also our results presented on the Figure 9 clearly show discrepant patterns of c-Fos and Zif268 expression in the amygdala following appetitive conditioning.…”

The Origins and Organization of Vertebrate Pavlovian Conditioning

“…Indeed, food-paired CSs can activate the gustatory region of the insular cortex (GC) in both rodents (Dardou et al 2006(Dardou et al , 2007 and humans (Veldhuizen et al 2007;Small et al 2008). Importantly, these CSs activate the very same neuronal ensembles in the GC that were activated by the food US itself, providing a neural substrate of CS retrieval of a reward representation (Saddoris et al 2009).…”