LONGEVITY OF BEHAVIORAL SENSITIZATION IN THE YOUNG RAT: REGIONAL DIFFERENCES IN FOS IMMUNOREACTIVITY. Sergios Charntikov, Anthony M. Cortez, Dennis A. Amodeo, Cynthia E. Martinez, Cynthia A. Crawford, Sanders A. McDougall.

Introduction: Sensitization/Adult Rats All images used for this presentation are + Novel Context Same Context Challenge “One-Shot” Paradigm “One-Shot” Paradigm Adults/Sensitized Response Behavioral Sensitization TrainingTesting Repeated Treatment “One-Shot” Treatment Context-DependentContext A Context-IndependentContext AContext B Distance Traveled

Introduction: Preweanling Rats/One-Shot Condition PD19 Test PD20 Home Cage Test Cage Test Cage

Purpose  To determine longevity of context-dependent and context- independent sensitization in preweanling rats.  To determine whether expression of context-dependent and context-independent sensitization will result in different patterns of Fos-IR.  Fos was measured in brain areas involved in the induction and expression of psychostimulant-induced behavioral sensitization: Nucleus accumbens Prefrontal Cortex Amygdala Striatum

Methods Condition PD19 Home Cage Test Cage Test PD20 Test Cage Test PD33 Test Cage Test PD22 Test Cage Test PD24 Test PD26 Test Cage Test Cage 1 hour after testing tissue was removed and processed later for Fos-IR Test PD80 Test Cage

Results

 Relative to an acute cocaine group, sensitized rats (PD 22) exhibited elevated Fos-IR in the striatum and prefrontal cortex. Fos-IR

 Findings suggest that:  persistence of the sensitized response cannot be used to dissociate the ontogeny of context-dependent and context-independent sensitization  Fos-IR data suggests that striatum and prefrontal cortex may be involved in mediating short-term behavioral sensitization in young rats. Summary

Acknowledgements  Dr. Sanders McDougall  Dr. Cynthia Crawford  Anthony Cortez  Dennis Amodeo  Cynthia Martinez  Department of Psychology, California State University, San Bernardino.

Theoretical model of Behavioral Sensitization (Anagnostaras, 2002) Summary of major effects. Saline. Paired rats exhibited a large CR to saline; ECS did not affect the CR. AMPH. During the first 15 min, as the drug is taken up, ECS did not affect the response to AMPH. In contrast, during the peak response (30-60 min), ECS revealed a strong sensitization in Unpaired rats. Panel B: Model. We suggest that two associative mechanisms contribute to contextual control over the expression of sensitization. By virtue of pairing of the drug with the context in a Pavlovian manner, saline can elicit a drug-like CR under circumstances when the drug would normally be received. Chronic, intermittent AMPH also sensitizes a neural substrate mediating the response to the drug and this is reflected in enhanced psychomotor activation. The excitatory CR observed to saline also contributes to the degree of psychomotor activity when the drug is given, especially shortly after drug administration. The effect of ECS was to reveal sensitization in Unpaired rats, in which there was no evidence of a CR. Thus, we suggest that a contextual memory mechanism (inhibition via occasion-setting) inhibits the expression of sensitization in environments where the drug has not been previously experienced.