Role of octopamine in an appetitive and an aversive conditioning in the crab.

LAURA KACZER; HECTOR MALDONADO

Congreso; I Congress IBRO/LARC of Neurosciences for Latin America, Caribbean and Iberian Peninsula,; 2008

An intriguing issue in the study of associative memories is to determine which compounds underlie these memory representations in the nervous system. Octopamine (OA) is a biogenic monoamine structurally related to noradrenaline that acts as a neurohormone neuromodulator and neurotransmitter in invertebrates. Results obtained in insects as the honeybee and the fruitfly have shown that OA would mediate the reinforcement in olfactory appetitive learning. Here, we attempt to study the putative participation of OA in two associative learning paradigms in the crab Chasmagnathus granulatus style, one appetitive and one aversive. Our basic hypothesis is that the action of an endogenous bioamine as OA would not be restricted to one type of learning. We use the aversive learning paradigm developed in our laboratory in the crab Chasmagnathus, the context-signal memory (CSM), extensively characterized from a behavioral and a neurobiological point of view. It consists in the association between the learning context (conditioned stimulus CS) and a visual danger stimulus, the negative reinforcement (unconditioned stimulus US). In addition, we developed a new appetitive learning paradigm using food as a positive reinforcement (US) and the same visual learning context (CS) as the one in the aversive paradigm. We explored the role of OA in these two conditioning paradigms, using injections of OA itself and its antagonists. The results demonstrated that OA is an amnesic agent of consolidation and reconsolidation of the CSM when injected temporally close to the end of training and reactivation respectively. In contrast, OA facilitates the appetitive learning, and an OA antagonist impairs the memory when applied previous to training. We propose, in agreement with the findings in insects, that OA could act as a positive signal that enhances appetitive learning, but the signal inverses its effects at facing an aversive learning, namely, that OA becomes signal that impairs the acquisition of the aversive memory.