The Role of Dopamine and Glutamate in Associative Learning by the Pigeon (Columba livia)

Abstract

Associative learning involves learning a connection between two events (two stimuli or a stimulus and a response) after their presentation so that the posterior occurrence of one of them activates the representation of the other. In the present dissertation, two associative learning paradigms are used in order to study the role of the glutamatergic and dopaminergic systems on learning. Apomorphine-induced learning and a simultaneous visual discrimination task are used to assess the participation of both systems mentioned above.<br />Chapter I includes a brief introduction to learning (especially classical conditioning), the use of drugs and of contextual cues as stimuli in this domain. It also treats discrimination learning and colour preferences in birds and in animals in general. The two paradigms used in this work are briefly described in the context of dopamine and glutamate involvement. A brief introduction to dopaminergic and glutamatergic systems introduces the associative learning model proposed by Wickens (1990). This model will be used as a basis for the design and interpretation of the following experiments.<br />Both the glutamatergic and dopaminergic systems in vertebrates are discussed in chapter II. A detailed description of the glutamatergic system is given and its relevance for the brain of vertebrates is analysed. Glutamate molecule synthesis and the most relevant glutamatergic process for learning, the long-term potentiation (LTP), are described. Further, a detailed description of the glutamatergic receptors as well as a general view of their participation in the different glutamatergic pathways are revised. Special emphasis falls on the NMDA glutamate receptor (an ionotropic channel receptor). Because of its critical role in learning, the corticostriatal glutamatergic pathway together with the remaining glutamatergic pathways is described. The hypothetical involvement of LTP in learning is discussed. Also a description of dopamine action mechanisms on a