Abstract

INTRODUCTION

THE ROLE OF THE TM IN NEURAL PLASTICITY

HISTAMINE, REINFORCEMENT AND MEMORY

HIPPOCAMPAL SIGNAL TRANSFER

REFERENCES

Discussion
Board

Brain histamine is exclusively contained within and released from neurons whose cell bodies are clustered in the tuberomammillary nucleus (TM) located in the posterior hypothalamus. A recent series of experiments showed that the histaminergic neuron system plays a role in reinforcement and mnemonic processes. First, lesions of the TM, which produced a marked decrease of TM-intrinsic histamine cells, increased the rate of rewarding hypothalamic stimulation and improved the performance of adult and aged rats on diverse learning tasks. Second, electrophysiological recordings in freely moving rats revealed that electrical stimulation of the TM interferes negatively with hippocampal signal transfer during learning- related exploratory behavior. Third, the administration of the histamine H1-receptor antagonist chlorpheniramine, but not the H2-receptor antagonist ranitidine, was found to exert reinforcing effects and to promote learning in parts of the brain known to be crucial for reward and memory processes, namely, in the nucleus basalis magnocellularis and in the nucleus accumbens. These findings indicate that neuronal histamine may exert inhibitory control over reinforcement and mnemonic processes under normal conditions. Reducing histaminergic activity either by a partial destruction of TM-intrinsic neurons or by blocking histaminergic transmission at H1-receptive sites may result in a disinhibition of reinforcement and facilitation of learning.

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Presentation Number SAhasenoehrl0223
Keywords: Histamine, Learning, Reinforcement, Neural plasticity, Aging