Abstract

Introduction

Materials & Methods

Results

Discussion & Conclusion

References

Discussion
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The possible role of histamine sensitive sites in hippocampus and the nucleus accumbens of rats on memory and exploratory motivation was studied. As a model of memory, the learning of an active avoiding response after an ultrasonic tone anticipating an electric shock was used. As a model of motivation, an asymmetric elevated plus-maze with arms differing in the presence or absence of walls (APM) was used. All rats were implanted with microinjection cannulas into the hippocampus or the nucleus accumbens. Animals were stimulated with histamine, with or without histamine antagonists 5 min before training trials in memory or exploration trials in the APM. Results show that histamine in hippocampus inhibits evoking, deteriorating the efficiency of learning (37.5±6.5% versus 75±5.2% of accumulated conditioned responses, histamine versus saline, p > 0.01). This inhibitory action was blocked by pyrilamine (histamine H1-antagonist) but not by ranitidine (histamine H2-antagonist). In the APM, histamine in the nucleus accumbens induced an increase of exploration of the 'anxiogenic' arms (45±12 counts/5 min versus 16±8 counts/5 min, histamine versus saline, p > 0.01) increasing the emotionality index. These effects were blocked by both antagonists. In conclusion: data suggest that histamine modulates learning and motivation processes in the brain.

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Presentation Number SAalvarez0117
Keywords: hippocampus, Nucleus accumbens, histamine, motivation, learning