Not Itself Histamine, but H3R Antagonists/Inverse Agonist Thioperamide Enhances Long-term Potentiation in the Dentate Gyrus of Urethane- Anesthetized Rats

Abstract

Purpose: Although the histamine receptor antagonists have been reported to enhance consolidation of memory in diverse disease states of the central nervous system, their contribution to the long-term potentiation (LTP), a cellular form of learning and memory, remains unknown. Herein, we evaluate the effect of H3 receptor (H3R) antagonist thioperamide (inverse agonist) on the LTP in healthy rats and compare the effect with that of histamine as an agonist, and pyrilamine, as a H2R antagonist. Methods: LTP was induced in the dentate gyrus, where field potentials were recorded during infusions of saline, histamine, thioperamide or pyrilamine alone by application of high- frequency stimulation protocols. Results: The short-term and long-temp potentiation of EPSP, not of PS, in the thioperamide group were significantly higher in comparison with controls, indicating that induction and maintenance of synaptic, not somatic, LTP further enhanced by H3R antagonism. There were also significant differences in short-term and long-term potentiation of PS between the histamine and pyrilamine groups, indicating H1R-mediated dyssynchrony in granule cell of the dentate gyrus. Conclusion: Histamine seems not to play a significant functional role in the perforant pathway- dentate gyrus synapses, but the antagonism of H3R should be considered in treatment of cognitive dysfunctions, although other forms of synaptic plasticity such as longterm depression and depotentiation of LTP are needed.